1 yuri shestakov budker institute of nuclear physics novosibirsk, russia tagging system of...
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Yuri Shestakov Budker Institute of Nuclear Physics
Novosibirsk, Russia
Tagging system of almost-real Tagging system of almost-real
photons for photonuclear photons for photonuclear
experiments at VEPP-3experiments at VEPP-3
Tagging system of almost-real Tagging system of almost-real
photons for photonuclear photons for photonuclear
experiments at VEPP-3experiments at VEPP-3
Moscow, 7 October, 2015
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Content
Introduction. Polarized target at VEPP-3. Photodisintegration of tensor polarized deuteron and
almost-real photon approach. Experimental upgrade: system for tagging of almost-real
photons (PTS). Test run at VEPP-3 to check the PTS. New possibilities for photo-nuclear reaction studying at
VEPP-3 with STP.
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VEPP-3 facility
Electron energy 2 GeV
Mean beam current 150 mA
Energy spread 0.05%
Revolution period 248.14 ns
Bunch length 15 cm
Vertical beam size 0.5 mm
Horizontal beam size 2.0 mm
Vertical -function 2 m
Horizontal -function 6 m
Injection beam energy 350 MeV
Injection rate 1.5*109 s-1
VEPP-3 parametersVEPP-3 parameters
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Novosibirsk Deuteron Collaboration
V.F.Dmitriev, A.V.Gramolin, V.N.Kudryavtsev, B.A.Lazarenko, S.I.Mishnev, D.M.Nikolenko, I.A.Rachek, R.Sh.Sadykov, L.I.Shekhtman, Yu.V.Shestakov,
D.K.Toporkov and S.A.Zevakov BINP, Novosibirsk, Russia
R.R.Dusaev, V.V.Gauzshtein and V.N.StibunovTPU, Tomsk, Russia
R.GilmanRutgers University, Piscataway, NJ, USA
R.J.Holt and D.H.PotterveldANL, Argonne, IL, USA
H. de VriesNIKHEF, Amsterdam, The Netherlands
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Liquid nitrogen
Tensor polarizationVector polarization
Cryostat
Turbopump
S1-S5 – superconducting sextupole magnets; MFT – medium field transition unit; SFT – strong field transition unit.
Polarized target :: Atomic Beam Source
Stern-Gerlach method is used to produce polarized atoms.
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What is “almost-real photon” ?
Photo-disintegration of d :: Almost-real photon approach
2 2020 21 22
1 1 3 31 [ (3cos 1) sin 2 cos sin cos2 ]
2 8 82{ }
ZZ H H H H H
d dP T T T
d d
Scattering angle is small -> Q2 close to zero -> almost real photon -> photo-disintegration
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Photo-disintegration of d :: Experimental results
I.A. Rachek et al., Phys.Rev.Lett 98 (2007)182303
Energy of almost-real photons50 – 500 MeV
Further progress in study of photo-nuclear reactions at VEPP-3 is possible with a system for tagging of almost-real photons.
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Tagging of almost-real photons :: The main idea
PTS has three ”warm” dipole magnets (D1,D2,D3) with magnetic field integrals of 0.248, -0.562, and 0.314Tm. The electrons that interact with target and are scattered into a very small angle (< 10) will have lost energy and will be bent away from the orbit of storage ring VEPP-3 at the dipole D2. By placing tracking detectors (GEM1,GEM2,GEM3) outside this dipole to determine the coordinates (X and Y) of these scattered electrons, a spectrometer will be realized.
Internal target
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Electronsandwich
GEMs (tracking detectors)
Dipole magnets of PTS
Storage cell
Atomic beam source
Tagging of almost-real photons :: Top view at the straight section
ABS – atomic beam source; SC – storage cell; D1,D2,D3 – dipole magnets; HF –holding field magnet; CP – croypump; GP – getter pump; QF,QD – VEPP-3 quadrupole magnets; V1,V2 – vacuum valves.
Photonsandwich
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Tagging of almost-real photons :: Receivers of a synchrotron radiation
Intense synchrotron radiation (SR) occurs during the passage of a high-energy electrons beam through a magnetic system of PTS.
Three radiation receivers (SRR1–SRR3 on picture) will be used to absorb the SR.
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Tagging of almost-real photons :: Energy and angular resolutions
Basic causes that affect the resolutions: error in determining the coordinates of the point of
interaction; multiple scattering of electrons on the material of the
vacuum chamber; resolution of the 2D tracking detectors (GEMs).
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Linear polarization of almost-real photons vs. its energy for energy interval covered by the tagging system
0
'
e''
1.
10
0 1.5
1.1% 0.3%
1
(
Result of computer simulation:
for 2.5 mr)e
e
GeV GeV
E
E
mr
E
Tagging of almost-real photons :: Energy and angular resolutions
=> the orientation of scattering planewill be determined with a 100 resolution => it’s possible to select polarized photons
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Tagging of almost-real photons :: Dipole magnets
D1 dipole magnet D2 dipole magnet
D3 dipole magnet
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Tagging of almost-real photons :: Tracking detectors
Detector element (material)
Rad.length, cm
x/X0
Si 300um Copper 5m Kapton 50 m Argon 1cm Triple-GEM detector (5 layers of kapton 50 m, 7 layers of copper 5 m, 7mm of Ar) Light Triple-GEM detector (5 layers of kapton 50 m, 7 layers of copper 1 m, 7mm of Ar)
9.4 1.44 28.57 11762
3.2*10-3
3.5*10-4
1.8*10-4
0.85*10-4
3.4*10-3
1.5*10-3
Front-end electronicsFront-end electronics
3mm3mm
1.5mm1.5mm1.5mm1.5mm
2mm2mm
DriftDriftelectrodeelectrode
GEM1GEM1
GEM2GEM2GEM3GEM3
The use of GEM tracking detectors with thin components will allow reduction of multiple scattering.
Resolution of GEM detectors < 100 µm
ReadoutReadoutboardboard
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Tagging of almost-real photons :: Tracking detectors :: Photo
The detector sensitive area is 160*40 mm2
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The new experimental straight section before the installation at VEPP-3.
In order to verify efficiency of the all components of PTS the experimental straight section was installed at VEPP-3 and the test run with electron beam energy Ee = 600 MeV was carried out.
Tagging of almost-real photons :: Test run at VEPP-3
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To test the PTS a process of producing a single photon on hydrogen (electron
bremsstrahlung) was used. The events were collected by detecting the scattered
electrons in coincidence with emitted photons. For this purpose two sandwiches
were installed at small-angle scattering.
GEANT-4 simulation
X1, X2 – radial coordinates of events into the tracking detectors GEM1 and GEM2.
Experimental data
X1, X2 – radial coordinates of events into the tracking detectors GEM1 and GEM2.
Tagging of almost-real photons :: Test run at VEPP-3
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Energy deposition into the sandwiches as a function of GEMs coordinates
X1, X2 – radial coordinates of events into the tracking detectors GEM1 and GEM2.
Blue points – GEANT-4 simulation.Red points – experimental data.
Electron sandwich
Gamma sandwich
Electron sandwich
Gamma sandwich
Tagging of almost-real photons :: Test run at VEPP-3
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Reconstructed energy of photon
X1, X2 – radial coordinates of events into the tracking detectors GEM1 and GEM2.
Blue points – GEANT-4 simulation.Red points – experimental data.
Tagging of almost-real photons :: Test run at VEPP-3
Initial electron energy – 600 MeV
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Tagging of almost-real photons :: New possibilities
The new research opportunities arise from the installation of PTS:
a complete kinematic reconstruction that permits to make a reliable
rejection of the background processes (in previous experiment
scattered electron was not detected, photon momentum was
reconstructed from reaction products);
an extension of the measurements to higher photon energy (up to 1.5
GeV);
a determination of the linear polarization of photon, thus enabling the
another kind of experiments – double-polarization experiments
(polarized photon + polarized target).
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Tagging of almost-real photons :: Example of future experiment
Deuteron photodisintegration at photon energy of 0.5-1.5 GeV
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Tagging of almost-real photons
THANK YOU !
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Tagging of almost-real photons :: Example of experiment
Deuteron photodisintegration at photon energy 1.0-1.5 GeV