1. Quark Hadron Physics and LEPS Takashi Nakano RCNP, Osaka University Physic Motivation LEPS facility  photo-production Pentaquark  + Summary LEPS ASPE2010, June 16 th, 2010, Osaka

2. Objective More than 98% of a proton mass is generated dynamically: a light quark gets heavy when it is confined in a hadron. A detailed mechanism is still unknown. A quark model describes structure of a hadron, but it is not perfect. Where does it work, where does not, and why? Breakthrough: New forms of hadrons which cannot be explained by a quark model (easily). Study the structure of the hadrons through production and decay by using a clean probe “high energy polarized photon”. Hadron Physics at LEPS/SPring-8

3. Quark and Proton Mass up quark: 1.5 ～ 3.0 MeV down quark: 3 ～ 7 MeV strange quark: 95±25 MeV Mass of proton （ uud ） : 938 MeV

4. Worldline and Mass x t Zero-mass particle Light particle Heavy particle  2 – p 2 =m 2 ∝ ∝∝  x m p E ∝ ∝∝  t

5. Confined quark x t x x ｔ ｔ Hadron mass is generated dynamically. But detailed mechnism is not well unserstood.

6. Spontaneous Breaking of Chiral Symmetry and Pions “Mass-less” quarks travel at the speed of light and conserve chirality. You can name light-handed quarks and right-handed quarks independently. The chiral symmetry sontaeously breaks when quarks are confined and acquire dynamical masses. “Mass –less” NG bosons appear if a symmetry is broken spontaneously. # of NG bosons = # of generators of a broken symmetry. SU(3): π 、 K 、  π + mass ： 140 MeV. Light! But not zero.

7. 7 Quantum Chromo Dynamics Perturbative region Non-Perturbative region Current quarkConsitituent quark Chiral symetry is a good symmetry Flavor SU(3) symmetry is a good symmetry Parton modelQuark model Color confinement Spontaneous breakdown of chiral symmetry Generation of Hadron mass Creation of NG bosons: , K,  Light Fast Heavy Slow

8. Constituent quark model Mainly 3 quark baryons: M ~ 3m q + (strangeness)+(symmetry) , K, and  are light: Nambu-Goldstone bosons of spontaneously broken chiral symmetry. m u ~ m d = 300 ~ 350 MeV, m s =m u(d) +130~180 MeV

9. 9 What are effective degrees of freedom ? Meson cloud picture: Thomas, Speth, Weise, Oset, Jido,Brodsky, Ma, … | p > ~ | uud > +   | n ( udd )  + (  du ) > +   |  ++ ( uuu )  - (  ud ) > +  ’ |  (uds) K + (  su ) > … SS u u SS d u du SS SS u u d Di-quark cluster (5-quark) picture: Zou, Riska,Jaffe,Wilczek | p > ~ | uud > +    [ud][ud]  d > +   | [ud][us]  s > + … or +

10. 10 Questions to be answered How are quarks confined in hadrons? Why does a constituent quark model work well? (and sometimes not?) What are effective degrees of freedom for hadrons? How can we learn about the structure of the hadrons from their decay? Does a pentaquark exist?

11. 11 Hadronic component of a photon contains a large fraction of ss. Isospin dependence is not trivial because a  contains both I=0 and I=1 components. Linear polarization can be used as a parity filter. The polarization can be changed easily. Disadvantage is low interaction rates.  Require high beam intensity and large detector acceptance.

12. Laser Electron Photon beamline at SPring-8

13. Energy Spectrum of the LEPS beam 2.4 GeV8 GeV Measured with PWO calorimeter Cross section

14. Polarization of LEP Beam Linear Polarization : 95 % at 2.4 GeV

15. LEPS detector (forward spectrometer system) 1m1m TOF wall MWDC 2 MWDC 3 MWDC 1 Dipole Magnet (0.7 T) Liquid Hydrogen Target (50mm thick) Start counter Silicon Vertex Detector Aerogel Cerenkov (n=1.03)  Large acceptance in the forward directions

16. Charged particle identification Mass(GeV) Momentum (GeV) K/  separation (positive charge) K+K+ ++ Mass/Charge (GeV) Events Reconstructed mass d p K+K+ K-K- ++ --  (mass) = 30 MeV(typ.) for 1 GeV/c Kaon

17. Mass measurement of unstable particles E 1 = E 2 + E 3 p 1 = p 2 + p 3 m 1 2 = E 1 2 – p 1 2 1 1 2 2 3 3 4 E 3 = E 1 + E 2 - E 4 p 3 = p 1 + p 2 – p 4 m 3 2 = E 3 2 - p 3 2  n K-K- ++

18. 18  (1020)

19. Diffractive Photoproduction of vector meson Vector Meson Dominance Meson Exchange Pomeron Exchange  N   N  (~ss) q _q_q _ qq =  Dominant at low energies Slowly increasing with energy uud    glueball

21. 21  photoproduction near production threshold Titov, Lee, Toki Phys.Rev C59(1999) 2993 P 2 : 2 nd pomeron ~ 0 + glueball (Nakano, Toki (1998)) Data from: SLAC('73), Bonn(’74),DESY(’78) Decay asymmetry helps to disentangle relative contributions ⊥ ⊥

22. 22 Differential cross section at t=-|t| min Phys. Rev. Lett. 95, 182001 (2005)

23. 23 Differential Cross Section Fit Fit of Ae -bt to the differential cross section A: (ds/dt)|t=t min (Forward xsec)  good approx. to the total cross section Good agreement with LEPS data near threshold Dip in region 2 < E  < 3 GeV David J. Tedeschi @ SNP2006

24. 24 Polarization observables with linearly polarized photon Decay Plane //  natural parity exchange (- 1) J (Pomeron, Scalar Glueball, Scalar mesons) K+K+ K+K+ K-K-  meson rest frame Decay Plane  unnatural parity exchange -(-1) J (Pseudoscalar mesons  )   Relative contributions from natural, unnatural parity exchanges Decay angular distribution of  p p K-K-

25. 25 Decay angular distribution 2.173<E  <2.373 GeV 1.973<E  <2.173 GeV cos      W W Curves are fit to the data. No energy dependence, except for  distribution. Natural parity exchange is dominant.

26. 26  + (1530)

27. c.f.  (1405): uudsu or uds e.g. uuddc, uussd What are pentaquarks?  Baryon.  Minimum quark content is 5 quarks.  “Exotic” penta-quarks are those where the antiquark has a different flavor than the other 4 quarks  Quantum numbers cannot be defined by 3 quarks alone.  + : uudds Baryon number = 1/3 + 1/3 + 1/3 + 1/3 – 1/3 = 1 Strangeness = 0 + 0 + 0 + 0 + 1 = 1

28.  Prediction of the  + Baryon M  1890-180*Y] MeV D. Diakonov, V. Petrov, and M. Polyakov, Z. Phys. A 359 (1997) 305. Exotic: S=+1 Low mass: 1530 MeV Narrow width: ~ 15 MeV J p =1/2 +

29. Baryon masses in constituent quark model Mainly 3 quark baryons: M ~ 3m q + (strangeness)+(symmetry) , K, and  are light: Nambu-Goldstone bosons of spontaneously broken chiral symmetry. 5-quark baryons, naively: M ~ 5m q + (strangeness) +(symmetry) 1700~1900 MeV for  + m u ~ m d = 300 ~ 350 MeV, m s =m u(d) +130~180 MeV

30. DPP predicted the   with M=1530MeV,  <15MeV, and J p =1/2 +. Naïve QM (and many Lattice calc.) gives M=1700~1900MeV with J p =1/2 -. But the negative parity state must have very wide width (~1 GeV) due to “fall apart” decay. Fall-apart decay problem For pentaquark Fall apart Ordinary baryons qq creation Positive parity requires P- state excitation. Expect state to get heavier. Need counter mechanism. diquark-diquark, diquark- triquark, or strong interaction with “pion” cloud? Positive Parity?

31.  What are the fundamental building blocks for  + (3 quarks) +  (K) cloud? N  K bound state? di-quark + di-quark + anti-quark? 5-quark? ….. …would be a breakthrough in hadron physics.

32. 32 First evidence from LEPS  n  K + K - n Phys.Rev.Lett. 91 (2003) 012002 hep-ex/0301020 ++ Low statistics: but Tight cut: 85% of events are rejected by the  exclusion cut. Unknown background: BG shape is not well understood. Events from a LH2 target were used to estimate it. Possible kinematical reflections. Correction: Fermi motion correction is necessary.

33. 33 Slope for mesons Slope for baryons Slope for pentaquarks??

34. Experimental status Not seen in the most of the high energy experiments: The production rate of  + /  (1520) is less than 1%. No published positive result from dedicated experiments CLAS  p  d, COSY-TOF pp, KEK-PS (  -,K - ), (K +,  + ) The width must be less than 1 MeV. (DIANA and KEK-B) reverse reaction of the  + decay:  +  n K + LEPS observed signals in   n  K + K - n and  d  (1520)KN reactions, which could be inconsistent with CLAS  d experiment (CLAS-g10). Not likely to an ordinary baryon. K* coupling should be VERY small. K coupling should be small.

35. t-channel photo-production of  + p ++ K* K0K0 n ++ K* + K-K- p ++ K0K0 K0K0 n ++ K+K+ K-K-    

36. Quasi-free production of  + and  (1520)  n p p n K-K- K+K+   p n n p K+K+ K-K-  Both reactions are quasi-free processes. Fermi-motion should be corrected. Existence of a spectator nucleon characterize both reactions. detected spectator E  =1.5~2.4 GeV Data was taken in 2002-2003. 36

37. Minimum Momentum Spectator Approximation γ d K-K- K+K+ Nucleon from decay or scattering Spectator nucleon p n 4 momentum of pn system M pn and p tot |p CM | and v pn p CM - p CM v pn We know Direction of p CM is assumed so that the spectator can have the minimum momentum for given |p CM | and v CM. at rest tagged detected

38. 2-fold roles of MMSA coherent inelastic quasi-free Clean-upEstimation of p F

39. Better M nK + mass resolution with MSSA M nK + mass resolution is improved by a factor of 2 compared to a simple ( ,K - ) missing mass resolution, where the initial neutron is assumed to be at rest. true neutron momentum (GeV/c) calculated neutron momentum (GeV/c) M nK + (GeV/c 2 ) MC data of  n  K -  +  K - K + n with Fermi motion  ~10 MeV/c 2 |p min |<70 MeV/c

40. Results of  (1520) analysis  (-2lnL) =55.1 for  ndf=27.1  Structure with a width less than 30 MeV/c 2 requires a physics process or fluctuation. The total cross section is ~1  b, which is consistent with the LAMP2 measurements. Simple ( ,K + ) missing mass: No correction on Fermi motion effect. pK - invariant mass with MMSA: Fermi motion effect corrected. 40

41. Results of   analysis  (-2lnL) =31.1 for  ndf=25.2  Simple ( ,K - ) missing mass: No correction on Fermi motion effect. nK + invariant mass with MMSA: Fermi motion effect corrected. “ The narrow peak appears only after Fermi motion correction.” 41 PRC 79, 025210 (2009)

42. Probability of 1/5000000 may not be low enough. “Extraordinary claim requires an extraordinary evidence.” High statistics data was collected in 2006-2007 with the same experimental setup. Blind analysis is under way to check the Θ + peak Next step

43. LEPS2 Project at SPring-8 Backward Compton Scattering Experimental hutch 8 GeV electron Recoil electron (Tagging) Better divergence beam  collimated photon beam Different focus points for multi CW laser injection GeV  -ray Inside building Outside building 30m long line （ LEPS 7.8m) Large 4  spectrometer based on BNL-E949 detector system. Better resolutions are expected. New DAQ system will be adopted. Laser or re-injected X-ray High intensity ： Multi (ex. 4) laser injection w/ large aperture beam-line & Laser beam shaping ~10 7 photons/s （ LEPS ~10 6 ） High energy ： Re-injection of X-ray from undulator E  < 7.5GeV (LEPS < 3GeV)

44. Summary 1.LEPS is a Backward Compton gamma beam facility at SPring-8. GeV  beam with high polarization is available. 2.LEPS provides essential information to understand production mechanism of hadrons. 3.5-   + peak was observed in the nK + invariant mass at 1.53 GeV/c 2. New data set with 3 times more statistics was taken. Blind analysis is under way. 4. LEPS2 project is ongoing: 10 times stronger beam & 4  coverage.

45. 45 LEPS Collaboration Research Center for Nuclear Physics, Osaka University ： D.S. Ahn, M. Fujiwara, T. Hotta, Y. Kato, H. Kohri, Y. Maeda, T. Mibe, N. Muramatsu, T. Nakano, S.Y. Ryu, T. Sawada, M. Yosoi, T. Yorita Department of Physics, Pusan National University ： J.K. Ahn School of Physics, Seoul National University ： H.C. Bhang Department of Physics, Konan University ： H. Akimune Japan Atomic Energy Research Institute / SPring-8 ： Y. Asano Institute of Physics, Academia Sinica ： W.C. Chang, J.Y. Chen Japan Synchrotron Radiation Research Institute (JASRI) / SPring-8 ： S. Date', H. Ejiri, N. Kumagai, Y. Ohashi, H. Ohkuma, H. Toyokawa Department of Physics and Astronomy, Ohio University ： K. Hicks Department of Physics, Kyoto University ： M. Niiyama, K. Imai, H. Fujimura, M. Miyabe, T. Tsunemi Department of Physics, Chiba University ： H. Kawai, T. Ooba, Y. Shiino Wakayama Medical University ： S. Makino Department of Physics and Astrophysics, Nagoya University ： S. Fukui Department of Physics, Yamagata University ： T. Iwata Department of Physics, Osaka University ： S. Ajimura, K. Horie, M. Nomachi, A. Sakaguchi, S. Shimizu, Y. Sugaya Department of Physics and Engineering Physics, University of Saskatchewan ： C. Rangacharyulu Laboratory of Nuclear Science, Tohoku University ： T. Ishikawa, H. Shimizu Department of Applied Physics, Miyazaki University ： T. Matsuda, Y. Toi Institute for Protein Research, Osaka University ： M. Yoshimura National Defense Academy in Japan ： T. Matsumura RIKEN ： Y. Nakatsugawa Department of Education, Gifu University ： M. Sumihama,