First Observation of B_s⁰ -> D_s^±K∓ and Measurement of the Ratio of Branching Fractions B(B_s⁰ -> D_s^±K∓)/B(B_s⁰ -> D_s⁺

Article

Reference

First Observation of B

-> D

K∓ and Measurement of the Ratio of Branching Fractions B(B

-> D

K∓)/B(B

-> D

π−)

CDF Collaboration

CLARK, Allan Geoffrey (Collab.), et al .

Abstract

A combined mass and particle identification fit is used to make the first observation of the decay B0s→D±sK∓ and measure the branching fraction of B0s→D±sK∓ relative to B0s→D+sπ−. This analysis uses 1.2  fb−1 integrated luminosity of pp collisions at s√=1.96  TeV collected with the CDF II detector at the Fermilab Tevatron collider. We observe a B0s→D±sK∓ signal with a statistical significance of 8.1σ and measure B(B0s→D±sK∓)/B(B0s→D+sπ−)=0.097±0.018(stat)±0.009(syst).

CDF Collaboration, CLARK, Allan Geoffrey (Collab.), et al . First Observation of B

-> D

K∓

and Measurement of the Ratio of Branching Fractions B(B

-> D

K∓)/B(B

-> D

π−). Physical Review Letters , 2009, vol. 103, no. 19, p. 191802

DOI : 10.1103/PhysRevLett.103.191802

Available at:

http://archive-ouverte.unige.ch/unige:38621

Disclaimer: layout of this document may differ from the published version.

1 / 1

First Observation of B

! D

K

and Measurement of the Ratio of Branching Fractions Bð B

! D

K

Þ=Bð B

! D

Þ

T. Aaltonen,²⁴J. Adelman,¹⁴T. Akimoto,⁵⁶M. G. Albrow,¹⁸B. A´ lvarez Gonza´lez,¹²S. Amerio,^44b,44aD. Amidei,³⁵ A. Anastassov,³⁹A. Annovi,²⁰J. Antos,¹⁵G. Apollinari,¹⁸A. Apresyan,⁴⁹T. Arisawa,⁵⁸A. Artikov,¹⁶W. Ashmanskas,¹⁸ A. Attal,⁴A. Aurisano,⁵⁴F. Azfar,⁴³P. Azzurri,^47d,47aW. Badgett,¹⁸A. Barbaro-Galtieri,²⁹V. E. Barnes,⁴⁹B. A. Barnett,²⁶ V. Bartsch,³¹G. Bauer,³³P.-H. Beauchemin,³⁴F. Bedeschi,^47aP. Bednar,¹⁵D. Beecher,³¹S. Behari,²⁶G. Bellettini,^47b,47a

J. Bellinger,⁶⁰D. Benjamin,¹⁷A. Beretvas,¹⁸J. Beringer,²⁹A. Bhatti,⁵¹M. Binkley,¹⁸D. Bisello,^44b,44aI. Bizjak,³¹ R. E. Blair,²C. Blocker,⁷B. Blumenfeld,²⁶A. Bocci,¹⁷A. Bodek,⁵⁰V. Boisvert,⁵⁰G. Bolla,⁴⁹D. Bortoletto,⁴⁹ J. Boudreau,⁴⁸A. Boveia,¹¹B. Brau,¹¹A. Bridgeman,²⁵L. Brigliadori,^44aC. Bromberg,³⁶E. Brubaker,¹⁴J. Budagov,¹⁶

H. S. Budd,⁵⁰S. Budd,²⁵K. Burkett,¹⁸G. Busetto,^44b,44aP. Bussey,^22,rA. Buzatu,³⁴K. L. Byrum,²S. Cabrera,^17,q C. Calancha,³²M. Campanelli,³⁶M. Campbell,³⁵F. Canelli,¹⁸A. Canepa,⁴⁶D. Carlsmith,⁶⁰R. Carosi,^47aS. Carrillo,^19,k

S. Carron,³⁴B. Casal,¹²M. Casarsa,¹⁸A. Castro,^6b,1P. Catastini,^47c,47aD. Cauz,^55b,55aV. Cavaliere,^47c,47a M. Cavalli-Sforza,⁴A. Cerri,²⁹L. Cerrito,^31,oS. H. Chang,²⁸Y. C. Chen,¹M. Chertok,⁸G. Chiarelli,^47aG. Chlachidze,¹⁸

F. Chlebana,¹⁸K. Cho,²⁸D. Chokheli,¹⁶J. P. Chou,²³G. Choudalakis,³³S. H. Chuang,⁵³K. Chung,¹³W. H. Chung,⁶⁰ Y. S. Chung,⁵⁰C. I. Ciobanu,⁴⁵M. A. Ciocci,^47c,47aA. Clark,²¹D. Clark,⁷G. Compostella,^44aM. E. Convery,¹⁸J. Conway,⁸

K. Copic,³⁵M. Cordelli,²⁰G. Cortiana,^44b,44aD. J. Cox,⁸F. Crescioli,^47b,47aC. Cuenca Almenar,^8,qJ. Cuevas,^12,n R. Culbertson,¹⁸J. C. Cully,³⁵D. Dagenhart,¹⁸M. Datta,¹⁸T. Davies,²²P. de Barbaro,⁵⁰S. De Cecco,^52aA. Deisher,²⁹

G. De Lorenzo,⁴M. Dell’Orso,^47b,47aC. Deluca,⁴L. Demortier,⁵¹J. Deng,¹⁷M. Deninno,¹P. F. Derwent,¹⁸ G. P. di Giovanni,⁴⁵C. Dionisi,^52b,52aB. Di Ruzza,^55b,55aJ. R. Dittmann,⁵M. D’Onofrio,⁴S. Donati,^47b,47aP. Dong,⁹

J. Donini,^44aT. Dorigo,^44aS. Dube,⁵³J. Efron,⁴⁰A. Elagin,⁵⁴R. Erbacher,⁸D. Errede,²⁵S. Errede,²⁵R. Eusebi,¹⁸ H. C. Fang,²⁹S. Farrington,⁴³W. T. Fedorko,¹⁴R. G. Feild,⁶¹M. Feindt,²⁷J. P. Fernandez,³²C. Ferrazza,^47d,47aR. Field,¹⁹

G. Flanagan,⁴⁹R. Forrest,⁸M. Franklin,²³J. C. Freeman,¹⁸I. Furic,¹⁹M. Gallinaro,^52aJ. Galyardt,¹³F. Garberson,¹¹ J. E. Garcia,^47aA. F. Garfinkel,⁴⁹K. Genser,¹⁸H. Gerberich,²⁵D. Gerdes,³⁵A. Gessler,²⁷S. Giagu,^52b,52a V. Giakoumopoulou,³P. Giannetti,^47aK. Gibson,⁴⁸J. L. Gimmell,⁵⁰C. M. Ginsburg,¹⁸N. Giokaris,³M. Giordani,^55b,55a

P. Giromini,²⁰M. Giunta,^47b,47aG. Giurgiu,²⁶V. Glagolev,¹⁶D. Glenzinski,¹⁸M. Gold,³⁸N. Goldschmidt,¹⁹ A. Golossanov,¹⁸G. Gomez,¹²G. Gomez-Ceballos,³³M. Goncharov,⁵⁴O. Gonza´lez,³²I. Gorelov,³⁸A. T. Goshaw,¹⁷

K. Goulianos,⁵¹A. Gresele,^44b,44aS. Grinstein,²³C. Grosso-Pilcher,¹⁴R. C. Group,¹⁸U. Grundler,²⁵ J. Guimaraes da Costa,²³Z. Gunay-Unalan,³⁶C. Haber,²⁹K. Hahn,³³S. R. Hahn,¹⁸E. Halkiadakis,⁵³B.-Y. Han,⁵⁰ J. Y. Han,⁵⁰R. Handler,⁶⁰F. Happacher,²⁰K. Hara,⁵⁶D. Hare,⁵³M. Hare,⁵⁷S. Harper,⁴³R. F. Harr,⁵⁹R. M. Harris,¹⁸

M. Hartz,⁴⁸K. Hatakeyama,⁵¹J. Hauser,⁹C. Hays,⁴³M. Heck,²⁷A. Heijboer,⁴⁶B. Heinemann,²⁹J. Heinrich,⁴⁶ C. Henderson,³³M. Herndon,⁶⁰J. Heuser,²⁷S. Hewamanage,⁵D. Hidas,¹⁷C. S. Hill,^11,dD. Hirschbuehl,²⁷A. Hocker,¹⁸

S. Hou,¹M. Houlden,³⁰S.-C. Hsu,¹⁰B. T. Huffman,⁴³R. E. Hughes,⁴⁰U. Husemann,⁶¹J. Huston,³⁶J. Incandela,¹¹ G. Introzzi,^47aM. Iori,^52b,52aA. Ivanov,⁸E. James,¹⁸B. Jayatilaka,¹⁷E. J. Jeon,²⁸M. K. Jha,¹S. Jindariani,¹⁸W. Johnson,⁸

M. Jones,⁴⁹K. K. Joo,²⁸S. Y. Jun,¹³J. E. Jung,²⁸T. R. Junk,¹⁸T. Kamon,⁵⁴D. Kar,¹⁹P. E. Karchin,⁵⁹Y. Kato,⁴² R. Kephart,¹⁸J. Keung,⁴⁶V. Khotilovich,⁵⁴B. Kilminster,⁴⁰D. H. Kim,²⁸H. S. Kim,²⁸J. E. Kim,²⁸M. J. Kim,²⁰ S. B. Kim,²⁸S. H. Kim,⁵⁶Y. K. Kim,¹⁴N. Kimura,⁵⁶L. Kirsch,⁷S. Klimenko,¹⁹B. Knuteson,³³B. R. Ko,¹⁷S. A. Koay,¹¹ K. Kondo,⁵⁸D. J. Kong,²⁸J. Konigsberg,¹⁹A. Korytov,¹⁹A. V. Kotwal,¹⁷M. Kreps,²⁷J. Kroll,⁴⁶D. Krop,¹⁴N. Krumnack,⁵

M. Kruse,¹⁷V. Krutelyov,¹¹T. Kubo,⁵⁶T. Kuhr,²⁷N. P. Kulkarni,⁵⁹M. Kurata,⁵⁶Y. Kusakabe,⁵⁸S. Kwang,¹⁴ A. T. Laasanen,⁴⁹S. Lami,^47aS. Lammel,¹⁸M. Lancaster,³¹R. L. Lander,⁸K. Lannon,⁴⁰A. Lath,⁵³G. Latino,^47c,47a I. Lazzizzera,^44b,44aT. LeCompte,²E. Lee,⁵⁴H. S. Lee,¹⁴S. W. Lee,^54,pS. Leone,^47aJ. D. Lewis,¹⁸C. S. Lin,²⁹J. Linacre,⁴³

M. Lindgren,¹⁸E. Lipeles,¹⁰A. Lister,⁸D. O. Litvintsev,¹⁸C. Liu,⁴⁸T. Liu,¹⁸N. S. Lockyer,⁴⁶A. Loginov,⁶¹ M. Loreti,^44b,44aL. Lovas,¹⁵R.-S. Lu,¹D. Lucchesi,^44b,44aJ. Lueck,²⁷C. Luci,^52b,52aP. Lujan,²⁹P. Lukens,¹⁸G. Lungu,⁵¹

L. Lyons,⁴³J. Lys,²⁹R. Lysak,¹⁵E. Lytken,⁴⁹P. Mack,²⁷D. MacQueen,³⁴R. Madrak,¹⁸K. Maeshima,¹⁸K. Makhoul,³³ T. Maki,²⁴P. Maksimovic,²⁶S. Malde,⁴³S. Malik,³¹G. Manca,^30,sA. Manousakis-Katsikakis,³F. Margaroli,⁴⁹ C. Marino,²⁷C. P. Marino,²⁵A. Martin,⁶¹V. Martin,^22,jM. Martı´nez,⁴R. Martı´nez-Balları´n,³²T. Maruyama,⁵⁶ P. Mastrandrea,^52aT. Masubuchi,⁵⁶M. E. Mattson,⁵⁹P. Mazzanti,¹K. S. McFarland,⁵⁰P. McIntyre,⁵⁴R. McNulty,^30,i

A. Mehta,³⁰P. Mehtala,²⁴A. Menzione,^47aP. Merkel,⁴⁹C. Mesropian,⁵¹T. Miao,¹⁸N. Miladinovic,⁷R. Miller,³⁶ C. Mills,²³M. Milnik,²⁷A. Mitra,¹G. Mitselmakher,¹⁹H. Miyake,⁵⁶N. Moggi,¹C. S. Moon,²⁸R. Moore,¹⁸ M. J. Morello,^47b,47aJ. Morlok,²⁷P. Movilla Fernandez,¹⁸J. Mu¨lmensta¨dt,²⁹A. Mukherjee,¹⁸Th. Muller,²⁷R. Mumford,²⁶

P. Murat,¹⁸M. Mussini,^6b,1J. Nachtman,¹⁸Y. Nagai,⁵⁶A. Nagano,⁵⁶J. Naganoma,⁵⁸K. Nakamura,⁵⁶I. Nakano,⁴¹ A. Napier,⁵⁷V. Necula,¹⁷C. Neu,⁴⁶M. S. Neubauer,²⁵J. Nielsen,^29,fL. Nodulman,²M. Norman,¹⁰O. Norniella,²⁵

E. Nurse,³¹L. Oakes,⁴³S. H. Oh,¹⁷Y. D. Oh,²⁸I. Oksuzian,¹⁹T. Okusawa,⁴²R. Orava,²⁴K. Osterberg,²⁴ S. Pagan Griso,^44b,44aC. Pagliarone,^47aE. Palencia,¹⁸V. Papadimitriou,¹⁸A. Papaikonomou,²⁷A. A. Paramonov,¹⁴

B. Parks,⁴⁰S. Pashapour,³⁴J. Patrick,¹⁸G. Pauletta,^55b,55aM. Paulini,¹³C. Paus,³³D. E. Pellett,⁸A. Penzo,^55a T. J. Phillips,¹⁷G. Piacentino,^47aE. Pianori,⁴⁶L. Pinera,¹⁹K. Pitts,²⁵C. Plager,⁹L. Pondrom,⁶⁰O. Poukhov,^16,a N. Pounder,⁴³F. Prakoshyn,¹⁶A. Pronko,¹⁸J. Proudfoot,²F. Ptohos,^18,hE. Pueschel,¹³G. Punzi,^47b,47aJ. Pursley,⁶⁰ J. Rademacker,^43,dA. Rahaman,⁴⁸V. Ramakrishnan,⁶⁰N. Ranjan,⁴⁹I. Redondo,³²B. Reisert,¹⁸V. Rekovic,³⁸P. Renton,⁴³

M. Rescigno,^52aS. Richter,²⁷F. Rimondi,^6b,1L. Ristori,^47aA. Robson,²²T. Rodrigo,¹²T. Rodriguez,⁴⁶E. Rogers,²⁵ S. Rolli,⁵⁷R. Roser,¹⁸M. Rossi,^55aR. Rossin,¹¹P. Roy,³⁴A. Ruiz,¹²J. Russ,¹³V. Rusu,¹⁸H. Saarikko,²⁴A. Safonov,⁵⁴ W. K. Sakumoto,⁵⁰O. Salto´,⁴L. Santi,^55b,55aS. Sarkar,^52b,52aL. Sartori,^47aK. Sato,¹⁸A. Savoy-Navarro,⁴⁵T. Scheidle,²⁷

P. Schlabach,¹⁸A. Schmidt,²⁷E. E. Schmidt,¹⁸M. A. Schmidt,¹⁴M. P. Schmidt,^61,aM. Schmitt,³⁹T. Schwarz,⁸ L. Scodellaro,¹²A. L. Scott,¹¹A. Scribano,^47c,47aF. Scuri,^47aA. Sedov,⁴⁹S. Seidel,³⁸Y. Seiya,⁴²A. Semenov,¹⁶ L. Sexton-Kennedy,¹⁸A. Sfyrla,²¹S. Z. Shalhout,⁵⁹M. D. Shapiro,²⁹T. Shears,³⁰P. F. Shepard,⁴⁸D. Sherman,²³ M. Shimojima,^56,mS. Shiraishi,¹⁴M. Shochet,¹⁴Y. Shon,⁶⁰I. Shreyber,³⁷A. Sidoti,^47aP. Sinervo,³⁴A. Sisakyan,¹⁶ A. J. Slaughter,¹⁸J. Slaunwhite,⁴⁰K. Sliwa,⁵⁷J. R. Smith,⁸F. D. Snider,¹⁸R. Snihur,³⁴A. Soha,⁸S. Somalwar,⁵³V. Sorin,³⁶

J. Spalding,¹⁸T. Spreitzer,³⁴P. Squillacioti,^47c,47aM. Stanitzki,⁶¹R. St. Denis,²²B. Stelzer,⁹O. Stelzer-Chilton,⁴³ D. Stentz,³⁹J. Strologas,³⁸D. Stuart,¹¹J. S. Suh,²⁸A. Sukhanov,¹⁹I. Suslov,¹⁶T. Suzuki,⁵⁶A. Taffard,^25,eR. Takashima,⁴¹ Y. Takeuchi,⁵⁶R. Tanaka,⁴¹M. Tecchio,³⁵P. K. Teng,¹K. Terashi,⁵¹J. Thom,^18,gA. S. Thompson,²²G. A. Thompson,²⁵ E. Thomson,⁴⁶P. Tipton,⁶¹V. Tiwari,¹³S. Tkaczyk,¹⁸D. Toback,⁵⁴S. Tokar,¹⁵K. Tollefson,³⁶T. Tomura,⁵⁶D. Tonelli,¹⁸

S. Torre,²⁰D. Torretta,¹⁸P. Totaro,^55b,55aS. Tourneur,⁴⁵Y. Tu,⁴⁶N. Turini,^47c,47aF. Ukegawa,⁵⁶S. Vallecorsa,²¹ N. van Remortel,^24,bA. Varganov,³⁵E. Vataga,^47d,47aF. Va´zquez,^19,kG. Velev,¹⁸C. Vellidis,³V. Veszpremi,⁴⁹M. Vidal,³²

R. Vidal,¹⁸I. Vila,¹²R. Vilar,¹²T. Vine,³¹M. Vogel,³⁸I. Volobouev,^29,pG. Volpi,^47b,47aF. Wu¨rthwein,¹⁰P. Wagner,⁵⁴ R. G. Wagner,²R. L. Wagner,¹⁸J. Wagner-Kuhr,²⁷W. Wagner,²⁷T. Wakisaka,⁴²R. Wallny,⁹S. M. Wang,¹A. Warburton,³⁴

D. Waters,³¹M. Weinberger,⁵⁴W. C. Wester III,¹⁸B. Whitehouse,⁵⁷D. Whiteson,^46,eA. B. Wicklund,²E. Wicklund,¹⁸ G. Williams,³⁴H. H. Williams,⁴⁶P. Wilson,¹⁸B. L. Winer,⁴⁰P. Wittich,^18,gS. Wolbers,¹⁸C. Wolfe,¹⁴T. Wright,³⁵X. Wu,²¹ S. M. Wynne,³⁰S. Xie,³³A. Yagil,¹⁰K. Yamamoto,⁴²J. Yamaoka,⁵³U. K. Yang,^14,lY. C. Yang,²⁸W. M. Yao,²⁹G. P. Yeh,¹⁸ J. Yoh,¹⁸K. Yorita,¹⁴T. Yoshida,⁴²G. B. Yu,⁵⁰I. Yu,²⁸S. S. Yu,¹⁸J. C. Yun,¹⁸L. Zanello,^52b,52aA. Zanetti,^55aI. Zaw,²³

X. Zhang,²⁵Y. Zheng,^9,cand S. Zucchelli^6b,1 (CDF Collaboration)

1Institute of Physics, Academia Sinica, Taipei, Taiwan 11529, Republic of China

2Argonne National Laboratory, Argonne, Illinois 60439, USA

3University of Athens, 157 71 Athens, Greece

4Institut de Fisica d’Altes Energies, Universitat Autonoma de Barcelona, E-08193, Bellaterra (Barcelona), Spain

5Baylor University, Waco, Texas 76798, USA

1Istituto Nazionale di Fisica Nucleare Bologna, I-40127 Bologna, Italy

6bUniversity of Bologna, I-40127 Bologna, Italy

7Brandeis University, Waltham, Massachusetts 02254, USA

8University of California, Davis, Davis, California 95616, USA

9University of California, Los Angeles, Los Angeles, California 90024, USA

10University of California, San Diego, La Jolla, California 92093, USA

11University of California, Santa Barbara, Santa Barbara, California 93106, USA

12Instituto de Fisica de Cantabria, CSIC-University of Cantabria, 39005 Santander, Spain

13Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA

14Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637, USA

15Comenius University, 842 48 Bratislava, Slovakia; Institute of Experimental Physics, 040 01 Kosice, Slovakia

16Joint Institute for Nuclear Research, RU-141980 Dubna, Russia

17Duke University, Durham, North Carolina 27708, USA

18Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA

19University of Florida, Gainesville, Florida 32611, USA

20Laboratori Nazionali di Frascati, Istituto Nazionale di Fisica Nucleare, I-00044 Frascati, Italy

21University of Geneva, CH-1211 Geneva 4, Switzerland

22Glasgow University, Glasgow G12 8QQ, United Kingdom

191802-2

23Harvard University, Cambridge, Massachusetts 02138, USA

24Division of High Energy Physics, Department of Physics, University of Helsinki and Helsinki Institute of Physics, FIN-00014, Helsinki, Finland

25University of Illinois, Urbana, Illinois 61801, USA

26The Johns Hopkins University, Baltimore, Maryland 21218, USA

27Institut fu¨r Experimentelle Kernphysik, Universita¨t Karlsruhe, 76128 Karlsruhe, Germany

28Center 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

29Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

30University of Liverpool, Liverpool L69 7ZE, United Kingdom

31University College London, London WC1E 6BT, United Kingdom

32Centro de Investigaciones Energeticas Medioambientales y Tecnologicas, E-28040 Madrid, Spain

33Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

34Institute of Particle Physics: McGill University, Montre´al, Canada H3A 2T8;

and University of Toronto, Toronto, Canada M5S 1A7

35University of Michigan, Ann Arbor, Michigan 48109, USA

36Michigan State University, East Lansing, Michigan 48824, USA

37Institution for Theoretical and Experimental Physics, ITEP, Moscow 117259, Russia

38University of New Mexico, Albuquerque, New Mexico 87131, USA

39Northwestern University, Evanston, Illinois 60208, USA

40The Ohio State University, Columbus, Ohio 43210, USA

41Okayama University, Okayama 700-8530, Japan

42Osaka City University, Osaka 588, Japan

43University of Oxford, Oxford OX1 3RH, United Kingdom

44aIstituto Nazionale di Fisica Nucleare, Sezione di Padova-Trento, I-35131 Padova, Italy

44bUniversity of Padova, I-35131 Padova, Italy

45LPNHE, Universite Pierre et Marie Curie/IN2P3-CNRS, UMR7585, Paris, F-75252 France

46University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA

47aIstituto Nazionale di Fisica Nucleare Pisa, I-56127 Pisa, Italy

47bUniversity of Pisa, I-56127 Pisa, Italy

47cUniversity of Siena, I-56127 Pisa, Italy

47dScuola Normale Superiore, I-56127 Pisa, Italy

48University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA

49Purdue University, West Lafayette, Indiana 47907, USA

50University of Rochester, Rochester, New York 14627, USA

51The Rockefeller University, New York, New York 10021, USA

52aIstituto Nazionale di Fisica Nucleare, Sezione di Roma 1, I-00185 Roma, Italy

52bSapienza Universita` di Roma, I-00185 Roma, Italy

53Rutgers University, Piscataway, New Jersey 08855, USA

54Texas A&M University, College Station, Texas 77843, USA

55aIstituto Nazionale di Fisica Nucleare Trieste/Udine, University of Trieste/Udine, Italy

55bUniversity of Trieste/Udine, Italy

56University of Tsukuba, Tsukuba, Ibaraki 305, Japan

57Tufts University, Medford, Massachusetts 02155, USA

58Waseda University, Tokyo 169, Japan

59Wayne State University, Detroit, Michigan 48201, USA

60University of Wisconsin, Madison, Wisconsin 53706, USA

61Yale University, New Haven, Connecticut 06520, USA

(Received 3 September 2008; revised manuscript received 28 September 2009; published 3 November 2009) A combined mass and particle identification fit is used to make the first observation of the decayB⁰s ! DsK and measure the branching fraction ofB⁰s!DsK relative toB⁰s!D^þs. This analysis uses 1:2 fb¹integrated luminosity ofppcollisions at ffiffiffi

ps

¼1:96 TeVcollected with the CDF II detector at the Fermilab Tevatron collider. We observe aB⁰s !DsKsignal with a statistical significance of8:1 and measureBðB⁰s !DsKÞ=BðB⁰s !D^þsÞ ¼0:0970:018ðstatÞ 0:009ðsystÞ.

DOI:10.1103/PhysRevLett.103.191802 PACS numbers: 13.25.Hw, 12.15.Hh

One of the remaining open questions in flavor physics is the precise value of the angle¼argðV_udV_ub =VcdV_cb Þ of the unitarity triangle [1]. Current measurements use the interference between b!ucs and b!cus diagrams in B!D^ðÞ0K^ðÞ and B!D^ðÞ0K^ðÞ decays when D⁰ and D⁰ are observed in common final states [2–7], but suffer from the large difference between the amplitudes of these decays. With a large sample of hadronic B⁰s

decays, it may be possible to determinefrom the inter- ference, throughB⁰_s–B⁰_s mixing, of the same diagrams in the decay modes B⁰s!D^þsK and B⁰s !DsK^þ [8,9], which are expected to have a more favorable amplitude ratio; the two decays proceed through color-allowed tree amplitudes whose ratio is suppressed by only a factor0:4 [10]. To determine, a time-dependent measurement of the decay rates of B⁰s!D^þsK, B⁰s!DsK^þ, B⁰s ! DsK^þ, and B⁰s !D^þsK is required. The first steps in this effort are to observe these decay modes (which we will collectively refer to asB⁰_s !D_sK) and to measure the CP-averaged branching ratioBðB⁰_s!D_sKÞ ¹₂½BðB⁰_s! D^þsKÞþBðB⁰s!DsK^þÞþBðB⁰s!DsK^þÞ þBðB⁰s! D^þ_sKÞ. In this Letter we report the first observation of the B⁰_s !D_sK decay modes and the first measurement of BðB⁰s !DsKÞ=BðB⁰s!D^þsÞ. We measure this branching fraction ratio since many of the systematic un- certainties cancel in the ratio andBðB⁰_s !D^þ_sÞis pre- cisely measured elsewhere [11,12].

We analyze pp collisions at ffiffiffi ps

¼1:96 TeV recorded by the CDF II detector at the Fermilab Tevatron collider with an integrated luminosity of1:2 fb¹. A detailed de- scription of the detector can be found elsewhere [13]. This analysis uses charged particle tracks reconstructed in the pseudorapidity [14] range jj&1from hits in a silicon microstrip vertex detector [15] and a cylindrical drift chamber [16] immersed in a 1.4 T axial magnetic field.

The specific ionization energy loss (dE=dx) of charged particles in the drift chamber is used for particle identifi- cation (PID). A sample rich in bottom hadrons is selected by triggering on events that have at least two tracks, each withpT >2 GeV=cand large impact parameter; the trig- ger further requires that these tracks originate from a secondary vertex well displaced from the primary interac- tion point [17].

We reconstruct B⁰_s !D^þ_sh candidates (where h¼ orK) as follows. First, we identifyD^þs !ð!KK^þÞ^þ candidates [18] using the invariant mass requirements 1013< mðKK^þÞ<1028 MeV=c² and 1948:3<

mðKK^þþÞ<1988:3 MeV=c². The D^þ_s decay tracks must satisfy a three-dimensional vertex fit. No PID require- ments are made on theD^þs decay tracks. We then pair the D^þs candidates with h tracks to define the B⁰s !D^þsh candidate sample. We further require the D^þs–h pair to satisfy a three-dimensional fit to theB⁰_s decay vertex. No mass constraint is used either on the or on the D^þ_s candidate. Finally, we define a mass variable mwhich is

the invariant mass of theD^þ_s–hcombination where theh is assigned the mass; m is used to provide kinematic separation between the B⁰s !DsK and B⁰s !D^þs signals.

To reduce combinatorial background, further selection requirements are made on the B⁰_s candidate: transverse impact parameter (jd0j<60m); longitudinal impact pa- rameter (jz0=z0j<3, wherez0 is the uncertainty onz0) [19]; transverse momentum (p_T>5:5 GeV=c); isolation I¼pTðB⁰sÞ=½p_TðB⁰sÞ þP

trackspTðtrackÞ>0:5, where the sum runs over tracks within R¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

²þ²

p <1

around theB⁰s direction originating from the same primary vertex; the opening angle [RðD^þs; hÞ<1:5] between the D^þs candidate and thehtrack; and the projection of theB⁰s

andD^þs decay lengths along the transverse momentum of theB⁰_scandidate [L_xyðB⁰_sÞ>300m,L_xyðB⁰_sÞ=_LxyðB⁰_sÞ>

8 (whereLxy is the uncertainty on Lxy), and LxyðD^þ_sÞ>

LxyðB⁰sÞ]. The dE=dx calibrations are based on large samples of D⁰ !K^þ decays taken with the displaced-track trigger. To avoid bias, the h track is required to pass the same pT>2 GeV=ctrigger require- ment as theD⁰ !K^þcalibration tracks.

Monte Carlo simulation is used to model signal and background and to determine trigger and reconstruction efficiencies. Single B⁰_s hadrons are produced with

BGENERATOR [20,21]; their decays are simulated with

EVTGEN[22] and a detailed detector and trigger simulation.

The greatest challenge in this analysis is to disentangle the various components contributing to the data sample.

Apart from theB⁰s !DsKandB⁰s !D^þssignals, the sample contains partially reconstructed B⁰s decays, reflec- tions from decays of other bottom hadron species, and combinatorial background. To separate the components and determine the number of candidates of each compo- nent type, we perform a maximum-likelihood fit. The fit variables are m and the PID variable Z, which is the logarithm of the ratio between the measured dE=dx and the expecteddE=dxfor a pion with the momentum of the h track. The likelihood function is Lðf1;. . .; fM1Þ ¼

Q_N

i¼1P_M

j¼1f_jp_jðm_iÞq_jðZ_iÞ, where f_M¼1P_M1

j¼1 f_j. The index i runs over the N candidates, andj runs over the Mcomponents;f_jis the fraction of candidates in the jth component, to be determined by the fit.

We group the fit components into three categories by source. Combinations where theD^þs candidate and theh track come from a single bottom hadron (B⁰,B,B⁰_s,⁰_b) are called single-Bcontributions. Nonbottom contributions where theD^þ_s candidate does not come from a realD^þ_s are called fake-D^þs combinatorial background. Combinations of a realD^þs with a track coming from fragmentation, the underlying event, or the other bottom hadron in the event are called real-D^þ_s combinatorial background. The single-B category is comprised of several independently normalized components, whose normalizations are free 191802-4

parameters of the fit: the B⁰_s!D_sK andB⁰_s!D^þ_s signals and the radiative tail of the B⁰s !D^þs, which will be discussed in more detail below; B⁰s!D^þs; B⁰s !D^þs ; B⁰ or B!D^þðK^þþÞX and ⁰_b ! ^þ_cðpK^þÞX, which have narrow reflections with masses close to the signal peaks and which have separate fit normalizations; B⁰!D^ðÞs h decays (where h¼, K), whose relative yields are fixed to the values reported in [23]; and partially reconstructedB⁰s decay modes missing more than one decay product or a neutrino, which are grouped together in the fit.

Mass probability density functions (PDF’s) p_jðmÞ for the single-B components are extracted from large simu- lated samples of B decays. Separate mass templates are extracted for each of the components described above.

Rather than parameterizing the mass shapes, which are complicated for most of the single-Bcomponents, we use histograms as mass PDF’s. Sufficiently large Monte Carlo samples (approximately 50 000 candidates after cuts of B⁰s !D^þs and B⁰s !DsK) are generated to make the statistical fluctuations in the PDF’s small.

Special care has to be taken in the treatment of the low- mass radiative tail of the decay modeB⁰s!D^þs, which overlaps with the B⁰s !DsK mass PDF. Improper ac- counting for the tail can bias the measurement of both the B⁰_s !D^þ_syield and theB⁰_s !D_sKyield by misiden- tifying a fraction of theB⁰s !D^þs contribution as part of the (much smaller)B⁰s!DsK contribution. The ra- diative tail is modeled in EVTGEN by using the PHOTOS

algorithm for radiative corrections [24] with a cutoff for photon emission at 10 MeV. We allow the normalization to float in the fit to account for uncertainties in thePHOTOS

prediction of the size of the radiative tail. (The radiative tail of B⁰_s!D_sK does not require special treatment. The kaon radiates less, and any resulting misidentified B⁰s ! DsK contribution is easily absorbed by the other fit components, which dominate at m below the B⁰s ! DsKpeak.)

The mass distribution of the fake-D^þs background is parameterized with a function of the form pbgðmÞ / expðmÞ þ . The shape parametersand are deter- mined in an ancillary mass-only fit ofB⁰s candidates pop- ulating the sidebands of the D^þs mass distribution. To model the real-D^þs background, we use a sample of same-sign D^þ_s^þ candidates. A fit to the D^þ_s^þ mass distribution was performed using the same form for the mass distribution that was used for the fake-D^þ_s parame- terization. Given the limited statistics of the signal sample, we cannot separately resolve the real-D^þs and fake-D^þs

combinatorial backgrounds; in the default fit we therefore combine the two types of background. We assess a system- atic uncertainty by allowing the relative size of the two background types to vary.

We determine the Z PDF’s qjðZÞ for pions and kaons from D^þ!D⁰ðK^þÞ^þ decays. The flavor of the

daughter tracks of the D⁰ in the decay D^þ! D⁰ðK^þÞ^þ is tagged by the charge of the soft pion from theD^þdecay. Taken together with the large signal- to-background ratio of the m¼mðK^þþÞ mðK^þÞ peak, this charge tagging yields a very clean sample of pions and kaons. We further reduce background contamination by sideband-subtracting in m. The mean values of Zfor kaons and pions are separated by approxi- mately 1.4 standard deviations. TheZdistributions for both species have similar widths. Because the data sample con- tains semileptonic decays, we need to model the dE=dx distributions of muons and electrons as well. For muons, which are a small contribution in the mass region of interest, the pion template can be used without introducing a significant systematic uncertainty. For electrons, we de- rive a template from a J=c !e^þesample. The ZPDF for the fake-D^þs combinatorial background is determined from data by selecting candidates from the sidebands of the D^þs mass distribution. All Z PDF’s are represented as histograms.

Figures1and2show the fit projections in mass andZ. The yields determined by the fit are 112587 B⁰s! D^þs and 10218 B⁰s !DsK candidates. The branching fraction of B⁰s!DsK relative to B⁰s! D^þ_s, corrected for the relative reconstruction efficiency, is BðB⁰_s !D_sKÞ=BðB⁰_s!D^þ_sÞ ¼0:0970:018.

The reconstruction efficiency differs between the two modes due to the kinematics of the decay and due to the nuclear interaction and decay-in-flight probabilities of kaons and pions [25]. A Monte Carlo simulation of the detector and trigger based onGEANT[26] is used to deter- mine the relative reconstruction efficiency between kaons and pions=_K¼1:0710:028, where the uncertainty is due to Monte Carlo statistics; this uncertainty is included in the systematic uncertainty on the ratio of branching fractions. A fit performed with the B⁰s !DsKyield set to zero is worse than the default fit by logL¼ 32:52;

the corresponding statistical significance of the B⁰s! DsK signal is 8.1 standard deviations.

Systematic uncertainties on BðB⁰s !DsKÞ=BðB⁰s! D^þsÞ are studied by incorporating each effect in the generation of simulated experiments which are then fitted using the default configuration. The bias on BðB⁰_s! D_sKÞ=BðB⁰_s !D^þ_sÞ, averaged over 10 000 simulated experiments, is used as the systematic uncertainty associ- ated with the effect under study. Table I summarizes the systematic uncertainties. The systematic uncertainties are dominated by the modeling of thedE=dx(0.007), specifi- cally by the differences between theZdistributions ofD^þ daughter tracks (from which the kaon and pionZPDF’s are derived) and B⁰s daughter tracks; these differences arise from effects such as the greater particle abundance in the vicinity of a promptD^þ compared to aB⁰s, and hence a higher probability for D^þdaughter tracks to contain ex- traneous hits. Modeling of the mass distributions of the single-B components (0.004), which includes statistical

fluctuations in the mass PDF’s, modeling of the combinatorial-background mass shape (0.002), and un- certainty induced in theZtemplate by the poorly known particle content for theB⁰,B, and_b reflections (0.002) are comparatively minor contributions. The total system- atic uncertainty is obtained by adding the individual sys- tematic uncertainties in quadrature; at 0.009, it is about half as large as the statistical uncertainty.

One of the dominant sources of uncertainty is theB⁰ ! D^þðK^þþÞX reflection, which is strongly anticorre- lated with the B⁰s !DsK signal. The normalization of the reflection (like all other background components) is allowed to vary independently of the other contributions in the fit; the uncertainty due to the size of the reflection is therefore accounted for as part of the statistical uncertainty onBðB⁰s !DsKÞ=BðB⁰s !D^þsÞ.

The analysis procedure was crosschecked in several ways. Most importantly, before performing the measure- ment on the B⁰_s!D^þ_sX signal sample, we verified our method using two control samples,B⁰ !D^þXandB⁰ ! D^þX. In both cases, our results are statistically consistent

with world-average values. We measure BðB⁰! D^þKÞ=BðB⁰ !D^þÞ ¼0:0860:005ðstatÞ, 1.0 stan- dard deviations above the world average; and BðB⁰! D^þKÞ=BðB⁰!D^þÞ ¼0:0800:008ðstatÞ, 0.3 standard deviations above the world average [1]. The rela- tive branching fractions BðB⁰!D^þÞ=BðB⁰! D^þÞ, BðB⁰ !D^þÞ=BðB⁰ !D^þÞ, and BðB⁰!D^þÞ=BðB⁰ !D^þÞ were also found to be consistent within 2 standard deviations with world averages. Finally, the fractional sizes of the radiative tails of B⁰!D^þ, B⁰!D^þ, and B⁰ !D^þ_s are

TABLE I. Systematic uncertainties on BðB⁰s!DsKÞ=

BðB⁰s !D^þsÞ.

Source Systematic uncertainty

dE=dxPDF modeling 0.007

Mass PDF modeling 0.004

RelativeKtoefficiency 0.003

Combinatorial-background model 0.002 Composition ofB⁰,B,_b reflections 0.002 Fitter bias due to finite statistics 0.001

Sum in quadrature 0.009

candidates/0.02

10 20 30 40 50

10 20 30 40 50

data fit

π Ds

→ Bs

sK

→D Bs

→DX B comb. bg.

Z

-0.4 -0.2 0 0.2 0.4

)σresidual ( -4

-2 0 2 4

FIG. 2. Z projection of the likelihood fit in the region of interest for B⁰s !DsK (5:26< m <5:35 GeV=c²). Fit com- ponents are stacked. The residual plot at the bottom is calculated as in Fig.1. The² of the projection is 30.7 for 14 degrees of freedom.

candidates/10 MeV

50 100 150 200 250

50 100 150 200 250

data fit

π Ds

→ Bs

sK

→D Bs

→DX B comb. bg.

m(GeV)

4.8 5 5.2 5.4 5.6 5.8 6 6.2 6.4

)σresidual ( -4

-2 0 2 4

FIG. 1. Mass projection of the likelihood fit. Fit components are stacked.B!DX denotes all single-B contributions except B⁰s !D^þs andB⁰s !DsK; the small peak in theB!DX slice is due to theB⁰!D^þðK^þþÞreflection. Although these components are combined in the graph, they are allowed to vary independently in the fit. The residual plot at the bottom shows the discrepancy (data minus fit) in units of standard deviation (); for the bins with low statistics, neighboring bins are combined until the predicted number of events is greater than five. The²of the projection is 79.0 for 72 degrees of freedom.

191802-6

found to be in agreement with each other (and about twice as large as thePHOTOSprediction).

In conclusion, we have presented the first observation of theB⁰_s!D_sKdecay mode with a statistical significance of 8.1 standard deviations. TheB⁰_s !D_sKevent yield is 10218(statistical uncertainty only). We use this sample to measureBðB⁰s !DsKÞ=BðB⁰s!D^þsÞ ¼0:097 0:018ðstatÞ 0:009ðsystÞ. This result is consistent with naive expectations based on the branching fraction ratio for the analogousB⁰ andB decays, taking into account also the expected contribution fromB⁰s!DsK^þ decays [10].

We thank the Fermilab staff and the technical staffs of the participating institutions for their vital contributions.

This work was supported by the U. S. Department of Energy and National Science Foundation; the Italian Istituto Nazionale di Fisica Nucleare; the Ministry of Education, Culture, Sports, Science and Technology of Japan; the Natural Sciences and Engineering Research Council of Canada; the National Science Council of the Republic of China; the Swiss National Science Founda- tion; the A. P. Sloan Foundation; the Bundesministerium fu¨r Bildung und Forschung, Germany; the Korean Science and Engineering Foundation and the Korean Research Foundation; the Science and Technology Facilities Council and the Royal Society, UK; the Institut National de Physique Nucleaire et Physique des Particules/CNRS;

the Russian Foundation for Basic Research; the Ministerio de Ciencia e Innovacio´n, Spain; the Slovak R&D Agency;

and the Academy of Finland.

aDeceased.

bVisitor from a Universiteit Antwerpen, B-2610 Antwerp, Belgium.

cVisitor from Chinese Academy of Sciences, Beijing 100864, China.

dVisitor from University of Bristol, Bristol BS8 1TL, United Kingdom.

eVisitor from University of California Irvine, Irvine, CA 92697, USA.

fVisitor from University of California Santa Cruz, Santa Cruz, CA 95064, USA.

gVisitor from Cornell University, Ithaca, NY 14853, USA.

hVisitor from University of Cyprus, Nicosia CY-1678, Cyprus.

iVisitor from University College Dublin, Dublin 4, Ireland.

jVisitor from University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom.

kVisitor from Universidad Iberoamericana, Mexico D.F., Mexico.

lVisitor from University of Manchester, Manchester M13 9PL, England.

mVisitor from Nagasaki Institute of Applied Science, Nagasaki, Japan.

nVisitor from University de Oviedo, E-33007 Oviedo, Spain.

oVisitor from Queen Mary, University of London, London, E1 4NS, England.

pVisitor from Texas Tech University, Lubbock, TX 79409, USA

qVisitor from IFIC(CSIC-Universitat de Valencia), 46071 Valencia, Spain.

rVisitor from Royal Society of Edinburgh, Scotland.

sVisitor from Istituto Nazionale di Fisica Nucleare, Sezione di Cagliari, 09042 Monserrato (Cagliari), Italy.

[1] C. Amsleret al., Phys. Lett. B667, 1 (2008), and refer- ences therein.

[2] M. Gronau and D. London, Phys. Lett. B 253, 483 (1991).

[3] M. Gronau and D. Wyler, Phys. Lett. B 265, 172 (1991).

[4] D. Atwood, I. Dunietz, and A. Soni, Phys. Rev. Lett.78, 3257 (1997).

[5] A. Giri, Y. Grossman, A. Soffer, and J. Zupan, Phys.

Rev. D68, 054018 (2003).

[6] J. Charles et al., Eur. Phys. J. C 41, 1 (2005); updated results and plots available at: http://ckmfitter.in2p3.fr.

[7] M. Bonaet al., J. High Energy Phys. 10 (2006) 081.

[8] R. Aleksan, I. Dunietz, and B. Kayser, Z. Phys. C54, 653 (1992).

[9] I. Dunietz, Phys. Rev. D52, 3048 (1995).

[10] R. Fleischer, Nucl. Phys.B671, 459 (2003).

[11] A. Abulenciaet al., Phys. Rev. Lett.98, 061802 (2007).

[12] A. Drutskoyet al., Phys. Rev. D76, 012002 (2007).

[13] D. Acostaet al., Phys. Rev. D71, 032001 (2005).

[14] CDF II uses a right-handed coordinate system with the origin at the center of the detector, in which thezaxis is along the proton direction, theyaxis points up,and are the polar and azimuthal angles, and r is the radial distance in thex-yplane. The pseudorapidityis defined aslog tanð=2Þ.

[15] A. Sill, Nucl. Instrum. Methods Phys. Res., Sect. A447, 1 (2000).

[16] T. Affolderet al., Nucl. Instrum. Methods Phys. Res., Sect.

A526, 249 (2004).

[17] B. Ashmanskaset al., Nucl. Instrum. Methods Phys. Res., Sect. A518, 532 (2004).

[18] Reference to the charge-conjugate decays is implied here and throughout the text.

[19] The impact parameter is defined as the distance of closest approach of theB⁰s candidate’s trajectory with the event- by-event primary vertex. In events with more than one reconstructed primary vertex, the vertex with the largest scalar sum of trackpTis used.

[20] P. Nason, S. Dawson, and R. K. Ellis, Nucl. Phys.B303, 607 (1988).

[21] P. Nason, S. Dawson, and R. K. Ellis, Nucl. Phys.B327, 49 (1989).

[22] D. J. Lange, Nucl. Instrum. Methods Phys. Res., Sect. A 462, 152 (2001).

[23] B. Aubertet al., Phys. Rev. Lett.98, 081801 (2007).

[24] E. Barberio and Z. Was, Comput. Phys. Commun.79, 291 (1994).

[25] D. E. Acostaet al., Phys. Rev. Lett.94, 122001 (2005).

[26] R. Brun, R. Hagelberg, M. Hansroul, and J. C. Lassalle, CERN Report No. CERN-DD-78-2-REV.