Results from BESIII. SLAC Experimental Seminar Aug. 9, Frederick A. Harris University of Hawaii. University of Hawaii 1

Transcription

1 Results from BESIII SLAC Experimental Seminar Aug. 9, 2016 Frederick A. Harris University of Hawaii University of Hawaii 1

2 OUTLINE Introduction BEPC/BES beginnings and the SLAC connection BEPCII/BESIII Physics results Anomalous magnetic moment of the μ D and D s physics Λ c branching fractions XYZ results Search for dark photon Search for CP-odd light Higgs Summary IHEP 2

3 OUTLINE Thanks to Fang Yi, Yiping Guo, Ryan Mitchell, Ron Poling, Wei Shan, Weimin Song, and many others. Special thanks to the BESIII collaboration for all the fine results. IHEP 3

4 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. + σ ( e e hadrons) Often this is given as a ratio: R = + + σ ( e e μ μ ) BES 4

5 Physics of tau charm region Charmonium: cc Like positronium Nobel prize open charm threshold for τ pairs Λ c XYZ states 5 Very rich and interesting energy region.

6 BEPC/BES beginnings and the SLAC connection 6

7 BEPC/BES beginnings and the SLAC connection After long turbulent period, end of Ching dynasty, founding of Republic of China (1912) warlords, nationalists, communists ( ) Japanese invasion of Manchuria and WWII ( ) Founding of People s Republic of China, Mao Zedong (1949) China begins to open up: Nixon visit (1972) Richard Nixon meets Mao Zedong, Feb (from White House Photo Office ( ) via Wikipedia) 7

8 BEPC/BES beginnings and the SLAC connection Also scientifically - not self reliance and hard struggle. Chinese physicists visit US to consult on future major facility (1972). Return to China with idea of GeV proton accelerator. Proton accelerator approved (1975). Pief invited to visit China, suggests e + e - collider better choice (1976). Cultural revolution ( ) ends; Deng Xiaoping takes over. Zhang Wenyu visits SLAC in 1972 (from Panofsky on Physics, Politics, and Peace) 8

9 BEPC/BES beginnings and the SLAC connection Carter and Deng sign a United States China agreement on Cooperation in Science and Technology (1979) Joint Committee on Cooperation in High Energy Physics established (1979). From Across the Ocean, Institute of High Energy Physics, Chinese Academy of Science First US/PRC Joint Committee meeting, June 1979 T.D. Lee and Pief Panofsky were founding members and attended over 25 years. 9

10 BEPC/BES beginnings and the SLAC connection Proton accelerator killed (1981) Chinese government agrees to sponsor construction of Beijing Electron Positron Collider (BEPC/BES). 30 engineers and physicists come to SLAC in 1982 to make preliminary design. From Jean Deken, SLAC Archives and History Office 10

11 BEPC/BES beginnings and the SLAC connection China authorizes construction. Construction begins (1984). Cooperation with SLAC continues. First collisions, Oct. 16, 1988 Inaugural celebration, Oct. 24, Deng at ground breaking (Oct. 7, 1984) TD and Deng on tour of collider, Oct. 24,

12 BEPC/BES beginnings and the SLAC connection BESI detector modeled on Mark III with improvements. 10 M J/Ψ events accumulated (May 1991). American scientists join in 1991 to measure τmass: (Boston University, Caltech, UC Irvine, Colorado State, MIT, SLAC, SSC, University of Texas at Dallas, and University of Washington). BESI detector τthreshold scan Nov. 91 Jan

13 13 BEPC/BES beginnings and the SLAC connection Mass ofτlepton l e l l e l m G B π τ υυ = τ μ μ τ τ μ υυ μ υυ τ τ τ e e e e B B m m G G 5 2 = Before BES:

14 BEPC/BES beginnings and the SLAC connection 14

15 BEPC/BES beginnings and the SLAC connection Mass ofτlepton Peeking ahead to BESIII 15

16 Advertisement To appear in the Annual Reviews of Nuclear and Particle Science :

17 BEPCII/BESIII 17

18 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 18

19 E cm = GeV Peak luminosity: 1.0 x cm -2 s -1 19

20 BESIII Detector Magnet Yoke TOF: 80 ps barrel 60 ps end cap upgraded (MRPC) Be beam pipe 1 T SC magnet RPC 9 layers 1 m MDC: δp/p = 0.5%, de/dx ~ 6% at 1 GeV CsI(Tl) calorimeter: Int. J. Mod. Phys. A24, 377 (2009) δe = 2.5% at 1 GeV 20 NIM A614, 345 (2010)

21 BESIII Data Sets J/ψ ψ 1.3x x fb fb fb fb -1 ψ(3770) 2.9 fb fb points R Scan fb fb -1 World largest/unique samples from e + e - collision : J/ψ, ψ(2s), ψ(3770), Y(4260) 21

22 Anomalous magnetic moment of the μ 22

23 e + e - π + π - and the Anomalous Magnetic Moment of the Muon There is curently a 3σ difference between the Standard Model (SM) and the experimental (E821) value for the anomalous magnetic moment of the muon [a μ = (g μ -2)/2]: The error in the SM calculation is dominated by the Hadronic Vacuum Polarization (HVP), which is estimated using experimental input from ee hadrons. The cross section is dominated by e + e - π + π - in the region of the rho. But there are differences between BaBar and KLOE 23

24 e + e - π + π - and the Anomalous Magnetic Moment of the Muon This can be addressed using ISR from 2.9 fb -1 of data at GeV by BESIII. First measure σ(e + e - π + π - ): Then use a dispersion relation [ZPC 67, 585 (1995)]: BESIII confirms the 3σ difference in a μ 24

25 D and D s Physics 25

26 Charm Physics at Threshold At Ψ(3770) charm production is D o D o and D + D - Double tag technique: Hadronic tag on one side gives beam of D o or D + on the other side for leptonic or semileptonic studies. Neutrino reconstructed from missing energy and momentum. High tagging efficiency and very clean. ΔE M BC = E = D E E 2 Beam Beam p 2 D Ψ(3770): 2.93 fb -1 26

27 Leptonic D (s) Decays Precision measurements of f D and f Ds test theory (LQCD) Apply LQCD to B physics to determine V td and V ts Determine V cd and V cs to check unitarity of CKM matrix Sensitive to new physics 27

28 D + μ + ν PRD 89, (2014) 28

29 0.482 fb -1 at E cm = GeV K s K - K + K - π - K + K - π - π o D s + μ + ν μν Preliminary BESIII preliminary τν K s K + π - π - π + π - π - π - η D s + bkg π - π o η π - η ( π + π - η) π - η ( π + π - γ) M BC (GeV/c 2 ) M BC (GeV/c 2 ) M BC (GeV/c 2 ) SM-constrained fit R=Γ(D s τν)/γ(d s μν) = 9.76 non D s + bkg 29

30 D s + μ + ν Preliminary Precision of LQCD calculations of f D at 0.5%; challenging for s experiments Expect improvement from 3 fb -1 of BESIII data in the future. 30

31 Semileptonic Decays Measure form factors f + D K (q 2 = 0) and f + D π (q 2 = 0) to test LQCD. Use LQCD input to determine V cd and V cs 31

32 D o K - e + ν e, π - e + ν e PRD 92, (2015) Ψ(3770) 2.93 fb -1 32

33 D o K - e + ν e, π - e + ν e PRD 92, (2015) Ψ(3770) 2.93 fb -1 LQCD: 33

34 D + K o e + ν e, π o e + ν e Preliminary Ψ(3770) 2.93 fb -1 B(D + K 0 e + ν) = (8.604±0.056±0.151)% B(D + π 0 e + ν) = (3.631±0.075±0.051)x

35 D + K o e + ν e, π o e + ν e Preliminary Ψ(3770) 2.93 fb -1 35

36 Form Factors f + D K(π) (0) Preliminary Ψ(3770) 2.93 fb -1 To determine f + D K(π) (0), use measurements of f + D K(π) (0) V cs(d) and PDG values for V cs(d) (assuming unitarity) BESIII has most precise determinations Experimental accuracy better than predictions 36

37 More Results No time for: D + K o e + ν e via K o π o π o arxiv: D + K o μ + ν μ arxiv: D + K - π + e + ν e arxiv: D + ωe + ν e and D + φe + ν e PRD 92, R (2015) See talk at ICHEP by Ron Poling for details. All based on 2.93 fb -1 Ψ(3770) sample BESIII has large, clean e + e - samples near threshold, optimal for precision measurements of leptonic and semileptonic charm decays. First results on D s decays are statistics limited. Many more with greater precision coming soon with 3 fb -1 data sample at 4.18 GeV. Longer term: additional Ψ(3770) and more data at 37 higher energy.

38 Λ c absolute branching fractions 38

39 Λ c Lowest charmed baryon J not well determined BFs poorly determined Energy (GeV) Lum. (pb -1 ) In 2014, BESIII took data at 4.6 GeV, just above Λ c Λ c pair threshold. First time to study Λ c at threshold. 39

40 Single tag one reconstructed Double tag - both 40

41 Single tag Λ c yields ST sum ~ 15 K 41

42 Double tag Λ c yields DT i N is sum over all tag modes 42

43 Λ c absolute branching fractions Branching fraction results Some systematic errors cancel Belle: B(Λ c pk - π + ) = 6.84 ± PRL 116, (2016) BESIII result about 2 σ below Belle; other modes improved by factors of

44 Total measured branching fractions only about 60%. No measurements with neutron in final state. Like previous analysis. Use 11 single tag modes with ST events. Use missing mass to identify signal against tag. M 2 miss (GeV 2 /c 4 ) 44

45 Fit to M 2 miss and M π + π - and their sidebands. 83 ± 11 net signal events. Preliminary B(Λ c + nk s o π + ) = (1.82 ± 0.23 ± 0.11)% First observation of decays to final states with neutrons. 45

46 Absolute branching fraction of Λ c + Λl + ν) Analysis like previous, except ν is missing. U miss used. 567/pb 4.6 GeV U miss = E miss c p miss Λ c + Λe + ν Λ c + Λμ + ν Double tag plots 103±10.9 events BESIII preliminary 78.7±10.5 events U miss (GeV) 46

47 Absolute branching fraction of Λ c + Λl + ν Decay is a c sl + ν l process No absolute BF previously available. Theory predictions: % Important for LQCD BESIII Results: Λ c + c u d s Λ B[Λ c + Λ e + ν e ] = (3.63 ± 0.38 ± 0.20)% PRL 115, (2015) B[Λ c + Λμ + ν μ ] = (3.49 ± 0.46 ± 0.26)% Preliminary PDG: B(Λe + ν e ) = (2.1 ± 0.6)% B(Λμ + ν μ ) = (2.0 ± 0.7)% Γ[Λ c + Λμ + ν μ ]/Γ[Λ c + Λ e + ν e ] Preliminary = (0.96 ± 0.16 ± 0.04)% Branching fractions measured with highest precision by BESIII. 47

48 XYZ results 48

49 e + e - π + π - J/Ψ and the Y States 49

50 e + e - π + π - J/Ψ and the Y States Includes R scan 50

51 e + e - π + π - Ψ(2S) and the Y States 51

52 e + e - π + π - h c and the Y States 52

53 e + e - π + π - J/Ψ and the X States The x(3872) (J PC = 1 ++ ) was the first discovered and best studied of the XYZ states. It was discovered in 2003 by Belle in B Kπ + π - J/Ψ. PRL 91, (2003). X(3872) 53

54 e + e - π + π - J/Ψ and the X States 54

55 e + e - π + π - J/Ψ and the Z States In 2012, BESIII took data at E cm = 4.26 GeV and observed e + e - π - Z c (3900) + π - π + J/Ψ. M(Z c (3900)) = ±2.8±1.4 MeV Γ(Z c (3900)) = 46±10±20 MeV Confirmed by Belle [PRL 110, (2013)] and CLEOc data [PLB 727, 366 (2013)]. PRL 110, (2013) 55

56 More BESIII Z States 56

57 Search for Dark Photon 57

58 Search for Dark Photon A is the dark sector force carrier [N. Arkani-Hamad et al., PRD 79, (2009)]. Couples to SM particles via kinetic mixing [B. Holdom, PLB 166, 196 (1986)]. ε is mixing strength. Could explain e + cosmic ray anomaly Also (g -2) deviation in SM BESIII: use 2.9 fb Ψ(3770) data and Initial State Radiation (ISR) process: + + e e γ γ γ μ μ Search for narrow structure on top of QED background e + e γ ISR ISR γ γ isr isr e + e 58

59 Search for Dark Photon J/Ψ J/Ψ Mass region covered: GeV/c 2 < 1.5 GeV/c 2 : π + π - background dominates > 3.4 GeV/c 2 : qq background close to beam energy Narrow peaks not observed. 59

60 Search for Dark Photon 60

61 Search for Dark Photon No dark photon with significance > 3 σ found 61

62 Search for CP-Odd Light Higgs 62

63 Search for CP-odd Light Higgs Next to minimal super-symmetric Standard Model (NMSSM): Contains 3 CP-even, 2 CP-odd, and 2 charged Higgs Mass of lightest CP-odd (A o ) may be < 2*m c B( V B( V γa l G m g C m ) F q q QCD + = A 2 l ) 2πα mv V = Υ or J/Ψ l e or μ C QCD QCD and relativistic correction to B(V γ A 0 ) g c = cos θ A /tan β for c quark g b = cos θ A *tan β for b quark tan β ratio of up and down types of Higgs doublets cos θ A is fraction of non-singlet component in the A 0 - would be small for a mostly singlet pseudoscalar 0 A 0 can be produced in decay of J/Ψ 63

64 Search for CP-odd Light Higgs Expected B(J/Ψ γj/ψ) = ~ 10-9 to 10-7 Search for narrow signal of J/Ψ γa 0, A 0 μ + μ - above background with 225 M J/Ψ events. No significant signal; set UL 64

65 Search for CP-odd Light Higgs BaBar also has set limits [PRD 98, (2013)] in B decay. Can compare limits using gb = g c tan β B( A μ μ ) for different values of tan β. For low mass region (tan β < 0.6), BESIII limit lower. Both constraints can be combined to place a limit on cosθ B( A μ μ ) 0 + Says A 0 is constrained to be mostly singlet. A BESIII: PRD 93, (2016) 65

66 Summary BEPCII/BESII very successful: Peak Luminosity of 1*10 33 cm -2 s -1 achieved. BESIII has many beautiful data sets at many energy points between 2 and 4.6 GeV. They allow a wide variety of physics topics to be pursued at threshold, as well as topics available through ISR. End cap TOF MRPC upgrade with 60 ps resolution; future MDC upgrade. SLAC and Pief helped at the beginning of BES/BEPC. Many exciting results with much, much more to come. BES is unique. 66

67 Backup Slides

68 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(3770), 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 68 t b

69 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. ψ(3770) ψ(4040), etc.: D, D*, D S Very rich and interesting energy region. 69

70 BESIII Data Samples ( ) State or energy (GeV) J/Ψ 1.3 x 10 9 evts LHS Ψ(2S) 0.5 x 10 9 evts charmonium Ψ(3770) 2.9 fb -1 D Ψ(4040) 0.5 fb -1 D, D s τscan fb -1 τmass 4.23, 4.26, 4.36, 4.42, 4 fb -1 XYZ, D, D*, D s 4.47, , 104 pts 0.8 fb -1 R scan, form factors, etc fb -1 Λ c 4.18 in fb -1 D s 70

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