Recent BES charmonium results Frederick A. Harris University of Hawaii Jiangchuan CHEN Institute of High Energy Physics Beijing, China HEP2003 Europhysics Conference on High Energy Physics July 17 – 23, Aachen, Germany Representing:

OUTLINE  Introduction  J/    p p-bar   c mass, width, and BFs   c  Λ Λ-bar   (2S), J/   K S K L   (3770)  π + π - J/ψ  Summary

The Beijing Electron Positron Collider L ~ ~5  /cm 2  s at J/  peak E cm ~2-5 GeV A unique e + e - machine in the  -charm energy region since Beijing, China

BESII Detector VC:  xy = 100  m TOF:  T = 180 ps  counter:  r  = 3 cm MDC:  xy = 220  m BSC:  E/  E= 22 %  z = 5.5 cm  dE/dx = 8.5 %   = 7.9 mr B field: 0.4 T  p/p=1.7  (1+p 2 )  z = 2.3 cm

BESII Monte Carlo Simulation A Geant3 based package SIMBES for BESII simulation. We check the data/MC consistency in J/ψ  e + e -, μ + μ -, pp, ρπ, ΛΛ high purity channels. The consistency is reasonable. It is applied in the BES analysis at J/ψ energy region the first time.

Data Collected with BESI and BESII This year:  ~20 pb -1 below  (2S) ~ 6 pb -1

World J/  and  (2S) Samples (×10 6 ) J/   (2S)

NN bound states (baryonium)?? + n+  deuteron: loosely bound 3-q 3-q color singlets with M d = 2m p -  baryonium: loosely bound 3-q 3-q color singlets with M b = 2m p -  ? attractive nuclear force attractive force?? There is lots & lots of literature about this possibility

study pp from J/    pp pp  e + e  Bardin etal e + e   hadrons FENICE e+e6e+e6 2m p Fit: M = 1870 ± 10 MeV  = 10 ± 5 MeV R. Calabrese PEP-N work-shop proceedings DM2 unpub. Motivations: Is there a narrow J PC =1  pp system near M pp =2m p ?

study pp from J/    pp C-parity = + S (P?)-wave (for M pp  2m p )  probes J PC = 0  (0  ?)states complements pp  e  e  and e  e  annihilation unpolluted (by other hadrons) environment

Use BESII ’ s 58M J/  decays J/    pp Select J/    pp 4-C kinematic fit dE/dx for proton id non-pp bkg small main bkg from J/     pp ???? J/    c  c   pp (calibration reaction)

Study J/    0 pp bkg with MC & data J/    0 pp (data) three-body phase space Monte Carlo J/    0 pp   pp (MC) M(pp)-2m p (GeV) no peak!!

Fit to data M=1859 MeV/c 2  < 30 MeV/c 2 (90% CL) J/    pp M(pp)-2m p (GeV) body phase space acceptance  2 /dof=56/56 fitted peak location acceptance weighted BW  10  25

PPbar cos   distribution 1+cos 2   (expected for J/     ) sin 2   M(pp)<1.9 GeV

mass determination bias threshold observed peak BW “peak” below-threshold mass & widths measurements can be biased when there is background

include possible biases as (asymmetric) statistical & systematic errors if what we see is an S-wave resonance: M=1859 MeV/c 2  < 30 MeV/c 2 (90% CL)  10  25 Phys. Rev. Lett. 91, (2003). J/    pp Results

 c Parameters Precise (m J  - m  c ) needed for potential models. But  c mass not well determined: PDG02 CL = 0.001

Previous BES Results 4 M  (2S) Sample: Phys. Rev. D60 (1999) 7.8 M J/  Sample: Phys Rev.D62 (2000)

Width Measurements

 C measurements with BESII 58 M J/  sample Channels: J/   C,  C  K + K -  +  -,  +  -  +  -, K +/- K 0 S  -/+, , and pp. Use PID for  /K/p separation. Select events based on chisquare from kinematic fit. Use U miss = E miss – p miss and P 2 t  (transverse momentum relative to  ) to remove  0 background.

M( pp) J/   C,  C  PP

M(K + K -  +  - ) M(  +  -  +  - ) M(K +/- K 0 S  -/+ ) M(  )

Results: Mass and Width Combined fit of five channels: M(  C ) =  1.0  1.2 MeV/c 2  (  C ) = 17.0  3.7  7.4 MeV/c 2 PDG M(  C ) =  1.5 MeV  (  C ) = MeV Phys. Lett. B555, 174 (2003) J/    η c

Results: Mass and Width PDG2002 BES2003 J/    η c

Results: Branching Fraction Preliminary Systematic Errors Product Branching Fractions J/    η c

Results: Branching Fraction Preliminary Dividing by B(J/    η c ) = 1.3 ± 0.4 % (PDG2002) B(η c  φ φ) is smaller than PDG and agrees with Belle measurement (hep-ex/ ). † H.C. Huang et al., hep-ex/ * Calculated from results in F. Fang, et al., PRL 90:071801,2003. J/    η c

 CJ  Λ Λ-bar Color octet mechanism (COM) important for P-wave quarkonium decays. G. T. Bodwin et al., Phys Rev. Lett. D51, 1125 (1995). H.-W. Huang and K.-T. Chao, Phys. Rev. D54, 6850 (1996). J. Bolz et al., Phys. Lett. B392, 198 (1997). COM and a nucleon wave function give reasonable agreement with BES Γ (  cJ  p p-bar) and other results. The partial widths of other baryons can be predicted: Γ (  cJ  Λ Λ-bar) ~½ Γ(  cJ  p p-bar) for  c1 and  c2 S. M. Wong, Eur. Phys. J. C14, 643 (2000).

 CJ  Λ Λ-bar Here we study:  (2s)   cJ   ΛΛ-bar   p  - p-bar  +. Select events with 4 charged tracks and > 0  ’ s. Use PID for charged tracks. Prob > C kinematic fit. Select smallest chi-square and require Prob > See clear Λ Λ-bar signal.

 CJ  Λ Λ-bar Select events around cluster. See clear lambda peak in m(  p). m Λ = ( ± 0.5) MeV/c 2. Agrees well with PDG.

 CJ  Λ Λ-bar Sideband background Monte Carlo Comparison Plot m(Λ Λ-bar)

 CJ  Λ Λ-bar Main physics backgrounds:  (2s)  Λ Λ-bar   0  0 -bar    cJ,  cJ   0  0 -bar Fit: Monte Carlo background shape. Background level floating. Fix  cJ widths to PDG values. Use Monte Carlo mass resolutions. Fitted masses agree with PDG.

 CJ  Λ Λ-bar Results B(  CJ  p p-bar)(10 -4 ) 2.2 ± ± ± 0.10 Phys. Rev. D67, (2003). For N(  (2s) )use  (2s)  +  - J/ , J/  p p-bar. Many systematic errors cancel. PDG

First Observation of ψ(2S) decay to K S 0 K L 0 and measurement of J/ψ decay to K S 0 K L 0 Motivations --Phase between the 3-gluon and single photon annihilation amplitudes: ±90 ° at J/ψ 180 ° at ψ(2S) two body decay (M. Suzuki, Phys. Rev. D (2001) --12% rule test Br(ψ (2S)  K S 0 K L 0 )=Br(J/ψ  K S 0 K L 0 )*12% ? Br(J/ψ  K S K L ) comes from DMII and MARK III more than 14 years ago, with relative errors 18%. -- Here we report a measurement of ψ(2S) decay to K S 0 K L 0 to test above phase rule.

Event selection criteria --Only two good charged tracks and assumed to be π + and π –. --Neutral clusters E γ tot < 1.0 GeV is used to remove the backgrounds. Only reconstruct K S, look at K S momentum for signal P Ks ~ GeV ψ (2S)  K S 0 K L 0

K S 0 momentum distribution. The K S 0 mass sideband background is shown by shaded histogram. K S 0 K L 0 signal K S sideband ψ (2S)  K S 0 K L 0

Background in K S 0 momentum distribution. (f) the dots are data, blue shaded histogram is background from(e), the green shaded region is the sum of the background from (a-d). χ c0  K S 0 K S 0 K S 0 mass sideband (f)

Fit of the K S 0 momentum Spectrum: dots are data, and shaded histograms are from sideband events and other MC simulated backgrounds. The fit yields 164±14 events, and the efficiency for detecting with is(41.44±0.49)% from MC. ψ (2S)  K S 0 K L 0 (1768.5±3.3)MeV/c Preliminary

Fit to the K S 0 momentum spectrum: dots are data, shaded histograms are from mass sideband and other MC simulated backgrounds. K s mass sideband background (1488.2±0.7)MeV/c Preliminary The fit yields 2127±45 events, and the efficiency for detecting with is (37.57±0.22)% from MC. Data Analysis J/ψ  K S K L (With the same way)

Preliminary Results --- With above branching ratio and the branching ratio of, from PDG, phase angle between strong decays and the electromagnetic of the ψ(2S) to pseudoscalar meson pairs is found to be about 90° --- ψ (2S)  K S 0 K L 0

Preliminary Results (PDG value: Br(J/ψ  K S K L )=(1.08±0.14)× ) The interesting is that Q h is enhanced relative to the “12% rule”, while in most cases where it disagrees, it is suppressed. J/ψ  K S K L

Evidence of ψ(3770) non- decay to π + π – J/ψ Motivation ---ψ(3770) is believed to be a mixture of the 2 3 S 1 and 1 3 D 1 states of the system and to decay almost entirely to pure. (P.A. Rapidis et al., (MARK-I), Phys. Rev. Lett. 39, 526(1978)) --- Recently, some theoretical calculations point out that ψ(3770) could decay to non- final states. (H.J. Lipikin, Phys. Lett. B179, 278(1986), Y.P. Kuang, Phys. Rev. D65, (2002) )

Data sample and Monte Carlo -- Data sample: 6.6±0.4 pb -1 of data taken at E cm =3.773 GeV 1.4±0.1 pb -1 at E cm =3.738 GeV to 3.885GeV (by BESII/BEPC) --Event generator: We developed a new generator isrpsi which included J/ψ and ψ(2S) and other resonance production due to initial state radiation effect.

Event Selection for ψ(3770) → π + π J/ψ, J/ψ→ ll 4 good charged tracks PID for e and mu Remove events with photon conversion 4-c kinematic fit

In the figure open circles are data, and the histogram are MC. In the (b), the solid smooth curve is the fit to the data.

Results ---Data sample: Number of ψ(3770) = (5.7±1.3)× Signal events: N evt = 6.8±3.0 (N tot = 9.0 ±3.0, in which 2.2 ±0.4 from backgrounds) Efficiency: 0.171±0.002 ψ(3770) → π + π J/ψ

Summary  Observation of an enhancement in pp system near 2m p in J/    pp. If S-wave: M=1859 MeV/c 2  < 30 MeV/c 2 (90% CL) Exclude all possibilities from known mesons. Baryonium?  10  25

Summary  New  C mass and width: M(  C ) =  1.0  1.2 MeV/c 2  (  C ) = 17.0  3.7  7.4 MeV/c 2  New  C Branching fractions - preliminary

Summary  New branching ratio results on B(  cJ  Λ Λ-bar). Disagrees with Color Octet Model?  First observation of K S 0 K L 0 in ψ(2S) decays:

Summary Measurement of the branching fraction for J/ψ decay to K S 0 K L 0 Evidence of ψ(3770) non- decay to π + π - J/ψ (PDG value: Br(J/ψ  K S K L )=(1.08±0.14)× )

Thank You!

BESII Simulation A Geant3 based package SIMBES for BESII. It agrees with data well and is applied in the BES analysis at Charm energy region first time. J/ψ, ψ (2S)  hadrons. Where shaded are BES data and solid histograms are SIMBES results. J/ψJ/ψJ/ψJ/ψ ψ(2S)

Ks KLKL π+π+ π - Event selection criteria --Only 2 good charge tracks --The 2 charged tracks are assumed to be π + and π -. --Neutral clusters E γ tot < 1.0 GeV is used to remove the backgrounds. Only reconstruct K S, look at K S momentum for signal P Ks ~ GeV --Without extra photon ψ (2S)  K S 0 K L 0

Trigger P KS >1.7 GeV Fig.1 Scatter plot of π + π – invariant mass versus the decay length in the transverse XY plane for events with K S 0 momentum greater than 1.7 GeV/c.

Fit of π + π – invariant mass distribution. ψ (2S)  K S 0 K L 0

Tigger effect Fig.3 the comparison of the K S 0 decay length. Since no trigger effect in the MC simulation now, use a correction factor (76.0±1.8)% to the MC efficiency for ψ(2S) decay to K S 0 K L 0 Cut here(L XY >1cm) Fig.4 The K S 0 momentum distribution. The K S 0 mass sideband background is shown by shaded histogram. K S 0 K L 0 signal K S sideband

Psi(2S)->K S K L systematice erorr

Psi(2S)->K S K L Phase angle C.Z. Yuan et al. Phys. Lett. B567 (2003) 67-72