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Measurement of CP-Asymmetries for the Decays B+- to D_cp Kstar+- with the BABAR Detector

a r X i v :h e p -e x /0408069v 2 29 A u g 2004B A B A R -CONF-04/012

SLAC-PUB-10639

August 2004

Measurement of C P -Asymmetries for the Decays B ±→D 0CP K ?±with the BABAR Detector The B A B A R Collaboration February 7,2008Abstract Using a sample of 227million Υ(4S )→B

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/9b5019695.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/9b5019695.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/9b5019695.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/9b5019695.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/9b5019695.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/9b5019695.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/9b5019695.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/9b5019695.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/9b5019695.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/9b5019695.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/9b5019695.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/9b5019695.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/9b5019695.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

The measurement of CP violation in B meson decays o?ers the means to over-constrain the unitarity

triangle.A theoretically clean measurement of the angleγ=arg(?V ud V?ub/V cd V?cb)is provided by

the B?→D(?)0K(?)?[1]decay channels in which the favoured b→c cs penguin-less processes interfere[2].In this paper we implement the method proposed by Gronau,

Wyler and London by looking at the interference between B?→D0K??and B?→

D0decay to a CP eigenstate.

We de?ne[3]:

A CP±=Γ(B?→D0CP±K??)?Γ(B+→D0CP±K?+)

Γ(B?→D0K??).(2) A CP±are the direct CP-violating asymmetries associated to each D0CP eigenstate.R CP±is twice the ratio of the charge-averaged branching fraction of the B→D0CP±K?decays to that of B?→D0K??.The latter branching fraction has been measured previously by B A B A R[4],CLEO[5] and Belle[6].These measurements average to(5.7±0.6)·10?4.Both A CP±and R CP±carry CP-violating information.Neglecting D0-

D0K??(suppressed)amplitudes,γis the CP-violating weak phase di?erence in the same processes and r B?0.1-0.3is the magnitude of the ratio of the amplitudes[3].

2THE B A B A R DETECTOR AND DATASET

We look for B?→D0CP K??decays with the data collected near theΥ(4S)resonance with the B A B A R detector at the PEP-II storage ring between October1999and May2004.We accumulated an integrated luminosity of205fb?1on the peak(227million B

3ANALYSIS METHOD

We reconstruct B?→D0K?(892)?decays.We select K??candidates in the K??→K0Sπ?mode and D0candidates in8decay channels.We optimize our event-selection criteria to minimize the statistical error on the signal yield,determined for each channel using simulated signal and background events.In order to maximize statistics and as we measure ratios(asymmetries and ratios of branching fractions),we use rather relaxed criteria to de?ne a track or a photon candidate. In general a track must originate from the interaction point within1.5cm in the transverse plane and10cm along the beam.Very soft tracks,measured only by the SVT are also used.Loose criteria are employed to separate charged pions and kaons.Pions(kaons)are identi?ed with more than95%(90%)e?ciency by an algorithm which rejects more than85%(95%)of the kaons(pions) in the geometrical acceptance of the DIRC.Photon candidates are isolated energy deposits in the EMC with an energy above30MeV and a shape consistent with that of a photon-induced shower.

S candidates are made from oppositely charged tracks assumed to be pions.K0

used to

make D0CP±(K?)candidates are mass(mass and vertex)constrained.The pion pairs are selected according to their reconstructed invariant mass,required to be within13MeV/c2from the known value[9].For those used to search for a K?we further require their?ight direction and length

to be as expected for a K0

S coming from the interaction point.The K0

candidate?ight path and

momentum have to make an acute angle.The K0

candidate?ight length in the transverse plane has to exceed its uncertainty by3standard deviations.π0candidates combine pairs of photons with a total energy greater than200MeV and an invariant mass between115and150MeV/c2.A mass constraint?t is applied to the selectedπ0candidates.K?candidates combine a K0

and a charged particle which are constrained to come from a single decay vertex.We select K?candidates which have an invariant mass within75MeV/c2of the known value[9].Finally,since the K?in B→D0K?is polarized,we require|cosθK?hel|≥0.35,whereθK?hel is the angle in the K?rest frame between the daughter pion and the parent B momenta.Here and in other occurrences the helicity distribution discriminates well between a B meson decay and an event from the e+e?→q

q reactions,q∈{u,d,s,c},we require|cosθB|≤0.9as,in theΥ(4S)rest frame,B mesons are produced with a sin2θB distribution of the angleθB

of their momentum with the beam axis.We also use global event shape variables which translate quantitatively the fact that in theΥ(4S)rest frame,q

B events are more spherical.We require|cosθthrust|≤0.9whereθthrust is the angle between the thrust axes of the B candidate and the rest of the event(i.e.what is left after removing the tracks and clusters associated with the B candidate).We construct a Fisher discriminant[11]from cosθthrust and Legendre monomials[12]describing the energy?ow in the rest of the event.

We identify?nal B candidates using two[nearly]independant kinematic variables:the beam-energy-substituted mass m ES=

s/2,where the subscripts0and B refer to the e+e?-beam-system and the B candidate respectively;s is the square of the center-of-mass(CM)energy and the asterisk labels the CM frame.For all signal modes,the m ES distributions are described by the same Gaussian function G centered at the B mass with a2.6MeV/c2resolution(except K0Sπ0which has a2.8MeV/c2 resolution).The?E distribution depends more strongly on the signal mode.?E is centered on

π0for which the resolution zero for signal with a resolution of11–13MeV for all channels except K0

is asymmetric and about30MeV.We de?ne a signal region|?E|<25MeV for all modes except π0which uses<50MeV.

For those events consistent with more than one B candidate—this occurs in<25%of selected events depending on the D0mode—we choose that with the smallestχ2formed from the di?erences of the measured and true D0and K?masses scaled by the mass spread which includes the resolution and,for the K?,the natural width.Simulations prove that no bias is introduced by this choice and the correct candidate is picked at least82%of the time.

The total reconstruction e?ciencies6after corrections,according to simulation of signal events, are:12.5%and12.9%for the CP+modes D0→K+K?andπ+π?;5.0%,10.2%and2.3%for the CP?modes D0→K0Sπ0,K0Sφand K0Sω;13.5%,5.2%and8.0%for the D0→K?π+,K?π+π0and K?π+π+π?non-CP modes.

4PEAKING BACKGROUNDS

To study B

6The branching fractions of the unstable daughter particles are not included.

branching fraction.We therefore explicitly veto any selected B-candidate containing a(K0

π+π?)

S combination within25MeV/c2of the D0mass.

5YIELD AND C P FIT

An unbinned extended maximum likelihood?t to m ES distributions in the range5.2≤m ES≤5.3GeV/c2is used to determine yields and CP-violating quantities A CP and R CP.We use a uni-versal Gaussian function G to describe the signal shape for all modes considered.The combinatorial background in the m ES distribution is modeled using a threshold function A rg?rst considered by

the Argus collaboration[13].Its shape is governed by one parameterξthat is left to?oat in the

√

?t and a second,E MAX=

non-CP CP?

34.4±6.9

2.5±1.3

?0.09±0.20

1.77±0.37

Table1:Results from the?ts.For each D0mode class,we give the event yield,the peaking background contribution,A CP and R CP.The uncertainties are statistical only.

The?t stability and accuracy have been studied by performing1000simulated experiments at

Figure1:The simultaneous?t.The m ES distributions are shown for the non-CP modes in the?rst column,CP+modes in the second column and CP?in the third.The?ts in the signal region are shown in the top two rows,?ts of the peaking background in the m D0sideband are in the third row and the?ts of the background in the?E sideband are in the fourth.For the CP modes in the signal region,B+and B?distributions are shown separately in the?rst and second rows.

the optimum found by the?t in the parameter space.The value of the likelihood function in the ?t falls well within the range observed with the simulated experiments.

The yields we observe for the non-CP modes are compatible with our previous measurements of the B?→D0K??branching ratio[4].The statistical signi?cance of the CP+(CP?)yields are 6.8(2.9)standard deviations.It should be noted that the measured A CP?could di?er from the physical quantity,as background under theφandωresonances with odd and even CP could be present.These possible interference e?ects are accounted for in the systematics.

6SYSTEMATIC STUDIES

6.1C P-asymmetries

Although most systematic errors cancel in the asymmetries,three e?ects must be considered.An asymmetry inherent to the detector or analysis may exist.After running the analysis code on a high statistics B?→D0π?sample(with K?cuts removed),the?nal selection shows an asymmetry of (?1.9±0.8)%.We quote a systematic uncertainty of±2.7%.

The second substantial systematic e?ect is that due to a possible CP-asymmetry in the peaking background.Although there is no physics ansatz that requires the peaking background to be asymmetric,it cannot be excluded.To get an estimate,we remark that if there is an asymmetry A peak,a systematic error on A CP is given by A peak×b

7PHYSICS RESULTS

We quote the?nal results:

A CP+=?0.09±0.20(stat.)±0.06(syst.)

A CP?=?0.33±0.34(stat.)±0.10(syst.)(+0.15±0.10)·(A CP??A CP+)(bias)

R CP+=+1.77±0.37(stat.)±0.12(syst.)

(bias)

R CP?=+0.76±0.29(stat.)±0.06(syst.)?0.04

?0.14

For the CP?measurements,the third uncertainty re?ects a possible bias due to interference e?ects in the?nal states withφandωresonances.

These can be compared with the preliminary results by the Belle collaboration[6]using95.8 B

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