CALIBRATION AND MONITORING METHODS (C&M) FOR THE LIQUID XENON CALORIMETER AND FOR THE WHOLE MEG DETECTOR........ Xe calorimeter, wire-chamber spectrometer, timing counters an updated discussion on : advantages, disadvantages, open problems, etc. of proposed methods.
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THE LIQUID XENON CALORIMETER
FOR THE WHOLE MEG DETECTOR........
Xe calorimeter, wire-chamber spectrometer, timing counters
an updated discussion on:
advantages, disadvantages, open problems, etc.
of proposed methods
BVR, July 18th 2005, CB + T. Iwamoto
requested by the
INFN MEG Referees
KEEP MEG UNDER CONTROL
PARTICULARLY AT HIGH (AND VARIABLE) BEAM INTENSITIES.........
BR eg~ 10-13
Beam Intensity ~ 5 107 /s
no single calibration method has all the required characteristics
use complementary (and redundant) methods,
make the best use of their intrinsic properties
500 KV PROTON ACCELERATOR AND LITIUM TARGET FOR A
17.6 MEV GAMMA LINE
[P.R. 73, 666 (1948), N.P. 21 1 (1960),
Zeitschrift f. Physik A351 229 (1995)]
E sigma error S-factor error (MeV) (b) (b) (MeV b) (MeV b)
0.375 1.44E-03 8.5E-05 5.10E-02 3.00E-03
0.384 5.86E-03 1.5E-04 2.02E-01 5.00E-03
0.388 4.44E-03 1.8E-04 1.51E-01 6.00E-03
1.0057.59E-05 4.3E-06 1.23E-037.00E-05
at the Tp* 384 keV resonance and compound nucleus formation
+ non resonant direct reaction elsewhere
E0 = 17.6 MeV
E1 = 14.6
Bpeak 0/(0+ 1)= 0.720.07
resonant at Ep= 440 keV =14 keV peak = 5 mb
13H (p,) 24HeE ~ 20 MeV !! used in SNO
in : Hahn et al. PRC 51 1624 (1995)
but Tritium....and low rate.......
Cecil et al. NP A539 75 (1992)
10x10 cm NaI crystal
resonant at Ep= 163 keV
= 7 keV
E0 = 16.1 MeV peak = 5.5 b
E1 = 11.7 + 4.4 peak = 152 b
lower proton energy !
lower rate at 50 A !!
ENERGY, TARGET THICKNESS AND -LINE QUALITY
correspondence between resonanceand range intervalR
“thin target” R “thick target” R >>
if Tp = 445 keV and R =
R = 0.120 N=7 x 1017 LiF/cm2
at 80 A Ip Np= 5x1014 p/s N= 1.8x106 /s(up to 1.6x105 in calorimeter)
very clean -line (more difficult calibration tuning)
if Tp = 445 keV and R = Range (445 keV) >>
R = 413 N = 2.5 x 1019 LiF/cm2
at 80 A Ip Np= 5x1014 p/s N= 6x105 /s (+ N=1.8x106 /s)
-line with appreciable left shoulder from 17.6 to 17.1 MeV
(simple calibration tuning)
of the total 5x1014 p/s, 2x106 p/sproduce photons at resonance,
some of the residual 2.5x108 p/s produce direct photons of lower energy (if Tp > resonant energy, right tail also.........)
H2+ ion effects........(30% of CW-beam)
N= 1.8x106 /s over 4(up to 1.6x105 /sinto the whole calorimeter)
(PMT non linearity over Ia = 4 A, therefore at about 2x105 /sin the calorimeter)
Very high -intensity
(other optional reactions have smaller cross-section)
(possibility of using low-efficiency selective triggers)
MEG aquisition rate is about 100 Hz
The accelerator current can be easily limited, but one can also test
the calorimeter and the PMT behaviour
as a function of an increasing -rate in the calorimeter......
Cockroft-Walton, Van der Graaf, Radio Frequency Quadrupole
HV Engineering, NEC, AccSys, Neue Technologien GmbH
If one wants to use the machine for the MEG start-up
an order must be issued as soon as possible (September !)
FULLY TESTED......PRECISE CALIBRATION
TWO POSSIBLE WAYS TO PERFORM THE º CALIBRATION
No bearing ball
Linear slider: http://www.tollo.com
an interesting possibility for a calibration in MEG
angle between ’s defined by impact points on LXe-Cal
and “ special counter”
(angles 1800 useful for calibrating at different energies)
loss at conversion but huge increase in solid angle
MC METHOD SIMULATION RESULTS (F.Cei)
A FULL TEST OF THE WIRE-CHAMBERS SPECTROMETER
CAN ALSO BE PERFORMED !
(at full COBRA field)
by - p 0 n and -1 conversion into an e+ e– pair
by - p n and conversion into an e+ e– pair
(a pair spectrometer and a -line !!)
but also the Cockroft-Walton allows a calibration of the
LXe Cal and, wire-chamber spectrometer, timing counters
g energy release: increased statistics
0.1 X0, NDC > 4,
relative angle > 1750
from natural angular width
of e+e- pair production and
multiple scattering in the
spectrometer and timing counters.
gamma conversion in Tungsten.
tracks reconstructed. Pair spectrometer !
energy calibration point for the wire-chamber
(normally not easily obtainable......).
(> 4 chambers)
Large errors due to
small statistics, but
promising results; 0.1 X0 looks the best choice.
Generated 100000 events in the
whole solid angle (4 p).
~ 400 Hz
FWHM ~ 0.7 0.9 %
This FWHM must
be compared with
the value quoted
in the Proposal:
e+ + e- momentum (MeV)
BVR February 2005
Sources in production.
Soon available for all LXe devices.
Wire presently mounted in “Large Prototype”
reconstruction of the 8 -source positions in gaseous Xe.
Recent measurement with the large-prototype.
(Po-source produced in Genoa)
the ring radius
the Rayleigh scattering length
QE for 4 different PMTs by
the use of 4 dot-wire-sources
in Xe gas of the large-prototype
the relative QEs are given by
the slope of the linear fits.
in the large-prototype
the line is worse.....
(thermal neutrons in LXe !)
the measurement must be
repeated, protecting LXe from
thermal neutrons by a borated-foil
EXTRA SLIDES CALORIMETER
Pe+ + Pe- = Eg
Region to be
At least 4 chambers
(7 hits) required
RADIO FREQUENCY QUADRUPOLE ACCELERATOR CALORIMETER
stopping target (10 cm length x 5 cm diameter);
target; thickness between 0.05 X0and 0.3 X0;
the correct energy and angular distributions;
required to define a track;
Converter thickness 0.15 X0
converter FWHM ~ 60
FWHM < 20
and multiple scattering effect
2nd g–e+relative angle
vs energy loss in LXe
Region to be selected
for energy calibration
Higher density of points
forDE< 60 MeV
Converter thickness 0.15 X0
Uniform coverage of
the whole calorimeter
Relative angle g2-e+
Dq > 1750
FWHM(energy) 4 - 5%
(> 4 chambers)
Generated 100000 events in the solid
angle covered by the LXe calorimeter
~ 23 Hz
Reconstruction and trigger efficiencies under evaluation
Solid angle factor
(20 30) x (Rp0/106) Hz(max.MEG acquisition rate 100 Hz)
(216 PMTs in groups of 4):
(< 1000 events/location would be sufficient)
1000 events/50 s total for 50 locations 2500 s < 1 h
Assuming CALORIMETERN0 = 106 129 MeV photons/s:
N(e+e- pairs detected)/s =
N0 x epair ~ 400/s.
Requiring 106 pairs in the wire-chamber
spectrometer (at a rate of 100 Hz:
Time = 106/(100/s) = 104 s
(less than three hours).