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 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 Quark and Proton Mass up quark: 1.5 3.0 MeV down quark: 3 7 MeV strange quark: 9525 MeV Mass of proton uud : 938 MeV Worldline and Mass x t Zero-mass particle Light particle Heavy particle 2 p 2 =m 2 x m p E t Confined quark x t x x Hadron mass is generated dynamically. But detailed mechnism is not well unserstood. 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): K + mass 140 MeV. Light! But not zero. 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 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 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 ) > SS u u SS d u du SS SS u u d Di-quark cluster (5-quark) picture: Zou, Riska,Jaffe,Wilczek | p > ~ | uud > + [ud][ud] d > + | [ud][us] s > + or + 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 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. Laser Electron Photon beamline at SPring-8 Energy Spectrum of the LEPS beam 2.4 GeV8 GeV Measured with PWO calorimeter Cross section Polarization of LEP Beam Linear Polarization : 95 % at 2.4 GeV 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 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 Mass measurement of unstable particles E 1 = E 2 + E 3 p 1 = p 2 + p 3 m 1 2 = E 1 2 p E 3 = E 1 + E 2 - E 4 p 3 = p 1 + p 2 p 4 m 3 2 = E p 3 2 n K-K- ++ 18 (1020) 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 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 Differential cross section at t=-|t| min Phys. Rev. Lett. 95, (2005) 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. SNP2006 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 Decay angular distribution 2.173