Highlights on hadron physics at CLAS. K. Hicks (Ohio U.) Hadron 2011 Conference June 16, 2011

Transcription

1 Highlights on hadron physics at CLAS K. Hicks (Ohio U.) Hadron 2011 Conference June 16, 2011

2 Outline Meson-Baryon Cloud (MBC) Effects New results on baryon photocouplings Need for coupled-channels analysis Spectroscopy of baryons and mesons New and future analysis of KL New data: 2p, K*Y, KY*, etc. Future upgrade to CLAS12 Probe transition from MBC to quark core. 2

3 Hadron Structure with Electromagnetic Probes quark mass (GeV) p,r,w N,N *,D,D * resolution low Quark mass extrapolated to the chiral limit, where q is the momentum variable of the tree-level quark propagator (curve=dse, data=lqcd). 3q-core+MB-cloud meson dressed quark LQCD, DSE and confinement 3q-core current quark pqcd high 3

4 NΔ Transition Form Factor (G M ) from EBAC analysis One third of G * M at low Q 2 is due to contributions from meson baryon (MB) dressing: The area of Q 2 <7.0 GeV 2 is far from pqcd domain Meson- Baryon Cloud Effect CLAS Hall A Hall C MAMI Bates In the relativistic QM framework, the bare-core contribution is well described by the three-quark component of the wavefunction. bare quark core Q 2 =5GeV 2 B.Julia-Diaz et al., PRC 69, (2004) 4

5 Dynamical coupled-channels model of EBAC Partial wave (LSJ) amplitude of a b reaction: For details see Matsuyama, Sato, Lee, Phys. Rep. 439,193 (2007) Reaction channels: coupled-channels effect Transition potentials: Meson-exchange potentials (Derived from Lagrangians) bare N* states 5

6 Dynamical coupled-channels model of EBAC Partial wave (LSJ) amplitude of a b reaction: Physical N*s will be a mixture of the two pictures: For details see Matsuyama, Sato, Lee, Phys. Rep. 439,193 (2007) Reaction channels: baryon coupled-channels effect meson cloud meson core Transition potentials: exchange potentials of ground state mesons and baryons bare N* states 6

7 Jefferson Lab Today Hall B A Large acceptance spectrometer electron/photon beams B C 7

8 Radiative Decay of Strange Baryons 8

9 General Motivation Electromagnetic interactions are the cleanest way to access information on wavefunctions. For strange baryons, the EM coupling can only be studied by measuring the decay. SU(6) wavefunctions provide a zeroth-order prediction for M1 transitions. SU(6) symmetry provides a link between N* and Y* radiative decays: constrain SU(6) symmetries. 9

10 U-spin: connects D and S* decays SU(3) has three equal symmetries: I-spin: exchange of u and d quarks U-spin: exchange of d and s quarks V-spin: exchange of u and s quarks With respect to known symmetries: I-spin conserves chiral symmetry (mass) U-spin conserves EM symmetry (charge) V-spin conserves neither chiral nor EM symmetry 10

11 Group structure of U-spin: 11

12 How is this useful? 12

13 CLAS result ~10% uncert. PhD thesis, Dustin Keller 13

14 Predictions from other models Experiment: 660 +/ /

15 Interpretation Meson-Baryon Cloud effects are substantial for the Y* resonances also. U-spin relation works better than QM, etc. We can now make a prediction for S* + decay. The Wigner-Eckart theorem requires that the branching ratios D + pg and D 0 ng are equal. U-spin predicts a ratio: 15

16 New CLAS result Preliminary! 16

17 The MBC in electroproduction 17

18 N* electrocouplings from analyses of exclusive channels Resonant amplitudes p, h, pp,.. Non-resonant amplitudes p, h, pp,.. γ v * N*, N N A 3/2, A 1/2, S 1/2 G M, G E, G C + N N Separation of resonant/non-resonant contributions N* s can couple to various exclusive channels with entirely different nonresonant amplitudes, while their electrocouplings should remain the same. Consistent results from the analyses of Np and Npp electroproduction channels show that model uncertainties are under control. See the afternoon talk today by Victor Mokeev. 18

19 g v NN* electrocouplings from Np/Npp production Npp CLAS (New!) preliminary. Np CLAS I. Aznauryan,V. Burkert, et al., PRC 80, (2009). A 1/2 S 1/2 P 11 (1440) P 11 (1440) Np world V. Burkert, et al., PRC 67, (2003). Np Q 2 =0, PDG. A 3/2 D 13 (1520) A 3/2 Np Q 2 =0, CLAS M. Dugger, et al., PRC 79, (2009). F 15 (1685) Good agreement between the Np and Npp channels. N* electrocouplings are measurable and model independent. 19

20 High lying resonance electrocouplings from p + p - p Δ(1700)D 33 Npp CLAS preliminary. A 1/2 A 3/2 S 1/2 Np world V.D.Burkert, et al., PRC 67, (2003). Np Q 2 =0, PDG. Np Q 2 =0, CLAS M.Dugger, et al., PRC 79, (2009). Electrocouplings of S 31 (1620), S 11 (1650), F 35 (1685), D 33 (1700),and P 13 (1720) states were obtained for the first time from p + p - p electroproduction data. 20

21 Mystery of P 11 (1440) structure is solved Quark models: I. Aznauryan LC S. Capstick LC S 1/2 Relativistic covariant approach by Ramalho & Gross A 1/2 EBAC-DCC MB dressing (absolute values). The electrocouplings are consistent with P 11 (1440) structure as combination: a) quark core as a first radial excitation of the nucleon, and b) meson-baryon dressing. MBC effects could explain the data at low Q 2. 21

22 Coupled-channels effect in various reactions Pion photoproductions Full c.c. effect of ppn(pd,rn,sn) & hn off Pion electroproductions Full c.c. effect of ppn(pd,rn,sn) & hn off Double pion productions Full c.c effect off EBAC 22

23 Lineshape of the L(1405) 23

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26 K. Moriya & R. Schumacher (CMU/IU) (CMU) 26

27 Interpretation For a baryon resonance with a single pole, isospin symmetry S + p - = S - p +. The data favor a dynamically-generated resonance (two-pole solution Sp and NK). Evidence of MB coupled-channels effects? 27

28 Spectroscopy with KY, K*Y and KY* 28

29 Quark Model Classification of N* D 13 (1520) S 11 (1535) New P 11, P 13, or D 13 states? + q³g + q³qq + N-Meson + D(1232) Roper P 11 (1440) 29

30 Amplitude Uncertainty in gp K + L A. Sandorfi et al., J. Phys. G 38 (2011) CLAS (g1c, g11a) and GRAAL Real parts of the PWA multipoles s, C x, C z, s, P and S, T, P, O x, O z BoGa (dot-dashed), MAID (dashed), SAID (dotted), JSLT (solid) 30

31 FROST/HD gn pn, hn, KL, KS, Npp γp K + Λ weak decay has large analyzing power Discussed Monday, talk by V. Cede Process is described by 4 complex, parity conserving amplitudes 8 well-chosen measurements are needed to determine amplitude For hyperon finals state 16 observables will be measured in CLAS large redundancy in determining the photoproduction amplitudes allows many cross checks 8 observables measured in reactions without recoil polarization 31

32 K* + Y Photoproduction Motivation: 1. Search for higher-mass N* resonances 2. Compare with KY and K* 0 Y a. K * Y coupling sensitive to K 0 (800). b. K 0 (800) is part of the scalar nonet. c. K 0 (800) has not been directly observed. g p N* Y K* Oh and Kim, Phys Rev C 74, (2006). 32

33 Differential cross sections of K* + Λ: GeV GeV Preliminary result 33

34 Differential cross sections of K* + Σ 0 : GeV GeV Preliminary result 34

35 Total Cross Sections g + p *+ K + L g + p K * + + S 0 PhD thesis of Wei Tang 16 June 2011 Hadron 2011 Meeting 35

36 P. Mattione, Rice/CMU 36

37 Meson Spectroscopy 37

38 See Thursday afternoon talks by D. Weygand, C. Bookwalter 38

39 New: Scalar Mesons from gp K s K s p CLAS g11 E g max =3.8 CLAS g12 E g max =5.7 4-p Invariant mass (GeV) 39

40 The future: CLAS12 40

41 CLAS12 CLAS12 Forward Detector Luminosity > cm -2 s -1 Hermeticity Polarization Baryon Spectroscopy Elastic Form Factors N to N* Form Factors GPDs and TMDs DIS and SIDIS Nucleon Spin Structure Color Transpareny Central Detector 1m 41

42 Forward Photon Tagger for Spectroscopy M. Battaglieri

43 A new N* regime at Q 2 >3.5 GeV 2? Data appear to reach a plateau at Q 2 >3.5 GeV 2, but conclusive tests require S 11 higher Q 2 P 11 Transition to photon interactions with dressed quarks? D 13 43

44 quark mass (GeV) Resonance Transitions at 12 GeV Experiment E will extend access to transition FF for many prominent states in the range to Q 2 =12GeV 2. Electromagnetic form factors are sensitive to the effective quark mass. accessible at 6 GeV accessible at 12 GeV CLAS12 projected At 12 GeV we probe the transition from dressed quarks to elementary quarks. 44

45 Summary The Meson-Baryon Cloud has significant effects on photon coupling observables We cannot ignore coupled-channel effects! There are precise new data on KY, K*Y, KY* This will help the search for missing resonances K* data will determine the role of the K 0 (800). PWA for mesons: exotics & scalar mixing Future: CLAS12: transition to current quarks. 45

46 Backup Slides 46

47 t-dependence of f(1500) 47