Status and Prospects of Hadron Physics at LEPS in Japan Takashi Nakano (RCNP, Osaka Univ.) International School of Nuclear Physics 37 th Course: Probing hadron structure with lepton and hadron beams September, Erice-Sicily 1

SPring-8/LEPS, LEPS2 LEPS LEPS2 2

Laser Electron Photon beamline at SPring-8 3 Operated since 2000.

Recoil electron (tagging) LEP (GeV  -ray) Laser room Inside SR bldg 30m long line 8 GeV electron Laser Outside SR bldg Experimental bldg Beam dump BGOegg LEPS2 spectrometer Storage ring 10 times high intensity: Multi-laser injection & Laser beam shaping Best e-beam divergence (12  rad)  Photon beam does not spread out  Construct experimental apparatus outside SR bldg Backward Compton scattering BGO EM calorimeter Large LEPS2 spectrometer using BNL/E949 magnet  expect better resolutions ~135 m 4

Backward-Compton Scattered Photon 5 PWO measurement tagged Linear Polarization of  beam photon energy [GeV]photon energy [MeV] 8 GeV electrons in SPring nm(260nm) laser  maximum 2.4 GeV(2.9 GeV) photon Laser Power ~6 W  Photon Flux ~1 Mcps E  measured by tagging a recoil electron  E  >1.4 GeV,  E  ~10 MeV Laser linear polarization % ⇒ Highly polarized  beam

Decay polarization with linearly polarized photons  parity filter Decay Plane //  natural parity exchange (-1) J (Pomeron, Scalar mesons (  ), K * ) Photon Polarization KK KK  Decay Plane  unnatural parity exchange -(-1) J (Pseudoscalar mesons  )         K  +    K* 0  K  +   6

LEPS spectrometer K-K- K+K+ DC3 DC2 DC1 Beam Start counter (STC) SSD AC ・ Dipole magnet : 0.7 Tesla ・ Acceptance : Hori : ± 20° Vert : ± 10° ・ AC index : 1.03 (reject 0.6 GeV/c π ) x z y ・ E γ = 1.5 ~ 2.4 GeV ・ tagger rate : ~10 6 cps ・ trigger rate : ~ 100 cps 7

 p  p T. Mibe et al., Phys. Rev. Lett. 95, (2005) From decay asymmetry, the relative strength of natural-party processes to unnatural-parity ones is the same in the peak and off-peak regions. Possible presence of additional natural parity exchange  signature of 0+ glueball trajectory?? 8

Decay Angular Distributions of  p  p W ∝ sin 2   helicity-conserving processes are dominating.   0.2  N/(N+UN) ~70%.  =0.197 ±0.030  =0.189 ±0.024 Peak Off Peak 9

Possible interference between  and    photo-productions 10

Data analysis 11

Interference between M  and M  (1520) Scatter Plots of the K-K+ and K-p Masses Interference Yields (K+K-) 12

Interference between M  and M  (1520) Strong constructive interference is seen when the K+K- pairs are observed at forward angles. However, the interference cannot account for 2.0GeV bump structure in forward differential cross sections for photo- production. constructive destructive S. Y. Ryu, PhD thesis, (2015) 13

 + search Pentaquark (uudds) low mass 1540 MeV (naïve QM ~1900 MeV) narrow width Γ < 10 MeV experimental search First evidences from LEPS & DIANA in 2003 negative results from CLAS(2006) & many other experiments 14

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γ n p K+K+ K-K- p n Θ+Θ+ spectator signal events γ n p K-K- K+K+ p n Λ(1520) spectator reference events Θ + study at LEPS Θ + production via γd → K - Θ + → K - K + pn Spectator can not escape from the target. signal events : γn → K - K + n reference events : γp → K - K + p n/p separation is possible by improving the proton detection efficiency. 16

Effect of proton rejection proton rejection cut z-vertex cut 90% of proton events (with a neutron spectator) are identified by selecting events stemming from the downstream part of the target. Enhancement is seen in the Θ + signal region. Repeat the experiment with improved proton detection efficiency & data 17

Large STC (LSTC) x : 780 mm y : 340 mm z : 10 mm Large STC (LSTC) x : 780 mm y : 340 mm z : 10 mm Small STC x : 150 mm y : 94 mm z : 5 mm Small STC x : 150 mm y : 94 mm z : 5 mm

proton detection with STC Proton detection efficiency is improved by using large-area start counter (STC) in run. energy loss at STC p K+K+ K-K- n K+K+ K-K- or proton untagged with STC p K+K+ K-K- proton tagged with STC signal K +,K - detect K +,K - detect K +,K -,p detect K +,K -,p detect LH LH 2 K +,K - detect K +,K - detect K +,K -,p detect K +,K -,p detect 19

% point % point efficiency becomes ~90 % for events with z-vertex > -960 mm for data with z-vertex > mm for data z-vertex [mm] Counts : LH 2 : LH 2 z-vertex point dependence Overall proton detection efficiency is: ~60% for data ~85% for data Events from LH2 target. Measured proton detection efficiency 20

γp → K + X γd → K + X MM(K + ) [GeV/c 2 ] Counts assuming proton mass for missing mass calculation Quality of K + missing mass spectra are the almost same. K + missing mass spectra 21 New  + result from LEPS will be reported in several months.

LEPS2 Detector 22  TPC DC  counter RPC TOP B=1 T :  p/p  1% for  TPC Prototype Residual RMS=117  m RPC ToF time distribution 2.22 m 5 m >3  K/  GeV/c 2

Exp. hall was constructed. (2010.Oct-2012Jan) Installation of the E949 magnet (2011.Nev-Dec)  counters were installed. (2012.June) Beam pipe (2012.May) 23

 + Search at LEPS2 24 pK s invariant mass K * missing mass (t-channel K-exchange is possible) No Fermi motion correction. No φ background. Measure angular dependence of production rate in large angle region, up to CLAS acceptance.

Two pole structure of  (1405) 25 ChUT model prediction by D. Jido, et al. NPA725(2003)

E  K* K  p   K*(890) Λ(1405) photoproduction with linearly polarized photon T.Hyodo et. al, PLB Commissioning of LEPS2 detector will start in 2017.

BGO-Egg : ELPH, Tohoku U. Large acceptance photon detector (BGO-Egg) 1320 BGO crystals Covering 24 o ~144 o polar angle 1.3% energy resolution for 1 GeV 27

Experimental Setup 28  BGOegg Inner Plastic Scintillator (IPS) Drift Chamber (DC) Resistive Plate Chamber (RPC) Cylindrical Drift Chamber (CDC) Target 6.8  z=0 m 1.28 m E949  -counter 2 m (Vertical) x 3.2 m (Horizontal) 6.8  z=12.5 m 21  E949 Magnet z=1.6 m Upstream Charge Veto Counter Tagged Photon Energy : 1.3 – 2.4 GeV (355 nm UV laser) Tagged Photon Intensity : 1.4 – 1.8 Mcps (3 or 4 laser injection)

Combination of BGOegg and RPC(TOF) Proton missing mass for 2 gammas Momentum conservation Invariant mass and proton missing mass consistency Invariant mass of 2 gammas Invariant mass of 6 gammas Proton missing mass for 6 gammas By using both BGOegg and RPC, background events are cleaned up. MeV    ’’ ’’ ’’   ’’  require   and  29

Mass modification of PS mesons in finite density Mass of  ’ is possibly modified under the finite density compared with the vacuum  m  ’ ～  0  m  ～ +  0 P. Rehberg, et al. Phys. Rev. C53(1996) p410 H. Nagahiro, M Takizawa, S. Hirenzaki Phys. Rev. C 74, (2006) 30

v γ + 12 C -> η’ x 11 B + p Experimental method Identify η’ production by η tag BGOegg calorimeter 1m 2 γ 3π 0 ->6 γ → → η (39%) 2m 3.2m Search for a bound state Forward TOF 12.5m from the target Vert : ± 7 ° Hori: ± 4 ° (33%) bound E ex -E 0 (MeV) H. Nagahiro η’ + N -> η + N 31

Proton missing mass spectra γ + 12 C -> X + p (γ + 12 C -> η’ x 11 B + p) Mx – M 11B - M η’ η tag missM ’ (MeV ) hard to see signal shape by only tagging η side band Signal region (-200~200MeV) is masked. 1/20 of full data 32

back-to-back  p tag BGOegg cluster =7 : ~50 % 7 th cluster = charged : ~50% cos (ηp Opening angle) BG -200 < MisM <200MeV masked proton acceptance when η is tagged : ~100% signal 7 th cluster = charged : 50% ( proton in nucleus) proton FSI : ~40% loss x20 statistics (~full 2015A) x20 statistics (~full 2015A) ~10 events ~100 events 90% C.L. cos(Open angle) < -0.9 : 100% x20 statistics (~full 2015A) x20 statistics (~full 2015A) Fermi motion (p p = p η ~ MeV/c) signal region no events in < -0.9 In addition, momentum cut proton ID by BGOegg is possible cosOpen 1 order margin (-200<MisM<200MeV) 33

 ->2  mode Mx – M 11B - M η’ signal yield ~ x2 of 3π 0 mode (BGOegg acceptance) missM(MeV) BGOegg cluster = 2 or 3 η mass region (  45 MeV) sideband region (  45  90 MeV) similar S/N ratio as 3π 0 mode estimated signal 34

Summary 35 LEPS Study of  interference Updates on Θ + LEPS2 Two different experimental setups. Solenoid spectrometer Study of 2-pole structure of Λ(1405) BGOegg + TOF(RPC) Backward meson production from proton and nuclei BGOegg experiment was started last year!