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Exclusive Baryonic B decays

Exclusive Baryonic B decays. Hai-Yang Cheng Academia Sinica Two-body baryonic B decays Three-body baryonic B decays Radiative baryonic B decays. 3 rd ICFP, NCU, Chung-li, Oct 3-8, 2005. Baryonic B decays. QCD05, Beijing.

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Exclusive Baryonic B decays

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  1. Exclusive Baryonic B decays • Hai-Yang Cheng • Academia Sinica • Two-body baryonic B decays • Three-body baryonic B decays • Radiative baryonic B decays 3rd ICFP, NCU, Chung-li, Oct 3-8, 2005

  2. Baryonic B decays QCD05, Beijing 3-body baryonic B deacys were found to have larger BRs than 2-body decays There are extensive studies of baryonic B decays in Taiwan both experimentally and theoretically Theory Expt. Belle group at NTU Chua, Geng, Hou, Hsiao, Tsai, Yang, HYC,… B-→ppK-: first observation of charmless baryonic B decay B→pp(K,K*,) →p(,K) →K B→pp, , p (stringent limits) Publication after 2001: (hep-ph) 0008079, 0107110, 0108068, 0110263, 0112245, 0112294, 0204185, 0204186, 0208185, 0210275, 0211240, 0302110,0303079, 0306092, 0307307, 0311035, 0503264, PRD(05, not on hep-ph) C.Q. Geng, this afternoon B→p: first observation of b→s penguin in baryonic B decays 0201015, 0405283 first paper on radiative baryonic B decays

  3. History A baryon pair is allowed in the final state of hadronic B decays ARGUS (’87): • stimulate extensive studies (16 theory papers) during 1988-92 • pole model: Deshpande, Trampetic, Soni; Jarfi et al. • QCD sum rule: Chernyak, Zhitnitsky • diquark model: Ball, Dosch • symmetry: He, McKeller, Wu; Sheikholeslami, Khanna Experimental & theoretical activities faded away after 1992 and revived again mainly after 2000.

  4. 1997: first measurement of BcpX (X=0, , ) by CLEO • 2000: first observation of B0D*-pn & B0D*-pp+ by CLEO • 2001: first observation of charmless B-ppK- by Belle • 2002: observation of cpX (X=,) by Belle, CLEO, D(*)0pp by Belle • 2003: first observation of 2-body decay: B0cp (Belle), first evidence of J/p (BaBar) • 2004: first observation of b→s penguin in baryonic B decays (Belle): Bp • 2005: doubly charmed baryon modes Bcc, BccK (Belle) • active theoretical studies since 2001

  5. Charmful baryonic B decays B-J/p (12+9-6)10-6 by BaBar, (11.62.8+1.8-2.3)10-6 by Belle

  6. 2-body baryonic B decays charmless: charmful: Br(c0-+)=1.3%, Br(c+-++)=7.1% (HYC,Tseng; Korner et al.)  Br(B-c0c-)  410-3, Br(B0c+c-)  1.310-3 cc  10-3 >> cp  10-5 >> p  10-7

  7. Charmless 3-body baryonic B decays: first observation of charmless baryonic B decay Belle group at NTU has made major contributions • Recently Belle has measured angular distribution and BaBar measured Dalitz plot asymmetry, providing information on the decay mechanism • For charmless baryonic B decays, (3-body)>(2-body) e.g. p+( 10-6) >> p(10-7) • For charmful decays, one also has c+p+-(10-3) > c+p-(10-4) > c+p(10-5) due mainly to resonant contributions to 3-body and 4-body decays • For doubly charmful baryonic B decays ccK ( 7 10-4) cc ( 10-3)

  8. Threshold or low mass enhancement effect B0p- B-c+p Spectrum of three-body baryonic B decays shows a low mass enhancement of the baryon pair • Br(B0p-) >> Br(B-p), Br(B-→ppK) >> Br(B0→pp) • Threshold effect was conjectured by Hou & Soni (2001): energy release must be reduced in order to have larger baryonic B rate • Dunietz (1999): In Dalitz plot for budu transition, the invariant mass of ud tends to peak at the highest possible value due to its (V-A) structure

  9. 2-body baryonic B decays BB1B2 via internal W-emission, bd(s) penguin, annihilation Internal W emission is color suppressed in mesonic B decays, but not necessarily so in baryonic B decays due to baryon w.f. totally antisymmetric in color indices effective Hamiltonian approach  A(BB1B2 ) (c1-c2)  c2+c1/3 for tree-dominated 2-body decay mode

  10. Expt  cc  10-3 >> cp  10-5 >> p 10-7 • Theoretical expectation: • (BB1B2)=|CKM|2 f(energy release)-1 • CKM(cc)=VcbVcs* and CKM(cp)=VcbVud* Br(c+p)=Br(cc) (dynamical suppression) ⇒ d.s.  10-2 • Br(p) = Br(c+p)|Vub/Vcb|2 (d.s.)’ = 2.210-7 (d.s.)’ • To have quantitative predictions, we use the pole model to evaluate the nonfactorizable decay amplitude and apply the MIT bag model to compute baryon-baryon transition (HYC,Yang 02) • Other approaches: • -- diquark model (Ball, Dosch 91) (Chang, Hou 01) • -- sum rules (Chernyak, Zhitnisky 90) • -- quark-diagram analysis: • charmless baryonic B (Chua 03), charmful decay (Luo, Rosner 03)

  11. charmless 2-body baryonic B decays (CZ=Chernyak & Zhitnitsky)

  12. 2-body singly charmed baryonic B decays All previous predictions based on QCD sum rule, pole model and diquark model are too large compared to experiment 2-body doubly charmed baryonic B decays Earlier predictions based on QCD sum rule and diquark model ⇒ c0p cc ⇒ dynamical suppression effect for the former is missing We (Chua, Tsai, HYC) are now working on the d.s. effect

  13. 3-body baryonic B decays • 8 distinct quark diagrams: 2 external W-emission, 4 internal W-emission, and 2 annihilation • Internal W-emission diagrams (c), (d) are color suppressed (e.g. J/p), but (e) and (f) are not. The decays B0c0p+(0) that proceed only via the latter have rates similar to c++p- which proceeds via external W-emission (a).

  14. Factorizable contributions to 3-body baryonic B decays: • current-induced process: • <B1B2|(q1q2)|0> can be related to some measurable quantities (e.g. nucleon EM form factors) for octet baryon pair • can be readily evaluated under factorization and QCD counting rule for form factors (Chua, Hou, Tsai 01,02) • transition process: • use QCD counting rule to make power expansion of 1/m212 for form factors in 3-body matrix element and then use charmless 3-body decay data to fit form factors (Chua, Hou, Tsai) • use pole model to evaluate 3-body matrix element: a dynamical calculation (HYC, Yang 02)

  15. Chua, Hou, Tsai -- charmful: B D*pn -- charmless: B np(), ppK(), ()p • HYC, Yang (pole model) -- charmful: B cp, cp, D*pn, D*pp -- charmless: B np(), ppK(), p • Geng, Hsiao -- B K() -- T violation in B p see Geng, Hsiao parallel session (Thursday)

  16. - Threshold effect in pnguin-dominated B-ppK- - u K- s b u p B- p - u K- K- p s b,b K- b + p ’,,… p B- p p p - (a) (b) u (a): Invariant mass of Kp tends to be small, supported by Belle observation that p prefers to be parallel to K and BaBar measurement that K is correlated more strongly to p than to p⇒ dominance of penguin contribution (b): maximal propagator when invariant mass pp is close to the threshold  low mass enhancement effect

  17. Low mass enhancement effect from near-threshold resonances ? • gluonic resonance  pp in BppK (Chua, Hou, Tsai 02) • not favored by measurements of angular distribution (Belle) & Dalitz plot asymmetry (BaBar) • structure of cp in Bcp can be parametrized as a Breit-Wigner • with m=3.35+0.02-0.03 GeV & • width=0.07+0.06-0.05 GeV (Belle) • Br(B→ccK)  10-8 vs 710-4 (expt.) due to tiny phase space available & color suppression ! A big surprise ! • ⇒ a charmonium ( 4.65 GeV)→cc with large coupling and • narrow width ? (Chua,Tsai, HYC 05) B-c+p

  18. Radiative baryonic B decays Owing to large mt, bs penguin transition is neither quark mixing nor loop suppressed. At mesonic level, it manifests as BK*. What happens at baryonic level ? • Consider b pole diagram and apply HQS and static b quark limit to relate the tensor matrix element with b form factors • Br(B-p)  Br(B-0-) = 1.210-6 (HYC, Yang, 2002) • Br(B-0p)= 2.910-9 We concluded three years ago that penguin-induced B-p and B-0- should be readily accessible to B factories

  19. Geng & Hsiao [PL B610, 67 (2005)] use QCD counting rules and data of charmless baryonic B to constrain the relevant matrix elements • Br(B-p) = (0.90.2) 10-6 • Br(B-0p) = (1.71.5) 10-7 • Quark diagram analysis (Kohara 04) Belle [Lee & Wang et al. PRL 95, 061802 (2005)] Br(B-p) = (2.16+0.58-0.530.20)10-6 Br(B-0p) < 3.310-6 first observation of bs in baryonic B decay see Min-ru Wang’s talk tomorrow Measurement of B-0p could be used to discriminate between different models

  20. Conclusions • Threshold effect is a key ingredient for understanding 2-body and 3-body baryonic B decays • BR of charmless 2-body decay is predicted to be of order 10-7 • Penguin-induced radiative baryonic B decays should be explored more both experimentally and theoretically

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