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CLEO RESULTS on B MESON DECAY Cleo Collaboration B CLEO RESULTS ON B MESON DECAY Cleo Collaboration B. Gittelman To cite this version: B. Gittelman. CLEO RESULTS ON B MESON DECAY Cleo Collaboration. Journal de Physique Colloques, 1982, 43 (C3), pp.C3-110-C3-113. 10.1051/jphyscol:1982325. jpa-00221878 HAL Id: jpa-00221878 https://hal.archives-ouvertes.fr/jpa-00221878 Submitted on 1 Jan 1982 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. JOURNAL DE PHYSIQUE ColZoque C3, suppZe'ment au no 12, Tome 43, de'cembre 1982 page C3- 1 10 CLEO RESULTS ON B MESON DECAY CLEO Collaboration Presented by B. Gittelman Department of Physics, Cornell University, Ithaca, NY 14853, U.S.A. Introduction The T(4S) state at a mass of 10.548 G~v(')is the fourth member of the-T family. It has a measured width of T = 20 MeV and is thought to decay into a B and B meson. The cross section at the peak for e"e- + T(4S) is 1.0 nb. The resonance sits on top of a 2.5 nb continuum cross section. Properties of the T(4S), or equivalently, BB mesons, are inferred from data recorded at the T(4S) peak after making an appropriate subtract using data from nearby energies below the resonance. With the CLEO DetectodP1, we have measured some general properties of the T(45) decays: the branching fraction i o ept~ns'~);the inclusive y d of charged and neutral kaons, protons, and lambda~Y~*~j;the charged mu1 tip1icityipj ; and the average charged energy fraction. These results may be considered independent of explicit models of B decay. In this note, we report on the theoretical implications of these measure- ments. B meson decays are found to be consistent with the standard SU(2) x U(l) model. Other models are ruled out by the data. We present an upper limit on the amplitude for b + u relative to b + c. A program for reconstructing B mesons is discussed. Preliminary results of this program have yielded an upper limit for the branching fraction B + (Y + anything) and the first direct evidence for B + Do. Models of b Quark Decay In the Standard SU(2) X U(1) Model, the b quark is the Q = -1/3 member of the third generation of weak isodoublets. It mixes with the s and the d quark and therefore, can decay through the charged current into anu or c quark. Current data support this model to the extent: a) One has observed leptons and therefore be- 1ieves the B meqon deca s weakly; b) The lepton branching fractions, Br(B + evx) = ~r(~+~vx)=0.124+0.025(37 , are approxi a ely equal to values one calculates for free quark decay ithin the Standard Modelbj; c) There are %1.4 kaons in the final state of a B decayY4y5). Theoretical estimates suggest b-x should dominate and the strong kaon yield is consistent with this. However, since no direct evidence has been presented for the existence of the Q = 2/3 member of the isodoublet, the t quark, a number of alternative models have been suggested. Our data already permit us to rule out most of these. We present a brief description of four types of models and the main reason for their rejection. The reader will find 8,gyt-e complete discussion of the reasons in CLEO reports submitted to the conference( . 1. The b quark is stable. This we rule out immediately, since we observe many particles in the T(4S) final decay products. 2. The b uark is in a weak left handed isosinglet but mixes with the s and d quai-ks?lO). Hence it can decay through the usual charged current. Since there is no t quark, there is no+ mechanism - to suppress the neutral current and one expects to observe b -+ qZO -+ qe e or q2u-. M. Peskin and G. Kane have put a lower limit on the branching fraction for these decay modes (ll). They find Br(B + 1'1-x)/ Br(B -+ 1-vx) must be greater than 118. Unlike sign dilepton events can arise from several sources. However, a non zero signal in the quantity + (Nee + Nvu - New - Nve), where N is the number of events containing an e and a ev p-, etc, is evidence of a neutral current. We find no signal in this quantity Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982325 5. Gittelman C3-111 and are able to set a 90% confidence upper limit of 0.09 for the ratio of branching fractions(8). 3. The b quark always deca s to a lepton plus a pair of light antiquarks (blqi). Theories of this class(") are disproved primarily because we do not observe baryons associated with the T(4S). An attempt to salvage these models by sug- gesting the baryons might be neutrons is ruled out by the observed charged energy fraction. 4. The b quark always decays to two leptons and a quark, (b + llq)(13). This hypothesis is unable to account simultane usly for the measured lepton branching fractions and the charged energy fractionP9). An Upper Limit on Br(b + u)/Br(b + c) Within the context of the Standard Model, one wants to know the relative strength of the coupling of b to u versus b to c. Data on the kaon yield from the T(4S) and the lepton momentum spectrum indicate that the b quark decays primarily to the c quark. We have obtained limits on the magnitude of b + uW- decays(495914). The kaon yields are given in table 1. To reduce systematic errors, we consider the ratio* p, of kaons per BE event to kaons per continuum event. The mean value of p is (p- + p0)/2 =((1.76 k 0.16) + (1.39 k 0.24))/2 = 1.58 k 0.15. From a Monte Carlo calculation based on the standard model of b decay(15), we expect p = 1.8 + 0.1 for b + c and p = 0.95 + 0.1 for b -t u. Assuming the branching fractions Br(b + u) + Br(b + c) = 1, we can write 1.58 ? 0.15 = (0.95 + O.l)Br(b + u) + (1.8 k 0.1) Br(b + c). Solving for the ratio, R = Br(b + u)/Br(b + c),we obtain the 1 Std Devia- tion limits, 0.09 < R < 0.79. Table 1 - Kaon Yields from T(4S) and Nearby Continuum K+ + K- KO t P1 (event-' ) (event ) T(4S) = BB 1.58+0.13 1.24k0.21 Continuum 0.90k0.04 0.89k0.04 A more restrictive limit on R is derived from the lepton momentum spectra (14) . The measured spectra are shown in figure 1. The solid curves are the expected dis- tribution for B + 1vD and B + IvD* with equal frequency. The two dashed curves are calculations for B -+ lvx where x is a hadronic system having mass of 0.14 and 1.0 GeV. These correspond to typical hadronic masses one expects for b + lvu decays. We have obtained an upper limit to the branching fraction ratio, R, by fitting the measured spectra with the functional form, F(p) = A (0.5 f(p,MD) + 0.5 f(p,MD,) + R f(p,M )), where f(p,M ) is a theoretical spectrum for B -+ lvx, M is the mass of the hadl(onic system, an6 A is a normalization constant. Fits were hiade for A and R Figure 1 b) Muon Momentum c) Upper Limit on a) Electron Momentum Spectrum Spectrum Br(b-w)/Br(k) vs Mass of the 12- Hadronic Spectrum for budecays. B- evO(5O%l O 1'0 20 3 0 Pm,.(GeV/Cl P,- P,- (GeVlcl UlvlOtYl FOR 0-lev JOURNAL DE PHYSIQUE at discrete values of Mx between 0.14 and 1.5 GeV. We find no evidence for any b+u component tie, all fits were consistent with R=O). The 90% confidence upper limit on R is plotted in figure lc. We conclude, if the mean mass M, in B+lvx for bw is less than 1.0 GeV, the branching fraction ratio, Ur(h)/Er(~m)is less tr~an10%. Using the spectator model, we compute the phase space factor for the branching fraction, Br(h)lBr(b-.c)= 2.5 x 1V v I*, and obtain a limit on the matrix elements /v~~/v~1 < 0.2 (90% cok~Jence%vel). Reconstruction of B Mesons Reconstruction of B mesons from the final charged particle tracks is needed to provide a precise measurement of the B mass. To reconstruct B mesons at the ~(4s)is difficult. Since B and B are produced simultaneously and since their momentum is low, their decay products do not separate in phase space. Hence there is no way to distinguish which track to associate with B and which with B. The average charged multiplicity of ~(4s)final states is 11.5. Hence, one must consider many combina- tions in associating tracks with B and B. For example, for a final state having 10 charged tracks and no photons, there are 325 track combinations to be considered.
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