Phi-Psi, Feb.-Mar. , 2006, S.Uehara 1

Experimental studies of charmonia in two-photon collisions at Belle

S.Uehara (KEK) for the Belle Collaboration

e+e From phi to psi,Feb.27-Mar.2, 2006,BINP, Novosibirsk

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Two-photon formation of a single resonance

Collision of two quasi-real photons (Q2<0.001GeV2) Kinematics: |pt| (E/E’) Q2 < ~ 100 MeV/c

Exclusive detections in W=0.8 - 4.5 GeV QCD, Light-quark resonances and Charmonia

Can detect the internal quarks

a meson with [Q=0, C=+]

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Physics of two-photon “single-meson formation”

Spin-parity determination conservation rules: C=+, JP = (even) or (odd)+ and J1 dynamic properties: (J=2,=2) and/or low-L state of qq are favored Measurement of Two-photon partial decay width RBRfinal state Identify “concrete candidates” for the sequential qq mesons, if their two-photon decay widths are appropriately large.

Study of decay branches detecting “Just exclusively” --- combinatorial backgrounds are minimized

Charmonia observed: 0 : c1Sc(2S)0 c0

2c2(1P), c2(2P)?2 : None observed

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The KEKB/Belle ExperimentThe KEKB Accelerator e+e collisions at s 10.6 GeV (asymmetric 3.5 on 8 GeV) The world-highest luminosity 1.621034cm-2 s-1

and integrated luminosity >550 fb-1 　 (as of Feb.,2006)

The Belle Detector Excellent energy/momentum resolutions and particle-separation capabilities

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)

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New charmonium in DD production

Search for radial excitation states, ’cJ ( cJ (2P)) (J= 0 or 2) predicted in 3.8 – 4.0 GeV mass region.

DD candidates are selected in four combinations of decays in 395fb-1 data.

A D-meson is tagged at the opposite side

Belle hep-ex/0512035, to appear in PRL

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Resonance( Z(3930) )parameters: M=3929 5 2 MeV = 29 10 2 MeV Yield = 64 18 eventsStat. Significance: 5.3

|pt| < 50 MeV/c Fit function : 3.8 – 4.2 GeV Breit-Wigner + M

Invariant-mass distributions

Major systematic-error sourcesTracking eff. 7% Selection eff. 8% Kaon ID 　 4%Fit of M(DD) 5% Luminosity func. 5% BR in D decays 9%

Others / 17% in total

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Properties of Z(3930) – a candidate of ’c2

B(Z(3930)DD) =0.18 0.05 0.03 keVB(Z(3930)D+D-)/B(Z(3930)D0D0)= 0.74 0.43 0.16 (isospin invariance)

All the properties show this is a ’c2 candidate

|pt| distribution of the eventsin the peak region consistent with exclusive DD decays

Angular distribution is consistent with J=2 (D-wave decay), helicity=2

spin-2

spin-0

sideband

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cJ in and KK

Study of QCD at 2.4 <W<4.1 GeV and cJ production

Selection criteria Two tracks (pt>0.8GeV/c) Reject -inclusive events pt-balance: 50(100)MeV/c for(KK) Rejection of X decaysParticle identification Rejection of e+e, , pp K/separation, Correction for background using MC

Belle PLB 615, 39 (2005)

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Invariant mass distribution

Charmonia c0, c2 seen in both and K+K-

(first observation in this process)

in 87.7 fb-1 data

Consistent with B measurements in other decay modes

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PreliminaryAlmost background-free KSKS signal samples

Continuum component: K0K0 << K+K-

(c0)B(c0KSKS) = 7.070.610.62eV(c2)B(c2KSKS) = 0.300.050.03eVconsistent to K+Kisospin invariance KSKS:K+K- = 1:2)

c0 (161 41 events)

c2 (44 7 events) (first observation in this process)

cJ inK0SK0

S

A preliminary analysis of

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cin pp Belle PLB 621, 41 (2005)

Studies of baryon-pair production mechanism, QCD and c production

Selection criteria Two tracks: proton and anti-proton (particle-identification, TOF, dE/dx, Aerogel Cherenkov) pt balance < 0.2 GeV/c

c seen in 89fb -1 data (first observation in this process)

c　　 J/background

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Measurement ofc production

our measurement: B(c pp) = 7.20 1.53 0.67 eV (first observation in this process)

0.75

Comparison to previous pp-incident Experiments at FermiLab

also consistent with previousB(c KSK) and BF measurements.

pp c

c pp

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c2 measurement in J/ modeBelle measurement in 2002

= 13.5 1.5 1.1 eV Previous inconsistency issue between and pp experiments solved (using a recent value of B(c2 J/) ) A recent CLEO measurement of the same process gives a consistent result.

Helicity-2 dominancein production supported

Belle PLB 540, 33 (2002)

hel.=0

hel.=2

(32.6fb-1)

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c”4”c0 K

+K”2K2

”c2 K

+K-K+K-”4K”c(2S) (with Ld

t=280fb-1)

Event Selection

Two-photon Exclusive 4-prong event

pt-balance -- pt < 0.1 GeV/c in the e+e- CM frame

(Exclusive requirement)

/K separation - combined information from (CDC+ACC+TOF)

Charmonium production in four-meson decay modesA preliminary analysis of

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Distributions of four-meson invariant masses

cc0 , and c2

seen in all the modes,

c c0 c2

42K2

4K

misidentified (2S)

Preliminary

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Resonance signals in decay products

Uppers: crosses: signal region, histogram: sideband regionsLowers: after sideband subtraction =charmonium contribution

K*0 K in c2 2K2 KK in c0 4K

M(K) (GeV)

0 f2(1270)

in c 4

M() (GeV)

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Results of G B (each decay mode)

Upper limits – 95%CL obtained by the 2 fits

Indirect:

Gindir(RX) = G(RA) Br(RX)/Br(RA)

RA - normalization process

G/B(cKsK) ,G/B(c0), G/B(c2J)

( )

Preliminary

Process Present G(eV) previous (PDG2004) direct indirect

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Search for c(2S) in four-meson decay modes

Rejection of (2S) is applied

Preliminary

Upper limits – 95%CL obtained by the 2 fits

No peak seen at c(2S) mass in these channelsLines corresponds

to the upper limit

c(2S) KSKhas been observed by CLEO and BaBar experiments.

M(c(2S)) --- float in 3.63-3.67GeV/c2

(c(2S)) --- float in 10 – 40 MeV

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Summary

We have observed a ’c2 (2 3P2) candidate at 3.93GeV/c2 in the DD process and measured a number of new reactions and decay modes. c0/c2 /K+K-/KSKS, c pp, c 4. c f2f2, c2 K*K* The measured c0 and c2 production rates are consistent with previously measured ’s and BFs.

cpp is consistent with previous measurements. In c four mesons, we find some deviations from previous measurements of B and BF.

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Backup slides

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Meson observations in two-photon reactions

Observed mesons in two-photon reactions could be “concrete candidates” for the sequential qq mesons,if their two-photon decay widths are appropriately large.

Light-quark mesons: 0 : ’0f0(980), f0’s (in 1.3 – 1.8 GeV) region?; a0(980)2f2(1270), f2’(1525), f2(2050) …? ; a2(1320), a2(1700), …2: 2(1860)?Charmonia: 0 : c1Sc(2S)0 c0

2c2(1P), c2(2P)?2 : None observed

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K0SK0

S preliminary results

Very clean KsKs signal samples (almost background free)

pt

Ksreconstruction

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3.5 GeV(e+), 8 GeV(e)

　　　 Ecm(ee) = 10.6 GeV = m((4S))

World-highest luminosity

KEKB Accelerator

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Good momentum/energy/vertex resolutions

Drift chamber(CDC)+1.5T solenoid,

CsI EM calorimeters, Silicon vertex detector

Excellent Particle-ID performance

　 CsI calorimeter – Electron identification

TOF counter, Aerogel-Cherenkov(ACC), dE/dx

-- Excellent performance of (e,)/K/p separation in wide momentum range

High muon detection efficiency

RPC for KL and muon detections (KLM)

Belle Detector

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c c0 　　　 c

2

Fits of the invariant-mass distributions

4

2K2

4K

Fit: background – 2nd-order polynomial charmonium – c,c0 --- finite and

fixed Mto MC

c2 --- assume is negligibly

small (~2MeV comparingtoM

Preliminary

Preliminary

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Study of two-meson resonances in their decays

Searches for resonance components decaying into , K, KK resonances

The intervals c – 50MeV, c0 – 50 MeV, c2 – 30MeV

0

f2(1270)

K*0(892) K+

K+K

f2’(1525) K+K

etc.

Sideband-subtraction technique

Watch distributions in “signal sideband”

27

Two-body decays to two two-meson-resonance 　　　　　　　　　　　　 combinations

M()(heavier) (GeV)

M() (GeV)

c f2f24

M(K)(heavier) (GeV)M

(K)

(lig

hte

r) (

Ge

V)

c2 K*0K*02K2

28

Two-body decays to two two-meson-resonance 　　　　 combinations (cont.)c0 4K

M(K)

(lig

hte

r) (

Ge

V)

M(KK) (GeV)

Number of events after the correctionfor the sideband-subtraction efficiencies

Here, statistical errors only.Upper limits – 95%CL obtained by 2 fits

29

Systematic Error Sources

Trigger efficiency ---- 4%Track reconstruction ---- 6%K-ID efficiency --- 0%(4), 4%(2K2), 8%(4K)Neutral pion veto etc. --- 3%Charmonium sideband subtraction ---- 12% (c) ,11% (c0), 3%(c2)MC statistics ---- 2 - 4%Luminosity function ---- 5%

Total systematic errors 4 final states: 9 – 15% 2K2 final states: 10 – 16% 4K final states: 13 – 17%