b

Physics Letters B 625 (2005) 196–202

www.elsevier.com/locate/physlet

Measurement of branching fractions for the inclusiveCabibbo-favoredK∗0(892) and Cabibbo-suppressedK∗0(892)

decays of neutral and chargedD mesons

BES Collaboration

M. Ablikim a, J.Z. Baia, Y. Bank, J.G. Biana, X. Caia, J.F. Changa, H.F. Chenp,H.S. Chena, H.X. Chena, J.C. Chena, Jin Chena, Jun Cheng, M.L. Chena, Y.B. Chena,

S.P. Chib, Y.P. Chua, X.Z. Cuia, H.L. Daia, Y.S. Dair, Z.Y. Denga, L.Y. Donga,1,Q.F. Dongo, S.X. Dua, Z.Z. Dua, J. Fanga, S.S. Fangb, C.D. Fua, H.Y. Fua, C.S. Gaoa,

Y.N. Gaoo, M.Y. Gonga, W.X. Gonga, S.D. Gua, Y.N. Guoa, Y.Q. Guoa, K.L. Hea,M. Hel, X. Hea, Y.K. Henga, H.M. Hua, T. Hua, X.P. Huanga, X.T. Huangl, X.B. Jia,C.H. Jianga, X.S. Jianga, D.P. Jina, S. Jina, Y. Jina, Yi Jin a, Y.F. Laia, F. Li a, G. Li b,H.H. Li a, J. Li a, J.C. Lia, Q.J. Lia, R.Y. Li a, S.M. Li a, W.D. Li a, W.G. Li a, X.L. Li h,X.Q. Li j, Y.L. Li d, Y.F. Liangn, H.B. Liaof, C.X. Liu a, F. Liu f, Fang Liup, H.H. Liu a,

H.M. Liu a, J. Liuk, J.B. Liua, J.P. Liuq, R.G. Liua, Z.A. Liu a, Z.X. Liu a, F. Lua,G.R. Lue, H.J. Lup, J.G. Lua, C.L. Luoi, L.X. Luo d, X.L. Luo a, F.C. Mah, H.L. Maa,J.M. Maa, L.L. Ma a, Q.M. Maa, X.B. Mae, X.Y. Ma a, Z.P. Maoa, X.H. Mo a, J. Niea,

Z.D. Niea, H.P. Pengp, N.D. Qia, C.D. Qianm, H. Qini, J.F. Qiua, Z.Y. Rena, G. Ronga,L.Y. Shana, L. Shanga, D.L. Shena, X.Y. Shena, H.Y. Shenga, F. Shia, X. Shik,3,

H.S. Suna, J.F. Suna, S.S. Suna, Y.Z. Suna, Z.J. Suna, X. Tanga, N. Taop, Y.R. Tiano,G.L. Tonga, D.Y. Wanga, J.Z. Wanga, K. Wangp, L. Wanga, L.S. Wanga, M. Wanga,

P. Wanga, P.L. Wanga, S.Z. Wanga, W.F. Wanga,4, Y.F. Wanga, Z. Wanga, Z.Y. Wanga,Zhe Wanga, Zheng Wangb, C.L. Weia, D.H. Weia, N. Wua, Y.M. Wu a, X.M. Xia a,

X.X. Xie a, B. Xin h,2, G.F. Xua, H. Xua, S.T. Xuea, M.L. Yanp, F. Yangj, H.X. Yanga,J. Yangp, Y.X. Yangc, M. Yea, M.H. Yeb, Y.X. Ye p, L.H. Yi g, Z.Y. Yi a, C.S. Yua,G.W. Yua, C.Z. Yuana, J.M. Yuana, Y. Yuana, S.L. Zanga, Y. Zengg, Yu Zenga,B.X. Zhanga, B.Y. Zhanga, C.C. Zhanga, D.H. Zhanga, H.Y. Zhanga, J. Zhanga,J.W. Zhanga, J.Y. Zhanga, Q.J. Zhanga, S.Q. Zhanga, X.M. Zhanga, X.Y. Zhangl,Y.Y. Zhanga, Yiyun Zhangn, Z.P. Zhangp, Z.Q. Zhange, D.X. Zhaoa, J.B. Zhaoa,

J.W. Zhaoa, M.G. Zhaoj, P.P. Zhaoa, W.R. Zhaoa, X.J. Zhaoa, Y.B. Zhaoa,

0370-2693/$ – see front matter 2005 Elsevier B.V. All rights reserved.doi:10.1016/j.physletb.2005.08.013

BES Collaboration / Physics Letters B 625 (2005) 196–202 197

-ES-II

H.Q. Zhengk, J.P. Zhenga, L.S. Zhenga, Z.P. Zhenga, X.C. Zhonga, B.Q. Zhoua,G.M. Zhoua, L. Zhoua, N.F. Zhoua, K.J. Zhua, Q.M. Zhua, Y.C. Zhua, Y.S. Zhua,

Yingchun Zhua,5, Z.A. Zhua, B.A. Zhuanga, X.A. Zhuanga, B.S. Zoua

a Institute of High Energy Physics, Beijing 100049, PR Chinab China Center for Advanced Science and Technology (CCAST), Beijing 100080, PR China

c Guangxi Normal University, Guilin 541004, PR Chinad Guangxi University, Nanning 530004, PR China

e Henan Normal University, Xinxiang 453002, PR Chinaf Huazhong Normal University, Wuhan 430079, PR China

g Hunan University, Changsha 410082, PR Chinah Liaoning University, Shenyang 110036, PR China

i Nanjing Normal University, Nanjing 210097, PR Chinaj Nankai University, Tianjin 300071, PR Chinak Peking University, Beijing 100871, PR Chinal Shandong University, Jinan 250100, PR China

m Shanghai Jiaotong University, Shanghai 200030, PR Chinan Sichuan University, Chengdu 610064, PR Chinao Tsinghua University, Beijing 100084, PR China

p University of Science and Technology of China, Hefei 230026, PR Chinaq Wuhan University, Wuhan 430072, PR China

r Zhejiang University, Hangzhou 310028, PR China

Received 8 June 2005; accepted 5 August 2005

Available online 15 August 2005

Editor: M. Doser

Abstract

The branching fractions for the inclusive Cabibbo-favoredK∗0 and Cabibbo-suppressedK∗0 decays ofD mesons are measured based on a data sample of 33 pb−1 collected at and around the center-of-mass energy of 3.773 GeV with the Bdetector at the BEPC collider. The branching fractions for the decaysD+(0) → K∗0(892)X andD0 → K∗0(892)X are de-termined to be BF(D0 → K∗0X) = (8.7 ± 4.0 ± 1.2)%, BF(D+ → K∗0X) = (23.2 ± 4.5 ± 3.0)% and BF(D0 → K∗0X) =(2.8 ± 1.2 ± 0.4)%. An upper limit on the branching fraction at 90% C.L. for the decayD+ → K∗0(892)X is set to beBF(D+ → K∗0X) < 6.6%. 2005 Elsevier B.V. All rights reserved.

PACS:13.20.Fc; 13.25.Ft; 13.85.Ni; 14.40.Lb

60,

07,

.F-

l anns

onandgg

E-mail address:chenjc@mail.ihep.ac.cn(J.C. Chen).1 Current address: Iowa State University, Ames, IA 50011-31

USA.2 Current address: Purdue University, West Lafayette, IN 479

USA.3 Current address: Cornell University, Ithaca, NY 14853, USA4 Current address: Laboratoire de l’Accélératear Linéaire,

91898 Orsay, France.5 Current address: DESY, D-22607, Hamburg, Germany.

1. Introduction

AlthoughD mesons were found 29 years ago[1,2],the study of charm meson decay properties is stilinteresting field. Measurement of branching fractiofor the D meson decay modes containingK∗0(K∗0)in the final states can provide useful informatiabout the relative strength of the Cabibbo-favoredCabibbo-suppressedD decays. The total branchinfractions for the exclusiveD decay modes containin

198 BES Collaboration / Physics Letters B 625 (2005) 196–202

of-o-dn-for

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K∗0 are summed to be BF(D0 → K∗0X) = (8.1 ±0.8)% and BF(D+ → K∗0X) = (23.1 ± 2.0)% (X =any particles) with the known branching fractionsneutral and chargedD mesons[3]. The measurement of branching fractions for the inclusive Cabibbfavored decayD → K∗0X and Cabibbo-suppressedecayD → K∗0X cannot only serve as an indepedent check on the sum of the branching fractionsthe exclusiveD decay modes containingK∗0 mesonin the final states, which indicates the need to seafor new decay modes, but also provides valuable inmation in understanding the weak decay mechanThe knowledge of the inclusiveD meson decay properties will also help one to understandB decays.

This Letter reports the measurement of braning fractions for the inclusive Cabibbo-favored dcayD → K∗0X and Cabibbo-suppressed decayD →K∗0X of neutral and chargedD mesons using a double tag method described in Section3, based on ananalysis of about 33 pb−1 of data collected with theupgraded Beijing Spectrometer (BES-II) ine+e− an-nihilation at and around

√s = 3.773 GeV.

2. The Beijing spectrometer

BES is a conventional cylindrical magnetic detetor [4] operated at the Beijing Electron–Positron Clider (BEPC) [5]. BESII is the upgraded version othe BES detector[6]. A 12-layer vertex chamber (VCsurrounding the beam pipe provides trigger informtion. A forty-layer main drift chamber (MDC) locateoutside the VC performs trajectory and ionization eergy loss (dE/dx) measurement with a solid angcoverage of 85% of 4π for charged tracks. Momentum resolution ofσp/p = 1.7%

√1+ p2 (p in GeV/c)

and dE/dx resolution of 8.5% for Bhabha scattering electrons are obtained for the data taken at

√s =

3.773 GeV. An array of 48 scintillation counters surounds the MDC and measures the time of flight (TOof charged tracks with a resolution of about 200 psthe electrons. Surrounding the TOF is a 12-radiatilength, lead-gas barrel shower counter (BSC) operin limited streamer mode, which measures the egies of electrons and photons over 80% of the tosolid angle, and has an energy resolution ofσE/E =0.22/

√E (E in GeV), spatial resolutions ofσφ = 7.9

mrad andσZ = 2.3 cm for the electrons. Outside o

the BSC is a solenoidal magnet which provides a 0magnetic field in the central tracking region of the dtector. Three double-layer muon counters instrumthe magnet flux return, and serve to identify muowith momentum greater than 500 MeV/c. They cover68% of the total solid angle with longitudinal (tranverse) spatial resolution of 5 cm (3 cm). End-cap timof-flight and shower counters extend coverage toforward and backward regions. A Monte Carlo paage based on GEANT3 has been developed for BEdetector simulation and comparisons with data shthat the simulation is generally satisfactory[7].

3. Data analysis

3.1. Event selection

For each event it is required that at least 2 (butmore than 10) charged tracks are well reconstructethe MDC with good helix fits. All tracks, save thosfrom K0

S decays, must originate from the interactiregion, which requires that for a charged track, thetance of closest approach be less than 2 cm in thexy

plane, and less than 20 cm in thez direction. For theπ+ and π− from the K0

S decay, the secondary vetex position is required to be less than 8 cm inxy plane and within±20 cm in thez direction to theprimary interaction point. In addition, in order to otimize the momentum resolution and charged partidentification, a geometry cut|cosθ | � 0.85 (θ is thepolar angle of the track) is applied. For the chargparticle mass assignment, a combined confidencecalculated using thedE/dx and TOF measurementsrequired to be greater than 0.1% for the pion hypoth-esis. For the kaon identification, the confidence lefor the kaon hypothesis is required to be greater tthat for the pion hypothesis.

The π0 is reconstructed through the decayπ0 →γ γ . For theγ from π0 decay, the energy depositein the BSC is required to be greater than 70 Methe electromagnetic shower is required to start infirst 5 readout layers; and the angle between theγ andthe nearest charged track is required to be greater22◦.

3.2. Singly taggedD0 andD−

Around the center-of-mass energy of 3.773 Gthe ψ(3770) resonance is produced in electron–po

BES Collaboration / Physics Letters B 625 (2005) 196–202 199

pre-

h-

-

ein

vergych

ndi-

b-

an

c-

on. A

a-lti--

in-ersnd)eri-

ss

und

d

tron (e+e−) annihilation. Theψ(3770) lies just aboveopen charm pair production threshold and decaysdominantly intoDD pairs. If oneD meson is fully re-constructed (this is called a singly taggedD event), theotherD meson must exist on the recoil side. Througout the Letter, charge conjugation is implied.

For the analysis, singly taggedD events are reconstructed in three hadronicD0 decay modes (K+π−,K+π−π−π+, and K+π−π0) and in nineD− de-cay modes (K+π−π−, K0π−, K0K−, K+K−π−,K0π−π−π+, K0π−π0, K+π−π−π0, K+π+π−-π−π− and π+π−π−). The reconstruction for thsingly taggedD events is the same as that usedthe previous works[8,9].

In order to reduce the background and improthe momentum resolution, a center-of-mass eneconstraint kinematic fit (1C-fit) is imposed on eamKnπ (m = 0,1,2; n = 1,2,3,4) combination. Forthe singly taggedD decay modes with a neutral kaoor a neutral pion in the daughter particles, an adtional constraint kinematic fit for theK0

S → π+π− orπ0 → γ γ is also performed. The kinematic fit proability P(χ2) is required to be greater than 0.1%. Ifmore than one combination satisfies the criteria inevent, only the combination with the largestP(χ2) isretained.

Fig. 1 and Fig. 2 show the invariant mass spetra for mKnπ combinations in the singly taggedD0

andD− decay modes, which are calculated basedthe track momentum vectors from the kinematic fitmaximum likelihood fit to the mass spectrum withGaussian function for theD signal and a special background function (ARGUS background shape muplied by a polynomial function)[8] to describe backgrounds yields a total number of 7033± 193± 316singly taggedD0 events and 5321± 149± 160 singlytaggedD− events (as well as the numbers for thedividual decay channels). The errors on the numbof events are statistical (first) and systematic (secowhere the later is obtained by varying the parametzation of the background.

3.3. Doubly tagged events

3.3.1. Inclusive decayD → K∗0(K∗0)X

The inclusive decayD → K∗0X is reconstructedon the recoil side of the singly taggedD, where theK∗0 is reconstructed through its decay toK−π+. The

Fig. 1. Invariant mass spectra forKnπ (n = 1,2,3) combinations inthe singly taggedD0 decay modes: (a)K+π−, (b) K+π−π−π+and (c)K+π−π0.

Fig. 2. Invariant mass spectra formKnπ (m = 0,1,2,n = 1,2,3,4)combinations in the singly taggedD− decay modes: (a)K+π−π−,(b) K0π−, (c) K0K−, (d) K+K−π−, (e) K0π−π−π+, (f)K0π−π0, (g) K+π−π−π0, (h) K+π+π−π−π−, (i) π+π−π−and (j) sum of nine modes.

regions within a±3σMDwindow around the fittedD

masses in the invariant mass spectra formKnπ com-binations, as shown inFig. 1 andFig. 2, are definedas the singly taggedD signal regions (D tag region),whereσMD

are the standard deviations of the maspectra. Those outside a±4σMD

window around thefitted D masses are taken as the sideband backgrocontrol regions (D sideband). In the estimation of thenumber of background events in theD tag region, thenumber of the events in theD sideband is normalizeto the area of the fitted background in theD tag region.

200 BES Collaboration / Physics Letters B 625 (2005) 196–202

nay

dda

m-

per

ce-

ned

ned

a

theec-n

Fig. 3. Invariant mass spectra forK−π+ combinations observed othe recoil side of theD0 tags for study of the Cabibbo-favored decD0 → K∗0X: (a) the mass spectrum for the events with aD0 tag,(b) the normalized mass spectrum for theD0 sideband events.

Fig. 4. Invariant mass spectra forK−π+ combinations observeon the recoil side of theD− tags for study of the Cabibbo-favoredecayD+ → K∗0X: (a) the mass spectrum for the events withD− tag, (b) the normalized mass spectrum for theD− sidebandevents.

Due to particle misidentification and random cobination, the invariant mass forK−π+ combinationcould enter into mass spectra more than onceevent. To avoid this problem, only theK−π+ com-bination with the maximum product of the confidenlevels for theK hypothesis andπ hypothesis is retained in an event.

Fig. 5. Invariant mass spectra forK+π− combinations observed othe recoil side of theD0 tags for study of the Cabibbo-suppressdecayD0 → K∗0X: (a) the mass spectrum for the events with aD0

tag, (b) the normalized mass spectrum for theD0 sideband events.

Fig. 6. Invariant mass spectra forK+π− combinations observed othe recoil side of theD− tags for study of the Cabibbo-suppressdecayD+ → K∗0X: (a) the mass spectrum for the events withD− tag, (b) the normalized mass spectrum for theD− sidebandevents.

Invariant mass spectra forK−π+ combinations ob-served on the recoil side of theD0 tags (themKnπ

combinations) are shown inFig. 3 for study of theCabibbo-favored decayD0 → K∗0X, where (a) showsthe mass spectrum for the events with a taggedD0,and (b) shows the normalized mass spectrum ofD0 sideband events. By fitting the invariant mass sptra for K−π+ combinations with a Gaussian functio

BES Collaboration / Physics Letters B 625 (2005) 196–202 201

,

k-

, the

um

nd

traof

c-

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Table 1Number ofK∗0/K∗0 events observed on the recoil side of theD

tags, whereN andNb are the number ofK∗0/K∗0 events observedfrom the events in which the invariant masses of themKnπ com-binations are in theD signal region and in theD sideband regionrespectively.n is the number of the signal events forD decays

Decay mode N Nb n

D0 → K∗0X 188.5± 37.3 92.6± 23.5 95.9± 44.1D0 → K∗0X 30.8± 13.2 0.0± 0.1 30.8± 13.2

D+ → K∗0X 232.5± 30.9 43.4± 18.4 189.1± 36.0D+ → K∗0X 43.7± 17.6 31.4± 15.2 12.3± 23.3

for theK∗0 signal and a polynomial to describe bacground, the numbers of the observedK∗0 events areobtained to be 188.5 ± 37.3 and 92.6 ± 23.5 for thetagged and sideband events, respectively. In the fitmass and width ofK∗0 are fixed at 0.8961 GeV/c2

and 0.0507 GeV/c2 quoted from PDG[3], and the de-tector resolution is set to be 0.0078 GeV/c2, whichis obtained by fitting the invariant mass spectrfor K−π+ combinations from bothD0 andD+ de-cays. After subtracting the number of the backgrouevents, we obtain 95.9 ± 44.1 signal events for theD0 → K∗0X decay.

Similarly, Fig. 4 shows the invariant mass specfor K−π+ combinations selected on the recoil sideD− tags to study the Cabibbo-favored decayD+ →K∗0X. Fig. 5andFig. 6show the invariant mass spetra for K+π− combinations on the recoil side ofD0

andD− tags to study the Cabibbo-suppressed decD0 → K∗0X andD+ → K∗0X. With the same analysis procedure as above, the numbers of the obseK∗0/K∗0 events are obtained (Table 1). After subtract-ing the number of the background events, we ob189.1±36.0, 30.8±13.2 and 12.3±23.3 signal eventsfor D+ → K∗0X, D0 → K∗0X andD+ → K∗0X de-cays, respectively.

3.3.2. Efficiencies forD → K∗0(K∗0)X

The efficiencies for reconstruction of the inclusiK∗0 decays ofD mesons are estimated with the MonCarlo simulation. The Monte Carlo events are genated ase+e− → DD, whereD decays into the singlytaggedD modes andD decays intoK∗0X. The parti-cle trajectories are simulated with the GEANT3 basMonte Carlo simulation package of the BESII detec[7]. The average efficiencies are obtained by weiging the branching fractions ofD meson decays quote

from PDG[3] and the numbers of the singly taggD events. The efficiencies are 0.1575± 0.0015 for thedecayD0 → K∗0(K∗0)X and 0.1529±0.0021 for thedecayD+ → K∗0(K∗0)X.

4. Results

With the numbers of the observed signal evefor the decayD → K∗0X, the numbers of the singltaggedD mesons and the reconstruction efficiencthe branching fractions for the Cabibbo-favored deD → K∗0X are determined to be

(1)BF(D0 → K∗0X

) = (8.7± 4.0± 1.2)%

and

(2)BF(D+ → K∗0X

) = (23.2± 4.5± 3.0)%.

These results are consistent with those measurethe BES Collaboration based on the data taken√

s = 4.03 GeV[10].For the Cabibbo-suppressed decayD0 → K∗0X

the branching fraction is obtained to be

(3)BF(D0 → K∗0X

) = (2.8± 1.2± 0.4)%.

An upper limit on the branching fraction at 90% C.for the Cabibbo-suppressed decayD+ → K∗0X is setto be

(4)BF(D+ → K∗0X

)< 6.6%,

which includes the systematic uncertainty.If we treat the observed events as signal events

branching fraction for the Cabibbo-suppressed deD+ → K∗0X is

(5)BF(D+ → K∗0X

) = (1.5+2.9

−1.0 ± 0.2)%.

In the measured branching fractions, the firstror is statistical and second systematic. The systemerror arises from the uncertainties in particle idetification (∼1.0%) [8], in tracking (2.0% per track)in the numbers of the singly taggedD0 (∼4.5%)andD− (∼3.0%)[8], in background parameterizatio(∼12%), and in Monte Carlo statistics (0.16% forD0

and 0.31% forD+). These uncertainties are addedquadrature to obtain the total systematic error, whis 13.5% for theD0 decay and 13.0% for theD+ de-cay.

202 BES Collaboration / Physics Letters B 625 (2005) 196–202

er,ive

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orrtina525,No.erl-

os.alo.

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1.

alali-

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9th8),

5. Summary

Based on an analysis of about 33 pb−1 of data col-lected with the BES-II detector at the BEPC collidwe measured branching fractions for the inclusCabibbo-favored decayD → K∗0X and Cabibbo-suppressed decayD → K∗0X. The results are BF(D0

→ K∗0X) = (8.7±4.0±1.2)%, BF(D+ → K∗0X) =(23.2 ± 4.5 ± 3.0)% and BF(D0 → K∗0X) = (2.8 ±1.2 ± 0.4)%. We set an upper limit on the branchinfraction at 90% C.L. for the decayD+ → K∗0X to beBF(D+ → K∗0X) < 6.6%.

Acknowledgements

BES Collaboration thanks the staff of BEPC ftheir diligent efforts. This work is supported in paby the National Natural Science Foundation of Chunder contracts Nos. 10491300, 10225524, 10225the Chinese Academy of Sciences under contractKJ 95T-03, the 100 Talents Program of CAS undContract Nos. U-11, U-24, U-25, and the Know

edge Innovation Project of CAS under Contract NU-602, U-34 (IHEP); and by the National NaturScience Foundation of China under Contract N10175060 (USTC), and No. 10225522 (Tsinghua Uversity).

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