Combination of measurements of the top-quark pair production cross section from the Tevatron Collider

arXiv:1309.7570v1 [hep-ex] 29 Sep 2013

Combination of measurements of the top-quark pair production cross section from the

Tevatron Collider

T. Aaltonen†_,21_{V.M. Abazov}‡_,86 _{B. Abbott}‡_,117 _{B.S. Acharya}‡_,80 _{M. Adams}‡_,99 _{T. Adams}‡_,98 _{J.P. Agnew}‡_,95 G.D. Alexeev‡_,86 _{G. Alkhazov}‡_,90_{A. Alton}‡ii_,31 _{S. Amerio}†tt_,39_{D. Amidei}†_,31 _{A. Anastassov}†v_,15 _{A. Annovi}†_,17

J. Antos†_,12 _{G. Apollinari}†_,15 _{J.A. Appel}†_,15 _{T. Arisawa}†_,52_{A. Artikov}†_,13 _{J. Asaadi}†_,47 _{W. Ashmanskas}†_,15 A. Askew‡_,98_{S. Atkins}‡_,107 _{B. Auerbach}†_,2 _{K. Augsten}‡_,62_{A. Aurisano}†_,47_{C. Avila}‡_,60 _{F. Azfar}†_,38 _{F. Badaud}‡_,65

W. Badgett†_,15 _{T. Bae}†_,25 _{L. Bagby}‡_,15 _{B. Baldin}‡_,15 _{D.V. Bandurin}‡_,98_{S. Banerjee}‡_,80 _{A. Barbaro-Galtieri}†_,26 E. Barberis‡_,108 _{P. Baringer}‡_,106 _{V.E. Barnes}†_,43_{B.A. Barnett}†_,23 _{P. Barria}†vv_,41 _{J.F. Bartlett}‡_,15 _{P. Bartos}†_,12

U. Bassler‡_,70 _{M. Bauce}†tt_,39 _{V. Bazterra}‡_,99 _{A. Bean}‡_,106 _{F. Bedeschi}†_,41 _{M. Begalli}‡_,57 _{S. Behari}†_,15 L. Bellantoni‡_,15 _{G. Bellettini}†uu_,41 _{J. Bellinger}†_,54 _{D. Benjamin}†_,14_{A. Beretvas}†_,15 _{S.B. Beri}‡_,78 _{G. Bernardi}‡_,69

R. Bernhard‡_,74 _{I. Bertram}‡_,93 _{M. Besan¸con}‡_,70 _{R. Beuselinck}‡_,94 _{P.C. Bhat}‡_,15_{S. Bhatia}‡_,109 _{V. Bhatnagar}‡_,78 A. Bhatti†_,45 _{K.R. Bland}†_,5 _{G. Blazey}‡_,100 _{S. Blessing}‡_,98 _{K. Bloom}‡_,110 _{B. Blumenfeld}†_,23 _{A. Bocci}†_,14 A. Bodek†_,44 _{A. Boehnlein}‡_,15 _{D. Boline}‡_,114 _{E.E. Boos}‡_,88 _{G. Borissov}‡_,93 _{D. Bortoletto}†_,43 _{J. Boudreau}†_,42

A. Boveia†_,11 _{A. Brandt}‡_,120 _{O. Brandt}‡_,75 _{L. Brigliadori}†ss_,6 _{R. Brock}‡_,32 _{C. Bromberg}†_,32 _{A. Bross}‡_,15 D. Brown‡_,69 _{E. Brucken}†_,21 _{X.B. Bu}‡_,15 _{J. Budagov}†_,13 _{H.S. Budd}†_,44 _{M. Buehler}‡_,15 _{V. Buescher}‡_,76 V. Bunichev‡_,88_{S. Burdin}‡jj_,93 _{K. Burkett}†_,15_{G. Busetto}†tt_,39 _{P. Bussey}†_,19 _{C.P. Buszello}‡_,92 _{P. Butti}†uu_,41 A. Buzatu†_,19 _{A. Calamba}†_,10 _{E. Camacho-P´erez}‡_,83 _{S. Camarda}†_,4 _{M. Campanelli}†_,28 _{F. Canelli}†cc_,11 _{B. Carls}†_,22

D. Carlsmith†_,54 _{R. Carosi}†_,41_{S. Carrillo}†l_,16 _{B. Casal}†j_,9 _{M. Casarsa}†_,48_{B.C.K. Casey}‡_,15 _{H. Castilla-Valdez}‡_,83 A. Castro†ss_,6 _{P. Catastini}†_,20 _{S. Caughron}‡_,32_{D. Cauz}†aaabbb_,48 _{V. Cavaliere}†_,22 _{M. Cavalli-Sforza}†_,4 _{A. Cerri}†e_,26

L. Cerrito†q_,28 _{S. Chakrabarti}‡_,114 _{K.M. Chan}‡_,104 _{A. Chandra}‡_,122 _{E. Chapon}‡_,70 _{G. Chen}‡_,106 _{Y.C. Chen}†_,1 M. Chertok†_,7 _{G. Chiarelli}†_,41 _{G. Chlachidze}†_,15 _{K. Cho}†_,25 _{S.W. Cho}‡_,82 _{S. Choi}‡_,82 _{D. Chokheli}†_,13 B. Choudhary‡_,79 _{S. Cihangir}‡_,15 _{D. Claes}‡_,110 _{A. Clark}†_,18 _{C. Clarke}†_,53 _{J. Clutter}‡_,106 _{M.E. Convery}†_,15 J. Conway†_,7 _{M. Cooke}‡_,15_{W.E. Cooper}‡_,15 _{M. Corbo}†y_,15 _{M. Corcoran}‡_,122 _{M. Cordelli}†_,17 _{F. Couderc}‡_,70

M.-C. Cousinou‡_,67 _{C.A. Cox}†_,7 _{D.J. Cox}†_,7 _{M. Cremonesi}†_,41 _{D. Cruz}†_,47 _{J. Cuevas}†x_,9 _{R. Culbertson}†_,15 D. Cutts‡_,119 _{A. Das}‡_,96_{N. d’Ascenzo}†u_,15 _{M. Datta}†f f_,15 _{G. Davies}‡_,94 _{P. de Barbaro}†_,44 _{S.J. de Jong}‡_,84, 85

E. De La Cruz-Burelo‡_,83 _{F. D´eliot}‡_,70 _{R. Demina}‡_,44 _{L. Demortier}†_,45 _{M. Deninno}†_,6 _{D. Denisov}‡_,15 S.P. Denisov‡_,89 _{M. D’Errico}†tt_,39 _{S. Desai}‡_,15 _{C. Deterre}‡kk_,75_{K. DeVaughan}‡_,110_{F. Devoto}†_,21 _{A. Di Canto}†uu_,41 B. Di Ruzza†p_,15 _{H.T. Diehl}‡_,15 _{M. Diesburg}‡_,15 _{P.F. Ding}‡_,95_{J.R. Dittmann}†_,5 _{A. Dominguez}‡_,110_{S. Donati}†uu_,41 M. D’Onofrio†_,27 _{M. Dorigo}†ccc_,48_{A. Driutti}† aaabbb_,48 _{A. Dubey}‡_,79 _{L.V. Dudko}‡_,88 _{A. Duperrin}‡_,67 _{S. Dutt}‡_,78 M. Eads‡_,100_{K. Ebina}†_,52 _{R. Edgar}†_,31_{D. Edmunds}‡_,32 _{A. Elagin}†_,47 _{J. Ellison}‡_,97_{V.D. Elvira}‡_,15_{Y. Enari}‡_,69

R. Erbacher†_,7 _{S. Errede}†_,22 _{B. Esham}†_,22 _{H. Evans}‡_,102 _{V.N. Evdokimov}‡_,89 _{S. Farrington}†_,38 _{L. Feng}‡_,100 T. Ferbel‡_,44 _{J.P. Fern´andez Ramos}†_,29 _{F. Fiedler}‡_,76 _{R. Field}†_,16 _{F. Filthaut}‡_,84, 85 _{W. Fisher}‡_,32 _{H.E. Fisk}‡_,15

G. Flanagan†s_,15 _{R. Forrest}†_,7 _{M. Fortner}‡_,100 _{H. Fox}‡_,93 _{M. Franklin}†_,20 _{J.C. Freeman}†_,15 _{H. Frisch}†_,11 S. Fuess‡_,15_{Y. Funakoshi}†_,52 _{C. Galloni}†uu_,41_{P.H. Garbincius}‡_,15 _{A. Garcia-Bellido}‡_,44 _{J.A. Garc´ıa-Gonz´alez}‡_,83 A.F. Garfinkel†_,43 _{P. Garosi}†vv_,41_{V. Gavrilov}‡_,87_{W. Geng}‡_,67, 32 _{C.E. Gerber}‡_,99_{H. Gerberich}†_,22 _{E. Gerchtein}†_,15

Y. Gershtein‡_,111 _{S. Giagu}†_,46 _{V. Giakoumopoulou}†_,3 _{K. Gibson}†_,42 _{C.M. Ginsburg}†_,15 _{G. Ginther}‡_,15, 44 N. Giokaris†_,3 _{P. Giromini}†_,17 _{G. Giurgiu}†_,23 _{V. Glagolev}†_,13 _{D. Glenzinski}†_,15 _{M. Gold}†_,34 _{D. Goldin}†_,47 A. Golossanov†_,15 _{G. Golovanov}‡_,86 _{G. Gomez}†_,9 _{G. Gomez-Ceballos}†_,30_{M. Goncharov}†_,30 _{O. Gonz´alez L´opez}†_,29

I. Gorelov†_,34 _{A.T. Goshaw}†_,14 _{K. Goulianos}†_,45 _{E. Gramellini}†_,6_{P.D. Grannis}‡_,114 _{S. Greder}‡_,71 _{H. Greenlee}‡_,15 G. Grenier‡_,72 _{S. Grinstein}†_,4 _{Ph. Gris}‡_,65 _{J.-F. Grivaz}‡_,68 _{A. Grohsjean}‡kk_,70 _{C. Grosso-Pilcher}†_,11 R.C. Group†_,51, 15 _{S. Gr¨unendahl}‡_,15 _{M.W. Gr¨unewald}‡_,81 _{T. Guillemin}‡_,68 _{J. Guimaraes da Costa}†_,20 G. Gutierrez‡_,15 _{P. Gutierrez}‡_,117 _{S.R. Hahn}†_,15 _{J. Haley}‡_,117 _{J.Y. Han}†_,44 _{L. Han}‡_,59 _{F. Happacher}†_,17 K. Hara†_,49 _{K. Harder}‡_,95_{M. Hare}†_,50 _{A. Harel}‡_,44 _{R.F. Harr}†_,53 _{T. Harrington-Taber}†m_,15_{K. Hatakeyama}†_,5 J.M. Hauptman‡_,105_{C. Hays}†_,38_{J. Hays}‡_,94_{T. Head}‡_,95_{T. Hebbeker}‡_,73_{D. Hedin}‡_,100_{H. Hegab}‡_,118_{J. Heinrich}†_,40

A.P. Heinson‡_,97 _{U. Heintz}‡_,119 _{C. Hensel}‡_,75 _{I. Heredia-De La Cruz}‡ll_,83 _{M. Herndon}†_,54 _{K. Herner}‡_,15 G. Hesketh‡nn_,95_{M.D. Hildreth}‡_,104 _{R. Hirosky}‡_,123 _{T. Hoang}‡_,98 _{J.D. Hobbs}‡_,114 _{A. Hocker}†_,15 _{B. Hoeneisen}‡_,64

J. Hogan‡_,122 _{M. Hohlfeld}‡_,76 _{J.L. Holzbauer}‡_,109 _{Z. Hong}†_,47 _{W. Hopkins}†f_,15 _{S. Hou}†_,1 _{I. Howley}‡_,120 Z. Hubacek‡_,62, 70 _{R.E. Hughes}†_,35 _{U. Husemann}†_,55 _{M. Hussein}†aa_,32 _{J. Huston}†_,32 _{V. Hynek}‡_,62 _{I. Iashvili}‡_,113

Y. Ilchenko‡_,121 _{R. Illingworth}‡_,15 _{G. Introzzi}†xxyy_,41 _{M. Iori}†zz_,46 _{A.S. Ito}‡_,15 _{A. Ivanov}†o_,7 _{S. Jabeen}‡_,119 M. Jaffr´e‡_,68 _{E. James}†_,15 _{D. Jang}†_,10_{A. Jayasinghe}‡_,117 _{B. Jayatilaka}†_,15 _{E.J. Jeon}†_,25 _{M.S. Jeong}‡_,82 _{R. Jesik}‡_,94

P. Jonsson‡_,94 _{K.K. Joo}†_,25 _{J. Joshi}‡_,97 _{S.Y. Jun}†_,10 _{A.W. Jung}‡_,15 _{T.R. Junk}†_,15_{A. Juste}‡_,91 _{E. Kajfasz}‡_,67 M. Kambeitz†_,24_{T. Kamon}†_,25, 47 _{P.E. Karchin}†_,53 _{D. Karmanov}‡_,88 _{A. Kasmi}†_,5 _{Y. Kato}†n_,37_{I. Katsanos}‡_,110 R. Kehoe‡_,121_{S. Kermiche}‡_,67 _{W. Ketchum}†gg_,11 _{J. Keung}†_,40_{N. Khalatyan}‡_,15_{A. Khanov}‡_,118_{A. Kharchilava}‡_,113

Y.N. Kharzheev‡_,86_{B. Kilminster}†cc_,15 _{D.H. Kim}†_,25 _{H.S. Kim}†_,25 _{J.E. Kim}†_,25 _{M.J. Kim}†_,17 _{S.H. Kim}†_,49 S.B. Kim†_,25_{Y.J. Kim}†_,25_{Y.K. Kim}†_,11 _{N. Kimura}†_,52_{M. Kirby}†_,15_{I. Kiselevich}‡_,87_{K. Knoepfel}†_,15 _{J.M. Kohli}‡_,78

K. Kondo†_,52,∗ _{D.J. Kong}†_,25 _{J. Konigsberg}†_,16 _{A.V. Kotwal}†_,14 _{A.V. Kozelov}‡_,89 _{J. Kraus}‡_,109 _{M. Kreps}†_,24 J. Kroll†_,40 _{M. Kruse}†_,14 _{T. Kuhr}†_,24 _{A. Kumar}‡_,113 _{A. Kupco}‡_,63 _{M. Kurata}†_,49 _{T. Kurˇca}‡_,72 _{V.A. Kuzmin}‡_,88 A.T. Laasanen†_,43 _{S. Lammel}†_,15 _{S. Lammers}‡_,102 _{M. Lancaster}†_,28 _{K. Lannon}†w_,35 _{G. Latino}†vv_,41 _{P. Lebrun}‡_,72 H.S. Lee‡_,82 _{H.S. Lee}†_,25 _{J.S. Lee}†_,25 _{S.W. Lee}‡_,105 _{W.M. Lee}‡_,15 _{X. Lei}‡_,96 _{J. Lellouch}‡_,69 _{S. Leo}†_,41_{S. Leone}†_,41

J.D. Lewis†_,15 _{D. Li}‡_,69 _{H. Li}‡_,123 _{L. Li}‡_,97 _{Q.Z. Li}‡_,15 _{J.K. Lim}‡_,82 _{A. Limosani}†r_,14 _{D. Lincoln}‡_,15 J. Linnemann‡_,32 _{V.V. Lipaev}‡_,89 _{E. Lipeles}†_,40 _{R. Lipton}‡_,15 _{A. Lister}†a_,18_{H. Liu}†_,51 _{H. Liu}‡_,121 _{Q. Liu}†_,43

T. Liu†_,15 _{Y. Liu}‡_,59 _{A. Lobodenko}‡_,90 _{S. Lockwitz}†_,55 _{A. Loginov}†_,55_{M. Lokajicek}‡_,63 _{R. Lopes de Sa}‡_,114 D. Lucchesi†tt_,39 _{A. Luc`a}†_,17 _{J. Lueck}†_,24 _{P. Lujan}†_,26 _{P. Lukens}†_,15 _{R. Luna-Garcia}‡oo_,83 _{G. Lungu}†_,45

A.L. Lyon‡_,15 _{J. Lys}†_,26 _{R. Lysak}†d_,12 _{A.K.A. Maciel}‡_,56 _{R. Madar}‡_,74 _{R. Madrak}†_,15 _{P. Maestro}†vv_,41 R. Maga˜na-Villalba‡_,83_{S. Malik}†_,45 _{S. Malik}‡_,110 _{V.L. Malyshev}‡_,86 _{G. Manca}†b_,27_{A. Manousakis-Katsikakis}†_,3

J. Mansour‡_,75 _{L. Marchese}†hh_,6 _{F. Margaroli}†_,46 _{P. Marino}†ww_,41 _{J. Mart´ınez-Ortega}‡_,83 _{M. Mart´ınez}†_,4 K. Matera†_,22 _{M.E. Mattson}†_,53 _{A. Mazzacane}†_,15 _{P. Mazzanti}†_,6 _{R. McCarthy}‡_,114 _{C.L. McGivern}‡_,95

R. McNulty†i_,27 _{A. Mehta}†_,27 _{P. Mehtala}†_,21 _{M.M. Meijer}‡_,84, 85 _{A. Melnitchouk}‡_,15 _{D. Menezes}‡_,100 P.G. Mercadante‡_,58 _{M. Merkin}‡_,88 _{C. Mesropian}†_,45 _{A. Meyer}‡_,73 _{J. Meyer}‡qq_,75_{T. Miao}†_,15 _{F. Miconi}‡_,71

D. Mietlicki†_,31 _{A. Mitra}†_,1 _{H. Miyake}†_,49 _{S. Moed}†_,15 _{N. Moggi}†_,6 _{N.K. Mondal}‡_,80 _{C.S. Moon}†y_,15 R. Moore†ddee_,15 _{M.J. Morello}†ww_,41 _{A. Mukherjee}†_,15 _{M. Mulhearn}‡_,123 _{Th. Muller}†_,24 _{P. Murat}†_,15 M. Mussini†ss_,6 _{J. Nachtman}†m_,15 _{Y. Nagai}†_,49 _{J. Naganoma}†_,52 _{E. Nagy}‡_,67 _{I. Nakano}†_,36 _{A. Napier}†_,50

M. Narain‡_,119 _{R. Nayyar}‡_,96 _{H.A. Neal}‡_,31 _{J.P. Negret}‡_,60 _{J. Nett}†_,47 _{C. Neu}†_,51 _{P. Neustroev}‡_,90 H.T. Nguyen‡_,123 _{T. Nigmanov}†_,42 _{L. Nodulman}†_,2 _{S.Y. Noh}†_,25 _{O. Norniella}†_,22 _{T. Nunnemann}‡_,77_{L. Oakes}†_,38

S.H. Oh†_,14 _{Y.D. Oh}†_,25 _{I. Oksuzian}†_,51 _{T. Okusawa}†_,37 _{R. Orava}†_,21 _{J. Orduna}‡_,122 _{L. Ortolan}†_,4 N. Osman‡_,67 _{J. Osta}‡_,104 _{C. Pagliarone}†_,48 _{A. Pal}‡_,120 _{E. Palencia}†e_,9 _{P. Palni}†_,34 _{V. Papadimitriou}†_,15 N. Parashar‡_,103 _{V. Parihar}‡_,119 _{S.K. Park}‡_,82 _{W. Parker}†_,54 _{R. Partridge}‡mm_,119 _{N. Parua}‡_,102 _{A. Patwa}‡rr_,115

G. Pauletta†aaabbb_,48 _{M. Paulini}†_,10 _{C. Paus}†_,30 _{B. Penning}‡_,15 _{M. Perfilov}‡_,88 _{Y. Peters}‡_,75 _{K. Petridis}‡_,95 G. Petrillo‡_,44 _{P. P´etroff}‡_,68 _{T.J. Phillips}†_,14 _{G. Piacentino}†_,41 _{E. Pianori}†_,40 _{J. Pilot}†_,7 _{K. Pitts}†_,22 _{C. Plager}†_,8

M.-A. Pleier‡_,115 _{V.M. Podstavkov}‡_,15 _{L. Pondrom}†_,54 _{A.V. Popov}‡_,89 _{S. Poprocki}†f_,15 _{K. Potamianos}†_,26 A. Pranko†_,26 _{M. Prewitt}‡_,122_{D. Price}‡_,95 _{N. Prokopenko}‡_,89 _{F. Prokoshin}†z_,13 _{F. Ptohos}†g_,17 _{G. Punzi}†uu_,41 J. Qian‡_,31 _{A. Quadt}‡_,75 _{B. Quinn}‡_,109 _{N. Ranjan}†_,43_{P.N. Ratoff}‡_,93 _{I. Razumov}‡_,89 _{I. Redondo Fern´andez}†_,29

P. Renton†_,38 _{M. Rescigno}†_,46 _{F. Rimondi}†_,6,∗ _{I. Ripp-Baudot}‡_,71 _{L. Ristori}†_,41, 15 _{F. Rizatdinova}‡_,118 A. Robson†_,19 _{T. Rodriguez}†_,40 _{S. Rolli}†h_,50 _{M. Rominsky}‡_,15 _{M. Ronzani}†uu_,41 _{R. Roser}†_,15 _{J.L. Rosner}†_,11

A. Ross‡_,93 _{C. Royon}‡_,70 _{P. Rubinov}‡_,15 _{R. Ruchti}‡_,104 _{F. Ruffini}† vv_,41 _{A. Ruiz}†_,9 _{J. Russ}†_,10 _{V. Rusu}†_,15 G. Sajot‡_,66 _{W.K. Sakumoto}†_,44 _{Y. Sakurai}†_,52 _{A. S´anchez-Hern´andez}‡_,83 _{M.P. Sanders}‡_,77 _{L. Santi}†aaabbb_,48 A.S. Santos‡pp_,56 _{K. Sato}†_,49 _{G. Savage}‡_,15_{V. Saveliev}†u_,15 _{A. Savoy-Navarro}†y_,15 _{L. Sawyer}‡_,107_{T. Scanlon}‡_,94 R.D. Schamberger‡_,114_{Y. Scheglov}‡_,90 _{H. Schellman}‡_,101_{P. Schlabach}†_,15_{E.E. Schmidt}†_,15 _{C. Schwanenberger}‡_,95

T. Schwarz†_,31 _{R. Schwienhorst}‡_,32 _{L. Scodellaro}†_,9 _{F. Scuri}†_,41 _{S. Seidel}†_,34 _{Y. Seiya}†_,37 _{J. Sekaric}‡_,106 A. Semenov†_,13 _{H. Severini}‡_,117 _{F. Sforza}†uu_,41 _{E. Shabalina}‡_,75 _{S.Z. Shalhout}†_,7 _{V. Shary}‡_,70 _{S. Shaw}‡_,32 A.A. Shchukin‡_,89 _{T. Shears}†_,27 _{P.F. Shepard}†_,42 _{M. Shimojima}†t_,49 _{M. Shochet}†_,11 _{I. Shreyber-Tecker}†_,33 V. Simak‡_,62 _{A. Simonenko}†_,13 _{P. Skubic}‡_,117 _{P. Slattery}‡_,44 _{K. Sliwa}†_,50 _{D. Smirnov}‡_,104 _{J.R. Smith}†_,7 F.D. Snider†_,15 _{G.R. Snow}‡_,110 _{J. Snow}‡_,116 _{S. Snyder}‡_,115_{S. S¨oldner-Rembold}‡_,95 _{H. Song}†_,42 _{L. Sonnenschein}‡_,73

V. Sorin†_,4 _{K. Soustruznik}‡_,61 _{R. St. Denis}†_,19 _{M. Stancari}†_,15 _{J. Stark}‡_,66 _{D. Stentz}†v_,15 _{D.A. Stoyanova}‡_,89 M. Strauss‡_,117 _{J. Strologas}†_,34 _{Y. Sudo}†_,49 _{A. Sukhanov}†_,15 _{I. Suslov}†_,13 _{L. Suter}‡_,95 _{P. Svoisky}‡_,117 K. Takemasa†_,49 _{Y. Takeuchi}†_,49 _{J. Tang}†_,11 _{M. Tecchio}†_,31 _{P.K. Teng}†_,1 _{J. Thom}†f_,15 _{E. Thomson}†_,40 V. Thukral†_,47 _{M. Titov}‡_,70 _{D. Toback}†_,47 _{S. Tokar}†_,12 _{V.V. Tokmenin}‡_,86 _{K. Tollefson}†_,32 _{T. Tomura}†_,49 D. Tonelli†e_,15 _{S. Torre}†_,17_{D. Torretta}†_,15 _{P. Totaro}†_,39 _{M. Trovato}†ww_,41 _{Y.-T. Tsai}‡_,44 _{D. Tsybychev}‡_,114

B. Tuchming‡_,70 _{C. Tully}‡_,112 _{F. Ukegawa}†_,49 _{S. Uozumi}†_,25 _{L. Uvarov}‡_,90 _{S. Uvarov}‡_,90 _{S. Uzunyan}‡_,100 R. Van Kooten‡_,102_{W.M. van Leeuwen}‡_,84 _{N. Varelas}‡_,99 _{E.W. Varnes}‡_,96 _{I.A. Vasilyev}‡_,89 _{F. V´azquez}†l_,16

G. Velev†_,15 _{C. Vellidis}†_,15 _{A.Y. Verkheev}‡_,86 _{C. Vernieri}†ww_,41 _{L.S. Vertogradov}‡_,86 _{M. Verzocchi}‡_,15 M. Vesterinen‡_,95 _{M. Vidal}†_,43 _{D. Vilanova}‡_,70 _{R. Vilar}†_,9 _{J. Viz´an}†bb_,9 _{M. Vogel}†_,34 _{P. Vokac}‡_,62 _{G. Volpi}†_,17

G. Watts‡_,124 _{M. Wayne}‡_,104 _{J. Weichert}‡_,76 _{L. Welty-Rieger}‡_,101 _{W.C. Wester III}†_,15 _{D. Whiteson}†c_,40 A.B. Wicklund†_,2 _{S. Wilbur}†_,7 _{H.H. Williams}†_,40 _{M.R.J. Williams}‡_,102 _{G.W. Wilson}‡_,106 _{J.S. Wilson}†_,31 P. Wilson†_,15 _{B.L. Winer}†_,35 _{P. Wittich}†f_,15 _{M. Wobisch}‡_,107 _{S. Wolbers}†_,15 _{H. Wolfe}†_,35 _{D.R. Wood}‡_,108 T. Wright†_,31_{X. Wu}†_,18 _{Z. Wu}†_,5 _{T.R. Wyatt}‡_,95_{Y. Xie}‡_,15 _{R. Yamada}‡_,15 _{K. Yamamoto}†_,37 _{D. Yamato}†_,37

S. Yang‡_,59 _{T. Yang}†_,15 _{U.K. Yang}†_,25 _{Y.C. Yang}†_,25 _{W.-M. Yao}†_,26 _{T. Yasuda}‡_,15 _{Y.A. Yatsunenko}‡_,86 W. Ye‡_,114 _{Z. Ye}‡_,15 _{G.P. Yeh}†_,15 _{K. Yi}†m_,15 _{H. Yin}‡_,15_{K. Yip}‡_,115_{J. Yoh}†_,15_{K. Yorita}†_,52_{T. Yoshida}†k_,37 S.W. Youn‡_,15 _{G.B. Yu}†_,14 _{I. Yu}†_,25 _{J.M. Yu}‡_,31 _{A.M. Zanetti}†_,48 _{Y. Zeng}†_,14 _{J. Zennamo}‡_,113 _{T.G. Zhao}‡_,95 B. Zhou‡_,31 _{C. Zhou}†_,14 _{J. Zhu}‡_,31 _{M. Zielinski}‡_,44 _{D. Zieminska}‡_,102 _{L. Zivkovic}‡_,69 _{and S. Zucchelli}†ss6

(CDF Collaboration),† (D0 Collaboration),‡

1_{Institute of Physics, Academia Sinica, Taipei, Taiwan 11529, Republic of China} 2_{Argonne National Laboratory, Argonne, Illinois 60439, USA}

3_{University of Athens, 157 71 Athens, Greece}

4_{Institut de Fisica d’Altes Energies, ICREA, Universitat Autonoma de Barcelona, E-08193, Bellaterra (Barcelona), Spain} 5_{Baylor University, Waco, Texas 76798, USA}

6_{Istituto Nazionale di Fisica Nucleare Bologna,} ss_{University of Bologna, I-40127 Bologna, Italy} 7_{University of California, Davis, Davis, California 95616, USA}

8_{University of California, Los Angeles, Los Angeles, California 90024, USA} 9_{Instituto de Fisica de Cantabria, CSIC-University of Cantabria, 39005 Santander, Spain}

10_{Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA} 11_{Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637, USA}

12_{Comenius University, 842 48 Bratislava, Slovakia; Institute of Experimental Physics, 040 01 Kosice, Slovakia} 13_{Joint Institute for Nuclear Research, RU-141980 Dubna, Russia}

14_{Duke University, Durham, North Carolina 27708, USA} 15_{Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA}

16_{University of Florida, Gainesville, Florida 32611, USA}

17_{Laboratori Nazionali di Frascati, Istituto Nazionale di Fisica Nucleare, I-00044 Frascati, Italy} 18_{University of Geneva, CH-1211 Geneva 4, Switzerland}

19_{Glasgow University, Glasgow G12 8QQ, United Kingdom} 20_{Harvard University, Cambridge, Massachusetts 02138, USA}

21_{Division of High Energy Physics, Department of Physics, University of Helsinki,}

FIN-00014, Helsinki, Finland; Helsinki Institute of Physics, FIN-00014, Helsinki, Finland

22_{University of Illinois, Urbana, Illinois 61801, USA} 23_{The Johns Hopkins University, Baltimore, Maryland 21218, USA}

24_{Institut f¨ur Experimentelle Kernphysik, Karlsruhe Institute of Technology, D-76131 Karlsruhe, Germany} 25_{Center for High Energy Physics: Kyungpook National University,}

Daegu 702-701, Korea; Seoul National University, Seoul 151-742, Korea; Sungkyunkwan University, Suwon 440-746, Korea; Korea Institute of Science and Technology Information,

Daejeon 305-806, Korea; Chonnam National University, Gwangju 500-757, Korea; Chonbuk National University, Jeonju 561-756,

Korea; Ewha Womans University, Seoul, 120-750, Korea

26_{Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA} 27_{University of Liverpool, Liverpool L69 7ZE, United Kingdom}

28_{University College London, London WC1E 6BT, United Kingdom}

29_{Centro de Investigaciones Energeticas Medioambientales y Tecnologicas, E-28040 Madrid, Spain} 30_{Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA}

31_{University of Michigan, Ann Arbor, Michigan 48109, USA} 32_{Michigan State University, East Lansing, Michigan 48824, USA}

33_{Institution for Theoretical and Experimental Physics, ITEP, Moscow 117259, Russia} 34_{University of New Mexico, Albuquerque, New Mexico 87131, USA}

35_{The Ohio State University, Columbus, Ohio 43210, USA} 36_{Okayama University, Okayama 700-8530, Japan}

37_{Osaka City University, Osaka 558-8585, Japan} 38_{University of Oxford, Oxford OX1 3RH, United Kingdom}

39_{Istituto Nazionale di Fisica Nucleare, Sezione di Padova,} tt_{University of Padova, I-35131 Padova, Italy} 40_{University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA}

41_{Istituto Nazionale di Fisica Nucleare Pisa,} uu_{University of Pisa,} vv_{University of Siena,} ww_{Scuola Normale Superiore,}

I-56127 Pisa, Italy, xx_{INFN Pavia, I-27100 Pavia,}

42_{University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA} 43_{Purdue University, West Lafayette, Indiana 47907, USA} 44_{University of Rochester, Rochester, New York 14627, USA} 45_{The Rockefeller University, New York, New York 10065, USA}

46_{Istituto Nazionale di Fisica Nucleare, Sezione di Roma 1,} zz_{Sapienza Universit`a di Roma, I-00185 Roma, Italy} 47_{Mitchell Institute for Fundamental Physics and Astronomy,}

Texas A&M University, College Station, Texas 77843, USA

48_{Istituto Nazionale di Fisica Nucleare Trieste,} aaa_{Gruppo Collegato di Udine,} bbb_{University of Udine, I-33100 Udine, Italy,} ccc_{University of Trieste, I-34127 Trieste, Italy}

49_{University of Tsukuba, Tsukuba, Ibaraki 305, Japan} 50_{Tufts University, Medford, Massachusetts 02155, USA} 51_{University of Virginia, Charlottesville, Virginia 22906, USA}

52_{Waseda University, Tokyo 169, Japan}

53_{Wayne State University, Detroit, Michigan 48201, USA} 54_{University of Wisconsin, Madison, Wisconsin 53706, USA}

55_{Yale University, New Haven, Connecticut 06520, USA}

56_{LAFEX, Centro Brasileiro de Pesquisas F´ısicas, Rio de Janeiro, Brazil} 57_{Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brazil}

58_{Universidade Federal do ABC, Santo Andr´e, Brazil}

59_{University of Science and Technology of China, Hefei, People’s Republic of China} 60_{Universidad de los Andes, Bogot´a, Colombia}

61_{Charles University, Faculty of Mathematics and Physics,}

Center for Particle Physics, Prague, Czech Republic

62_{Czech Technical University in Prague, Prague, Czech Republic}

63_{Institute of Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic} 64_{Universidad San Francisco de Quito, Quito, Ecuador}

65_{LPC, Universit´e Blaise Pascal, CNRS/IN2P3, Clermont, France} 66_{LPSC, Universit´e Joseph Fourier Grenoble 1, CNRS/IN2P3,}

Institut National Polytechnique de Grenoble, Grenoble, France

67_{CPPM, Aix-Marseille Universit´e, CNRS/IN2P3, Marseille, France} 68_{LAL, Universit´e Paris-Sud, CNRS/IN2P3, Orsay, France} 69_{LPNHE, Universit´es Paris VI and VII, CNRS/IN2P3, Paris, France}

70_{CEA, Irfu, SPP, Saclay, France}

71_{IPHC, Universit´e de Strasbourg, CNRS/IN2P3, Strasbourg, France}

72_{IPNL, Universit´e Lyon 1, CNRS/IN2P3, Villeurbanne, France and Universit´e de Lyon, Lyon, France} 73_{III. Physikalisches Institut A, RWTH Aachen University, Aachen, Germany}

74_{Physikalisches Institut, Universit¨at Freiburg, Freiburg, Germany}

75_{II. Physikalisches Institut, Georg-August-Universit¨at G¨ottingen, G¨ottingen, Germany} 76_{Institut f¨ur Physik, Universit¨at Mainz, Mainz, Germany}

77_{Ludwig-Maximilians-Universit¨at M¨unchen, M¨unchen, Germany} 78_{Panjab University, Chandigarh, India}

79_{Delhi University, Delhi, India}

80_{Tata Institute of Fundamental Research, Mumbai, India} 81_{University College Dublin, Dublin, Ireland}

82_{Korea Detector Laboratory, Korea University, Seoul, Korea} 83_{CINVESTAV, Mexico City, Mexico}

84_{Nikhef, Science Park, Amsterdam, the Netherlands} 85_{Radboud University Nijmegen, Nijmegen, the Netherlands}

86_{Joint Institute for Nuclear Research, Dubna, Russia} 87_{Institute for Theoretical and Experimental Physics, Moscow, Russia}

88_{Moscow State University, Moscow, Russia} 89_{Institute for High Energy Physics, Protvino, Russia} 90_{Petersburg Nuclear Physics Institute, St. Petersburg, Russia}

91_{Instituci´o Catalana de Recerca i Estudis Avan¸cats (ICREA) and Institut de F´ısica d’Altes Energies (IFAE), Barcelona, Spain} 92_{Uppsala University, Uppsala, Sweden}

93_{Lancaster University, Lancaster LA1 4YB, United Kingdom} 94_{Imperial College London, London SW7 2AZ, United Kingdom} 95_{The University of Manchester, Manchester M13 9PL, United Kingdom}

96_{University of Arizona, Tucson, Arizona 85721, USA} 97_{University of California Riverside, Riverside, California 92521, USA}

98_{Florida State University, Tallahassee, Florida 32306, USA} 99_{University of Illinois at Chicago, Chicago, Illinois 60607, USA}

101_{Northwestern University, Evanston, Illinois 60208, USA} 102_{Indiana University, Bloomington, Indiana 47405, USA} 103_{Purdue University Calumet, Hammond, Indiana 46323, USA} 104_{University of Notre Dame, Notre Dame, Indiana 46556, USA}

105_{Iowa State University, Ames, Iowa 50011, USA} 106_{University of Kansas, Lawrence, Kansas 66045, USA} 107_{Louisiana Tech University, Ruston, Louisiana 71272, USA} 108_{Northeastern University, Boston, Massachusetts 02115, USA} 109_{University of Mississippi, University, Mississippi 38677, USA}

110_{University of Nebraska, Lincoln, Nebraska 68588, USA} 111_{Rutgers University, Piscataway, New Jersey 08855, USA} 112_{Princeton University, Princeton, New Jersey 08544, USA} 113_{State University of New York, Buffalo, New York 14260, USA} 114_{State University of New York, Stony Brook, New York 11794, USA}

115_{Brookhaven National Laboratory, Upton, New York 11973, USA} 116_{Langston University, Langston, Oklahoma 73050, USA} 117_{University of Oklahoma, Norman, Oklahoma 73019, USA} 118_{Oklahoma State University, Stillwater, Oklahoma 74078, USA}

119_{Brown University, Providence, Rhode Island 02912, USA} 120_{University of Texas, Arlington, Texas 76019, USA} 121_{Southern Methodist University, Dallas, Texas 75275, USA}

122_{Rice University, Houston, Texas 77005, USA} 123_{University of Virginia, Charlottesville, Virginia 22904, USA} 124_{University of Washington, Seattle, Washington 98195, USA}

(Dated: September 27th, 2013)

We combine six measurements of the inclusive top-quark pair (t¯t) production cross section (σt¯t)

from data collected with the CDF and D0 detectors at the Fermilab Tevatron with proton anti-proton collisions at√s = 1.96 TeV. The data correspond to integrated luminosities of up to 8.8 fb−1_{. We}

obtain a value of σt¯t= 7.60 ± 0.41 pb for a top-quark mass of mt= 172.5 GeV. The contributions

to the uncertainty are 0.20 pb from statistical sources, 0.29 pb from systematic sources, and 0.21 pb from the uncertainty on the integrated luminosity. The result is in good agreement with the standard model expectation of 7.35+0.28

−0.33pb at NNLO+NNLL in pertubative QCD.

PACS numbers: 14.65.Ha, 12.38.Qk, 13.85.Qk

∗_Deceased

†_{With visitors from}a_{University of British Columbia, Vancouver,}

BC V6T 1Z1, Canada, b_{Istituto Nazionale di Fisica Nucleare,}

Sezione di Cagliari, 09042 Monserrato (Cagliari), Italy,c_University

of California Irvine, Irvine, CA 92697, USA,d_{Institute of Physics,}

Academy of Sciences of the Czech Republic, 182 21, Czech Re-public, e_{CERN, CH-1211 Geneva, Switzerland,} f_Cornell

Univer-sity, Ithaca, NY 14853, USA, g_{University of Cyprus, Nicosia}

CY-1678, Cyprus, h_{Office of Science, U.S. Department of}

En-ergy, Washington, DC 20585, USA, i_{University College Dublin,}

Dublin 4, Ireland,j_{ETH, 8092 Z¨urich, Switzerland,}k_{University of}

Fukui, Fukui City, Fukui Prefecture, Japan 910-0017,l_Universidad

Iberoamericana, Lomas de Santa Fe, M´exico, C.P. 01219, Dis-trito Federal, m_{University of Iowa, Iowa City, IA 52242, USA,} n_{Kinki University, Higashi-Osaka City, Japan 577-8502,} o_Kansas

State University, Manhattan, KS 66506, USA, p_Brookhaven

Na-tional Laboratory, Upton, NY 11973, USA,q_{Queen Mary,}

Univer-sity of London, London, E1 4NS, United Kingdom, r_University

of Melbourne, Victoria 3010, Australia, s_{Muons, Inc., Batavia,}

IL 60510, USA,t_{Nagasaki Institute of Applied Science, Nagasaki}

851-0193, Japan,u_{National Research Nuclear University, Moscow}

115409, Russia, v_{Northwestern University, Evanston, IL 60208,}

USA,w_{University of Notre Dame, Notre Dame, IN 46556, USA,} x_{Universidad de Oviedo, E-33007 Oviedo, Spain,} y_CNRS-IN2P3,

Paris, F-75205 France,z_{Universidad Tecnica Federico Santa Maria,}

110v Valparaiso, Chile,aa_{The University of Jordan, Amman 11942,}

I. INTRODUCTION

The top quark, the most massive elementary particle to date and the final member of the three families of quarks of the standard model (SM), was first observed in 1995 by the CDF and D0 experiments at the Fermilab Tevatron proton-antiproton (p¯p) collider [1, 2]. The large mass of the top quark of mt= 173.20 ±0.87 GeV [3] and its short

Jordan, bb_{Universite catholique de Louvain, 1348}

Louvain-La-Neuve, Belgium, cc_{University of Z¨urich, 8006 Z¨urich,}

Switzer-land,dd_{Massachusetts General Hospital, Boston, MA 02114 USA,} ee_{Harvard Medical School, Boston, MA 02114 USA,} f f_Hampton

University, Hampton, VA 23668, USA,gg_{Los Alamos National}

Lab-oratory, Los Alamos, NM 87544, USA,hh_{Universit`a degli Studi di}

Napoli Federico I, I-80138 Napoli, Italy

‡_{With visitors from} ii_{Augustana College, Sioux Falls, SD, USA,} jj_{The University of Liverpool, Liverpool, UK,}kk_{DESY, Hamburg,}

Germany, ll_{Universidad Michoacana de San Nicolas de Hidalgo,}

Morelia, Mexico,mm_{SLAC, Menlo Park, CA, USA,}nn_University

College London, London, UK,oo_{Centro de Investigacion en}

Com-putacion - IPN, Mexico City, Mexico, pp_{Universidade Estadual}

Paulista, S˜ao Paulo, Brazil,qq_{Karlsruher Institut f¨ur Technologie}

(KIT) - Steinbuch Centre for Computing (SCC),rr_{Office of}

lifetime of approximately 10−25 _{s [4, 5] are of special} in-terest. The lifetime is far shorter than the hadronization time, and provides the opportunity to study the proper-ties of essentially a bare quark. The large mass suggests that the top quark may play a special role in the mech-anism of electroweak symmetry breaking, and thereby provide sensitivity to probe a broad class of SM exten-sions. In addition, with the recent discovery of a Higgs boson [6, 7], the properties of the top quark are expected to be related to the stability of the vacuum in the uni-verse [8].

The properties of the top quark can be assessed through precise determinations of its production mech-anisms and decay rates, in comparison to SM expecta-tions. Particles and couplings predicted by extensions of the SM can affect the observed production cross sections of top quarks. For example, the observed top-quark pair (t¯t) production cross section in all of the experimental fi-nal states may be enhanced above the SM expectation by the production of new resonances [9, 10], or the observed production cross section in some of the experimental fi-nal states may be altered from the SM expectation by top quark decay into new channels, such as a hypothesized charged Higgs boson and b quark [11, 12].

In this article, we report on the first combination of measurements by the CDF and D0 experiments at the Fermilab Tevatron of the inclusive t¯t production cross section (σt¯t), with the goal of reducing the experimental uncertainty and thereby providing a better test of the SM prediction. The inclusive t¯t cross section has also been measured at the LHC at different center of mass ener-gies [13, 14]. In the remainder of this section, the status of the theoretical predictions and the experimental sig-natures of the t¯t final states are described. Section II reviews all six measurements, reports the first combina-tion of the four CDF results, and reviews the combinacombina-tion of the two D0 results [15]. The categories of systematic uncertainties and their correlations among the measure-ments are detailed in Sec. III. The first combination of the CDF and D0 measurements is reported in Sec. IV and conclusions are drawn in Sec. V.

A. Predictions for thet¯t production cross section According to the SM, production of top quarks at hadron colliders takes place through strong interactions that produce t¯t, or through electroweak processes that produce a single top quark. At the Tevatron p¯p collider, with a center of mass energy of √s = 1.96 TeV, top quark production occurs mainly through t¯t production, which is the focus of this article. The contribution to t¯t production is approximately 85% from quark-antiquark annihilation (q ¯q → t¯t) and 15% from gluon-gluon fusion (gg → t¯t).

SM predictions for inclusive t¯t production at the Teva-tron, calculated to different orders in perturbative quan-tum chromodynamics (QCD), are available in Refs. [16–

24]. The first calculations at full next-to-leading-order (NLO) QCD were performed before the discovery of the top quark [16], and have been updated using the more re-cent CTEQ6.6 parton distribution functions (PDF) [17]. These full NLO calculations were further improved by adding resummations of logarithmic corrections to the cross section from higher-order soft-gluon radiation, in particular by including next-to-leading logarithmic (NLL) soft-gluon resummation [18] and the more recent PDF [19]. Also available are NLO calculations with soft-gluon resummation to next-to-next-to-leading logarith-mic (NNLL) accuracy, and approximations at next-to-next-to-leading-order (NNLO) obtained by re-expanding the result from NLO+NNLL in a fixed-order series in the strong coupling constant αs (NNLOapprox) [20–23]. Differences between these calculations include using a momentum-space or N -space approach, and resumma-tion of the total cross secresumma-tion or integraresumma-tion of the differ-ential cross section over phase space.

The computation at full NNLO QCD was performed for the first time in 2013 [24], with an uncertainty on σt¯tof approximately 4% when matched with NNLL soft-gluon resummation. To estimate the uncertainty on σt¯t for a given top-quark mass, the factorization and renor-malization scales are changed by factors of two or one half relative to their nominal values. The sensitivity to choice of PDF is evaluated by changing all the PDF parame-ters within their uncertainties [17]. The predicted values of σt¯t and their corresponding uncertainties, calculated with the Top++ program [25], are provided in Table I at NLO, NLO+NLL, and NNLO+NNLL. The top-quark mass for these calculations is set to mt= 172.5 GeV, with the PDF set corresponding to either MSTW2008nlo68cl or MSTW2008nnlo68cl [26].

We use the full NNLO+NNLL prediction as the de-fault value for comparison with the measurements since it has the smallest uncertainty. The benefit of the re-cent theoretical advance to full NNLO+NNLL consists of an approximate 4% increase of the cross section and a reduction in the scale uncertainty with respect to the NLO+NLL prediction.

TABLE I: SM predictions of σt¯tat different orders in

pertur-bative QCD, using Top++ [25].

Calculation σt¯t (pb) ∆σscale(pb) ∆σPDF(pb) NLO 6.85 +0.37 −0.77 +0.19 −0.13 NLO+NLL 7.09 +0.28 −0.51 +0.19 −0.13 NNLO+NNLL 7.35 +0.11 −0.21 +0.17 −0.12

B. Experimental final states

In the SM, the top quark decays through the weak in-teraction into a W+_{boson and a down-type quark, where} decays into W+_{s and W}+_{d are expected to be suppressed}

relative to W+_{b by the square of the} Cabibbo-Kobayashi-Maskawa [27] matrix elements Vts and Vtd. Hence, the decay t → W+_{b, and its charge conjugate, is expected} to occur with a branching fraction above ≈ 99.8%. The W+ _{boson subsequently decays either leptonically into} e+_ν

e, µ+νµ, or τ+ντ; or into u ¯d or c¯s quarks [28]. All the quarks in the final state evolve into jets of hadrons. In studies of t¯t → W+_bW−_{¯b, different final states are} defined by the decays of the two W bosons. The main channels are the following:

(i) Dilepton: Events where both W bosons decay into eνe, µνµ, or τ ντ with the τ decaying leptonically, comprise the dilepton channel. While the branch-ing fraction for this channel is only about 4%, its analysis benefits from having a low background.

(ii) Lepton+jets: This channel (ℓ+jets) consists of events where one W boson decays into quarks and the other into eνe, µνµ, or τ ντ with the τ decaying leptonically. The branching fraction of this chan-nel is approximately 35%. The main background contribution is from the production of W bosons in association with jets.

(iii) All-jets: Events where both W bosons decay into quarks form the channel with the largest branching fraction of about 46%. Experimentally, this chan-nel suffers from a large background contribution from multijet production.

The remaining two channels are from final states where at least one of the W bosons decays into τ ντ with the τ decaying into hadrons and ντ. These channels have larger uncertainties, because of the difficulty of reconstructing the hadronic τ decays. Hence, they are not used in this combination.

C. Selection and modeling

The measurement of the t¯t production cross section in each individual final state requires specific event-selection criteria to enrich the t¯t content of each sample, a detailed understanding of background contributions, as well as good modeling of the SM expectation for the signal and for all background processes. This section briefly dis-cusses these essential ingredients. The CDF II and D0 detectors are described in Refs. [29] and [30], respectively.

1. Event selection

Candidate t¯t events are collected by triggering on lep-tons of large transverse momentum (pT), and on charac-teristics of ℓ+jets or multijet events that depend on the specific final state. Differences in topology and kinematic properties between t¯t events and background processes in each final state are exploited to enrich the t¯t content of

the data samples. The discriminating observables used at CDF and D0 for these selections are based on the properties of jets, electrons, muons, and the imbalance in transverse momentum (/p_T) in such events. At D0, jets are reconstructed using an iterative midpoint jet cone al-gorithm [31] with R = 0.5 [32], while CDF uses a similar algorithm [33] with R = 0.4. Electrons are reconstructed using information from the electromagnetic calorimeter, and also require a track from the central tracker that is matched to the energy cluster in the calorimeter. Muons are reconstructed using information from the muon sys-tem, and also require a matching track from the central tracker. Isolation criteria are applied to identify electrons and muons from W → ℓνℓdecays. The reconstructed pri-mary interaction vertex must be within 60 cm of the lon-gitudinal center of the detector, corresponding to about 95% of the luminous region.

A common feature of all t¯t events are the two b-quark jets from t → W b decays. The t¯t content of the selected event samples can therefore be enriched by demanding that they contain identified b jets. At CDF, b jets are identified through the presence of a displaced, secondary vertex [34], while at D0, a neural-network (NN) based b-jet identification algorithm is used for this purpose [35]. The NN-based algorithm combines the information about the impact parameters of charged particle tracks and the properties of reconstructed secondary vertices into a sin-gle discriminant.

The /p_T is reconstructed using the energy deposited in calorimeter cells, incorporating corrections for the pT of leptons and jets. More details on identification crite-ria for these quantities at CDF and D0 can be found in Ref. [36].

General topologies of each of the three channels are de-scribed below, with specific selections dede-scribed in the re-spective references to the individual measurements cited in Sec. II. The selections are designed so that the chan-nels are mutually exclusive.

(i) Dilepton candidates are selected by requiring at least two central jets with high pT; two high-pT, isolated leptons of opposite charge; and large /p_T to account for the undetected neutrinos from the W → ℓνℓ decays. Other selections based on the global properties of the event are applied to reduce backgrounds in each of the e+_e−_{, e}±_µ∓_{, and µ}+_µ− final states.

(ii) ℓ+jets candidates must have at least three high-pT jets; one high-pT, isolated electron or muon within a fiducial region; and significant /p_T to account for the undetected neutrino from the W → ℓνℓ decay. In addition, requirements are applied on the az-imuthal angle between the lepton direction and /p_T, to reduce contributions from multijet background. (iii) All-jets candidates must have at least six central jets with large pT. Events containing an isolated electron or muon are vetoed, and the event /p_T has

to be compatible with its resolution as there are no neutrinos from the W boson decays in this final state.

2. Modeling of signal

A top-quark mass of mt= 172.5 GeV, which is close to the measured top-quark mass [3], is used in the simula-tion of t¯t production. Several other values are also simu-lated in order to describe the dependence of the measure-ment of σt¯ton the assumed value of mtin the simulation. This dependence is described in Sec. IV.

All of the experimental measurements use LO simula-tions to predict the fraction of t¯t production passing the selection requirements and to model the kinematic prop-erties of t¯t production. These quantities are less sensitive to higher-order QCD corrections than the absolute rate. Contributions to the systematic uncertainty from t¯t mod-eling are estimated to be approximately 1% due to the effect of higher-order QCD corrections. At D0, t¯t duction and decay are simulated using the alpgen pro-gram [37]. Parton showering and hadronization are sim-ulated using the pythia [38] program. Double-counting of partonic event configurations is avoided by using a jet-parton matching scheme [39]. The generated events are subsequently processed through a geant-based [40] sim-ulation of the D0 detector. The presence of additional p¯p interactions is modeled by overlaying data from random p¯p crossings on the events. At CDF, t¯t events are sim-ulated using standalone pythia, and subsequently pro-cessed through a geant-based simulation of the CDF II detector [41, 42], with additional p¯p collisions modeled using simulation. Finally, the events are reconstructed with the same algorithms as used for data. Both col-laborations implement additional correction factors to take into account any differences between data and sim-ulation. In particular, corrections are made to the jet-energy scale, jet-jet-energy resolution, electron and muon energy scales, trigger efficiencies, and b-jet identification performance [15, 43–46]. At D0, the CTEQ6L1 PDF set is used for event generation [47], while CDF uses the CTEQ6.6 [17] or CTEQ5L PDF parametrizations [48].

3. Modeling of backgrounds

Different sources of backgrounds contribute to different final states. In the dilepton channel, the dominant source of background is from Drell-Yan production of Z bosons or virtual photons through q ¯q → Z or γ∗_{and associated} jets, with the Z/γ∗_{decaying into a pair of leptons. In} ad-dition, electroweak diboson production (W W , W Z, and ZZ) and instrumental background arising from multijet and W +jets production, where a jet is misidentified as a lepton, contribute to the dilepton final state. At CDF, W γ production is considered separately, while at D0 this contribution is included in the instrumental background

when the γ is misidentified as a lepton or as a jet. For ℓ+jets final states, the major background contribution is from W +jets production, where the W boson decays into ℓνℓ. Backgrounds from single top-quark production, diboson production, Z/γ∗_{+jets, and multijet production} are also considered. The dominant background contri-bution to all-jets events is from multijet production pro-cesses.

Contributions from Z/γ∗_{+jets and W +jets} back-grounds are modeled using alpgen, followed by pythia for parton showering and hadronization. Contributions from heavy flavor (HF) quarks, namely from W + b¯b, W + c¯c, W + c, Z/γ∗_{+ b¯b, and Z/γ}∗_{+ c¯c are simulated} separately.

The diboson contributions to dilepton and ℓ+jets final states are simulated using standalone pythia, normal-ized to the NLO cross section calculated using mcfm [49]. Single top-quark contributions are simulated using the comphep_{generator [50] at D0, and madevent [51] at} CDF, and normalized to the approximate NNNLO [52] and NLO [53] predictions, respectively. The separate background contribution from W γ production at CDF is simulated using the baur program [54].

The instrumental and multijet backgrounds are esti-mated using data-driven methods in different ways for each final state at CDF and D0.

II. CDF AND D0 COMBINATIONS We present the first combination of four CDF measure-ments, which gives the most precise CDF result to date, and then review the result of a published combination of two D0 measurements.

A. CDF measurements and their combination CDF includes four measurements in the combination: one from the dilepton channel [43], two from the lep-ton+jets channel [44], and one from the all-jets chan-nel [45]. Table II summarizes these CDF measurements of σt¯t and their uncertainties. A detailed description of the sources of systematic uncertainty and their correla-tions is given in Section III.

The dilepton (DIL) measurement, σt¯t= 7.09±0.83 pb, relies on counting events with at least one identified b jet, and uses the full Run II data set corresponding to an integrated luminosity of 8.8 fb−1_{[43]. Backgrounds from} diboson and Z/γ∗ _{events are predicted from simulation,} with additional correction factors extracted from control samples in data. The largest systematic uncertainties for this measurement are from the luminosity and the modeling of the detector’s b-jet identification.

The two CDF measurements in the ℓ+jets channel are based on 4.6 fb−1 _{of data and apply complementary} methods to discriminate signal from background [44].

TABLE II: CDF measurements of σt¯t and their combination (in pb), with individual contributions to their uncertainties (in

pb).

DIL LJ-ANN LJ-SVX HAD CDF combined Central value of σtt¯ 7.09 7.82 7.32 7.21 7.63

Sources of systematic uncertainty

Modeling of the detector 0.39 0.11 0.34 0.41 0.17

Modeling of signal 0.23 0.23 0.23 0.44 0.21

Modeling of jets 0.23 0.23 0.29 0.71 0.21

Method of extracting σt¯t 0.00 0.01 0.01 0.08 0.01

Background modeled from theory 0.01 0.13 0.29 – 0.10 Background based on data 0.15 0.07 0.11 0.59 0.08 Normalization of Z/γ∗_{prediction – 0.16 0.15 – 0.13}

Luminosity: inelastic p¯p cross section 0.28 – – 0.29 0.05

Luminosity: detector 0.30 0.02 0.02 0.30 0.06

Total systematic uncertainty 0.67 0.41 0.61 1.18 0.39 Statistical uncertainty 0.49 0.38 0.36 0.50 0.31

Total uncertainty 0.83 0.56 0.71 1.28 0.50

The first measurement, σt¯t= 7.82 ± 0.56 pb, uses an ar-tificial neural network to exploit differences between the kinematic properties of signal and W +jets background, without employing b-jet identification. This analysis is referred to as LJ-ANN. Due to the large mass of the top quark, its decay products have larger pT and are more isotropic than the main backgrounds from W +jets and multijet production. Seven kinematic properties are se-lected for analysis in an artificial NN in order to mini-mize the statistical uncertainty and the systematic un-certainty from the calibration of the jet energy. Since W +jets production is the dominant background in the ℓ+jets channel before the application of b-jet identifica-tion requirements, the NN is trained using only t¯t and W +jets simulated samples. The number of t¯t events is then extracted from a maximum likelihood fit to the dis-tribution of NN output in data with three or more jets. The largest systematic uncertainties are from the calibra-tion of jet energy and the modeling of the t¯t signal.

The second ℓ+jets measurement, σt¯t= 7.32 ± 0.71 pb, suppresses the dominant W +jets background by recon-struction of displaced secondary vertices to identify b jets. This analysis is referred to as LJ-SVX. The σt¯t is ex-tracted from a maximum likelihood fit to the observed number of events in data with at least one identified b jet, given the predicted background. The W +HF contribu-tion is determined by applying the b-jet identificacontribu-tion ef-ficiency and a corrected HF fraction to an estimate of W +jets before b-jet identification. The HF fraction pre-dicted by the simulation is an underestimate of the yield in data, and a correction factor is derived from a data control sample. The estimate of W +jets is the number of observed events in data before b-jet identification mi-nus the contribution from other processes (t¯t, multijet, single-top, diboson, and Z/γ∗_{+jets). The contribution} from events with jets misidentified as b jets is found by applying a parameterized probability function to the data

before the b-jet identification requirement. The largest systematic uncertainties in this method arise from the correction for the W +HF background and the modeling of the b-jet identification efficiency.

Both ℓ+jets measurements reduce the uncertainty from luminosity by using the ratio of the t¯t to the Z/γ∗_cross sections measured concurrently. This ratio is multiplied by the more precise theoretical prediction for the Z/γ∗ cross section [55], thereby replacing the 6% uncertainty on luminosity with a 2% uncertainty from the smaller theoretical and experimental uncertainties on the Z/γ∗ cross section.

The ℓ+jets measurements use subsets of events that pass a common selection. Their 32% statistical corre-lation is evaluated through 1000 simulated experiments. The σt¯tis extracted for each such simulated experiment; for LJ-ANN, through a maximum likelihood fit to the NN distribution, and for LJ-SVX, through the observed number of events with at least one identified b jet in each simulated experiment.

In the all-jets (HAD) measurement, σt¯t = 7.21 ± 1.28 pb, a signal sample is selected by requiring six to eight jets in an event [45]. Additional criteria require the presence of identified b jets and restrictions on the value of a NN discriminant. The latter involves 13 ob-servables as input, and is trained to suppress the large backgrounds from multijet events. To improve the sta-tistical significance of the measurement, the requirement on the value of the discriminant is optimized separately for events with only one b jet and for events with more than one b jet. The σt¯tvalue is extracted from a simul-taneous fit to the reconstructed top-quark mass in both samples. The measurement uses only data corresponding to an integrated luminosity of 2.9 fb−1_{, but the largest} single uncertainty arises from the limited knowledge of the calibration of jet energy.

un-biased estimate (BLUE) [56–58] is calculated for σt¯twith the goal of minimizing the total uncertainty. A covari-ance matrix is constructed from the statistical and sys-tematic uncertainties of each result, and from their statis-tical and systematic correlations. The matrix is inverted to obtain a weight for each result. These weights are applied to the results to obtain the best estimate.

Three iterations of the BLUE combination procedure are performed to eliminate a small bias. For a measure-ment with N observed events, inspection of the simple expression σt¯t = (N − B)/(ǫL) shows that the uncer-tainty on the background estimate B gives a systematic uncertainty on σt¯t that is independent of the measured value of σt¯t. However, the uncertainties on the t¯t selec-tion efficiency ǫ and the luminosity L produce systematic uncertainties on σt¯tthat are directly proportional to the measured value of σt¯t. This means that measurements that observe a low value for σt¯t have a smaller system-atic uncertainty and a larger weight in the BLUE combi-nation than measurements that observe a high value for σt¯t. Hence, the BLUE combination underestimates σt¯t and its uncertainty. This bias is removed by calculating the size of the systematic uncertainties on σt¯t from the t¯t selection efficiency and luminosity by using the BLUE combination value from the previous iteration, instead of each measurement’s value of σt¯t. The first iteration uses an arbitrary initial value of 6 pb. Simulated experiments show that this procedure removes the bias.

The combined CDF measurement is

σt¯t(CDF) = 7.63±0.31 (stat)±0.36 (syst)±0.15 (lumi) pb, for mt = 172.5 GeV. The total uncertainty is 0.50 pb. Table II shows the individual contributions to the uncer-tainties. The luminosity uncertainty quoted above is the sum in quadrature of two sources of uncertainty, from the inelastic p¯p cross section and from detector-specific effects. The combination has a χ2 _{of 0.86 for three} de-grees of freedom, corresponding to a probability of 84% to have a less consistent set of measurements.

The largest weight in the BLUE combination of CDF measurements is 70% for the ℓ+jets channel LJ-ANN re-sult. The dilepton result has a weight of 22%, and the measurement using b-jet identification in the ℓ+jets chan-nel has a weight of 15%. The measurement in the all-jets channel has a weight of −7%. Such negative weights can occur when the correlation between the two mea-surements is larger than the ratio of their total uncer-tainties [56]. The correlation matrix, including statis-tical and systematic effects, is given in Table III. The largest correlation is 51% between the DIL and HAD measurements, due to the correlation between system-atic uncertainties on detector modeling (primarily b-jet identification), signal modeling, jet energy scale, and lu-minosity. Next largest is the 50% correlation between the LJ-ANN and LJ-SVX measurements, which arises from a subset of common events and correlation between sys-tematic uncertainties from signal modeling, jet energy scale, and normalization of the Z/γ∗ _{cross section. The}

central value and the total uncertainty change by less than 0.01 pb when the statistical correlation of 32% be-tween the LJ-ANN and LJ-SVX measurements is varied by 10% absolute to 22% or 42%.

TABLE III: Correlation matrix for CDF σt¯t measurements,

including statistical and systematic correlations among the methods.

Correlation LJ-ANN LJ-SVX DIL HAD

LJ-ANN 1 0.50 0.25 0.34

LJ-SVX 1 0.44 0.47

DIL 1 0.51

HAD 1

B. D0 measurements and their combination D0 includes two measurements in the combination: one from the dilepton channel and one from the ℓ+jets chan-nel. In the dilepton channel, using data corresponding to an integrated luminosity of 5.4 fb−1_{, D0 measures} σt¯t= 7.36+0.90−0.79 pb through a likelihood fit to a discrim-inant based on a NN b-jet identification algorithm [15]. The σt¯t is extracted from a fit to the distribution of the smallest of the NN output values from the two jets of highest energy. The total uncertainty is not limited by the finite sample size but by the systematic uncertainty on the integrated luminosity.

In the ℓ+jets channel, using data corresponding to an integrated luminosity of 5.3 fb−1_{, D0 measures σ}

t¯t = 7.90+0.78

−0.69 pb by selecting events with at least three jets and splitting them into subsamples according to the total number of jets and the number of identified b jets [46]. In the background-dominated subsamples (three-jet events with no b jet, three-jet events with one b jet, and events with at least four jets and no b jet), a random forest multivariate discriminant [59] is used to separate signal from background. The σt¯t is extracted by fitting si-multaneously the direct event count in the subsamples with a large t¯t content (three-jet events with at least two b jets, events with at least four jets and one b jet, and events with at least four jets and at least two b-jets) and the random forest discriminant in the background-dominated samples. The leading systematic uncertain-ties are treated as nuisance parameters, constrained by Gaussian prior probability density functions, that are al-lowed to vary in the fit. The dominant systematic uncer-tainty is from the unceruncer-tainty on the luminosity, followed by uncertainties from the modeling of the detector.

The measurements in the dilepton and ℓ+jets chan-nels have been combined and published in the dilepton paper [15] with the same nuisance-parameter technique used in the individual measurements, accounting for cor-relations among common systematic sources. The result is σt¯t(D0) = 7.56+0.63−0.56 pb. For the combination with CDF, we separate the statistical and systematic contri-butions into the categories discussed in the next section.

We also use the average of the asymmetric uncertainties of the original D0 measurement. This gives for the com-bined D0 measurement

σt¯t(D0) = 7.56 ± 0.20(stat) ± 0.32 (syst) ± 0.46 (lumi) pb, for mt = 172.5 GeV. The total uncertainty is 0.59 pb. Table IV provides the individual contributions to the un-certainties. The luminosity uncertainty quoted above is the sum in quadrature of two sources of uncertainty, from the inelastic p¯p cross section and from detector-specific effects.

III. OVERVIEW OF SYSTEMATIC UNCERTAINTIES

Sources of systematic uncertainty have been catego-rized into nine classes with similar correlation properties to facilitate the combination of the measurements. Be-low, we discuss each component of the uncertainty on the combined cross section. The values of the CDF and D0 systematic uncertainties are summarized in Tables II and IV.

A. Modeling of the detector

This category includes detector-specific uncertainties on the trigger and lepton-identification efficiency, b-jet identification efficiency, and modeling of multiple p¯p in-teractions. In addition, for CDF measurements, this cat-egory includes the uncertainty on the fraction of the lumi-nous region within the acceptance of the CDF II detector, track-identification efficiencies for the ANN and LJ-SVX measurements, and the uncertainty on the lepton-energy scales. For D0 measurements, additional uncer-tainties in this category arise from vertex reconstruction and identification efficiency and lepton-energy resolution. These sources are treated as correlated within the same experiment, but uncorrelated between experiments.

B. Modeling of signal

The uncertainties in this category arise from several sources and are considered fully correlated among all measurements.

(i) t¯t generator: This is the source of the largest con-tribution (1 − 2%) to the signal modeling system-atic. For both CDF and D0 measurements this un-certainty includes the difference between pythia and herwig [60] samples resulting from different models for hadronization, for parton showering and for the underlying event, which describes the rem-nants of the p and ¯p break-up accompanying the hard partonic collision. Uncertainties from higher-order QCD corrections are also included for D0

measurements by comparing results from alpgen to mc@nlo [61]. Although there are reported measurements of a larger-than-expected forward-backward asymmetry [62, 63] that could be due to non-SM sources, no additional systematic is as-signed as its size would be highly dependent on the particular hypothesis for the source.

(ii) Parton distribution functions: The uncertainties on the PDF reflect the uncertainty on determining the probability of finding a particular parton car-rying a particular fraction of the p or ¯p momen-tum. This in turn affects the kinematic distribu-tions of the final-state particles in t¯t production and decay, as well as the event selection efficiency. The default acceptances are calculated using the LO CTEQ5L and CTEQ6L PDF sets for CDF and D0, respectively. The systematic uncertainty in-cludes uncertainties evaluated using the prescribed NLO error vectors from CTEQ6M for CDF, and CTEQ6.1M for D0, following the recommendations of the CTEQ collaboration [64]. For CDF mea-surements, this uncertainty also includes the differ-ence between the central values from LO and NLO PDF [65].

(iii) Initial and final-state radiation: The amount of gluon radiation from partons in the initial or final state, which affects the t¯t efficiency and kinematic properties, is set by parameters of the pythia generator used to simulate t¯t events. The un-certainties on these parameters are taken from a study of initial state radiation in Drell-Yan events, q ¯q → Z/γ∗_{→ µ}+_µ−_{, that share the same initial q ¯q} state as most of the t¯t signal [65, 66].

(iv) Color reconnection: This uncertainty is evalu-ated by comparing pythia configurations with dif-ferent parameters that affect the exchange of mo-mentum and energy via gluons between the color-connected top-quark and antitop-quark systems. Specifically, the difference in t¯t efficiency obtained with pythia using the A-pro and the ACR-pro configurations [67] is quoted as the systematic un-certainty [65].

(v) Leptonic decay branching fractions for W bosons: This uncertainty alters the proportion of t¯t decays that cause the dilepton, ℓ+jets, and all-jets final states. It is evaluated by changing the branching fractions in the W -boson decay by their uncertainties [27].

C. Modeling of jets

Uncertainties on the modeling of jets affect the t¯t se-lection efficiency and the kinematic distributions used to extract σt¯t. They arise from the calibration of light-quark