Hadron Physics with Photon Beam at LEPS/ LEPS2 Takashi Nakano (RCNP, Osaka Univ.) HHIQCD2015, March 3rd, 2015

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1 Hadron Physics with Photon Beam at LEPS/ LEPS2 Takashi Nakano (RCNP, Osaka Univ.) HHIQCD2015, March 3rd,

2 Outline LEPS Overview Some recent results LEPS2 Physics Motivation Overview First experiment Summary 2

3 Laser Electron Photon beamline at SPring-8 Operated since

4 Photon tagging and experiment Timing and position of a scattered electron is measured at a counting rate of ~1 M /sec. E γ 1.5 GeV : about 40% of (0<E γ <E max ) photons For incident photon number normalization For trigger : rate ~ 100 /sec

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

6 Setup of LEPS Detectors Only FWD spectrometer ±20 x ±

7 Setup of LEPS Detectors 1.5 γ E // B Polarized HD target will be ready soon. 7

8 Linearly Polarized Photons γ (1) Vector K* (1) Natural parity (2) Unnatural parity (2) p Exchanged particle Hyperon Decayed Particles 8

9 Scaler κ exchange in Σ + production K : Pseudoscalar meson à unnatural exchange κ: Scalar meson à natural exchange 9

Parity Spin Asymmetry PRL 108, 092001 (2012) w/ κ-exchange Y. Oh and H.

10 Parity Spin Asymmetry PRL 108, (2012) w/ κ-exchange Y. Oh and H. Kim, PRC 74, (2006) w/o κ-exchange Dominance of natural-parity exchange is indicated at forward angles. Consistent with κ(800) meson exchange. 10

11 Kaonic nuclei search γ K/K * π π + Κ + p Virtual K, K * N K N π K 0 direct K-exchange is forbidden in (π +,Κ + ) reaction. 11

12 Physics motivation K-N interaction is strongly attractive (I=0). weakly attractive (I=1). à KNN bound state (K - pp, K - pn, K - nn) K - pp the strongest bound state Theory: B.E. = MeV, Γ= MeV Experiment : FINUDA (B.E. =115 MeV, Γ = 67MeV) DISTO (B.E. =103 MeV, Γ = 118MeV) 12

13 K - pp search via γ + d à K + + π - + X MM(K + π - ) Upper limit of cross section (95% C.L.) d 3 σ/dcosθ lab K+ dcosθlab /dm π- (μb / 20 [MeV/c 2 ]) (a) n Λ Σ Λ * /Σ * 0.5 Search Region K - pp threshold MM d (K + π - ) [GeV/c 2 ] Upper Limit of K - pp production (d 2 σ/dcosθ lab K+ dcosθlab [μb]) π (b) Γ = 20 MeV Γ = 60 MeV Γ = 100 MeV ~10% of Q.F. 13 processes MM d (K + π - ) [GeV/c 2 ] So far, no peak was From likelihood ratio method; Search region GeV/c 2 observed in inclusive modes. We will try to detect decay products. Γ = 20 MeV : µb Significant peak cannot Larger be acceptance, observed. LEPS2. Γ = 60 MeV : µb à ~ 10% of Q.F. processes Γ = 100 MeV : µb

14 Prediction of the Θ + Baryon ud s D. Diakonov, V. Petrov, and M. Polyakov, Z. Phys. A 359 (1997) 305. M = [ *Y] MeV Exotic: S=+1 Low mass: 1530 MeV Narrow width: < 15 MeV J p =1/2 + 14

15 Previous result γ d K + K - pn reaction Data taken in <E γ <2.4 GeV. Significance of 5.1σ from shape analysis. (Δ(-2lnL) with/without signal) Mass=1524±2+3MeV/c 2. If the peak is real, ü It should be reproducible. ü It should appear in M(nK + ). ü It should not appear in M(nK - ) nor in M(pK + ). 15

16 Results of Inclusive Analysis New data contains 2.6 times more statistics than the previous data. New data previous data χ 2 /ndf=56.4/66 K.S test 58.8% Blind analysis: Cuts are pre-determined. Narrow strong structure is not seen in the signal region. The significance is ~ 2σ if we perform the same shape analysis as the previous analysis. Two data sets are normalized by the entry. In total, two data sets are consistent. Fluctuation? Human bias? Over/under-estimation? Exclusive analysis 16

17 Exclusive Analysis K - K + γ γ K - K + d n spectator p 0.3~0.8 GeV/c d p spectator n Λ(1520), φ,... Θ +, φ,...

18 Proton detection by using de/dx in Start Counter n K + K - or p K + K - Pid = (Measured energy loss in SC) (Expectation of KK) (Half of expectation of proton) K - Proton not tagged K + (Proton rejected) Proton tagged (ε ~60%) p KKn and a part of KKp KKp only Signal enhancement is seen in proton rejected events. should be associated with γn reaction. p/n ratio: 1.6 before proton rejection 0.6 after proton rejection 18

19 Two methods to reduce leaked proton BG 1. de/dx-based exclusive analysis Proton rejection efficiency becomes 60% 90% by selecting downstream of target p Efficiency K + K - leaked proton BG 2. MC-based exclusive analysis Proton contribution is estimated by fitting realistic MC distributions to proton-tagged spectra. The estimated leaked proton contributions are subtracted from full data sample (without z-vertex). M(pK - ) χ 2 /ndf = 34.4/37 φ and non-resonant KK Λ(1520) Λ(1405) Summed 19

20 M(nK - ) distribution ü The peak did not appear in M(nK - ) n and p(leaked) subtracted 20

21 M(nK + ) with two methods MC-based exclusive events de/dx-based exclusive events Counts/12.5 MeV M(nK + ) (GeV/c 2 )

22 M(nK + ) with two methods MC-based exclusive events de/dx-based exclusive events Subtract proton contribution. 22

23 M(nK + ) with two methods MC-based exclusive events de/dx-based exclusive events Overlay with normalization by entry 23

24 Large Start Counter to improve proton tag/ rejection efficiency. 24

Proton detection efficiency Counts 450 400 350 300 250 200 150 100 50 0 After φ exclusion 0.98 1 1.02 1.04 1.06 1.08 1.1 M(K + K - ) [GeV/c 2 ] proton detection efficiency 1 0.9 0.8 0.7 0.6 0.5 0.4 0.

25 Proton detection efficiency Counts After φ exclusion M(K + K - ) [GeV/c 2 ] proton detection efficiency : New setup ( ) : Old setup ( ) lower limit of vertex position [mm] We have just finished data taking with the new setup. Data with new setup! Data with old setup

Backward Compton Scattering 8 GeV electron LEPS2 Facility Recoil electron (Tagging) 10 times high intensity: Multi laser injection & Laser beam shaping

26 Backward Compton Scattering 8 GeV electron LEPS2 Facility Recoil electron (Tagging) 10 times high intensity: Multi laser injection & Laser beam shaping Laser LEP (GeV γ -ray) Best emittance photon beam does not spread Large 4π spectrometer based on BNL-E949 detector system. Better resolutions are expected. 26

27 Divergence of LEP beam LEPS2 LEPS BL31 <σ x >=14 µrad. BL33 <σ x >=58 µrad. e - à e - à Reaction region (30m) Tagging point Reaction region (7.8m) Tagging point Better divergence à Better tagging resolution Smaller beam size at long distance

28 γ Θ + Search at LEPS2 n γ u d d K u s u p d d K 0 Θ + u u d d s s d K 0 u u d p Θ + u u d d s d s π + K π No Fermi motion π correction. + No φ background. pk s invariant mass To measure angular dependence of production rate in large angle region, up to CLAS acceptance. (t- channel K- exchange is possible) K * missing mass A large acceptance and better resolution detector is necessary. 28

29 Two pole structure of Λ(1405) D. Jido, et al. NPA725(2003) V.K. Magas, E. Oset and A. Ramos, PRL 95 29

30 K*(890) Λ(1405) photoproduction with linearly polarized photon E γ K* K π K - p Λ(1405) Σ(1385) 30

31 K*(890) Λ(1405) photoproduction with linearly polarized photon E γ K* K π K- T.Hyodo et. al, PLB593 p Λ(1405) Σ(1385) 31

32 LEPS2 Detector 2.22 m B=1 T : Δp/p 1% for θ >7 γ counter RPC RMS=117 µm TOP TPC Prototype Residual RPC ToF time distribution γ 2.96 m TPC DC >3σ K/π GeV/c 2 32

33 Installation of the E949 magnet (2011.Nev-Dec) Transport each disk

34 Open the roof of LEPS2 building

35 Insert each disk using 360t crane

36 Installation was finished after painting

37 γ counters were installed. (2012.June) Installation of the E949 magnet (2011.Nev-Dec) Beam pipe (2012.May) 37 Exp. hall was constructed. (2010.Oct-2012Jan)

38 Comparison of LEPS and LEPS2 LEPS LEPS2 Beam Intensity (~2.4 GeV) 2~3x10 6 (2 lasers) <10 7 (4 high-power lasers) Beam Intensity (~2.9 GeV) 2~3x10 5 (2 lasers) <10 6 (4 high-power lasers) Polarization Linear/Circular Linear/Circular Detector Area 42m 2 x 3m(h) 198m 2 x 10m(h) Charged Particle Acceptance 0~30 degrees 7~120 degrees Momentum Resolution 0.5% (for 1-GeV kaon) 1~1.5% (for 1-GeV kaon) Photon Coverage none 30~110 degrees 38

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

40 BGOegg calibration (a) π 0 (σ=6.7 MeV/c 2 ) (b) 36 target 24 counts / 1 MeV η (σ=14.4 MeV/c 2 ) 2γ invariant mass (MeV/c 2 ) Obtained mass resolutions are consistent with MC simulation results. Timing resolution was measured to be 340 ps by checking π 0 2γ.

41 Experimental setup γ + 12 C -> η x 11 B + p Tagging counter BGOegg calorimeter Forward TOF Storage Ring e - γ LEPS2 building MeV target 12.5m Drift Chamber Tracking H.Nagahiro et al. PRC74(2006)

42 Experimental method γ + 12 C - > η x 11 B + p IdenLfy η produclon by η tag Search for a bound state 2 γ (39%) η 3π 0 - >6 γ (33%) 1m BGOegg calorimeter 3.2m 2m Forward TOF 12.5m from the target Vert : ±7 Hori: ±4 42

counts ΔE=28MeV bound NJL model calculation bound -100 0 100 E ex -E

43 Expected energy spectrum 2.4 GeV γ 0 η tag (6γ) No shift 150MeV shift counts ΔE=28MeV bound counts ΔE=28MeV bound NJL model calculation bound E ex -E 0 (MeV) H. Nagahiro E ex -E 0 (MeV) Secondary η multi π E ex -E 0 (MeV) Small background See signals in bound region 43

44 Summary n LEPS n Kaonic nuclei search, updates on Θ +. n LEPS2 n x10 luminosity. ~10Mcps. n Two different experimental setups. n Solenoid spectrometer n Θ +, Λ(1405) n BGO EGG + TOF n Backward meson production from proton and nuclei n BGO EGG experiment was started last year! 44

LEPS Physics HOTTA, Tomoaki (RCNP, Osaka University) on behalf of the LEPS&LEPS2 collaboration

LCS2014 International Workshop LEPS Physics HOTTA, Tomoaki (RCNP, Osaka University) on behalf of the LEPS&LEPS2 collaboration Outline Overview of the LEPS&LEPS2 beamlines Recent results from LEPS Search