Electron Veto Electron Veto CounterCounter

Masashi Kaneta2006/4/13

K0 meeting

The Main back ground: eThe Main back ground: e++ee-- pair pair

• e+e-:Photon conversion is the main background in the NKS2 experiment– Trigger will be made by (IH_Hits2 OH_Hits2)

• Those tracks will be on a plane– e+e- direction is almost same with photon– bended in a magnet field

• Need to remove them on a trigger level

Trajectory of eTrajectory of e++ee- -

• 0.0-1.2GeV/c of electron/positron– Bremsstrahlung photon energy is up to 1.2GeV– Energy sharing Ee/E is 0 to 1

• Hits on both IH and OH

Rev. M

od. Phys. 13 (1941) 240

Ee/E0.0

108 [eV]109 [eV]

107 [eV]

1.0 Trajectories of electronas a function of momentum(0.2–1.2 GeV/c with 0.2 GeV/c step)

Hit distributions at OH positionHit distributions at OH position

• Monte-Carlo studies are done by Kenta Futatsukawa

• Hits information from OHH and OHV– there is a overlap around 55 degree

e+e-

from K0S

from K0S

p from

from

z range[cm]

fraction ofe+e- [%]

|z|<0.5 22.0

|z|<1.0 41.4

|z|<1.5 54.1

|z|<2.0 61.8

|z|<2.5 67.7

|z|<3.0 73.4

|z|<3.5 76.9

|z|<4.0 79.7

z [c

m]

[degree]

DesignDesign

• 5 cm height– same with Previous experimet (NKS)

• Hybrid counters• Plastic Scintilator counter (1cm thickness)• Lucite Cherenkov counter (2cm thickness)

– will place on the same plane

• Separated as 4 counters– to avoid absorption of light in the counter– but can not have so many counters– PMT’s used in NKS will be recycled

DesignDesign