Tagging system for the polarized beams at U-70 accelerator

1. Tagging system for the polarized beams at U-70 accelerator V. V. Abramov1, S. I. Bukreeva1, V. I. Garkusha1, A. Y. Klepikov1,2, A. P. Meschanin1, V. V. Mochalov1,2,S. B.Nurushev1,2, M. B. Nurusheva2, A. V. Ryazantsev1, V. L.Rykov2, S. V. Ryzhikov1, P. A. Semenov1,2, M. N. Strikhanov2, A. N. Vasiliev1,2, A. E. Yakutin1, V. N. Zapolsky1 1Institute For High Energy Physics National Research Centre Kurchatov Institute, Protvino, Moscow region, 142280, Russia 2National Research Nuclear University (Moscow Engineering Physics Institute), Moscow, 115409, Russia ICPPA-2016, Moscow October 13, 2016

2. Outline Tagging system principals Parameters of the polarization measurements Detectors of the tagging system Photodetectors Tagging system readout thoughts

3. Beam tagging system •  - hyperon decay produces the longitudinally polarized proton aligned with proton momentum (in  rest frame) • Protons will have transverse spin component in lab. frame depending on proton emission angle. Therefore the spin states of protons are separated in space • This method was successfully used in E-704 (FNAL) and FODS (IHEP, Protvino) experiments • Base for the beam polarization tagging system

4. Polarization dependence on virtual source vertical position

5. SPASCHARM tagging system • Tagging system similar to the one used in E704. Image of the virtual polarized (anti)proton source in the intermediate focus plane with 1.7 magnification factor will be used to improve polarization detection accuracy • Scintillator hodoscopes in vertical direction will be used to measure position of the virtual source (polarization), horizontal – to measure the beam momentum with a precision of ~1%, which can improve the polarization measurement • POLx tagging station 48 channels of scintillating counters with cross section of 3x4 mm2 covering 70x130 mm2 to measure virtual source position

6. Scintillating counters planes for the SPASCHARM tagging system • Each (plane 70x130) mm2 48 counters 70 mm in length • Trapezium shape to avoid gaps • Tyvek wrapping for efficient light collection 3mm 3mm

7. Photodetectors for tagging system • Traditional PMTs is not always suitable – some of the tagging system part will be situated very close to the dipole magnet or lenses • Hamamatsu MPPC – very good detection efficiancy(50%), reasonable noise (500 kHz), high gain (4x106), can be connected directly to the scintillating counter (3x3 mm2 with fill factor up to 82%) • SensL SiPM – high gain, low noise (300 kHz for 3x3 mm2), compact sizes, lower effeciency 35%, but cheaper

8. Data readout • Read out by fast deep register modules (128 inputs up to 1 us with a step of 5 ns) made by IHEP electronics department • Each event from the tagging system obtained with a minimum bias trigger (beam telescope coincidence) has a high precision time mark to find a relation for the other detector data later and make on-line event selection (software trigger)

9. Conclusion • Beam of the polarised (anti)protons at the beam line 24A at IHEP will be supplied with polarization tagging system to increase the beam use efficiency, beam polarization and reduce systematic errors • Tagging system, consisting of three planes of vertical scintillating hodoscopes and seven planes of horizontal hodoscopes and analyzing magnet will provide the beam polarization measurement with 5% accuracy (down to 1% with good momentum analysis) • Readout of the tagging system electronics with minimum bias trigger reduces the influence of the tagging system to the SPASCHARM DAQ system.