1 / 20

Exciting Discoveries in Baryonic B Decays

This article discusses the recent advancements and significant observations in the field of baryonic B decays, including two-body and three-body decays, as well as radiative decays. It also highlights the pioneering contributions of the Belle group at NTU in Taiwan.

jenniferk
Download Presentation

Exciting Discoveries in Baryonic B Decays

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related