Tagging System for Almost-Real Photons in Photonuclear Experiments

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

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. VEPP-3 facility VEPP-3 parameters

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. Polarized target :: Atomic Beam Source Stern-Gerlach method is used to produce polarized atoms. Cryostat Liquid nitrogen Turbo pump S1-S5– superconducting sextupole magnets;MFT– medium field transition unit;SFT– strong field transition unit. Tensor polarization Vector polarization

6. Photo-disintegration of d :: Almost-real photon approach What is “almost-real photon” ? Scattering angle is small -> Q2 close to zero -> almost real photon -> photo-disintegration

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

8. Tagging of almost-real photons :: The main idea Internal target 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 dipoleto determine the coordinates (X and Y)of these scattered electrons, a spectrometer will be realized.

9. Tagging of almost-real photons :: Top view at the straight section Atomic beam source Storage cell GEMs (tracking detectors) Electron sandwich Photon sandwich Dipole magnets of PTS 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.

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. 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. Tagging of almost-real photons :: Energy and angular resolutions Linear polarization of almost-real photons vs. its energy for energy interval covered by the tagging system => the orientation of scattering plane will be determined with a 100 resolution => it’s possible to select polarized photons

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

14. Tagging of almost-real photons :: Tracking detectors Drift electrode 3mm GEM1 1.5mm GEM2 1.5mm GEM3 2mm Front-end electronics Readout board The use of GEM tracking detectors with thin components will allow reduction of multiple scattering. Resolution ofGEM detectors < 100 µm

15. Tagging of almost-real photons :: Tracking detectors :: Photo The detector sensitive area is 160*40 mm2

16. Tagging of almost-real photons :: Test run at VEPP-3 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.

17. Tagging of almost-real photons :: Test run at VEPP-3 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 andGEM2. Experimental data X1,X2 – radial coordinates of events into the tracking detectors GEM1 andGEM2.

18. Tagging of almost-real photons :: Test run at VEPP-3 Energy deposition into the sandwiches as a function of GEMs coordinates X1,X2 – radial coordinates of events into the tracking detectors GEM1 andGEM2. Blue points – GEANT-4 simulation. Red points – experimentaldata. Gamma sandwich Electron sandwich Gamma sandwich Electron sandwich

19. Tagging of almost-real photons :: Test run at VEPP-3 Reconstructed energy of photon X1,X2 – radial coordinates of events into the tracking detectors GEM1 andGEM2. Blue points – GEANT-4 simulation. Red points – experimentaldata. Initial electron energy – 600 MeV

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

22. Tagging of almost-real photons THANK YOU !

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