A. Zelenski a , G. Atoian a *, A. Bogdanov b , D.Raparia a , M.Runtso b , D. Steski a , V. Zajic a

1. Precision, Absolute Proton Beam Polarimeter at 200MeV A. Zelenskia, G. Atoiana*, A. Bogdanovb, D.Rapariaa, M.Runtsob, D. Steskia, V. Zajica aBrookhaven National Laboratory, Upton, NY, 11973, USA bMoscow Engineering Physical Institute (MEPHI), Moscow 115409, Russia PSTP-2013

2. Polarization facilities at RHIC. Absolute H-jet polarimeter RHIC pC “CNI” polarimeters RHIC PHENIX STAR BOOSTER 2.5 GeV OPPIS LINAC AGS, 24GeV 200MeV polarimeter AGS pC “CNI” polarimeter G. Atoian 2 9/12/2013

3. Polarized injector, 200MeV LINAC and injection lines Booster OPPIS RFQ 200MeV LINAC 200MeV polarimeter G. Atoian 3 9/12/2013

4. The 200 MeV LINAC Polarimeter Scattered proton proton 200MeV Recoil Atom Target A new polarimeter for absolute proton beam polarization measurements at 200 MeV to accuracy better than ±0.5% has been developed as a part of the RHIC polarized source upgrade. The polarimeter is based on the elastic pC scattering at 16.2° angle, where the analyzing power is large 99.35% and was measured with high accuracy. The elastically and in-elastically scattered protons are clearly identified by the difference in the propagation through variable copper absorber and energy deposition of the stopped protons in the detectors. The 16.2° elastic scattering polarimeter was used for calibration of a high rate inclusive 12° polarimer, which was used for the on-line polarization tuning and monitoring. G. Atoian 4 9/12/2013

5. Cross section and analyzing power for pC scattering at 200 MeV Edward J. Stephenson, 10/22/2009 ~99.35% ~82% ~50mb/sr ~5mb/sr ~12 ~16.2o Measurements of the cross section and analyzing power for proton scattering from 12C at 200 MeV. The blue curves correspond to protons exiting from the ground state of carbon. The green curve corresponds two protons exiting from the first excited state (-4.44MeV). The black curve represents the sum of the two data sets. 9/12/2013 G. Atoian 5

6. GEANT calculation ofpC polarimeter for 200MeV proton beam We have shown the possibility of suppression of an inelastic scattering proton from a carbon by an absorber. Sc1 Sc2 Sc3 C- target P-beam 41mm of Cu Ep=194.3MeV inelastic Ep=198.7MeV elastic 9/12/2013 G. Atoian 6

7. GEANT calculation of pC polarimeter for 200MeV proton beam N, particles stopped in the slice of absorber Energy deposited in the scintillator elastic inelastic inelastic elastic E, MeV A sharp edges promises a good separation of the inelastic scattered proton from an elastic Ratio N(Inelastic)/N(elastic) by the Cu absorber thickness ~41mm with energy threshold ~15MeV is less than 0.5% 9/12/2013 G. Atoian 7 3.7 3.8 3.9 4.0 4.1 4.2 4.4 4.3 L, cm

8. Beam setup of the polarimeter 9/12/2013 G. Atoian 8

9. Polarimeter setup for 200MeV proton beam Horizontal 16.20 polarimeter Horizontal 120 and vertical 16.20 polarimeters Mostly the elastic protons passed through the absorber (41mm) and absorbed into the second scintillator, depositing ~5-40.0MeV of energy. Absorber: Cu from 0 to 38.1 mm (step by 12.7mm) Counters: Sc3 Sc2 Sc1 Absorber: Cu from 0 to 9 mm (step by 1mm) Cu collimator: D=8mm Cu ~5 mm Absorber: Cu from 0 to 1 mm (step by 0.1mm) Fast photomultiplier with fast scintillator BC-404 (decay time ~1.8nsec) gave the output pulse less than 15nsec (rise time ~2.4nsec). Coincidence signal is formed in the vicinity of the detector in the beam line by fast discriminators. Time resolution without amplitude correction is less then 0.5nsec. Motion system 9/12/2013 G. Atoian 9

10. Spectrum of counters and efficiency vs. threshold of discriminator 9/12/2013 G. Atoian 10

11. Systematic error an analyzing power Scattered proton proton 200MeV Recoil Carbon C target The systematic error of the Ay by: • detector alignment 5mm • energy of the beam 2001.0 MeV • size of the scintillators ~10x10mm • multiple scattering in target, vacuum wall and air Is about 0.2 %. 9/12/2013 G. Atoian 11

12. Horizontal scan of the beam by vertical polarimeter By the different targets we can change the rate of the detector almost 4 times. 9/12/2013 G. Atoian 12

13. Systematic error in polarization measurement by beam halo Systematic error an accidental coincidence by: • beam halo (depends on the adjustment of the LINAC) and • the rate of the detector. (By Linac elements and using different targets we can change the rate of the detector almost 4 times). Average counts in the target ‘out’ are less than 1 and target ‘in’ ~250, gave the systematic error ~0.3% Target position ‘OUT’ 9/12/2013 G. Atoian 13

14. 84.2+/-0.5% I(T9)=295mkA (4.9*10^11) 15 min 83.9+/-0.7% 9/12/2013 G. Atoian 14

15. Polarization fluctuation of 200Mev beam (March 1-4, 2013 ~83% 9/12/2013 G. Atoian 15

16. Measured Analyzing Power vs thickness of absorber 9/12/2013 G. Atoian 16

17. Suppression of the inelastic scattering proton to first excited state by absorber Inelastic scattering protons well suppression First excited state drops the analyzing power ~ 2% Prototype of the first excited state (Energy was decreases by the LINAC) Ratio of the rate Sc1*Sc2: R(200)/R(200-4.4) > 10 for the 41mm thick of Cu absorber 9/12/2013 G. Atoian 17

18. Calibration curve of energy monitoring using 16.20polarimeter Difference of the rate in the subsequent detectors of the telescope in both arms was used for the beam energy monitoring and tuning to improve polarization measurement accuracy. The energy calibration 16.20 polarimeter with accuracy better than 0.5 MeV were done by using the magnetic spectrometer and cross-checked at injection to the Booster. Beam energy vs. ratio S3*S1/S2*S1x100 (thickness of absorber 40.1mm) Sc3 Sc2 Sc1 9/12/2013 G. Atoian 18

19. Time chart of energy monitoring using calibration curve Ratio N(Sc1*Sc2) / N(Sc1*Sc3) is simple and stabile monitor of beam energy with accuracy better than 0.5 MeV per tens of pulses. 9/12/2013 G. Atoian 19

20. Horizontal scan and polarization profile of the beam We have a program that makes automatic measurements of a horizontal scan and polarization profile of the beam. 9/12/2013 G. Atoian 20

21. Polarization vs current of the spin rotator Polarization at the horizontal 16.20 polarimeter ~ 80.5% 9/12/2013 G. Atoian 21

22. 16.20 polarimeter used for the determine of analyzing power 120 polarimeter and reference polarization measurement; Rate effect for polarization measurement less 0.2% to 400 event/pulse (~1.3MHz) and the estimated systematic error ~0.3 %; Polarization dependence of gain of PMT and threshold of discriminators are insignificant. Deposited energy on the scintillators more then 10MeV (5-40MeV); Ratio N(Sc1*Sc2)/N(Sc1*Sc3) is simple and stabile monitor of beam energy with accuracy better than 0.5MeV per tens of pulses; We are capable accuracy measurement of horizontal beam and polarization profile. Summery The analyzing power of the elastic scattering proton from 12C is well known with good accuracyand for 16.2 degree scattering angle it is close to 100%. (Phys. Rev. C, Vol. 45 number 2, 504 -1992)We shown possibility of suppression of the inelastic scattering proton from an elastic for 41mm cupper absorber is about 1% ( ~10 times by cross section and more than ~10 times by absorber ). The identified elastic protons were used for polarization measurement. 9/12/2013 G. Atoian 22

23. Backup 9/12/2013 G. Atoian 23

24. Beam setup of 200MeV proton polarimeter (before) pD-polarimeter: • The analyzing power for pD known with good accuracy: A = 0.507 +/- 0.002 (IUCF); • pD polarimeter was used for calibration of the 12 deg. pC polarimeter • The rate - less then 1 event per pulse => In 8 hrs a statistical accuracy about 2%; G. Atoian

25. 25 G. Atoian