液体重水素標的を用いた+バリオン光生成の研究 JPS meeting @Matsuyama, 29 Mar. 2006 液体重水素標的を用いた+バリオン光生成の研究 村松　憲仁 大阪大学　核物理研究センター For the LEPS Collaboration

阪大RCNP　村松憲仁，中野貴志，A，D.S.Ahn，郡英輝, 藤原守, 堀田智明， 堀江圭都, 與曽井優 甲南大　 秋宗秀俊 釜山大　 J.K.Ahn 東北大核理研　石川貴嗣, 清水肇 京大理　 今井憲一, 新山雅之, 藤村寿子, 宮部学 JASRI　 大橋裕二, 伊達伸, 依田哲彦 Academia Sinica　D.S.Oshuev, W.C.Chang 東大CNS　 木野幸一 阪大理 　阪口篤志, 菅谷頼仁 千葉大　 椎野祐樹 東北大理 住浜水季 NSCLMSU R.G.T.Zegers 宮崎大 戸井裕也, 松田達郎 Ohio Univ. K.Hicks, 三部勉 名古屋大 福井崇時 防衛大 松村徹 Univ. of Saskatchewan C.Rangacharyulu 他SPring-8/LEPS Collaboration

Contents Introduction (+ Status) d+(1520) - BG estimation - Signal-like behavior - Cross section measurement Summary & Prospects

Pentaquark Status @ EINN 2005 Group Signal Backgr. Significance publ. Comments ---------------------------------------------------------------------- SPring8 19 17 4.6s 3.2s SPring8 90 260 4.8s SAPHIR 55 56 4.8s 5.2s DIANA 29 44 4.4s 3.4s CLAS(d) 43 54 5.2s 4.4s CLAS(p) 41 35 7.8s 4.7s  18 9 6.7 3.5s HERMES 51 150 4.3-6.2 3.6s ZEUS 230 1080 4.6 6.4s COSY 57 95 4-6 4.7s SVD 41 87 5.6 3.6s SVD-2 370 2000 7.5s Improved analysis NA49 38 43 4.2 4.2s H1 50.6 51.7 5-6 5.0s SPring8 80 200 4.8s L*(K+n) STAR 2,250 150,000 3.5-5s Q++ candidate s/ b+s G11 CLAS-p G10 CLAS-d ? BELLE Q+ ? BABAR This slide summarizes the remaining evidence for any pentaquark. The new CLAS results eliminated two signals one on hydrogen and one on deuterium. The two non-Theta+ signals at H1 and NA49 are highly questionable and contradict later results from ZEUS and HERA-B with higher sensitivity. Finally, the very new CLAS data on deuterium, presented here for the first time, should be confronted with the LEPS deuterium results from SPring8 which have lower statistics. On the side favoring pentaquark signal is some positive news: The SVD-2 improved analysis gives many more events with high significance. SprinG8 claims a signal in L*(K+n) with 5s, and there is a signal of a doubly charged Q++ from STAR at RHIC. X5 HERA-B, CDF, COMPASS ZEUS, FOCUS, BABAR Q0c From Burkert @ EINN05

CLAS upper limits p+K0 <2 nb vs. SAPHIR 300 nb / 50 nb d+K-p <450 pb But acceptance coverage is very different from LEPS (forward region). ↓ + is not killed.

LEPS LD2 runs Collected Data (LH2 and LD2 runs) Dec.2000 – June 2001　LH2 50 mm　~5×1012 photons 　　　　　　　 published data May 2002 – Apr 2003　LH2 150 mm　~1.4×1012 photons　　 Oct. 2002 – June 2003　LD2 150 mm　~2×1012 photons #neutrons × #photons in K＋K－ detection mode 　　 LD2 runs = 5mm-thick STC in short LH2 runs × ~5 K－p detection mode w/o Fermi correction :γd→＋K－p

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

K－p detection mode ＋ is identified by pK－ missing mass from deuteron. ⇒ No Fermi correction is needed. Inclusive (n / p reaction + rescattering, or other mechanism) γ ＋ p K－ n (1520) p

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.

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 ? Important to understand BG shape reliably Quasi-Free BG = K(1520) + p + Non-resonant KKp + … MC-based & real data-based BG estimations Non-resonant KKp (1520)  Fermi-corrected MMp(,p) M(pK-) GeV/c2 [LH2] M(KK) GeV/c2 [LH2]  (1520) M(pK-) GeV/c2 [LD2] M(KK) GeV/c2 [LD2]

MC-based BG estimation by using LH2 data - 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. K* KKp p M(pK－) GeV/c2 M(KK) GeV/c2

2 test of MC to LH2 data in MMd(,pK－) distribution 1.50<M(pK－)<1.54 GeV/c2 (Signal region) (1+2+3) 1.400 – 1.700 GeV 2 = 34.154 ndf = 30 prob. = 0.275 (1) 1.400 – 1.500 GeV 2 = 15.253 ndf = 10 prob. = 0.123 (2) 1.500 – 1.600 GeV 2 = 5.895 ndf = 10 prob. = 0.824 (3) 1.600 – 1.700 GeV 2 = 13.006 ndf = 10 prob. = 0.223 (1) (2) (3) MMd(,pK－) GeV/c2

M(pK－) distribution in LD2 Fermi motion is turned on in MC. Preliminary Extra events, which are not seen in LH2 data 　　　　　　↓ Kinematical filters were made from LD2 data outside the signal region. KKp K* p M(pK－) GeV/c2

MMd(,pK－) in (1520) region [LD2 data] 1.50<M(pK－)<1.54 GeV/c2 + Preliminary Preliminary 1.6 GeV bump MMd(,pK－) GeV/c2 MMd(,pK－) GeV/c2 Conservative statistical significance ~ 4 Gaussian fit (temporary) ⇒ mass ~1.53 GeV/c2, width ~10 MeV

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

Real data-based BG estimation (Sideband subtraction method) LH2 * * Non-resonant BGs + p M(K－p) GeV/c2 M(K－p) GeV/c2 - Non-resonant BGs +  p : Deduced by 0.4 x [1.45<M(K－p)<1.50 or 1.54<M(K－p)<1.59 GeV/c2] - K(1520) : LH2 data after sideband subtraction Linearity was checked by comparing two independent sideband regions.

K－p missing mass spectrum K(1520) fit to all MMd(,pK－) region - BG level : 6.5% more. - c2/ndf=2.8 * 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

Comparisons of the two methods Two methods in BG estimation (Complementary) Sideband method Filtering method Any BG involved realistically Not affected by statistics Affected by LH2 statistics Possibility of Model variations * may be slightly under-estimated

MMd(pK－) in different M(pK-) gates around (1520) mass 10 MeV/c2 20 MeV/c2 (Standard) The peak structure looks associated with (1520) production. S/N ratio gets lower by widening M(pK-) gate, but the peak height looks constant. MMd(γ,K－p) GeV/c2 MMd(γ,K－p) GeV/c2 50 MeV/c2 100 MeV/c2 MMd(γ,K－p) GeV/c2 MMd(γ,K－p) GeV/c2

Photon energy dependence Eg > 2.1 GeV Eg < 2.1 GeV Counts/5 MeV MMd(,pK－) GeV/c2 + is seen in both lower and higher energy regions.

1.6 GeV bump & higher M(pK) tail in LD2 ECMS<2.18 ECMS<2.10 2.10<ECMS <2.18 MMd(,pK－) GeV/c2 M(pK－) GeV/c2 M(pK－) GeV/c2 2.18<ECMS <2.26 2.26<ECMS 2.18<ECMS MMd(,pK－) GeV/c2 M(pK－) GeV/c2 M(pK－) GeV/c2 1.6 GeV bump: n contribution? Hyperon-spectator nucleon interaction? pion association? Higher M(pK) tail : n contribution? Proton-neutron interaction?

Summary Confirmation of + by using LD2 data with K－p mode in MMd(,pK－) spectrum - Two methods in BG shape estimation (MC-based & sideband method) are complementary. - 1.53 GeV/c2 peak (~4σ,preliminary) + 1.6 GeV/c2 bump associated with (1520) production - Signal-like behavior [different M(pK－) gates, E dependence]

Prospects Differential cross section is being measured. Luminosity(LD2) ~0.6 pb-1. Planning to take another data sets with LD2 target and forward spectrometer this year. Tagger update is necessary. 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. Started to discussing about constructing new beamline at SPring-8. Upgrades of beam intensity and energy are expected. 4π detector with good resolutions are under considerations.