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Pentaquark search at SPring-8 LEPS

DIS0 6 @Tsukuba, 22 Apr. 2006. Pentaquark search at SPring-8 LEPS. Norihito Muramatsu RCNP, Osaka University For the LEPS Collaboration. 　　　　　　　　 　～～～ Today’s menu ～～～ - Overview of  + status and standpoint of LEPS experiment -  + search in d +  (1520)

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Pentaquark search at SPring-8 LEPS

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  1. DIS06 @Tsukuba, 22 Apr. 2006 Pentaquark search at SPring-8 LEPS Norihito Muramatsu RCNP, Osaka University For the LEPS Collaboration 　　　　　　　　 　～～～ Today’s menu ～～～ - Overview of + status and standpoint of LEPS experiment - + search in d+(1520) - Future prospects at LEPS, new beamline and J-PARC

  2. Overview of + status searched mass width statistical mode [MeV/c2] [MeV/c2] significance LEPS(C) C  K+K-X 154010 < 25 4.6 DIANA K+Xe  KS0pX 15392 < 9 4.4 Belle ? CLAS(d) d  K+K-p(n) 15425 < 21 5.2 CLAS(d) SAPHIR p  K+K0(n) 15406 < 25 4.8 CLAS(p) ITEP A  KS0pX 15335 < 20 6.7 CLAS(p) p+K-K+(n) 155510 < 26 7.8 HERMES e+d  KS0pX 15283 139 ~5 ZEUS e+p  e’KS0pX 15223 84 ~5 COSY pp  KS0p+15305 < 18 4-6 SVD(2004) pAKS0pX 15264 < 24 5.6 SVD(2005) pAKS0pX 15234 < 14 8.0 independent sample KEK E522 -pK-X 15313 < 10 ~2.5 P=1.92 GeV/c only New results will appear from LEPS(d), DIANA, COSY, … Negative results in high energy experiments. (BES, BaBar, Belle, LEP, HERA-B, SPHINX, HyperCP, CDF, FOCUS, PHENIX) d+K-p<450 pb, but acceptance coverage is different from LEPS (forward region). ⇒ + is not killed.

  3. γ ＋ p K－ n (1520) p LEPS LD2 runs • Still need to confirm +existence • Collected Data (LH2 and LD2 runs) Dec.2000 – June 2001LH2 50 mm~5×1012 photons published data set [using 5 mm-thick plastic counter] May 2002 – Apr. 2003LH2 150 mm~1.4×1012 photons Oct. 2002 – June 2003LD2 150 mm~2×1012 photons #neutrons×#photons in K＋K－detection mode (n→＋K－K+nK－) = 5×short LH2 runs • K－p detection mode :γd→＋K－p ＋is identified by pK－ missing mass from deuteron. ⇒ No Fermi correction is needed.

  4. TOF SVTX DC1 AC(n=1.03) Target Dipole Magnet 0.7 Tesla DC2 DC3 Start Counter LEPS Experiment －8 GeV electrons in SPring-8 + 351nm Ar laser (3.5eV） ⇒ 1.5-2.4 GeV photons(Backward Compton Scattering) －Photon Flux ~106cps, Photon Energy Resolution ~10 MeV －Charged particle spectrometer with forward acceptance －PID from momentum and time-of-flight measurements PWO measurement  tagged

  5. The LEPS Collaboration Research Center for Nuclear Physics, Osaka University：T. Nakano, D.S. Ahn, M. Fujiwara, K. Horie, T. Hotta, Y. Kato, K. Kino, H. Kohri, N. Muramatsu, T. Sawada, T. Tsunemi, M. Uchida, M. Yosoi, R.G.T. Zegers Department of Physics, Pusan National University：J.K. Ahn, J.Y. Park School of Physics, Seoul National University：H.C. Bhang, K.H. Tshoo Department of Physics, Konan University：H. Akimune Japan Atomic Energy Research Institute / SPring-8：Y. Asano, A. Titov Institute of Physics, Academia Sinica：W.C. Chang, D.S. Oshuev, Japan Synchrotron Radiation Research Institute (JASRI) / SPring-8：H. Ejiri, S. Date', N. Kumagai, Y. Ohashi, H. Ohkuma, H. Toyokawa, T. Yorita Department of Physics and Astronomy, Ohio University：K. Hicks, T. Mibe Department of Physics, Kyoto University：K. Imai, H. Fujimura, M. Miyabe, Y. Nakatsugawa, M. Niiyama Department of Physics, Chiba University：H. Kawai, T. Ooba, Y. Shiino Wakayama Medical University：S. Makino Department of Physics and Astrophysics, Nagoya University：S. Fukui Department of Physics, Yamagata University：T. Iwata Department of Physics, Osaka University：S. Ajimura, M. Nomachi, A. Sakaguchi, S. Shimizu, Y. Sugaya Department of Physics and Engineering Physics, University of Saskatchewan：C. Rangacharyulu Department of Physics, Tohoku University：M. Sumihama Laboratory of Nuclear Science, Tohoku University：T. Ishikawa, H. Shimizu Department of Applied Physics, Miyazaki University：T. Matsuda, Y. Toi Institute for Protein Research, Osaka University：M. Yoshimura National Defense Academy in Japan：T. Matsumura

  6. Event selections in K－p mode K＋mass : 0.40 – 0.62 GeV/c2 Λ(1520) : 1.50 – 1.54 GeV/c2 Non-resonant KKp + p + … γp→K－pKπ π－mis-ID as K－ MMp(γ,K－p) GeV/c2 M(K－p) GeV/c2 Events with Λ(1520) production were selected. E > 1.75 GeV was also applied.

  7. K－p missing mass in 1.50<M(pK－)<1.54 GeV/c2 ? ? preliminary 5 MeV bins Θ＋signal？ ~1.53 GeV/c2 MMd(γ,K－p) GeV/c2 ? ? preliminary 3 MeV bins MMd(γ,K－p) GeV/c2 Fluctuation or not? ⇒ Two complementary BG estimations (MC-based & real data-based) ⇒ smoothening missing mass spectrum by smearing E resolution

  8. 10-MeV E smearing to remove fluctuations preliminary preliminary E-smeared spectrum [1.50<M(K-p)<1.54 GeV/c2] (1520) production [side-band subtracted] Counts/5 MeV Counts/5 MeV side-band averaged spectrum MM(K－p) GeV/c2 MM(K－p) GeV/c2 Any structure which is finer than detector resolution is due to fluctuations. ⇒ A magnitude which roughly equals to detector resolution was smeared with 100 times more statistics.

  9. MC-based BG estimation by using LH2 data Quasi-Free BG in LD2 data= K(1520) + p + Non-resonant KKp + … - BGs were simulated by including Fermi motion. (MC ~ 20 x real data) - Kinematics at CMS were adjusted to real LH2 data.  ‘Filters’ in ECMS, CMS(pK－), CMS(proton), PCMS(proton), PCMS(K－) - Non-resonant KKp ⇒ K+* ⇒ p were adjusted step by step. LH2 data LH2 data (1520)  K* Fermi-corrected MMp(,p) KKp p M(pK－) GeV/c2 M(KK) GeV/c2

  10. MMd(,pK－) in (1520) region + LH2 data (preliminary) 1.50< M(pK－)<1.54 GeV/c2 LD2 data (preliminary) 1.50< M(pK－)<1.54 GeV/c2 1.6 GeV bump MMd(,pK－) GeV/c2 MMd(,pK－) GeV/c2 Assuming dueteron mass mass ~1.53 GeV/c2 s/sqrt[s+b] ~ 4 Possibility of model variations 2 test at 1.4-1.7 GeV/c2 2 = 34.154 ndf = 30 prob. = 0.275

  11. MMd(,pK－) below/above (1520) region [LD2] M(pK－)<1.50 GeV/c2 M(pK－)>1.54 GeV/c2 Preliminary Preliminary MMd(,pK－) GeV/c2 MMd(,pK－) GeV/c2

  12. Real data-based BG estimation LD2 data red : inside blue: outside 10-MeV E smeared * Non-resonant BGs + p + … correction for f contribution M(K－p) GeV/c2 MMd(γ,K－p) GeV/c2 - Non-resonant BGs +  p : Deduced by 0.4 x sum of spectra in side bands - K(1520) : LH2 data after sideband subtraction Linearity was checked by comparing two independent sideband regions. K* MC black: Fermi off red : Fermi on

  13. K－p missing mass spectrum * fitted in MM<1.52 GeV/c2 + preliminary preliminary 1.6 GeV bump Counts/5 MeV Counts/5 MeV * from sidebands MMd(γ,K－p) GeV/c2 MMd(γ,K－p) GeV/c2 mass ~1.53 GeV/c2 s/sqrt[s+b] ~ 5 Possibility to be affected by statistics in real data K(1520) fit to all MMd(,pK－) region - BG level : 6.5% more. -c2/ndf=2.8

  14. (1520) mass gate dependence & photon energy dependence 10 MeV/c2 20 MeV/c2 (Standard) Eg> 2.1 GeV Eg < 2.1 GeV MMd(γ,K－p) GeV/c2 MMd(γ,K－p) GeV/c2 50 MeV/c2 100 MeV/c2 MMd(,pK－) GeV/c2 MMd(γ,K－p) GeV/c2 MMd(γ,K－p) GeV/c2

  15. Prospects at LEPS • Planning to take another data set with LD2 target and forward spectrometer this year. Photon beam intensity will be twice by injecting two lasers. • Time Projection Chamber is being prepared to increase acceptance coverage. CLAS region can be covered.

  16. New beamline at SPring-8 • Started to discussing about constructing new beamline at SPring-8. Upgrades of beam intensity (multi-laser injection, Long Range Non-diffractive Beam) and energy (deep-UV laser with =257 nm, x-ray injection) are planned. 4π detector with good resolutions are under considerations (BNL-E949 detector). • Better kinematical coverage and energy extension in + photoproduction are expected. 8 GeV electron 100 eV photon

  17. Pentaquark Search with E949 Detector(possible extension at J-PARC) K＋n→+→KS0p→π＋π－p • π＋π－detection at UTC M(π＋π－)=M(KS0) M(+)=M(K＋n)- [MM(K＋,π＋π－)-M(p)] Fermi-correction • π＋π－detection at UTC & proton detection at Sci. Tgt. M(π＋π－)=M(KS0) M(Θ＋)=M(KS0p) (26 mb for Γ=1 MeV) vs. CEX BG is forward peaked. (7 mb in PRD15 (1977) 1846) π＋ ΔP/P=1.3% K＋beam 417 MeV/c σ=8.4 MeV proton π－ TOF Δv/v=Δt/t, v=L/t, Δt=200 psec ⇒ L=4 m is equivalent to σ=8.4 MeV K/π separation : ~6 nsec Important to confirm the existence and to extract width, (spin), …

  18. Summary • Confirmation of + by using LD2 data with K－p detection modein MMd(,pK－) spectrum - Two methods in BG shape estimation (MC-based & sideband method) are complementary. - 1.53 GeV/c2 peak (4-5σ,preliminary) + 1.6 GeV/c2 bump associated with (1520) production - Signal-like behavior[M(pK－) gate & E dependence] • Differential cross section is being measured. Luminosity(LD2) ~0.6 pb-1. • Efforts for further confirmations are in progress. Better kinematical coverage and energy extension are expected in future.

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