phi-psi, feb.-mar., 2006, s.uehara1 experimental studies of charmonia in two-photon collisions at...
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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
Phi-Psi, Feb.-Mar. , 2006, S.Uehara 2
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=+]
Phi-Psi, Feb.-Mar. , 2006, S.Uehara 3
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
Phi-Psi, Feb.-Mar. , 2006, S.Uehara 4
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)
Phi-Psi, Feb.-Mar. , 2006, S.Uehara 5
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
Phi-Psi, Feb.-Mar. , 2006, S.Uehara 6
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
Phi-Psi, Feb.-Mar. , 2006, S.Uehara 7
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
Phi-Psi, Feb.-Mar. , 2006, S.Uehara 8
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)
Phi-Psi, Feb.-Mar. , 2006, S.Uehara 9
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
Phi-Psi, Feb.-Mar. , 2006, S.Uehara 10
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
Phi-Psi, Feb.-Mar. , 2006, S.Uehara 11
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
Phi-Psi, Feb.-Mar. , 2006, S.Uehara 12
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
Phi-Psi, Feb.-Mar. , 2006, S.Uehara 13
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)
Phi-Psi, Feb.-Mar. , 2006, S.Uehara 14
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
Phi-Psi, Feb.-Mar. , 2006, S.Uehara 15
Distributions of four-meson invariant masses
cc0 , and c2
seen in all the modes,
c c0 c2
42K2
4K
misidentified (2S)
Preliminary
Phi-Psi, Feb.-Mar. , 2006, S.Uehara 16
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)
Phi-Psi, Feb.-Mar. , 2006, S.Uehara 17
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
Phi-Psi, Feb.-Mar. , 2006, S.Uehara 18
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
Phi-Psi, Feb.-Mar. , 2006, S.Uehara 19
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.
Phi-Psi, Feb.-Mar. , 2006, S.Uehara 20
Backup slides
Phi-Psi, Feb.-Mar. , 2006, S.Uehara 21
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
Phi-Psi, Feb.-Mar. , 2006, S.Uehara 22
K0SK0
S preliminary results
Very clean KsKs signal samples (almost background free)
pt
Ksreconstruction
Phi-Psi, Feb.-Mar. , 2006, S.Uehara 23
3.5 GeV(e+), 8 GeV(e)
Ecm(ee) = 10.6 GeV = m((4S))
World-highest luminosity
KEKB Accelerator
Phi-Psi, Feb.-Mar. , 2006, S.Uehara 24
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
Phi-Psi, Feb.-Mar. , 2006, S.Uehara 25
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
Phi-Psi, Feb.-Mar. , 2006, S.Uehara 26
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%
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