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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CALIBRATION AND MONITORING METHODS (C&M)
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
an internal note
requested by the
INFN MEG Referees
MEG internal note and then NIM collaboration paper
KEEP MEG UNDER CONTROL
PARTICULARLY AT HIGH (AND VARIABLE) BEAM INTENSITIES.........
BR eg~ 10-13
Beam Intensity ~ 5 107 /s
TWO MAIN TARGETS:
no single calibration method has all the required characteristics
use complementary (and redundant) methods,
make the best use of their intrinsic properties
attempt to grade the different C&M methods
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
other interesting possibilities..... :
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......
CHOICE OF THE ACCELERATOR
Cockroft-Walton, Van der Graaf, Radio Frequency Quadrupole
HV Engineering, NEC, AccSys, Neue Technologien GmbH
STRONG PREFERENCE FOR A COCKROFT-WALTON
If one wants to use the machine for the MEG start-up
an order must be issued as soon as possible (September !)
model: “coaxial SINGLETRON”
BVR February 2005
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)
TRIGGER UNDER STUDY
A FULL TEST OF THE WIRE-CHAMBERS SPECTROMETER
CAN ALSO BE PERFORMED !
WIRE CHAMBER SPECTROMETER AND TIMING COUNTERS TEST
(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
Total momentum distribution
FWHM ~ 0.7 0.9 %
This FWHM must
be compared with
the value quoted
in the Proposal:
e+ + e- momentum (MeV)
Am SOURCES ON WIRE AND WALLS
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
Determination of the relative
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.
C&M by NEUTRONS AND NICKEL-LINE , AT THE BACK OF THE CALORIMETER
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
Pe+ + Pe- = Eg
Region to be
At least 4 chambers
(7 hits) required
RADIO FREQUENCY QUADRUPOLE ACCELERATOR
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 N0 = 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).