22 September 2005 Haw05 1 (1405) photoproduction at SPring-8/LEPS H. Fujimura, Kyoto University...

22 September 2005 Haw05 1

(1405) photoproduction at SPring-8/LEPS

H. Fujimura, Kyoto University

Kyoto University, JapanK. Imai, M. Niiyama

Research Center for Nuclear Physics, Osaka University, JapanT. Nakano

for the LEPS collabration

Collaborators1. Physics Motivation2. Mechanical Design of TPC3. Experiment Setup at SPring-8/LEPS4. Current status of Analysis5. Summary and Prospects 　

Contents


Physics Motivation structure of Λ*(1405) JP =1/2-

• Chiral perturbation theory describe (1405) as a meson-bariyon resonance and predict its lineshape to be different in different decay channel , +.

→ J.K.Ahn et al

They predict the modification of invariant mass distribution of (1405) in nuclear matter.

E. Oset et al., Nucl. Lett. B455 55(1999)

Lutz…,

3-quark state or KN bound state ?

Large mass difference between (1520) JP=3/2- and (1405) JP =1/2- cannot be explained by quark model.

KN threshold

3/2-

1/2-

)

)30 MeV


Physics Motivation Experimental Data• Thomas et al. Nucl. Phys. B56 15 (1973)

　　　 470 events

• Hemingway et al. Nucl. Phys. B253 742 (1985)

　• J.K.Ahn et al. Nucl. Phys. A721 　 (2003) 　　　　　　　

It is necessary to detect to identify (1405)

develop Time Projection Chamber(TPC) as 4 detector to detect decay topology

pK

KKn

KKp

NKKKp

)1385(

)1385(

)1405(00

00 )1405( KKp

)()1405()1660(pK

KKp )1405(

Σ+π- 766 eventsΣ-π+ 1106 events


880mm

585 mm

Up stream

Solenoid Magnet

Down stream view

600mm

TPC is designed to be installed in Solenoid Magnet.

Hexagonal cylinder 880mm in length 585 mm in diameter

Design of TPC

E // B

700mm

Target holder

High voltage plane

Wire & padplane

Drift field cage

Beam

Active volume (cylindrical shape) 700 mm in length 400 mm in diameter

Drift time → z position

To detect trajectory as close as a few cm from target, target holder is mounted in TPC.


Design of TPC Pad Plane

Signals from TPC are read out through cathode pads and anode wires.

The position resolution (required value)Drift direction : 550 m (700 m)

Pad plane : 340 m (350m)

Invariant mass of (1405) → 1% accuracy

# of Cathode pads : 1055 # of Anode wires : 95

Beam

E // B

400mm

Large pads 8mm x 13mmSmall pads 4mm x 8mm

3-dimentional position information pad-plane → x-y position drift time → z positiondE/dX, momentum → PID


Experimental setup at SPring-8/LEPS

E // B


Solenoid Magnet

DipoleMagnet TPC

BufferCollimator 24Φ

Collimator 2 １ Φ

BeamBeam

TPC


Beam Time

CH2 113Mtrig : 110k K+ in spectrometer

500 (1405) in K+-TPC+)

600 (1405) in K+spec+-)

C 60 Mtrig : 60k K+ in spectrometer

Cu 41 Mtrig : 12k K+ in spectrometer

Jan – Mar Commissioning runApr – Jul Physics runSep – Dec Physics run

2004

How to Identify (1405) events

Missing Mass of p ( , K+ + -)

Spectrometer TPC

nK

K

Kp )1405( Missing mass of p ( , K+ + -) → n Missing mass of p ( , K+ ) → ±

Select decay mode ( ) by the kinematical fit.

)1405(

In this talk, missing mass spectrum of p(, K+)X is shown by selecting + - in TPC to extract (1405) events.


Proton

++

dE

/dx

(arb

itra

ry u

nit)

Momentum×charge (GeV/c)

PID by TPC

p

K+

K-

+-

Mass x Charge (GeV/c2)

Particle Identification

PID by Spectrometer

TOF, Momentum → Mass


Missing mass of p ( , K+) X

CH2

C(1116)(1193) (1520)

(1405)/(1385)

CH2 -　C

p (, K+) X (GeV/c2)

K+ were detected by Spectrometer PDG:1.115683 1.1155±0.0005 GeV0 PDG:1.1926421.1894±0.0005 GeV

(1502 PDG:1.5195 1.5192±0.006 GeV

E and Momentum calibration of LEPS Spectrometer system have been done.


(1385) events

0

0)1116(

)1385(

pK

K

Kp

Spectrometer TPC

Invariant mass of (p, -) (GeV/c2)

Select (1116) by TPC

CH2

C

p (, K+) X (GeV/c2)


CH2

C

CH2 -　C

neutron

Missing mass p ( , K+ + -) (GeV/c2)

Event Selection by TPCMissing mass of p ( , K+ + -)

Missing Mass

p ( , K+ + -)

Spectrometer TPC

nK

K

Kp )1405(

Selection - Spectrometer

1 track, K+

2 prob 0.02≧ - TPC 2 tracks, + -

scattering angle of + - > 40°

Momentum calibration of TPC is underway


CH2

C

p (, K+) X (GeV/c2)

Missing mass of p (, K+) Xselected by + - in TPC

CH2 -　C

(1520)

Next step: select decay mode 　　　 by identifying in p (, K+ )X.


Summary and Prospects• (1405) is an unique object to study the dynamics of QCD. Some theoretical

models describing (1405) as meson-baryon molecular state あ and predict the different lineshape in different decay channel and the modification of lineshape of (1405) in nuclear matter.

• We have performed hyperon photoproduction experiment at SPring-8/LEPS. The CH2, C, and Cu targets were used. The energy range of the backward compton scattering photon was 1.5 – 2.4 GeV.

• To identify the (1405) from (1385), we have constructed a TPC as a 4 detector to measure decay topology.

• The physics run has been done in the year 2004. We identified 100K of K+

production events measured by forward spectrometer from CH2 target. Among K+ events tagged by spectrometer, 600 events of (1405) are expected.

• LEPS forward spectrometer system was used to detect forward going particles. E and momentum calibration of LEPS spectrometer system was finished.

• Momentum calibration of TPC is underway. We will extract (1405) lineshape from different decay mode by identifying in p (, K+ )X.

• The modification of invariant mass shape of (1405) in the nuclear matter will be studied.

22 September 2005 Haw05 1 (1405) photoproduction at SPring-8/LEPS H. Fujimura, Kyoto University...

Documents

Transcript of 22 September 2005 Haw05 1 (1405) photoproduction at SPring-8/LEPS H. Fujimura, Kyoto University...