Experimental study of a positron source using channeling
Experimental study at CERN of a positron source using channeling R. Chehaba , R. Cizeron, C. Sylvia
Laboratoire de l'Accelerateur Lineaire, IN2P3-CNRS et Universite de Paris-Sud, BP 34, 91898 Orsay Cedex, France
V. Baier, K. Beloborodov, A. Bukin, S. Burdin, T. Dimova, A. Drozdetsky, V. Druzhinin, M. Dubrovinb , V. Golubev, S. Serednyakov, V. Shary, V. Strakhovenko BINP, Av. Lavrentyeva, 630090 Novosibirsk, Russia X. Artru, M. Chevallier, D. Dauvergne, R. Kirsch, Ph. Lautesse, J-C. Poizat, J. Remillieux IPN-Lyon, Universite Claude Bernard, 69622 Villeurbanne, France A. Jejcic LMD, Universite Paris, Jussieu 75005-Paris, France P. Keppler, J. Major Max-Planck Institute, Heisenberg Str. 70569 Stuttgart, Germany L. Gatignon CERN, CH-1211 Geneve 23, Switzerland G. Bochek, V. Kulibaba, N. Maslov KIPT, Academisheskaya Str. 310108 Kharkov, Ukraine A. Bogdanov, A. Potylitsin, I. Vnukov NPI-TPU, Prospekt Lenina, 634050 Tomsk, Russia
a
[email protected] Research under INTAS contract 97-562 b presently at Wayne State University - Cornell, Ithaca NY, USA
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Experimental study of a positron source using channeling
Abstract Axially oriented crystals, penetrated by high energy electrons, are powerful photon sources and, henceforth, intense positron sources. Such kinds of positron sources have been studied experimentally at CERN, during the summers 2000 and 2001, with the tertiary electron beam of the SPS having an energy of 6 and 10 GeV. Four and eight mm thick tungsten crystals and a compound target made of a 4 mm crystal followed by a 4 mm amorphous disk, were used with an orientation along the < 111 > axis. A 20 mm tungsten amorphous target was also used. The positrons were detected by a Drift Chamber, partially immersed in a magnetic field, of 0.1 or 0.4 Tesla, working as a magnetic spectrometer in the positron energy range up to 150 MeV. The magnetic field was parallel to the wires. The positron trajectories were reconstructed in the Drift Chamber and allowed the determination of the energy spectrum and of the angular distribution for all the targets. Significant enhancements were observed for the crystal source when compared to the amorphous one. The gain was larger than 4 for the 4 mm target and larger than 2 for the 8 mm and the compound target when the crystal was aligned with the beam direction, compared to the non-aligned case corresponding to an amorphous target. These results are described after short presentations of the experimental set-up and of the method of track reconstruction.
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Experimental study of a positron source using channeling
INTRODUCTION The objective of the experiment is to measure
the enhancement in positron production when the incident electron beam is in channeling conditions - at glancing angles to the rows- in a crystal. The main physical parameters, which can be measured, are the emission angle and the momentum of the positrons. These quantities are needed to determine the phase space of such positron source for a comparison with the conventional one in the framework of a possible use in the future e+ e; linear colliders.
The interest
a large number of soft photons giving correspondingly
a large number of soft positrons easily captured by the known optical matching devices a thinner thickness for the targets leading to less energy deposition Moreover, the diculties encountered by the conventional devices where excessive heating and mechanical stresses are met brings some additional interest.
We present here: some preliminary results of our experiment RREPS'01
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Experimental study of a positron source using channeling
The experimental conditions An experiment has been carried out during two weeks in July|August 2000, after a calibration run at the end of May 2000. The experiment was resumed in July 2001. The experiment installed on the X5A transfer line of the SPS provided data on the positrons and photons created in the tungsten targets:
a 4 mm thick crystal, a 8 mm thick crystal, a compound target made of a 4 mm crystal followed by a 4 mm thick amorphous disk, an amorphous tungsten target 20 mm thick
The electron incident energy was taken in the range 5 to 40 GeV mainly at 6 and 10 GeV. The positrons were measured in a magnetic spectrometer made of a Drift Chamber partially immersed in a magnetic eld two values of the magnetic eld were used: 1 and 4 kGauss. These eld values allowed to investigate the energy domain up to 80|100 MeV. Data has been taken on:
the Drift Chamber (DC), the positron counters installed on two lateral walls of the DC, with a specic domain of acceptance for each of them, with respect to the positron energy level, the preshower and the calorimeter for the photons.
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Experimental study of a positron source using channeling
The experimental set-up Crystal
Counters 1 0 00 11 00 0 00 1 1100 11 11 00 11 11 00 11 00 00 11 11 1100 00 00 11 1 0 00 11 0 1 00 11 00 11 00 11 00 00 1111 0 1 00 11 00 0 11 1 0 11 00 00 11 00 11 1 00 11 0011 11 00 0 0 1 00 1 11 0 1 00 11 11 1 00 11 00 0 00 11 0 1 1 0
e-
1 0 0 1 0 1 1 0 0 1 1 0 11 00 0 1 0 1 0 1 0 1 00 11 0 1 0 1
Trigger
TDC LeCroy 4291
Discriminator Amplifier Shaper 0.T CRRC2
300 channels
1111111 0000000 0000000 1111111 0000000 1111111 0000000 1111111 0000000 1111111 0000000 1111111 0000000 1111111 0000000 1111111 0000000 1111111
Pentium II Windows NT
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GPIB
Buffer LeCroy 4299
TDC controller LeCroy 4298
CAMAC
CAMAC controller LeCroy 8901A HYTEC LP 1341
CAMAC
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Experimental study of a positron source using channeling
The results obtained with reconstructed positron tracks A reconstruction process, taking into account the actual
magnetic eld distribution in the Drift Chamber, has been operated. Magnetic eld = 1 or 4 kGs as maximum value with fringe eld at the entrance of the Drift Chamber Method of templates (trajectories of determined energy and angle) inuence of interaction processes in the medium is studied geometrical track average track for tracks aected by multiple scattering angular domain: ;5 to 35 (steps of 0:5 ) energy domain: 5 to 150 MeV (steps of 1 MeV ) Parametrisation with 9-degree polynomial y(x)] Coecients are stored in the database x
y
Set of positron tracks with Sketch of the DC with the energy 20 MeV and angle positron counters and the 10 simulated by GEANT. cells near to the lateral walls. Magnetic eld is 1 kGs.
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Experimental study of a positron source using channeling The reconstruction programme makes 2 maps of the functions:
L0(Ei k) =
(1)
X
N1 +N2
j d ; rn j 1 exp ( ; n N1 + N2 n ) L2(Ei k) = (2) N2 1 exp (; j dn ; rn j ) with = 1cm
N2
X n
representing the distance between the simulated tracks of known initial angle and energy and the hitted wires of the DC. Indexes 1 and 2 mean DC1 (part of the DC outside of the magnetic pole) or DC2 (part of the DC inside of the magnetic pole), N | number of hitted wires, = 1 cm | coecient characterising the dimension of the DC cells, dn cm] | distance between the track (Ei k ) and the n-th wire, rn cm] | the radius calculated from TDC value of the n-th wire. k > lim = 5 ! L0 k 7 degree. All results presented for DC magnetic eld 1 kGs.
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Simulation and experiment Events / number of electrons
Blue points | simulation. Black one | experiment. 8 mm crystal, 10 GeV. Energy spectrum. Entries
4728
0.035 0.03
0.025 0.02
0.015 0.01
0.005 0 5
10 15 20 25 30 35 40 45 Energy, MeV
Events / number of electrons
Angular spectrum. Entries
4728
0.05 0.04 0.03 0.02 0.01 0 0
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10
15 20 25 Angle, Degree
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Experimental study of a positron source using channeling
Simulation and experiment Corrected by eciency.
Blue points | simulation. Black one | experiment. 8 mm crystal, 10 GeV. Positrons / number of electrons
Energy spectrum. Entries
8787
0.05 0.04 0.03 0.02 0.01 0 5
10 15 20 25 30 35 40 45 Energy, MeV
Positrons / number of electrons
Angular spectrum. Entries
8787
0.1
0.08 0.06 0.04 0.02 0 0
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10
15 20 25 Angle, Degree
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Experimental study of a positron source using channeling
Comparison data from 2000, 2001 Corrected by eciency. Red points | year 2001. Black one | 2000. 8 mm crystal, 10 GeV. Positrons / number of electrons
Energy spectrum. Entries
10580
0.06 0.05 0.04 0.03 0.02 0.01 0 5
10 15 20 25 30 35 40 45 Energy, MeV
Positrons / number of electrons
Angular spectrum. Entries
10580
0.12 0.1
0.08 0.06 0.04 0.02 0 0
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10
15 20 25 Angle, Degree
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Experimental study of a positron source using channeling
Amorphous 8mm target Events / number of electrons
Blue points | simulation. Black one | experiment. Energy 10 GeV. Energy spectrum. Entries
0.014
2164
0.012 0.01
0.008 0.006 0.004 0.002 0 5
10 15 20 25 30 35 40 45 Energy, MeV
Angular spectrum. Events / number of electrons
0.0225
Entries
2164
0.02
0.0175 0.015
0.0125 0.01
0.0075 0.005
0.0025 0 0
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10
15 20 25 Angle, Degree
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Experimental study of a positron source using channeling
Amorphous 8mm target
Corrected by eciency. Blue points |
simulation. Black one | experiment. E = 10 GeV . Positrons / number of electrons
Energy spectrum. Entries
0.03
3818
0.025 0.02
0.015 0.01
0.005 0 5
10 15 20 25 30 35 40 45 Energy, MeV
Positrons / number of electrons
Angular spectrum. Entries
3818
0.06 0.05 0.04 0.03 0.02 0.01 0 0
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10
15 20 25 Angle, Degree
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Experimental study of a positron source using channeling
Crystal and amorphous targets Corrected by eciency. Red points | Entries
8787
0.05 0.04
Entries
8787
0.1
0.08
0.03
0.06
0.02
0.04
0.01 0 5
Positrons / number of electrons
Positrons / number of electrons
crystal. Black one | amorphous. 8 mm, 10 GeV
0.02 0 0
10 15 20 25 30 35 40 45 Energy, MeV
Energy spectrum
5
10
15 20 25 Angle, Degree
Angular spectrum.
3.5
Entries
12605
3
Ratio
Ratio
Positrons ratio between crystal and amorphous targets 5
Entries
12605
4
2.5 3
2 1.5
2
1 1 0.5 0 5
10 15 20 25 30 35 40 45 Energy, MeV
Energy spectrum
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5
10
15 20 25 Angle, Degree
Angular spectrum. Page 19
Experimental study of a positron source using channeling
Crystal 8 mm & 20 mm amorphous
Events / number of electrons
Blue points | 8mm crystal. Black | 20 mm amorphous. Energy 10 GeV. Energy spectrum. Entries
5263
0.12 0.1
0.08 0.06 0.04 0.02 0 5
10 15 20 25 30 35 40 45 Energy, MeV
Angular spectrum. Events / number of electrons
0.225
Entries
5263
0.2
0.175 0.15
0.125 0.1
0.075 0.05
0.025 0 0
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15 20 25 Angle, Degree
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Experimental study of a positron source using channeling
4 mm targets, 10 Gev, 1 kGs Corrected by eciency. Blue points | 0.025
Entries
11896
Positrons / number of electrons
Positrons / number of electrons
simulation. Black one | experiment. Crystal target Entries
5729
0.06
0.02
0.05 0.04
0.015
0.03
0.01
0.02
0.005 0 5
0.01 0 0
10 15 20 25 30 35 40 45 Energy, MeV
Energy spectrum
5
10
15 20 25 Angle, Degree
Angular spectrum.
0.008
Entries
2308
0.006
2308
0.02
0.005
0.015
0.004 0.003
0.01
0.002
0.005
0.001 10 15 20 25 30 35 40 45 Energy, MeV
Energy spectrum
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0.025
0.007
0 5
0.03
Positrons / number of electrons
Positrons / number of electrons
Amorphous target
0 0
5
10
15 20 25 Angle, Degree
Angular spectrum. Page 21
Experimental study of a positron source using channeling
Crystal / amorphous 4mm targets Corrected by eciency. Red points |
Positrons / number of electrons
0.0225
Entries
5729
0.02
Entries
5729
0.06
0.0175
0.05
0.015
0.04
0.0125 0.01
0.03
0.0075
0.02
0.005
0.01
0.0025 0 5
Positrons / number of electrons
crystal. Black one | amorphous. Energy 10 GeV
0 0
10 15 20 25 30 35 40 45 Energy, MeV
Energy spectrum
5
10
15 20 25 Angle, Degree
Angular spectrum.
6
Entries
8037
5
Ratio
Ratio
Positrons ratio between crystal and amorphous targets Entries
8037
6 5
4 4 3
3
2
2
1 0 5
1 10 15 20 25 30 35 40 45 Energy, MeV
Energy spectrum
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5
10
15 20 25 Angle, Degree
Angular spectrum. Page 22
Experimental study of a positron source using channeling
8 mm targets, 6 GeV, 1 kGs Corrected by eciency. Corrected by eciency. Red points | crystal. Black one | 0.045 0.04 0.035 0.03 0.025 0.02 0.015 0.01 0.005 0 5
Entries
5016
Positrons / number of electrons
Positrons / number of electrons
amorphous.
Entries
0.12
5016
0.1
0.08 0.06 0.04 0.02 0 0
10 15 20 25 30 35 40 45 Energy, MeV
Energy spectrum
5
10
15 20 25 Angle, Degree
Angular spectrum.
4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 5
Entries
10 15 20 25 30 35 40 45 Energy, MeV
Energy spectrum
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Ratio
Ratio
Positrons ratio between crystal and amorphous targets 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 5
Entries
7808
10 15 20 25 30 35 40 45 Energy, MeV
Angular spectrum. Page 23
Experimental study of a positron source using channeling
SUMMARY / CONCLUSIONS the reconstruction programme works the experimental results are in good agreement with the simulations enhancements in e+ production for the 4 mm as for the 8 mm crystal, for 10 and 6 GeV electron beam, are noticeable when comparing crystal and amorphous targets of the same thickness
enhancement somewhat larger than 3, for the 4mm target enhancement somewhat larger than 2, for the 8 mm target
in the regions of interest (in energy and angle) the enhancements show good perspectives for low energy and small angle positrons. This is more pronounced for the 4 mm target Estimation of systematic error (dierence between simulation and experiment, between dierent experiment) is 20 %. Further analysis is necessary for decreasing the systematic error photon detectors used mainly for crystal orientation gave also indications on the enhancement in photon production on the axis The preliminary results represent an analysis of part of the gathered data. The full analysis will be completed in nearest future
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