Transcript Determination of position of muons for the KIMS experiment

Muon flux at Y2L and
reconstruction of muon tracks
JingJun Zhu
Tsinghua University &
KIMS collaboration
2004 Jan. 29-31 TEXONO-KIMS Joint Workshop
Muon background at underground
●
●
●
●
In WIMP search experiment, muon is one of the
main background.
Energetic muon can easily penetrate rocks to deep
underground.
When muon penetrate through the shielding
materials, the interaction of them can induce neutron
inside shielding. This is very harmful. Because the
events induced by neutron in CsI crystal is
undistinguishable with that induced by WIMP.
In order to monitor the muon background at
underground lab, we constructed veto detector for
muon.
Structure of Muon Detector
●
To moniter the muon backgound we constructed muon
detectors surronding the main detector as active shielding,
whick is 30cm thick, filled with liquid scintillator, using PMT
to read out.
MUD 7
4
MUD 28
MUD
MUD
MUD
MUD MUD 1
6
MUD 3
MUD 5
CSI
2x2” PMT for each channel
8 muon modules , 28 signal channels
Liquid Scintillator 5 %
PC 1 liter + PPO 4 g + POPOP 15 mg
Mineral Oil 95 %
10-5 times of ground Muon rate at Y2L
Attenuation length of muon
detector
Use small scintillator for trigger muon events in specific position
Fitting function : two exponential decay function
Fitting results : fast term - 50 cm
Detection efficiency of muon
detector
Trigger Muon using two other scintillator detectors in the Ground lab
Use one(MUD2) of muon modules
Muon spectra & Flux
●
YangYang ( ~ 700m underground) :
~ 380 /day.m2 = 4.4 x 10-7 /s.cm2
●
CheongPyoung ( ~ 350m underground) :
~1450 /day.m2 = 1.7 x 10-6 /s.cm2
Determination of position of muons
●
●
Besides flux, another important thing is to determine the
position where muon hit the detector and reconstruct the
track of muons.
Minimum square method :
–
Choose one point, calculate the energy response
according to distance to PMT and attenuation length of
liquid scintillator
–
Compare the calculated result to the measured one, get
a square value
–
Change the assumed position and calculated again, until
found the point which has minimum square
Calibration of muon hit position
●
To verify the effect of this method, we put a plastic scintillator at
the center of top detector to choose the muon events only
around center.
A plastic scintillator ( 85 x 20 cm2 )
has been put at the top as trigger
Hit reconstruction on Muon
Detector
Plastic scintillator position
and the calculated result
Hit position projected to x-axis
Reconstructed Hit Position of
Muon
●
Calculated result of background data (without plastic
scintillator as trigger) .
Tracking and veto
●
After finished position determination for all the detector, we
can get the track of each muon event, and then we can
reject the muon events which pass through the CsI crystal.
Muon detector
Copper box for
CsI crystal
Muon track
Monte Carlo simulation
• Generate muon from a rectangular area above the detector, the
size of this area is 2 times of that of the top detector. Muon is
generated at random position inside of this area and in random
direction (downward 2π angle).
Muon generated area
Detector area
Optical photon collected by PMT
MD8
MD7
MD4
MD6
MD5
MD3 MD2
MD1
Energy spectra of muon from
simulation
More about simulation
●
●
Try more amount of muon events to get
better energy spectra.
Try graphic mode to show muon track in 3
dimensional mode.
Summary
●
●
●
We measured muon flux at 700m underground
laboratory, it is about 380 /day.m2 ( equal to 4.4 x
10-7 /s.cm2 )
Hit reconstruction of Muon has been tested and
Track Reconstruction is in progress. The track
reconstruction
give the information to reject muon events from
WIMP candidate data.
We performed Monte Carlo simulation for muon
detector. For next step, we will try
–
More amount of muon events to get better energy
spectra;
–
Graphical mode to show muon track in 3-dimensional