Search for New Particles in B Decay at Belle

Fang Fang

University of Hawaii

ICHEP’04, Beijing, August 2004

BK J/event candidates

M()

M(J

/

)BKJ/

BK X(3872)

J/

253 fb1

1st: look at BK J/Dalitz Plot

M

Mbc

EM

2(J

/

)

M2(K)

K

cut here ( >1.62 GeV2)

BK** J/

Slice into 40 MeV-wide M(J/) bins

Large deviationfrom phase-space

Fit

/d.o.f.=

Slice into 40 MeV-wide M(J/) bins

Adding a BWhelps

FitM≈3941±11 MeV≈ 91±24 MeV

M(K) for the signal region

M(K) (GeV)

3880 <M(J/)<3900 MeV

No peakingIn M(K)

What is it?• A broad -J/ resonance?

– Above DD & DD* threshold!

• More than one overlapping narrow states?– Expt’l M(J/) resolution is ≈ 6 MeV

• Some kind of -J/ threshold interaction?– Does the J/ act like an ordinary hadron?

• cc-gluon charmonium hybrid?– Predicted by lattice QCD but with Masses ~ 4.4 GeV

Next: BK X(3872) J/

M()

M(J

/

)

BK X(3872)

J/

look along here

BKX(3872); X J/

M(

all events

Nevt=15.4 ± 6.3 S/N = 0.8/1

These events arealmost pure signal

Nevt=10.0 ± 3.6S/N = 5/1

Signif = 5.8

events with M(3)>0.75 GeV

Consistent with sub-threshold X(3872) J/

• M + MJ/ = 3879 MeV (7 MeV above 3872)

– X J/ occur via virtual ’s, 3 masses cluster at the kinematic limit.

• (XJ/)/(X J/) = 0.8 ±0.3± 0.1

• In agreement with Swanson’s DD* bound-state model for the X(3872) [PLB 588,189 (2004)]

Other new results on the X(3872)

• (X c2)/(XJ/) <1.1 (90%)

– Below expectations for X = 3D3 (3)

• J/ helicity dist. inconsistent with JPC = 1

– rules out X=21P1 (hc’)

Mbc Mc2

X

2=75/9

|cosJ/

Other new results on the X(3872), cont’d

• (X J)/(XJ/) <0.4 (90%)– well below expectations for X = 23P1 (c1’)

Look at B J K

BKc1; c1J/

No X(3872)

M( J/)-M(J/)

No good cc candidates for X(3872)

c”

hc’

c1’

2

c2

3

M too low and too small

c should dominateJ/

J/ decays violate isospin

angular dist’n rules out 1

J/ way too small

c too small; (PRL 93, 2003)

c& DD) too small

Search for the hc meson• Charmonium spectrum

c (1S)

J/ (1S)

c’ (2S) ’ (2S)

c(1P)

c (1P)c (1P)

hc (1P)

0 1 1 0 1 2

3654

2979

3097

3686

3525(c.o.g)??

3415

35103556

E7603526 MeV

J/

Strategy for the hc search

• M. Suzuki; Y.F. Gu et.al. suggest looking for the hc in Bhc K

– B(hc c ) is large ~ 50%.

c KSK+ is very clean

• Belle has used B decays to discover the c (2S) & X(3872)

• Select S in hc mass region and look for B signals– Mbc

E

hc c c S

Are there B signals in the hc region?

3.17 – 3.27

3.57 – 3.67

3.27 – 3.37

3.47 – 3.573.37 – 3.47

• Mbc distributions in five 100 MeV-wide M(KSK+bins

No signal is seen

cinvariant mass distribution

Consistent with being only background

Mbc sideband data

c.o.g.

3.17 – 3.67

Upper limits on B(hcK)

• Assume B(hc c ) = 0.5, we obtain upper limits on B(hcK) at 90% C.L.

c.o.g.

B(hcK)<310for 3.47<M(c) <3.57 MeV

Colangelo, De Fazio and Pham, hep-ph/0310084

Summary

• We have observed a near-threshold J/mass enhancement in B J/What is it?

• Observation of X(3872) J/supports the DD* molecular interpretation of X. No natural charmonium assignments.

• We have searched for the hc meson in the decay chain hc K, hc c, c KSK+ No significant signals are seen for 3.17 < M(cGeV.

Backup Slides

Look back at the masses

76’s 20’s26’s

28’s

Very clear signal