Measurement of Branching Fractions in Radiative B Decays to $\eta K \gamma$ and Search for B Decays to $\eta' K \gamma$

arXiv:hep-ex/0603054v1 29 Mar 2006

SLAC-PUB-11780

Measurement of Branching Fractions in Radiative B Decays to ηKγ and Search for B

Decays to η

_Kγ

B. Aubert,1 _{R. Barate,}1 _{M. Bona,}1_{D. Boutigny,}1 _{F. Couderc,}1 _{Y. Karyotakis,}1 _{J. P. Lees,}1 _{V. Poireau,}1

V. Tisserand,1 A. Zghiche,1 E. Grauges,2A. Palano,3M. Pappagallo,3J. C. Chen,4N. D. Qi,4 G. Rong,4 P. Wang,4 Y. S. Zhu,4 _{G. Eigen,}5 _{I. Ofte,}5_{B. Stugu,}5 _{G. S. Abrams,}6 _{M. Battaglia,}6_{D. N. Brown,}6 _{J. Button-Shafer,}6

R. N. Cahn,6 _{E. Charles,}6_{C. T. Day,}6 _{M. S. Gill,}6 _{Y. Groysman,}6_{R. G. Jacobsen,}6 _{J. A. Kadyk,}6_{L. T. Kerth,}6

Yu. G. Kolomensky,6_{G. Kukartsev,}6 _{G. Lynch,}6 _{L. M. Mir,}6 _{P. J. Oddone,}6 _{T. J. Orimoto,}6_{M. Pripstein,}6

N. A. Roe,6 _{M. T. Ronan,}6_{W. A. Wenzel,}6_{M. Barrett,}7_{K. E. Ford,}7_{T. J. Harrison,}7_{A. J. Hart,}7 _{C. M. Hawkes,}7

S. E. Morgan,7 _{A. T. Watson,}7 _{K. Goetzen,}8 _{T. Held,}8 _{H. Koch,}8 _{B. Lewandowski,}8 _{M. Pelizaeus,}8 _{K. Peters,}8

T. Schroeder,8_{M. Steinke,}8_{J. T. Boyd,}9 _{J. P. Burke,}9_{W. N. Cottingham,}9_{D. Walker,}9_{T. Cuhadar-Donszelmann,}10

B. G. Fulsom,10 _{C. Hearty,}10 _{N. S. Knecht,}10 _{T. S. Mattison,}10 _{J. A. McKenna,}10 _{A. Khan,}11 _{P. Kyberd,}11

M. Saleem,11 _{L. Teodorescu,}11_{V. E. Blinov,}12 _{A. D. Bukin,}12 _{V. P. Druzhinin,}12 _{V. B. Golubev,}12 _{A. P. Onuchin,}12

S. I. Serednyakov,12 _{Yu. I. Skovpen,}12 _{E. P. Solodov,}12 _{K. Yu Todyshev,}12 _{D. S. Best,}13 _{M. Bondioli,}13

M. Bruinsma,13_{M. Chao,}13_{S. Curry,}13_{I. Eschrich,}13 _{D. Kirkby,}13_{A. J. Lankford,}13 _{P. Lund,}13 _{M. Mandelkern,}13

R. K. Mommsen,13 _{W. Roethel,}13 _{D. P. Stoker,}13 _{S. Abachi,}14 _{C. Buchanan,}14_{S. D. Foulkes,}15 _{J. W. Gary,}15

O. Long,15 _{B. C. Shen,}15_{K. Wang,}15 _{L. Zhang,}15 _{H. K. Hadavand,}16 _{E. J. Hill,}16 _{H. P. Paar,}16_{S. Rahatlou,}16

V. Sharma,16_{J. W. Berryhill,}17 _{C. Campagnari,}17 _{A. Cunha,}17 _{B. Dahmes,}17 _{T. M. Hong,}17_{D. Kovalskyi,}17

J. D. Richman,17T. W. Beck,18 A. M. Eisner,18C. J. Flacco,18 C. A. Heusch,18 J. Kroseberg,18 W. S. Lockman,18 G. Nesom,18 _{T. Schalk,}18 _{B. A. Schumm,}18 _{A. Seiden,}18 _{P. Spradlin,}18 _{D. C. Williams,}18 _{M. G. Wilson,}18

J. Albert,19 _{E. Chen,}19 _{A. Dvoretskii,}19 _{D. G. Hitlin,}19 _{I. Narsky,}19_{T. Piatenko,}19 _{F. C. Porter,}19 _{A. Ryd,}19

A. Samuel,19 _{R. Andreassen,}20 _{G. Mancinelli,}20 _{B. T. Meadows,}20_{M. D. Sokoloff,}20 _{F. Blanc,}21 _{P. C. Bloom,}21

S. Chen,21 _{W. T. Ford,}21 _{J. F. Hirschauer,}21_{A. Kreisel,}21_{U. Nauenberg,}21_{A. Olivas,}21_{W. O. Ruddick,}21

J. G. Smith,21_{K. A. Ulmer,}21 _{S. R. Wagner,}21_{J. Zhang,}21 _{A. Chen,}22 _{E. A. Eckhart,}22_{A. Soffer,}22_{W. H. Toki,}22

R. J. Wilson,22 _{F. Winklmeier,}22_{Q. Zeng,}22 _{D. D. Altenburg,}23_{E. Feltresi,}23 _{A. Hauke,}23_{H. Jasper,}23 _{B. Spaan,}23

T. Brandt,24 _{V. Klose,}24 _{H. M. Lacker,}24 _{W. F. Mader,}24 _{R. Nogowski,}24 _{A. Petzold,}24 _{J. Schubert,}24

K. R. Schubert,24 _{R. Schwierz,}24_{J. E. Sundermann,}24 _{A. Volk,}24_{D. Bernard,}25 _{G. R. Bonneaud,}25 _{P. Grenier,}25, ∗

E. Latour,25_{Ch. Thiebaux,}25 _{M. Verderi,}25 _{D. J. Bard,}26 _{P. J. Clark,}26 _{W. Gradl,}26 _{F. Muheim,}26 _{S. Playfer,}26

A. I. Robertson,26 _{Y. Xie,}26 _{M. Andreotti,}27 _{D. Bettoni,}27_{C. Bozzi,}27 _{R. Calabrese,}27 _{G. Cibinetto,}27 _{E. Luppi,}27

M. Negrini,27 _{A. Petrella,}27 _{L. Piemontese,}27 _{E. Prencipe,}27 _{F. Anulli,}28 _{R. Baldini-Ferroli,}28 _{A. Calcaterra,}28

R. de Sangro,28_{G. Finocchiaro,}28 _{S. Pacetti,}28 _{P. Patteri,}28_{I. M. Peruzzi,}28, † _{M. Piccolo,}28 _{M. Rama,}28

A. Zallo,28_{A. Buzzo,}29_{R. Capra,}29_{R. Contri,}29_{M. Lo Vetere,}29 _{M. M. Macri,}29_{M. R. Monge,}29 _{S. Passaggio,}29

C. Patrignani,29 _{E. Robutti,}29 _{A. Santroni,}29_{S. Tosi,}29 _{G. Brandenburg,}30 _{K. S. Chaisanguanthum,}30 _{M. Morii,}30

J. Wu,30 _{R. S. Dubitzky,}31 _{J. Marks,}31 _{S. Schenk,}31_{U. Uwer,}31 _{W. Bhimji,}32_{D. A. Bowerman,}32_{P. D. Dauncey,}32

U. Egede,32 _{R. L. Flack,}32_{J. R. Gaillard,}32 _{J .A. Nash,}32 _{M. B. Nikolich,}32_{W. Panduro Vazquez,}32 _{X. Chai,}33

M. J. Charles,33_{U. Mallik,}33 _{N. T. Meyer,}33 _{V. Ziegler,}33_{J. Cochran,}34 _{H. B. Crawley,}34_{L. Dong,}34_{V. Eyges,}34

W. T. Meyer,34_{S. Prell,}34 _{E. I. Rosenberg,}34 _{A. E. Rubin,}34 _{A. V. Gritsan,}35 _{M. Fritsch,}36 _{G. Schott,}36

N. Arnaud,37 _{M. Davier,}37 _{G. Grosdidier,}37_{A. H¨ocker,}37 _{F. Le Diberder,}37 _{V. Lepeltier,}37 _{A. M. Lutz,}37

A. Oyanguren,37_{S. Pruvot,}37_{S. Rodier,}37 _{P. Roudeau,}37 _{M. H. Schune,}37 _{A. Stocchi,}37 _{W. F. Wang,}37

G. Wormser,37 _{C. H. Cheng,}38 _{D. J. Lange,}38 _{D. M. Wright,}38 _{C. A. Chavez,}39 _{I. J. Forster,}39 _{J. R. Fry,}39

E. Gabathuler,39 _{R. Gamet,}39 _{K. A. George,}39 _{D. E. Hutchcroft,}39 _{D. J. Payne,}39 _{K. C. Schofield,}39

C. Touramanis,39 _{A. J. Bevan,}40 _{F. Di Lodovico,}40 _{W. Menges,}40 _{R. Sacco,}40 _{C. L. Brown,}41_{G. Cowan,}41

H. U. Flaecher,41 _{D. A. Hopkins,}41_{P. S. Jackson,}41_{T. R. McMahon,}41_{S. Ricciardi,}41_{F. Salvatore,}41_{D. N. Brown,}42

C. L. Davis,42 _{J. Allison,}43 _{N. R. Barlow,}43 _{R. J. Barlow,}43 _{Y. M. Chia,}43 _{C. L. Edgar,}43_{M. P. Kelly,}43

G. D. Lafferty,43 _{M. T. Naisbit,}43 _{J. C. Williams,}43 _{J. I. Yi,}43 _{C. Chen,}44 _{W. D. Hulsbergen,}44 _{A. Jawahery,}44

C. K. Lae,44_{D. A. Roberts,}44_{G. Simi,}44_{G. Blaylock,}45_{C. Dallapiccola,}45_{S. S. Hertzbach,}45_{X. Li,}45 _{T. B. Moore,}45

S. Saremi,45 _{H. Staengle,}45_{S. Y. Willocq,}45 _{R. Cowan,}46_{K. Koeneke,}46 _{G. Sciolla,}46_{S. J. Sekula,}46_{M. Spitznagel,}46

V. Lombardo,48_{F. Palombo,}48_{J. M. Bauer,}49 _{L. Cremaldi,}49 _{V. Eschenburg,}49_{R. Godang,}49 _{R. Kroeger,}49

J. Reidy,49_{D. A. Sanders,}49_{D. J. Summers,}49 _{H. W. Zhao,}49 _{S. Brunet,}50_{D. Cˆot´e,}50 _{M. Simard,}50_{P. Taras,}50

F. B. Viaud,50_{H. Nicholson,}51 _{N. Cavallo,}52, ‡_{G. De Nardo,}52 _{D. del Re,}52 _{F. Fabozzi,}52, ‡ _{C. Gatto,}52 _{L. Lista,}52

D. Monorchio,52_{D. Piccolo,}52_{C. Sciacca,}52 _{M. Baak,}53_{H. Bulten,}53 _{G. Raven,}53 _{H. L. Snoek,}53 _{C. P. Jessop,}54

J. M. LoSecco,54 _{T. Allmendinger,}55_{G. Benelli,}55 _{K. K. Gan,}55 _{K. Honscheid,}55_{D. Hufnagel,}55 _{P. D. Jackson,}55

H. Kagan,55_{R. Kass,}55_{T. Pulliam,}55 _{A. M. Rahimi,}55_{R. Ter-Antonyan,}55_{Q. K. Wong,}55_{N. L. Blount,}56 _{J. Brau,}56

R. Frey,56 _{O. Igonkina,}56 _{M. Lu,}56 _{R. Rahmat,}56 _{N. B. Sinev,}56 _{D. Strom,}56 _{J. Strube,}56 _{E. Torrence,}56

F. Galeazzi,57 _{A. Gaz,}57_{M. Margoni,}57 _{M. Morandin,}57 _{A. Pompili,}57_{M. Posocco,}57 _{M. Rotondo,}57_{F. Simonetto,}57

R. Stroili,57 _{C. Voci,}57 _{M. Benayoun,}58 _{J. Chauveau,}58 _{P. David,}58 _{L. Del Buono,}58 _{Ch. de la Vaissi`ere,}58

O. Hamon,58 _{B. L. Hartfiel,}58 _{M. J. J. John,}58_{Ph. Leruste,}58 _{J. Malcl`es,}58_{J. Ocariz,}58_{L. Roos,}58_{G. Therin,}58

P. K. Behera,59 _{L. Gladney,}59_{J. Panetta,}59_{M. Biasini,}60_{R. Covarelli,}60_{M. Pioppi,}60_{C. Angelini,}61 _{G. Batignani,}61

S. Bettarini,61 F. Bucci,61 G. Calderini,61M. Carpinelli,61R. Cenci,61 F. Forti,61 M. A. Giorgi,61A. Lusiani,61 G. Marchiori,61 _{M. A. Mazur,}61 _{M. Morganti,}61_{N. Neri,}61 _{E. Paoloni,}61_{G. Rizzo,}61_{J. Walsh,}61 _{M. Haire,}62

D. Judd,62 _{D. E. Wagoner,}62 _{J. Biesiada,}63 _{N. Danielson,}63 _{P. Elmer,}63 _{Y. P. Lau,}63 _{C. Lu,}63 _{J. Olsen,}63

A. J. S. Smith,63 _{A. V. Telnov,}63 _{F. Bellini,}64 _{G. Cavoto,}64_{A. D’Orazio,}64 _{E. Di Marco,}64 _{R. Faccini,}64

F. Ferrarotto,64 _{F. Ferroni,}64_{M. Gaspero,}64 _{L. Li Gioi,}64 _{M. A. Mazzoni,}64_{S. Morganti,}64_{G. Piredda,}64_{F. Polci,}64

F. Safai Tehrani,64_{C. Voena,}64 _{M. Ebert,}65 _{H. Schr¨oder,}65_{R. Waldi,}65 _{T. Adye,}66_{N. De Groot,}66 _{B. Franek,}66

E. O. Olaiya,66_{F. F. Wilson,}66 _{S. Emery,}67_{A. Gaidot,}67 _{S. F. Ganzhur,}67 _{G. Hamel de Monchenault,}67

W. Kozanecki,67 _{M. Legendre,}67 _{B. Mayer,}67_{G. Vasseur,}67 _{Ch. Y`eche,}67_{M. Zito,}67 _{W. Park,}68_{M. V. Purohit,}68

A. W. Weidemann,68 _{J. R. Wilson,}68 _{M. T. Allen,}69 _{D. Aston,}69 _{R. Bartoldus,}69 _{P. Bechtle,}69_{N. Berger,}69

A. M. Boyarski,69 _{R. Claus,}69_{J. P. Coleman,}69_{M. R. Convery,}69_{M. Cristinziani,}69 _{J. C. Dingfelder,}69 _{D. Dong,}69

J. Dorfan,69_{G. P. Dubois-Felsmann,}69_{D. Dujmic,}69_{W. Dunwoodie,}69_{R. C. Field,}69_{T. Glanzman,}69_{S. J. Gowdy,}69

M. T. Graham,69 _{V. Halyo,}69 _{C. Hast,}69 _{T. Hryn’ova,}69 _{W. R. Innes,}69 _{M. H. Kelsey,}69 _{P. Kim,}69 _{M. L. Kocian,}69

D. W. G. S. Leith,69 _{S. Li,}69 _{J. Libby,}69 _{S. Luitz,}69_{V. Luth,}69_{H. L. Lynch,}69_{D. B. MacFarlane,}69 _{H. Marsiske,}69

R. Messner,69 _{D. R. Muller,}69 _{C. P. O’Grady,}69 _{V. E. Ozcan,}69 _{A. Perazzo,}69 _{M. Perl,}69_{B. N. Ratcliff,}69

A. Roodman,69 _{A. A. Salnikov,}69 _{R. H. Schindler,}69 _{J. Schwiening,}69 _{A. Snyder,}69 _{J. Stelzer,}69 _{D. Su,}69

M. K. Sullivan,69 _{K. Suzuki,}69 _{S. K. Swain,}69 _{J. M. Thompson,}69_{J. Va’vra,}69_{N. van Bakel,}69_{M. Weaver,}69

A. J. R. Weinstein,69 _{W. J. Wisniewski,}69_{M. Wittgen,}69 _{D. H. Wright,}69 _{A. K. Yarritu,}69_{K. Yi,}69_{C. C. Young,}69

P. R. Burchat,70 _{A. J. Edwards,}70 _{S. A. Majewski,}70_{B. A. Petersen,}70_{C. Roat,}70_{L. Wilden,}70 _{S. Ahmed,}71

M. S. Alam,71 _{R. Bula,}71 _{J. A. Ernst,}71 _{V. Jain,}71_{B. Pan,}71 _{M. A. Saeed,}71 _{F. R. Wappler,}71 _{S. B. Zain,}71

W. Bugg,72_{M. Krishnamurthy,}72_{S. M. Spanier,}72 _{R. Eckmann,}73 _{J. L. Ritchie,}73 _{A. Satpathy,}73_{C. J. Schilling,}73

R. F. Schwitters,73 _{J. M. Izen,}74 _{I. Kitayama,}74 _{X. C. Lou,}74 _{S. Ye,}74 _{F. Bianchi,}75 _{F. Gallo,}75_{D. Gamba,}75

M. Bomben,76 _{L. Bosisio,}76 _{C. Cartaro,}76_{F. Cossutti,}76 _{G. Della Ricca,}76 _{S. Dittongo,}76 _{S. Grancagnolo,}76

L. Lanceri,76 _{L. Vitale,}76 _{V. Azzolini,}77 _{F. Martinez-Vidal,}77 _{Sw. Banerjee,}78 _{B. Bhuyan,}78 _{C. M. Brown,}78

D. Fortin,78 _{K. Hamano,}78 _{R. Kowalewski,}78 _{I. M. Nugent,}78 _{J. M. Roney,}78 _{R. J. Sobie,}78 _{J. J. Back,}79

P. F. Harrison,79_{T. E. Latham,}79 _{G. B. Mohanty,}79 _{H. R. Band,}80 _{X. Chen,}80 _{B. Cheng,}80 _{S. Dasu,}80 _{M. Datta,}80

A. M. Eichenbaum,80 _{K. T. Flood,}80 _{J. J. Hollar,}80_{J. R. Johnson,}80_{P. E. Kutter,}80 _{H. Li,}80_{R. Liu,}80 _{B. Mellado,}80

A. Mihalyi,80_{A. K. Mohapatra,}80_{Y. Pan,}80_{M. Pierini,}80_{R. Prepost,}80 _{P. Tan,}80_{S. L. Wu,}80_{Z. Yu,}80_{and H. Neal}81

(The BA_BAR Collaboration)

1_{Laboratoire de Physique des Particules, F-74941 Annecy-le-Vieux, France}

2_{Universitat de Barcelona Fac. Fisica. Dept. ECM Avda Diagonal 647, 6a planta E-08028 Barcelona, Spain}

3_{Universit`a di Bari, Dipartimento di Fisica and INFN, I-70126 Bari, Italy}

4_{Institute of High Energy Physics, Beijing 100039, China}

5_{University of Bergen, Institute of Physics, N-5007 Bergen, Norway}

6_{Lawrence Berkeley National Laboratory and University of California, Berkeley, California 94720, USA}

7_{University of Birmingham, Birmingham, B15 2TT, United Kingdom}

8_{Ruhr Universit¨at Bochum, Institut f¨ur Experimentalphysik 1, D-44780 Bochum, Germany}

9_{University of Bristol, Bristol BS8 1TL, United Kingdom}

10_{University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1}

11_{Brunel University, Uxbridge, Middlesex UB8 3PH, United Kingdom}

12_{Budker Institute of Nuclear Physics, Novosibirsk 630090, Russia}

13_{University of California at Irvine, Irvine, California 92697, USA}

14_{University of California at Los Angeles, Los Angeles, California 90024, USA}

16_{University of California at San Diego, La Jolla, California 92093, USA}

17_{University of California at Santa Barbara, Santa Barbara, California 93106, USA}

18_{University of California at Santa Cruz, Institute for Particle Physics, Santa Cruz, California 95064, USA}

19_{California Institute of Technology, Pasadena, California 91125, USA}

20_{University of Cincinnati, Cincinnati, Ohio 45221, USA}

21_{University of Colorado, Boulder, Colorado 80309, USA}

22_{Colorado State University, Fort Collins, Colorado 80523, USA}

23_{Universit¨at Dortmund, Institut f¨ur Physik, D-44221 Dortmund, Germany}

24_{Technische Universit¨at Dresden, Institut f¨ur Kern- und Teilchenphysik, D-01062 Dresden, Germany}

25_{Ecole Polytechnique, LLR, F-91128 Palaiseau, France}

26_{University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom}

27_{Universit`a di Ferrara, Dipartimento di Fisica and INFN, I-44100 Ferrara, Italy}

28_{Laboratori Nazionali di Frascati dell’INFN, I-00044 Frascati, Italy}

29_{Universit`a di Genova, Dipartimento di Fisica and INFN, I-16146 Genova, Italy}

30_{Harvard University, Cambridge, Massachusetts 02138, USA}

31_{Universit¨at Heidelberg, Physikalisches Institut, Philosophenweg 12, D-69120 Heidelberg, Germany}

32_{Imperial College London, London, SW7 2AZ, United Kingdom}

33_{University of Iowa, Iowa City, Iowa 52242, USA}

34_{Iowa State University, Ames, Iowa 50011-3160, USA}

35_{Johns Hopkins Univ. Dept of Physics & Astronomy 3400 N. Charles Street Baltimore, Maryland 21218}

36_{Universit¨at Karlsruhe, Institut f¨ur Experimentelle Kernphysik, D-76021 Karlsruhe, Germany}

37_{Laboratoire de l’Acc´el´erateur Lin´eaire, IN2P3-CNRS et Universit´e Paris-Sud 11,}

Centre Scientifique d’Orsay, B.P. 34, F-91898 ORSAY Cedex, France

38_{Lawrence Livermore National Laboratory, Livermore, California 94550, USA}

39_{University of Liverpool, Liverpool L69 7ZE, United Kingdom}

40_{Queen Mary, University of London, E1 4NS, United Kingdom}

41_{University of London, Royal Holloway and Bedford New College, Egham, Surrey TW20 0EX, United Kingdom}

42_{University of Louisville, Louisville, Kentucky 40292, USA}

43_{University of Manchester, Manchester M13 9PL, United Kingdom}

44_{University of Maryland, College Park, Maryland 20742, USA}

45_{University of Massachusetts, Amherst, Massachusetts 01003, USA}

46_{Massachusetts Institute of Technology, Laboratory for Nuclear Science, Cambridge, Massachusetts 02139, USA}

47_{McGill University, Montr´eal, Qu´ebec, Canada H3A 2T8}

48_{Universit`a di Milano, Dipartimento di Fisica and INFN, I-20133 Milano, Italy}

49_{University of Mississippi, University, Mississippi 38677, USA}

50_{Universit´e de Montr´eal, Physique des Particules, Montr´eal, Qu´ebec, Canada H3C 3J7}

51_{Mount Holyoke College, South Hadley, Massachusetts 01075, USA}

52_{Universit`a di Napoli Federico II, Dipartimento di Scienze Fisiche and INFN, I-80126, Napoli, Italy}

53_{NIKHEF, National Institute for Nuclear Physics and High Energy Physics, NL-1009 DB Amsterdam, The Netherlands}

54_{University of Notre Dame, Notre Dame, Indiana 46556, USA}

55_{Ohio State University, Columbus, Ohio 43210, USA}

56_{University of Oregon, Eugene, Oregon 97403, USA}

57_{Universit`a di Padova, Dipartimento di Fisica and INFN, I-35131 Padova, Italy}

58_{Universit´es Paris VI et VII, Laboratoire de Physique Nucl´eaire et de Hautes Energies, F-75252 Paris, France}

59_{University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA}

60_{Universit`a di Perugia, Dipartimento di Fisica and INFN, I-06100 Perugia, Italy}

61_{Universit`a di Pisa, Dipartimento di Fisica, Scuola Normale Superiore and INFN, I-56127 Pisa, Italy}

62_{Prairie View A&M University, Prairie View, Texas 77446, USA}

63_{Princeton University, Princeton, New Jersey 08544, USA}

64_{Universit`a di Roma La Sapienza, Dipartimento di Fisica and INFN, I-00185 Roma, Italy}

65_{Universit¨at Rostock, D-18051 Rostock, Germany}

66_{Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, United Kingdom}

67_{DSM/Dapnia, CEA/Saclay, F-91191 Gif-sur-Yvette, France}

68_{University of South Carolina, Columbia, South Carolina 29208, USA}

69_{Stanford Linear Accelerator Center, Stanford, California 94309, USA}

70_{Stanford University, Stanford, California 94305-4060, USA}

71_{State University of New York, Albany, New York 12222, USA}

72_{University of Tennessee, Knoxville, Tennessee 37996, USA}

73_{University of Texas at Austin, Austin, Texas 78712, USA}

74_{University of Texas at Dallas, Richardson, Texas 75083, USA}

75_{Universit`a di Torino, Dipartimento di Fisica Sperimentale and INFN, I-10125 Torino, Italy}

76_{Universit`a di Trieste, Dipartimento di Fisica and INFN, I-34127 Trieste, Italy}

77_{IFIC, Universitat de Valencia-CSIC, E-46071 Valencia, Spain}

79_{Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom}

80_{University of Wisconsin, Madison, Wisconsin 53706, USA}

81_{Yale University, New Haven, Connecticut 06511, USA}

(Dated: August 29, 2018)

We present measurements of the B → ηKγ branching fractions and upper limits for the B → η′

Kγ

branching fractions. For B+_{→ ηK}+

γ we also measure the time-integrated charge asymmetry.

The data sample, collected with the BA_BAR_{detector at the Stanford Linear Accelerator Center,}

represents 232 × 106 _{produced BB pairs. The results for branching fractions and upper limits at}

90% C.L. in units of 10−6_{are: B(B}0_{→ ηK}0_{γ) = 11.3}+2.8

−2.6±0.6, B(B

+_{→ ηK}+_{γ) = 10.0 ± 1.3 ± 0.5,}

B_(B0_{→ η}′

K0γ) < 6.6, B(B+_{→ η}′

K+γ) < 4.2. The charge asymmetry in the decay B+_{→ ηK}+

γ

is Ach= −0.09 ± 0.12 ± 0.01. The first errors are statistical and the second systematic.

PACS numbers: 13.25.Hw, 12.15.Hh, 11.30.Er

Radiative B meson decays have long been recognized as a sensitive probe to test the Standard Model (SM) and to look for new physics (NP) [1] . In the SM, flavor-changing neutral current processes such as b → sγ pro-ceed via radiative loop (penguin) diagrams. The loop dia-grams may also contain new heavy particles, and there-fore are sensitive to NP. Measurements of the branch-ing fractions of a few of the exclusive decay modes ex-ist: K∗_{(892)γ [2, 3], K}

1(1270)γ [4], K2∗(1430)γ [2, 5],

Kππγ [5], φKγ [6] and K+_{ηγ [7]. The measured}

branch-ing fraction of inclusive b → sγ and exclusive radiative B decays are in good agreement with SM predictions [8, 9]. Direct [10] and mixing-induced [11] CP asymmetries in exclusive radiative B decays are expected to be very small in the SM. Measurement of direct CP asymmetries in exclusive radiative decays can provide a clear sign of NP [12].

We present analyses of the exclusive decay modes B+_{→ ηK}+_{γ and B}0_{→ ηK}0_{γ [13] , which have}

pre-viously been measured by the Belle Collaboration [7], and B+_{→ η}′_K+_{γ and B}0_{→ η}′_K0_{γ which are studied}

for the first time. The results presented here are based on data collected with the BA_BAR detector [14] at the

PEP-II asymmetric-energy e+_e− _{collider [15] located at}

the Stanford Linear Accelerator Center. The analyses use an integrated luminosity of 211 fb−1_{, corresponding}

to 232 million BB pairs, recorded at the Υ(4S) resonance (at a center-of-mass energy of√s = 10.58 GeV).

Charged particles from e+_e−_{interactions are detected,}

and their momenta measured, by a combination of a ver-tex tracker (SVT) consisting of five layers of double-sided silicon microstrip detectors, and a 40-layer central drift chamber (DCH), both operating in the 1.5 T magnetic field of a superconducting solenoid. We identify photons and electrons using a CsI(Tl) electromagnetic calorime-ter (EMC). Further charged-particle identification is pro-vided by the average energy loss (dE/dx) in the track-ing devices and by an internally reflecttrack-ing rtrack-ing-imagtrack-ing Cherenkov detector (DIRC) covering the central region. A K/π separation of better than four standard deviations is achieved for momenta below 3 GeV/c, decreasing to 2.5σ at the highest momenta in the B decay final states.

We reconstruct the primary photon, originating from the B decay candidate, using an EMC shower not associ-ated with a track. We require that the photon candidate fall within the fiducial region of the EMC, has the ex-pected lateral shower shape, and is well-separated from other tracks and showers in the EMC. The primary pho-ton energy, calculated in the Υ(4S) frame, is required to be in the range 1.6 – 2.7 GeV. We veto photons from π0_{(η) decays by requiring that the invariant mass of the}

primary photon candidates combined with any other pho-ton candidate of laboratory energy greater than 50 (250) MeV not be within the range 115-155 (507-587) MeV/c2. Charged K candidates are selected from tracks, by us-ing particle identification from the DIRC and the dE/dx measured in the SVT and DCH.

The B decay daughter candidates are reconstructed through their decays π0 _{→ γγ, η → γγ (η}

γγ), η →

π+_π−_π0 _(η

3π), η′ → ηγγπ+π− (η′ηππ), and η′ → ρ0γ

(η′

ργ), where ρ0→ π+π−. Here we require the laboratory

energy of the photons to be greater than 50 MeV (200 MeV for η′

ργ). We impose the following requirements

on the invariant mass in MeV/c2 _{of these particles’ final}

states: 120 < m(γγ) < 150 for π0_{, 490 < m(γγ) < 600}

for ηγγ, 520 < m(π+π−π0) < 570 for η3π, 930 <

m(π+_π−_{η) < 990 for η}′

ηππ, 910 < m(π+π−γ) < 1000

for η′

ργ, and 510 < m(π+π−) < 1000 for ρ0. For the

η′ _{and η these requirements are sufficiently loose as to}

include sidebands, since these observables are used in the maximum-likelihood (ML) fit described below. Sec-ondary pions in η′ _{and η candidates are rejected if their}

DIRC and dE/dx signatures satisfy tight requirements for being consistent with protons, kaons, or electrons.

Neutral K candidates are formed from pairs of oppositely-charged tracks with a vertex χ2 _probability

larger than 0.001, 486 < m(π+_π−_{) < 510 MeV/c}2 _{and a}

reconstructed decay length greater than three times its uncertainty. We require the momentum of the η or η′

in the Υ(4S) frame to be greater than 0.9 GeV/c (0.6 GeV/c in modes with η′

ηππ). The invariant mass of ηK

and η′_{K systems is required to be less than 3.25 GeV/c}2_.

In η′_{Kγ final states, we suppress background from the}

reconstructed η′_{γ invariant mass. Defining the helicity}

frame for a meson as its rest frame with polar axis along the direction of the boost from the parent rest frame, and the decay angle θdec as the polar angle of a daughter

mo-mentum in this helicity frame, we require for the η′

ργ

de-cays | cos θρdec| < 0.9, and for ηγγ decays | cos θ η

dec| < 0.9,

to suppress combinatorial background.

A B meson candidate is reconstructed by combin-ing an η or η′ _{candidate, a charged or neutral kaon}

and a primary photon candidate. It is characterized kinematically by the energy-substituted mass mES ≡

p(s/2 + p0· pB)2/E02− p2Band energy difference ∆E ≡

E∗

B − 12

√

s, where the subscripts 0 and B refer to the initial Υ(4S) and to the B candidate in the lab-frame, respectively, and the asterisk denotes the Υ(4S) frame.

Background arises primarily from random track com-binations in e+_e− _{→ q¯q events. We reduce this}

back-ground by using the angle θT between the thrust axis

of the B candidate in the Υ(4S) frame and the thrust axis of the rest of the event. The distribution of | cos θT|

is sharply peaked near 1 for combinations drawn from jet-like q ¯q events, and is nearly uniform for BB events. We require | cos θT| < 0.9. Furthermore events should

contain at least the number of charged tracks in the can-didate decay mode plus one. For ηγγK+γ we require

at least 3 charged tracks in the event. If an event has multiple B candidates, we select the candidate with the highest B vertex χ2 _probability.

We obtain signal event yields from unbinned extended maximum-likelihood fits. The principal input observ-ables are ∆E, mESand a Fisher discriminant F. Where

relevant, the invariant masses mres of the intermediate

resonances and | cos θρdec| are also used. The Fisher

dis-criminant F combines four variables: the angles with respect to the beam axis of the B momentum and the B decay product’s thrust axis (in the Υ(4S) frame), and the zeroth and second angular moments L0,2 of the

en-ergy flow about the B0 _{thrust axis. The moments are}

defined by Lj = P_ipi× |cos θi|j, where θi is the angle

with respect to the B thrust axis of track or neutral clus-ter i, pi is its momentum, and the sum excludes the B

candidate daughters.

We estimate BB backgrounds using simulated samples of B decays [16]. Signal and inclusive b → sγ events are simulated according to the Kagan-Neubert model [17]. The branching fractions in the simulation are based on measured values and theoretical predictions.

For each event i and hypothesis j (signal, continuum or BB background), the likelihood function is

L = e−(P nj) N Y i=1   3 X j=1 njPj(xi)  , (1)

where N is the number of input events, nj is the

num-ber of events for hypothesis j and Pj(xi) is the

corre-sponding probability density function (PDF), evaluated

with the observables xi of the ith event. Since

corre-lations among the observables are small, we take each P as the product of the PDFs for the separate vari-ables. We determine the PDF parameters from Monte Carlo simulation for the signal and BB background, while using sideband data (5.25 < mES < 5.27 GeV/c2;

0.1 < |∆E| < 0.2 GeV) to model the PDFs of contin-uum background. We parameterize each of the func-tions Psig(mES), Psig(∆E), Pj(F), and the

compo-nents of Pj(mres) that peak in mES with either a

Gaus-sian, the sum of two Gaussian distributions, or an asym-metric Gaussian function, as required, to describe the distribution. Distributions of ∆E for BB and contin-uum background and | cos θρdec| are represented by linear

or quadratic functions. The BB and continuum back-ground in mES is described by the ARGUS function

x√1 − x2_{exp−ξ(1 − x}2_{), with x ≡ 2m}

ES/√s and a

parameter ξ [18]. We allow continuum background PDF parameters to vary in the fit.

Large control samples of B decays to charmed final states of similar topology are used to verify the simu-lated resolutions in ∆E and mES. Where the control data

samples reveal differences from the Monte Carlo (MC) in mass or energy resolution, we shift or scale the resolu-tion used in the likelihood fits. Any bias in the fit is determined from a large set of simulated experiments in which the q ¯q background is generated from the PDFs, and into which we have embedded the expected number of BB background and signal events chosen randomly from fully simulated Monte Carlo samples.

In Table I we show the signal yield, the efficiency, and the product of daughter branching fractions for each de-cay mode. The efficiency is calculated as the ratio of the number of signal MC events entering into the ML fit to the total generated. We compute the branching fractions from the fitted signal event yields, reconstruction effi-ciencies, daughter branching fractions, and the number of produced B mesons, assuming equal production rates of charged and neutral B pairs. We correct the yield for any bias estimated by the simulations. We combine results from different channels by combining their like-lihood functions, taking into account the correlated and uncorrelated systematic errors. We report the statistical significance and branching fraction for the individual de-cay channel; for combined measurements having a signifi-cance smaller than 5σ, we also report the 90% confidence level (C.L.) upper limit.

The statistical error on the signal yield is taken as the change in the central value when the quantity −2 ln L increases by one unit from its minimum value. The sig-nificance is the square root of the difference between the value of −2 ln L (with systematic uncertainties included) for zero signal and the value at its minimum. The 90% C.L. upper limit is taken to be the branching fraction below which lies 90% of the total likelihood integral in the positive branching fraction region.

TABLE I: Signal yield, detection efficiency ǫ (%), daughter branching fraction product Q Bi, significance S (σ)(including systematic uncertainties), measured branching fraction B with statistical error for each decay mode. For the combined mea-surements we give the significance (with systematic uncertainties included) and the branching fraction with statistical and

systematic uncertainty (in parentheses the 90% C.L. upper limit). For the ηK+

γmode we also list the measured signal charge

asymmetry Ach. Mode Yield ǫ(%) Q B_{i (%)} S _(σ) B₍₁₀−6_{) A} ch(10−2) ηγγK0γ 36+13−12 10.2 13.6 4.6 11.2 +4.0 −3.7 η3πK0γ 14+8−7 7.0 7.8 2.9 11.5 +6.1 −5.3 ηK0γ 5_.3 11_.3+2.8 −2.6± 0.6 ηγγK+γ 110+22−21 12.9 39.4 8.0 9.4 +1.8 −1.7 −1.3 ± 15.3 η3πK+γ 53+14−13 8.8 22.6 6.6 11.4 +3.0 −2.8 −21.9 ± 20.5 ηK+γ 10_.0 10_{.0 ± 1.3 ± 0.5 −8.6 ± 12.0 ± 1.0} η′ ηππK0γ 1 +2 −2 6.2 6.0 0.4 0.6 +2.8 −2.0 η′ργK0γ 14+16−14 5.3 10.2 1.2 11.2 +12.8 −11.0 η′_K0_{γ 0.6 1.1}+2.8 −2.0± 0.1(< 6.6) η′ ηππK+γ 6 +6 −5 8.2 17.5 1.6 1.9 +1.8 −1.4 η′ργK+γ 10+27−24 9.9 29.5 0.5 1.5 +3.9 −3.6 η′_K+_{γ 1.7 1.9}+1.5 −1.2± 0.1(< 4.2)

The measured charge asymmetry in the decay B+_{→ ηK}+_{γ is corrected for an estimated bias of}

−0.005 ± 0.010, determined from studies of signal Monte Carlo events and data control samples and from calcula-tion of the asymmetry due to particles interacting in the detector. The result is Ach = −0.09 ± 0.12 ± 0.01 with

an asymmetry interval [−0.282, 0.113] at 90% C.L.. Figure 1 shows, as representative fits, the projections onto mES and ∆E for the decays ηK+γ, ηK0γ, η′K+γ

and η′_K0_{γ for a subset of the data for which the signal}

likelihood (computed without using the variable plotted) exceeds a mode-dependent threshold that optimizes the sensitivity.

Figure 2 shows the distribution of the ηK invariant mass for signal events obtained by the event-weighting technique (sPlot) described in Ref. [19]. We use the co-variance matrix and PDFs from the ML fit to determine a probability for each signal event. The resulting distri-butions (points with errors) are normalized to the signal yield. This mass distribution is useful to compare with theoretical predictions for radiative decays [17].

The main sources of systematic error include uncer-tainties in the PDF parameterization and ML fit bias. For the signal, the uncertainties in PDF parameters are estimated by comparing MC and data in control sam-ples. Varying the signal PDF parameters within these errors, we estimate yield uncertainties of 1–2 events, de-pending on the mode. The uncertainty from fit bias is taken as half the correction itself (1–3 events). System-atic uncertainties due to lack of knowledge of the pri-mary photon spectrum are estimated to be in the range 2-6% depending on the decay mode. Uncertainties in our knowledge of the efficiency, found from auxiliary studies, include 0.8% × Nt and 1.5% × Nγ, where Nt and Nγ

are the numbers of tracks and photons, respectively, in

5.25 5.26 5.27 5.28 5.29 2 Events / 2 MeV/c 10 20 30 5.25 5.26 5.27 5.28 5.29 2 Events / 2 MeV/c 10 20 30 -0.2 -0.1 0 0.1 0.2 Events / 20 MeV 10 20 30 40 -0.2 -0.1 0 0.1 0.2 Events / 20 MeV 10 20 30 40 5.25 5.26 5.27 5.28 5.29 5 10 15 20 5.25 5.26 5.27 5.28 5.29 5 10 15 20 -0.2 -0.1 0 0.1 0.2 5 10 15 -0.2 -0.1 0 0.1 0.2 5 10 15 5.25 5.26 5.27 5.28 5.29 10 20 5.25 5.26 5.27 5.28 5.29 10 20 -0.2 -0.1 0 0.1 0.2 5 10 15 20 -0.2 -0.1 0 0.1 0.2 5 10 15 20 ) 2 (GeV/c ES m 5.250 5.26 5.27 5.28 5.29 5 10 15 ) 2 (GeV/c ES m 5.250 5.26 5.27 5.28 5.29 5 10 15 E (GeV) ∆ -0.20 -0.1 0 0.1 0.2 5 10 15 E (GeV) ∆ -0.20 -0.1 0 0.1 0.2 5 10 15 (a) (b) (c) (d) (e) (f) (g) (h)

FIG. 1: The B candidate mESand ∆E projections for ηK+γ

(a, b), ηK0

γ (c, d), η′

K+γ (e, f) and η′

K0γ (g, h). Points

with error bars represent the data, the solid line the full fit function, and the dashed line its background component.

the B candidate. There is a systematic error of 2.1% in the efficiency of K0

S reconstruction. The uncertainty

in the total number of BB pairs in the data sample is 1.1%. Published data [8] provide the uncertainties in the B daughter product branching fractions (0.7-3.4%). We assign a systematic uncertainty of 0.010 to Ach for the

bias correction.

In conclusion, we have measured the central values and 90% C.L. upper limits in units of 10−6 _{for the}

branching fractions: B(B0_{→ ηK}0_{γ) = 11.3}+2.8 −2.6± 0.6 ,

) 2 (GeV/c K η m 1 1.5 2 2.5 3 2 Events / 100 MeV/c 0 10 20 30 _(a) ) 2 (GeV/c K η m 1 1.5 2 2.5 3 2 Events / 100 MeV/c 0 5 10 (b)

FIG. 2: Plot of ηK invariant mass for signal using the weight-ing technique described in the text for the combined sub-decay modes: (a) charged modes, (b) neutral modes.

B(B+_{→ ηK}+_{γ) = 10.0 ± 1.3 ± 0.5 , B(B}0_{→ η}′_K0_{γ) =}

1.1+2.8−2.0 ± 0.1 (< 6.6), B(B+→ η′K+γ) = 1.9+1.5−1.2 ±

0.1 (< 4.2). The measured branching fractions of the decay modes B+_{→ ηK}+_{γ and B}0_{→ ηK}0_{γ are in good}

agreement with the values reported by the Belle Col-laboration [7]. We do not find evidence of the decays B0_{→ η}′_K0_{γ and B}+_{→ η}′_K+_{γ. The B → η}′_{Kγ decays}

may be suppressed with respect to B → ηKγ decays due to destructive interference between two penguin ampli-tudes [20]. This effect has been measured in B decays to η′_{K and ηK, for which the branching fraction of the}

for-mer is enhanced with respect to that of the latter [21]. We have also measured the charge asymmetry in the decay B+_{→ ηK}+_{γ to be A}

ch= −0.09 ± 0.12 ± 0.01, consistent

with zero. The Ach interval at 90% C.L. is [−0.28, 0.11].

We are grateful for the excellent luminosity and ma-chine conditions provided by our PEP-II colleagues, and for the substantial dedicated effort from the comput-ing organizations that support BA_BAR. The

collaborat-ing institutions wish to thank SLAC for its support and kind hospitality. This work is supported by DOE and NSF (USA), NSERC (Canada), IHEP (China), CEA and CNRS-IN2P3 (France), BMBF and DFG (Germany), INFN (Italy), FOM (The Netherlands), NFR (Norway), MIST (Russia), and PPARC (United Kingdom). Indi-viduals have received support from CONACyT (Mex-ico), Marie Curie EIF (European Union), the A. P. Sloan Foundation, the Research Corporation, and the Alexan-der von Humboldt Foundation.

∗ _{Also at Laboratoire de Physique Corpusculaire,}

Clermont-Ferrand, France

† _{Also with Universit`a di Perugia, Dipartimento di Fisica,}

Perugia, Italy

‡ _{Also with Universit`a della Basilicata, Potenza, Italy}

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