Measurement of the Branching Fractions and CP Asymmetries of B--D0(cp)K- Decays with the Ba
a r X i v :h e p -e x /0408082v 1 17 A u g 2004B A B A R -CONF-04/039
SLAC-PUB-10655
Measurement of the Branching Fractions and CP Asymmetries of B ?→D 0(CP )K ?Decays with the B A B A R Detector The B A B A R Collaboration February 7,2008Abstract We present a study of B ?→D 0(CP )K ?decays,where D 0(CP )is reconstructed in ?avor (K ?π+),CP -even (K ?K +,π?π+)and CP -odd (K 0S π0)eigenstates,based on a sample of about 214million Υ(4S )→B
B (B ?→D 0K ?)/B (B ?→D 0π?)
=0.87±0.14(stat)±0.06(syst),
R ?≡
B (B ?→D 0CP ?K ?)/B (B ?→D 0CP ?π?)B (B ?→D 0CP +K ?)+B (B +→D 0CP +K +)
=0.40±0.15(stat)±0.08(syst)
B(B?→D0CP?K?)?B(B+→D0CP?K+)
A CP?≡
Work supported in part by Department of Energy contract DE-AC03-76SF00515.
The B A B A R Collaboration,
B.Aubert,R.Barate,D.Boutigny,F.Couderc,J.-M.Gaillard,A.Hicheur,Y.Karyotakis,J.P.Lees,
V.Tisserand,A.Zghiche
Laboratoire de Physique des Particules,F-74941Annecy-le-Vieux,France
A.Palano,A.Pompili
Universit`a di Bari,Dipartimento di Fisica and INFN,I-70126Bari,Italy
J.C.Chen,N.D.Qi,G.Rong,P.Wang,Y.S.Zhu
Institute of High Energy Physics,Beijing100039,China
G.Eigen,I.Ofte,B.Stugu
University of Bergen,Inst.of Physics,N-5007Bergen,Norway
G.S.Abrams,A.W.Borgland,A.B.Breon,D.N.Brown,J.Button-Shafer,R.N.Cahn,E.Charles, C.T.Day,M.S.Gill,A.V.Gritsan,Y.Groysman,R.G.Jacobsen,R.W.Kadel,J.Kadyk,L.T.Kerth,
Yu.G.Kolomensky,G.Kukartsev,G.Lynch,L.M.Mir,P.J.Oddone,T.J.Orimoto,M.Pripstein,
N.A.Roe,M.T.Ronan,V.G.Shelkov,W.A.Wenzel
Lawrence Berkeley National Laboratory and University of California,Berkeley,CA94720,USA
M.Barrett,K.E.Ford,T.J.Harrison,A.J.Hart,C.M.Hawkes,S.E.Morgan,A.T.Watson University of Birmingham,Birmingham,B152TT,United Kingdom
M.Fritsch,K.Goetzen,T.Held,H.Koch,B.Lewandowski,M.Pelizaeus,M.Steinke
Ruhr Universit¨a t Bochum,Institut f¨u r Experimentalphysik1,D-44780Bochum,Germany
J.T.Boyd,N.Chevalier,W.N.Cottingham,M.P.Kelly,https://www.wendangku.net/doc/5611807225.html,tham,F.F.Wilson
University of Bristol,Bristol BS81TL,United Kingdom
T.Cuhadar-Donszelmann,C.Hearty,N.S.Knecht,T.S.Mattison,J.A.McKenna,D.Thiessen University of British Columbia,Vancouver,BC,Canada V6T1Z1
A.Khan,P.Kyberd,L.Teodorescu
Brunel University,Uxbridge,Middlesex UB83PH,United Kingdom
A.E.Blinov,V.E.Blinov,V.P.Druzhinin,V.
B.Golubev,V.N.Ivanchenko,E.A.Kravchenko,
A.P.Onuchin,S.I.Serednyakov,Yu.I.Skovpen,E.P.Solodov,A.N.Yushkov
Budker Institute of Nuclear Physics,Novosibirsk630090,Russia
D.Best,M.Bruinsma,M.Chao,I.Eschrich,D.Kirkby,https://www.wendangku.net/doc/5611807225.html,nkford,M.Mandelkern,R.K.Mommsen,
W.Roethel,D.P.Stoker
University of California at Irvine,Irvine,CA92697,USA
C.Buchanan,B.L.Hart?el
University of California at Los Angeles,Los Angeles,CA90024,USA
S.D.Foulkes,J.W.Gary,B.C.Shen,K.Wang
University of California at Riverside,Riverside,CA92521,USA
D.del Re,H.K.Hadavand,
E.J.Hill,D.B.MacFarlane,H.P.Paar,Sh.Rahatlou,V.Sharma
University of California at San Diego,La Jolla,CA92093,USA
J.W.Berryhill,C.Campagnari,B.Dahmes,O.Long,A.Lu,M.A.Mazur,J.D.Richman,W.Verkerke University of California at Santa Barbara,Santa Barbara,CA93106,USA
T.W.Beck,A.M.Eisner,C.A.Heusch,J.Kroseberg,W.S.Lockman,G.Nesom,T.Schalk,
B.A.Schumm,A.Seiden,P.Spradlin,D.
C.Williams,M.G.Wilson
University of California at Santa Cruz,Institute for Particle Physics,Santa Cruz,CA95064,USA
J.Albert,E.Chen,G.P.Dubois-Felsmann,A.Dvoretskii,D.G.Hitlin,I.Narsky,T.Piatenko,
F.C.Porter,A.Ryd,A.Samuel,S.Yang
California Institute of Technology,Pasadena,CA91125,USA
S.Jayatilleke,G.Mancinelli,B.T.Meadows,M.D.Sokolo?
University of Cincinnati,Cincinnati,OH45221,USA
T.Abe,F.Blanc,P.Bloom,S.Chen,W.T.Ford,U.Nauenberg,A.Olivas,P.Rankin,J.G.Smith,
J.Zhang,L.Zhang
University of Colorado,Boulder,CO80309,USA
A.Chen,J.L.Harton,A.So?er,W.H.Toki,R.J.Wilson,Q.Zeng
Colorado State University,Fort Collins,CO80523,USA
D.Altenburg,T.Brandt,J.Brose,M.Dickopp,
E.Feltresi,A.Hauke,https://www.wendangku.net/doc/5611807225.html,cker,R.M¨u ller-Pfe?erkorn, R.Nogowski,S.Otto,A.Petzold,J.Schubert,K.R.Schubert,R.Schwierz,B.Spaan,J.E.Sundermann Technische Universit¨a t Dresden,Institut f¨u r Kern-und Teilchenphysik,D-01062Dresden,Germany
D.Bernard,G.R.Bonneaud,F.Brochard,P.Grenier,S.Schrenk,Ch.Thiebaux,G.Vasileiadis,M.Verderi
Ecole Polytechnique,LLR,F-91128Palaiseau,France
D.J.Bard,P.J.Clark,https://www.wendangku.net/doc/5611807225.html,vin,F.Muheim,S.Playfer,Y.Xie
University of Edinburgh,Edinburgh EH93JZ,United Kingdom
M.Andreotti,V.Azzolini,D.Bettoni,C.Bozzi,R.Calabrese,G.Cibinetto,E.Luppi,M.Negrini,
L.Piemontese,A.Sarti
Universit`a di Ferrara,Dipartimento di Fisica and INFN,I-44100Ferrara,Italy
E.Treadwell
Florida A&M University,Tallahassee,FL32307,USA
F.Anulli,R.Baldini-Ferroli,A.Calcaterra,R.de Sangro,
G.Finocchiaro,P.Patteri,I.M.Peruzzi,
M.Piccolo,A.Zallo
Laboratori Nazionali di Frascati dell’INFN,I-00044Frascati,Italy
A.Buzzo,R.Capra,R.Contri,G.Crosetti,M.Lo Vetere,M.Macri,M.R.Monge,S.Passaggio,
C.Patrignani,E.Robutti,A.Santroni,S.Tosi
Universit`a di Genova,Dipartimento di Fisica and INFN,I-16146Genova,Italy
S.Bailey,G.Brandenburg,K.S.Chaisanguanthum,M.Morii,E.Won
Harvard University,Cambridge,MA02138,USA
R.S.Dubitzky,https://www.wendangku.net/doc/5611807225.html,ngenegger
Universit¨a t Heidelberg,Physikalisches Institut,Philosophenweg12,D-69120Heidelberg,Germany W.Bhimji,D.A.Bowerman,P.D.Dauncey,U.Egede,J.R.Gaillard,G.W.Morton,J.A.Nash,
M.B.Nikolich,G.P.Taylor
Imperial College London,London,SW72AZ,United Kingdom
M.J.Charles,G.J.Grenier,U.Mallik
University of Iowa,Iowa City,IA52242,USA
J.Cochran,H.B.Crawley,https://www.wendangku.net/doc/5611807225.html,msa,W.T.Meyer,S.Prell,E.I.Rosenberg,A.E.Rubin,J.Yi
Iowa State University,Ames,IA50011-3160,USA
M.Biasini,R.Covarelli,M.Pioppi
Universit`a di Perugia,Dipartimento di Fisica and INFN,I-06100Perugia,Italy
M.Davier,X.Giroux,G.Grosdidier,A.H¨o cker,https://www.wendangku.net/doc/5611807225.html,place,F.Le Diberder,V.Lepeltier,A.M.Lutz, T.C.Petersen,S.Plaszczynski,M.H.Schune,L.Tantot,G.Wormser
Laboratoire de l’Acc′e l′e rateur Lin′e aire,F-91898Orsay,France
C.H.Cheng,
https://www.wendangku.net/doc/5611807225.html,nge,M.C.Simani,D.M.Wright
Lawrence Livermore National Laboratory,Livermore,CA94550,USA
A.J.Bevan,C.A.Chavez,J.P.Coleman,I.J.Forster,J.R.Fry,E.Gabathuler,R.Gamet,
D.E.Hutchcroft,R.J.Parry,D.J.Payne,R.J.Sloane,C.Touramanis
University of Liverpool,Liverpool L6972E,United Kingdom
J.J.Back,1C.M.Cormack,P.F.Harrison,1F.Di Lodovico,G.B.Mohanty1
Queen Mary,University of London,E14NS,United Kingdom
C.L.Brown,G.Cowan,R.L.Flack,H.U.Flaecher,M.G.Green,P.S.Jackson,T.R.McMahon,
S.Ricciardi,F.Salvatore,M.A.Winter
University of London,Royal Holloway and Bedford New College,Egham,Surrey TW200EX,
United Kingdom
D.Brown,C.L.Davis
University of Louisville,Louisville,KY40292,USA
J.Allison,N.R.Barlow,R.J.Barlow,P.A.Hart,M.C.Hodgkinson,https://www.wendangku.net/doc/5611807225.html,?erty,A.J.Lyon,
J.C.Williams
University of Manchester,Manchester M139PL,United Kingdom
A.Farbin,W.D.Hulsbergen,A.Jawahery,D.Kovalskyi,https://www.wendangku.net/doc/5611807225.html,e,V.Lillard,D.A.Roberts
University of Maryland,College Park,MD20742,USA
G.Blaylock,C.Dallapiccola,K.T.Flood,S.S.Hertzbach,R.Ko?er,V.B.Koptchev,T.B.Moore,
S.Saremi,H.Staengle,S.Willocq
University of Massachusetts,Amherst,MA01003,USA
R.Cowan,G.Sciolla,S.J.Sekula,F.Taylor,R.K.Yamamoto Massachusetts Institute of Technology,Laboratory for Nuclear Science,Cambridge,MA02139,USA
D.J.J.Mangeol,P.M.Patel,S.H.Robertson
McGill University,Montr′e al,QC,Canada H3A2T8
https://www.wendangku.net/doc/5611807225.html,zzaro,V.Lombardo,F.Palombo
Universit`a di Milano,Dipartimento di Fisica and INFN,I-20133Milano,Italy
J.M.Bauer,L.Cremaldi,V.Eschenburg,R.Godang,R.Kroeger,J.Reidy,D.A.Sanders,D.J.Summers,
H.W.Zhao
University of Mississippi,University,MS38677,USA
S.Brunet,D.C?o t′e,P.Taras
Universit′e de Montr′e al,Laboratoire Ren′e J.A.L′e vesque,Montr′e al,QC,Canada H3C3J7
H.Nicholson
Mount Holyoke College,South Hadley,MA01075,USA
N.Cavallo,2F.Fabozzi,2C.Gatto,L.Lista,D.Monorchio,P.Paolucci,D.Piccolo,C.Sciacca Universit`a di Napoli Federico II,Dipartimento di Scienze Fisiche and INFN,I-80126,Napoli,Italy
M.Baak,H.Bulten,G.Raven,H.L.Snoek,L.Wilden
NIKHEF,National Institute for Nuclear Physics and High Energy Physics,NL-1009DB Amsterdam,
The Netherlands
C.P.Jessop,J.M.LoSecco
University of Notre Dame,Notre Dame,IN46556,USA
T.Allmendinger,K.K.Gan,K.Honscheid,D.Hufnagel,H.Kagan,R.Kass,T.Pulliam,A.M.Rahimi,
R.Ter-Antonyan,Q.K.Wong
Ohio State University,Columbus,OH43210,USA
J.Brau,R.Frey,O.Igonkina,C.T.Potter,N.B.Sinev,D.Strom,E.Torrence
University of Oregon,Eugene,OR97403,USA
F.Colecchia,A.Dorigo,F.Galeazzi,M.Margoni,M.Morandin,M.Posocco,M.Rotondo,F.Simonetto,
R.Stroili,G.Tiozzo,C.Voci
Universit`a di Padova,Dipartimento di Fisica and INFN,I-35131Padova,Italy
M.Benayoun,H.Briand,J.Chauveau,P.David,Ch.de la Vaissi`e re,L.Del Buono,O.Hamon,
M.J.J.John,Ph.Leruste,J.Malcles,J.Ocariz,M.Pivk,L.Roos,S.T’Jampens,G.Therin Universit′e s Paris VI et VII,Laboratoire de Physique Nucl′e aire et de Hautes Energies,F-75252Paris,
France
P.F.Manfredi,V.Re
Universit`a di Pavia,Dipartimento di Elettronica and INFN,I-27100Pavia,Italy
P.K.Behera,L.Gladney,Q.H.Guo,J.Panetta
University of Pennsylvania,Philadelphia,PA19104,USA
C.Angelini,G.Batignani,S.Bettarini,M.Bondioli,F.Bucci,G.Calderini,M.Carpinelli,F.Forti, M.A.Giorgi,A.Lusiani,G.Marchiori,F.Martinez-Vidal,3M.Morganti,N.Neri,E.Paoloni,M.Rama,
G.Rizzo,F.Sandrelli,J.Walsh
Universit`a di Pisa,Dipartimento di Fisica,Scuola Normale Superiore and INFN,I-56127Pisa,Italy
M.Haire,D.Judd,K.Paick,D.E.Wagoner
Prairie View A&M University,Prairie View,TX77446,USA
N.Danielson,P.Elmer,https://www.wendangku.net/doc/5611807225.html,u,C.Lu,V.Miftakov,J.Olsen,A.J.S.Smith,A.V.Telnov
Princeton University,Princeton,NJ08544,USA
F.Bellini,
G.Cavoto,4R.Faccini,F.Ferrarotto,F.Ferroni,M.Gaspero,L.Li Gioi,M.A.Mazzoni,
S.Morganti,M.Pierini,G.Piredda,F.Safai Tehrani,C.Voena
Universit`a di Roma La Sapienza,Dipartimento di Fisica and INFN,I-00185Roma,Italy
S.Christ,G.Wagner,R.Waldi
Universit¨a t Rostock,D-18051Rostock,Germany
T.Adye,N.De Groot,B.Franek,N.I.Geddes,G.P.Gopal,E.O.Olaiya Rutherford Appleton Laboratory,Chilton,Didcot,Oxon,OX110QX,United Kingdom
R.Aleksan,S.Emery,A.Gaidot,S.F.Ganzhur,P.-F.Giraud,G.Hamel de Monchenault,W.Kozanecki, M.Legendre,G.W.London,B.Mayer,G.Schott,G.Vasseur,Ch.Y`e che,M.Zito
DSM/Dapnia,CEA/Saclay,F-91191Gif-sur-Yvette,France
M.V.Purohit,A.W.Weidemann,J.R.Wilson,F.X.Yumiceva
University of South Carolina,Columbia,SC29208,USA
D.Aston,R.Bartoldus,N.Berger,A.M.Boyarski,O.L.Buchmueller,R.Claus,M.R.Convery,
M.Cristinziani,G.De Nardo,D.Dong,J.Dorfan,D.Dujmic,W.Dunwoodie,E.E.Elsen,S.Fan, R.C.Field,T.Glanzman,S.J.Gowdy,T.Hadig,V.Halyo,C.Hast,T.Hryn’ova,W.R.Innes, M.H.Kelsey,P.Kim,M.L.Kocian,D.W.G.S.Leith,J.Libby,S.Luitz,V.Luth,H.L.Lynch,
H.Marsiske,R.Messner,D.R.Muller,C.P.O’Grady,V.E.Ozcan,A.Perazzo,M.Perl,S.Petrak, B.N.Ratcli?,A.Roodman,A.A.Salnikov,R.H.Schindler,J.Schwiening,G.Simi,A.Snyder,A.Soha,
J.Stelzer,D.Su,M.K.Sullivan,J.Va’vra,S.R.Wagner,M.Weaver,A.J.R.Weinstein, W.J.Wisniewski,M.Wittgen,D.H.Wright,A.K.Yarritu,C.C.Young
Stanford Linear Accelerator Center,Stanford,CA94309,USA
P.R.Burchat,A.J.Edwards,T.I.Meyer,B.A.Petersen,C.Roat
Stanford University,Stanford,CA94305-4060,USA
S.Ahmed,M.S.Alam,J.A.Ernst,M.A.Saeed,M.Saleem,F.R.Wappler
State University of New York,Albany,NY12222,USA
W.Bugg,M.Krishnamurthy,S.M.Spanier
University of Tennessee,Knoxville,TN37996,USA
R.Eckmann,H.Kim,J.L.Ritchie,A.Satpathy,R.F.Schwitters
University of Texas at Austin,Austin,TX78712,USA
J.M.Izen,I.Kitayama,X.C.Lou,S.Ye
University of Texas at Dallas,Richardson,TX75083,USA
F.Bianchi,M.Bona,F.Gallo,D.Gamba
Universit`a di Torino,Dipartimento di Fisica Sperimentale and INFN,I-10125Torino,Italy
L.Bosisio,C.Cartaro,F.Cossutti,G.Della Ricca,S.Dittongo,S.Grancagnolo,https://www.wendangku.net/doc/5611807225.html,nceri,P.Poropat,5
L.Vitale,G.Vuagnin
Universit`a di Trieste,Dipartimento di Fisica and INFN,I-34127Trieste,Italy
R.S.Panvini
Vanderbilt University,Nashville,TN37235,USA
Sw.Banerjee,C.M.Brown,D.Fortin,P.D.Jackson,R.Kowalewski,J.M.Roney,R.J.Sobie
University of Victoria,Victoria,BC,Canada V8W3P6
H.R.Band,B.Cheng,S.Dasu,M.Datta,A.M.Eichenbaum,M.Graham,J.J.Hollar,J.R.Johnson,
P.E.Kutter,H.Li,R.Liu,A.Mihalyi,A.K.Mohapatra,Y.Pan,R.Prepost,P.Tan,J.H.von
Wimmersperg-Toeller,J.Wu,S.L.Wu,Z.Yu
University of Wisconsin,Madison,WI53706,USA
M.G.Greene,H.Neal
Yale University,New Haven,CT06511,USA
1INTRODUCTION
A theoretically clean measurement of the angleγ=arg(?V ud V?ub/V cd V?cb)can be obtained from the study of B?→D(?)0K(?)?decays by exploiting the interference between the b→cˉu s and b→uˉc s decay amplitudes[1].The method originally proposed by Gronau,Wyler and London is based on the interference between B?→D0K?and B?→D0decay to CP eigenstates.
We de?ne the ratios R and R CP±of Cabibbo-suppressed to Cabibbo-favored branching fractions
R(CP±)≡B(B?→D0
(CP±)
K?)+B(B+→
B(B?→D0
(CP±)
π?)+B(B+→
B(B?→D0CP±K?)+B(B+→D0CP±K+)
.(2)
Neglecting the D0?D0π?)/A(B?→D0π?)of the amplitudes of the B?→
D0K?)/A(B?→D0K?)|is the magnitude of the ratio of the amplitudes for the processes B?→
B pairs collected with the B A B A R detector at the PEP-II asymmetric-energy B factory.The B A B A R detector is described in detail elsewhere[2].Charged-particle tracking is provided by a?ve-layer silicon vertex tracker(SVT)and a40-layer drift chamber(DCH).For charged-particle identi?cation,ionization energy loss in the DCH and SVT,and Cherenkov radia-tion detected in a ring-imaging device(DIRC)are used.Photons are identi?ed by the electromag-netic calorimeter(EMC),which comprises6580thallium-doped CsI crystals.These systems are mounted inside a1.5-T solenoidal superconducting magnet.The segmented?ux return,including endcaps,is instrumented with resistive plate chambers(IFR)for muon and K0
L
identi?cation.We use the GEANT[3]software to simulate interactions of particles traversing the detector,taking into account the varying accelerator and detector conditions.
3ANALYSIS METHOD
We reconstruct B?→D0h?decays,where the prompt track h?is a kaon or a pion.Reference to the charge-conjugate state is implied here and throughout the text unless otherwise stated.Candidates for D0are reconstructed in the CP-even eigenstatesπ?π+and K?K+,in the CP-odd eigenstate K0Sπ0,and in the non-CP?avor eigenstate K?π+.K0
S
candidates are selected in theπ?π+channel.
The prompt particle h?is required to have momentum greater than1.4GeV/c.Particle ID
information from the drift chamber and,when available,from the DIRC must be consistent with the kaon hypothesis for the K meson candidate in all D0modes and with the pion hypothesis for theπ±meson candidates in the D0→π?π+mode.For the prompt track to be identi?ed as a pion or a kaon,we require that at least?ve Cherenkov photons are detected to insure a good measurement of the Cherenkov angle.We reject a candidate track if its Cherenkov angle is not within3σof the expected value for either the kaon or pion mass hypothesis.We also reject candidate tracks that are identi?ed as electrons by the DCH and the EMC or as muons by the DCH and the IFR.
Photon candidates are clusters in the EMC that are not matched to any charged track,have a raw energy greater than30MeV and lateral shower shape consistent with the expected pattern of energy deposit from an electromagnetic shower.Photon pairs with invariant mass within the range 115–150MeV/c2(～3σ)and total energy greater than200MeV are consideredπ0candidates. To improve the momentum resolution,theπ0candidates are kinematically?t with their mass constrained to the nominalπ0mass[4].
Neutral kaons are reconstructed from pairs of oppositely charged tracks with the invariant mass within10MeV(～3σ)from the nominal K0mass.We also require that the ratio between the?ight length distance in the plane transverse to the beams direction and its uncertainty is greater than 3.
The invariant mass of a D0candidate,m(D0),must be within3σof the D0mass.The D0mass resolutionσis about7.5MeV in the K?π+,K?K+andπ?π+modes,and about21MeV in the π0mode.Selected D0candidates are?tted with a constraint to the nominal D0mass.
K0
S
We reconstruct B meson candidates by combining a D0candidate with a track h?.For the K?π+mode,the charge of the track h?must match that of the kaon from the D0me-
son decay.We select B meson candidates by using the beam-energy-substituted mass m ES=
rejects more than90%of the continuum background while retaining77%of the signal in the K?π+, K?K+and K0
π0modes and65%in theπ?π+channel.
S
Multiple B?→D0h?candidates are found in about4%of the events for the K0Sπ0and in less than1%of the events for the other D0decays.In these events aχ2is constructed from m(π0)(for K0Sπ0only),m(D0),and m ES and only the candidate with the smallestχ2is retained.The total reconstruction e?ciencies,based on simulated signal events,are about33%(K?π+),28%(K?K+), 26%(π?π+)and17%(K0Sπ0).
The main contributions to the B
B events,in which the prompt track is either a pion or a kaon.
The input variables to the?t are?E and a particle identi?cation probability for the prompt track based on the Cherenkov angleθC,the momentum p and the polar angleθof the track.The extended likelihood function L is de?ned as
L=exp ?M i=1n i N j=1 M i=1n i P i(?E,θC; αi) ,(3)
where N is the total number of observed events.The M functions P i(?E,θC; αi)are the probability density functions(PDFs)for the variables?E,θC,given the set of parameters αi.Since these two quantities are su?ciently uncorrelated,their probability density functions are evaluated as a product P i=P i(?E; αi)×P i(θC; αi).
The?E distribution for B?→D0K?signal events is parametrized with a Gaussian function. The?E distribution for B?→D0π?is parametrized with the same Gaussian used for B?→D0K?with a relative shift of the mean,computed event by event as a function of the prompt track momentum,arising from the wrong mass assignment to the prompt track.The o?set and width of the Gaussian are kept?oating in the?t and are determined from data together with the yields.
The?E distribution for the continuum background is parametrized with a linear function whose slope is determined from o?-resonance data.The?E distribution for the B
4PHYSICS RESULTS AND SYSTEMATIC STUDIES
The results of the?t are summarized in Table1.Figure1shows the distributions of?E for the K?π+,CP+and CP?modes after enhancing the B→D0K purity by requiring that the prompt track be consistent with the kaon hypothesis.This requirement is about95%e?cient for the B?→D0K?signal while retaining only4%of the B?→D0π?candidates.The projection of a likelihood?t,modi?ed to take into account the tighter selection criteria,is overlaid in the?gure. Table1:Results of the B?→D0K?and B?→D0π?yields from the maximum-likelihood?t on data.
D0mode N(B→D0π)N(B→D0K)N(B?→D0K?)N(B+→
K?π+11930±120897±34441±24456±25
K0Sπ01248±4076+13
?1246+10
?9
30+9?8
The double ratios R±are computed by scaling the ratios of the numbers of B?→D0K?and B?→D0π?mesons by correction factors(ranging from0.997to1.020depending on the D0mode) that account for small di?erences in the e?ciency between the B?→D0K?and B?→D0π?selec-tions,estimated with simulated signal samples.The results are listed in Table2.
The direct CP asymmetries A CP±for the B±→D0CP±K±decays are calculated from the measured yields of positive and negative charged meson decays and the results are reported in Table2.
Table2:Measured double branching fraction ratios R±and CP asymmetries A CP±for di?erent D0decay modes.The?rst error is statistical,the second is systematic.
D0decay mode R CP/R A CP
K?K+0.92±0.16±0.070.43±0.16±0.09
π?π+0.70±0.29±0.090.27±0.40±0.09
CP-even combined0.87±0.14±0.060.40±0.15±0.08
The uncertainties in the branching fractions of the channels contributing to the B
[6]Belle Collaboration,K.Abe et al.,Phys.Rev.D6*******(2002);B A B A R Collaboration,B.
Aubert et al.,hep-ex/0308065,submitted to Phys.Rev.Lett..
[7]B A B A R Collaboration,B.Aubert et al.,Phys.Rev.Lett.92202002(2004).
Figure1:?E distributions of B?→D0h?candidates,where a charged kaon mass hypothesis is assumed for h.Events are enhanced in B?→D0K?purity by requiring the Cherenkov angle of the track h to be within2σof the kaon hypothesis.Top:B?→D0[K?π+]K?;middle:B?→
π0]K?.Solid curves represent projections of D0CP+[K?K+,π?π+]K?;bottom:B?→D0CP?[K0
S
the maximum likelihood?t;dashed-dotted,dotted and dashed curves represent the B→D0K,
B→D0πand background contributions.