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Physics at BES

Physics at BES. Shan JIN (for the BESIII Collaboration) Institute of High Energy Physics (IHEP) jins@mail.ihep.ac.cn USTRON09, Poland September 12-16, 2009. Outline. Introduction of BES experiments and Physics at BES Highlights at BESII Status of BESIII and preliminary results

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Physics at BES

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  1. Physics at BES Shan JIN (for the BESIII Collaboration) Institute of High Energy Physics (IHEP) jins@mail.ihep.ac.cn USTRON09, Poland September 12-16, 2009

  2. Outline • Introduction of BES experiments and Physics at BES • Highlights at BESII • Status of BESIII and preliminary results • Future prospects at BESIII • Conclusion

  3. Beijing Electron Positron Collider (BEPC) at IHEP Linac Storage Ring BESI: 1989-1998 BESII: 1999-2004 L ~ 51030 /cm2s at J/ Ebeam~ 1 – 2.5 GeV BES BSRF BESIII: 2008- Physics run started in March, 2009. 100M (2S) and 200M J/ events collected BEPCII: L reached 31032/cm2sat (3770) designed L: 1033/cm2s 3

  4. 北京正负电子对撞机（BEPC）示意图 储存环的周长为240.4米 注入器长202米 对撞能量2-5GeV 物理目标

  5. Why tau-charm physics is interesting in the past in the era of LHC in the future Abundant resonances(J/y family, huge Xsections) Tau-charm threshold production(in pairs tagging  background free, no fragmentation, kinematic constrains, quantum coherence,…) Charm quark: A bridge between pQCD and non-pQCD A ruler for LQCD J/y decay Gluon rich environment Flavor physics Complementary to LHC: virtual vs real A broad spectrum & efficient machine:

  6. What (highlight) physics interested us hep-ex/0809.1869 • Light hadron spectroscopy • Full spectra: normal & exotic hadrons QCD • How quarks form a hadron ? non-pQCD • Charm physics • CKM matrix elements  SM and beyond • mixing and CPV  SM and beyond • Charmonium physics • Spectroscopy and transition  pQCD & non-pQCD • New states above open charm thresholds  exotic hadrons ? • pQCD: rp puzzle  a probe to non-pQCD or ? • Tau physics and QCD • Precision measurement of the tau mass and R value • Search for rare and forbidden decays Precision test of SM and search for new physics

  7. Light hadron spectroscopy Glueball spectrum from LQCD Many results in BESII: ~ 50 publications Much more from BESIII: 100 statistics, 10 g resolution • Motivation: • Establish spectrum of light hadrons • Search for non-conventional hadrons • Understand how hadrons are formed • Study chiral symmetry in QCD • Why at a tau-charm collider ? • Gluon rich • Larger phase space than at higher energies • Clean environment, JPC filter Y. Chen et al., PRD 73 (2006) 014516

  8. Multi-quark State, Glueball and Hybrid • Hadrons consist of 2 or 3 quarks： Naive Quark Model： • New forms of hadrons: • Multi-quark states：Number of quarks >＝ 4 • Hybrids：qqg，qqqg … • Glueballs：gg， ggg … Meson（ qq ） Baryon（q q q） How quarks/gluons form a hadron is far from being well understood.

  9. Multi-quark states, glueballs and hybrids have been searched for experimentally for a very long time, but none is established.However, the effort has never been stopped, especially, during the past three years, a lot of surprising experimental evidences showed the existence of hadrons that cannot (easily) be explained in the conventional quark model. Searches for new forms of hadrons are of special importance at BES since J/psi decays are believed as an ideal factory to search and to study exotic hadrons.

  10. Charmonium physics • Examples of interesting/long standing issues: • rp puzzle • Missing states ? • Mixing states ? • New states above open charm thre.(X,Y,Z,…) • What to study ? • Production, decays, transition, spectrum • For what ? • A lab for pQCD and non-pQCD • Calibrate LQCD • How quarks form a hadron ? • Why at a tau-charm collider ? • A clean environment • Tagging possible • Abundantly produced

  11. Highlights at BESII

  12. BESII 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+p2) z = 2.3 cm

  13. World J/ and (2S) Samples (106) Largest from BES J/ (2S) 2002 2001

  14. Phys. Rev. Lett. 91, 022001 (2003) Observation of an anomalous enhancement near the threshold of mass spectrum at BES II J/ygpp BES II acceptance weighted BW +3 +5 -10 -25 M=1859 MeV/c2 G < 30 MeV/c2 (90% CL) c2/dof=56/56 0 0.1 0.2 0.3 M(pp)-2mp (GeV) 3-body phase space acceptance

  15. Phys. Rev. Lett. 95, 262001 (2005) At BESII: Observation of X(1835) in Statistical Significance 7.7  BES II The same origin as ppbar mass threshold?  a ppbar bound state? The +- mass spectrum for  decaying into +- and  

  16. Phys. Rev. Lett. 93, 112002 (2004) Observation of an anomalous enhancement near the threshold of mass spectrum at BES II BES II 3-body phase space For a S-wave BW fit: M = 2075 12  5 MeV Γ = 90  35  9 MeV

  17. Observation of  mass threshold structure X(1810) in J/   at BESII BES II Background X(1810) M2(g) M2(gw) M() Jpc favors 0++ Phys. Rev. Lett., 96 (2006) 162002 Possible theoretical interpretations: glueball, hybrid, multiquark?

  18. Very broad 1- - resonance X(1580) observed in K+K- mass spectrum in J/ K+K-0 at BESII BES II Background Phys. Rev. Lett. 97 (2006) 142002 So far the only reasonable interpretation is a multiquark state due to its very broad width

  19. σ at BES • BES II observed σ in J/  +-. • Pole position from PWA: BES II

  20. κ at BESII • BESII firmly established neutral  in J/  K*0K  KK in 2006: • PWA result Pole position: BES II

  21. Observation of charged  at BESII • New result: Charged  observed at BESII in • Different parameterizations are tried in PWA. The pole position: BESII Preliminary K*(1410), K*(1430) consistent with neutral  M(K0) GeV/c2 

  22. QCD studies at low energies ? BESIII: < 2% Phys.Lett.B677,(2009)239 • Understand where exactly pQCD becomes invalid • Precision measurement of as running • Precision measurement of R • input to • Related toaQED (s), prediction of higgs mass and g-2 • A new measurement at BESII on R • Precision at ~ 3.5% • A new determination of s(s): s(M2Z) = 0.1170.012 In good agreement with previous results

  23. Resonance parameter fit Probability =31.8% Phys. Lett. B660, (2008)315 Heavy charmonia parameters were fitted with the data between 3.7–5.0GeV, taking into accounts the phase angles, interference, energy-dependent width, etc.

  24. Anomalous y(3770) lineshape Black dots: data Red dots: data subtracting J/y, y(3686) and continuum contribution Green line: fit with one y(3770) hypothesis; Red line: fit with two cross section Blue line: fit with two amplitude Check all lines !!! PRL101 (2008) 102004

  25. Status of BESIII and preliminary results

  26. BEPC II Storage ring: Large angle, double-ring RF SR RF Beam energy: 1.0-2 .3GeV Luminosity: 1×1033 cm-2s-1 Optimum energy: 1.89 GeV Energy spread: 5.16 ×10-4 No. of bunches: 93 Bunch length: 1.5 cm Total current: 0.91 A BESIII detector IP

  27. BESIII Commissioning and data taking milestones Mar. 2008: first full cosmic-ray event April 30, 2008: Move the BESIII to IP July 18, 2008: First e+e- collision event in BESIII Nov. 2008: ~ 14M y(2S) events collected April 14, 2009 ~100M y(2S) events collected May 30, 2009 42 pb-1 at continuum collected July 28, 2009 ~200M J/y events collected Peak Lumi. @ Nov. 2008: 1.2 1032cm-2s-1 Peak Lumi. @ May 2009: 3.21032cm-2s-1

  28. Detector performance and calibration ●Layer 7 ●Layer 22 Wire reso. Design: 130 mm dE/dx reso.: 5.80% Design：6-8% CsI(Tl) energy reso. Design: 2.5%@ 1 GeV Barrel TOF reso.: 78 ps Design：80-90 ps Bhabha

  29. E1 transitions: inclusive photon spectrum c1 c2 co c1,2 J/ c BESIII preliminary

  30. Observation of hc: E1-tagged y(2S)p0hc,hcghc background subtracted BESIII preliminary BESIII preliminary N(hc)= 2540±261 c2/d.o.f = 39.5/41.0 Systematic errors under study CLEO’s results (arXiv 0805.4599v1) : M(hc)Inc= 3525.35±0.23±0.15 MeV Br(y’p0hc)×Br(hcghc)Inc =(4.22±0.44±0.52) ×10-4 (G(hc) fixed at G(cc1) ~0.9MeV CLEOc: Combined E1-photon-tagged spectrum and exclusive analysis M(hc)avg= 3525.28±0.19±0.12 MeV Br(y’p0hc)×Br(hcghc)avg =(4.19±0.32±0.45) ×10-4 (arXiv 0805.4599v1) Select E1-photon to tag hc A fit of D-Gaussian signal+ sideband bkg. yield: M(hc)Inc = 3525.16±0.16±0.10 MeV G(hc)Inc = 0.89±0.57±0.23 MeV (First measurement) Br(y’p0hc)×Br(hcghc)Inc =(4.69±0.48(stat)) ×10-4 (G(hc) floated) =(4.69±0.29(stat)) ×10-4 (G(hc) fixed at G(cc1))

  31. Observation of hc : Inclusive y(2S)p0hc BESIII preliminary BESIII preliminary Inclusive p0 recoil mass spectrum background subtracted Systematic errors under study Select inclusive p0 A fit of D-Gaussian signal + 4th Poly. bkg yield N(hc) = 9233±935, c2/d.o.f = 38.8/38.0 Combined inclusive and E1-photon-tagged spectrum Br(y’p0hc) =(8.42±1.29(stat)) ×10-4 (First measurement) Br(hcghc) =(55.7±6.3(stat))% (First measurement) 31

  32. Study of (2S)→ 00 , ( → ,0 → ) (2S)00 Nc016645±175 Nc24149±82 (2S) Nc01541±56 Nc2291±23 • Interesting channels for glueball searches • Based on 110M y(2S) • BK study from 100M inclusive MC sample and 42pb-1 continuum sample • Unbinned Maximum Likelihood fit: • Signal: PDF from MC signal • Background: 2nd order Poly. CLEO-c arxiv:0811.0586

  33. Confirmation of the BESII observation: pp threshold enhancement in J/y decays  BES III preliminary BES II (2S)→ J/y 0.3 M(pp)-2mp (GeV) +3 +5 -10 -25 M=1864.6 ± 5.3MeV/c2 G < 33 MeV/c2 (90% CL) M=1859 MeV/c2 G < 30 MeV/c2 (90% CL) PRL 91 (2003) 022001

  34. Confirmation of BESII observation: No pp threshold enhancement in y’ decays  BES III preliminary BES II Mpp(GeV) No significant narrow enhancement near threshold (~2 if fitted with X(1860)) No enhancement in y’ decays In fact, no enhancement in ψ’ ,ϒ(1S) decays and in the process of J/y wppbar show that FSI unlikely . PRL 99 (2007) 011802

  35. Study of ccJ VV, V=w,f • Backgrounds from sideband & 100M MC events • Clear cc1 ff signal • to be understood BESIII preliminary Test QCD-based theory at ccJ decays Puzzles for cc0  VV: no helicity suppress cc1 ff, ww highly suppressed owing to symmetry of identical particles cc1 fw OZI doubly suppressed

  36. First observation of cc1 wf BESIII preliminary Background from sideband & 100M MC events Clear signal from cc1 w(p+p-p0/rp0)f(K+K-)

  37. Future prospects at BESIII

  38. Event statistics at BESIII *CLEO took 10 nb D production cross section while we took 5 nb

  39. Precision measurement of CKM:Branching rations of charm mesons • Vcd /Vcs: Leptonic and semi-leptonic decays • Vcb: Hadronic decays • Vtd /Vts: fD and fDs fromLeptonic decays • Vub: Form factors of semi-leptonic decays • Unitarity Test of CKM matrix

  40. CKM matrix elements measurement

  41. Precision test of SMand Search for new Physics • DDbar mixing DDbar mixing in SM ~ 10 –3 -10 –10 DDbar mixing sensitive to “new physics” Our sensitivity : ~ 10-4 • Lepton universality • CP violation • Rare decays FCNC, Lepton no. violation, ...

  42. QCD and hadron production • R-value measurement • pQCD and non-pQCD boundary • Measurement of as at low energies • Hadron production at J/y, y’, and continium • Multiplicity and other topology of hadron event • BEC, correlations, form factors, resonance, etc.

  43. R-value measurement Errors on R will be reduced to 2% from current 6%

  44. Prospects of glueball searches at BESIII

  45. J/ decays are an ideal factory to search for and study light exotic hadrons: • The production cross section of J/ is high. • The production BR of hadrons in J/ decays are one order higher than ’ decays (“12% rule”). • The phase space to 1-3 GeV hadrons in J/ decays are larger than  decays. • Exotic hadrons are naively expected to have larger or similar production BR to conventional hadrons in J/ decays. • Clean background environment compared with hadron collision experiments, e.g., “JP, I” filter.

  46. One Important Physics Goal of BESIII With 1010 J/psi events, we hope to answer: • Whether glueballs exist or not? • Naively, we estimate in each exclusive decay mode: • If the eff. is about 20%, we would have 20000 events for each decay mode  we should observe a relative narrow (width: 50~200MeV) glueball if it exists.

  47. Difficulties (I) • Theoretically: • Predictions on glueball masses from LQCD may be unreliable due to quench approximation. • No predictions on the widths so far (even the order). • No prediction on the production rate (J/  G). • Mix with qqbar mesons or even with 4q, qqg mesons? (dirty?) What is the mixing mechanism from the first principle?

  48. Difficulties (II) • Experimentally: • Data sample is not big enough (it is not a problem for BESIII) • No good way modeling background at low energy, in many cases we have to study bck via data. • Interferences among mesons make the mass/Dalitz plots very complicated  • PWA is crucial for hadron spectroscopy at BESIII • But PWA may face many uncertainties.

  49. About scalar glueball • Many scalar mesons in the mass range 1.4~1.8 GeV, where a scalar glueball is predicted to be. More studies will be performed at BESIII. • More theoretical studies are also needed: • Not only glueball mass, but also width • Decay patterns • Production rate in J/psi radiative decays • Mixing mechanism

  50. 2++ glueball candidates • Lattice QCD predicts the 2++ glueball mass in the range of 2.2~2.4 GeV • (2230) was a candidate of 2++ glueball: • It was first observed at MARKIII in J/KK • It was observed at BES I in J/KK, , ppbar • It was not observed at DM2.

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