Download new TPC (NTPC)

Next-stage experiments with
new LEPS standard setup
Physics motivation

g  p K

*0

( K *  K )
new TPC (NTPC)
2.97 GeV g
New LH2,LD2 target
g  n     K *

g  p     K (  )    (  )

g  A  backward  production

g  p  *( 1405 )  K *
etc.
Decay asymmetry of K*
 sensitive to the parity of exchange particle(s)
information of both missing masses and invariant masses
Final Design of New TPC (2005 Jan.)
560
750
900
Pad size: 5.1mm x 14.5 mm (gap : 0.5 mm)
Pad row : parallel to anode wires, 9 layers
3 anode wires with 5mm spacing are on one pad layer.
Inefficient region : 10 % of the whole region
TPC construction was completed in early 2006 and it was tested.
Add some new counters
(based on the experience of 1st TPC exp.)
• To improve trigger condition  inner scintillators
Select events from target
Cut BG events from upstream
• To improve particle identification
 reconstruct outer scintillators with both-side readout
TOF information for PI
• To improve the momentum resolution for forward going
particles  thin drift chamber with 60cm effective area
New DC is also used in place of SSD for the forward spectrometer.
• To put the TPC& DC close to the dipole
 modify the forward scintillators
Particle Identification
de/dx vs Momentum and/or TOF vs Momentum
(PI is difficult for higher momentum due to small inner diameter of the solenoid !)
K 2s separation at 0.5 GeV/c  s(TOF)= 150ps or s(de/dx)/(dedx)=16%
Ar, 1 atm
L=25 cm
300 ps
1.22 keV
LH2 target
New DC
Outer scinti.
TPC
Inner scinti.
Solenoid
Illustrated by J.Y.Chen
One thing I know it should be changed, but it still not be improved.
 Time constant (CR) of the PreAmp
4pF×33kW =132 ns
On the dip angle dependence of the TPC pulse height
wire
plane
Charged particle
b

Charge sensitive PreAmp.
total charge Q ∝ b/cos
time difference of charge collection
Dt = b tan/ v
(b~15mm (pad), ~5mm(anode)
v~5cm/msec )
Simple model for the input charge
T0: charge collection time
i0=Q/T0 (t<T0)
Vout is analytically
solved
Vout
Q (1  e t / CR )

C (T0 / CR)
(t  T0 )
Q (eT0 / CR  1)  e t / CR

C
(T0 / CR)
(t  T0 )
for pad,
=30° T0=173 ns
=45° T0=300 ns
=60° T0=520 ns
dip-angle dependence
of the pulse height and
peak time should
be corrected in the
offline analysis !!
From the end of next January,
new experiments will start.
Please come and join us.
Enjoy physics from new data !