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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

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Baryonic B decays

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

B-→ppK- : first observation of charmless baryonic B decay

B→pp(K,K*,)

→p(,K)

→K

B→pp, , pstringent limits)

B→p: first observation of b→s penguin in baryonic B decays

Expt.

Theory

Chua, Geng, Hou, Hsiao, Tsai, Yang, HYC,…

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)

0201015, 0405283

Belle group at NTU

first paper on radiative baryonic B decays

C.Q. Geng, this afternoon

QCD05, Beijing

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History

A baryon pair is allowed in the final state of hadronic B decays

ARGUS (’87): 40

4

10)9.10.6()(

10)9.17.3()(

ppBBr

ppBBr

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.

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1997: first measurement of BcpX (X=0, , ) by CLEO

2000: first observation of B0D*-pn & B0D*-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: B0cp (Belle), first

evidence of J/p (BaBar)

2004: first observation of b→s penguin in baryonic B decays

(Belle): Bp

2005: doubly charmed baryon modes Bcc, BccK (Belle)

active theoretical studies since 2001

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Charmful baryonic B decays

B-J/p (12+9-6)10-6 by BaBar, (11.62.8+1.8

-2.3)10-6 by Belle

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2-body baryonic B decays

Br(c0-+)=1.3%, Br(c

+-++)=7.1% (HYC,Tseng; Korner et al.)

Br(B-c0c

-) 410-3, Br(B0c+c

-) 1.310-3

charmless:

charmful:

cc 10-3 >> cp 10-5 >> p 10-7

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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

ccK ( 7 10-4) cc ( 10-3)

first observation of charmless baryonic B decay

Charmless 3-body baryonic B decays:

Belle group at NTU has made major contributions

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Threshold or low mass enhancement effect

B0p-

Br(B0p-) >> 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 budu transition, the invariant mass of ud tends to peak at the highest possible value due to its (V-A) structure

Spectrum of three-body baryonic B decays shows a low mass enhancement of the baryon pair

B-c+p

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2-body baryonic B decays

BB1B2 via internal W-emission, bd(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(BB1B2 ) (c1-c2) c2+c1/3

for tree-dominated 2-body decay mode

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Expt cc 10-3 >> cp 10-5 >> p 10-7

Theoretical expectation:

BB1B2)=|CKM|2 f(energy release)-1

CKM(cc)=VcbVcs* and CKM(cp)=VcbVud

*

Br(c+p)=Br(cc) (dynamical suppression) d.s. ⇒ 10-2

Br(p) = Br(c+p)|Vub/Vcb|2 (d.s.)’ = 2.210-7 (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)

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(CZ=Chernyak & Zhitnitsky)

charmless 2-body baryonic B decays

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CZ Jarfi et al. HYC, Yang Expt

B0c+p 410-

4 1.110-3 1.110-5 (2.190.84) 10-5

B-c0p 310-3 1.510-2

6.010-5 (3.67+0.56

-0.510.18) 10-5

B0c0n 5.810-3

6.010-7

B-c+-- 210-

4

3.610-2

1.910-5 (0.65+0.56-0.510.18) 10-5

All previous predictions based on QCD sum rule, pole model and diquark model are too large compared to experiment

2-body singly charmed baryonic B decays

2-body doubly charmed baryonic B decays

Earlier predictions based on QCD sum rule and diquark model

⇒ c0p cc ⇒ dynamical suppression effect for the former is

missingWe (Chua, Tsai, HYC) are now working on the d.s. effect

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3-body baryonic B decays

Internal W-emission diagrams (c), (d) are color suppressed (e.g. J/p), but (e) and (f) are not. The decays B0c

0p+(0) that proceed only via the latter have rates similar to c

++p- which proceeds via external W-emission (a).

8 distinct quark diagrams: 2 external W-emission, 4 internal W-emission, and 2 annihilation

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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 f

orm 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)

BbqBBqqM |)(|0|)(| 12123

BbqMqqBB |)(|0|)(| 32121

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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)

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b u

b s

us K-

p

p

K-

p

p

B-

B-p

p

pp

K- K-

b,b

’,,…

10,8,6,4,1

9,5,3,2

for |)(|0|)(|

for |)(|0|...)(|

aBbuppusK

aBbsKuupp

-

-u

-u

Threshold effect in pnguin-dominated B-ppK-

+

(a) (b)

(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

-

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Low mass enhancement effect from near-threshold resonances ?

gluonic resonance pp in BppK (Chua, Hou, Tsai 02)

not favored by measurements of angular distribution (Belle) & Dalitz plot asymmetry (BaBar)

structure of cp in Bcp 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→ccK) 10-8 vs 710-4 (expt.) due to tiny phase space availabl

e & color suppression ! A big surpriseA big surprise !

⇒ a charmonium ( 4.65 GeV)→cc with large coupling and narrow width ? (Chua,Tsai, HYC 05)

B-c+p

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Radiative baryonic B decays

Owing to large mt, bs penguin transition is neither quark mixing nor loop suppressed. At mesonic level, it manifests as BK*. 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-) = 1.210-6 (HYC, Yang, 2002)

Br(B-0p)= 2.910-9

We concluded three years ago that penguin-induced B-p and B-

0- should be readily accessible to B factories

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Br(B-p) = (2.16+0.58-0.530.20)10-6

Br(B-0p) < 3.310-6

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) = (0.90.2) 10-6 Br(B-0p) = (1.71.5) 10-7

Quark diagram analysis (Kohara 04)

first observation of bs in baryonic B decay

Belle [Lee & Wang et al. PRL 95, 061802 (2005)]

Measurement of B-0p could be used to discriminate between different models

see Min-ru Wang’s talk tomorrow

2020

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-

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Penguin-induced radiative baryonic B decays should be explored more both experimentally and theoretically