Charm in China: BEPCII/BESIII

Transcription

1 Charm in China: BEPCII/BESIII 10 th International Workshop on Meson Production, Properties, and Interaction Krakow, Poland June 10-15, 2010 Frederick A. Harris June 10, For the BES Collaboration

2 OUTLINE Introduction BEPCII/BESIII Physics results χ cj (See talk by Kai Zhu) ψ γγj/ψ (See talk by Xiao-Rui Lu) h c(see talk by Kai Zhu) X(1860) & X(1835) f 0 (980) a 0 (980) mixing Beam energy measurement Summary Thanks to Li Haibo, Xu Guofa, Nik Berger, and many other BESIII members. IHEP 2

3 Physics of tau charm region Light hadron spectroscopy. Charmonium: J/ψ, ψ(2s), η C (1S), χ C{0,1,2}, η C (2S), h C ( 1 P 1 ), ψ(1d), etc. New Charmonium states above open charm threshold (X, Y, Z). In J/ψ and ψ(2s) hadronic decays: Exotics : hybrids, glueballs, and other exotics. Baryons and excited baryons. Mesons and mixing of quarks and gluons. Electromagnetic form factors and QCD cross section (R values). High precision tau and charm physics near threshold. Tau mass. Tremendous variety: e ν e μ τ ν μ ν τ u d c s 3 t b

4 Physics of tau charm region Open charm factory : Absolute BR measurements of D and Ds decays Rare D decay D 0 -D 0 bar mixing Quantum correlations (ψ ) CP violation, strong phase. f D+, f Ds, form factors in leptonic D decays Can provide calibrations and tests of lattice QCD. precise measurement (~1.6%) of CKM (Vcd, Vcs) light meson spectroscopy in D 0 and D + Dalitz plot analyses. Search for new physics. Very rich and interesting energy region. 4

5 The Beijing Electron Positron Collider (BEPC) BESII CM Energy ranges from 2 to 5 GeV Luminosity at J/ψ ~ 5 x cm 2 s -1 Beijing, China BESII detector removed in 2004.

6 CLEO-c Late comer to tau charm energy region. Lowered CESR CM energy in 2003 to run in taucharm region. Stopped in Peak luminosity ~0.6 x pb -1 s -1. Luminosity at ψ(3770) ~800 pb -1. ψ : ~25 M. Well understood, state of the art detector. BESIII has a comparable detector and higher luminosity. Future belongs to BESIII.

7 BEPCII/BESIII 7

8 BEPCII: a high luminosity double ring collider Beam energy: GeV Luminosity: cm -2 s -1 Optimum energy: 1.89 GeV No. of bunches: 93 Bunch length: 1.5 cm Total current: 0.91 A SR mode: 2.5 GeV 22 mrad crossing angle Use many bunches and SC mini-beta. SC RF Beam magnets 8

9 BEPCII/BESIII Milestones Mar. 2008: Collisions at 500 ma 500 ma, Lum.: cm -2 s -1 Apr. 30, 2008: Move BESIII to IP July 18, 2008: First e+e- collision event in BESIII Apr. 14, 2009 BESIII 106 M ψ(2s) events July 28, 2009 ~226 M J/ψ events June 1, 2010 ~0.8 fb -1 at ψ(3770) with goal of 1 fb -1 Record Luminosity on May 14, X cm -2 s -1 or 5 X CESRc 30 X BEPC May 15, 2008: detector at IP; 9 First collision event installing SC quads and beam pipe.

10 World J/ψ and ψ(2s) Samples ( 10 6 ) BESIII: J/ψ 2009 ~226M ψ(2s) M MarkIII DM2 BESI BESII BESIII BESII: J/ψ 58M MKI MKII MKIII CBAL BESI BESII CLEO BESIII 10 ψ(2s) 14M

11 Magnet Yoke BESIII Detector SC magnet RPC TOF Be beam pipe MDC CsI(Tl) calorimeter 11

12 BESIII Detector Berylium beam pipe Small-celled, helium-based MDC: cos θ < 0.83 (all 43 layers), < 0.93 (20 layers) σ p /p = 0.58 % at 1 GeV/c; de/dx resol = 6% at 1 GeV/c (hadron) TOF (2 layers in barrel; 1 layer endcap) σ T = 80 ps barrel (Bhabha); σ T = 100 ps endcap CsI electromagnetic calorimeter crystal length: 28 cm (15 X 0 ) energy: 2.5%, space 0.6 cm at 1 GeV Superconducting Magnet 1 T Muon Counter 9 layers of RPCs in barrel; 8 in endcap For details, see talk by F. Harris at Meson

13 April Installation complete 13

14 BESIII Collaboration 300 physicists 43 institutions from 9 countries 14

15 χ cj results 15

16 Radiative decays: ψ(2s) γx Clean exclusive signal High statistics Clear inclusive photon spectrum Excellent photon resolution BESIII preliminary BESIII χ c2 χ c1 χco χ c1,2 γ J/ψ BESIII preliminary η c 16

17 χ cj decays Good place to study gluonium: χ c gg (qq)(qq). C. Amsler and F. E. Close,Phys. Rev. D 53, 295 (1996). Color octet mechanism can be tested. 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., Eur. Phys. J. C 2, 705 (1998). Color singlet graphs (qq) for χ CJ ππ. Color octet graphs (qqg) 17

18 χ cj decays Test of color singlet/octet models in χ cj decays [3] J. Bolz et. al., Eur. Phys. J. C 2:705 (1998) Study of higher mass resonances (η and η ) offers possibility to investigate doubly-ozi suppressed decays, which may compete with the singly-ozi suppressed decays. Q. Zhao, Phys. Lett. B 659, 221 (2008). SOZI DOZI 18

19 Study of ψ(2s) γχ cj ; χ cj π 0 π 0, ηη (η, π 0 γγ ) ψ(2s) γπ 0 π 0 ψ(2s) γηη BESIII BESIII: PRD 81, (2010). CLEOc: PRD 79, (2009). χ c1 ππ, ηη not allowed by parity conservation. Decay mode χ c0 (10-3 ) χ c2 (10-3 ) π 0 π 0 BESIII 3.23±0.03±0.23± ±0.02±0.06±0.04 PDG ± ±0.08 CLEOc 2.94±0.07±0.32± ±0.03±0.07±0.04 ηη BESIII 3.44±0.10±0.24± ±0.04±0.05±0.03 PDG08 2.4±0.4 < 0.5 CLEOc 3.18±0.13±0.31± ±0.05±0.05±0.03 CLEOc used their own branching ratios for ψ γχ cj. 19

20 χ cj 4π 0 from ψ γχ cj decays Branching fraction excluding Ks π 0 π BESIII BESIII Preliminary Branching fraction for χ cj KsKs E γ (GeV) B(χ c0 K S K S ) χ c0 (10-3 ) χ c2 (10-3 ) BESIII 4.1 ± 0.4 stat 0.6 ± 0.2 stat PDG08 CLEOc 2.82 ± ± 0.08 ± 0.18 ± ± ± 0.03 ± 0.03 ± 0.03 CLEO Collaboration, Phys. Rev. D79: (2009). 20

21 Events / ( 0.01 GeV/c 2 ) Measurements of χ cj γv, V=φ,ρ,ω χ c1 γφ χ 120 c1 γρ χ 60 c1 γω BESIII preliminary Events / ( GeV/c 2 ) BESIII preliminary Events / ( 0.01 GeV/c 2 ) BESIII preliminary BESIII M M γ ω (GeV/c ) γ ρ (GeV/c ) H M γ φ (GeV/c ) H H M γ hφ (GeV/c2 ) These decays important for evaluating theoretical techniques. B (10-6 ) BESIII CLEOc pqcd χ c0 γφ < 14.8 < χ c1 γφ 27.3 ± 5.5 stat < χ c2 γφ < 7.8 < χ c0 γρ 0 < 9.5 < χ c1 γρ ± 14 stat 243 ± 19 ± χ c2 γρ 0 < 19.7 < χ c0 γω < 11.7 < χ c1 γω 73.5 ± 7.6 stat 83 ± 15 ± χ c2 γω < 5.8 < BESIII: Only statistical errors are shown M γ hρ (GeV/c2 ) CLEOc: PRL 101, (2008) M γ hω (GeV/c2 ) χ c1 γφobserved for first time. pqcd predictions x10 too low. Difference may be explained by non-perturbative QCD loop corrections. D.Y Chen et al, arxiv: v2[hep-ph]. 21 pqcd: Y.J. Gao et al., hep-ph/

22 Measurements of χ cj γv, V=φ,ρ,ω Helicity angle θ is the angle between the vector meson direction in the χ c1 rest frame and a daughter meson in the vector meson rest frame (ρ and φ) or the normal to the decay plane in the ω rest frame. Longitudinal polarization (transverse) exhibits a cos θ 2 (sin θ 2 ) dependence. Longitudinal polarization dominant in χ c1 γv decays. CLEO-c determines ratio of transverse to longitudinal polarization (f T ) : f f T T = = for χ c1 γρ for χ c1 γω φ helicity ρ helicity ω helicity BESIII CLEOc: PRL 101, (2008) cos θ 22 BESIII preliminary

23 Study of χ cj VV, V = ω, φ Important laboratory to test QCD: Previous measurements from BESII. They do not show expected helicity suppression. BR(10 3 ) χ c0 χ c2 φφ 0.94±0.21± ±0.30±0.25 ωω 2.29±0.58± ±0.47±0.36 BESII, PLB 642, 197 (2006) BESII, PLB 630, 7 (2005) BESIII sees clear χ cj φφ χ c2 4K signals BR(10-3 ) BESIII PDG08 χ c0 φφ 0.80 ± ± 0.20 χ c1 φφ 0.42 ± χ c2 φφ 1.15 ± ± 0.30 χ c0 χ c1 Errors statistical only. First observation of χ c1 φφ 23

24 Study of χ cj VV, V = ω, φ χ c1 φφ(and ωω) should be highly suppressed because C-parity requires L = 2. BESIII And clear χ cj ωω 2(π + π - π 0 ) And clear χ cj ωφ (π + π - π 0 )(KK) ωω χ c 1 χ c 0 χ c 2 χ c0 χ c1 χ c 2? First observation of χ c1 ωω. Doubly OZI suppressed χ cj ωφ signals are observed for the first 24 time.

25 First observation of ψ γγj/ψ 25

26 First observation of ψ γγj/ψ Two photon transitions are well known in excitations of molecules, atomic hydrogen, and positronium. A. Quattropani etal, PRA 25, 3079 (1982). F. Bassani etal, PRL 39, 1070 (1977). A. Quattropani etal, PRL 50, 1258 (1983). CLEO observed two photon transitions in Upsilon(3S) Upsilon(2S). F. Butler etal, PRD 49, 40 (1994). Never been observed in the charmonium system. Observation helpful to understanding QCD. Theoretically: potential models give discrete spectra (ψ γχ cj,χ cj γj/ψ) coupled channel models can give continuous spectra. theoretical work ongoing. 26

27 First observation of ψ γγj/ψ select ψ γγj/ψ, J/ψ l + l - events. J/ψ ee channel (μμ similar): γ 1 - high energy gamma, γ 2 - low energy gamma RM γ2 BESIII ee ee data M γ1γ2 background MC + continuum continuum only signal (phase space; BR = 1 x 10-3 ) select events in box to enhance signal. see clear excess over BG + continuum in M J/ψ distribution. B(ψ γγj/ψ) [both ee and μμ] = (1.02 ± ) x 10-3 (see talk by Xiao-Rui Lu) preliminary ee 27 M J/ψ

28 h c 28

29 h c ( 1 P 1 ) M(h C ) important to learn about hyperfine (spinspin) interaction of P wave states. Hyperfine or triplet-singlet splitting determined by spin-spin term in QCD potential models. h c : 1 st seen by E835 and CLEO in 2005 E835: Evidence in pp h c γη c CLEO: Observation in ψ π o h c ; h c γη c CLEOc in 2008: 25 M Ψ(2S) events Combining with earlier CLEO results: M(h C ) AVG = ± 0.18 ± 0.12 MeV/c 2 (B 1 x B 2 ) AVG = (4.16 ± 0.30 ± 0.37) x 10-4 CLEO Using the spin weighted centroid of 3 P J states, <M( 3 P J )>, to represent M( 3 P J ): ΔM hf (1P) = <M( 3 P J )> - M( 1 P 1 ) = ± 0.18 ± 0.12 MeV Consistent with lowest order expectation of 0. PRL 101, (2008). 29

30 Observation of h c : Tagged ψ(2s) π 0 h c, h c γη c Select events with E1-photon to tag h c γ η c Plot mass recoiling from inclusive π 0 (ψ π 0 h c ) Fit with double-gaussian signal x BW + sideband bkg: BESIII M(h c ) = ± 0.13 ± 0.18 MeV/c 2 Γ(h c ) = 0.73 ± 0.45 ± 0.28 MeV/c 2 (< 1.44 MeV/c 90% CL) (First measurement) Br(ψ π 0 h c ) Br(h c γh c ) = (4.58 ± 0.40 ± 0.50) 10-4 background subtracted BES Collab., PRL 104, (2010) 30

31 Observation of h c : Inclusive ψ(2s) π 0 h c Select inclusive π 0 (untagged) Plot mass recoiling against π o. Fit with double-gaussian x BW signal + 4 th Poly. bkg (mass and width fixed to tagged values) Combine with tagged results to determine: Br(ψ π 0 h c ) = (8.4 ± 1.3 ± 1.0) 10-4 (First measurement) Br(h c γη c ) = (54.3 ± 6.7 ± 5.2) % (First measurement) BESIII BES Collaboration, PRL 104, (2010) background subtracted 31

32 h c : analysis summary BES Collaboration, PRL 104, (2010) BESIII CLEOc Th(Kuang) Br(ψ π 0 h c ) 4.58±0.40± ±0.30±0.37 Br(h c γη c )[10-4 ] M [MeV/c 2 ] ±0.13± ±0.18±0.12 Γ [MeV] 0.73±0.45±0.28 < 90%CL ΔM hf (1P) [MeV/c 2 ] 0.10±0.13± ±0.18± (NRQCD) 0.51 (PQCD) CLEO-c Collaboration, PRL 101, (2008) BESIII theoretical predictions Br(ψ π 0 h c) [10-4 ] 8.4±1.3± Kuang Br(h c γη c ) [%] 54.3±6.7± (NRQCD) Kuang 88 (PQCD) Kuang 38 Godfrey, Rosner Theoretical predictions: Kuang, PRD65, (2002), Godfrey & Rosner, PRD 66, (2002). 32 3

33 X(1835) & X(1860) 33

34 Threshold enhancement in J/ψ γp p BESII: enhancement seen near threshold in M pp in J/ψ γ p p. fitted peak location BESII 3-body phase space If fitted with an S - wave resonance: M = 1859 MeV/c 2 Γ < 30 MeV/c 2 (90% CL) Phys. Rev. Lett. 91, (2003) 162 citations X(1860) J/ψ γpp M(pp) - 2m p (GeV) The BES Particle acceptance Klempt: Glueballs, Hybrids, and Pentaquarks 34

35 pp bound state (baryonium)? There is lots & lots of literature about this possibility deuteron: attractive nuclear force + M.L. n Yan et al., hep-ph/ loosely bound 3-q 3-q color singlets with M d = 2m p - ε E. Fermi, C.N. Yang, Phys. Rev. 76, 1739 (1949) baryonium: I.S. Sharpiro, Phys. Rept. 35, 129 (1978) C.B. Dover, M. Goldhaber, attractive PRD 15, 1997 force? (1977) A. Datta, P.J. O Donnell, PLB 567, 273 (2003)] B. Loiseau et al., hep-ph/ loosely bound 3-q 3-q color singlets with M b = 2m p -δ? 35

36 Several non-observations... pp threshold enhancement PRL 99 (2007) PRD 73 (2006) No significant signal of X(1860) found (only 2σ significance) EPJ C53 (2008) 15 36

37 pp threshold BESIII + ψ π π J/ ψ,j/ ψ γpp BESIII ψ(2s) ππj/ψ BESIII preliminary J / ψ γ pp M= MeV/c2 Γ < 38 MeV/c 2 (90% CL) Published in Chinese Physics C 34, 421 (2010) Consistent observation by BESIII! M= ± 0.8 MeV/c 2 Γ < 8 MeV/c 2 (90% CL) 37

38 pp threshold CLEOc CLEO-c does fit the same as BES and obtains: agrees with BESII results [PRL91(2003)022011]. CLEO-c fits with three contributions: QWG2010 Z. Metreveli CLEO-c preliminary BES considered these (2) and (3) as systematic errors. 38

39 X(1835) at BESII The X(1860) should be detected in other decay modes. G.J. Ding and M.L. Yan suggest η ππ to be a favorable mode. (Hepph/ ) there is gluon content in pp η has strong coupling to gluons Confirmation of X(1835) is necessary with BESIII 226M J/ψ data sample J ψ γπ + π η The π + π - η mass spectrum for η decaying into η π + π - η and η γρ PRL 95, (2005) 39

40 X(1835) at BESIII BESIII Stat. sig. ~18σ Stat. sig. ~9σ??? The possibility that there are two new resonances is under further study. M = ± 2.8( stat) MeV Γ= 99.2 ± 9.2( stat) MeV Fit result: Stat. sig. ~ 21 σ X(1835) confirmed by BESIII 40

41 a0(980) f0(980) mixing 41

42 a 0 (980) f 0 (980) mixing Light scalar mesons f 0 and a 0 are still controversial. Described as quark-antiquarks, four quarks, KK-bar molecule, qq-bar g hybrids, etc. Study of mixing important to clarify their nature. J/ψ φf 0 φa 0 φηπ and χ c1 a 0 π 0 f 0 π 0 π + π - π 0 provide complementary information: 42

43 a 0 (980) f 0 (980) mixing Mixing peaks expected at ~991 MeV/c 2 with 8 MeV/c 2 width. 43

44 a 0 (980) f 0 (980) mixing BESIII Preliminary 44

45 a 0 (980) f 0 (980) mixing BESIII Preliminary 45

46 a 0 (980) f 0 (980) mixing a 0 (980) f 0 (980) mixing BESIII Preliminary 46

47 Beam Energy Measurement 47

48 Tau Mass status: KEDR: Most precise: M KEDR τ = ± MeV Consistent with BES 1996: M τ = PDG (2008): Tau mass measurements ± 0.17 MeV MeV KEDR used two methods to calibrate beam energies: Resonant spin depolarization technique (<~30 KeV) Compton back scattering (<~60 KeV) to be used by BESIII Also measured masses of J/ψ, ψ(2s), ψ(3770) BABAR 2008 KEDR 2008 BELLE 2007 KEDR 2007 OPAL 2000 CLEO 1997 BES 1996 ARGUS m τ , MeV PLB573, 63 (2003). Nucl. Phys. B (Proc. Suppl.) , 311 (2008). 48

49 49 Importance of τ Mass Measurement M(τ) is fundamental parameter of SM. M(e) and M(μ) are known to δm/m ~ 10-8 while M(τ) is only known ~ Improved precision important to test universality: At present: ) )(1 (1 ), ( ), ( ) ( ) ( 5 2 γ τ μ τ μ τ μ μ τ δ δ υυ μ υυ τ τ τ + + = W e e m m F m m F e B e B m m g g = 1 ± μ τ g g Tests universality at 0.2% level. A. Pich, arxiv (2007).

50 BESIII Beam Energy Measurement BESIII can improve τ mass measurement but precision is limited by knowledge of beam energy. Use BINP method: measure energies of back scattered Compton photons produced by a CO 2 laser beams on both the e + and e - beams: 1. Beam energy ε determined by max energy (ω max ) of back scattered photons: ε = 2 ωmax me ω0ω where ω 0 is laser photon energy. 2. Back scattered photons measured with High Purity Ge (HPGe) detector with precision of δε/ε ~ 1 x Absolute calibration of energy scale done using γ-active radionuclides. 4. Expected resolution at BESIII Δε = 40 kev. max measured at VEPP-4M Δ m τ 0.08 MeV/c 2 ; PDG08, Δ m τ 0.17 MeV/c 2 50

51 BESIII Beam Energy Measurement First BESIII upgrade. Collaboration by IHEP, BINP, and U. of Hawaii. Scheme: Test system in fall

52 BESIII Beam Energy Measurement 52

53 BESIII Beam Energy Measurement Laser beam 53

54 Summary BEPCII/BESIII completed successfully: Peak Luminosity of 3.2*10 32 achieved. 106 M ψ(2s) and ~226 M J/ψ events obtained in ~800 pb -1 at ψ(3770) so far in Many exciting results with much, much more to come. Rich physics after CLEOc. BES is unique. 54

55 Backup Slides

56 X(1860) in ψ(2s) decays (preliminary) BESIII checks also for enhancement in ψ decays. Confirmation of no observation of enhancement in ψ(2s) channel! pure FSI effect unlikely CLEOc also checks: Fit, assuming M(pp)=1859 MeV, Γ=20MeV from BESII J/ψ γ pp : QWG2010 Z. Metreveli CLEO-c preliminary 56

57 X(1835) same as X(1860)? X(1835) mass is consistent with the mass of the s-wave resonance X(1860). Its width is 1.9 σ higher than the upper limit of the width obtained from ppbar mass threshold enhancement. However, if FSI effects are included in the fit of the ppbar mass spectrum, the width of the resonance near ppbar mass threshold will become larger. BESII 57

58 Re-fit to J/ψ γp pbar including FSI Include FSI curve from A.Sirbirtsev et al. ( Phys.Rev.D71:054010, 2005 ) in the fit (I = 0) M = ± 6.7 MeV Γ = < 153 BESII M 2m pp p In good agreement with X(1835) 58