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.