Baryonic B decays

Moriond QCD '05 1

Baryonic B decaysJ. Schümann

National Taiwan University

(Belle Collaboration)Outline:

IntroductionB+ K+

Threshold enhancementPentaquark searchB+ p Charmed baryonic modes Two body decaysConclusion

Moriond QCD ‘[email protected]

J.SchJ.Schüümann,mann, 13.03.’05 Moriond QCD '05 2

The KEKB-factoryElectron 8 GeV

Electron 8 GeVPositron3.5 GeV

Positron3.5 GeV

Υ(4S) (10.58GeV/c2) = 0.425

Υ(4S) (10.58GeV/c2) = 0.425

Interaction Point

3Km

Tsukuba


Accumulated Data

Lpeak = 15.16 nb-1s-1

Lday 1 fb-1 Ltot = 377 fb-1


Belle Detector Aerogel Cherenkov Cnt. n=1.015~1.030

KLM / KL detection 14/15 lyr. RPC+Fe

TOF counter

ECL CsI(Tl)

SC solenoid 1.5T

Silicon Vertex

Detector

Central Drift Chamber small cell +He/C2H6

8 GeV e-

3.5 GeV e+

Extreme Forward Calorimeter


Introduction

Baryonic decays: a unique and well-established feature of B meson decay (but not charm decay)

B(2 body) < B(3 body) < B(4 body)Threshold enhancement in the invariant mass of the baryon-antibaryon system for 3-body BKBB decaysAngular distributions discriminate between decay mechanisms, e.g. two-body decays and fragmentationCan search for exotic states in 3-body and 4-body decays


gb s s

s B+ΛΛK+

First observation of bs s s decay

Signal Yield in 2D fit: 19.9Efficiency: 4.0%-6.9%Statistical Significance: 7.4σ

B : (2.91 0.38) x 10-6

+6.5- 5.1

+0.90- 0.70 PRL 93, 211801PRL 93, 211801

1.1. First Charmless B decay First Charmless B decay with two with two ΛΛ! !

2.2. Threshold enhancement.Threshold enhancement.

3.3. Complements BComplements BφφKK(*)(*)

(b(bsss penguin)sss penguin)

1.1. First Charmless B decay First Charmless B decay with two with two ΛΛ! !

2.2. Threshold enhancement.Threshold enhancement.

3.3. Complements BComplements BφφKK(*)(*)

(b(bsss penguin)sss penguin)

140fb-1

threshold peaking


Search for B+ΛΛπ+

No significant signal found

90% confidence-level upper-limit:

B (B+ΛΛπ+)<2.8x10-6

PRL 93, 211801PRL 93, 211801

140fb-1

1.1. Compare with BCompare with Bppppππ

2.2. bbuud transition with ss uud transition with ss poppingpopping

1.1. Compare with BCompare with Bppppππ

2.2. bbuud transition with ss uud transition with ss poppingpopping

ResultResult

Number of Background:

37.5±1.0Number of Observed events ：

41Number of Signal UL:

< 21.7

b u


Improved B+ppK+measurement

Signal Yield in 2D fit: 216.5

Efficiency: 28.3%-35.2% with Mpp<2.85 GeV/c2

B(Belle): (4.59 0.50) x 10-6 (4.89 x 10-6 PRL92, 131801, 2004)

B(Belle): (5.30 0.58) x 10-6 , full range (charm veto for Mpp)

B(BABAR): (6.7 0.9 0.6) x 10-6 (81 fb-1, hep-ex/0408037)

+17.3- 16.6

140fb-1

+0.38- 0.34

threshold peaking

+0.45- 0.39

b s


Angular distribution: ppK+

& glueball search

Proton against K- (p against K

+) : flavor dependence!

ppK signal

bs dominant processFragmentation picture

us

uudduuus

K+ pp

p

p

K+ӨpX

at pp rest frame

No significant signal: B (B+ glueball K+) x B ( glueball pp) < 4.1x10-7

Possible Hints and Search for Glueball Production in Charmless Rare B DecaysChun-Khiang Chua, Wei-Shu Hou and Shang-Yuu Tsai(PLB544,2002)

Angular-Asymmetry:

A = N+-N-

N++N-

= 0.59 +0.08- 0.07


Improved B0ppKs measurement

threshold peaking


Efficiency: 15.4%-21.0% with Mpp<2.85 GeV/c2

B : (1.04 0.12) x 10-6 ( 0.78 x 10-6 PRL92, 131801, 2004)

B : (1.20 0.14) x 10-6 (full range, charm veto)

+6.5- 5.8

140fb-1

+0.26- 0.19

+0.32- 0.22

b s


Pentaquark search in BppKs, ppK+

Θ+(1540) : uudds (Belle) Θ+ K+ n Θ+ K0 p

B0 Θ+ pB0 ppK0, B ppKs

Search for B signal with a 20 MeV pKs mass window cut at 1540MeV, the nominal mass of the pentaquark

Θ++(1540) : uuuds (Belle,BABAR) B0 Θ++ p Θ++ K+ p

ddu us

Θ+K+n

su

ddu uu

d

p

d s

K0

Θ+

uudsd


Pentaquark search in ppKs/K+

Fixed background shape from sideband data

Count the events in signal region and compare with background estimation

Upper limit B(B0+p)x B(+pK0s)< 2.3x10-7

at 90% C.L.

+: Belle : 140 fb-1 ++: BABAR : 81 fb-1

++: Belle: B < 9.1 x 10-8


Improved B0pΛπ- measurement


Efficiency: 10.4%-12.6%

B: (2.62 0.31) x 10-6 (Mpp < 2.85 GeV/c2)

B: (3. 27 0.39) x 10-6 (full range) (3.97 x 10-6 PRL90, 201802, 2003)

140fb-1

+8.2- 7.5

+0.62- 0.51

threshold peaking

+0.44- 0.40

b s


Angular distribution: pΛπ-

π-

Λ

p

ӨpX

at pΛ rest frame

Λ

p

π-

ӨpX

at pπ- rest frame

Fragmentation picture


Theoretical prediction:Theoretical prediction:*Pole Model*Pole Model: Phys.Lett. B533 (2002)

B(B pΛγ ) ~ 1.2x10-6

B(B pΣ0γ) ~ 2.9x10-9

*QCD counting rules*QCD counting rules: (hep-ph/0405283)

B(B pΛγ ) ~ (1.2-2.4)x10-7

B(B pΣ0γ) ~ (2.8-6.5)x10-7

B+pΛγ

First observation!Simultaneous fit on BpΛγ & BpΣ0γSignal Yield for BpΛγ with MpΛ<2.4GeV/c2: 34.1

Statistical Significance: 8.6σ

B(BpΛγ ): (2.16 0.20) x10-6

B(BpΣ0γ):<3.3 x 10-6

140fb-1

+7.1- 6.6

+0.58- 0.53

bsγ MCpΛγSignal

threshold peaking

b s


B- C+ p -

264±264±20 20 signalsignalss

CC(2455)(2455)00

CC(2520)(2520)00

sidebasidebandnd

32.632.6

12.12.88

+ 6.6+ 6.6 - 5.9- 5.9

+ 5.7+ 5.7 - 5.0- 5.0

B-c+p- 20.1±1.5 ±2.0±5.2

B-c0

2455 p 3.67 ±0.36 ±0.95

B-c0

2520 p 1.26 ±0.12 ±0.33

B x 10-5

+0.74- 0.66+0.56- 0.49

~ 25% of the total Bcp- BF

b c u

d

Observation of a new 2-body decay

140fb-1


(c+p) massCC

++p)p)

M(c+ -)>2.6 & M(p-) >1.6GeV/c2

to remove c(2455/2520) & (1232)

B signals by E fit for each mass bin

B- C+ p -- M(c

+p) structure

B = ( 3.87 0.43 1.01 ) x 10 - 5

BW = 0.07 ±0.04

M = 3.35 0.02

6.2 significance

CC00CC

++--))

Low mass structure

+0.77- 0.72

+0.01-0.02

+0.04-0.03


MC J 2 /ndSolid line : 0 0.97Dashed line : 1 1.58

B- C+ p -

( by E fit for each mass bin )

Helicity distribution

data: dotsMC : histograms

M(c+p) <3.6GeV/c2

c+

(c+p)

direc.

in B - at rest

Helicity angle

p

Angular-Asymmetry:

A = |N+-N-|N++N-

= 0.32 0.14


B0 p, pp and other

140fb-1

B0 pp: 4.1 x 10-7

B0 p: 4.9 x 10-7

B0 : 6.9 x 10-7

90% confidence level UL:

Belle, 78fb-1 BABAR, 81fb-1

Belle: B+ J/p: 4.1 x 10-5

BABAR: B+ J/p: 2.6 x 10-5 B+ J/pp: 1.9 x 10-5


Conclusion

First b → sss hyperonic decay found

First b → s γ baryonic decay found

The threshold enhancement in the baryon-antibaryon pair for 3-body Bbaryon decayse supports the fragmentation picture

Intriguing structure found in the cp mass for Bcp- decays

No hints for pentaquarks and glueballs yet

Keep searching for all kinds of baryonic

decay channels, possible pentaquarks,

glueballs and especially direct CP violation

with increasing statistics


Λ

γ

p

θx

Photon energy and Angular distribution

Fit results in bins of cosθX with Mp<4.0GeV/c2

(Assuming XpΛ, calculated in X rest frame.)

bsγ MCSignal Yield

qq backgroundSignal Yield

Lab frame


BB0 0 ( (cc++p) p) --

M(c+p) structure

in 3, 4 body decays

CC++/0++/0 (2455/2520) excluded (2455/2520) excluded

BB- - ( (cc++p) p) --

B Signals byE fit

MC phase space, consistent with 4-body fine structures ?

MC 4-body phase spaceMC 4-body phase space

Prelim

inar

y

Prelim

inar

y


B0 C+ p - -

cc++++(2455)(2455) cc

00(2455)(2455)

cc++++(2520)(2520) cc

00(2520)(2520)

M(M(cc++))

Intermediate 3-body decaysIntermediate 3-body decays

B0 c+ p 10.3±0.9 ±1.2 ±2.7(*1)

B0 c2455++ p 1.15±0.22 ±0.14 ±0.30

B0 c24550 p 0.97±0.21 ±0.12 ±0.25

B0 c2520++ p 1.04±0.234±0.12 ±0.27

B0 c25200 p 0.33±0.19 ±0.054±0.09

41.0±8.0 35.2±7.8

58±14 19±11

M(c+)+c.c.

M(c+)+c.c.

(*1) total BF

140fb-1


Glueball SearchPossible Hints and Search for Glueball Production in Charmless Rare B DecaysChun-Khiang Chua, Wei-Shu Hou and Shang-Yuu Tsai(PLB544,2002)

Scanning through the mass region from 2.2 to 2.4 GeV regionNo significant signal

90% confidence-level upper limit:BF(B+ glueball K+) x BF( glueball pp) < 4.1x10-7


Particle Selection

We use the PID (ACC+CDC+TOF)PID (ACC+CDC+TOF) system to identify the charged particles.

Proton:

Kaon:

Pion:

Λ: reconstructed from Λpπ-

6.0 Kp

p

LL

L3.0

LL

L

p

p

6.0 LL

L

K

K

4.0 LL

L

K

K

pp KK ππ

(p)(p)

(K)(K) ~9% ~10%

((ππ)) ~4% ~8%Fake rate

Fro

m

TO


B Signal ReconstructionIn Υ(4S) rest frame:

e- e+

Υ(4S)

B

Be- e+

∆E

Mbc

2D scatter plot2D scatter plot

1D projection plot1D projection plot


B decay continuum events

Υ(4S)

The main background for B0pΛπ- and B+ΛΛπ+ is continuum qq events. (q=u,d,s,c). The Topology of continuum events and B decays are different. We choose |cosθThrust| S⊥ R2

so R4so R2

oo R3oo R4

oo as the fisher input and combine it with cosθB to calculate the likelihood ratio.

We define the Super-fox wolfram moment (F) like:

We use Fisher’s discriminant to optimize the coefficients.

Background suppression

SRRF Thrustsoi

ii

ooi

ii |cos|

4,24,3,2


udsuds

offoff Data sidebandData sideband

charmcharm

Background SuppressionSFW Moment (F)SFW Moment (F)

cosθB distributioncosθB distribution

udsuds


charmcharmSignal MC

udsuds charmcharm


Likelihood Ratio (LR)Likelihood Ratio (LR)

bs

s

LL

LLR

Optimized by

studybs

s


Signal Extraction

PDFs: Background modeling: a line (curve)

to represent the ∆E and the following parametrization first suggested by ARGUS group to represent the Mbc.

Signal modeling: a double Gaussian for ∆E and a Gaussian for Mbc.

])/(1(exp[)/(1)( 22beambcbeambcbcbc EMEMMMf

N

iibcibibcis

BS EMBPEMSPeL1

)( )],(),([

1D-binned fit: maximum Likelihood fit Branching fraction are calculated by ∆E fit Mbc fit for cross-check.

2D-unbinned fit (∆E-Mbc): Extended maximum likelihood fit.

∆E

∆E Mbc

Mbc


Angular distribution: ppK+

Background yield of ppK+

Consistent with qq background process

No fragmentation signature in J/ψK+

J/ψK+ (J/ψpp)

Baryonic B decays

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