The BGO-OD experiment at ELSA

Transcription

1 The BGO-OD experiment at ELSA Hartmut Schmieden Physikalisches Institut Universität Bonn The house began to feel familiar. Everywhere,, that is, except the basement. It just always put me off, and I avoided going gown there as best as I could. Cliff Barlow SFB/TR-16 Particle Physics Seminar Bonn July

2 The BGO-OD experiment at ELSA In the Lion's Den nucleon structure in the realm of strong QCD (N. JLab NSTAR conference) Hartmut Schmieden Physikalisches Institut Universität Bonn The house began to feel familiar. Everywhere,, that is, except the basement. It just always put me off, and I avoided going gown there as best as I could. Cliff Barlow SFB/TR-16 Particle Physics Seminar Bonn July

3 The BGO-OD experiment at ELSA Overview General motivation Excited baryons Meson sector Experimental requirements meson photoproduction BGO-OD experiment setup Preliminary (commissioning) results Summary SFB/TR-16 Particle Physics Seminar Bonn July

4 Nucleon Structure still interesting? up up down 4

5 Nucleon Structure still interesting? up up down 5

6 Nucleon Structure still interesting? mass up up down 6

7 Nucleon Structure still interesting? mass up up down MASS 7

8 Phenomenologic QCD potential fit of the quarkonia spectra obtained with strong coupling V QCD = 4 3 α S r + k r linear confinement best fit values (charmonium & bottomonium) α S 0.2 k 1 GeV fm 1 F = V 1 ev = 1.6x10-19 Nm 1.6 x 10 5 N 16 t 8

9 Running Coupling α S confinement asymptotic freedom Lion's Den R/m QFT w/o perturbative expansion 9

10 Confinement & nucleon mass G a µν G a µν 0 Δp Δx > ħ trace anomaly scale noninvariance energy E pot ~ r m = E/c 2 mass without mass J. Wheeler F. Wilczek distance delocalization kinetic energy potential energy 10

11 QCD potential & Lattice QCD generators SU(3) color λ a ij L QCD = q i ( i µ γ µ δ ij + g A a µ γµ mδ ij ) F a µν Fa µν gluon field F a µν = µ Aν ν A µ + gf abc A b µ Ac ν time-ordered product gluon self-coupling (1) short distance (ultraviolet) regularization mesh of discrete lattice points (2) infrared cutoff finite lattice volume (3) functional integrals oscillate rapidly t x 0 = -ix 4 4-dim Euklidian space damping of oscillation quark gauge field (transporter) 11

12 Lattice QCD G.S. Bali, Phys. Rep. 343 (2001) 1 slope = k 1 GeV/fm Energy density distribution inside nucleon in LQCD simulation (F. Wilczek, Physics today 11/99 & 1/00) 12

13 Lattice QCD top 10 science achievements 2008 S. Dürr et al. (BMW-collaboration), Science 322 (2008) 1224 "unquenched" calculation realistic quark masses 13

14 Excited states energy Δ(1232) S 11 (1535) Ba Ca atom nucleon cross section mb 14

15 Excited states: Quark Model Energy "mutually-generated" potential for quarks approximate confinement linear large r plus corrections, e.g. Metsch et al.: t'hoft Instanton interaction no spin-orbit forces BUT: no coupling to continuum è field energy materializes 15

16 Excited states: Quark Model N* resonances "missing resonances" Roper(1440) P = + Nucleon P = + S 11 (1535) P = exp. values U. Löring et al. Eur.Phys.J. A10 (2001) 395 parity pattern + +!?! effective degrees of freedom?? 16

17 Excited states: LQCD m π = 396 MeV nucleon P = + Roper(1440) P = + S 11 (1535) P = reproduces q-models wrong parity pattern but: no decays! R.G. Edwards et al., Phys. Rev. D84 (2011)

18 Λ hyperons: Quark Model Λ(1600) P = + Λ g.s. P = + Λ(1405) P = Metsch, Löring, Petry, EPJ A10 (2001) 18

19 Λ hyperons: Quark Model Λ(1600) P = + Λ g.s. P = + Λ(1405) P = parity OK mass < 1535? angular mom. Metsch, Löring, Petry, EPJ A10 (2001) 19

20 Threshold Dynamics? Λ(1405) narrow peak & cusp in η n/p narrow peak in ϕp cusp in KΣ S 11 (1535) p η 1.49 p ω 1.7 K N p η' p ϕ K* Λ K + Λ(1520) 1.43 K Σ cm energy / GeV 20

21 Λ(1405): LQCD genuine 3q J.M.M. Hall et al. [Adelaide group], arxiv:: v2 (2015) 21

22 Λ(1405): LQCD "molecule" as dominating Fock component genuine 3q J.M.M. Hall et al. [Adelaide group], arxiv:: v2 (2015) 22

23 Meson sector: X(3872) PRL91, (2003) Observed by Belle in B ± K ± π + π - J/ψ Ψ' X(3872) arxiv: (2008) (ICHEP 2008) M(π + π - l + l - )- M(l + l - ) 23

24 Meson sector: X(3872) BaBar / SLAC arxiv: (2008) PRL 110 (2013) CDF / Tevatron arxiv: (2009) J PC = 1 ++ J PC =

25 Meson sector: X(3872) mass M(X(3872)), MeV/c 2 Γ(X(3872)), MeV/c 2 B XK ±0.37± % C.L. (2003) B XK ±0.6±0.1 90% C.L. (2008) X J/ψπ + π ±0.16±0.19 average ±0.19 M(D 0 )+M(D *0 ) ± (fixed from first two) "molecule" possible bound state of D 0 D* 0 J P =

26 Meson sector: X(3872) Interpretation CP quantum numbers determined J PC = 1 ++ X(3872) likely not a charmonium state radial excitation of χc1 (JPC = 1++) expected at 3950 MeV/c2 ηc2 (JPC = 2-+) should have X J/ψγ suppressed no satisfactory cc assignment D 0 D *0 molecule? N.A. Törnqvist, Phys. Lett. B590, 209 (2004) explains proximity of D 0 D *0 threshold favors DD* decay over J/ψππ over J/ψγ (as observed) isospin I = 0 favoured expect X ψ(2s)γ to be suppressed (contrary to observation) tetraquark state? L. Maiani et al., Phys. Rev. D71, (2005) 2 neutral and 2 charged states predicted neutral states produced in B 0 and B + decays: Δm (7 ± 2) MeV measurement Δm = (+0.18±0.89±0.26) MeV in B J/ψπ+π- expect charged partners (contrary to observation) Dynamic interplay of quark & meson thresholds? components in Fock expansion V. Baru et al., Eur. Phys. J. A 44, 93 (2011) Something else?... not yet settled 26

27 Baryon sector unresolved issues w/ low-lying states unexpected narrow structures in threshold vicinity, e.g GeV K 0 Σ 2.0 GeV 2.1 GeV example Λ(1405) measurements of line shape etc multiple pole structure Meißner et al. meson-baryon dynamics significant genuine 3q structure unlikely t-dependence?? Schumacher et al. (CLAS/JLab) structure / dynamics of (low lying) states/structures still unresolved meson-baryon vs. 3q interactions? 27

28 γ + p K S 0 + Σ + K* cusp? most forward bin <θ K cm > = 0.83 R. Ewald et al. (CBELSA), PLB 713 (2012) full: present data open: Castelijns et al. 28

29 γ + p K S 0 + Σ + K* cusp? total x-sec R. Ewald et al. (CBELSA), PLB 713 (2012) full: present data open: Castelijns et al. 29

30 γ + p K S 0 + Σ + K* cusp? K* Σ + cross section added M. Nanova et al., EPJ A35 (2008) 333 R. Ewald et al. (CBELSA), PLB 713 (2012) full: present data open: Castelijns et al. 30

31 γ + p K S 0 + Σ + K* cusp? K* Σ + cross section added M. Nanova et al., EPJ A35 (2008) 333 K* K K π R. Ewald et al. (CBELSA), PLB 713 (2012) N Λ/Σ 31

32 Experimental Reqirements K* K K π N Λ/Σ K + K - K p Λ(1405) p p 32

33 Experimental Reqirements K* K "parallel" kinematics K π N Λ/Σ K + K - low t K p Λ(1405) p p 33

34 Experimental Reqirements K* K "parallel" kinematics N K π Λ/Σ forward (charged) particle high momentum K + K - low t K p Λ(1405) p p 34

35 Experimental Reqirements K* K "parallel" kinematics N K π Λ/Σ forward (charged) particle high momentum K + low t K K - 4π decay charged & neutral p Λ(1405) p p 35

36 BGO-OD experiment SciRi 96 ch. scint. pads, APD 36

37 BGO-OD experiment at ELSA 37 Vorstellung Fachschaft Dezember 2014

38 BGO-OD incident beam ELSA e beam 3.5 GeV tagged γ beam 3 GeV Current 2nA, ideal for tagging Linearly polarised γ beam using coherent bremsstrahlung off a diamond radiator Circularly polarised γ beam w/ longitudinally polarised e beam maximum polarisation at E e ~ 1.7GeV (E cm ~ 2GeV) Energy region of unresolved resonances and threshold structures covered 38

39 Analysis* Overview (Commissioning Data) * work of Tom Jude 39

40 BGO ball: K + identification time delayed weak decay within BGO ball T.C. Jude et al., PLB 735 (2014)

41 Missing hyperon masses from K + in BGO (γ beam,k + ) missing mass data subset w/ Σ 0 Λγ tagged Σ 0 Λγ efficiency ~ 60% false assignment < 10% 41

42 Particle id in OD spectrometer pions protons kaons 42

43 Missing (Y) mass from K + in OD spectrometer 43

44 Missing (Y) mass from K + in OD spectrometer 44

45 SciRi detector π 0 η ω π 0 γ η ω p π + π - π 0 2/3 cluster in BGO proton in SciRi η' p π + π - η MSc thesis G. Scheluchin 45

46 Summary BGO-OD addresses interesting physics programme meson-baryon dynamics narrow structures η, η', KY, ω, ϕ photoproduction η' mesic nuclei unique detector setup complementary to Crystal Barrel, CLAS, LEPS,... polarised beams & hyperon recoil polarimetry successful commissioning data taking ahead

47 Summary BGO-OD addresses interesting physics programme meson-baryon dynamics narrow structures η, η', KY, ω, ϕ photoproduction η' mesic nuclei unique detector setup complementary to Crystal Barrel, CLAS, LEPS,... polarised beams & hyperon recoil polarimetry successful commissioning data taking ahead Thanks to DFG SFB/TR-16 all Students (Bachelor, Master, Diploma, PhD) & postdocs postdocs: T. Jude, V. Vegna technical coordinators: D. Elsner, J. Hannappel 47

48 BGO-OD Collaboration spokespersons: P. Levi Sandri (INFN Frascati) & H.S. l Physikalisches Institut Bonn Germany l HISKP Bonn Germany l Petersburg Nuclear Physics Institute Gatchina Russia l Institut für Physik Basel Switzerland l II. Physikalisches Institut Giessen Germany l INFN Pavia Pavia Italy l National Science Center Kharkov Ukraine l Universaita degli Studi Messina Italy l INFN Catania Catania Italy l INFN Roma Tor Vergata Rome Italy l University of Rome Rome Italy l INFN Torino Torino Italy l INFN Roma La Sapienza Rome Italy l Istituto Superiore di Sanita Rome Italy l INFN Frascati Frascati Italy l The University of Edinburgh Edinburgh UK l Russian Academy of Sciences Moscow Russia l Glasgow University Glasgow UK l Idaho State University Pocatello USA 48

49 BGO-OD Voyager spacecraft The Sounds of Earth Johnny B. Goode (Chuck Berry) 49