Liquid Xenon Detector and Related Topics

1
Liquid Xenon Detector and Related Topics

• Liquid Xenon Optical Properties (TN-020)
• PMT Test Facility
• TERAS Beam Test Preliminary Results
• Beam Test in Oct-Dec 03 at PSI
• Cryostat
• Schedule
• S.Mihara
• For Liquid Xenon Detector Group

2
LXe optical properties (MEG-TN020)

• The ?att, ?abs and n are not very well known
  properties for LXe in the VUV
• Contraddictory measurements ? contaminations?
• Controlled measurements of epsilon, n exist in
  gas phase
• CAN WE EXTRAPOLATE FROM THE GASEOUS TO THE LIQUID
  PHASE?
• Yes we can extrapolate ? give a prediction for n
• Measurement of ?R (LP) ? measurement of n

3
Dielectric properties vs density

• In gaseous phase Clausius-Mossotti
  (Lorentz-Lorenz)
• LINEAR IN !!
• At increasing density non linear effects (virial
  expansion)

2 molecules 3 molecules .

• Molar liquid density 0.0229 cm-3 ? reasonable
• Xe is a non polar atom

4
Check linearity at different wavelengths
On the absorption lines the FLL function is only
marginally valid but it can be considered an
acceptable approximation still at the LXe
emission line...
5
near the absorption line?
The Xe has the first absorption band at ?146.9
nm (h?8.4 eV)
Re e Im e
2.24 10-2
Liquid
r

• Wannier excitons

Gas
Increasing
4.49 10-5
Exciton Xe absorption
It can test the linearity on ? of the FLL
function on a large range of density
6
A(?) in VUV gas-liquid
...as it can be seen directly from the results
obtained.
A(?) ? n
experimental data dilute gas
extrapolated value (fit)
7
n extrapolation

• We can extrapolate a value of n1.69 0.02 at
  175 nm
• How this compares to published measurements?
• Subtil et al. (1987) 1.71
• Chepel et al. (2002) 1.69
• Barkov et al. (1996) 1.56 (180 nm)
• Pretty good agreement

8
A relation between n and ?R

• In gaseous phase
• In liquid phase fluctuations (Einstein equation)
• Hence
• A measurement of ?R gives a hint on n
• ?R (29 2) cm ? n (1.71 0.015) !
• Ishida et al, NIM A384 (1997) 380

8th power
9
PMT Test Facility
10
MEG PMT cryogenic test facility PURPOSES

• - SYSTEMATIC TEST OF THE PMTs FOR MEG IN
  OPERATING CONDITIONS immersed in liquid Xe
• BUILD AN EVOLUTIVE CRYOSTAT
• PHASE 1 MANUAL OPERATION WITH LXe
  EMPTING/FILLING FOR EACH PMT
• PHASE 2 MANUAL OPERATION WITHOUT LXe EMPTING
• PHASE 3 TEST OF CARTRIDGE OF PMTs WITHOUT LXe
  EMPTING
• - SETUP A CRYOGENIC LABORATORY AT INFN-PISA
• - GET EXPERIENCE IN HANDLING LXe
• - OTHER MEASUREMENTS ON LXe

11
MEG PMTct Cryogenic/Vacuum Diagram
Phase II
12
MEG PMTct - Cryostat
13
Cryostat delivered from CINEL phase I

• Almost all material delivered
• Cryostat
• Pumping system
• Leak detector
• Feed-throughs
• Signal
• Xenon
• Gases
• Oxisorb
• Material for phase 2/3
• Waiting for
• Xe transportation tank (needed CE certification)
• Clean pipes
• Slow control
• PMTs!

14
and phase II linear motion and gate valves

• In phase II/III Xe should be kept liquid
• Gate valve
• The PMT can be extracted from the top of the
• cryostat
• Cross
• Linear movement attuator

15
Calibration source ? and ? (LED)
25 mm

• ?-source that is stable in liquid Xenon
• 3 kBq 241Am deposited on a micro-etched surface
• Ordered to Campoverde srl.
• Quotation from a Czech factory which provides
  gold-plated sources.
• Source and PMT holder under
• construction
• Reference PMT
• Hamamatsu R7400-9

16
?-source
Difference in a and ß waveform in Xe
17
In parallel PMT test at warm temperature

• Blue LED pulser (same as LP) to study the PMTs in
  controlled conditions
• Gain vs T
• Gain vs time
• Waiting for
• VME LED
• pulser (this
• week)

LED fiber filter PMT
18
PMT Test Facility Status

• The PMT test facilty is close to be operational
• Almost all material delivered also for phase
  II/III
• Sources in preparation
• In parallel test at warm temperature.

19
TERAS BEAM TEST

• Overview of the test
• Energy measurement
• Position reconstruction
• Timing measurement

20
TERAS beam in April 03

• Xenon liquefaction completed 10 days before the
  beam time.
• Purification of xenon in gas phase.
• Data acquisition
• 40MeV(main), 20MeV, 10MeV
• Different incident positions
• Different incident Angles
• Materials in front of the detector
• PMT high gain runs

21
Gas Phase Purification System

• Xenon extracted from the chamber is purified by
  passing through the getter.
• Purified xenon is returned to the chamber and
  liquefied again.
• Circulation speed 5-6cc/minute

• Enomoto Micro Pump MX-808ST-S
• 25 liter/m
• Teflon, SUS

22
TERAS g Beam Line

• Compton Spectrum
• (Eg-Ec/2)2(Ec/2)2

• Electron beam
• Energy 764MeV
• Energy spread 0.48(sigma)
• Divergence lt0.1mrad(sigma)
• Beam size 1.6mm(sigma)
• Laser photon
• Energy 1.17e-6x4 eV (for 40MeV)
• Energy spread 2x10-5 (FWHM)
• Divergence unknown
• Beam size unknown

Collimator size
23

• D depth parameter

MC simulation
Data
D
D
Short labs
Previous Test
D
D 20100 ? 025cm
D
Long labs
This Test
D
D
24
Effect of Material

• 5mmt, 10mmt, 15mmt Al
• 15mmt Al4mmt Stainless Steel
• 5mmt Pb

Al, Stainless, Pb plates
LP
5mm Al 0.053X0
10mm Al 0.11X0
15mm Al 0.16X0
15mm Al 4mm Stainless Stell 0.398X0
5mmt Pb 0.89X0
2nd collimator
COBRA thickness 0.197 X0
25
Position/Incident Angle Scan

• Incident Position
• 10 different positions for 40MeV g (blue and red)
• 2 different positions for 10MeV and 20MeV g (red)

• Incident Angle (40MeV)
• 0, 7.5, and 15 degree on the center
• Not analyzed yet

q
LP
62mm
26
Detector Operation Status

• No serious trouble during the test
• Except one of two TDC modules was broken in the
  final run (PMT high gain run)
• Total amount of xenon used 120 liter
• Stable operation by the pulse-tube
  refrigerator/Liquid Nitrogen cooling pipe (only
  while circulation)
• PMT calibration as usual (LED/alpha/cold gas
  alpha)

27
Energy Measurement
28
Energy Spectrum Fitting

• Principle

• For understanding simply
• Suppose Response function is an asymmetric
  Gaussian

Response function
Compton Spectrum
Eg
Npe
s left
Convolution of Compton Spectrum Response
Function
s right
29
Energy Spectrum Fitting contd

• Require D(depth parameter)gt45
• 34 of events in the range of 40MeV/-4MeV are
  discarded by this requirement
• Suppose Compton Spectrum around the edge
• (E-Ec/2)2Ec2/4
• Detector Response Function
• Gaussian with Exponential tail
• f(x) Nexpt/s2(t/2-(x-x0), xltx0t
• Nexp-1/2((x-x0)/s)2, xgtx0t
• Convolution
• Integration /- 5s

• Fitting is done in two steps
• Determine the edge position
• Fix the edge in the 2nd fitting for determining
  the other prams

Detection efficiency (estimated by MC) 74
within /- 4 energy cut at 52.8 MeV (cf.
Progress Report Jul 02) (16 of events are lost
due to interaction with material in front of the
active volume)
26
30
Dependence on Eg

• Very preliminary
• Typical 10, 20, 40MeV data fit using the
  convolution function
• Error estimation is not finalized. Conservatively
  30 error for the energy resolution is supposed.
• Resolution is shown in sigma.

31
Energy Resolution vs. Depth Parameter

• For g incident at the detector center
• D gt 35, 45, 55.85
• Resolution lt 2 in sigma except shallow events
  (Dlt45).

D
Number of Photoelectrons
32
Material Effect on the Resolution

• No apparent deterioration of the resolution
• Loss of efficiency

Al 5mm
Pb 5mm
Trigger Threshold
COBRA Thickness
33
Position Dependence
1.85 in s
1.83 in s
1.80 in s
34
Measurement with half the front PMT switched off

• To simulate the convex front geometry of the
  cryostat
• MC simulation (reported in the last review
  meeting)
• TERAS data
• Switch off half of the PMTs in the front face
• Use 4x4 PMTs out of 6x6 PMTs
• Switch off PMTs on the side walls

35
VLP and Curved Detector

• Shape studies
• Compare LiXe and a VLP (100 x 50 x 50 cm3) to
  check the effects of a different geometry on
  position and energy resolution.
• no difference with the curved detector for
  position resolution (10.6 mm FWHM in both cases
  for a realistic situation) a 3 systematic
  correction is needed on both coordinates for VLP
• slight improvement in energy resolution (from 4
  to 3.5)
• however, more critical problems of energy
  containment
• a much larger volume (1.5 m3) of Xenon would
  be needed (and PMTs!).

36
TERAS Data
Only 4x4 PMTs on the front face

• Switching off half the front PMTs
• Compton Edge shifts by 6.2
• Resolutions are almost same (1.84 to 1.85 in s)
  before and after switching off.
• Switching off PMTs on the
• side wall(s)
• 1 plane off ? 2.05 in s
• 2 planes off ? 2.22 in s
• 3, 4 planes off ? gt 3 in s

Number of Photoelectrons
37
Switching off PMTs on side walls
D

• Deterioration of the energy resolution when
  switching off PMTs is not mainly caused by loss
  of Npe.
• PMTs on the side walls compensate 1st conversion
  point dependence.

1 plane off
Number of Photoelectrons
3 planes off
D
Number of Photoelectrons
38
Effect of a faulty PMT

• All PMTs on s1.8
• Switching off one PMT on the front wall.
• the nearest PMT ?s2.3
• 2nd nearest PMT ?s1.9
• 3rd nearest PMT ?s1.9
• 300 PMTs on the front face in the final detector
• 4/300 1.3 loss of acceptance

F30 off s2.3
F22 off s1.9
F28 off s1.9
39
Position Reconstruction

• Simple weighted average
• Using all PMTs on the front
• Very fast, but not so good resolution and bias
  exits
• Localized weight method
• Using only selected PMTs around the energy
  release points to reduce the shower fluctuation
  effect

40
Simple Average Method
Depth

• Data and MC are in good agreement.
• Reconstruction bias exists.

Depth
Depth
41
Localized Weight Method

• Projection to x and y directions.
• Peak point and distribution spread

• Position reconstruction using the selected PMT

42
Samples of Reconstruction
1mm
43
Reconstruction Bias
44
Position ReconstructionResolution
45
Timing Measurement

• 128 TDC channels for the PMTs around the front
  face.
• Leading-edge discriminator with threshold level
  at 12mV.
• Start timing of the TDCs is determined by the
  xenon detector itself.
• Laser start timing ?1ms jitter.
• Electron tagging counter was placed in a TERAS
  Q-magnet. Difficult to achieve good resolution as
  a reference.

• Same method as in KSR electron beam test is
  employed for timing measurement.
• Detector is divided to left and right groups and
  arrival time difference was compared to evaluate
  the resolution.

46
Timing MeasurementVery Preliminary Result

• We observed that
• Timing resolution improves as the PMT gain
  increases.
• Timing resolution improves as Npe increases.
• The best value (48.8 psec in sigma) was obtained
  for gt160MeV synchrotron radiation light taken in
  a dedicated run

Left
Effect of shower fluctuation along the g incident
direction is canceled, while the effect
perpendicular to it is not.
g
Right
47
Open Questions

• Compton Spectrum Shape
• Broader than simulated shape
• Detector effect ?
• Reflection or absorption on the PMT window?
• Rate Dependence

48
Compton Spectrum Shape

• Broad peak of the total photoelectrons.
• Many low energy events.

Maybe beam spectrum
We have not a clear answer
threshold
49
Comparison with revised MCCompton g spectrum
shape
MC
Data

• Electron beam spread at the collision point
• Collimator position

50
Reflection or Absorption on the PMT window?
D
(Qsum-Qfront)/Qsum
Qsum
51
Discrepancy at Low Energy Side
zlt0
Data
MC
0ltzlt3
total photoelectrons
total photoelectrons
z first conversion depth cm , 0 means surface
of LXe.
52
Absorption in the Mn layer?
Previous

• Reflection cannot explain simultaneously both
  gamma and alpha data.
• The previous model (in LP) uses a Mn layer to
  keep the surface conductivity of the PD at low
  temperature.
• The new model uses Al strip instead of the Mn
  layer.
• Compare responses for different incident angles
  of light.

window
light
Mn layer
Photocathode
New
300um Al strip
53
Rate Dependence
LED

• Rate dependence
• In case of high current in TERAS, SR light
  background is huge to decrease the effective gain
  of the PMTs.
• Data with a 60Co source in front of the entrance
  wall at different distance to simulate g
  background.
• Detailed analysis to interpret the measured
  dependence for the actual detector operating
  condition is not finished yet

a
54
Oct-Dec 03 Beam Test at pE1
55
The elementary process
? - (essentially) at rest captured on protons ?
- p ? ?0 n ? - p ? n ? ?0 ? ? ?
Photon spectrum
129 MeV
54.9
82.9
56
CM and Lab frame
M?/2
?M?/2(1??cos?)
?
M?/2
Eg55 MeV ? ? ?
57
Angular selection

• ?s back to back in lab 55 and 84 MeV
• ?E?/ E? lt 1 ? ??? lt 5o
• This fixes the angular acceptance to
• 6?10-4 /56 1.07 ? 10-5

5o 87mrad 8.7cm _at_1m
?? ?-?
(83-55)/0.5
58
Experimental configuration
TARGET?

• Rate
• Background
• Thin/small (angle/X0)
• Handling

NaI
Previous use

• GH2 (Panofsky.)
• LH2 (PIBETA)
• CH2 (MEGA)
• LiH (??e ? at SIN)

LXe
Coincidence C !A NaI (Offline LXe)
59
CH2 target(1)

• Easy to handle
• Active (scintillator) but ...
• Capture rate on Carbon 1300 capture rate on
  protons (s-wave capture ?Z4) ? rate
  suppression by factor 650
• Range R ? p3 ? a few cm
• ?R/R(200 me /m?)1/2 f(E/m?)
  (Segre, Ritson,Rossi)
• 3.5 ? OK
• Background?

60
CH2 target(2)

• Capture on C dominant
• Radiative ?- capture ? ok. Dominant BKG is gamma
  from radiative pion capture nuclear (i.e. few
  MeV) de-excitation
• Danger from ?- C ? ?0 B
• EThreshold 10 MeV no ?- at rest (pth 55 MeV/c)
• ?0 emitted in forward direction

61
Fitzgerald et al.

• fast ? - on (CH2)N
• Comparable rate (incoherent capture,a factor of
  three expected)
• BKG measured with graphite target
• 14 MeV difference!

?0 kinetic energy
C-ex on Carbon C-ex on H
62
Applied in MEGA

• A CH2 calibration target was used in MEGA
• The BKG from ?- c-ex in flight is visible in the
  low energy tail
• Could be measured (graphite target) and subtracted

3.3FWHM
5.7FWHM
63
Possibility of CH2?

• A clear peak is visible
• We can trigger on the target
• Need to measure BKG with Carbon target?
• RATE??

64
Hydrogen target
LH2

• The most natural choice
• ? 0.071 g/cm3
• Range p 80 MeV/c ? R ? 14 cm, ?R ? 0.5 cm
• 110 MeV/c ? R ? 41 cm, ?R ?
  1.4 cm

GH2

• Already available
• ? 6.7?10-3 g/cm3
• Range p 80 MeV/c ? R ? 150 cm, ?R ? 5.6 cm
  
• 110 MeV/c ? R ? 450 cm, ?R
  ? 15 cm

65
Rate

• dp/p up to 0.8 FWHM
• ?- flux 8105/s at 1.6mA

66
1999 measurement
10FWHM

• D100 cm
• 10 x 10 window
• 9.5 hours
• no light in LYSO
• 60 cm (NaI) 75 cm (CsI)
• 11 x 13 window

67
Cryostat Design
68
Cryostat

• Fabrizio Raffaelli has joined the
  design/construction group for the cryostat.
• All information can be found at http//meg.psi.ch
• ?subproject ? calorimeter ?Design and
  Construction

69
Thickness of the Walls/Covers

• Suppose the pressure tolerance of 0.3MPa for the
  inner vessel and 0.1MPa for the outer vessel
  (vacuum insulation layer).

70
Stress Distribution
71
Deformation
72
Strength Calculation forthe G10 Support and the
Brace
73
Heat Load Calculation

• See also T. Haruyamas talk on Jul 2002 review
  meeting.
• Main contribution is from PMT and cables.
• One pulse tube refrigerator can compensate the
  load.

74
Metal gasket for the inner vessel flanges

• One possible manufacture (in Japan) is USUI.
• Usage condition
• Pressure 0 - 0.3 MPa
• Temperature -110 100 degree C
• Fluid Liquid xenon
• Flange and bolt SUS316L
• U-tight seal dimension
• Cross section 5.5 mm diam
• Material Aluminum(outer), Stainless(Inner),
  Spring(Inconel)

Cover
Flange
Special Shape ?We need a mold for casting.
75
T. Haruyamas talk on Jul 2002 review meeting
76
Operation Scheme
T. Haruyamas talk on Jul 2002 review meeting
77
Some questions and remarks after seeing the
Cryostat drawingsby Fabrizio Raffaelli

• Which is the design pressure for the inner vessel
  ?
• Is the testing procedure has been already studied
  during the fabrication steps and which are the
  final acceptance tests?
• Is the safety has been already studied?
• The of safety relief devices are already
  implemented? For instance if there is a xenon
  leak into the vacuum the pressure on the outer
  vessel can increase more than 1 atm.
• Is the cold sealing has been already chosen and
  which are the specification for the groove
  accuracy ?
• Is the cold window has been already studied ?
• The pre-cooling system is already implemented in
  the inner vessel but its efficiency is already
  studied?
• Is an heating system has been considered to empty
  the inner vessel?
• Which are the envisaged mounting steps?
• Which adjustments are envisaged to position the
  Inner vessel in cold condition ?
• A lot of other questions will raise going in the
  drawing details.

78
Remarks after seeing the drawingsby Fabrizio
Raffaelli

• Covers
• I see that the polished area of the sealing
  surface is not protected and it is not well
  localized from the point of view of machining
  operations and further hands polished operation.
• The inner vessel flange is quite slim (30 mm) and
  I am worry that after the welding with the I.V.
  body we are not able to guarantee the necessary
  flatness.
• I think we need to study the technological
  construction step and may be weld a long collar
  before machining the flange.
• Since the shape of the cover is not simple the
  oring especially the cold one should be custum
  made and I think will require a mold.

79
Photon Detector
2002
2003
2004
2005
Large Prototype
Beam Test
Beam Test
Engineering runs
Vessel Design
Assembly Test
Manufactoring
PMT Delivery Testing
Assembly
Test
Refrigerator
Manufactoring
Assembly
Liq. Purification
Test
Milestone
Assembly
Design
Manufactoring
80
Summary

• Liquid Xenon optical properties (TN-020).
• PMT test facility (Phase I) is close to be
  operational.
• TERAS beam test results
• Energy Resolution at 40 MeV 2 in sigma
• Needs more careful analysis to treat shallow
  events
• Large Prototype beam test at pE1 in Oct-Dec 03.
• CH2, GH2, LH2
• Cryostat design will be finalized in 2003.