Search for + via K+p +X reaction with high-resolution spectrometer syste

m

Kyoto University

S. Dairaku

for E559 collaboration

E559 collaboration

Gifu U. T. Kameyama, K. Nakazawa, T. Watanabe

KEK S. Ishimoto, T. Nagae, H, Noumi, Y. Sato, S. Sawada, M. Sekimoto, S. Suzuki, H. Takahashi, T. Takahashi, N. Tanaka, A. Toyoda

Kyoto U. S. Dairaku, H. Funahashi, K. Imai*, K. Miwa, K. Shoji, M. Hayata,M. Miyabe, M. Niiyama, N. Saito, Y. Seki

Ohio U. K. Hicks, R. Zavislak

Osaka U. S. Ajimura

Osaka EC U. T. Fukuda

RCNP T. Nakano, M. Yosoi

RIKEN M. Naruki, K. Tanida

Tohoku U. S. Kinoshita, T. Koike, Y. Ma, Y. Miura, K. Shirotori, H. Tamura

U. Paris-Sud J. Arvieux

U. Tokyo H. Fujioka, T. Maruta, D. Nakajima, T. N. Takahashi

Purpose

Search for + Pentaquark ( E559 at KEK-PS K6) if + exists, < 1 MeV/c2 (M=1530 1540 MeV/c2)High Resolution spectrometer SKS & K6beamline

⇒resolution ： 2.4 MeV/c2 (FWHM)

High statisticsHadronic reaction K+p +X1.2 GeV/c K+ beam and liquid H2 target

Determination of decay angle distributionLarge solid angle Drift Chamber & Range Counter do

wnstream of targetSpin and Parity

K+ (1.2GeV/c)

SKS

K+

+

For π+veto

π+(0.5 0.6 GeV/c)

Solid angle0 60 deg

1.6 T

mass2(GeV/c2)2

+

Setup

Data set

RUN2 ( 2005/12/13 2005/12/28 )

H(K+,+) run @1.2GeV/c for + K+ yield : 2.79x109

Empty target run @1.2GeV/c for B.G.H(+,K+) run @1.1GeV/c for +

RUN1 ( 2005/5/24 2005/7/1 )

H(K+,+) run @1.2GeV/c for + K+ yield : 2.09x109

Empty target run @1.2GeV/c for B.G.H(+,K+) run @1.1GeV/c for +

Resolution for + and

1st run

2nd run

1st run is consistent with 2nd run

Missing mass value

Resolution K6 : p/p = 0.047% (FWHM)SKS : p/p = 0.43% (FWHM)

(simulation) for 2.4 MeV/c2 (FWHM)

M=1189.31 ± 0.03 MeV/c2

=2.03 ± 0.06 MeV/c2

M=1189.33±0.03 MeV/c2

=1.94±0.07 MeV/c2

Mass(GeV/c2)

Mass(GeV/c2)

(simulation) for + 1.98 MeV/c2 (FWHM)This is consistent with real data

Vertex distribution (before B.G. cut)

1st run 2nd run

(K+, +)

(+, +)

vertex z(mm) vertex z(mm)

(K+, +) reaction : large background from K+ decay

(K+, +)

(+, +)

Suppression of K+ decay events(SDC1 analysis cut)

K+

( to SKS )

K+p reaction event

K+

( to SKS )

K+ decay event

SKS

RCSDC1

TargetAerogel

Beam line chamber

K+

SDC2

π+

π+veto

vertex

SDC1 analysis cut

Even charged &Large scattered angle

98.0% of K+ decay events are suppressed (simulation)

70.1% of + production events remain(simulation --- assume isotropic angular distribution)

drift chamber

vertex distribution (after B.G. cut)

16900 event (-30<z<100) 11900 event (-40<z<85)

1st run 2nd run

vertex z(mm)vertex z(mm)

Missing Mass (pX)

1530MeV/c2

=50bisotropic distribution

Assumption

Expected peakunder assumption

Sum of 1st and 2nd runs

Preliminary

Missing Mass (pX)

Preliminary

170 ( 90% C.L. upper limit)

Upper limity)(efficienc

Ktgt NN

N

N Counts(90% C.L.)

Ntgt 5.04x1023

NK+ 4.88x109

Survival rate 0.858

Interaction factor 0.94

K6 efficiency 0.935(K6 tracking)

SKS efficiency 0.953(SdcOut)x0.875(SdcIn)

x0.93(SksTrack)=0.775

SDC1 analysis cut 0.701 ( assume angular distribution )

vertex cut 0.85

Trigger efficiency 0.95(LC)x0.99(TOF)

Acceptance 0.11sr(Laboratory frame)

0.0293(assume angular distribution)

Preliminary

90% C.L. upper limit

90% C.L. upper limit

Cross section of H(K+,π+) reaction

gK*N= ＋ gKNgK*N= － gKNgK*N= 0

W/O F.F. =1.2GeV

Y. Oh et al. Phys. Rev. D 69, 074016

=1MeV

√s=1.89GeV ( E559 exp. )

Cross section of H(K+,π+) reaction

W/O F.F. =1.2GeV

gK*N= ＋ gKNgK*N= － gKNgK*N= 0

Y. Oh et al. Phys. Rev. D 69, 074016

Preliminary

=1MeV

E559 exp. 90% C.L. upper limit

Summary

Search for + via H(K+, +) reaction at KEK-PS K6 beamline

K+ beam yield 4.88x109 reaction event 28800 (after SDC1 cut)

No significant peak (1520 － 1560 MeV/c2) cross section 7.0b, 1.9b/sr

90% C. L. upper limit(assume angular distribution)

much smaller than theoretical value under K* exchange (calculated by Y.Oh )

Preliminary

END

peak at SDC1 position

SDC1

SDC2

Decay

K+ beam

RC

Target

20cm

(K+, +)

(+, +)

SKS Gap

20cm

Vertex collect near SDC1

Background in H(K+,+)reaction

K+ decay event * SKS

K+ 1.000

K+ 0.151

K+ e+e 0.122

K+ 0.129K+p reaction event SKS

K+p K++ +K+n 0.008

K+p 　 +K+n

0.006

K+p K0++ +K0p 0.101

K+p K+p 　　 +K0p 0.046

K+p 　 +K0p 0.008

Angle cut study

SKS

TargetK+ π+

1

2K+

nSelection of 2

select kinematics?

No correlation between() and (K+, p)

Simulation

2 (degree)

1 (

degre

e)

SDC1 analysis

• If we assume that + decay is isotropic in center of mass frame, accepted ratio of each decay mode – K+n : 0.637– K0

Sp : 0.729– K0

Lp : 0.804

• Weighted mean with decay ratio ( 0.5:0.25:0.250.701 )→ 　 0.701

0

10

20

30

40

50

60

-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0

Q2=q2-w2

kaon 1.2GeV/cphoton 2.4GeVphoton 1.8GeVphoton 3.0GeVpion 1.9GeV/c

Q2 of reactions

Q2=q2-2 [GeV2]

Ang

le [

degr

ee]

LEPS

CLAS

E559(K+,)1.2GeV/c

E522(,K)1.9GeV/c