Recent Results from BESIII

Transcription

1 Recent Results from BESIII XLIX International Winter Meeting on Nuclear Physics, Bormio, Italy Frederick A. Harris University of Hawaii 1 Jan. 27, 2011

2 OUTLINE Introduction BEPCII/BESIII Physics results h c cj decays X(1860) & X(1835) f 0 (980) a 0 (980) mixing ψ P Beam energy measurement Summary IHEP 2

3 e + e - Colliders μ + e + J/ e - e + e - colliders all the energy can be used to create new particles. Understood process. Operational (in 2011): Maximum Collider Location Energy (GeV) Luminosity (cm -2 s -1 ) Dane Italy x VEPP 4M Russia x BEPCII Beijing x Previously (US): PEPII (SLAC), CESR (Cornell) Future: Super KEKB (Japan), Super B (Italy), Linear Collider?? BEPCII is unique μ - N events = L 3

4 Standard Model Standard Model particles are made of quarks, leptons, and the force carriers. Visible matter. p = uud n = udd BEPCII operates in the GeV energy region so it can study the lighter quarks (u, d, c, and s) and the leptons. τ charm factory 4

5 The November Revolution: J/ψ Discovery On Nov. 11, 1974, Burt Richter (SLAC) announced the discovery of the ψ and Sam Ting (Brookhaven) announced the discovery of the J. They received the Nobel Prize in 1976 for their discovery. The J/ψ with a mass of GeV was soon interpreted as being made up of a c and a c-bar quark. The existence of the charmed quark had been predicted by Glashow, Iliopoulo, and Maiani to explain the absence of stangeness changing neutral currents. The discovery led physicists to finally take quarks seriously. Sam Ting with few hundred J/ s 5

6 Physics of tau charm region An important measurement at an e + e - collider is the cross section for e + e - hadrons, σ(e + e - hadrons), as a function of the energy. ( e e hadrons) Often this is given as a ratio: R ( e e ) BES In Quantum Chromodynamics (QCD), <R> Σ(Q i ) 2 R(u, d, s) = 3*[(2/3) 2 + (-1/3) 2 + (-1/3 )2] = ~2 R(u, d, c, s) = 3*[(2/3) 2 + (-1/3) 2 + (2/3) 2 + (-1/3) 2 ] = ~3 1/3 6

7 Physics of tau charm region Charmonium: cc Like positronium Nobel prize open charm threshold for pairs Very rich and interesting energy region. 7

8 Physics of tau charm region Open charm factory: ψ DD 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. (3770) (4040), etc.: D, D*, D S Very rich and interesting energy region. 8

9 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. But BESIII has a comparable detector and higher luminosity. Future belongs to BESIII.

10 BEPCII/BESIII 10

11 BEPCII: a high luminosity double ring collider 22 mrad crossing angle 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 Circumference: 237 m Use many bunches and SC mini-beta. SC RF Beam magnets 11

12 Magnet Yoke BESIII Detector SC magnet RPC TOF Be beam pipe 1 m MDC CsI(Tl) calorimeter 12

13 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 BEPCII and BESIII, Int. J. Mod. Phys. A24, 377 (2009). Design and Construction of the BESIII Detector, NIM A614, 345 (2010). 13

14 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, M ψ events July 28, M J/ψ events June 27, fb -1 at ψ(3770) (includes 75 pb -1 scan) Peak Luminosity > 5.3 X cm -2 s -1 or ~ 8 X CESRc 50 X BEPC May 15, 2008: detector at 14 IP; First collision event installing SC quads and beam pipe.

15 World J/ and Samples ( 10 6 ) BESIII: J/ M M MarkIII DM2 BESI BESII BESIII BESII: J/ 58M MKI MKII MKIII CBAL BESI BESII CLEO BESIII 15 14M

16 BESIII Collaboration Europe (10) Germany: U. Bochum, U. Giessen, Mainz(2), GSI Darmstadt Russia: JINR Dubna, BINP Novosibirsk Italy: Torino, INFN Netherlands: KVI/U. Gronigen Korea (1) Seoul Nat. University) >300 physicists 48 institutions from 9 countries 16

17 BESIII Publications Title Measurement of h c ( 1 P 1 ) in decay PRL 104, (2010) Branching fractions of c0 and c2 to π 0 π 0 and ηη Observation of a p p-bar mass threshold enhancement in π + π - J/, J/ pp-bar First observation of the decays cj π 0 π 0 π 0 π 0 PRD 81, (2010) Chinese Phys C 34, 421 (2010) Acc. by PRD Evidence for ' decays into π 0 and η PRL 105, (2010) Study of a 0 (980) - f 0 (980) mixing M. Ablikim et al. Acc. by PRL Measurement of the matrix element for PRD 83, (2011) η'ηπ + π - Confirmation of the X(1835) and observation of the X(2120) and X(2370) in J/ π + π - η' Acc. by PRL 17

18 h c 18

19 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 : Confirmed by E835 and CLEO in 2005 E835: Evidence in pp h c η c CLEO: Observation in ψ π o h c ; h c η c CLEOc in 2008: 25 M Ψ(2S) events Combining with earlier CLEO results: M(h C ) AVG = 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 ): M 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). 19

20 Observation of h c : Tagged 0 h c, h c c Select events with E1-photon to tag h c c Plot mass recoiling from inclusive π 0 ( 0 h c ) BESIII tag background subtracted M(h c ) = ± 0.13 ± 0.18 MeV/c 2 (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 h c ) = (4.58 ± 0.40 ± 0.50) 10-4 BES Collab., PRL 104, (2010) 20

21 Observation of h c : Inclusive 0 h c Select inclusive 0 (untagged) Plot mass recoiling against π o. BESIII background subtracted BES Collaboration, PRL 104, (2010) Combine with tagged results to determine: Br( h c ) = (8.4 ± 1.3 ± 1.0) 10-4 Br(h c c ) = (54.3 ± 6.7 ± 5.2) % (First measurement) (First measurement) 21

22 h c : analysis summary BES Collaboration, PRL 104, (2010) BESIII CLEOc Th(Kuang) Br( 0 h c ) 4.58±0.40± ±0.30±0.37 Br(h c c )[10-4 ] M [MeV/c 2 ] [MeV] 0.73±0.45±0.28 < 90%CL M hf (1P) [MeV/c 2 ] 0.10±0.13± ±0.18±0.12 CLEO-c Collaboration, PRL 101, (2008) BESIII Br( 0 h c ) [10-4 ] 8.4±1.3± Kuang theoretical predictions Br(h c c ) [%] (NRQCD) Kuang 88 (PQCD) Kuang 38 Godfrey, Rosner Theoretical predictions: Kuang, PRD65, (2002), Godfrey & Rosner, PRD 66, (2002). 1.1 (NRQCD) 0.51 (PQCD) 22 2

23 cj results 23

24 Radiative decays: X Clean exclusive signal High statistics Clear inclusive photon spectrum Excellent photon resolution BESIII preliminary BESIII c2 c1 co c1,2 J/ BESIII preliminary c 24

25 cj decays Good place to study gluonium: c gg (qq)(qq). C. Amsler and F. E. Close,Phys. Rev. D 53, 295 (1996). Color octet mechanism important. 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 CJ. Color octet graphs (qqg) 25

26 Study of cj ; cj 0 0, (, 0 ) BESIII: PRD 81, (2010). 0 0 χ c0 χ χ c2 c2 χ c0 BESIII c1 ππ, ηη not allowed by parity conservation. Decay mode c0 (10-3 ) c2 (10-3 ) 0 0 BESIII 3.23 ± 0.03 ± 0.23 ± ± 0.02 ± 0.06 ± 0.04 PDG ± ± 0.05 Theory BESIII 3.44 ± 0.10 ± 0.24 ± ± 0.04 ± 0.05 ± 0.03 PDG ± ± 0.08 Theory Theory: J. Bolz et. al., Eur. Phys. J. C 2:705 (1998) 26

27 cj 4π 0 from cj decays Allow 9 photon candidates Select 4 π 0 Require χ 2 (4C) <15 π 0 BESIII χ c2 χ c1 χ c0 BESIII χ c0 π 0 π 0 For future study. E GeV) Branching fraction excluding Ks π 0 π 0 B(χ c0 4π 0 ) = (3.34 ± 0.06 ± 0.44) x10-3 B(χ c1 4π 0 ) = (0.57 ± 0.03 ± 0.08) x10-3 B(χ c2 4π 0 ) = (1.21 ± 0.05 ± 0.16) x10-3 Observed for the first time. Accepted by PRD arxiv:

28 X(1860) and X(1835) 28

29 Threshold enhancement in J/ p p BESII: enhancement seen near threshold in M pp in J/ p p. fitted peak location BESII 3-body phase space If fitted with an S - wave resonance: M = 1859 MeV/c 2 < 30 MeV/c 2 (90% CL) Phys. Rev. Lett. 91, (2003) 162 citations X(1860) J/pp M(pp) - 2m p (GeV) acceptance 29

30 pp bound state (baryonium)? There is lots & lots of literature about this possibility deuteron: attractive nuclear force baryonium: attractive force? + n + loosely bound 3-q 3-q color singlets with M d = 2m p - loosely bound 3-q 3-q color singlets with M b = 2m p -? 30

31 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 - 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 -? 31

32 pp threshold BESIII J/,J/ pp BESIII (2S) J/ BESIII preliminary J / pp M= MeV/c2 < 38 MeV/c 2 (90% CL) M= MeV/c 2 < 8 MeV/c 2 (90% CL) Published in Chinese Physics C 34, 421 (2010) Consistent observation by BESIII! 32

33 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. (PRD C72, (2005).) there is gluon content in pp η has strong coupling to gluons X(1835) at BESII J + - and BESII M = ± 6.1 ± 2.7 MeV/c 2 = 67.7 ± 20.3 ± 7.7 MeV/c 2 PRL 95, (2005) 33

34 X(1835) at BESIII BESIII J J Stat. sig. ~18 Stat. sig. ~9??? M MeV MeV / c / c 2 2 combined X(1835) confirmed by BESIII Two new resonances? 34

35 X(1835) at BESIII Combine two decay channels. Fit with four resonances (f 1 (1510) + 3 higher mass) Three background components: Accepted by PRL, arxiv: BESIII background plus non-resonant π + π - η' production η' sideband and π 0 π + πη backgrnd Angular distribution of radiative photon for X(1835) consistent with a pseudoscalar Mass (MeV/c 2 ) Width (MeV/c 2 ) Significance X(1835) X(2120) X(2370) > 20 σ 7.2 σ 6.4 σ 35

36 a0(980) f0(980) mixing 36

37 a 0 (980) f 0 (980) mixing From PDG f 0 and a 0 still controversial. Described as qq, qqqq, KK-bar molecule, qqg hybrids, etc. 37

38 a 0 (980) f 0 (980) mixing Study of mixing may clarify their nature. Mixing suggested by N.N. Achasov et al. [PL 88B, 367 (1979)]. Suggestions made for BESIII to study this J/ψ J. Wu, Q. Zhao, B. Zou PR D75, (2007). C. Hanhart et al, PRD76, (2007) f 0 a 0 J. Wu, B. Zou PR D78, (2008). a 0 f 0 J/ψ f 0 a 0 ηπ and c1 a 0 π 0 f 0 π 0 π + π - π 0 provide complementary information. 38

39 J/ψ f 0 a 0 ηπ 0 a 0 (980) f 0 (980) mixing 3.4 σ Branching fraction and mixing intensity ξ fa : f 0 a 0 N(mix) = 25.8 ± 8.6 B(J/ψ f 0 a 0 ηπ 0 ) = (3.3 ± 1.1 ± 0.8) x 10-6 or < 5.4 x 90 % CL Mixing intensity: Fit: Signal expect narrow peak (8 MeV/c 2 ) between K + K - and K 0 K 0 thresholds ( MeV/c 2 ). sideband background wide a 0 from J/ψ * /K * K a 0. fa B( J / f B( J 0 / f a 0 ( ( sys) 0.26( par.))% or 90% C. L. 0 0 ) ) 39

40 a 0 (980) f 0 (980) mixing ψ χ c1, χ c1 a 0 π 0, a 0 f 0, f 0 π + π σ Branching fraction and mixing intensity ξ af : a 0 f 0 N(mix) = 6.4 ± 3.2 B(ψ χ c1 )xb(χ c1 a 0 π 0 f 0 π 0 π + π - π 0 ) = (2.7 ± 1.4 ± 0.5) x 10-7 or < 6.0 x 90 % CL Mixing intensity: Fit: Narrow signal. sideband background wide f 0 from other processes. af B( c1 B( 0 a c1 0 a 0 0 (980) 0 ) 0 ) ( ( sys.) 0.03( par.))% or C. L. f

41 a 0 (980) f 0 (980) mixing Mixing intensity ξ af versus ξ fa limits } } models calculations measurements First direct measurements. Accepted by PRD, arxiv:

42 ' P (P = π,η, and η') 42

43 ' P (P = π 0,η, and η') BESIII Important for testing various phenomenological mechanisms: vector meson dominance, η c η ( ) mixing, 2 gluon couplings to qq states, and final state radiation by light quarks. R J/ = B(J/ η)/b(j/ η ) predicted by 1 st order perturbation theory. R ' = B(' η)/b(' η ) R J/ is expected. B(' π 0 ) expected to be small (2.2 x 10-7 ). Rosner, PRD 79, (2009) Recently, CLEOc reported on J/,, P: Found no evidence for π 0 or η. Determine B( π 0 ) < 5 x Obtain R ' < 1.8% at 90% CL and R J/ = (21.1 +/- 0.9)%. R ' << R J/ poses a significant challenge to theory. CLEOc, PRD 79, (2009) 43

44 ' P (P = π,η, and η') BESIII studies: ' π 0 using π 0. ' η using η π + π - π 0 and π 0 π 0 π 0. ' η' using η' π + π - and π + π - η withη. BESIII π 0 η π + π - π 0 η π 0 π 0 π 0 η' π + π - η π + π - η 44

45 ' P (P = π,η, and η') BESIII Branching Ratios (x 10-6 ) Measured branching ratios for π 0 and η for first time. First measurement of R ' = (1.10 ± 0.38 ± 0.07). R ' << R J/ Phys. Rev. Lett 105, (2010). 45

46 Beam Energy Measurement 46

47 Tau Mass status: KEDR: Most precise: M KEDR 0.17 τ MeV Consistent with BES 1996: M = PDG (2010): Tau mass measurements MeV ± 0.16 MeV KEDR used two methods to calibrate beam energies: Resonant spin depolarization technique (<~30 KeV) Compton back scattering (<~60 KeV) 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). 47

48 48 Importance of Mass Measurement M() is fundamental parameter of SM. M(e) and M(μ) are known to δm/m ~ 10-8 while M() is only known ~ Improved precision important to test universality: At present: ) )(1 (1 ), ( ), ( ) ( ) ( 5 2 W e e m m F m m F e B e B m m g g g g Tests universality at 0.2% level. A. Pich, arxiv (2007).

49 BESIII Beam Energy Measurement BESIII can improve mass measurement but must determine beam energy precisely. 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 determined by max energy (ω max ) of back scattered photons: 2 max me where ω 0 is laser photon energy. 2. Back scattered photons measured with High Purity Ge (HPGe) detector with precision of δ/ ~ 1 x Absolute calibration of energy scale done using -active radionuclides. 4. Expected resolution at BESIII = 40 kev. max measured at VEPP-4M m 0.08 MeV/c 2 ; PDG10, m 0.16 MeV/c 2 49

50 BESIII Beam Energy Measurement First BESIII upgrade. Collaboration by IHEP, BINP, and U. of Hawaii. Scheme: λ = μm (0.114 ev) 50

51 BESIII Beam Energy Measurement Supplied by U. of Hawaii 51

52 BESIII Beam Energy Measurement photons Laser beam 52

53 BESIII Beam Energy Measurement First Test Results: positrons 53

54 BESIII Beam Energy Measurement First Test Results: ψ scan Preliminary PDG2010: ± 0.04 MeV Online results Very preliminary offline results: no efficiency correction other missing corrections statistical errors x 10 54

55 Summary BEPCII/BESIII completed successfully: Peak Luminosity > 5 x cm -2 s -1 achieved. 106 M ψ(2s) and 225 M J/ψ events obtained in pb -1 obtained at ψ(3770) in Running again at (3770) now. Many exciting results with much, much more to come. Rich physics after CLEOc. BES is unique. 55

56 Backup Slides

57 Measurements of cj V, V=,ρ, ψ χ cj, χ cj V (, ρ, ) K + K -, ρ π + π -, π + π - π 0 BESIII m KK m ππ m πππ Events / ( 0.01 GeV/c 2 ) c1 120 c1 ρ 60 c1 BESIII preliminary Events / ( GeV/c 2 ) BESIII preliminary Events / ( 0.01 GeV/c 2 ) BESIII preliminary M γ φ (GeV/c ) H M h (GeV/c2 ) M M γ ω (GeV/c ) γ ρ (GeV/c ) H H M hρ (GeV/c2 ) M h (GeV/c2 ) c1 observed for first time. 57

58 Measurements of cj V, V=,ρ, These decays important for evaluating theoretical techniques. B (10-6 ) BESIII CLEOc pqcd c0 < 14.8 < c ± 5.5 stat < c2 < 7.8 < c0 ρ 0 < 9.5 < c1 ρ ± 14 stat 243 ± 19 ± c2 ρ 0 < 19.7 < c0 < 11.7 < c ± 7.6 stat 83 ± 15 ± c2 < 5.8 < CLEOc: PRL 101, (2008) BESIII pqcd: Y.J. Gao et al., hep-ph/ BESIII: Only statistical errors are shown BESIII preliminary pqcd predictions x10 too low. Difference may be explained by non-perturbative QCD loop corrections. D.Y Chen et al, arxiv: v2[hep-ph]. 58

59 Measurements of cj V, V=,ρ, Helicity angle θ is the angle between V direction in the c1 rest frame and a daughter meson in the vector meson rest frame (ρ and ) or the normal to the decay plane in the rest frame. Longitudinal polarization (transverse) exhibits a cos θ 2 (sin θ 2 ) dependence. BESIII preliminary f T = N T /(N T + R*N L ); R= T / L c1 f t - BESIII f t CLEOc * errors assume background either long. or trans. polarized. * calculated from PRL 101, (2008) Longitudinal polarization dominant in c1 Vdecays cosθ(k,φ) helicity ρ helicity helicity cosθ(π,ρ) cosθ(ω,normal of ω) cos θ BESIII 59

60 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 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 60

61 Re-fit to J/p pbar including FSI Include FSI curve from A.Sirbirtsev et al. ( Phys.Rev.D71:054010, 2005 ) in the fit (I = 0) M = MeV = < 153 BESII M 2m pp p In good agreement with X(1835) 61

62 62