We review recent experimental results on hadronic decays and lifetimes of
hadrons containing b and c quarks. We discuss charm counting and the
semileptonic branching fraction in B decays, the color suppressed amplitude in
B and D decay, and the search for gluonic penguins in B decay.Comment: To appear in the Proceedings of the 1996 Warsaw ICHEP Conferenc

Browder, T. E.

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We review recent experimental results on hadronic decays and lifetimes of hadrons containing b and c quarks. We discuss charm counting and the semileptonic branching fraction in B decays, the color suppressed amplitude in B and D decay, and the search for gluonic penguins in B decay

Browder, T E

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Hadronic Decays and Lifetimes of B and D MesonsT.E. BrowderUniversity of Hawaii at Manoa, Honolulu, HI 96822, U.S.A.University of Hawaii Preprint UH-511-857-96(To appear in the Proceedings of the 1996 Warsaw ICHEP Conference)We review recent experimental results on hadronic decays and lifetimes of hadrons containing b and c quarks.1We discuss charm counting and the semileptonic branching fraction in B decays, the color suppressed amplitudein B and D decay, and the search for gluonic penguins in B decay.1 Charm counting and the semileptonicbranching fraction1.1 The Experimental ObservationsA complete picture of inclusive B decay is be-ginning to emerge from recent measurements byCLEO II and the LEP experiments. These mea-surements can be used to address the question ofwhether the hadronic decay of the B meson is com-patible with its semileptonic branching fraction.Three facts emerge from the experimental ex-amination of inclusive B decay:nc= 1:15 0:05where ncis the number of charm quarks pro-duced per B decay taking an average of AR-GUS, CLEO 1.5, and CLEO II results and usingB(D0! K +) = (3:76 0:15%).B(B ! X`) = 10:23 0:39%This value is the average of the CLEO and ARGUSmodel independent measurements using dileptons.The third quantity is calculated from the inclusiveB ! Ds, B ! (cc)X , and B ! cbranchingfractions,B(b! ccs) = 0:158 0:028%:It is determined assuming no contribution from Dproduction, an assumption which can be checkedusing data.1.2 Theoretical InterpretationIn the usual parton model, it is dicult to accomo-date a low semileptonic branching fraction unlessthe hadronic width of the B meson is increased.3The explanations for the semileptonic branch-ing fraction which have been proposed can be for-mulated by expressing the hadronic width of theB meson in terms of three components: hadronic(b) =  (b! ccs)+ (b! cud)+ (b! s g):If the semileptonic branching fraction is to be re-duced to the observed level, then one of these com-ponents must be enhanced.A large number of explanations have been pro-posed in the last few years. These explanationscan be logically classied as follows:1. An enhancement of b ! ccs due to largeQCD corrections or the breakdown of localduality.4; 5; 6; 72. An enhancement of b ! cud due to non-perturbative eects.8; 9; 10; 113. An enhancement of b! s g or b! d g fromNew Physics.12; 13; 144. The cocktail solution: For example, if boththe b ! ccs and the b ! cud mechanismsare increased, this could suce to explainthe inclusive observations.5. There might also be a systematic experimen-tal problem in the determination of eithernc, B(b! ccs), or B(B ! X`).151.3 Other experimental cluesInclusive charm particle-lepton correlations can beused to probe the B decay mechanism and givefurther insight into this problem. High momentumleptons are used p`> 1:4 GeV to tag the avor of1the B. The angular correlation between the mesonand the lepton is then employed to select eventsin which the tagging lepton and meson are fromdierent Bs.For example, the sign of c-lepton correlationsdistinguishes between the b! cud and the b! ccsmechanisms. Similiarly, examination of Ds-leptoncorrelations shows that most Dsmesons originatefrom b ! ccs rather than from b ! cud with ssquark popping at the lower vertex. The same ex-perimental technique can also be applied to D-lepton correlations.The conventional b ! cud mechanism whichwas previously assumed to be responsible for allD production in B decay will give D   `+cor-relations. If a signicant fraction of D mesonsarise from b! ccs with light quark popping at theupper vertex. This new mechanism proposed byBuchalla, Dunietz, and Yamamoto will giveD ` correlations.5Preliminary results of this study have beenpresented by CLEO II which nds,  (B !D X)= (B !DX) = 0:107  0:029  0:018.16This implies a new contribution to the b ! ccswidthB(B ! DX) = 0:081 0:026:ALEPH nds evidence for B ! D0D0X +D0DX decays with a substantial branching frac-tion of 12:8  2:7  2:6%.17DELPHI reports theobservation of B ! D+D X decays with abranching fraction of 1:0  0:2  0:3%.19SinceCLEO has set upper limits on the Cabibbo sup-pressed exclusive decay modes B ! DD andB ! DDin the 10 3range,20this implies thatthe signals observed by ALEPH and DELPHI in-volve the production of a pair ofD mesons and ad-ditional particles. The rate observed by ALEPHis consistent with the rate of wrong sign D-leptoncorrelation reported by CLEO. It is possible thatthese channels are actually resonant modes of theform B ! DDsdecays, where the p-wave Dsorradially excited D0sdecays toD()K.We can now recalculateB(b! ccs) = 0:239 0:038;which would suggest a larger charm yield (nc1:24). This supports hypothesis (1), large QCDcorrections in b ! ccs. BUT the charm yield ncas computed in the usual way is unchanged. TheB ! DDK source was properly accounted for inthe computation of nc. This suggests that the ex-perimental situation is still problematic. Is therean error in the normalization B(D0! K +) oris there still room for enhanced B(b! cud) ?We note that ALEPH has recently reporteda value for ncin Z ! bb18. They nd nZc=1:230 0:036 0:038 0:053. The rate of Dsandcproduction is signicantly higher than what isobserved at the (4S). It is not clear whether thequantity being measured is the same as ncat the(4S), which would be the case if the spectatormodel holds and if the contribution of Bsand bcould be neglected. OPAL has reported a some-what lower value of nc.There are other implications of these obser-vations. A B decay mechanism with a O(10%)branching fraction has been found which was notpreviously included in the CLEO or LEP MonteCarlo simulations of B decay. This may have con-sequences for other analyses of particle-lepton cor-relations. For example, CLEO has re-examinedthe model independent dilepton measurement ofB(B ! X`). Due to the lepton threshold of 0.6GeV and the soft spectrum of leptons, that mea-surement is fortuitously unchanged.2 The sign of the color suppressed ampli-tude and lifetimesThe sign and magnitude of the color suppressedamplitude can be determined using several classesof decay modes in charm and bottom mesons.The numerical determination assumes factoriza-tion and uses form factors from various phen-emonological models.For D decay one uses exclusive modes such asD ! K, D ! K etc., and obtainsa1= 1:10 0:03; a2=  0:50 0:03The destructive interference observed in two bodyD+decays leads to the D+-D0lifetime dierence.For B decay, one can nd the magnitude ofja1j from the branching fractions for the decaymodesB0! D()+ ,B0! D+() . Thisgives ja1j = 1:06  0:03  0:06. One can also ex-tract ja1j from measurements of branching frac-tions B ! D+;(0)D() s. The magnitude ja2j canbe determined from the branching fractions forB !  K(). This yields ja2j = 0:23 0:01 0:01.2The value of a2=a1can be found by comparingB decays where both the external and spectatordiagrams contribute toB0decays where only theexternal spectator decays contribute. The modelof Neubert et al. predicts the following ratios:R1=B(B ! D0 )B(B0! D+ )= (1 + 1:23a2=a1)2(1)R2=B(B ! D0 )B(B0! D+ )= (1 + 0:66a2=a1)2(2)R3=B(B ! D0 )B(B0! D+ )= (1 + 1:29a2=a1)2(3)R4=B(B ! D0 )B(B0! D+ ) (1 + 0:75a2=a1)2(4)Using the latest branching fractions, we nda2=a1= 0:26 0:05 0:09;where the second error is due to the uncer-tainty ( 20%) in the relative production of B+and B0mesons at the (4S). This is consis-tent with ja2j/ja1j where ja2j is computed fromB !  modes and ja1j is computed fromB0!D();D() modes.If the constructive interference which is ob-served in these B decays is present in all B decays, then we expect a signicant B -B0life-time dierence ( B< B0), of order 15   20%.This is only marginally consistent with experimen-tal measurements of lifetimes; the world averagecomputed in our review1isB =B0= 1:00 0:05:It is possible that the hadronicB decays thathave been observed so far are atypical. The re-maining higher multiplicity B decays could havedestructive interference or no interference. Or per-haps there is a mechanism which also enhances theB0width to compensate for the increase in theB width and which maintains the B+=B0life-time ratio near unity. Such a mechanism would berelevant to the charm counting and semileptonicbranching fraction problem. In either case, therewill be experimental consequences in the patternof hadronic B branching fractions.3 The search for the gluonic penguinIt is important to measure the size of A(b! s g),the amplitude for the gluonic penguin, in order tointerpret the CP violating asymmetries which willbe observed at future facilities. Gluonic penguinmodes will also be used to search for direct CPviolation.CLEO-II has observed a signal in the sum ofB0! K+ andB0! + with a branch-ing fraction of (1:8+0:6+0:2 0:5 0:3)  10 5and for theindividual modes B(B0! + ) < 2:0  10 5,B(B0! K+ ) < 1:7  10 5. Similiar resultswith consistent branching fractions have been re-ported by DELPHI21and ALEPH22. CLEO-II hasalso observed a signal in the sum of B ! K !and B !  !.23The combined branching frac-tion is (2:81:10:5)10 5. In all of these cases,due to the paucity of events and the diculty ofdistinguishing high momentum kaons and pions,the conclusion is that either b ! u or b ! s gdecays or a combination of the two has been ob-served.Another approach using quasi-inclusive de-cays is described in a recent CLEO contribution.24At the (4S), two body decays from b! s g canbe distinguished from b ! c decays by examina-tion of the inclusive particle momentum spectrum;the b ! s g decays populate a region beyond thekinematic limit for b! c. This approach has beenapplied to inclusive 0, Ks, and  production.A search for inclusive signatures of b ! sgluon rather than exclusive signatures has twopossible advantages. The inclusive rate may becalculable from rst principles and is expected tobe at least an order of magnitude larger than therate for any exclusive channel. For example, thebranching fraction for b! sqq (where q = u; d; s)is O(1%)25,26and the branching fraction for the in-clusive process b! sss is expected to be  0:23%in the Standard Model26, while low multiplicitydecay modes such asB0! KsorB0! K +are expected to have branching fractions of order10 5. The disadvantage of employing an inclusivemethod is the severe continuum background thatmust be subtracted or suppressed.The decay B ! 0Xs, where Xsdenotes ameson containing an s quark, is dominated by thegluonic penguins, b ! sgg! ss, g! uu org! dd. The decay B ! KsX , where X denotesa meson which contains no s quark, arises from a3similiar gluonic penguin, b! sg! sdd.An analogous search for b ! sg, g! sswas carried out by CLEO using high momentum production29. In the search for high momentum production, limits were obtained using two com-plementary techniques. A purely inclusive tech-nique with shape cuts gave a limit B(B ! Xs) <2:210 4for 2:0 < p< 2:6 GeV. Using the B re-construction technique, in which combinations ofthe  candidate, a kaon, and up to 4 pions were re-quired to be consistent with a B candidate, gave alimit of B(B ! Xs) < 1:1 10 4for MXs< 2:0GeV, corresponding to p> 2:1 GeV. These re-sults can be compared to the Standard Model cal-culation of Deshpande et al.27, which predicts thatthe branching fraction for this process should liein the range (0:6   2:0)  10 4and that 90% ofthe  mesons from this mechanism will lie in therange of the experimental search. Ciuchini et al.28predict a branching fraction for B(B ! Xs) inthe range (1:10:9)10 4. One sees that the sen-sitivity of the inclusive method is nearly sucientto observe a signal from Standard Model b! s g.Using the purely inclusive technique, a mod-est excess was observed in the signal region forquasi two-body B ! 0Xsdecays. A 90% con-dence level upper limit of for the momentum in-terval 0:39 < x0< 0:52,B(B ! 0Xs) < 1:7 10 3is obtained. Further work is in progress to improvethe sensitivity in this channel. Examination ofhigh momentum Ksproduction gives a 90% con-dence level upper limit ofB(B ! KsX) < 7:5 10 4for 0:4 < xKs< 0:54. More theoretical work isrequired to convert these limits into constraintson b! s g; g! qq.References1. T.E. Browder, K. Honscheid, and D.Pedrini, UH-515-848-96, OHSTPY-HEP-E-96-006, to appear in the 1996 edition of An-nual Reviews of Nuclear and Particle Sci-ence.2. T.E. Browder and K. Honscheid, Progressin Nuclear and Particle Physics, Vol. 35, ed.K. Faessler, p. 81-220 (1995).3. I.I. Bigi, B. Blok, M. Shifman, A. Vainshtein,Phys. Lett. B 323, 408 (1994).4. A. Falk, M. Wise, I. Dunietz, Phys. Rev. D51, 1183 (1995); Phys. Lett. B 73, 1075(1995).5. M. Buchalla, I. Dunietz, H. Yamamoto,Phys. Lett. B 364, 188 (1995).6. E. Bagan, P. Ball, V. Braun, P. Gosdzinsky,Nucl. Phys. B 432, 3 (1994); Phys. Lett. B342, 362 (1995) and Erratum; Phys. Lett.B 374, 363 (1996).7. W.F.Palmer and B. Stech, Phys. Rev. D 48,4174 (1993).8. K. Honscheid, K.R. Schubert, and R. Waldi,Z. Phys. C 63, 117 (1994).9. M. Neubert, CERN-TH-96-120 , hep-ph/960525610. G. Altarelli, G. Martinelli, S. Petrarca,and F. Rapuano, CERN-TH-96-77, hep-ph/960420211. I.L. Grach, I.M. Narodetskii, G. Simula, andK.A. Ter-Martirosyan, hep-ph/9603239.12. A. L. Kagan, Phys. Rev. D 51, 6196 (1995).13. L. Roszkowski, M. Shifman, Phys. Rev. D53, 404 (1996).14. B. Grzadowski and W.S. Hou, Phys. Lett.B 272, 383 (1992).15. I. Dunietz, FERMILAB-PUB-96/104-T16. Y. Kwon (CLEO Collaboration), contribu-tion to the Proceedings of the 1996 Rencon-tres de Moriond, Editions Frontieres.17. ALEPH Collaboration, ICHEP96 PA05-06018. D. Buskulic et al. (ALEPH Collaboration),CERN PPE 96-117, submitted to PhysicsLetters B.19. DELPHI Collaboration, ICHEP96 PA01-108, DELPHI 96-97 CONF 26.20. M. Bishai et al. (CLEO Collaboration),CLEO-CONF 96-10, ICHEP96, PA05-07221. W. Adam et al. (DELPHI Collaboration),CERN-PPE 96-6722. D. Buskulic et al. (ALEPH Collaboration),CERN-PPE 96-104.23. B. Barish et al. (CLEO Collaboration),CLEO CONF 96-23, ICHEP96 PA05-095.24. M. Artuso et al. (CLEO Collaboration),CLEO CONF 96-18, ICHEP96 PA05-73.25. R. Grigjanis, P.J. O'Donnell, M. Sutherland,and H. Navelet, Phys. Lett. B 224, 209(1989).26. N. G. Deshpande, X.-G. He and J. Tram-4petic, Phys. Lett. B 377, 161 (1996).27. N. G. Deshpande, G. Eilam, X.-G. He and J.Trampetic, Phys. Lett. B 366, 300 (1996).28. M. Ciuchini, E. Gabrielli, and G.F. Guidice,CERN-TH-96-073, hep-ph/9604438 and pri-vate communication.29. K. W. Edwards et al. (CLEO Collabora-tion), CLEO CONF 95-8.5

Hadronic Decays and Lifetimes of B and D Mesons

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Hadronic Decays and Lifetimes of B and D Mesons

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