Transcript 0505_COUPP2_Collar7_Coseners.ppt

First prototypes:
~20 ml active volume
Pressure: 0-150 psi
Temp: -80 to + 40 degrees C
Stereo photography of
bubbles
Three triggers: acoustic,
pressure and video
filter
pressure
sensor
Propylene glycol buffer
liquid prevents evaporation
of superheated liquid.
Safety shield box
gas
gas
Glass dewar
air
Exhaust to Room
glycol
glycol
Glass dewar with
heat-exchange fluid
3-way valve
liquid
Compressed Air @ 140 psi
Quartz pressure vessel
Camera
(1 of 2)
Acoustic sensor
Piston
Recirculating chiller
(-10 degrees)
J.I. Collar
UoM HEP seminar
Superheated CF3Br
Cameras
Mar. 21, 2005
J.I. Collar
UoM HEP seminar
Mar. 21, 2005
A Typical Scattering Event with Am-Be Neutron Source
(bubble expansion ~1 mm/ms)
X Camera
J.I. Collar
Y Camera
UoM HEP seminar
Mar. 21, 2005
Can Bubble Chambers be made stable enough?
SEE ->

Old Bubble Chambers radiation-ready for only few ms at
a time (coincident with beam spill)

Gas pockets in surface imperfections and motes can act
as inhomogeneous nucleation centers.

A BC dedicated to WIMP searches must remain
superheated indefinitely, except for radiation-induced events.
Low degree of superheat helps, but is not enough.

Recent progress in neutralization of inhomogeneous
nucleation sites (from work unrelated to bubble chambers!).
E.g. use of liquid “lid”, outgassing in presence of buffer
liquid, cleaning techniques and wetting improvement via
vapor deposition.
P. Reinke, Exp. Heat Transf. 10 (1997) 133
J.I. Collar
UoM HEP seminar
Mar. 21, 2005
Background Counting Rate at ~ 6 m.w.e.
Ź
Ź
• Mean survival time for superheated state varies due to periodic episodes
of nucleation on chamber walls, but is usually ~ 10 minutes.
• Live time (due to long recompression cycle) is already 62%.
• Counting rate for “real events” is 4/hour (compatible with measured fast
neutron flux in the lab).
•Intrinsic gamma rejection factor (from absence of excess nucleation
rate in presence of Y-88  1.3E6 g interactions / s) is  1E9 ( 14C not
a concern even at the multiton level)
Ź
Ź
2
Ź
Ź
Ź
Energy
Neutron Flux (n/cm /s)
Ground 6mwe
50 mwe
Level
Lab
Pit
Ź
Ź
Ź
Ź
Ź
<.5 eV
.5eV-100keV
100keV-10MeV
10 MeV-50MeV
Total
0.00394
0.00384
0.0015
0.00454
0.01382
4.65E-04
5.61E-04
6.87E-04
0.00E+00
1.71E-03
4.37E-05
1.60E-04
1.48E-04
0.00E+00
3.52E-04
Bonner sphere(s) n flux measurement in LASR underground lab
J.I. Collar
UoM HEP seminar
Mar. 21, 2005
Background Counting Rate at ~ 6 m.w.e.
Ź
Ź
• Mean survival time for superheated state varies due to periodic episodes
of nucleation on chamber walls, but is usually ~ 10 minutes.
• Live time (due to long recompression cycle) is already 62%.
• Counting rate for “real events” is 4/hour (compatible with measured fast
neutron flux in the lab).
•Intrinsic gamma rejection factor (from absence of excess nucleation
rate in presence of Y-88  1.3E6 g interactions / s) is  1E9 ( 14C not
a concern even at the multiton level)
Ź
Ź
2
Ź
Ź
Ź
Energy
Neutron Flux (n/cm /s)
Ground 6mwe
50 mwe
Level
Lab
Pit
Ź
Ź
Ź
Ź
Ź
<.5 eV
.5eV-100keV
100keV-10MeV
10 MeV-50MeV
Total
0.00394
0.00384
0.0015
0.00454
0.01382
J.I. Collar
4.65E-04
5.61E-04
6.87E-04
0.00E+00
1.71E-03
4.37E-05
1.60E-04
1.48E-04
0.00E+00
3.52E-04
UoM HEP seminar
Mar. 21, 2005
Well-defined low energy threshold
Lines show Seitz model
prediction for top boundary
of data point distribution
(onset of sensitivity
during decompression)
Sensitivity to < 7 keV recoils
demonstrated (while having no
response to 3mCi g source).
In agreement with models.
CF3Br data
(CF3I in progress
and looking good)
Sensitivity to ~1 keV recoils in
progress (Sb-124/Be source)
Further studies in progress
(efficiency, sharpness of
threshold, disentanglement
of I and F response).
Detector is insensitive to gammas (see previous
transparency) yet fully responsive to low-E recoils
J.I. Collar
UoM HEP seminar
Mar. 21, 2005
Fancy: Position Reconstruction
• Bubble positions can be reconstructed in 3 dimensions by scanning images taken
by two cameras offset by 90 degrees.
• Position resolution is currently 530 microns r.m.s. (approximately 1/4 bubble diameter)
• Uniform spatial distribution of background events, consistent with background neutrons.
163 background events (1.5 live days)
intermediate step in automatic
inspection algorithm using
NI Vision Development Module
(2 kg chamber)
J.I. Collar
UoM HEP seminar
Mar. 21, 2005
Neutron Background Rejection Potential
• Multiple simultaneous bubbles are present in
~4% of events in our “background” data set.
Neutrons can do this, WIMPs cannot.
• The response to neutrons and WIMPs interacting
mostly via SI is very different for refrigerants
containing F only (C3F8) and F+I (CF3I); more
favorable situation than Ge/Si to verify a WIMP
signal (generally speaking)
J.I. Collar
UoM HEP seminar
Mar. 21, 2005
Meet COUPP
(2 kg CF3I target, installation at 300 m.w.e. (FNAL) Jan. 2005)
• Central design issue is how to avoid metal contact with superheated liquid.
•Bellows mechanism compensates pressure inside and outside of inner
vessel in present design
J.I. Collar
UoM HEP seminar
Mar. 21, 2005
Meet COUPP
(2 kg CF3I target, installation at 300 m.w.e. (FNAL) Jan. 2005)
• Central design issue is how to avoid metal contact with superheated liquid.
•Bellows mechanism compensates pressure inside and outside of inner
vessel in present design
J.I. Collar
UoM HEP seminar
Mar. 21, 2005
Meet COUPP
(2 kg CF3I target, installation at 300 m.w.e. (FNAL) Jan. 2005)
• Central design issue is how to avoid metal contact with superheated liquid.
•Bellows mechanism compensates pressure inside and outside of inner
vessel in present design
triple n-induced nucleations in 2 kg CF3I movie available from
http://cfcp.uchicago.edu/~collar/triple_bubble(0.4s).mov
QuickTime™ and a
MPEG-4 Video decompressor
are needed to see this picture.
J.I. Collar
UoM HEP seminar
Mar. 21, 2005
J.I. Collar
UoM HEP seminar
Mar. 21, 2005
Can be made to operate like a “regular” BC
muon tracks visible at high degrees of superheat
J.I. Collar
UoM HEP seminar
Mar. 21, 2005
COUPP (Chicagoland Observatory for Underground Particle Physics)
Where we might be by end of 2005 with 2 kg. Take these with a grain of salt)
~latest CDMS
are these projections overly
cautious? Better safe than sorry
(e.g., alpha backgrounds from Rn
emanation from steel - however
only few mBq/m2 expected if some
precautions taken - The inner
chamber is a closed system to Rn
penetration)
J.I. Collar
UoM HEP seminar
Mar. 21, 2005
COUPP (Chicagoland Observatory for Underground Particle Physics)
Where we might be by end of 2005 with 2 kg. Take these with a grain of salt)
~latest CDMS
are these projections overly
cautious? Better safe than sorry
(e.g., alpha backgrounds from Rn
emanation from steel - however
only few mBq/m2 expected if some
precautions taken - The inner
chamber is a closed system to Rn
penetration)
J.I. Collar
UoM HEP seminar
Mar. 21, 2005