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Charmonium Physics at BESIII

Charmonium Physics at BESIII. Changzheng YUAN IHEP, Beijing Jan. 14, 2004. There were many discussions on charmonium physics There were talks on BESIII Here is a talk connect these two topics. Charmonia production at BESIII. J/   (2S)  (3770)  (4040)  (4160). Ecm of BEPCII

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Charmonium Physics at BESIII

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  1. Charmonium Physics at BESIII Changzheng YUAN IHEP, Beijing Jan. 14, 2004

  2. There were many discussions on charmonium physics • There were talks on BESIII • Here is a talk connect these two topics

  3. Charmonia production at BESIII • J/ • (2S) • (3770) • (4040) • (4160) Ecm of BEPCII 2.0 GeV -4.2 GeV charmonium + states from their decays

  4. Charmonia production at BESIII ISR also need to be considered: Observed cross section: At BESIII:

  5. Charmonia production at BESIII Average lum.=0.5×peak lum. 1yr=107s data taking time • The big (2S) sample is extremely • useful for the charmonium physics • study, since it can produce all n=1 • charmonium states and n=2 S-wave • spin-singlet state c(2S). • The huge J/  sample for light • hadron spectroscopy study, the big • samples (many years’ data taking) • of (3770), (4040) and (4160) • for charmed meson studies also • supply information for charmonium • physics study.

  6. Here we will focus on --- • Search for hc(1P1) state • Hadronic decay dynamics and “” puzzle • The continuum amplitude and the data taking strategy • J/ψ study via ψ(2S) sample • e+e-charmonium+X for a study of charmonium production mechanism

  7. Search for hc(1P1) state hc(1P1): the only missing charmonium state below charm threshold. ψ(3770) Charm threshold n2S+1LJ

  8. Search for hc(1P1) state (in history) E760 • Inconclusive evidence from R704 at ISR (1984), 5 events, • m=3525.4±0.8 MeV • Better evidence claimed by E760 (1989-91) inpp→hc→p0J/y, J/y →e+e-. • m=3526.20±0.25 MeV • Mass close to the center-of-gravity of the triplet P-states (as expected if there are no long range spin-spin interactions) • More statistics taken by E835 • Not confirmed. • Not observed in B decays in the light hadron channel for ηc’observation. • Where it can be found: • B decays at B factories • ψ(2S) decays at CLEOc (if take data!) • Hera-B or a similar • hadron machine • [ PRD63, 014007(2001) ] • 4. BESIII

  9. Search for hc(1P1) state Mass: c.o.g. of cJ states ≈ 3526 MeV tot ～ 510 keV (pQCD) ～1100 keV (NRQCD) (ψ’hcπ0)=0.12(αM/αE) keV B(ψ’hcπ0)=(4.3±0.5) (αM/αE) ×10-4 (αM/αE =1-3) With S-D mixing (θ=-12°) (ψ’hcπ0)=0.06(αM/αE) keV B(ψ’hcπ0)=(2.2±0.2) (αM/αE) ×10-4 (ψ’hcπ0)=0.84 keV B(ψ’hcπ0)=30 ×10-4 Kuang, Tuan, Yan PRD37, 1210 (1988) Kuang, PRD65, 094024 (2002) P. Ko, PRD52, 1710 (1995) (0.6-9.0) ×106ψ’hcπ0 in 3 ×109 produced ψ’s. B(ψ’hcπ0)=(2-30) ×10-4

  10. Search for hc(1P1) state PQCD: B(hcγηc)=80% B(hcLH)=13% Kuang, Tuan, Yan PRD37, 1210 (1988) PQCD: B(hcγηc)=88% B(hcLH)=8.8% NRQCD: B(hcγηc)=41% B(hcLH)=48% Kuang, PRD65, 094024 (2002) • In all cases, hcγηc is the dominant decay mode, so one can • search for hc with the hadronic decay channels of ηc. • In some cases, direct search for hc in hadronic decays also possible.

  11. Search for hc(1P1) state Br = (0.5 – 7.5)×10-6 60-900 events/year • y(2S)  p0 hc(1P1) ggg hc  ggg 4K Backgrounds: y(2S)  g cc1, gcc2,, hy,p0p0y • Very small! There are many more exclusive hc decay modes!

  12. Search for hc(1P1) state • In case observed by others, what BESIII can do: • Precision measurements of mass, decay modes • Absolute decay branching fractions • Production rates in ψ’ decays, χc2 decays …

  13. Search for hc(1P1) state in inclusive π0 spectrum • MC samples: • 2M inclusive ψ’ decays by lund_charm • 1M ψ’π0hc(1P1)ggg hc by phase space BESIII 2004 Simulation (very preliminary) Momentum resolution (4.0 MeV/c) Efficiency is about 30%! χ2 of 1C fit Raw γγ mass Cut here Input hc(1P1) parameters: mass: 3525 MeV width: 1 MeV ψ’π0hc(1P1)

  14. Search for hc(1P1) state in inclusive π0 spectrum BESIII 2004 Simulation (very preliminary) 3G ψ’anything Parametri- zation, Scaling, sampling 2M ψ’anything Data=inclusive+signal×BR Fit with polynomial+ Gaussian smeared BW 1M ψ’π0hc(1P1)

  15. Search for hc(1P1) state in inclusive π0 spectrum B(ψ’hcπ0)=2×10-4 B(ψ’hcπ0)=4×10-4 BESIII 2004 Simulation (very preliminary) B(ψ’hcπ0)=10×10-4 B(ψ’hcπ0)=20×10-4 B(ψ’hcπ0)=30×10-4 Even the signal cannot be Seen by eyes, significance Still can be large!

  16. Search for hc(1P1) state in inclusive π0 spectrum • Very rough simulation indicates observation of hc(1P1) is possible if the BR is not very small, so that absolute hc(1P1) decay branching fractions can be measured. • A better simulation code is desired, and a set of optimized π0 selection criteria is needed (background will be lower, efficiency will be higher). • The parameterization of the background shape is crucial for the fitting procedure. • The non-Gaussian tails of the resolution function need careful measurement from real data.

  17. Absolute BR of ηc(2S) at BESIII BESIII 2004 Simulation (very preliminary) 100k ψ(2S)γηc (2S) ηc(2S) mass: 3638 MeV width: 18 MeV Energy resolution 6 MeV. One expects small bump in the photon spectrum for the ηc(2S) at E = 48 MeV!

  18. Absolute BR of ηc(2S) at BESIII 2M ψ(2S)anything (lund_charm) More studies needed to further improve the S/N at low energy! It could be hard to observe in the inclusive photon spectrum, considering the expected extremely low production rate in ψ(2S) decays. 100k ψ(2S)γηc (2S) (phase space) BESIII 2004 Simulation (very preliminary)

  19. pQCD rule and “ρπ puzzle” Review pQCD predicts Qh = ≈ 12% “15% rule”, “14% rule”, “12% rule” in literatures ----- “pQCD rule” Mark-II at SPEAR found while many channels give ratios around 12%, ψ(2S) and J/ψρπ violate “pQCD rule”, so does K*K. ψ(2S) decays suppressed ----- “ρπ puzzle” K*K The assumptions: 1. pQCD is valid at c-quark mass 2. “pQCD rule” derived for inclusive decays holds for exclusive channels. ρπ

  20. pQCD rule and “ρπ puzzle” Review Many experimental results (esp. from BES) Many theoretical models Explanation still not satisfactory ضء@#$%^&* *()&%*)(#%дмфёЊ حشع٣ؤضء ž¤&ùÐ… • Questions need to be fixed: • Is the abnormal in J/ψ or in ψ(2S) decays or in both? • Are there assumptions behind the experiments and/or theories? • What is the key issue to solve the problem? The puzzle remains a puzzle … Both experimentalists and theorists are working hard …

  21. pQCD rule and “ρπ puzzle” Recent progress • Continuum amplitude is very important in ψ decay study • [Ping Wang, Changzheng Yuan and Xiaohu Mo] • --the experimental data need to be revised • --theoretical inferences need to be reexamined • The missing ψ’ρπ may due to mixing of ψ(2S) and ψ(1D) • [J. L. Rosner] • --pQCD hold for J/ψ and ψ(2S) • --abnormal is in ψ(1D) decays

  22. The continuum amplitude In e+e- annihilation experiment for charmonium production, continuum amplitude contributes to all decay channels … e+e-ψ(2S) @ BESII Except for scan experiment, the continuum amplitude has been overlooked in both experiment and theory!

  23. The continuum amplitude σtheo σ’exp

  24. The continuum amplitude Continuum contribution becomes larger after considering ISR and beam spread!

  25. The continuum amplitude There is interference… J/ψ ψ(2S) • |aggg|=0 • |aggg|=|a| • |aggg|=3.4|a| • |aggg|=5|a| • |aggg|=10|aγ|

  26. The continuum amplitude CESRc The consequences: 1. Results from different experiments not comparable a) beam spread (reduce/shift peak) b) data taking energy (hadron peak) c) selection criteria (s-dependent) 2. Wrong theoretical inferences a) the form factors b) the relative phase between strong and electromagnetic decays BEPC2 PLB574, 41 (2003) (e+e-ρπ) at Ecm=mψ(3770). 0.5 MeV shift 90-95 % RES

  27. The form factors  0 and +- P. Wang et al., PLB557, 192(2003)

  28. The universal -90°phase The phase between strong and EM decays of resonance |φ| J/ψ Decays: 1. AP: 90 ° M. Suzuki, PRD63, 054021 (2001) 2. VP: (106 ±10) ° J. Jousset et al., PRD41, 1389 (1990) D. Coffman et al., PRD38, 2695 (1988) N. N. Achasov, talk at Hadron2001 3. PP: (90 ±10) ° M. Suzuki, PRD60, 051501 (1999) (103 ±7) ° BES, PRD69, (2004) 4. VV: (138 ±37) ° L. Köpke and N. Wermes, Phys. Rep. 74, 67 (1989) 5. NN: (89 ±15) ° R. Baldini et al., PLB444, 111 (1998) ψ(2S)VP 1. φ=180 °(± 90 ° ruled out!) M. Suzuki, PRD63, 054021 (2001)

  29. The universal -90°phase Haber and Perrier, PRD32, 2961(1985) VP Four equations for four unknowns:

  30. The universal -90°phase J/ψVP hep-ph/0303144 with continuum! Two solutions With opposite Sign!

  31. The universal -90°phase ψ(2S)VP Assuming Rψ(2S)=RJ/ψ hep-ph/0303144 with continuum! • Can’t rule out (nearly) orthogonal phase • The phase is negative PRD63, 054021 (2001) Without continuum!

  32. The universal -90°phase ψ(2S)PP B ((2S) KS KL ) =5.2410 – 5 K+K– & +  inputs ; Input 1:DASP; Input 2:BESI ; Input 3: K+K– from BESI & + by form factor. Yuan, Wang, Mo PLB567 (2003)73 BESII hep-ex/0310024 ψ(2S) π+π- ψ(2S) K+K- ψ(2S) KS KL First measurement of the phase in (2S) decays φ –82±29° 121 ±27 °

  33. The universal -90°phase ψ(3770)ρπ Using mixing angle θ=12°, assuming ψ(2S)ρπ completely missing, ψ(3770)ρπ is enhanced! or Using ωπ form factor to estimate ρπ form factor: Comparable! Interference?

  34. The universal -90°phase ψ(3770)ρπ To measure B(ψ(3770)ρπ), the best way is to do the energy scan! The band is for non-zero B(ψ(2S)ρπ)! σ(K*0K0+c.c.) For φ=-90°! Wang, Yuan and Mo PLB574, 41(2003). MK3 UL (<6.3pb) Favors φ=-90°! Missing ρπ signal and/or enhanced K*0K0 signal indicate BRs at 10-4 level. Destructive/constructive interference

  35. The hidden assumptions VP: • Assumptions: • EM amplitude (EM form factor) only depends on the quark charge • a3g and ε have same phase • Higher order term negligible • ISR affects all channels the same (all measurements assumed ISR negligible) PP: Need high precision ψ’ and J/ψdata to check!

  36. Rosner’s model for “ρπ puzzle” • Assumptions: • pQCD works for ψ(1S) and ψ(2S)  ρπ • Missing ψ’ ρπ due to 2S and 1D mixing Using mixing angle θ=12° This means a big ψ(3770) ρπ decay partial width (9 keV!), or, big 1D  ρπ transition matrix element. Why?

  37. Rosner’s model for KSKL mode Wang, Mo, Yuan • Assumptions: • pQCD works for ψ(1S) and ψ(2S) KSKL • Enhanced ψ’ KSKLdue to 2S and 1D mixing BES2003: B(ψ’ KSKL) =(5.24±0.47 ±0.48) ×10-5 B(J/ψ KSKL)=(1.82±0.04 ±0.13) ×10-4 Qh=(28.2 ±3.7)% Using mixing angle θ=12° Range due to phase between two amplitudes B(ψ(3770) KSKL)=(0.12-4.0) ×10-5 Current data can reach upper bound, CLEOc/BESIII can reach lower bound!

  38. Test of the Rosner’s model Measurement of the light hadron decays of ψ(3770) is crucial for testing this model for solving the “ρπ” puzzle. Need high precision data [ψ(3770)] to check! High precision data [ψ(4040), ψ(4160)] may also supply information! Is the “puzzle” in ψ(3770) decays?

  39. The small BR channels at BESIII: an example hep-ph/ 0303144 ψ’KSK+π-+c.c. ψ’KSK+π-+c.c. B(ψ’K*+K-+c.c.)=2×10-5 B(ψ’K*+K-+c.c.)=0.4×10-5 Still room to suppress the background! BR at 10-5 level can be measured in high precision. BESIII 2004 Simulation (very preliminary) KSπ mass (GeV) KSπ mass (GeV)

  40. Energy scan: the way for high precision BR measurement e+e-ρπ @ ψ(3770) e+e-X @ ψ(2S) All the channels should be measured by a energy scan! Data sample should be taken at a few energy points, instead of at resonance peak only.

  41. Data taking strategy To separate continuum from resonance, at least data at three energy points should be taken (if resonance parameters need to be measured, more points needed). Different channel has different phase and amplitude ratio, three points may not result in optimized precisions for all the channels. • How many points? • At what energies? • How to distribute luminosity? Use toy Monte Carlo to optimize!

  42. Data taking strategy: the MC model

  43. Data taking strategy: how many points?

  44. Data taking strategy: the energies?

  45. Data taking strategy: the luminosities?

  46. Data taking strategy: summary We are working hard … No problem to finish before BESIII running …

  47. J/ψ study using ψ(2S) sample Best precisions on B(J/ψμ+μ-) and B(J/ψπ+π-π0) are achieved with ψ(2S) samples. • Advantages: • High precision total number of events • No QED background • No beam associated background • Trigger efficiency free • It is suitable for • High precision measurement for channels with large BR; • Searching for some of the rare decay modes • Disadvantages: • Sample is small • Two more tracks • J/ψ is moving Need more investigation on the light hadron spectroscopy study using partial wave analysis method with ψ(2S)π+π-J/ψ.

  48. J/ψ study using ψ(2S) sample 3×109 ψ (2S)= 1×109 J/ψ Measurement of B(J/ψπ+π-π0) /B(J/ψμ+μ-) B(J/ψπ+π-π0) B(J/ψμ+μ-) J/ψe+e- J/ψπ+π-π0 BESIII 2004 Simulation (very preliminary) J/ψμ+μ- Kinematic fit + (ECAL+dE/dx) for J/ψμ+μ- selection. Kinematic fit + (ECAL+dE/dx+MU) for J/ψ π+π-π0 selection.

  49. Measurement of B(J/ψπ+π-π0) /B(J/ψμ+μ-): errors Lots of systematic errors cancel out! Only the residual differences affect relative BR measurement. backgrounds Systematic uncertainties on tracking kinematic fit photon/π0 efficiency backgrounds … can be studied with large data sample. Particle ID is not used!

  50. Measurement of B(J/ψπ+π-π0) /B(J/ψμ+μ-): errors Depends on the precisions of the background channels and simulation Current WA dominated by BES result from about 4 M ψ(2S) ～1% precision on BR is a big challenge! PDG2002: B(J/ψπ+π-π0)=(1.5 ±0.2 )%! BESII(prel.): B(J/ψπ+π-π0)=(2.10 ±0.12 )%! PDG2010: B(J/ψπ+π-π0)=(2.xxx±0.017)%! BESII preliminary

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