1. 1 Yuri Shestakov Budker Institute of Nuclear Physics Novosibirsk, Russia Tagging system of almost-real photons for photonuclear experiments at VEPP-3 Moscow, 7 October, 2015

2. 2 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.

3. 3 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*10 9 s -1 VEPP-3 parameters

4. 4 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.Stibunov TPU, Tomsk, Russia R.Gilman Rutgers University, Piscataway, NJ, USA R.J.Holt and D.H.Potterveld ANL, Argonne, IL, USA H. de Vries NIKHEF, Amsterdam, The Netherlands

5. 5 Liquid nitrogen Tensor polarization Vector polarization Cryostat Turbo pump 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.

6. 6 What is “almost-real photon” ? Photo-disintegration of d :: Almost-real photon approach Scattering angle is small -> Q 2 close to zero -> almost real photon -> photo-disintegration

7. 7 Photo-disintegration of d :: Experimental results I.A. Rachek et al., Phys.Rev.Lett 98 (2007)182303 Energy of almost-real photons 50 – 500 MeV Further progress in study of photo-nuclear reactions at VEPP-3 is possible with a system for tagging of almost-real photons.

8. 8 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 (< 1 0 ) 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

9. 9 Electron sandwich 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. Photon sandwich

10. 10 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.

11. 11 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).

12. 12 Linear polarization of almost-real photons vs. its energy for energy interval covered by the tagging system Tagging of almost-real photons :: Energy and angular resolutions => the orientation of scattering plane will be determined with a 10 0 resolution => it’s possible to select polarized photons

13. 13 Tagging of almost-real photons :: Dipole magnets D1 dipole magnet D2 dipole magnet D3 dipole magnet

14. 14 Tagging of almost-real photons :: Tracking detectors Detector element (material) Rad.leng th, cm x/X0 Si 300um Copper 5  m 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 electronics 3mm 1.5mm 1.5mm 2mm Driftelectrode GEM1 GEM2 GEM3 The use of GEM tracking detectors with thin components will allow reduction of multiple scattering. Resolution of GEM detectors < 100 µm Readoutboard

15. 15 Tagging of almost-real photons :: Tracking detectors :: Photo The detector sensitive area is 160*40 mm 2

16. 16 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 E e = 600 MeV was carried out. Tagging of almost-real photons :: Test run at VEPP-3

17. 17 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

18. 18 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

19. 19 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

20. 20 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).

21. 21 Tagging of almost-real photons :: Example of future experiment Deuteron photodisintegration at photon energy of 0.5-1.5 GeV

22. 22 Tagging of almost-real photons THANK YOU !

23. 23 Tagging of almost-real photons :: Example of experiment Deuteron photodisintegration at photon energy 1.0-1.5 GeV