Pion and kaon photoproduction at SPring-8/LEPS Sep / 12 / 2018 RCNP Osaka University / Nagoya University Hideki Kohri

Super Photon ring ‐ 8 GeV Electron storage ring 8 GeV electron beam Diameter ≈457 m RF 508 MHz 1‐bunch spread is 　　within σ＝12 psec． Beam Current = 100 mA 120 km distant from Osaka SPring-8 XFEL SACLA

SPring-8 beamline map LEPS2 LEPS beamlines

LEPS facility constructed in 2000 Collision 8 GeV electron Recoil electron SPring-8 SR ring Electron tagging Laser hutch Laser light Inverse Compton 　　　　　　g-ray 20m 10m Photon beam Energy Eg = 1.5-2.9 GeV Intensity ~106 g/s Polarization linearly and circularly polarized beams. P~90% at the maximum photon energy. Experiment hutch

LEPS detector (optimized to detect f decaying to K+K-) Aerogel Cerenkov (n=1.03) TOF wall Dipole Magnet (0.7 T) K+ Start counter Target LH2, LD2 K- g MWDC 3 MWDC 1 1m MWDC 2 Silicon Vertex Detector

Various meson and baryon photoproduction at SPring-8/LEPS K g + p → p+ + X n D0 + p → p + X g + p → f + p

We are analyzing the data taken for K We are analyzing the data taken for K*0S+ photoproduction in 2007 -> K+p- Eg=1.5-2.4 GeV -> Eg=1.5-3.0 GeV S.H. Hwang Ph.D. thesis Pusan National University (2012)

One of our physics objectives is to understand how hadrons are produced I want to obtain unified understanding of various qq productions. g p -> p+ n reaction dd production in the final state (2) g p -> K+L and K+S0 reactions ss production in the final state (3) g p -> p- D++ reaction uu production in the final state (4) g p -> p+ D0 reaction dd production in the final state

Another physics objective Missing resonance search Quark models predict more nucleon resonances than observed experimentally. Such missing nucleon resonances may be coupled to other channels than pN. Simon Capstick and W. Robers Phys. Rev. D 58 074011 (1998)

Reaction mechanisms of KY photoproduction s channel t channel u channel Strong when a meson is produced at forward angles. Very weak when a meson is produced at forward angles.

Measurements of photon-beam asymmetry We used linearly polarized photon beams. Photon-beam asymmetry (S) is sensitive to reaction mechanisms. S Positive p < r Natural parity exchange Positive K < K* Negative p > r Unnatural parity exchange Positive p < r g p -> p+ n reaction (2) g p -> K+L and K+S0 reaction (3) g p -> p- D++ reaction (4) g p -> p+ D0 reaction

H. Kohri, S.Y. Wang, S.H. Shiu, W.C. Chang, Y. Yanai et al. (1) Differential cross section and photon-beam asymmetry for the g p -> p+ n reaction at forward p+ angles at Eg=1.5-2.95 GeV H. Kohri, S.Y. Wang, S.H. Shiu, W.C. Chang, Y. Yanai et al. LEPS Collaboration Abstract Published in Phys. Rev. C 015205 (2018) on the 22nd of Jan.

Missing mass p(g, p+)X Neutron peaks are separately observed for 0.6 < cosq < 0.966. Positron mis-identification produces background between n and D0 for 0.966 < cosq < 1.

Differential cross sections for gp -> p+n Forward peaking cross sections are observed. t-channel reaction is found to be dominant.

Differential cross sections for gp -> p+n ds/dcosq decreases as Eg increases for 0.6 < cosq < 0.9. The energy dependence of Eg < 2.2 GeV is different for 0.9 < cosq < 1. This energy dependence might be due to N* or D*, as reported by the DESY group. Good agreement with CLAS(□) and DESY(▲) data. (2009) (1996, 1997)

Ratio (NV – NH) / (NV + NH) p+ prefers to scatter at fp angles perpendicular to the polarization plane. Photon-beam asymmetries for g p -> p+ n are found to be positive.

Photon-beam asymmetry S for gp -> p+n First photon-beam asymmetry data for Eg > 1.9 GeV. Positive asymmetries are basically explained by r-meson exchange in the t-channel. The asymmetries become larger as cosq increases. SLAC data (1979) Eg=3.4 GeV Eg=16 GeV PLB 400 (1997) 6

(2) Photoproduction of L and S0 hyperons off protons with linearly polarized photons at Eg=1.5-3.0 GeV S.H. Shiu, H. Kohri, W.C. Chang et al. LEPS Collaboration Abstract Published in Phys. Rev. C 97 015208 (2018) on the 31st of Jan.

Missing mass p(g, K+)X 2007 data Eg=1.5-3.0 GeV

Difficulty in particle identification for high momentum K+

Background p+D0(1232) produces a peak at around 1 Background p+D0(1232) produces a peak at around 1.15 GeV if kaon mass is used in missing mass calculation g + p → p+ + X n D0 Missing mass (GeV) calculated by pion mass

Differential cross sections for gp -> K+L and K+S0 First cross section data for LEPS at 2.4 < Eg < 3 GeV. K+L cross sections are larger than K+S0 cross sections. No evident structure due to N* or D*.

Ratio (nNV – NH) / (nNV + NH) K+ prefers to scatter at fK angles perpendicular to the polarization plane. Photon-beam asymmetries are found to be positive for both the reactions, suggesting dominance of K*-exchange.

Photon-beam asymmetry for K+L and K+S0 First photon-beam asymmetries data for Eg > 2.4 GeV. The asymmetries increase gradually as Eg increases for both the reactions. K*-exchange contribution becomes larger. SLAC data (1979)

(3) Differential cross section and photon-beam asymmetry for the g p -> p- D++(1232) reaction at forward p- angles for Eg=1.5-2.95 GeV H. Kohri, S.H. Shiu, W.C. Chang, Y. Yanai, et al. LEPS Collaboration Abstract Published in Phys. Rev. Lett. 120 202004 (2018) on the 18th of May.

Missing mass p(g, p-)X All BG D 2p/r D All BG 2p/r 3p 3p

Differential cross sections for gp -> p-D++ First high-statistics cross section data. ds/dcosq decreases as Eg increases. Strong forward peaking (p-exchange). Theoretical calculations by S.i. Nam well reproduce the data by optimizing the cutoff mass parameter from 450 to 500 MeV. The energy dependence of Eg < 1.8 GeV cannot be reproduced for cosq > 0.9. N* or D* ?

Comparison of ds/dcosq between p-D++(●) and p+n(■) Strong forward peaking cross sections suggest t-channel reaction is dominant.

SAPHIR total cross sections Tail of s-channel resonances seems to continue up to ~Eg=2 GeV s(mb) C. Wu et al. Eur. Phys. J. A 23 (2005) 317 Eg (GeV)

Ratio (NV – NH ) / (NV + NH ) p- prefers to scatter at fp angles parallel to the polarization plane. Asymmetries are found to be negative in most of LEPS kinematical regions.

Photon-beam asymmetry for gp -> p-D++ First asymmetry data for 1.5 < Eg < 2.8 GeV. Asymmetries are found to be negative for most of LEPS kinematical regions, suggesting p-exchange dominance. Theoretical calculations by S.i. Nam well reproduce negative asymmetries for cosq > 0.933. The calculations cannot reproduce the data for cosq < 0.9. Additional unnatural parity exchange is needed.

Why only p-D++ reaction favors light meson exchange ? S 　Negative 　 Positive (1) g p -> p+ n p(140 MeV) or r(770 MeV) dd production spin 0 spin 1 (2) g p -> K+ L K(490 MeV) or K*(890 MeV) ss production spin 0 spin 1 (3) g p -> p- D++ p(140 MeV) or r(770 MeV) spin 0 spin 1 uu production Other pseudoscalar meson photoproduction such as p+D0、p0p、hp has positive S. Heavy meson exchange is dominant.

Yukawa theory Uncertainty principle DE Dt ~ ℏ Strong interaction between nucleons is mediated by mesons. Uncertainty principle 　DE Dt ~ ℏ　 Energy conservation violates in a short time. A partile flying 1 fm with c has a mass, M ～ ℏc / (c Dt) = ~200 MeV fm / 1 fm. Meson Proton Neutron Meson Light p meson can reach long distance. Interactions with heavy r, K* mesons are limited at short distances. Proton Neutron

My personal interpretation for these results g p+ r-meson exchange We detected mesons at forward angles. Small momentum transfer suggests reactions occur near the surface of the proton. (1) p+n reaction exchanges u quark with d. (2) K+L reaction exchanges u quark with s. (3) p-D++ reaction exchanges d quark with u. meson exchange is long ranged. d quark may live in the central region of the proton ? (1) (2) (3) n p g K+ K*-meson exchange p L g p- p-meson exchange D++ p

d-quark staying in the central region of the proton Proton in diquark model　　　 Proton in pion cloud model p+ n u and d quarks are coupled to spin=0. Good diquark.

Summary We took high momentum charged pion data for the first time in 2007. It enables us to study uu, dd, and ss productions and we want to obtain unified understanding of these qq productions. g p -> p+ n reaction data Published in Phys. Rev. C on Jan/22/2018 (2) g p -> K+L and K+S0 reaction data Published in Phys. Rev. C on Jan/31/2018 (3) g p -> p- D++ reaction data Published in Phys. Rev. Lett. on May/18/2018 (4) g p -> p+ D0 reaction data. Physics paper is prepared. dd production ss production uu production dd production

Missing mass p(g, p )X Missing mass spectrum is fitted with relativistic Breit-Wigner shape for D, 2p / r, 3p, and e- or e+ curves. p(g, p-)X p(g, p+)X 0.7<cosqp<1 0.7<cosqp<1 Eg=1.5-3.0 GeV Eg=1.5-3.0 GeV

D++ D0 g p- p+ g p p uu and dd productions uu production is precisely compared with dd production by the γp→ π- Δ++ and π+Δ0 reactions D++ Simultaneous measurements g p p- Same proton target Same acceptance p p+ g D0 I expect this comparison would give important information to understand how hadrons are produced.

Ratio s(p+D0)/s(p-D++) (dd production / uu production ) Preliminary dd production is enhanced or uu production is suppressed. 1/3 is expected from isospin=1 exchange in the t-channel

d / u > 1 suggested by Drell-Yan experiments Proton charge distribution Drell-Yan experiment PRD 64 (2001) 052002 Bare proton d / u Pion cloud (ud) Pion cloud model p+ (ud) may enhance p+D0 prodution(dd production) -> Larger s(p+D0)/s(p-D++) (dd / uu )

Semi-Inclusive Deep Inelastic Scattering Hadrons with high momenta are considered to be produced from a quark or an anti-quark in the target nucleon. ud

Experiment using polarized HD target and polarized g beam provide rich physics observables Dilution refrigerator produced by Leiden cryogenics Target cell

Summary We took high momentum charged pion data for the first time in 2007. It enables us to study uu, dd, and ss productions and we want to obtain unified understanding of these qq productions. g p -> p+ n reaction data Published in Phys. Rev. C on Jan/22/2018 (2) g p -> K+L and K+S0 reaction data Published in Phys. Rev. C on Jan/31/2018 (3) g p -> p- D++ reaction data Published in Phys. Rev. Lett. on May/18/2018 (4) g p -> p+ D0 reaction data. Physics paper is prepared. dd production ss production uu production dd production

s2 scaling g p -> p+ n CLAS data g p -> p+ n In the simplest Regge picture involving the exchange of a single trajectory, the cross sections can be written as, a(t), C(t) are functions of t only. s0 = 1 GeV2.

Effective a(t) p- p -> p0 n Successful example r5(2350) a(t) values are obtained for each t by fitting to ds/dt with . a(t) values do not change largely. s dependence for LEPS data is close to that for SLAC data. a(t) for small | t | favors the single p-trajectory. t-channel is dominant Successful example p- p -> p0 n pLab = 3.7, 5.9, 13.3 GeV/c r5(2350) r-trajectory r3(1690) r(770)

Photon-beam asymmetry S for gp -> p+n The asymmetries become larger as | t | approaches 0. The r-meson exchange contribution is inferred to be small at small | t |. The p-meson exchange cannot explain positive asymmetries. Large asymmetries at small | t | could be due to p-exchange interference with the s-channel as shown by Nucl. Phys. A 627, 645 (1997) M. Guidal, J.-M. Laget, M. Vanderhaeghen.