Hadron physics with meson photoproduction at LEPS/SPring-8 Tomoaki Hotta (RCNP, Osaka University) for LEPS Collaboration MESON 2010 CRACOW, POLAND 12 JUNE 2010
Outline LEPS (Laser-Electron Photon at SPring-8) Experiment Brief summary of the recent results Some Selected topics – Backward meson photoproduction – Photoproduction of (1405) Future prospects: LEPS2
Super Photon ring-8 GeV SPring-8 8 GeV, 100 mA, e - ring Third-generation synchrotron radiation facility 62 beamlines
LEPS Beamline Compton backscattering: 8 GeV e - + UV Laser E = 1.5 GeV (tagged) – 2.4 GeV, 3.0 GeV 100 % polarized (direction can be changed easily). Intensity: 2x10 6 /sec for E max = 2.4 GeV 2x10 5 /sec for E max = 3.0 GeV 8-GeV e - storage ring Scattering region E Tagging UV Laser = 351 nm, 257 nm Backscattered photon Backward Compton : Small fraction of the low energy background
LEPS spectrometer (forward) TOF Dipole Magnet 0.7 Tesla Target Start CounterDC2DC3 DC1SVTX AC(n=1.03) Charged particle spectrometer with forward acceptance PID from momentum and time-of-flight measurements Photons Momentum [GeV/c] K/ separation K+K+ ++ Mass/Charge [GeV/c 2 ] P ~6 MeV/c for 1 GeV/c, TOF ~150 ps, MASS ~30 MeV/c 2 for 1 GeV/c Kaon
Summary of Results from LEPS Backward meson prod. – PRC 80:052001R(‘09) – PLB 657:32(‘07) pentaquark – PRC79:025210(’09) – PRL 91:012002(‘03) photoproduction – Proton target PRL95:182001(‘05) – Nuclear targets PLB608:215(’05) – D target (coherent) PLB658:209(‘08) – D target (indoherent) PLB684:6 (‘10) Hyperon production – , (forward K + ) PRC73:035214(‘06), PRL91:092001(‘03) – (forward K + ) PRL 97:082003(‘06) – (1520) PRL 103:012001(‘09), PRL 104:172001(‘10) – (1385) PRL 102:012501(’09) – Backward PRC 76:042201(’07) – (1405), (1385) (with TPC) PRC 78:035202(‘08)
PRC79:025210(’09) γ n p p n K-K- K+K+ detected Peak at M(nK + ) = GeV/c 2 Statistical Significance = 5.2 Blind analysis for new data set with x3 higher statistics is underway Experiment with TPC, LEPS2
Selected Topics 1. Backward meson photoproduction
Meson photoproduction W ( √s ) = 1.9 – 2.3 GeV cos cm = 1 ~ 0.6 ( cm = 123 o – 180 o ) Resonance term +Born term M p p, N*, * s-channel Forward Backward meson exchange resonances Nucleon exchange p M p p, N*, * u-channel t-channel M p p M g NNM g NN*M …. Present data Tree-level diagrams:
Motivation: Baryon resonances Problems in the constituent quark models Mass-order-reverse problem for the lowest excited baryons. S 11 (1535) uud(L=1) ½- should be the lowest P 11 (1440) uud(n=1) ½+ *(1405) uud(L=1) ½- introducing additional qq to solve the problem. Missing baryon resonances The number of predicted states is much less than observed. coupling to (non- N) N, N, ’N, N channels? -
Backward Meson Production Data ’ Missing Mass 2 (GeV 2 /c 4 ) E = GeV cos cm = 0.9 Fitting result p p x p p p p p p p p ’ Proton (Forward) : measured Meson (Backward): Missing mass u-channel, s-channel N, N* contributions
Results: Differential cross sections for photoproduction LEPS data SAID -partial-wave analysis Eta-MAID - isobar model Bump-like structure is seen above W=2.0 GeV Jlab/CLAS data PRL89:222002(2002) Bonn/ELSA data PRL94:012004(2005)
13 Evidence for resonances CLAS : Evidence at W ~ 1850 MeV for S 11 (2090) ELSA : Evidence at W ~ 2070 MeV for D 15 (2068) No for S 11 (2090) PRL 89, (2002) PRL 94, (2005) BES : N* from J/ decay, J/ PRL 97, (2006) N*(1440) N*(1535).. N*(1650).. N*(2070) Particle Data Group P 11 (2100) N)/ tot = 0.61 in Pitt-ANL model Phys. Rep. 328, 181(2000) photoproduction
14 ’ Comparison of ’ and photoproductions cos cm = 0.8 ~ 0.7 PRC R (‘10)
Selected Topics 2. Photoproduction of (1405)
E // B 1.5 LEPS detector setup with TPC
17 Solenoid Magnet Dipole Magnet TPC Buffer Collimator 24Φ Collimator 2 1 Φ Beam TPC
Spectrometer TPC p K + + ∓ - n
The (1405) lineshape depends on the decay angles at its rest frame? cos 19
0.8< cos K+ < 1.0 t
Future prospects LEPS2 Project Polarized HD Target
New Beamline (LEPS2) 8-GeV e Detector UV Laser Smaller (1/4) beam divergence Multiple (x4) laser injection 8W 16W / laser tube improved optics Much higher intensity beam x 10 or higher Better tagged E resolution Smaller beam size Larger-acceptance detector ~50% of the total budget has been approved. Construction of the beamline &detectors started!! ~50% of the total budget has been approved. Construction of the beamline &detectors started!!
Design Concept of the Main detector Momentum resolution at forward angle p/p~1%. Good reaction tag. Large and smooth acceptance azimuthally Decay and polarization. Detection of decay product down to lower momentum 100 MeV/c Detection of neutral particle (Photon)
BNL-E949 Solenoid Magnet Large Angle Coverage P/P 10 degree TOF, E/ x, TOP, AC for PID Symmetric acceptance for positive and negative particles Collaboration with Belle and J-PARC, RIKEN RPC, TOPcounter, DSSD, GEM-TPC… Detailed design, R&D in progress LEPS2 detector
LEPS2 Schedule – Construction of Beamline – R&D of the detectors and DAQ – Construction of Experimental Hall – Transporting E949 magnet+detectors 2012 – Beam comissioning – Construction of main detector 2013 – Start LEPS2 experiment
Al wire 2.5cm Polarized HD target In-Beam Cryostat Polarize HD at 10 mK, 17 T at RCNP Transport to LEPS site Longstanding R&D at Syracuse, LEGS/BNL, and Orsay. Polarized successfully. Polarization measurement underway
W.Roberts PRC73,035215(2006) NK invariant mass (GeV) Polarization Observables in w/o
Summary LEPS experiment – Linearly polarized real photon beam ( 3 GeV) – Forward charged-particle spectrometer. – TPC+Solenoid, surrounding the target – Meson photproduction Production and decay of baryon resonances, Hyperon resonances, and exotic pentaquark. Backward meson photoproduction – evidence for N* contribution at w=2 GeV? Photoproduction of (1405) – line-shape analysis, (1405) vs *(1385) ratio Future Prospects – LEPS2: higher intensity beam + Large acceptance detector. – Pol. HD target
LEPS/LEPS2 Collaboration RCNP / Osaka Univ. Osaka Univ. Tohoku Univ. JASRI / SPring-8 Kyoto Univ. Tohoku Univ. JAEA Chiba Univ. Konan Univ. Wakayama Med. College RIKEN KEK Univ. of Tokyo Nagoya Univ. Yamagata Univ. Miyazaki Univ. National Defense Academy Tokyo Institute of Technology Academia Sinica (Taiwan) Ohio Univ. (USA) Pusan National Univ. (Korea) Seoul National Univ. (Korea) Univ. of Saskatchewan (Canada) JINR Dubna (Russia) Univ. of Connecticut (USA) National Chung Cheng Univ. (Taiwan)