Method of the photon beam linear polarization measurement using asymmetry ofthe recoil electrons in the triplet photoproduction process
We present a method of the photon beam linear polarization measurement which have been proposed and developed in Kharkov Institute of Physics and Technology and based on the using of the asymmetry of the recoil electrons in reaction g+e⁻→e⁻+e⁺+e⁻. It was found that asymmetry of the process has enoug...
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| Опубліковано в: : | Вопросы атомной науки и техники |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2003
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| Цитувати: | Method of the photon beam linear polarization measurement using asymmetry ofthe recoil electrons in the triplet photoproduction process / V.F. Boldyshev, E.A. Vinokurov, V.B. Ganenko, Yu.P. Peresunko, I.N. Shapoval // Вопросы атомной науки и техники. — 2003. — № 2. — С. 89-93. — Бібліогр.: 14 назв. — англ. |
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Boldyshev, V.F. Vinokurov, E.A. Ganenko, V.B. Peresunko, Yu.P. Shapoval, I.N. 2017-01-06T08:42:53Z 2017-01-06T08:42:53Z 2003 Method of the photon beam linear polarization measurement using asymmetry ofthe recoil electrons in the triplet photoproduction process / V.F. Boldyshev, E.A. Vinokurov, V.B. Ganenko, Yu.P. Peresunko, I.N. Shapoval // Вопросы атомной науки и техники. — 2003. — № 2. — С. 89-93. — Бібліогр.: 14 назв. — англ. 1562-6016 PACS: 29.27.Hj 29.90. +r https://nasplib.isofts.kiev.ua/handle/123456789/110711 We present a method of the photon beam linear polarization measurement which have been proposed and developed in Kharkov Institute of Physics and Technology and based on the using of the asymmetry of the recoil electrons in reaction g+e⁻→e⁻+e⁺+e⁻. It was found that asymmetry of the process has enough big value and weakly depend on photon energy in very wide range. So this method allows to measure the linearly polarization in the wide energy range from some tens MeV and up to TeV photon energies. The schemes of the existing polarimeters and effects distorting the measurement are considered. Розглянуто метод вимірювання лінійної поляризації фотонних пучків, якій був запропоновано в Харківському фізіко-технічному інституті. Метод засновано на вимірюванні асиметрії електронів віддачі в реакції фотоутворення електрон-позитронних пар на електронах, g+e⁻→e⁻+e⁺+e⁻. Азимутальна асиметрія даного процесу має достатньо велику величину і слабко залежить від енергії фотонів в дуже широкому діапазоні енергій, від кількох десятків МеВ і до ТеВ. Розглядаються схеми поляриметрів, що існують. Показано, що при вимірюванні поляризації необхідно брати до уваги ефекти багатократного розсіяння електронів віддачі, а також утворення d-електронів частками пари. Ці ефекти значно зменшують величину азимутальної асиметрії, що спостерігається. Рассматривается метод измерения линейной поляризации фотонных пучков, который был предложен и развит в Харьковском физико-техническом институте. Метод основан на измерении азимутальной асимметрии электронов отдачи в реакции фоторождения электрон-позитронных пар на электронах, g+e⁻→e⁻+e⁺+e⁻. Асимметрия данного процесса имеет достаточно большую величину и слабо зависит от энергии фотонов в широком диапазоне энергий. Это дает возможность измерять линейную поляризацию фотонов данным методом в диапазоне энергий от нескольких десятков МэВ до ТэВ. Рассматриваются схемы существующих поляриметров. Показано, что при измерении поляризации фотонов необходимо учитывать эффекты многократного рассеяния электронов отдачи и рождения d-электронов частицами пары. Данные эффекты существенно уменьшают наблюдаемую величину азимутальной асимметрии. Authors thank members of this group W. Briscoe, G. Feldman and G. O'Rielly for interest to the work, the given information on the first carried out experiments and fruitful discussions of the present work. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Experimental methods and processing of data Method of the photon beam linear polarization measurement using asymmetry ofthe recoil electrons in the triplet photoproduction process Метод вимірювання лінійної поляризації фотонних пучків по асиметрії електронів віддачі в процесі фотоутворення триплетів Метод измерения линейной поляризации фотонных пучков по асимметрии электронов отдачи в процессе фоторождения триплетов Article published earlier |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| title |
Method of the photon beam linear polarization measurement using asymmetry ofthe recoil electrons in the triplet photoproduction process |
| spellingShingle |
Method of the photon beam linear polarization measurement using asymmetry ofthe recoil electrons in the triplet photoproduction process Boldyshev, V.F. Vinokurov, E.A. Ganenko, V.B. Peresunko, Yu.P. Shapoval, I.N. Experimental methods and processing of data |
| title_short |
Method of the photon beam linear polarization measurement using asymmetry ofthe recoil electrons in the triplet photoproduction process |
| title_full |
Method of the photon beam linear polarization measurement using asymmetry ofthe recoil electrons in the triplet photoproduction process |
| title_fullStr |
Method of the photon beam linear polarization measurement using asymmetry ofthe recoil electrons in the triplet photoproduction process |
| title_full_unstemmed |
Method of the photon beam linear polarization measurement using asymmetry ofthe recoil electrons in the triplet photoproduction process |
| title_sort |
method of the photon beam linear polarization measurement using asymmetry ofthe recoil electrons in the triplet photoproduction process |
| author |
Boldyshev, V.F. Vinokurov, E.A. Ganenko, V.B. Peresunko, Yu.P. Shapoval, I.N. |
| author_facet |
Boldyshev, V.F. Vinokurov, E.A. Ganenko, V.B. Peresunko, Yu.P. Shapoval, I.N. |
| topic |
Experimental methods and processing of data |
| topic_facet |
Experimental methods and processing of data |
| publishDate |
2003 |
| language |
English |
| container_title |
Вопросы атомной науки и техники |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| format |
Article |
| title_alt |
Метод вимірювання лінійної поляризації фотонних пучків по асиметрії електронів віддачі в процесі фотоутворення триплетів Метод измерения линейной поляризации фотонных пучков по асимметрии электронов отдачи в процессе фоторождения триплетов |
| description |
We present a method of the photon beam linear polarization measurement which have been proposed and developed in Kharkov Institute of Physics and Technology and based on the using of the asymmetry of the recoil electrons in reaction g+e⁻→e⁻+e⁺+e⁻. It was found that asymmetry of the process has enough big value and weakly depend on photon energy in very wide range. So this method allows to measure the linearly polarization in the wide energy range from some tens MeV and up to TeV photon energies. The schemes of the existing polarimeters and effects distorting the measurement are considered.
Розглянуто метод вимірювання лінійної поляризації фотонних пучків, якій був запропоновано в Харківському фізіко-технічному інституті. Метод засновано на вимірюванні асиметрії електронів віддачі в реакції фотоутворення електрон-позитронних пар на електронах, g+e⁻→e⁻+e⁺+e⁻. Азимутальна асиметрія даного процесу має достатньо велику величину і слабко залежить від енергії фотонів в дуже широкому діапазоні енергій, від кількох десятків МеВ і до ТеВ. Розглядаються схеми поляриметрів, що існують. Показано, що при вимірюванні поляризації необхідно брати до уваги ефекти багатократного розсіяння електронів віддачі, а також утворення d-електронів частками пари. Ці ефекти значно зменшують величину азимутальної асиметрії, що спостерігається.
Рассматривается метод измерения линейной поляризации фотонных пучков, который был предложен и развит в Харьковском физико-техническом институте. Метод основан на измерении азимутальной асимметрии электронов отдачи в реакции фоторождения электрон-позитронных пар на электронах, g+e⁻→e⁻+e⁺+e⁻. Асимметрия данного процесса имеет достаточно большую величину и слабо зависит от энергии фотонов в широком диапазоне энергий. Это дает возможность измерять линейную поляризацию фотонов данным методом в диапазоне энергий от нескольких десятков МэВ до ТэВ. Рассматриваются схемы существующих поляриметров. Показано, что при измерении поляризации фотонов необходимо учитывать эффекты многократного рассеяния электронов отдачи и рождения d-электронов частицами пары. Данные эффекты существенно уменьшают наблюдаемую величину азимутальной асимметрии.
Authors thank members of this group W. Briscoe,
G. Feldman and G. O'Rielly for interest to the work, the
given information on the first carried out experiments
and fruitful discussions of the present work.
|
| issn |
1562-6016 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/110711 |
| citation_txt |
Method of the photon beam linear polarization measurement using asymmetry ofthe recoil electrons in the triplet photoproduction process / V.F. Boldyshev, E.A. Vinokurov, V.B. Ganenko, Yu.P. Peresunko, I.N. Shapoval // Вопросы атомной науки и техники. — 2003. — № 2. — С. 89-93. — Бібліогр.: 14 назв. — англ. |
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METHOD OF THE PHOTON BEAM LINEAR POLARIZATION
MEASUREMENT USING ASYMMETRY OF THE RECOIL ELECTRONS
IN THE TRIPLET PHOTOPRODUCTION PROCESS
V.F. Boldyshev, E.A. Vinokurov, V.B. Ganenko, Yu.P. Peresunko, I.N. Shapoval
National Science Center “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine
e-mail: ganenko@kipt.kharkov.ua
We present a method of the photon beam linear polarization measurement which have been proposed and
developed in Kharkov Institute of Physics and Technology and based on the using of the asymmetry of the recoil
electrons in reaction γ+e−→ e−+e++e−. It was found that asymmetry of the process has enough big value and weakly
depend on photon energy in very wide range. So this method allows to measure the linearly polarization in the wide
energy range from some tens MeV and up to TeV photon energies. The schemes of the existing polarimeters and
effects distorting the measurement are considered.
PACS: 29.27.Hj 29.90. +r
1. INTRODUCTION
Beams of the polarized photons have wide prospects
of application in the physics of electromagnetic
interactions of nucleus and hadrons. The most of
modern experiments in the field of photoproduction of
baryon resonances, for example, demand for the
restoration of the set of spiral amplitudes of the studied
processes an information which can be received only
with help of polarized photon beams. In experiments of
such type the degree of the photon polarization should
be known with high accuracy.
One of the most perspective method for linearly
photon polarization measurements have been proposed
and developed in Kharkov Institute of Physics and
Technology (KIPT) during last thirty years. It have been
pointed out that process of the triplet photoproduction
)()()1()()( +
++−
−+−→−+ pepepepekγ (1)
has rather large asymmetry of the recoil electrons yield
which furthermore weakly depend on photon energy in
very wide energy range. So it was presupposed this
process may be used for measuring photon polarization
in wide energy interval, from several tens MeV and up
to about TeV. Subsequently some photon polarimeters
on the base of this method have been constructed in a
number of scientific centers.
2. GENERAL CHARACTERISTICS
OF THE METHOD
Process of the triplet photoproduction (1) is
attractive to use for measurement of the linear
polarization of the photons because it is pure
electrodynamical process with very convenient for
measurement signature. All its characteristics can be
calculated with necessary accuracy. In the lowest order
of perturbation theory this process with taking into
account effects of final electron’s identity, is described
by 8 Feynman diagrams. For the case of linearly
polarized photon it was first theoretically investigated in
the Ref. [1,2]. There was shown that differential by
azimuthal angle φ1 cross section of the recoil electron
yield has following form
)12cos1()(
12cos)()(
1
2
ϕσ
ϕσσϕ
σπ
Λ−=
=−=
Pt
lPt
d
d
, (2)
where σ(t) is the total cross section of the process, σ(l) is
the part of cross section which depends on polarization,
P is degree of photon polarization, Λ=σ(l)/σ(t) is
analyzing power of the process.
In Ref. [3,4,5] it was shown that at photon energy
ω>20 mc2 influence of the identity effects may be
neglected and considered process with accuracy better
then 2% can be described by two Feynman diagrams.
The depending on photon polarization part of the cross
section σ(l) has been calculated in the [1] for different
values of photon energy. Calculations were carried out
with using of the technique which has been developed
by V.N. Baier et.al. [6] where the total cross sections for
different processes of pair production has been
considered. It was shown that with increasing the
photon energy the total cross section σ(t) grows from
1.187 mb at ω=20mc2 till 8.76 mb at ω=1000mc2 but
asymmetry slowly decreases, respectively, from
Λ=0.275 up to Λ=0.172 and even at asymptotically high
energy of photon 422)( cmpks > >+= the azimuthal
asymmetry of the yield of recoil electrons is Λ≈0.14.
These estimations are obtained in the assumption that all
recoil electrons can be registered. In the experiment it
can be reliably measured only recoil electrons with
momentum which exceeds some value q0≈1mc. The
analytical expressions for differential by the value of
transferred momentum X= -q2= -(p-p1)2 cross section
dσ(l)/dX and dσ(t)/dX has been obtained in the Ref. [2].
By the numerical integration of the obtained expressions
for different values of q0 from q0=0.05 MeV/c till
q0=1.25 MeV/c it was shown that introduction of the
threshold on registration of the recoil electron
momentum q0 leads to insignificant reduction
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2003, № 2.
Series: Nuclear Physics Investigations (41), p. 89-93. 89
asymmetry but to the fast decreasing cross section of the
process.
Further in KIPT the detailed analysis of the triplet
photoproduction process by linearly polarized photons
was carried. Results of this analysis were published in
review [5]. With the help of helium streamer chamber in
KIPT for the first time the linear polarization of the
coherent Bremsstruhlung photons with energy 60 MeV
has been measured by this method [5,7,8].
3. PECULIARITY OF THE PRACTICAL
REALIZATION
The general behavior of the cross section and
asymmetry of the process (1) can be characterized as
follows: almost in all physical regions of the
kinematical variables changing azimuthal asymmetry of
the recoil electrons is about Λ≈0.1. Near the border of
physical region asymmetry sharply grows up to values
Λ≈1. There are many offered ways of increasing
observable azimuthal asymmetry of recoil electrons
yield. As it is shown in [9] the selection events of the
triplet photoproduction with invariant mass of the pair
2)( ++−=∆ pp in the vicinity of limiting value
m2=∆ increases the asymmetry up to value Λ≈0.95.
Possible design of the polarimeter in which selection of
events with Δ≈2m would be made with the help of a
magnetic spectrometer and the wire chamber has been
offered in Ref. [10]. Detecting recoil electrons also
would be carried out with the help of the wire chamber.
More simple and effective method of increasing
observable asymmetry was proposed by Japanese group
[11]. This method is based on observation that for
events of triplet photoproduction with opening angle of
e+e- pair θ±≈5m/ω asymmetry of recoil electron’s yield
sharply grows. This method is applicable at energy of
photons ω less then several GeV because at large
energies there are the difficulties connected with too
small necessary angles of the e+e- pair collimation.
At the very large photon energies the method of
increasing observable asymmetry suggested in the
Ref. [12] may be used. In this work it was shown that
asymmetry of recoil electron’s yield is maximal when
electron and positron of the e+e- pair had identical
energies. In the limit of the asymptotically high photon
energy azimuthal asymmetry of recoil electron’s yield
under selection such an event is increased in 1.8 times
in comparison with asymmetry without such selection.
As selection of events on energy of the components of
e+e- pairs can be easily realized with the help of a
magnetic spectrometer even at very high photon energy
this method is perspective at ω> 10 GeV.
Typical arrangement of the polarimeter based on the
effect of triplet photoproduction is shown in the Fig. 1.
The recoil electrons are detected by the scintillation
counters C2, C1 is polyethylene plate with some certain
thickness. This thickness is defined from condition that
electrons with momentum q<q0 will be absorbed in this
plate. Background of the charged particles presented in
the beam is eliminated by the veto counter V. The pair
fragments are detected by the counters P1 and P2 in
coincidence with a recoil electron. Each of the vertical
counters V1 and V2 and of horizontal counters H1 and H2
subtends azimuthal angles ϕ∆± around directions
φ=0, φ=π and φ=π/2, φ=3π/2, accordingly.
In real experiment the photon beam cannot be
focused in one point on a target and we shall assume
that the density of probability of distribution of photons
at crossing a target has Gauss form with dispersion ρ:
dxdy
yx
dxdyyxF )exp(
1
),( 2
22
2 ρπ ρ
+
−= . (3)
Let the triplet is created in the point A with polar
coordinates r and α and recoil electron is emitted under
azimuthal angle φ1 and it reaches counter in the point B
with coordinates R, φ. One can see that angles φ1 and φ
are connected as following
)cos(2
)cos(2)2cos()2cos(
)12cos( 22
22
αϕ
αϕϕα
ϕ
−−+
+−+
=
rRRr
rRRr
.(4)
If one substitutes formula (4) into the (2) and averages
result with distribution of photons (3) one can obtain
ϕρ+ρ−Λ−σ=
ϕ
σ
π
)2cos()(11)(
2
1
4
4
2
2
R
O
R
Pt
d
d
. (5)
Thus one con see that for good enough collimated
photon beam (ρ/R<<1) it is possible to neglect
influence of the photon beam’s initial size.
Integrating expression (5) on an azimuthal angle φ
within the limits of capture of each of detectors H1, H2
and V1, V2, we shall receive for number NH of recoil
electrons achieved horizontal H1, H2 and vertical V1,V2
counters:
( ))2sin(22
21
ϕϕσ ∆Λ−∆=+= PtCNNN
HHH
,
( ))2sin(2221 ϕϕσ ∆Λ+∆=+= PtCNNN VVV . (6)
Here C is product of the number of electrons
corresponding to the unit of the area of a target, on
number of photons during time of exposition. Thus, the
degree of polarization P can be determined from
experimentally measured asymmetry as follows:
HV
HV
NN
NN
K
P
+
−
∆Λ
=
)(
1
ϕ
. (7)
Here
ϕ
ϕ
ϕ
∆
∆
=∆
2
)2sin(
)(K is geometrical factor of the
device, Λ is theoretically calculated asymmetry at P=1.
It is easy to see, that the geometrical factor )( ϕ∆K
increases with reduction of angular capture of counters
Δφ. However figure of merit ∑Λ=∆ iNF 2)( ϕ has a
maximum at 78.662 ≈∆ ϕ . Therefore such value Δφ
should be used for measurement of polarization of
photon beams with low intensity.
90
C2C1
P2
P1
CollimatorTarget
V
γ
e-
e+
e-
Target
H2 H1
V2
V1
∆ ϕ α
A
O
B
∆ ϕ
ϕ 1 ϕ
y
x
Fig. 1. Principle scheme of the polarimeter. Side view
(top) and view along the beam (bottom)
In experiment [13] the CBR photon beam with
energy 240 … 600 MeV has been used. Asymmetry of
recoil electrons for the cases when opening angle of the
pair was less then 3.5° and 0.7° has been measured.
Analyzing power for these cases has been calculated
with taking into account effects of multiple scattering.
Expected asymmetry, as the product of this analyzing
power and polarization of photon, calculated on the base
of Uberall-Diamrini theory was obtained. Experi-
mentally observed asymmetry was in consistence with
this value, but statistics was not enough for detailed
comparison.
The test experiments [14], which have been carried
out by GWU group on the LEGS facility with Compton
backscattered photon beam (polarization ~95%), shown
that measured asymmetry is less then it is predicted by
the theory for pure process of triplet photoproduction.
The general reasons of this phenomenon are clear–
multiple scattering of low-energy recoil electrons in
substance of a target and in an air should reduce
observable azimuthal asymmetry of their yield. Besides
in considered experiment it is impossible to distinguish
process of photoproduction e+e- pair on electron and
process of photoproduction e+e- pair on nuclei with
subsequent knocking-on δ-electrons by fast components
of created e+e- pair. It is obvious that angular
distribution of emitting δ-electrons has not any
azimuthal asymmetry and contribution of such events
leads to reduction observable azimuthal asymmetry.
To receive necessary values of effective cross
section Σeff and effective asymmetry Λeff, the program of
numerical simulation of all electromagnetic processes
taking place in experimental installation during
measurement of the photon beam of polarization has
been developed. This program was created on the basis
of the known package GEANT which is directed on
numerical simulation of processes taking place in
detectors of modern physical facilities. However, there
is not code for generation of events of photoproduction
e+e- pair on electrons in the GEANT. Therefore program
GEANT has been modified as follows: case of approach
of event of photoproduction e+e- pairs among all other
possible events was determined in GEANT environment
as usually. After an entrance in a code of generation of
event of photoproduction e+e- pairs on atom with charge
Z it is sampled or event of a triplet photoproduction
with three final particles (e+e- pair and recoil electron),
or described in GEANT event of e+e-pair
photoproduction with two final particles. These events
were generated with probability
),(/),( 0 ZqZ pairtr ωσωσ and with probability
),(/),(1 0 ZqZ pairtr ωσωσ− , accordingly. Here
),( 0qtr ωσ is the total cross section of the triplet
production with minimal transferred momentum q0 by
photon with energy ω; ),( Zpair ωσ is total cross
section of production e+e- pair by photon with energy ω
on atom with charge Z. Generation of kinematical
variables of produced triplet and also calculation of
cross section ),( 0qtr ωσ were carried out with help of
code BASE/SPRING [14], which takes into account all
8 Feynman diagrams describing this process.
As an illustration of the importance of effects of
multiple scattering and of δ-ray knocking on in Fig. 2
the initial momentum-angular distribution of recoil
electrons, which are emitted during triplet
photoproduction processes in the target is shown. In the
Fig. 3 the analogous distribution for all charged
particles reached counters V1, V2, H1, H2 is shown.
One can see that specified effects lead to
deformation of initial angular-momentum distribution in
the region of measuring. This deformation is especially
increasing for region of small momenta of recoil
electrons. So to minimize this effect, the recoil counters
contain a layer C1 of a polyethylene film which absorbs
electrons with a momentum, less then some q0.
In order to increase value of the experimental
asymmetry it was investigated the possibility to use for
this goal the information about spectral characteristics
of the particles detected by the recoil counters. Because
scintillators have linear dependence between the
deposited in them energy of ionizing particles and
number of radiated due to scintillations photons, in
experiment spectrum of the particles reached detectors
can be measured. Therefore the formula (7) for
definition of the photon beam polarization degree
should be changed as follows:
91
Fig. 2. Original momentum (1<q<10MeV/c) and
polar angle (0°<θ <60°) distribution of produced in the
target recoil electrons. Photon energy ω=2.5 GeV
Fig. 3. Momentum (1<q<10 MeV/c) and polar
angle (0°<θ <60°) distribution of charged particles,
reached recoil counters. Photon energy ω=2.5 GeV
HV
HV
S SS
SS
K
P
+
−
∆Λ
=
)(
1
ϕ
, (8)
where SV, SH are number of counts of vertical and
horizontal scintillators with for given value of the
deposited in them energy, accordingly, ΛS is
theoretically calculated asymmetry for that case
1)(,1 =∆= ϕKP .
Results of the calculations are depicted in Fig. 4.
Calculations are carried out for the case of photon
energy ω=2.5 GeV and for different values of the
collimation angles. Target is a polystyrene with
thickness 1 mm. Recoil detectors consist of
polyethylene film C1 of 0.25 mm thickness and
scintillation counter C2 on the base of polystyrene with
thickness 3 mm. Histograms (1) correspond to (SV+SH)
and histograms (2) (SV-SH)×5 versus deposited energy
E. One can see that it is reasonable to consider as
observable asymmetry instead of ratio (8) for each
channel of deposited energy the following integrated
characteristic:
=ϕ∆Λ=Λ )()()( 0
int
0 KEE S
obs
S
( )
( )∫
∫
+
−
=
max
0
max
0
)()(
)()(
E
E
HV
E
E
HV
ESESdE
ESESdE
,
(9)
where integration carried out from given deposited
energy E0 and up to maximal deposited energy Emax.
Fig. 4. Calculated spectra of the particles versus of
the deposited energy E (see text). No collimation (top),
collimation angle of the e+e- pair θc=2 mrad (middle),
collimation angle θc=1 mrad (bottom)
This characteristic is shown in Fig. 5 for different
collimation angles. One can see that background
processes (multiple scattering and δ-electrons)
92
decreases the experimentally measured asymmetry in
polarimeter of this type up to very small value ~2-5%.
Selection on the deposited energy give a chance to
increase considerably its value in principle up to 20-
30%. But at large values E0 the statistical errors are too
increase and optimal is value E0≈0.5 MeV, where at the
collimation of the e+e- pairs in angle ~1 mrad one can
obtain asymmetry ~0.1.
Fig. 5. The observed asymmetry )( 0Eobs
SΛ for
different collimation angles of the e+e- pairs θc: 1–
θc=1 mrad; 2- θc=2 mrad; 3– no collimation
4. CONCLUSIONS
Thus the carried out consideration shows that
method of linear polarization of the high-energy
photons measurement based on triplet photoproduction
process is the only one from other methods known now,
which is suitable in wide region of the photon energies
from some tens MeV and up to asymptotically high
energies.
The program developed now on the basis of package
GEANT takes into account the contribution of all basic
electromagnetic processes, which take place in
experimental device during measurement, and allows
calculate all characteristics of the response of detectors,
which are necessary for measurements.
Necessary stage of the method development is
realization of a series of test experiments with
measurement of linear polarization of photon beams on
accelerators, which have photon beams with well-
known polarization. Such experiments are planned in
the near future by group of University G. Washington,
Washington, USA.
Authors thank members of this group W. Briscoe,
G. Feldman and G. O'Rielly for interest to the work, the
given information on the first carried out experiments
and fruitful discussions of the present work.
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94
National Science Center “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine
PACS: 29.27.Hj 29.90. +r
OF THE METHOD
4. CONCLUSIONS
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