Search for New Physics Using Quaero: A General Interface to - D0 Event Data

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Search for New Physics Using Quaero: A General

Interface to - D0 Event Data

V.M. Abazov, B. Abbott, Abdelmalek Abdesselam, M. Abolins, V. Abramov,

B.S. Acharya, D.L. Adams, M. Adams, S.N. Ahmed, G.D. Alexeev, et al.

To cite this version:

arXiv:hep-ex/0106039 v1 7 Jun 2001

Search for New Physics Using quaero: A General Interface to DØ Event Data

V.M. Abazov,23 _{B. Abbott,}58 _{A. Abdesselam,}11 _{M. Abolins,}51_{V. Abramov,}26_{B.S. Acharya,}17 _{D.L. Adams,}60

M. Adams,38 _{S.N. Ahmed,}21_{G.D. Alexeev,}23 _{G.A. Alves,}2 _{N. Amos,}50_{E.W. Anderson,}43 _{Y. Arnoud,}9

M.M. Baarmand,55 _{V.V. Babintsev,}26 _{L. Babukhadia,}55 _{T.C. Bacon,}28 _{A. Baden,}47 _{B. Baldin,}37_{P.W. Balm,}20

S. Banerjee,17 _{E. Barberis,}30 _{P. Baringer,}44 _{J. Barreto,}2 _{J.F. Bartlett,}37 _{U. Bassler,}12 _{D. Bauer,}28 _{A. Bean,}44

M. Begel,54_{A. Belyaev,}35_{S.B. Beri,}15 _{G. Bernardi,}12_{I. Bertram,}27 _{A. Besson,}9 _{R. Beuselinck,}28 _{V.A. Bezzubov,}26

P.C. Bhat,37 _{V. Bhatnagar,}11 _{M. Bhattacharjee,}55 _{G. Blazey,}39_{S. Blessing,}35_{A. Boehnlein,}37_{N.I. Bojko,}26

F. Borcherding,37 _{K. Bos,}20 _{A. Brandt,}60 _{R. Breedon,}31 _{G. Briskin,}59 _{R. Brock,}51_{G. Brooijmans,}37 _{A. Bross,}37

D. Buchholz,40 _{M. Buehler,}38 _{V. Buescher,}14 _{V.S. Burtovoi,}26 _{J.M. Butler,}48_{F. Canelli,}54_{W. Carvalho,}3

D. Casey,51_{Z. Casilum,}55_{H. Castilla-Valdez,}19_{D. Chakraborty,}39_{K.M. Chan,}54_{S.V. Chekulaev,}26 _{D.K. Cho,}54

S. Choi,34_{S. Chopra,}56 _{J.H. Christenson,}37 _{M. Chung,}38 _{D. Claes,}52 _{A.R. Clark,}30_{J. Cochran,}34_{L. Coney,}42

B. Connolly,35_{W.E. Cooper,}37 _{D. Coppage,}44_{S. Cr´ep´e-Renaudin,}9 _{M.A.C. Cummings,}39_{D. Cutts,}59_{G.A. Davis,}54

K. Davis,29 _{K. De,}60_{S.J. de Jong,}21_{K. Del Signore,}50_{M. Demarteau,}37 _{R. Demina,}45_{P. Demine,}9 _{D. Denisov,}37

S.P. Denisov,26_{S. Desai,}55 _{H.T. Diehl,}37_{M. Diesburg,}37_{G. Di Loreto,}51_{S. Doulas,}49_{P. Draper,}60 _{Y. Ducros,}13

L.V. Dudko,25_{S. Duensing,}21 _{L. Duflot,}11_{S.R. Dugad,}17_{A. Duperrin,}10_{A. Dyshkant,}39_{D. Edmunds,}51_{J. Ellison,}34

V.D. Elvira,37_{R. Engelmann,}55_{S. Eno,}47_{G. Eppley,}62_{P. Ermolov,}25_{O.V. Eroshin,}26 _{J. Estrada,}54 _{H. Evans,}53

V.N. Evdokimov,26_{T. Fahland,}33_{S. Feher,}37 _{D. Fein,}29 _{T. Ferbel,}54 _{F. Filthaut,}21_{H.E. Fisk,}37 _{Y. Fisyak,}56

E. Flattum,37_{F. Fleuret,}30 _{M. Fortner,}39 _{H. Fox,}40_{K.C. Frame,}51_{S. Fu,}53_{S. Fuess,}37_{E. Gallas,}37_{A.N. Galyaev,}26

M. Gao,53_{V. Gavrilov,}24_{R.J. Genik II,}27_{K. Genser,}37_{C.E. Gerber,}38_{Y. Gershtein,}59 _{R. Gilmartin,}35_{G. Ginther,}54

B. G´omez,5 _{G. G´omez,}47 _{P.I. Goncharov,}26_{J.L. Gonz´alez Sol´ıs,}19_{H. Gordon,}56_{L.T. Goss,}61 _{K. Gounder,}37

A. Goussiou,28_{N. Graf,}56_{G. Graham,}47_{P.D. Grannis,}55 _{J.A. Green,}43 _{H. Greenlee,}37 _{S. Grinstein,}1_{L. Groer,}53

S. Gr¨unendahl,37 _{A. Gupta,}17 _{S.N. Gurzhiev,}26_{G. Gutierrez,}37 _{P. Gutierrez,}58 _{N.J. Hadley,}47 _{H. Haggerty,}37

S. Hagopian,35_{V. Hagopian,}35_{R.E. Hall,}32 _{P. Hanlet,}49 _{S. Hansen,}37 _{J.M. Hauptman,}43_{C. Hays,}53 _{C. Hebert,}44

D. Hedin,39 _{J.M. Heinmiller,}38_{A.P. Heinson,}34 _{U. Heintz,}48_{T. Heuring,}35 _{M.D. Hildreth,}42_{R. Hirosky,}63

J.D. Hobbs,55 _{B. Hoeneisen,}8 _{Y. Huang,}50_{R. Illingworth,}28_{A.S. Ito,}37_{M. Jaffr´e,}11 _{S. Jain,}17_{R. Jesik,}28_{K. Johns,}29

M. Johnson,37 _{A. Jonckheere,}37 _{M. Jones,}36 _{H. J¨ostlein,}37_{A. Juste,}37 _{W. Kahl,}45 _{S. Kahn,}56_{E. Kajfasz,}10

A.M. Kalinin,23_{D. Karmanov,}25_{D. Karmgard,}42 _{Z. Ke,}4 _{R. Kehoe,}51 _{A. Khanov,}45_{A. Kharchilava,}42_{S.K. Kim,}18

B. Klima,37_{B. Knuteson,}30_{W. Ko,}31 _{J.M. Kohli,}15_{A.V. Kostritskiy,}26 _{J. Kotcher,}56 _{B. Kothari,}53_{A.V. Kotwal,}53

A.V. Kozelov,26_{E.A. Kozlovsky,}26_{J. Krane,}43_{M.R. Krishnaswamy,}17_{P. Krivkova,}6 _{S. Krzywdzinski,}37

M. Kubantsev,45 _{S. Kuleshov,}24 _{Y. Kulik,}55 _{S. Kunori,}47 _{A. Kupco,}7 _{V.E. Kuznetsov,}34 _{G. Landsberg,}59

W.M. Lee,35_{A. Leflat,}25 _{C. Leggett,}30 _{F. Lehner,}37,∗ _{J. Li,}60 _{Q.Z. Li,}37_{X. Li,}4 _{J.G.R. Lima,}3_{D. Lincoln,}37

S.L. Linn,35_{J. Linnemann,}51_{R. Lipton,}37 _{A. Lucotte,}9 _{L. Lueking,}37_{C. Lundstedt,}52 _{C. Luo,}41 _{A.K.A. Maciel,}39

R.J. Madaras,30 _{V.L. Malyshev,}23_{V. Manankov,}25_{H.S. Mao,}4_{T. Marshall,}41_{M.I. Martin,}39 _{R.D. Martin,}38

K.M. Mauritz,43 _{B. May,}40_{A.A. Mayorov,}41_{R. McCarthy,}55 _{T. McMahon,}57 _{H.L. Melanson,}37_{M. Merkin,}25

K.W. Merritt,37C. Miao,59H. Miettinen,62 D. Mihalcea,39C.S. Mishra,37 N. Mokhov,37N.K. Mondal,17 H.E. Montgomery,37_{R.W. Moore,}51 _{M. Mostafa,}1 _{H. da Motta,}2_{E. Nagy,}10_{F. Nang,}29_{M. Narain,}48

V.S. Narasimham,17_{H.A. Neal,}50_{J.P. Negret,}5 _{S. Negroni,}10_{T. Nunnemann,}37_{D. O’Neil,}51_{V. Oguri,}3_{B. Olivier,}12

N. Oshima,37_{P. Padley,}62_{L.J. Pan,}40_{K. Papageorgiou,}38_{A. Para,}37_{N. Parashar,}49_{R. Partridge,}59_{N. Parua,}55

M. Paterno,54 _{A. Patwa,}55 _{B. Pawlik,}22_{J. Perkins,}60 _{M. Peters,}36 _{O. Peters,}20 _{P. P´etroff,}11 _{R. Piegaia,}1

B.G. Pope,51 _{E. Popkov,}48_{H.B. Prosper,}35 _{S. Protopopescu,}56 _{J. Qian,}50_{R. Raja,}37_{S. Rajagopalan,}56

E. Ramberg,37 _{P.A. Rapidis,}37_{N.W. Reay,}45_{S. Reucroft,}49 _{M. Ridel,}11_{M. Rijssenbeek,}55 _{F. Rizatdinova,}45

T. Rockwell,51_{M. Roco,}37_{P. Rubinov,}37_{R. Ruchti,}42_{J. Rutherfoord,}29 _{B.M. Sabirov,}23_{G. Sajot,}9_{A. Santoro,}2

L. Sawyer,46 _{R.D. Schamberger,}55 _{H. Schellman,}40_{A. Schwartzman,}1_{N. Sen,}62_{E. Shabalina,}38_{R.K. Shivpuri,}16

D. Shpakov,49_{M. Shupe,}29 _{R.A. Sidwell,}45_{V. Simak,}7_{H. Singh,}34 _{J.B. Singh,}15 _{V. Sirotenko,}37_{P. Slattery,}54

E. Smith,58_{R.P. Smith,}37_{R. Snihur,}40_{G.R. Snow,}52 _{J. Snow,}57 _{S. Snyder,}56 _{J. Solomon,}38_{V. Sor´ın,}1_{M. Sosebee,}60

N. Sotnikova,25_{K. Soustruznik,}6 _{M. Souza,}2_{N.R. Stanton,}45 _{G. Steinbr¨uck,}53 _{R.W. Stephens,}60 _{F. Stichelbaut,}56

D. Stoker,33_{V. Stolin,}24_{A. Stone,}46_{D.A. Stoyanova,}26_{M. Strauss,}58 _{M. Strovink,}30_{L. Stutte,}37 _{A. Sznajder,}3

M. Talby,10_{W. Taylor,}55_{S. Tentindo-Repond,}35_{S.M. Tripathi,}31_{T.G. Trippe,}30_{A.S. Turcot,}56 _{P.M. Tuts,}53

P. van Gemmeren,37 _{V. Vaniev,}26_{R. Van Kooten,}41 _{N. Varelas,}38_{L.S. Vertogradov,}23_{F. Villeneuve-Seguier,}10

A.A. Volkov,26A.P. Vorobiev,26H.D. Wahl,35H. Wang,40Z.-M. Wang,55J. Warchol,42 G. Watts,64M. Wayne,42 H. Weerts,51 _{A. White,}60_{J.T. White,}61_{D. Whiteson,}30 _{J.A. Wightman,}43_{D.A. Wijngaarden,}21_{S. Willis,}39

S.J. Wimpenny,34_{J. Womersley,}37_{D.R. Wood,}49_{R. Yamada,}37 _{P. Yamin,}56_{T. Yasuda,}37 _{Y.A. Yatsunenko,}23

K. Yip,56 _{S. Youssef,}35 _{J. Yu,}37_{Z. Yu,}40 _{M. Zanabria,}5 _{H. Zheng,}42 _{Z. Zhou,}43 _{M. Zielinski,}54_{D. Zieminska,}41

A. Zieminski,41 _{V. Zutshi,}56 _{E.G. Zverev,}25 _{and A. Zylberstejn}13

1_{Universidad de Buenos Aires, Buenos Aires, Argentina}

2_{LAFEX, Centro Brasileiro de Pesquisas F´ısicas, Rio de Janeiro, Brazil}

3_{Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brazil}

4_{Institute of High Energy Physics, Beijing, People’s Republic of China}

5_{Universidad de los Andes, Bogot´a, Colombia}

6_{Charles University, Center for Particle Physics, Prague, Czech Republic}

7_{Institute of Physics, Academy of Sciences, Center for Particle Physics, Prague, Czech Republic}

8_{Universidad San Francisco de Quito, Quito, Ecuador}

9_{Institut des Sciences Nucl´eaires, IN2P3-CNRS, Universite de Grenoble 1, Grenoble, France}

10_{CPPM, IN2P3-CNRS, Universit´e de la M´editerran´ee, Marseille, France}

11_{Laboratoire de l’Acc´el´erateur Lin´eaire, IN2P3-CNRS, Orsay, France}

12_{LPNHE, Universit´es Paris VI and VII, IN2P3-CNRS, Paris, France}

13_{DAPNIA/Service de Physique des Particules, CEA, Saclay, France}

14_{Universit¨at Mainz, Institut f¨ur Physik, Mainz, Germany}

15_{Panjab University, Chandigarh, India}

16_{Delhi University, Delhi, India}

17_{Tata Institute of Fundamental Research, Mumbai, India}

18_{Seoul National University, Seoul, Korea}

19_{CINVESTAV, Mexico City, Mexico}

20_{FOM-Institute NIKHEF and University of Amsterdam/NIKHEF, Amsterdam, The Netherlands}

21_{University of Nijmegen/NIKHEF, Nijmegen, The Netherlands}

22_{Institute of Nuclear Physics, Krak´ow, Poland}

23_{Joint Institute for Nuclear Research, Dubna, Russia}

24_{Institute for Theoretical and Experimental Physics, Moscow, Russia}

25_{Moscow State University, Moscow, Russia}

26_{Institute for High Energy Physics, Protvino, Russia}

27_{Lancaster University, Lancaster, United Kingdom}

28_{Imperial College, London, United Kingdom}

29_{University of Arizona, Tucson, Arizona 85721}

30_{Lawrence Berkeley National Laboratory and University of California, Berkeley, California 94720}

31_{University of California, Davis, California 95616}

32_{California State University, Fresno, California 93740}

33_{University of California, Irvine, California 92697}

34_{University of California, Riverside, California 92521}

35_{Florida State University, Tallahassee, Florida 32306}

36_{University of Hawaii, Honolulu, Hawaii 96822}

37_{Fermi National Accelerator Laboratory, Batavia, Illinois 60510}

38_{University of Illinois at Chicago, Chicago, Illinois 60607}

39_{Northern Illinois University, DeKalb, Illinois 60115}

40_{Northwestern University, Evanston, Illinois 60208}

41_{Indiana University, Bloomington, Indiana 47405}

42_{University of Notre Dame, Notre Dame, Indiana 46556}

43_{Iowa State University, Ames, Iowa 50011}

44_{University of Kansas, Lawrence, Kansas 66045}

45_{Kansas State University, Manhattan, Kansas 66506}

46_{Louisiana Tech University, Ruston, Louisiana 71272}

47_{University of Maryland, College Park, Maryland 20742}

48_{Boston University, Boston, Massachusetts 02215}

49_{Northeastern University, Boston, Massachusetts 02115}

50_{University of Michigan, Ann Arbor, Michigan 48109}

51_{Michigan State University, East Lansing, Michigan 48824}

52_{University of Nebraska, Lincoln, Nebraska 68588}

53_{Columbia University, New York, New York 10027}

54_{University of Rochester, Rochester, New York 14627}

55_{State University of New York, Stony Brook, New York 11794}

56_{Brookhaven National Laboratory, Upton, New York 11973}

57_{Langston University, Langston, Oklahoma 73050}

58_{University of Oklahoma, Norman, Oklahoma 73019}

59_{Brown University, Providence, Rhode Island 02912}

61_{Texas A&M University, College Station, Texas 77843}

62_{Rice University, Houston, Texas 77005}

63_{University of Virginia, Charlottesville, Virginia 22901}

64_{University of Washington, Seattle, Washington 98195}

Abstract

We describe quaero, a method that i) enables the automatic optimization of searches for physics beyond the standard model, and ii) provides a mechanism for making high energy collider data

gen-erally available. We apply quaero to searches for standard model W W , ZZ, and t¯t production, and

to searches for these objects produced through a new heavy resonance. Through this interface, we

It is generally recognized that the standard model, a successful description of the fundamental particles and their interactions, must be incomplete. Models that ex-tend the standard model often predict rich phenomenol-ogy at the scale of a few hundred GeV, an energy regime accessible to the Fermilab Tevatron. Due in part to the complexity of the apparatus required to test models at such large energies, experimental responses to these ideas have not kept pace. Any technique that reduces the time required to test a particular candidate theory would al-low more such theories to be tested, reducing the possi-bility that the data contain overlooked evidence for new physics.

Once data are collected and the backgrounds have been understood, the testing of any specific model in principle follows a well-defined procedure. In practice, this process has been far from automatic. Even when the basic selec-tion criteria and background estimates are taken from a previous analysis, the reinterpretation of the data in the context of a new model often requires a substantial length of time.

Ideally, the data should be “published” in such a way that others in the community can easily use those data to test a variety of models. The publishing of experimental distributions in journals allows this to occur at some lev-el, but an effective publishing of a multidimensional data set has, to our knowledge, not yet been accomplished by a large particle physics experiment. The problem ap-pears to be that such data are context-specific, requiring detailed knowledge of the complexities of the apparatus. This knowledge must somehow be incorporated either in-to the data or inin-to whatever in-tool the non-expert would use to analyze those data.

Many data samples and backgrounds have been defined in the context of sleuth [1], a quasi-model-independent search strategy for new high pT physics that has been

ap-plied to a number of exclusive final states [2,3] in the data collected by the DØ detector [4] during 1992–1996 in Run I of the Fermilab Tevatron. In this Letter we describe a tool (quaero) that automatically optimizes an analysis for a particular signature, using these samples and stan-dard model backgrounds. sleuth and quaero are com-plementary approaches to searches for new phenomena, enabling analyses that are both general (sleuth) and fo-cused (quaero). We demonstrate the use of quaero in eleven separate searches: standard model W W and ZZ production; standard model t¯t production with leptonic and semileptonic decays; resonant W W , ZZ, W Z, and t¯t production; associated Higgs boson production; and pair production of first generation scalar leptoquarks. The data described here are accessible through quaero on the World Wide Web [5], for general use by the particle physics community.

The signals predicted by most theories of physics be-yond the standard model involve an increased number of predicted events in some region of an appropriate vari-able space. In this case the optimization of the analysis

variable space that minimizes σ95%_{, the expected 95%}

confidence level (CL) upper limit on the cross section of the signal in question, assuming the data contain no sig-nal. The optimization algorithm consists of a few simple steps:

(i) Kernel density estimation [6] is used to estimate the probability distributions p(~x|s) and p(~x|b) for the signal and background samples in a low-dimensional variable space _{V, where ~x ∈ V. The} signal sample is contained in a Monte Carlo file pro-vided as input to quaero. The background sample is constructed from all known standard model and instrumental sources.

(ii) A discriminant function D(~x) is defined by [7]

D(~x) = p(~x|s)

p(~x|s) + p(~x|b). (1) The semi-positive-definiteness of p(~x_{|s) and p(~x|b)} restricts D(~x) to the interval [0, 1] for all ~x. (iii) The sensitivity_{S of a particular threshold D}cuton

the discriminant function is defined as the recipro-cal of σ95%_{. D}

cutis chosen to maximizeS.

(iv) The region of variable space having D(~x) > Dcutis

used to determine the actual 95% CL cross section upper limit σ95% _[8].

When provided with a signal model and a choice of vari-ables_{V, quaero uses this algorithm and DØ Run I data} to compute an upper limit on the cross section of the sig-nal. Instructions for use are available from the quaero web site.

Table I shows the data available within quaero, and Table II summarizes the backgrounds. These data and their backgrounds are described in more detail in Ref. [3]. The final states are inclusive, with many events contain-ing one or more additional jets. Kolmogorov-Smirnov tests have been used to demonstrate agreement between data and the expected backgrounds in many distribu-tions. The fraction of events with true final state objects satisfying the cuts shown that satisfy these cuts after reconstruction is given as an “identification” efficiency (ID). Because electrons are more accurately measured

and more efficiently identified than muons in the DØ detector, the corresponding muon channels µ /ET2j and

µµ 2j have been excluded from these data.

To check standard model results, we remove W W and ZZ production from the background estimate and search (i) for standard model W W production in the space de-fined by the transverse momentum of the electron (pe

T)

and missing transverse energy ( /ET) in the final state

eµ /ET, and (ii) for standard model ZZ production in the

space defined by the invariant mass of the two electrons (mee) and two jets (mjj) in the final state ee 2j.

Re-moving t¯t production from the background estimate, we search for this process (iii) in the final state e /ET4j using

Final State Selection criteria ID RL dt

eµ pe,µ_T > 15 GeV

|ηµ det|< 1.7 0.30 108_{± 5 pb}−1 e /ET 2j pe,jT 1,2> 20 GeV / ET > 30 GeV pe /ET T > 40 GeV 0.61 115_{± 6 pb}−1 ee 2j pe1,2,j1,2 T > 20 GeV 0.70 123± 7 pb−1

TABLE I. A summary of the data available within

quaero, including the selection cuts applied and the efficien-cy of identification requirements. The final states are inclu-sive, with many events containing one or more additional jets.

Reconstructed jets satisfy pj

T > 15 GeV and|η

j

det|< 2.5, and

reconstructed electrons satisfy peT > 15 GeV and (|ηedet|< 1.1

or 1.5 <_|ηe

det|< 2.5), where ηdet is the pseudorapidity

mea-sured from the center of the detector.

Standard model backgrounds

Final State multijets W Z V V t¯t

eµ data data isajet pythia herwig

e /ET 2j data vecbos – pythia herwig

ee 2j data – pythia pythia –

TABLE II. Standard model backgrounds (often produced with accompanying jets) to the final states considered. V V denotes W W , W Z, and ZZ; “data” indicates backgrounds from jets misidentified as electrons estimated using data. Monte Carlo programs (isajet [9], pythia [10], herwig [11], and vecbos [12]) are used to estimate several sources of back-ground.

and (iv) in the final state eµ /ET2j, using the two variables

pe T and

P_pj

T, assuming a top quark mass of 175 GeV.

Including all standard model processes in the back-ground estimate, we look for evidence of new heavy res-onances. We search (v) for resonant W W production in the final state e /ET2j, using the single variable meνjj

after constraining meν and mjjto MW, and (vi) for

res-onant ZZ production in the final state ee 2j, using the variable meejj after constraining mjj to MZ. In both

cases we remove events that cannot be so constrained. To obtain a specific signal prediction, we assume that the resonance behaves like a standard model Higgs bo-son in its couplings to the W and Z bobo-sons. Constraining meν to MW and mjj to MZ, we use the quality of the

fit and meνjj to search (vii) for a massive W0 boson in

the extended gauge model of Ref. [13]. Using meν 4jafter

constraining meν to MW, we search (viii) for a massive

narrow Z0 _{resonance with Z-like couplings decaying to}

t¯t→ W+_bW−_{¯b → eν 4j.}

Non-resonant new phenomena are also considered. The variables mjj and either mTeν or mee are used to search

for a light Higgs boson produced (ix) in association with a W boson, and (x) in association with a Z boson. Final-ly, we search (xi) for first generation scalar leptoquarks with mass 225 GeV in the final state ee 2j using mee

and ST, the summed scalar transverse momentum of all

electrons and jets in the event. The numerical results of these searches are listed in Table III. Figures 1 and 2 present plots of the signal density, background density, and selected region in the variables considered.

Process sig ˆb Ndata σ95%× B

W W_{→ eµ /}ET 0.14 19.0± 4.0 23 1.1 pb ZZ_{→ ee 2j} 0.12 19.7_{± 4.1} 19 0.8 pb t¯t_{→ e /}ET4j 0.13 3.1± 0.9 8 0.8 pb t¯t_{→ eµ /}ET2j 0.14 0.6± 0.2 2 0.4 pb h175→ W W → e /ET 2j 0.02 29.6± 6.5 32 11.0 pb h200→ W W → e /ET 2j 0.07 66.0± 13.8 69 4.4 pb h225→ W W → e /ET 2j 0.06 43.1± 9.2 44 3.6 pb h200→ ZZ → ee 2j 0.15 17.9± 3.7 15 0.6 pb h225→ ZZ → ee 2j 0.15 18.8± 3.8 12 0.4 pb h250→ ZZ → ee 2j 0.17 18.1± 3.7 18 0.6 pb W2000 → W Z → e /ET 2j 0.05 27.7± 6.3 29 3.4 pb W3500 → W Z → e /ET 2j 0.23 22.7± 5.2 27 0.7 pb W5000 → W Z → e /ET 2j 0.26 2.1± 0.8 2 0.2 pb Z0 350 → t¯t→ e /ET4j 0.11 18.7± 4.0 20 1.1 pb Z4500 → t¯t→ e /ET4j 0.14 18.7± 4.0 20 0.9 pb Z5500 → t¯t→ e /ET4j 0.14 3.8± 1.0 2 0.3 pb W h115→ e /ET2j 0.08 37.3± 8.2 32 2.0 pb Zh115→ ee 2j 0.20 19.5± 4.1 25 0.8 pb LQ225LQ225→ ee 2j 0.33 0.3± 0.1 0 0.07 pb

TABLE III. Limits on cross section _{× branching fraction}

for the processes discussed in the text. All final states are inclusive in the number of additional jets. The fraction of the signal sample satisfying quaero’s selection criteria is denoted

sig; ˆb is the number of expected background events satisfying

these criteria; and Ndata is the number of events in the data

satisfying these criteria. The subscripts on h, W0, Z0, and

LQ denote assumed masses, in units of GeV.

We note slight indications of excess in the searches for t¯t _{→ e /}ET4j and t¯t → eµ /ET2j (corresponding to cross

section _{× branching fractions of σ × B = 0.39}+0.21_−0.19 pb and 0.14+0.15_−0.08pb) that are consistent with our measured t¯t production cross section of 5.5_{± 1.8 pb [14] and known} W boson branching fractions. Observing no compelling excess in any of these processes, limits on σ× B are de-termined at the 95% CL. As expected, we find these data insensitive to standard model ZZ production (with pre-dicted σ_{× B ≈ 0.05 pb), and to associated Higgs boson} production (with predicted σ× B<

∼ 0.01 pb). As a check of the method, quaero almost exactly duplicates a pre-vious search for LQLQ→ ee 2j [15].

in-Background density Signal density Selected region

(a) (b) (c)

FIG. 1. The background density (a), signal density (b), and selected region (shaded) (c) determined by quaero for the standard model processes discussed in the text. From

top to bottom the signals are: W W _{→ eµ /}ET, ZZ → ee 2j,

t¯t→ e /ET4j, and t¯t→ eµ /ET2j. The dots in the plots in the

rightmost column represent events observed in the data.

crease the facility with which new models may be tested in the future.

We thank the staffs at Fermilab and collaborating in-stitutions, and acknowledge support from the Depart-ment of Energy and National Science Foundation (USA), Commissariat `a L’Energie Atomique and CNRS/Institut National de Physique Nucl´eaire et de Physique des Par-ticules (France), Ministry for Science and Technology and Ministry for Atomic Energy (Russia), CAPES and CN-Pq (Brazil), Departments of Atomic Energy and Science and Education (India), Colciencias (Colombia), CONA-CyT (Mexico), Ministry of Education and KOSEF (Ko-rea), CONICET and UBACyT (Argentina), The Founda-tion for Fundamental Research on Matter (The Nether-lands), PPARC (United Kingdom), Ministry of Educa-tion (Czech Republic), and the A.P. Sloan FoundaEduca-tion.

Background density Signal density Selected region

(a) (b) (c)

FIG. 2. quaero’s analysis of signatures involving undis-covered particles. From top to bottom the hypothetical

sig-nals are: h200 → ZZ → ee 2j, Z5500 → t¯t → e /ET4j,

W h115 → e /ET 2j, and LQ225LQ225 → ee 2j. Plots (c) of the

first two rows show the discriminant D (curve), the threshold

Dcut (horizontal line), and the data (histogram); the region

with D > Dcutis selected.

∗ _{Visitor from University of Zurich, Zurich, Switzerland.}

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