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