Recent results and future prospects of LEPS and LEPS2 M. Miyabe ELPH, Tohoku University ELPH workshop C013 "Meson Production and Meson-Baryon Interaction"

Contents SPring-8/LEPS – Overview – Recent results – Future prospects LEPS2 – Overview – BGOegg experiment – Futre plan Summary

SPring-8 ELPH, Tohoku Univ SPring-8

SPring-8/LEPS, LEPS2 LEPS LEPS2

LEPS

SPring-8 LEPS LEPS backward compton scattering photon Eγ~2.4GeV, Eγ~2.9GeV Tagged photon Polarization ~95% > 1 Mcps LEPS forward spectrometers

Recent results from LEPS Search for K − pp bound state via γd→K + π − X reaction at E γ =1.5−2.4 GeV – Phys.Lett. B728 (2014) Backward-angle photo-production of ω and η′ mesons from protons in the photon energy range from 1.5 to 3.0 GeV – Prog. Theor. Exp. Phys. (2015) 013D01  photo-production  + search

KNN search K-N interaction is strongly attractive (I=0). weakly attractive (I=1). – KNN bound state (K - pp, K - pn, K - nn) KNN exist or not? – B.E. = MeV ? – Γ=60 – 110 MeV ? – Experimental result B.E. =115 MeV, Γ = 67MeV – (FINUDA) B.E. =103 MeV, Γ = 118MeV – ( DISTO )

Search for K − pp bound state (A.O. Tokiyasu, HYP2015.3a-4, 7.Sep.2015)

Search for K − pn bound state - large background from QF process in the inclusive measurement. - Identification of Final state is indispensable (KNN -> Y N)

Search for K − pn bound state No shift was observed in

Σπ invariant mass spectrum Under analysis – A.O. Tokiyasu, HYP2015.3a-4 No shift was observed.

Backward-angle photo-production of ω and η′ mesons E  1.5~3.0 GeV Large acceptance detector (TPC) around the LH2 target

Time projection chamber(TPC) hexagonal cylinder shape Length - 760mm Radius – 280mm Argon-methane – (90 % : 10 % )

Backward-angle photo-production of ω and η′ mesons  Differential cross section G(2190) resonance?  ’ differential cross section Bump structure ~ 2.35GeV

 photo-production Interference between and (1520) near Threshold  photo-production (  +p ->  p -> K + K - p)  (1520) photo-production (  +p -> K + X) T.Mibe et al, Phys.Rev.Lett (2005) H. Kohri et al, Phys.Rev.Lett 104, (2010)

Interference between M  and M  (1520) Relative phase measurement between  and  (1520) amplitudes in terms of energy in the interference region. maximum constructive maximum destructive

Fit with MC Templates for  p → K - K + (p)

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

Interference between M  and M  (1520) a strong constructive interference when the K+K- pairs are observed at forward angles, while destructive interferences when proton emits at forward angles. The  (1520) interference cannot account for 2.0GeV bump structure in forward differential cross sections for photo- production. constructive destructive S. Y. Ryu, PhD thesis, (2015)

 + search Θ+ : exotic 5-quark (uudds) low mass – 1540 MeV (sum of quark mass ~1900 MeV) narrow width – Γ < 11 MeV experimental search – First discovery from LEPS in 2003 – negative result from CLAS

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.

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

LEPS 2006/2007 γ + d -> K- K+ X – positive, proton rejection

J-PARC E19 π- + p -> K- + X – negative, upper limit of Γ

CLAS, DIANA γ + p -> K s 0 + K L 0 + p K + + n -> K s 0 + p (M=1538 MeV, Γ=0.34MeV)

Recent search result The situation is still controversial. Positive or negative? Observation of J=ψp Resonances at LHCb Check the consistency between LEPS and CLAS – high statistics – angle dependence of cross section at LEPS2

Future plan  photo-production at E  < 3GeV Polarized HD target experiment

 + search status MM D (K + ) [GeV/c 2 ]MM p (K + ) [GeV/c 2 ] Calibration quality is almost same as old data set.

Polarized HD target system Double polarized experiment –  beam and target proton polarized –  photo-production –  p → KΛ and Σ reaction final stage of construction

Physics at Polarized HD target A.I. Titov, PhysRevC  photo-production

Polarized HD target  p → KΛ and Σ reaction Polarized target and large acceptance spectrometer are needed for complete measurements for advanced N* studies. – Future LEPS2 experiment

Construction status

LEPS2

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

LEPS2 LEPS2 building

LEPS2 experimental building E949 solenoid BGOegg Dec. 2012

Recent status of LEPS2/BGOegg Obtained number of  event 2014A – C: 1.31x10 12, CH 2 : 1.58x B – Liquid H2 Horz: 2.24x10 12, CH 2 : 2.01x A – C: 9.77x10 12

 ’(958) and U A (1) anomaly The experimental mass of  ’ is more than 2 times larger expected value. – U A (1) anomaly effect. Origin of large  ’ mass – Chiral symmetry breaking – U A (1) anomaly Daisuke Jido, Hideko Nagahiro, and Satoru Hirenzaki, Phys. Rev. C 85 (2012) (R). No experimental information for U A (1) anomaly effect

Mass reduction of  ’(958) KMT interaction ： U A (1) anomaly Prediction from NJL model g D =constg D = 0 g D ~ exp[-(  /  0 ) 2 ] H. Nagahiro, M Takizawa, S. Hirenzaki Phys. Rev. C 74, (2006)

Mass modification 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)

 ’-mesic nuclei Strong attractive force and small absorption – Attractive force U A (1) anomaly effect – Absorption ReW 0 ～ MeV （ CB-ELSA ） M. Nanova et al., PLB 710, 600 (2012) Experimental results – Re a  ’N <0.8fm Phys. Lett. B474(2000)p416 – |a  ’N | <0.1fm Phys. Lett. B482(2000)p356 Optical potential with Chiral unitary model – ReV >> ImV (possible) → more detailed experiment! Search the  ’ mesic nuclei using nuclear target. Transparency ratio

Lower Recoil momentum of  ’ than hadron beam Experimental parameters – E  1.6~2.9 GeV – Target C – Forward proton detection C( , p )X missing mass 2011  ’ mesic nuclei in ( ,p) reaction

LEPS2 laser system simultaneous 4-laser injection Increase the laser power – 8 W -> 16 W or 24W Smaller beam size – Lower e - divergence =58  m -> 14  m Multi laser injection system

First beam observation at LEPS2 beam profile is well collimated consistent with the expectation Energy spectrum with large BGO crystal (  8 cm x L 30cm ) Deep UV laser 355nm laser Photon beam intensity ~ 7 MHz (for 0<E  <2.4 3-(355nm) laser

 ’ mesic nuclei search in LEPS2/BGOegg Missing mass spectrum of proton – High resolution Time of flight counter (RPC) tag from η’N->ηN conversion event – High resolution  counter BGOegg BG reduction and event selection – Charge identification detector – Caharged particle tracker chambers CDC, DC LEPS2 experiment hatch DC BGOEGG + Charge ID + CDC E949 Solenoid RPC ~18m ~12m 

BGOegg Egg like shape Total volume 264L Total weight 1.9t (crystal only) Two type photomultipliers – H11334 (metal package type) – H6524 (head on type) Very few dead-region – Without housing material – Only with 3M-Vikuity ESR film reflector. 0/0/  

BGOegg performance  invariant mass with BGOegg 00  ’’  ’’ Very high invariant mass resolution after calibration

Resistive Plate Chamber (RPC) Focus on mesic nuclei search – 12 MeV forward proton momentum resolution -> upto 80 psec time resolution at 12.5 m flight length 3m 2m 32 modules in wall

Resistive Plate Chamber (RPC) 200~300 μm High voltage Resistive plate （ glass ） Readout strip spacer Glass resistive plate with SF 6 gas Narrow gap →good time resolution Multilayer →high efficiency, resolution

RPC performance

 ’ related Baryon resonance

LEPS2 solenoid spectrometer experiment

Physics motivations Θ+ study Λ(1405) with K* photo-production Missing resonance search Modification of mesons in nucleus K-NN interaction

Status Time Projection Chamber (TPC) – Shipping until the end of this year – Front end electronics R&D Drift Chamber (DC) – 3 / 4 are completed Resistive Plate Chamber (RPC) – Test the new FEE in this year Inner start counters (SC) – Test experiment in ELPH Barrel Gamma – Ready, tested by Cosmic lay.

TPC

Summary LEPS – Recent results Search for K − pp bound state via γd→K + π − X reaction Backward-angle photoproduction of ω and η′ mesons  photo-production  + search – Future  photo-production upto 2.9GeV Polarized HD target experiment LEPS2/BGOegg – Physcis run started from 2014A. –  ’ mesic nuclei search with Carbon target in 2015A – Future More statistic at LH2 target, deuteron target LEPS2/Solenoid – Under construction – Many component will ready in this year. – Comissioning ~2017?