CLEO RESULTS ON B DECAY Cleo Collaboration B. Gittelman

To cite this version:

B. Gittelman. CLEO RESULTS ON 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

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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 , 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 , , 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 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 and therefore be- 1ieves the B meqon deca s weakly; b) The 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 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 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 associated with the T(4S). An attempt to salvage these models by sug- gesting the baryons might be 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 , 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) Momentum c) Upper Limit on a) 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 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 , there are 325 track combinations to be considered. One approach consists of attempting to reconstruct B and B in the same event without imposing overall momentum constraint. Then one is looking for a simultaneous peak at M = M-. Because of the large number of wrong combinations, good momentum resolu- tBon it r quired. Simple estimates indicate one needs 6p/p < 10-3 to obtain a signal with % lo0 BB decays. For this reason, we have been pursuing strategies in which we first search for events with a distinctive signature, and then attempt reconstruc- tion. We discuss two approaches, events containing Y's and events containing D's. We have searched for Y's in a sample of 13667 nb-' of data recorded at the peak of the T(4S). The Y's are recognized by their leptonic decay into e'e- or p+p-. At least one of the daughter leptons is identified to reduce the number of wrong combinations that have to be considered. Mass spectra of identified together with an oppositely charged track are shown in figure 2. In 2a, all oppositely charged tracks are considered, whereas in 2b, only tracks that produced a signal in the inner muon drift chambers are used. The dash-dot curve is the ex- pected background. Its shape is computed by combining the identified muon from one event with appropriate oppositely charged tracks from all other events. The back- ground curve is normalized to have the same area as the measured number of events. The dotted curves represent the expected signal for a branching fraction for B -." (Y + anything) of 1.9% in 2a and 1.4% in 2b. A similar analysis was made for the e+e- final states. We conclude that the branching fraction B + (Y + anything) is less than 1.4%.

30

- 3 $ 20 P 0 5 D *. 0 z - I! 2 2 2 0 5 f 2 I0 o 8 I

MrpQ.V /cal MII,,lG*YIca1 Figure 2 Mass spectrum of identified muons of momentum greater than 1.0 GeV/c with: a) a1 1 oppositely charged tracks b) oppositely charged muons identified in either the inner or outer muon chambers. B. Gittelman C3-113

We have searched for Po's in the same T(4S) data - A7 TI451 sample. The k'n-, k-n states were reconstructed. --- OFF T1451 To enhanc t e signal, a cut on the Fox Wolfram 25D parameteryl6! H IH < 0.3 was made. Only identi- fied kaons were2us?d and the Do momentum was re- stricted to be greater than 1 GeVIc. The kn mass plot is shown in Figure 3. One observes an en- hancement at 1.86 G~V/C~.There are 35 + 11 events in the peak. An analysis of continuum data recorded below the T(4S) gives 6.7 + 8.3 events for equivalent luminosity, thus proving the Do signal is coming from the BB decqys. Preliminary calculation gives 6+3 Do's per BB decay. One ex- pects between 1 and 2 depending upon the amount of D* production in B decay. This result is consis- tent with the conclusions we have drawn from the lepton spectra. 1.80 2 00 2 2C Summary IA..IG~YIC' 1 -. General ~ro~ertiesof B meson decav have been Figure 3 measured. the' data is consistent wi ti the Standard from decay SU(2) X U(1) Model and inconsistent with other suggested models. Our measured lepton momentum spectrum indicates a B meson usually decays to . We have also shown the first direct evi- dence for D mesons in final states of B decay. References 1. This energy is quoted in CESR units. A report submitted to the conference, "High Precision Measurement of the T Meson Mass", A.S. Artamonov, et al, Preprint 82-94 Institute of , Novosibirsk, USSR, gives a new value for the T(1S) mass. Using this value, we obtain 10.579 GeV for the ~(4s)mass. 2. The CLEO Detector, D. Andrews et al, Cornell Preprint CLNS 821538. Submitted to Nuclear Instruments and ~ethods'. 3. Semileptonic Decay of B Mesons, CLEO Collaboration. Submitted to Physical Review+. ++ 4. Charged Kaon and Production at the T Resonances and Nearby Continuum . 5. Neutral Kaon and Lambda Production in the Upsilon Region*'. 6. M.S. Alam, et al, Phys. Rev. Lett. 49, 357 (1982). 7. C. Quigg and J.L. Rosner, Phys. ~evr~,1532 (1979).++ 8. An Upper Limit on B Meson Decay Via the Neutral Current . 9. Proof that b Quark Decay is not ~xotic'. 10.V. Barger and S. Pakvasa, Phys. Lett. 81, 195 (1979). 11.G.L. Kane and M.E. Peskin, Nucl. Phys. B 195, 29 (1982). 12.H. Georgi and M. Machacek, Phys. Rev. LE'fE-", 1639 (1979). 13. E. Derman, Phys. Rev. D, 319 (1979) ; R.N. tbhaptra, Phys. Lett. 82, 101 (1979); H. Georgi and S.L. Glashow, Nucl. Phys. B,173 (1980). 14.limits on (b+~)/(b-tc) in Semileptonic B ~ecay++. 15.5. Levei 1le, Laboratory of Nuclear Studies Report CLNS 511505 (1981 ) , Cornel 1 University, Ithaca, NY 14853 USA. 16.G.C. Fox and S. Wolfram, Phys. Rev. Lett. -41, 1581 (1978). + Preprint available from the CLEO Preprint Secretary. ++ Report contained in "CLEO Contributions to the XXI International Conference on High Energy Physics", Paris - July, 1982; CLEO 82-06. CLEO Preprint Secretary, Depart- ment of Physics, University of Rochester, Rochester, NY 14627 USA.