moriond qcd, mar., 2007, s.uehara 1 new results on two-photon physics from belle s.uehara (kek) for...

Moriond QCD, Mar., 2007, S.Uehara 1

New Results on Two-Photon Physics from Belle

S.Uehara (KEK)for the Belle Collaboration

Rencontres de Moriond, QCD and Hadron interactionsMar.17-24, 2007


Motivation of Two-Photon Physics

1. Resonance formation

hadrons

2. Hard scattering with a quark line

Hadron production from two quasi-real photon (|q2|<0.001GeV2, with no-tag condition) Exclusive processes with W=0.8 - 4.5 GeV at KEKB/Belle 　　 Light-quark resonances, Charmonia Perturbative/Non-perturbative QCD,　　　 Hadron production mechanism Wide energy region --- Various physics aspects can be studied simultaneously.


KEKB Accelerator and Belle Detector• Asymmetric e- e+ collider

Beam crossing angle: 22mrad

•Continuous injection

•Luminosity Lmax=1.71x1034 cm-2s-1

∫ Ldt 710 fb-1 　　 (by the end of 2006)

8 GeV e- (HER) x 3.5 GeV e+ (LER)

s=10.58 GeV (4S)

High momentum/energy resolutions CDC+Solenid, CsIVertex measurement – Si stripsParticle identification TOF, Si-aerogel, CDC-dE/dx, RPC for KL/muon


Reactions at KEKB/Belle

The cross sections observable there e+e(4S)BB --- 1.1 nb e+eqq (uds) --- 2.1 nb e+ecc --- 1.2 nb e+e --- 0.9 nb hadrons (W>0.8GeV) --- ~1 nb (within the acceptance)

Luminosity Function for quasi-real collisions

d(in ee) = (in ) L(W) dW0.0001

0.001

0.01

0.1

0 1 2 3 4 5

W, gamma gamma c.m. energy (GeV)

Lum

inos

ity fu

nctio

n (1

/GeV

)

Calculated with equivalent-photon approximation

Ee+e-=10.58GeVQ2

max=1GeV2

Lum

inos

ity f

unct

ion

(1/G

eV)


C = + resonances: Peak structure in the invariant mass distributionTest of QCD: c.m.-energy (W) dependence and angular dependence in high energiesGeneral Analysis strategy Invariant-mass of hadron pair = W (c.m. energy of ) Quasi-real two-photon collisions with final state fully reconstructed --- strict transverse momentum balance is required (| pt| <50 - 200 MeV/c ) This gives efficient background rejection

Two-hadron exclusive final statesMeson/baryon

Meson/anti-baryon


K0SK0

S

M(KSKS) |cosθ|<0.6

hep-ex/0609042

Preliminary

Selection: - Ks reconstruction from pairs with a detached vertex - pt-balance requirement


Angular distribution; comparison with theories

- qq qqqq with wave function --- (M.Benayoun, V.L.Chernyak)- qq w/ hadronic exchange (handbag) --- (M.Diehl, P.Kroll, C.Vogt) cJ region (check evaluation of angular acceptance)

DKVBC

Preliminary

BC

DKV(handbag)


)(/)( 00 KKPLB615,39(2005) = 0.89±0.04±0.15

Cross section; KS0KS

0/K+K ratio

Previous study:

)6.0|cos(|

])[(0

nbW )()( 00

KKKK SS

W-n dep. Preliminary

σ0(KSKS)/σ0(K+K-) approaches BC as W→∞


cJ KS0KS

0 decays

process c0 KS0KS

0 c2 KS0KS

0

Br(KS0KS

0) (eV) 7.00 0.65 0.71

0.31 0.05 0.03

Br(KS0KS

0) / Br(K+K) 0.49 0.07 0.08

0.70 0.21 0.12

Consistent with isospin inv. ratio = 0.5

Preliminary

Product of two-photon decay width () and branching fraction to K0

SK0S

Preliminary


())( MvsM )()( 00

vsMM

- Select (X)- Combining

(X)

00cc

00 cwith unseen

hep-ex/0609048

p

Ldt= 464fb-1


Nxxc

00

2.10.34.162.101

0.02.12.91.36

49.052.001.121.6

98.003.150.280.9

13.007.011.007.014.089.0

20.014.018.015.036.040.1

])[( eVxxBr 310)( xxBr

49.036.1)(/)(

26.086.0)(/)(00

ppBrBr

ppBrBr

4.03.0)(/)(

5.0)(/)(00

ppBrBr

ppBrBrmay be slightly larger than diquark prediction of

c results from the three processes

pp (PLB 621,41(2005)) 7.201.53 0.670.75

Preliminary

Preliminary

BB Br(BB) [eV] Br(BB)

PRD 38, 3516 (1988)


<

460/fbPrelim.

Energy dependence of the cross sections

Preliminary

Compatible with L3 but not with CLEO

Cross sections ofthe three processescome close above3 GeV

<


f0(980) – is ordinary qq meson? - an exotic state? - some special theory needed?

The two-photon coupling is acrucial key.Prediction of uu, dd --- 1.3 – 1.8 keV ss --- 0.3 – 0.5 keV KK molecule --- 0.2 – 0.6keV

f0(980) appears as a small but statistically significant peak.

f2(1270)

f0(980)

separation:by comparing energy deposit in the ECL between data & MC

PRD　 75, 051101(R) (2007)f0(980) in

85.9fb-1


M [MeV/c2]

[MeV]

[eV]

1.12.16.15.16.985

8.89.135.28.112.34

1479511783205

Fit of the f0(980) line shape

)6.0|cos(|

])[(0

nbW

No ’(P and CP) seen near 958MeV/c2

New upper limit for Br(’), Preliminary(interference with the non-resonant process allowed) < 3.3 10-4 (no interference)

f0(980)


Other cJ(1P,2P) measurements

Nevents 64±18(5.3σ)

M[MeV/c2] 3929±5±2

[MeV] 29±10±2

Br [keV] 0.18±0.05±0.03

Observation of a new charmonium Z(3930)

Br （ c0Br （ cKK 1.6 2.3 Br （ c2 0.14 0.11

Br （ c20.44 0.76 0.14 Br （ c2J 11 9 2

DD

Previous two-photon measurements of(cJ(1P))Br from Belle (eV)

A c2(2P) candidate (from ang. distribution)

PLB 615, 39 (2005)

PLB 540, 33 (2002)

PRL 96, 082003 (2006)


Summary

Exclusive hadronic final states from two-photon collisions in no-tag mode are measured at Belle.

These results are used to study resonances and test QCD models.

- KS0KS

0 final state above 2.4 GeV much smaller cross section than K+K-

cJ charmonia measured

- preliminary results --- c seen, comparison with pp- f0(980) shows a small peak in

- Charmonia: two-photon decay width and/or ratios among branching fractions are measured for

c, c0, c2 and a c2(2P) candidate


Backup slides


K0S seletion

Selection: Ks reconstruction from pairs with a detached vertex


Fitting formula for f0(980)


Angular distribution

Amplitude analysis is now going on.

Preliminary


c2(2P) candidate

Nevents 64±18(5.3σ)

Mass[MeV/c2] 3929±5±2

[MeV] 29±10±2

B [keV] 0.18±0.05±0.03

Observation of a new charmonium Z(3930)DD

A candidate of c2(2P) (from angular distr.)

PRL 96, 082003 (2006)

395fb-1

Spin-0 (dashed)

Spin-2, helicity-2 (solid)

|pt| distribution


Other cJ(1P) measurements from Belle

r （ c0Br （ cKK 1.6 2.3 Br （ c2 0.14 0.11

Br （ c20.44 0.76 0.14 Br （ c2J 11 9 2

PLB 615, 39 (2005)

PLB 540, 33 (2002)

87.7fb-1

Previous two-photon measurements of(cJ(1P))B from Belle (eV)

M(ll)-M(ll)

moriond qcd, mar., 2007, s.uehara 1 new results on two-photon physics from belle s.uehara (kek) for...

Documents

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nb e ecc

nb e et t

nb e eqq uds

gev e ler s

gamma gamma

energy of gg quasireal

photon collisions