Recent results and future prospects of the Laser Electron Photon experiment at SPring-8

T. Hotta (RCNP Osaka University)

the LEPS collaboration

第六届中日核物理研讨会 , 上海 , 2006/05/18

• LEPS experiment • Search for the pentaquark• Upgrade of the LEPS facilty LEPS2

• SPring-8: world’s largest synchrotron radiation facility (8 GeV)• LEPS beamline: ~3 GeV polarized photon beam

produced by backward Compton scattering of Laser photon.

Laser Electron Photon beamline at SPring-8

1m

Magnetic spectrometer in the forward direction(, K, p, d)

Beam: GeV photonTarget: p, d, A

LEPS Experiment

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

Pentaquark

M1890-180*Y] MeV

D. Diakonov, V. Petrov, and M. Polyakov, Z. Phys. A 359 (1997) 305.

• Exotic: S=+1• Low mass: 1530 MeV• Narrow width: ~ 15 MeV• Jp=1/2+

The antiquark has a different flavor than the other 4 quarks.

γ + d (n ) 　 reactions

γ + p → p Ks0 　

γ + p → n K+ K- p+

K + (N) → p Ks0

lepton + D, A → p Ks0

p + A → pKs0 + X

p + p → pKs0 + +

Other + Upper Limits

BaBar

CLAS-d2

BELLE

ALEPH, ZSVD2

LEPS-d2LEPS-C CLAS-d1

DIANA

SAPHIR

SVD2

COSY-TOF

Hermes

JINR

CLAS-p

LEPS-d

BCZEUS

BES J,

CLAS g11

SPHINX HyperCP

HERA-B

FOCUS WA89CDF

: Positive result

: Negative result

　 2002 2003 　 2004 2005

• Both positive & negative results exist.• Confirmation of the existence is still most important.• Theoretical attempt to explain observation vs. non-observation. Hosaka: May 20, Session 15 in this symposium.

Time dependent experimental status of +

nKKnPhys.Rev.Lett. 91 (2003) 012002

hep-ex/0301020

+Low statistics: but

Tight cut: 85% of events are rejected by the exclusion cut.

Unknown background: BG shape is not well understood. Events from a LH2 target were used to estimate it. Possible kinematical reflections.

Correction: Fermi motion correction is necessary.

4.6S

B 3.2

S

S B

First evidence from LEPS

• Collected Data (LH2 and LD2 runs)

Dec.2000 – June 2001 　 LH2 50 mm 　 ~5×1012 photons

　　　　　 published data (target: 5mm plastic scint.)

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 ~ ×5 statistics

expected # of : 17 85

LEPS LD2 runs

MM (GeV) MM (GeV)

• A proton is a spectator (undetected).

• Fermi motion is corrected to get the missing mass spectra.

• Tight exclusion cut is essential.

• Background is estimated by mixed events.

preliminary

preliminary

(1520)

pK+K-p nK+K-n

Co

un

ts/1

2.5

MeV

Co

un

ts/1

2.5

MeV

Search for + in nK+K-n

• Θ ＋ is identified by K －p missing mass from deuteron. ⇒ No Fermi correction is needed.

• K- n and pn final state interactions are suppressed.• Isospin selection: some reaction mechanism may favor specific isospin state. • CLAS(d)@JLAB: <450 pb.

– acceptance coverage is different from LEPS (forward).

+ search in d (1520) KN reaction

γ

p

n

Θ ＋

K －

p

(1520)

detected

?

A possible reaction mechanism

• + can be produced by re-scattering of K+.• K momentum spectrum is soft for forward going (1520).

γ

p/n

n/p

(1520)

K+/K0

missing momentum

Formation momentum

LD2

Pmiss GeV/c

• Exchanged kaon can be on-shell. • KN formation cross section.

Background process

• Quasi-free (1520) production must be the major background.

• The effect can be estimated from the LH2 data. γ

p

n

(1520)

K+

n

The other background processes which do not have a strong pK- invariant mass dependence can be removed by sideband subtraction.

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

Sideband BG estimation

M(K － p) GeV/c2 MMd(γ,K － p) GeV/c2

correction for contribution

• 10-MeV E smearing has been applied to remove fine structure due to fluctuation.

• No visible signal.

• Validity of the sideband method with E smearing was checked by using two independent regions of the sideband.

Co

un

ts/5

MeVLD2

K － p missing mass spectrum

MMd(γ,K － p) GeV/c2

sideband

Quasi-free*

sum

Co

un

ts/5

MeV

C Excesses are seen at 1.53 GeV and at 1.6 GeV above the background level.

1.53-GeV peak:

pre

lim

inar

y

MMd(γ,K － p) GeV/c2

Co

un

ts/5

MeV

Normalization of * is obtained by fit in the region of MMd < 1.52 GeV.

(in the 5 bin = 25 MeV)

pre

lim

inar

y

No visible signal in sidebands.

+

5~BS

S

LD2

MM(K － p) GeV/c2MM(K － p) GeV/c2

Co

un

ts/5

MeV

Co

un

ts/5

MeV

pre

lim

inar

y

pre

lim

inar

y

Remove high frequency fluctuations by 10-MeV E smearing

All data & sideband BG data BG

Real peak or fluctuation? • Within existing data, robustness of the peak has been checked by E smearing (smoothing of the spectra).• Fine structure (< experimental resolution) must be statistical fluctuations.

•Normalization factor for LH2 data (green line) is 2.6. No large p/n asymmetry.

•Quasi-free process can be reproduced by free process. small effect from Fermi motion.

•Large cross-section compared with(1520).

•Missing Mass resolution is worse.

• No excess at 1.53 GeV nor at 1.6 GeV.

MMd(γ, － p) GeV/c2

Co

un

ts/5

MeV

preliminary

Search for d (1116) +

γ

pn

Θ ＋

－

p

(1116)

forward angle detection

Summary of search at LEPS

Confirmation of + by using LD2 data

• KK detection mode: – 1.53 GeV/c2 peak observed ~ expected # of events. – BG estimation is still underway.

• K-p detection mode in MMd(g,pK-) spectrum: – 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, & robustness of the peak under smearing.]

Prospects

Negative and positive results on • Negative results restrict the possibility of existence.

– New CLAS@JLAB data denied their evidence. But their kinematical condition is different from LEPS.

• There are still some positive evidences which cannot be excluded completely. – e.g. DIANA exp. (hep-ex/0603017)

• If exist, production mechanism should be also exotic.

Further measurements with wider kinematical coverage & high statistics are important.

• LEPS: Experiment w/ Large solid angle TPC will start soon.• LEPS2: New beamline is proposed.

Beamline map of Spring-8

BL31ID

Schematic view of the LEPS2 facilityBackward Compton Scattering

a) SPring-8 SR ring

b) Laser hutch

c) Experimental hutch

8 GeV electron

Recoil electron (Tagging)

Plan to move the BNL-E949 detector to Spring-8 (helped by RIKEN)

5 m

GeV -rayInsidebuilding Outside

building

30m long line

（ LEPS 7.8m)

4 detector （ Tohoku U. ）Large decay spectrometerForward spectrometerNew DAQ system

Laser or re-injected X-ray

High intensity ： Multi laser　　　　　　 LRNB Round beam　 ~10 7 photons/s （ LEPS ~10 6 ）High energy ： Re-injection of　　　　　　 X-ray from undulator　　　　　　　（ Tohoku U., JASRI ） E< 7.5GeV (LEPS < 3GeV)

modify ：JASRI Acc. group

Schedule

2006 2007 2008 2009

Decomposition of E949 detector (BNL)

Moving E949 det.

Construction of the decay spectrometer

Construction of the forward spectrometer

High speed DAQ system

Modify SR ring

Construction of the beamline

Building Exp hutch

Infrastructure

Radiation shield

Laser injection system

R&D of polarized HD target Experiment with HD target

X-ray re-injection system

4 photon detector

Submit LEPS2 proposal

Apply BL modification

Beam

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LEPS2 Collaboration

• Core institutes RCNP, Osaka U. LNS Tohoku U. JASRI (SPring-8) Accelerator group RIKEN Radiation Laboratory (new !)• Other LEPS members Kyoto U., Osaka U., Konan U., Chiba U., Yamagata U., Miyazaki U., Pusan U.(Korea), Seoul U.(Korea), Academia Sinica (Republic of China), Ohio U. (USA), Saskachewan U. (Canada) …etc.• New members National Defense Academy, … some members from the BNL-E949 experiment (domestic and foreign institutes (BNL, TRIUMF,…))

We are trying to expand the collaboration !!