Measurement of proton induced pion pair production in nuclei

1
Measurement of proton induced pion pair
production in nuclei
Tetsuro Itabashi (Osaka University)
2
Collaboration

• T. Itabashi, S. Ajimura, T. Hayakawa, T.
  Kishimoto,
• K. Matsuoka, S. Minami, A. Sakaguchi, Y. Shimizu,
  
• K. Sugita and K. Terai
• Osaka University
• T. Ogaito and K. Tamura
• Fukui Medical University
• H. Noumi and M. Sekimoto
• KEK
• T. Fukuda, W. Imoto and P.K. Saha
• Osaka Electro-communication University

3
Introduction

• QCD and spontaneous breaking of Chiral Symmetry
• quarks qluons ? hadrons at low energy
• Quark and anti-quark pair condensation
• ltqqgt0 ? ltqqgt?0
• hadrons have effective mass
• M?fp, fp2mp2mltqqgt
• Generate pion as Nambu-Goldstone boson
• Light pion mass

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Introduction

• How to confirm it experimentally
• Phase transition at high energy ltqqgt?0
• New phase of matter QGP
• Heavy ion collider RHIC, LHC
• Partial restoration in nuclear medium
• Meson mass shift in nuclear medium
• ?/?/f (KEK E325)
• s (CHAOS,TAPS)

quark condensate
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• smeson ( f0(600) or s I,Jp0,0 )
• Chiral partner of pion
• Change of spectral function at finite nuclear
  density
• Enhancement at just above 2mp threshold region
• Mpp distribution

F1-C?/?0
?(GeV)
T. Hatsuda, T. Kunihiro, H. Shimizu, PRL 82.
2840. (1999)
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• CHAOS
• pA?pp-A reaction
• heavier nuclear target, remarkable enhancement
  only in sigma channel
• Crystal ball
• p-A ? p0p0X
• No sharp peak

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• TAPS
• ?A?p0p0A reaction
• RPb/C has mass shift to lower
• Invariant mass region

Elementary process seems to be simple
Still not conclusive ? new type of experiments
are desirable
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Our Experiment

• pA?p p- X reaction
• Ring Cyclotron of RCNP _at_ Osaka university.
• Tp420MeV
• Proton beam
• Elementary process may be simple
• Subthreshold beam energy
• Tthre(pN) 600MeV for elementary process
• influence from secondary process is small
• Mass number dependence of Mpp-

CERSIUS PRL 88 (2002) 192301
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Subthreshold 2p production

• with beam energy Tp416MeV
• invariant mass region 2mp to 350 MeV/c2
• Enough to see around threshold region (
  observed in Mpp- lt300MeV/c2 )
• cross section 1nb/nucleon
• simple calculation using
• elementary pp?pp-pp cross section data
• Fermi motion distribution of nuclei
• nucleon binding in nuclei

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Experimental set up
solenoidal magnet (3kG) opening angle ?
15º-105º f 2p Cylindrical Drift Chamber (CDC)
? Momentum Inner Hodoscopes Outer
Hodoscopes ? Trigger,TOF acceptance for 2p
event 0.6
side view
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photo
You can see solenoidal magnet and CDC
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Trigger system

• spp is very small compared to proton scattering
• efficient trigger system is needed
• proton scattering s a few 10mb
• pn?ppp- s 50µb
• pN?pNpp- s 1nb
• negative charge trigger is quite useful for rare
  pp-

10 -3
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p- trigger --Design
?3
Tilted counters with magnetic field distinguish
charge by of hit negative particle ? 3
hits positive particle ? 2 hits Requiring 3
adjacent hits ? p- trigger
?2
front view
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photo
Hodoscopes before installing CDC
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p- trigger --Pulse Height cut
accept

• pulse height cut at proton peak
• For all 3 adjacent counters hit

p-
p
upper threshold
lower threshold
ADC of Outer hodoscope
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Efficiency of 3-coin.

• Efficiency of p- trigger
• Determined by geometry
• optimized for p- from subthreshold 2p production

pT distribution of p
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Test experiment

• Trigger performance test
• Search for pp- events
• Proton beam energy 392MeV
• Beam current 0.2nA
• Target Cu 50µm

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p- trigger performance
p -trigger (innerORouter3coin.OR pulse height
cut)
innerORouter3coin.OR
Inclusive innerORouterOR
p
p
p
p-
p-
p-
Trigger type inclusive 3-coin. 3-coin w/ p.h. cut
trigger rate (counts/nA) 1900k 41k 7.4k
2.2
0.34
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p- trigger performance
p- trigger innerORouter 3 coin.
Inclusive trigger innerORouterOR
p
p
p-
p-
Trigger type inclusive p-
trigger rate (counts/nA) 1900k 41k
2.1
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preliminary result
Search for p p - like pairs
One p- and another h 8 hours run (2.7h live
time) Sensitivity down to 0.1nb/nucleon Low
statistics
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• Improvement for p detection
• Additional new counters
• To catch some p which escapes through gaps of
  counters
• Separate p and p well in PID
• geometry is simple for determining
• flight length, dE/dx etc.

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Test experiment II

• To check performance of new counters, a
  part of counters were placed flatly
• proton beam energy 392MeV
• Beam current 0.1 nA
• Target Cu 50µm

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Particle ID by flat counter
preliminary
p
p
p
p

• Protons are dominant but p locus clearly seen
• We can distinguish p events from proton well

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Outlook

• Further trigger improvement for high statistics
• Combination of outer inner hodoscopes
• Combination of outer CDC wire hit
• require 2-cluster of them
• 2-track event/all1/10
• Trigger logic w/ ULM (FPGA base)

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• 4 days experiment with one target is approved
• Establish pp- measurement
• Present yield is too few
• Discuss pp- production more clearly
• Mpp, ppp and qpp distributions
• First step to measure A-dependence
• At least 2 more targets

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Summary

• Medium modification of pp- pair in sigma channel
  is still not conclusive
• We are preparing another experiment, proton
  induced subthreshold pion pair production in
  nuclei
• large acceptance detector and effective p-
  trigger
• pp- like events are seen, but low statistics
• With additional detectors and improved trigger
  system, we will perform 4-day experiment soon.

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4.10nb
1.34nb
0.38nb