Observation of Exclusive barB -- D() K- Decays
a r X i v :h e p -e x /0112033v 3 19 M a r 2002
CLNS 01-1772CLEO 01-25
Observation of Exclusive ˉB
→D (?)K ??Decays CLEO Collaboration
(December 11,2001)
Abstract
We report the ?rst observation of the exclusive decays ˉB
→D (?)K ??,using 9.66×106B
R.Mahapatra,1H.N.Nelson,1R.A.Briere,2G.P.Chen,2T.Ferguson,2G.Tatishvili,2
H.Vogel,2N.E.Adam,3J.P.Alexander,3C.Bebek,3K.Berkelman,3F.Blanc,3
V.Boisvert,3D.G.Cassel,3P.S.Drell,3J.E.Duboscq,3K.M.Ecklund,3R.Ehrlich,3 L.Gibbons,3B.Gittelman,3S.W.Gray,3D.L.Hartill,3B.K.Heltsley,3L.Hsu,3
C.D.Jones,3J.Kandaswamy,3D.L.Kreinick,3A.Magerkurth,3H.Mahlke-Kr¨u ger,3 T.O.Meyer,3N.B.Mistry,3E.Nordberg,3M.Palmer,3J.R.Patterson,3D.Peterson,3 J.Pivarski,3D.Riley,3A.J.Sado?,3H.Schwartho?,3M.R.Shepherd,3J.G.Thayer,3
D.Urner,3B.Valant-Spaight,3G.Viehhauser,3A.Warburton,3M.Weinberger,3
S.B.Athar,4P.Avery,4H.Stoeck,4J.Yelton,4G.Brandenburg,5A.Ershov,5
D.Y.-J.Kim,5R.Wilson,5K.Benslama,6B.I.Eisenstein,6J.Ernst,6G.D.Gollin,6 R.M.Hans,6I.Karliner,6N.Lowrey,6M.A.Marsh,6C.Plager,6C.Sedlack,6M.Selen,6 J.J.Thaler,6J.Williams,6K.W.Edwards,7R.Ammar,8D.Besson,8X.Zhao,8 S.Anderson,9V.V.Frolov,9Y.Kubota,9S.J.Lee,9S.Z.Li,9R.Poling,9A.Smith,9
C.J.Stepaniak,9J.Urheim,9S.Ahmed,10M.S.Alam,10L.Jian,10M.Saleem,10
F.Wappler,10E.Eckhart,11K.K.Gan,11C.Gwon,11T.Hart,11K.Honscheid,11
D.Hufnagel,11H.Kagan,11R.Kass,11T.K.Pedlar,11J.B.Thayer,11
E.von Toerne,11 T.Wilksen,11M.M.Zoeller,11H.Muramatsu,12S.J.Richichi,12H.Severini,12P.Skubic,12 S.A.Dytman,13S.Nam,13V.Savinov,13S.Chen,14J.W.Hinson,14J.Lee,https://www.wendangku.net/doc/2616591455.html,ler,14 V.Pavlunin,14E.I.Shibata,14I.P.J.Shipsey,14D.Cronin-Hennessy,15A.L.Lyon,15
C.S.Park,15W.Park,15E.H.Thorndike,15T.E.Coan,16Y.S.Gao,16F.Liu,16
Y.Maravin,16I.Narsky,16R.Stroynowski,16J.Ye,16M.Artuso,17C.Boulahouache,17 K.Bukin,17E.Dambasuren,17G.C.Moneti,17R.Mountain,17T.Skwarnicki,17S.Stone,17 J.C.Wang,17A.H.Mahmood,18S.E.Csorna,19I.Danko,19Z.Xu,19G.Bonvicini,20 D.Cinabro,20M.Dubrovin,20S.McGee,20A.Bornheim,21E.Lipeles,21S.P.Pappas,21
A.Shapiro,21W.M.Sun,21A.J.Weinstein,21G.Masek,22and H.P.Paar22
1University of California,Santa Barbara,California93106
2Carnegie Mellon University,Pittsburgh,Pennsylvania15213
3Cornell University,Ithaca,New York14853
4University of Florida,Gainesville,Florida32611
5Harvard University,Cambridge,Massachusetts02138
6University of Illinois,Urbana-Champaign,Illinois61801
7Carleton University,Ottawa,Ontario,Canada K1S5B6
and the Institute of Particle Physics,Canada M5S1A7
8University of Kansas,Lawrence,Kansas66045
9University of Minnesota,Minneapolis,Minnesota55455
10State University of New York at Albany,Albany,New York12222
11Ohio State University,Columbus,Ohio43210
12University of Oklahoma,Norman,Oklahoma73019
13University of Pittsburgh,Pittsburgh,Pennsylvania15260
14Purdue University,West Lafayette,Indiana47907
15University of Rochester,Rochester,New York14627
16Southern Methodist University,Dallas,Texas75275
17Syracuse University,Syracuse,New York13244
18University of Texas-Pan American,Edinburg,Texas78539
19Vanderbilt University,Nashville,Tennessee37235
20Wayne State University,Detroit,Michigan48202
21California Institute of Technology,Pasadena,California91125 22University of California,San Diego,La Jolla,California92093
The study of CP violation in B mesons provides a decisive test of the CP violation mechanism in the Standard Model(SM).In the SM,CP violation is the consequence of the complex phase in the Cabibbo-Kobayashi-Maskawa(CKM)quark-mixing matrix[1]. Comprehensive tests of the SM predictions on CP violation require precision measurements of the three sides and three angles of the CKM unitary triangle[2].The angleγcan be measured usingˉB→D(?)K(?)decays[2,3].The decay B?→D0K?was?rst observed at CLEO[4]and con?rmed by BELLE[5].In this Letter,we report the?rst observation of the exclusive hadronic B decaysˉB→D(?)K??.Charge-conjugate modes are implied throughout this Letter.
The data were collected with two con?gurations(CLEO II[6]and CLEO II.V[7])of the CLEO detector at the Cornell Electron Storage Ring(CESR).The data consist of9.13 fb?1taken at theΥ(4S),which corresponds to9.66×106BˉB pairs,and4.35fb?1taken below B
mass of the candidate which is de?ned as M B≡
M B (GeV)
E v e n t s / 2 M e V
M B (GeV)
E v e n t s / 2 M e V
M B (GeV)
E v e n t s / 2 M e V
M B (GeV)
E v e n t s / 2 M e V
FIG.1.The beam-constrained mass distributions for ˉB
→D (?)K ??decays with all sub-modes combined.The histograms show the data,the solid lines represent the overall ?t to the data,and the dashed lines represent the ?tted backgrounds under the peaks.
combinations in the continuum sample,and no enhancement is observed in the signal region.
To estimate the detection e?ciencies,we generated ˉB
→D (?)K ??Monte Carlo events and simulated the CLEO detector response with GEANT [13].Simulated events for the CLEO II and II.V con?gurations were processed in the same manner as the data.The resulting detection e?ciencies,which are listed in Table I,do not include the D (?)or K ??
decay branching fractions [9].For the ˉB
→D ?K ??decays,as we do not know the polar-ization of the two vector mesons,we generated both 00and 11helicity states for our Monte Carlo signal events to calculate the e?ciencies as shown in Tables I.
Systematic errors from event selection include uncertainties in dE/dx ,the Dalitz weight cut for D 0→K ?π+π0and Monte Carlo statistics.To estimate the e?ects of the π0veto and the E γ>100MeV requirement for the photon candidates in D ?0→D 0γdecays,we change the π0veto interval by 1σand the energy cut value by ±10MeV respectively,and take the di?erence in the e?ciency-corrected yields as the systematic error.The cross-feed
rates between ˉB
→D ?0K ??,where D ?0→D 0π0and D ?0→D 0γ,are less than 1.5%.We also use tighter and looser requirements of:1σ/3σfor the D (?)mass cut,50MeV/100MeV
TABLE I.Results for theˉB→D(?)K??decay modes with statistical errors only.ForˉB→D?K??,the two e?ciencies correspond to the00and11helicity states,respectively.The statistical signi?cance of the overall signal for each mode is given in parentheses.
Decay Mode E?ciency(%)Yield B(×10?4) B?→D0K??30.5±8.3(6.0σ)6.1±1.6
ˉB0→D?+(D0(K?π+)π+
s )K??14.9,17.10.8±1.10.9±1.3
0.8±1.1
ˉB0→D?+(D0(K?π+π0)π+
s )K?? 4.7,5.54.3±2.34.5±2.4
3.8±2.0
ˉB0→D?+(D0(K?π+π+π?)π+
s )K?? 6.5,8.15.5±2.57.5±3.4
6.1±2.8
B?→D?0(D0(K?π+)π0)K?? 6.7,8.0?0.12±0.07?0.3±0.2
?0.3±0.2 B?→D?0(D0(K?π+π0)π0)K?? 2.3,2.63.6±2.08.4±4.7
7.5±4.1 B?→D?0(D0(K?π+π+π?)π0)K?? 3.5,4.40.8±1.52.3±4.3
1.8±3.4 B?→D?0(D0(K?π+)γ)K?? 6.0,6.9
2.9±1.715.0±8.8
13.0±7.6 B?→D?0(D0(K?π+π0)γ)K?? 1.9,2.02.7±1.712.4±7.8
11.8±7.4 B?→D?0(D0(K?π+π+π?)γ)K?? 3.5,3.76.0±2.727.2±12.3
25.7±11.6
?nal state,we take the equally-weighted average of the two branching ratios,corresponding to the00and11helicity states from Table I,as the central value,and the di?erences as a systematic error.These di?erences are small compared to the statistical errors.
We have observed signi?cant signals in the exclusiveˉB→D(?)K??decay decays.The measured branching ratios are:
B(B?→D0K??)=(6.1±1.6±1.7)×10?4,
B(ˉB0→D+K??)=(3.7±1.5±1.0)×10?4,
B(ˉB0→D?+K??)=(3.8±1.3±0.8)×10?4,
B(B?→D?0K??)=(7.7±2.2±2.6)×10?4.
The errors shown are statistical and systematic,respectively.
With the assumption of the validity of factorization,SU(3)?avor symmetry relates the Cabibbo-suppressed decaysˉB→D(?)K??to the Cabibbo-favored onesˉB→D(?)ρ?by B(ˉB→D(?)K??)
V ud 2
f K??
B(ˉB→D(?)ρ?)are(4.6±1.8)%,(4.7±2.4)%,(5.6±3.6)%and(5.0±2.4)%respectively,
which are consistent with naive theoretical predictions within the errors[14].The branching ratios forˉB→D(?)ρ?decays are taken from PDG2000[9].Our results B(ˉB0→D(?)+K??) are in good agreement with the theoretic predictions within the errors[15].The rates for ˉB→D(?)K??suggest that these decays could provide a measurement of the angleγin the
unitary triangle using the color-allowed decays in the near future[16].
ACKNOWLEDGMENTS
We gratefully acknowledge the e?ort of the CESR sta?in providing us with excellent luminosity and running conditions.This work was supported by the National Science Foun-dation,the U.S.Department of Energy,the Research Corporation,and the Texas Advanced Research Program.
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