Observation of the Baryonic Flavor-Changing Neutral Current Decay Λ_b⁰ -> Λμ⁺μ⁻

Article

Reference

Observation of the Baryonic Flavor-Changing Neutral Current Decay Λ

-> Λμ

μ

CDF Collaboration

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

Abstract

We report the first observation of the baryonic flavor-changing neutral current decay Λ0b→Λμ+μ− with 24 signal events and a statistical significance of 5.8 Gaussian standard deviations. This measurement uses a pp collisions data sample corresponding to 6.8  fb−1 at s√=1.96  TeV collected by the CDF II detector at the Tevatron collider. The total and differential branching ratios for Λ0b→Λμ+μ− are measured. We find B(Λ0b→Λμ+μ−)=[1.73±0.42(stat)±(syst)]×10−6. We also report the first measurement of the differential branching ratio of B0s→ϕμ+μ−, using 49 signal events. In addition, we report branching ratios for B+→K+μ+μ−, B0→K0μ+μ−, and B→K∗(892)μ+μ− decays.

CDF Collaboration, CLARK, Allan Geoffrey (Collab.), et al . Observation of the Baryonic Flavor-Changing Neutral Current Decay Λ

-> Λμ

μ

. Physical Review Letters , 2011, vol.

107, no. 20, p. 201802

DOI : 10.1103/PhysRevLett.107.201802

Available at:

http://archive-ouverte.unige.ch/unige:38753

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

1 / 1

Observation of the Baryonic Flavor-Changing Neutral Current Decay

!

T. Aaltonen,²²B. A´ lvarez Gonza´lez,^10,wS. Amerio,^42aD. Amidei,³³A. Anastassov,³⁷A. Annovi,¹⁸J. Antos,¹³ G. Apollinari,¹⁶J. A. Appel,¹⁶A. Apresyan,⁴⁷T. Arisawa,⁵⁶A. Artikov,¹⁴J. Asaadi,⁵²W. Ashmanskas,¹⁶B. Auerbach,⁵⁹ A. Aurisano,⁵²F. Azfar,⁴¹W. Badgett,¹⁶A. Barbaro-Galtieri,²⁷V. E. Barnes,⁴⁷B. A. Barnett,²⁴P. Barria,^45c,45aP. Bartos,¹³ M. Bauce,^42b,42aG. Bauer,³¹F. Bedeschi,^45aD. Beecher,²⁹S. Behari,²⁴G. Bellettini,^45b,45aJ. Bellinger,⁵⁸D. Benjamin,¹⁵ A. Beretvas,¹⁶A. Bhatti,⁴⁹M. Binkley,^16,aD. Bisello,^42b,42aI. Bizjak,^29,ccK. R. Bland,⁵C. Blocker,⁷B. Blumenfeld,²⁴

A. Bocci,¹⁵A. Bodek,⁴⁸D. Bortoletto,⁴⁷J. Boudreau,⁴⁶A. Boveia,¹²B. Brau,^16,bL. Brigliadori,^6b,6aA. Brisuda,¹³ C. Bromberg,³⁴E. Brucken,²²M. Bucciantonio,^45b,45aJ. Budagov,¹⁴H. S. Budd,⁴⁸S. Budd,²³K. Burkett,¹⁶ G. Busetto,^42b,42aP. Bussey,²⁰A. Buzatu,³²S. Cabrera,^15,yC. Calancha,³⁰S. Camarda,⁴M. Campanelli,³⁴M. Campbell,³³ F. Canelli,^12,16A. Canepa,⁴⁴B. Carls,²³D. Carlsmith,⁵⁸R. Carosi,^45aS. Carrillo,^17,lS. Carron,¹⁶B. Casal,¹⁰M. Casarsa,¹⁶ A. Castro,^6b,6aP. Catastini,¹⁶D. Cauz,^53aV. Cavaliere,^45c,45aM. Cavalli-Sforza,⁴A. Cerri,^27,gL. Cerrito,^29,rY. C. Chen,¹ M. Chertok,⁸G. Chiarelli,^45aG. Chlachidze,¹⁶F. Chlebana,¹⁶K. Cho,²⁶D. Chokheli,¹⁴J. P. Chou,²¹W. H. Chung,⁵⁸

Y. S. Chung,⁴⁸C. I. Ciobanu,⁴³M. A. Ciocci,^45c,45aA. Clark,¹⁹D. Clark,⁷G. Compostella,^42b,42aM. E. Convery,¹⁶ J. Conway,⁸M. Corbo,⁴³M. Cordelli,¹⁸C. A. Cox,⁸D. J. Cox,⁸F. Crescioli,^45b,45aC. Cuenca Almenar,⁵⁹J. Cuevas,^10,w

R. Culbertson,¹⁶D. Dagenhart,¹⁶N. d’Ascenzo,^43,uM. Datta,¹⁶P. de Barbaro,⁴⁸S. De Cecco,^50aG. De Lorenzo,⁴ M. Dell’Orso,^45b,45aC. Deluca,⁴L. Demortier,⁴⁹J. Deng,^15,dM. Deninno,^6aF. Devoto,²²M. d’Errico,^42b,42a A. Di Canto,^45b,45aB. Di Ruzza,^45aJ. R. Dittmann,⁵M. D’Onofrio,²⁸S. Donati,^45b,45aP. Dong,¹⁶T. Dorigo,^42aK. Ebina,⁵⁶

A. Elagin,⁵²A. Eppig,³³R. Erbacher,⁸D. Errede,²³S. Errede,²³N. Ershaidat,^43,bbR. Eusebi,⁵²H. C. Fang,²⁷ S. Farrington,⁴¹M. Feindt,²⁵J. P. Fernandez,³⁰C. Ferrazza,^45d,45aR. Field,¹⁷G. Flanagan,^47,sR. Forrest,⁸M. J. Frank,⁵ M. Franklin,²¹J. C. Freeman,¹⁶I. Furic,¹⁷M. Gallinaro,⁴⁹J. Galyardt,¹¹J. E. Garcia,¹⁹A. F. Garfinkel,⁴⁷P. Garosi,^45c,45a

H. Gerberich,²³E. Gerchtein,¹⁶S. Giagu,^50b,50aV. Giakoumopoulou,³P. Giannetti,^45aK. Gibson,⁴⁶C. M. Ginsburg,¹⁶ N. Giokaris,³P. Giromini,¹⁸M. Giunta,^45aG. Giurgiu,²⁴V. Glagolev,¹⁴D. Glenzinski,¹⁶M. Gold,³⁶D. Goldin,⁵² N. Goldschmidt,¹⁷A. Golossanov,¹⁶G. Gomez,¹⁰G. Gomez-Ceballos,³¹M. Goncharov,³¹O. Gonza´lez,³⁰I. Gorelov,³⁶ A. T. Goshaw,¹⁵K. Goulianos,⁴⁹A. Gresele,^42aS. Grinstein,⁴C. Grosso-Pilcher,¹²R. C. Group,¹⁶J. Guimaraes da Costa,²¹ Z. Gunay-Unalan,³⁴C. Haber,²⁷S. R. Hahn,¹⁶E. Halkiadakis,⁵¹A. Hamaguchi,⁴⁰J. Y. Han,⁴⁸F. Happacher,¹⁸K. Hara,⁵⁴ D. Hare,⁵¹M. Hare,⁵⁵R. F. Harr,⁵⁷K. Hatakeyama,⁵C. Hays,⁴¹M. Heck,²⁵J. Heinrich,⁴⁴M. Herndon,⁵⁸S. Hewamanage,⁵ D. Hidas,⁵¹A. Hocker,¹⁶W. Hopkins,^16,hD. Horn,²⁵S. Hou,¹R. E. Hughes,³⁸M. Hurwitz,¹²U. Husemann,⁵⁹N. Hussain,³² M. Hussein,³⁴J. Huston,³⁴G. Introzzi,^45aM. Iori,^50b,50aA. Ivanov,^8,pE. James,¹⁶D. Jang,¹¹B. Jayatilaka,¹⁵E. J. Jeon,²⁶ M. K. Jha,^6aS. Jindariani,¹⁶W. Johnson,⁸M. Jones,⁴⁷K. K. Joo,²⁶S. Y. Jun,¹¹T. R. Junk,¹⁶T. Kamon,⁵²P. E. Karchin,⁵⁷

Y. Kato,^40,oW. Ketchum,¹²J. Keung,⁴⁴V. Khotilovich,⁵²B. Kilminster,¹⁶D. H. Kim,²⁶H. S. Kim,²⁶H. W. Kim,²⁶ J. E. Kim,²⁶M. J. Kim,¹⁸S. B. Kim,²⁶S. H. Kim,⁵⁴Y. K. Kim,¹²N. Kimura,⁵⁶S. Klimenko,¹⁷K. Kondo,⁵⁶D. J. Kong,²⁶

J. Konigsberg,¹⁷A. Korytov,¹⁷A. V. Kotwal,¹⁵M. Kreps,²⁵J. Kroll,⁴⁴D. Krop,¹²N. Krumnack,^5,mM. Kruse,¹⁵ V. Krutelyov,^52,eT. Kuhr,²⁵M. Kurata,⁵⁴S. Kwang,¹²A. T. Laasanen,⁴⁷S. Lami,^45aS. Lammel,¹⁶M. Lancaster,²⁹ R. L. Lander,⁸K. Lannon,^38,vA. Lath,⁵¹G. Latino,^45c,45aI. Lazzizzera,^42aT. LeCompte,²E. Lee,⁵²H. S. Lee,¹²J. S. Lee,²⁶ S. W. Lee,^52,xS. Leo,^45b,45aS. Leone,^45aJ. D. Lewis,¹⁶C.-J. Lin,²⁷J. Linacre,⁴¹M. Lindgren,¹⁶E. Lipeles,⁴⁴A. Lister,¹⁹

D. O. Litvintsev,¹⁶C. Liu,⁴⁶Q. Liu,⁴⁷T. Liu,¹⁶S. Lockwitz,⁵⁹N. S. Lockyer,⁴⁴A. Loginov,⁵⁹D. Lucchesi,^42b,42a J. Lueck,²⁵P. Lujan,²⁷P. Lukens,¹⁶G. Lungu,⁴⁹J. Lys,²⁷R. Lysak,¹³R. Madrak,¹⁶K. Maeshima,¹⁶K. Makhoul,³¹ P. Maksimovic,²⁴S. Malik,⁴⁹G. Manca,^28,cA. Manousakis-Katsikakis,³F. Margaroli,⁴⁷C. Marino,²⁵M. Martı´nez,⁴ R. Martı´nez-Balları´n,³⁰P. Mastrandrea,^50aM. Mathis,²⁴M. E. Mattson,⁵⁷P. Mazzanti,^6aK. S. McFarland,⁴⁸P. McIntyre,⁵²

R. McNulty,^28,jA. Mehta,²⁸P. Mehtala,²²A. Menzione,^45aC. Mesropian,⁴⁹T. Miao,¹⁶D. Mietlicki,³³A. Mitra,¹ H. Miyake,⁵⁴S. Moed,²¹N. Moggi,^6aM. N. Mondragon,^16,lC. S. Moon,²⁶R. Moore,¹⁶M. J. Morello,¹⁶J. Morlock,²⁵

P. Movilla Fernandez,¹⁶A. Mukherjee,¹⁶Th. Muller,²⁵P. Murat,¹⁶M. Mussini,^6b,6aJ. Nachtman,^16,nY. Nagai,⁵⁴ J. Naganoma,⁵⁶I. Nakano,³⁹A. Napier,⁵⁵J. Nett,⁵⁸C. Neu,^44,aaM. S. Neubauer,²³J. Nielsen,^27,fL. Nodulman,² O. Norniella,²³E. Nurse,²⁹L. Oakes,⁴¹S. H. Oh,¹⁵Y. D. Oh,²⁶I. Oksuzian,¹⁷T. Okusawa,⁴⁰R. Orava,²²L. Ortolan,⁴

S. Pagan Griso,^42b,42aC. Pagliarone,^53aE. Palencia,^10,gV. Papadimitriou,¹⁶A. A. Paramonov,²J. Patrick,¹⁶ G. Pauletta,^53b,53aM. Paulini,¹¹C. Paus,³¹D. E. Pellett,⁸A. Penzo,^53aT. J. Phillips,¹⁵G. Piacentino,^45aE. Pianori,⁴⁴

J. Pilot,³⁸K. Pitts,²³C. Plager,⁹L. Pondrom,⁵⁸K. Potamianos,⁴⁷O. Poukhov,^14,aF. Prokoshin,^14,zA. Pronko,¹⁶ F. Ptohos,^18,iE. Pueschel,¹¹G. Punzi,^45b,45aJ. Pursley,⁵⁸A. Rahaman,⁴⁶V. Ramakrishnan,⁵⁸N. Ranjan,⁴⁷I. Redondo,³⁰

P. Renton,⁴¹M. Rescigno,^50aF. Rimondi,^6b,6aL. Ristori,^45a,16A. Robson,²⁰T. Rodrigo,¹⁰T. Rodriguez,⁴⁴E. Rogers,²³

S. Rolli, R. Roser, M. Rossi, F. Ruffini, A. Ruiz, J. Russ, V. Rusu, A. Safonov, W. K. Sakumoto, L. Santi,^53b,53aL. Sartori,^45aK. Sato,⁵⁴V. Saveliev,^43,uA. Savoy-Navarro,⁴³P. Schlabach,¹⁶A. Schmidt,²⁵E. E. Schmidt,¹⁶

M. P. Schmidt,^59,aM. Schmitt,³⁷T. Schwarz,⁸L. Scodellaro,¹⁰A. Scribano,^45c,45aF. Scuri,^45aA. Sedov,⁴⁷S. Seidel,³⁶ Y. Seiya,⁴⁰A. Semenov,¹⁴F. Sforza,^45b,45aA. Sfyrla,²³S. Z. Shalhout,⁸T. Shears,²⁸P. F. Shepard,⁴⁶M. Shimojima,^54,t S. Shiraishi,¹²M. Shochet,¹²I. Shreyber,³⁵A. Simonenko,¹⁴P. Sinervo,³²A. Sissakian,^14,aK. Sliwa,⁵⁵J. R. Smith,⁸

F. D. Snider,¹⁶A. Soha,¹⁶S. Somalwar,⁵¹V. Sorin,⁴P. Squillacioti,¹⁶M. Stanitzki,⁵⁹R. St. Denis,²⁰B. Stelzer,³² O. Stelzer-Chilton,³²D. Stentz,³⁷J. Strologas,³⁶G. L. Strycker,³³Y. Sudo,⁵⁴A. Sukhanov,¹⁷I. Suslov,¹⁴K. Takemasa,⁵⁴

Y. Takeuchi,⁵⁴J. Tang,¹²M. Tecchio,³³P. K. Teng,¹J. Thom,^16,hJ. Thome,¹¹G. A. Thompson,²³E. Thomson,⁴⁴ P. Ttito-Guzma´n,³⁰S. Tkaczyk,¹⁶D. Toback,⁵²S. Tokar,¹³K. Tollefson,³⁴T. Tomura,⁵⁴D. Tonelli,¹⁶S. Torre,¹⁸ D. Torretta,¹⁶P. Totaro,^53b,53aM. Trovato,^45d,45aY. Tu,⁴⁴N. Turini,^45c,45aF. Ukegawa,⁵⁴S. Uozumi,²⁶A. Varganov,³³

E. Vataga,^45d,45aF. Va´zquez,^17,lG. Velev,¹⁶C. Vellidis,³M. Vidal,³⁰I. Vila,¹⁰R. Vilar,¹⁰M. Vogel,³⁶G. Volpi,^45b,45a P. Wagner,⁴⁴R. L. Wagner,¹⁶T. Wakisaka,⁴⁰R. Wallny,⁹S. M. Wang,¹A. Warburton,³²D. Waters,²⁹M. Weinberger,⁵²

H. Wenzel,¹⁶W. C. Wester III,¹⁶B. Whitehouse,⁵⁵D. Whiteson,^44,dA. B. Wicklund,²E. Wicklund,¹⁶S. Wilbur,¹² F. Wick,²⁵H. H. Williams,⁴⁴J. S. Wilson,³⁸P. Wilson,¹⁶B. L. Winer,³⁸P. Wittich,^16,hS. Wolbers,¹⁶ H. Wolfe,³⁸T. Wright,³³X. Wu,¹⁹Z. Wu,⁵K. Yamamoto,⁴⁰J. Yamaoka,¹⁵T. Yang,¹⁶U. K. Yang,^12,q

Y. C. Yang,²⁶W.-M. Yao,²⁷G. P. Yeh,¹⁶K. Yi,^16,nJ. Yoh,¹⁶K. Yorita,⁵⁶T. Yoshida,^40,kG. B. Yu,¹⁵ I. Yu,²⁶S. S. Yu,¹⁶J. C. Yun,¹⁶A. Zanetti,^53aY. Zeng,¹⁵and S. Zucchelli^6b,6a

(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

6aIstituto 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

10Instituto de Fisica de Cantabria, CSIC-University of Cantabria, 39005 Santander, Spain

11Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA

12Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637, USA

13Comenius University, 842 48 Bratislava, Slovakia; Institute of Experimental Physics, 040 01 Kosice, Slovakia

14Joint Institute for Nuclear Research, RU-141980 Dubna, Russia

15Duke University, Durham, North Carolina 27708, USA

16Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA

17University of Florida, Gainesville, Florida 32611, USA

18Laboratori Nazionali di Frascati, Istituto Nazionale di Fisica Nucleare, I-00044 Frascati, Italy

19University of Geneva, CH-1211 Geneva 4, Switzerland

20Glasgow University, Glasgow G12 8QQ, United Kingdom

21Harvard University, Cambridge, Massachusetts 02138, USA

22Division of High Energy Physics, Department of Physics,

University of Helsinki and Helsinki Institute of Physics, FIN-00014, Helsinki, Finland

23University of Illinois, Urbana, Illinois 61801, USA

24The Johns Hopkins University, Baltimore, Maryland 21218, USA

25Institut fu¨r Experimentelle Kernphysik, Karlsruhe Institute of Technology, D-76131 Karlsruhe, Germany

26Center 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

27Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

28University of Liverpool, Liverpool L69 7ZE, United Kingdom

29University College London, London WC1E 6BT, United Kingdom

30Centro de Investigaciones Energeticas Medioambientales y Tecnologicas, E-28040 Madrid, Spain

31Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

201802-2

32Institute of Particle Physics: McGill University, Montre´al, Que´bec, Canada H3A 2T8; Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6; University of Toronto, Toronto, Ontario, Canada M5S 1A7;

and TRIUMF, Vancouver, British Columbia, Canada V6T 2A3

33University of Michigan, Ann Arbor, Michigan 48109, USA

34Michigan State University, East Lansing, Michigan 48824, USA

35Institution for Theoretical and Experimental Physics, ITEP, Moscow 117259, Russia

36University of New Mexico, Albuquerque, New Mexico 87131, USA

37Northwestern University, Evanston, Illinois 60208, USA

38The Ohio State University, Columbus, Ohio 43210, USA

39Okayama University, Okayama 700-8530, Japan

40Osaka City University, Osaka 588, Japan

41University of Oxford, Oxford OX1 3RH, United Kingdom

42aIstituto Nazionale di Fisica Nucleare, Sezione di Padova-Trento, I-35131 Padova, Italy

42bUniversity of Padova, I-35131 Padova, Italy

43LPNHE, Universite Pierre et Marie Curie/IN2P3-CNRS, UMR7585, Paris, F-75252 France

44University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA

45aIstituto Nazionale di Fisica Nucleare Pisa, I-56127 Pisa, Italy

45bUniversity of Pisa, I-56127 Pisa, Italy

45cUniversity of Siena and I-56127 Pisa, Italy

45dScuola Normale Superiore, I-56127 Pisa, Italy

46University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA

47Purdue University, West Lafayette, Indiana 47907, USA

48University of Rochester, Rochester, New York 14627, USA

49The Rockefeller University, New York, New York 10065, USA

50aIstituto Nazionale di Fisica Nucleare, Sezione di Roma 1, I-00185 Roma, Italy

50bSapienza Universita` di Roma, I-00185 Roma, Italy

51Rutgers University, Piscataway, New Jersey 08855, USA

52Texas A&M University, College Station, Texas 77843, USA

53aIstituto Nazionale di Fisica Nucleare Trieste/Udine, I-34100 Trieste, I-33100 Udine, Italy

53bUniversity of Trieste/Udine, I-33100 Udine, Italy

54University of Tsukuba, Tsukuba, Ibaraki 305, Japan

55Tufts University, Medford, Massachusetts 02155, USA

56Waseda University, Tokyo 169, Japan

57Wayne State University, Detroit, Michigan 48201, USA

58University of Wisconsin, Madison, Wisconsin 53706, USA

59Yale University, New Haven, Connecticut 06520, USA (Received 18 July 2011; published 8 November 2011)

We report the first observation of the baryonic flavor-changing neutral current decay⁰_b!^þ with 24 signal events and a statistical significance of 5.8 Gaussian standard deviations. This measurement uses app collisions data sample corresponding to6:8 fb¹at ffiffiffi

ps

¼1:96 TeVcollected by the CDF II detector at the Tevatron collider. The total and differential branching ratios for ⁰_b!^þ are measured. We find Bð⁰_b!^þÞ ¼ ½1:730:42ðstatÞ ðsystÞ 10⁶. We also report the first measurement of the differential branching ratio ofB⁰s !^þ, using 49 signal events. In addition, we report branching ratios forB^þ!K^þþ,B⁰!K^0þ, andB!Kð892Þ^þdecays.

DOI:10.1103/PhysRevLett.107.201802 PACS numbers: 13.30.Ce, 12.15.Mm, 14.20.Mr

Rare decays of hadrons containing bottom quarks through the process b!s^þ, where b is a bottom quark andsis a strange quark, occur in the standard model (SM) with Oð10⁶Þ branching ratios [1,2]. The b and s quarks carry the same charge but different flavor, so this process is a flavor-changing neutral current (FCNC) decay.

FCNC decays are suppressed at tree level in the SM, and must occur through higher order, and more suppressed, loop amplitudes. Their suppressed nature and clean experi- mental signature, along with reliable theoretical predic- tions for their rates [1,3,4], make them excellent search

channels for new physics. With multibody final states, these decays offer sensitivity to new physics in a number of kinematic distributions in addition to the total branching ratio. In this Letter, we report measurements of the total branching ratios of FCNC decays, as well as their differ- ential branching ratios as a function ofq² M²c², where M is the dimuon invariant mass. Exclusive decays of B!K^ðÞþhave been observed byBABAR[5], Belle [6], and CDF [7]. The CDF experiment also recently reported the observation of B⁰_s !ð1020Þ^þ [7].

No significant departure from the SM has been found thus far.

In addition, the study of the baryonic b!s^þ decays is very important, since the baryonic FCNC decays are sensitive to the helicity structure of effective Hamiltonian, which is lost in the hadronization of the mesonic decays [8]. Although the theoretical calculations of the exclusive baryonicb!s^þ decays have large uncertainties compared to the mesonic decays due to addi- tional degrees of freedom in the baryon bound states, the measurements of the total and the differential branching ratios can help the improvement of the theoretical treat- ments. One can also compare the measurements of the mesonic b!s^þ decays with the baryonic decays, which follow the common quark transition. Measurements of both mesonic and baryonic FCNC decays therefore provide additional tests of the SM and its extensions.

However, no b baryon FCNC decay has been observed and there are few experimental constraints on their decay rates. The⁰_b!^þ decay is considered promising in this respect [8–11] and experimentally accessible since the branching ratio is predicted asð4:01:2Þ 10⁶[10].

The data sample used in the measurements reported in this Letter corresponds to an integrated luminosity of 6:8 fbffiffiffi ¹ frompp collisions at a center-of-mass energy of ps

¼1:96 TeV collected with the CDF II detector be- tween March 2002 and June 2010. The ⁰_b!^þ decay is reconstructed and measurements are made of the total branching ratio and the differential branching ratio as a function of q². Besides the updated branching ratios of B⁰_s !^þ, B^þ!K^þþ, and B⁰ ! Kð892Þ^0þ, we report the branching ratios of B⁰ ! K^0þ and B^þ!Kð892Þ^þþ, which are mea- sured for the first time in hadron collisions. We also report the first measurement of the differential branching ratio as a function ofq²ofB⁰s !^þ. To cancel the dominant systematic uncertainties, decay rates for each rare channel H_b!h^þare measured relative to the corresponding resonant channelH_b !J=chwith J=c ^!þ, used as a normalization, whereH_brepresents thebhadron andh stands for,,K^þ,K⁰_S,K⁰, andK^þ. Charge conjuga- tion is implied throughout the Letter.

The reconstruction of the exclusivebhadron events starts with a dimuon sample selected by the online trigger system [12] of the CDF II detector [13]. The trigger system utilizes information from muon detectors and the central outer tracker [14]. Muon chambers CMU and CMX [15] cover jj<0:6and0:6<jj<1:0, respectively, [16]. The CMP muon chamber coversjj<0:6and is located behind the CMU and an additional steel absorber. The dimuon trigger requires a pair of oppositely charged particles with a mo- mentum transverse to the beam line pT 1:5 GeV=c, which are matched to track segments in the CMU or CMX chambers. At least one of the muon tracks is required to have a CMU track segment. The trigger also requires that

the dimuon pair satisfies either L_xy>100m, where the transverse decay lengthLxyis the flight distance between the dimuon vertex and the event primary vertex [17], orp_T>

3:0 GeV=cand matched segments in both CMU and CMP chambers for one of the muon candidates.

Offline event selection starts with the triggered dimuon pairs. Each offline track is required to satisfy more strin- gent requirements on the number of hits used to reconstruct the track. The dimuon selection requirements used in the trigger are repeated with the higher quality offline tracks.

The decay length and invariant mass of each dimuon pair are calculated after a vertex fit using the muon tracks.

Dimuon pairs are classified according to their invariant mass M. Dimuons from FCNC b hadron decays are required to be inconsistent with decaying from J=c (c^ð2SÞ) mesons by requiringq²values outside the window of 8:68ð12:86Þ< q²<10:09ð14:18Þ GeV²=c² [7]. The J=c candidates are required to have M within 50 MeV=c² of the knownJ=c ^{mass [18].}

The⁰_b!^þcandidates are selected by combin- ing the dimuon pairs with baryons reconstructed from decays !p. The p pairs are required to have invariant mass consistent with the known mass [18], pT 1:0 GeV=c, and a vertex displaced from the dimuon vertex. The transverse momentum of the ⁰_b candidate is required to be greater than4:0 GeV=c. Candidates with an invariant mass calculated from two or three daughter par- ticles compatible with J=c^, c^ð2SÞ, D⁰, D^þ, D^þ_s, or _c masses are rejected to remove backgrounds from these charm-hadron decays [7]. The B⁰_s !^þ candidates are reconstructed from dimuons together with a pair of oppositely-charge kaons consistent with adecay with a selection similar to that of ⁰_b!^þ. The B^0;þ! K^0;þþ candidates, where K^0;þ is one of fK^þ; K_S⁰; K⁰; K^þg, are formed from a dimuon combined with up to three charged tracks. The K_S⁰ meson is recon- structed in its ^þ final state by requiring the dipion mass to be consistent with the knownK_S⁰mass [18]. Details about the reconstruction of the decays of K⁰ !K^þ and !K^þK can be found in Ref. [7]. Cross feed between ⁰_b!^þ and B⁰ !K_S^0þ is sup- pressed by evaluating the momentum imbalance of andK⁰_Sdaughters [19]. We utilize the correlation between invariant mass and the asymmetry ðq^þ_L q_LÞ=ðq^þ_L þ q_LÞ, where q^þðÞ_L is the longitudinal momentum of the positive (negative) decay product relative to the direction of theorK⁰_S. We reject candidates that satisfy0:26<

1:9MðK⁰_SÞ þ jj<0:15 for K_S^0þ and 4:73<

3:6MðÞ þ jj<4:78 for ^þ. We remove 76 (90)% of the cross feed while the signal loss is 11 (7)%

for ^þ (K_S^0þ). A residual cross-feed contami- nation of 0.1% (0.6%) to the^þ(K⁰_S^þ) signal is considered as a systematic uncertainty. To further optimize the event selection, an artificial neural network (NN) classifier is trained using simulated signal events and 201802-4

background events taken from H_b mass sidebands (0:1–0:36 GeV=c² far from the knownH_b mass) in data.

Some kinematical distributions of the simulated signal, e.g., the transverse momentum ofbhadron, and the energy depositions of muon candidates in the electromagnetic and hadron calorimeters, are corrected using scale factors ex- tracted by comparing simulation to data in the normaliza- tion channels. We use 70% of the sideband events for the training, and use the remaining events to check that the NN does not bias or over suppress the mass distribution. The optimized NN threshold is determined to maximize the average expected significance of the branching ratio, using many kinematic observables including transverse momen- tum, invariant mass, vertex fit qualities, and muon identi- fication qualities [7].

The signal yield of the ⁰_b!^þ candidates is obtained by an unbinned maximum likelihood fit to the ⁰_binvariant mass distribution with the signal probability density function (PDF) parametrized by Gaussian distribu- tions using simulated signals and the background PDF modeled by a linear function. We fix the ⁰_b mass width for the rare decay while it is floated for the normalization channel. Different mass width between data and the simu- lated signal is corrected by measured mass width ratio of the normalization channel between data and the simulated signal. The signal region is defined within 40 MeV=c² from the world average ⁰_b mass [7]. The statistical sig- nificance is obtained through a likelihood-ratio test be- tween the signal plus background and background-only hypotheses interpreted assuming it distributed as a ² variable. The invariant mass distribution of the ⁰_b! ^þcandidates is shown in Fig.1. In the signal region, we observe 245 events from ⁰_b!^þ decays while the total number of the signal candidates is 34. The statistical significance of the signal s corresponds to 5.8 Gaussian standard deviations. The signal yields of B⁰s! ^þand other FCNCBmeson decays are obtained by a similar procedure as that of⁰_b !^þ. Each chan- nel uses independent NN weight and PDF. The fit range for B^þandB⁰decays is from 5.18 to5:70 GeV=c²to avoid the region of 5:0–5:18 GeV=c², which is dominated by the feed-down background from multibody decays of bhad- rons. While the contribution from charmlessHbdecays is negligible due to the muon identification, we estimate a 1%

cross talk between B⁰!K^0þ and B⁰s !^þ using simulation, and correct for it. Invariant mass distri- butions of B⁰_s !^þ and other FCNC B meson decays are shown in Fig. 1and signal yields are listed in TableI.

The branching ratios of ⁰_b!^þ, B⁰_s! ^þ, andB!K^ðÞþ are calculated by compar- ing their signal event yield to that of the normalization decay modes ⁰_b!J=c, B⁰s !J=c, and B! J=cK^ðÞ, where J=c ^!þ, after the reconstruction efficiency correction:

2) ) (GeV/c µµΛ M(

5.3 5.4 5.5 5.6 5.7 5.8 5.9 6 )2Candidates / (20 MeV/c 024

6 8 10 12

14161820 (a) Λ⁰b→Λµ⁺µ-

2) ) (GeV/c µµφ M(

5 5.1 5.2 5.3 5.4 5.5 5.6 5.7 )2Candidates / (20 MeV/c 0

5 10 15 20 25 30

35 (b) B⁰s→φµ⁺µ-

2) K) (GeV/c µµ M(

5 5.1 5.2 5.3 5.4 5.5 5.6 5.7 )2Candidates / (20 MeV/c 0

20 40 60 80 100 120

140 (c) B⁺→ K⁺µ⁺µ-

2) ) (GeV/c K*0

µµ M(

5 5.1 5.2 5.3 5.4 5.5 5.6 5.7 )2Candidates / (20 MeV/c

0 20 40 60 80

100 (d) B⁰→ K^*0µ⁺µ-

2) ) (GeV/c KS

µµ M(

5 5.1 5.2 5.3 5.4 5.5 5.6 5.7 )2Candidates / (20 MeV/c 0

5 10 15 20 25

30 (e) B⁰→ KSµ⁺µ-

2) ) (GeV/c K*+

µµ M(

5 5.1 5.2 5.3 5.4 5.5 5.6 5.7 )2Candidates / (20 MeV/c

0 2 4 6 8 10 12 14 16

18 (f) B⁺→ K^*+µ⁺µ-

FIG. 1 (color online). Invariant mass of (a) ⁰_b!^þ, (b)B⁰_s!^þ, (c)B^þ!K^þþ, (d)B⁰!K^0þ, (e)B⁰!K_S^0þ, (f )B^þ!K^þþ, with fit results over- laid. The histograms are the data. Solid, dashed-dotted, and dotted curves show the total fit, the signal PDF, and the back- ground PDF, respectively.

TABLE I. Summary of observed yields, the statistical signifi- cances, and the relative efficiency"_rel.

Mode N_h^þ sðÞ N_J=ch "_rel ⁰_b!^þ 245 5.8 174050 0:330:01 B⁰_s !^þ 497 9.0 456080 0:560:01 B^þ!K^þþ 23419 13.7 72 200300 0:410:01 B⁰!K^0þ 16415 13.7 28 300200 0:450:02 B⁰!K_S^0þ 289 3.5 947090 0:470:01 B^þ!K^þþ 206 3.5 456080 0:380:02

TABLE II. Measured branching ratios of rare modes. First (second) uncertainty is statistical (systematic). The last two values are for the isospin average.

Mode RelativeBð10³Þ AbsoluteBð10⁶Þ ⁰_b !^þ 2:450:590:29 1:730:420:55 B⁰s!^þ 1:130:190:07 1:470:240:46 B^þ!K^þþ 0:460:040:02 0:460:040:02 B⁰!K^0þ 0:770:080:03 1:020:100:06 B⁰!K^0þ 0:370:120:02 0:320:100:02 B^þ!K^þþ 0:670:220:04 0:950:320:08 B!K^þ 0:420:040:02 B!K^þ 1:010:100:05

BðH_b!h^þÞ

BðHb!J=chÞ ¼N_h^þ N_J=ch

BðJ=c ^!þÞ

"_rel ; (1) where N_h^þ is the h^þ yield, N_J=ch is the J=ch yield for the normalization channel, and "_rel

"h^þ="J=chis the relative reconstruction efficiency de- termined from the simulation. The calculated relative and absolute branching ratios are listed in TableII. The abso- lute branching ratios are obtained using world averages of theJ=chdecay rates [18]. The branching ratios ofB⁰ ! K^0þandB^þ !K^þþare measured for the first time in hadron collisions.

The dominant sources of systematic uncertainty are the scale-factor reweighting of the simulated signal (the trigger efficiency near the threshold) which ranges from 0.5% to 4.0% (0.8% to 7.2%), depending on the channel. We esti- mate the former uncertainty from the comparison of the

relative efficiencies with and without reweighting and the latter uncertainty from the different p_T requirements for each trigger. In the ⁰_b!^þ case we consider an additional uncertainty of 6.6% due to the unknown⁰_b! J=cpolarization.

For the absolute branching ratio measurements we as- sign the uncertainties on the world average BðH_b! J=chÞ [18] or the most recent measurement [20].

Contributions from other sources (e.g., background PDF shape or the decay model of the simulated event) are minor (0.3%–3.4%).

The combined branching ratio is calculated by assuming isospin symmetry and using the B^þ andB⁰ total widths [18]. These numbers are consistent with our previous results [7],B-factory measurements [5,6], and theoretical expectations [9,10].

We also measure differential branching ratios with re- spect toq². We divide the signal region into six bins inq². We fit the signal yield in eachq²bin. In each fit, we fix the mean of theH_bmass and the background slope to the value from the global fit, so that only the signal fraction is allowed to vary in the fit. Figure2 shows the differential branching ratios for⁰_b !^þ,B⁰_s !^þ, and B!K^ðÞþ. For illustration, we superimpose the SM expectations, which are based on the formula in Ref. [1], with the form factors in Ref. [21], except for the case of ⁰_b!^þdecays which follows Ref. [10]. The cusp at q² 7 GeV²=c² is due to a change in parameter ap- proximations. TablesIIIandIVsummarize the differential branching ratio measurements. The two bottom rows in each table show the results for the semi-inclusive bins, which are included with ranges covering theoretically well-controlled regions.

In summary, we have updated our previous analysis of the flavor-changing neutral current decays b!s^þ using data corresponding to an integrated luminosity of 6:8 fb¹ and adding new decay channels. We report the first observation of⁰_b !^þ and measure the total and differential branching ratios of this decay with respect toq². We also measure the total and differential branching ratios ofB!K^ðÞþandB⁰_s!^þ, with respect to q². All measurements are consistent and competitive

2)

2/c (GeV q2

0 2 4 6 8 10 12 14 16 18 20 /c2/GeV-7 (102dB/dq

-1 -0.5 0 0.5 1 1.5 2 2.5 3

3.5 Λb→Λµ µ (a)

2)

2/c (GeV q2

0 2 4 6 8 10 12 14 16 18 /c2/GeV-7 (102dB/dq

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

1.8 BS→φµµ (b)

2)

2/c (GeV q2

0 2 4 6 8 101214 16182022 )2/c2/GeV-7 (102dB/dq

0 0.1 0.2 0.3 0.4 0.5

0.6 B⁺→ K⁺µ⁺µ- (c)

2)

2/c (GeV q2

0 2 4 6 8 10 12 14 16 18 )2/c2/GeV-7 (102dB/dq

0 0.2 0.4 0.6 0.8 1

1.2 B⁰→ K^*0µ⁺µ^- (d)

FIG. 2 (color online). Differential branching ratios of (a) ⁰_b!^þ, (b) B⁰_s !^þ, (c) B^þ!K^þþ, and (d)B⁰!K^0þ. The points are the fit result. The solid curves are the SM expectation [1,10,21]. The dashed line in the ⁰_b!^þplot is the SM prediction normalized to our total branching ratio measurement. The hatched regions are the char- monium veto regions.

TABLE III. Differential branching ratios of⁰_b!^þ,B^þ!K^þþ,B⁰!K^0þ, combinedB!K^þ, in units of10⁷. Theq²_max is 20.30ð23:00ÞGeV²=c² for^þ(K^þ). The first (second) uncertainty is statistical (systematic).

q²(GeV²=c²) ⁰_b!^þ B^þ!K^þþ B⁰!K^0þ B!K^þ

½0:00;2:00Þ 0:152:010:05 0:360:110:03 0:3120:3720:024 0:330:100:02

½2:00;4:30Þ 1:841:660:59 0:800:150:05 0:9290:4850:070 0:770:140:05

½4:30;8:68Þ 0:201:640:08 1:180:190:09 0:6630:5100:052 1:050:170:07

½10:09;12:86Þ 2:971:470:95 0:680:120:05 0:0300:2230:005 0:480:100:03

½14:18;16:00Þ 0:960:730:31 0:530:100:03 0:7260:2570:055 0:520:090:03

½16:00; q²_maxÞ 6:971:882:23 0:480:110:03 0:2140:1820:016 0:380:090:02

½0:00;4:30Þ 2:652:520:85 1:130:190:08 1:2680:6220:096 1:070:170:07

½1:00;6:00Þ 1:272:080:41 1:410:200:10 0:9800:6140:076 1:290:180:08

201802-6

with other results, and the differential measurements of B⁰_s !^þand⁰_b!^þare the first such mea- surements. At present there is no evidence of discrepancy from the SM prediction.

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 Foundation; the A. P. Sloan Foundation; the Bundesministerium fu¨r Bildung und Forschung, Germany; the World Class University Program, the National Research Foundation of Korea; 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, and Programa Consolider-Ingenio 2010, Spain; the Slovak R&D Agency; and the Academy of Finland.

aDeceased.

bVisitor from University of Massachusetts Amherst, Amherst, MA 01003, USA.

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

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

eVisitor from University of California Santa Barbara, Santa Barbara, CA 93106, USA.

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

gVisitor from CERN,CH-1211 Geneva, Switzerland.

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

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

jVisitor from University College Dublin, Dublin 4, Ireland.

kVisitor from University of Fukui, Fukui City, Fukui Prefecture, Japan 910-0017.

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

mVisitor from Iowa State University, Ames, IA 50011, USA.

nVisitor from University of Iowa, Iowa City, IA 52242, USA.

oVisitor from Kinki University, Higashi-Osaka City, Japan 577-8502.

pVisitor from, Kansas State University, Manhattan, KS 66506, USA.

qVisitor from University of Manchester, Manchester M13 9PL, United Kingdom.

rVisitor from Queen Mary, University of London, London, E1 4NS, United Kingdom.

sVisitor from Muons, Inc., Batavia, IL 60510, USA.

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

uVisitor from National Research Nuclear University, Moscow, Russia.

vVisitor from University of Notre Dame, Notre Dame, IN 46556, USA.

wVisitor from Universidad de Oviedo, E-33007 Oviedo, Spain.

xVisitor from Texas Tech University, Lubbock, TX 79609, USA.

yVisitor from IFIC(CSIC-Universitat de Valencia), 56071 Valencia, Spain.

zVisitor from Universidad Tecnica Federico Santa Maria, 110v Valparaiso, Chile.

aaVisitor from University of Virginia, Charlottesville, VA 22906, USA.

bbVisitor from Yarmouk University, Irbid 211-63, Jordan.

ccOn leave from J. Stefan Institute, Ljubljana, Sloveni.

[1] A. Aliet al.,Phys. Rev. D61, 074024 (2000).

[2] D. Melikhov, N. Nikitin, and S. Simula,Phys. Rev. D57, 6814 (1998).

[3] Q. Chan and Y.-H. Gao, Nucl. Phys. B845, 179 (2011).

[4] Y.-M. Wang, M. J. Aslam, and C.-D. Lu,Eur. Phys. J. C 59, 847 (2009).

[5] B. Aubertet al.(BABARCollaboration),Phys. Rev. Lett.

102, 091803 (2009).

[6] J. T. Weiet al.(Belle Collaboration),Phys. Rev. Lett.103, 171801 (2009).

TABLE IV. Differential branching ratios ofB⁰_s !^þ,B⁰!K^0þ,B^þ!K^þþ, and combinedB!K^þ, in units of10⁷. Theq²_maxis 18.90ð19:30ÞGeV²=c²for^þ(K^þ). The first (second) uncertainty is statistical (systematic).

q²(GeV²=c²) B⁰_s !^þ B⁰!K^0þ B^þ!K^þþ B!K^þ

½0:00;2:00Þ 2:780:950:89 1:800:360:11 1:300:980:14 1:730:330:10

½2:00;4:30Þ 0:580:550:19 0:840:280:06 0:711:000:15 0:820:260:06

½4:30;8:68Þ 1:340:830:43 1:730:430:15 1:711:580:49 1:720:410:14

½10:09;12:86Þ 2:980:950:95 1:770:360:12 1:970:990:22 1:770:340:11

½14:18;16:00Þ 1:860:660:59 1:340:260:08 0:520:610:09 1:210:240:07

½16:00; q²_maxÞ 2:320:760:74 0:970:260:07 1:570:960:17 0:880:220:05

½0:00;4:30Þ 3:301:091:05 2:600:450:17 2:011:390:27 2:530:430:15

½1:00;6:00Þ 1:140:790:36 1:420:410:12 2:571:610:40 1:480:390:12

[7] T. Aaltonenet al.(CDF Collaboration),Phys. Rev. D79, 011104 (2009); T. Aaltonen et al.(CDF Collaboration), Phys. Rev. Lett.106, 161801 (2011).

[8] Y.-M. Wang, Y. Li, and C.-D. Lu,Eur. Phys. J. C59, 861 (2009).

[9] C.-H. Chen and C. Q. Geng, Phys. Rev. D 64, 074001 (2001).

[10] T. M. Aliev, K. Azizi, and M. Savci, Phys. Rev. D 81, 056006 (2010).

[11] M. J. Aslam, Y.-M. Wang, and C.-D. Lu,Phys. Rev. D78, 114032 (2008).

[12] E. J. Thomson et al., IEEE Trans. Nucl. Sci. 49, 1063 (2002).

[13] D. Acosta et al.(CDF Collaboration), Phys. Rev. D 71, 032001 (2005).

[14] T. Aaltonen et al.(CDF Collaboration),Phys. Rev. Lett.

102, 242002 (2009), and references therein.

[15] G. Ascoliet al.,Nucl. Instrum. Methods Phys. Res., Sect.

A268, 33 (1988); T. Dorigo (CDF Collaboration),Nucl.

Instrum. Methods Phys. Res., Sect. A 461, 560 (2001).

[16] We use a cylindrical coordinate system in whichis the polar angle with respect to the proton beam line and pseudorapidity lnðtan=2Þ.

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

[18] K. Nakamuraet al.(Particle Data Group),J. Phys. G37, 075021 (2010).

[19] J. Podolanski and R. Armenteros, Philos. Mag. 45, 13 (1954).

[20] V. M. Abazovet al.(D0 Collaboration),Phys. Rev. D84, 031102 (2011).

[21] P. Ball and R. Zwicky,Phys. Rev. D71, 014015 (2005); P.

Ball and R. Zwicky,Phys. Rev. D71, 014029 (2005).

201802-8