Background study

1
Background study

• Naho Tanimoto (Duke)

2
Introduction

• Since Water Cherenkov detector can not detect
  more than one neutrino interaction per spill, it
  is important to make sure the fraction of muons
  coming from rock
• SIGNAL m start in the WC
• BG m from the rock hit the WC
• Add concrete block (10m?10m?5m) upstream side in
  experimental hall of T2K

Rock
WC
Muon
LAr
n beam
10m
5m
6m
14m
5.6m
6.5m gap
3
Hall top view
n beam
Rock
6.5m
4
Sanity check

• Material of Rock is
• SiO2, density2.7 g/cm3, dE/dx1.7 MeVcm2/g
• 2.7?1.74.59 MeV/cm 0.46GeV/m
• Loose 0.5GeV of energy per 1 m
• 5m thickness ? 2.5GeV muon will go through about
  5 m, then stop

5m
m start
m stop
It works!
5
Muon gun

• Most of muons are generated by nN?m-p
  interaction
• Muon gun has proper momentum distribution, its
  vertex is inside the rock
• How often we will see this?

Stopped inside the rock
Sometimes go through the rock, then hit WC
6
Momentum of muon

• 71.1 of events has muons in event
• (has m in event)/(generated) 35514/49970
  71.1
• Peak is at 0.4 GeV

GeV
GeV
7
Start point of muons
Rock
lAr
WC
MRD Scinti
xy position are given by textfile, but z is
random number
Projection to z
log
Z
8
Stop point of muons
End of the experimental hall
Rock
lAr
WC
MRD Scinti
Projection to z
log
Z
9
Fraction of digitized tubes

• Number of digitized WC tubes in event
• Has a huge peak at 0, because most of muons are
  stopped inside the rock, but some of them hit the
  WC and then digitized
• (Has digitized tubes at least one in event) / (
  of generated)
• 2917/499700.0584 5.84
• This is NOT small

x-axis scale is 0, 5000
10
Conclusion Plan

• Install the rock inside the experimental hall to
  see the fraction of the muons from the rock
• Change the thickness of the rock, and see how
  thick is enough to contain all events
• Construct realistic rock walls inside the hall