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Pentaquark search at SPring-8 LEPS
Norihito MuramatsuRCNP, Osaka University
For the LEPS Collaboration
DIS06 @Tsukuba, 22 Apr. 2006
~~~ Today’s menu ~~~- Overview of + status and standpoint of LEPS experiment- + search in d+(1520)- Future prospects at LEPS, new beamline and J-PARC
Overview of + status searched mass width statistical mode [MeV/c2] [MeV/c2] significanceLEPS(C) C K+K-X 154010 < 25 4.6DIANA K+Xe KS
0pX 15392 < 9 4.4 Belle ?CLAS(d) d K+K-p(n) 15425 < 21 5.2 CLAS(d)SAPHIR p K+K0(n) 15406 < 25 4.8 CLAS(p)ITEP A KS
0pX 15335 < 20 6.7CLAS(p) p +K-K+(n) 155510 < 26 7.8HERMES e+d KS
0pX 15283 139 ~5ZEUS e+p e’KS
0pX 15223 84 ~5COSY pp KS
0p+ 15305 < 18 4-6SVD(2004) pAKS
0pX 15264 < 24 5.6SVD(2005) pAKS
0pX 15234 < 14 8.0 independent sampleKEK E522 -pK-X 15313 < 10 ~2.5 P=1.92 GeV/c onlyNew 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.
LEPS LD2 runs• Still need to confirm + existence • Collected Data (LH2 and LD2 runs)
Dec.2000 – June 2001 LH2 50 mm ~5×1012 photons published data set [using 5 mm-thick plastic counter]
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
(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.
γ
p
n
+
K -
p
(1520)
LEPS Experiment
- 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
PWO measurement
tagged
TOF
Dipole Magnet 0.7 Tesla
Target
Start Counter DC2 DC3
DC1SVTX
AC(n=1.03)
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. ZegersDepartment of Physics, Pusan National University : J.K. Ahn, J.Y. Park School of Physics, Seoul National University : H.C. Bhang, K.H. TshooDepartment 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. MibeDepartment of Physics, Kyoto University : K. Imai, H. Fujimura, M. Miyabe, Y. Nakatsugawa, M. NiiyamaDepartment 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
The LEPS Collaboration
Event selections in K - p mode
MMp(γ,K - p) GeV/c2
π - mis-ID as K -
K + mass : 0.40 – 0.62 GeV/c2
M(K - p) GeV/c2
Λ(1520) : 1.50 – 1.54 GeV/c2
Events with Λ(1520) production were selected.E > 1.75 GeV was also applied.
Non-resonantKKp + p + …
γp→K - pKπ
Fluctuation or not?
⇒ Two complementary BG estimations (MC-based & real data-based)
⇒ smoothening missing mass spectrum by smearing E resolution
K - p missing mass in 1.50<M(pK - )<1.54 GeV/c2
MMd(γ,K - p) GeV/c2
Θ + signal ?~1.53 GeV/c2
preliminary
MMd(γ,K - p) GeV/c2
5 MeV bins
3 MeV bins
preliminary
? ?
? ?
MM(K - p) GeV/c2MM(K - p) GeV/c2C
ou
nts
/5 M
eV
Co
un
ts/5
MeV
preliminary preliminary
10-MeV E smearing to remove fluctuations
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.
side-band averaged spectrum
E-smeared spectrum[1.50<M(K-p)<1.54 GeV/c2] (1520) production
[side-band subtracted]
M(KK) GeV/c2M(pK - ) GeV/c2
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.
KKp
K*
p
(1520)
Fermi-corrected MMp(,p)
LH2 data LH2 data
MMd(,pK - ) in (1520) region
2 test at 1.4-1.7 GeV/c2
2 = 34.154 ndf = 30 prob. = 0.275
MMd(,pK - ) GeV/c2
Assuming dueteron mass
MMd(,pK - ) GeV/c2
+
1.6 GeV bump
mass ~1.53 GeV/c2
s/sqrt[s+b] ~ 4
Possibility of model variations
LH2 data (preliminary)1.50< M(pK - )<1.54 GeV/c2
LD2 data (preliminary)1.50< M(pK - )<1.54 GeV/c2
MMd(,pK - ) below/above (1520) region [LD2]
MMd(,pK - ) GeV/c2 MMd(,pK - ) GeV/c2
M(pK - )<1.50 GeV/c2 M(pK - )>1.54 GeV/c2
Preliminary Preliminary
Real data-based BG estimation
LD2 data
M(K - p) GeV/c2
*Non-resonant BGs + p + …
- 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.
MMd(γ,K - p) GeV/c2
correction for contribution
red : insideblue: outside
10-MeV E smeared
K* MCblack: Fermi offred : Fermi on
K - p missing mass spectrum
MMd(γ,K - p) GeV/c2
Co
un
ts/5
MeV
preliminary
* fitted in MM<1.52 GeV/c2
+
1.6 GeV bump
*
from sidebands
MMd(γ,K - p) GeV/c2
preliminary
Co
un
ts/5
MeV
K(1520) fit to all MMd(,pK - ) region - BG level : 6.5% more. -2/ndf=2.8
mass ~1.53 GeV/c2
s/sqrt[s+b] ~ 5Possibility to be affected by statistics in real data
(1520) mass gate dependence & photon energy dependence
MMd(γ,K - p) GeV/c2MMd(γ,K - p) GeV/c2
MMd(γ,K - p) GeV/c2MMd(γ,K - p) GeV/c2
10 MeV/c2 20 MeV/c2
(Standard)
50 MeV/c2 100 MeV/c2
MMd(,pK - ) GeV/c2
E< 2.1 GeV
E> 2.1 GeV
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.
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.
LRNB
distorted spherical wave front
8 GeV electron
100 eV photon
Pentaquark Search with E949 Detector(possible extension at J-PARC)
• 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)
TOFΔv/v=Δt/t, v=L/t, Δt=200 psec
⇒ L=4 m is equivalent to σ=8.4 MeVK/π separation : ~6 nsec
π +
π -
proton
K + beam 417 MeV/cσ=8.4 MeV
ΔP/P=1.3%
Important to confirm the existence and to extract width, (spin), …
K + n→+→KS0p→π + π - p
(26 mb for Γ=1 MeV) vs. CEX BG is forward peaked. (7 mb in PRD15 (1977) 1846)
Summary
• Confirmation of + by using LD2 data with K - p detection mode in 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.