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RHIC pC Polarimeters in Run9: Performance and Issues

RHIC pC Polarimeters in Run9: Performance and Issues. A.Bazilevsky for the RHIC CNI Group Polarimetry Worshop BNL, July 31, 2009. 6. 1. 2. 5. 3. 4. Ultra thin Carbon ribbon Target (5 m g/cm 2 ). pC: goals/strategy. 18cm. Polarization measurements for experiments Target Scan mode

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RHIC pC Polarimeters in Run9: Performance and Issues

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  1. RHIC pCPolarimeters in Run9: Performance and Issues A.Bazilevsky for the RHIC CNI Group PolarimetryWorshop BNL, July 31, 2009

  2. 6 1 2 5 3 4 Ultra thin Carbon ribbon Target (5 mg/cm2) pC: goals/strategy 18cm • Polarization measurements for experiments • Target Scan mode • Provides polarization at beam center, polarization profile, average polarization over profile • 10-30 sec per measurement • For stat. precision 2-3% • 4-5 measurements per fill, per ring • Controls polarization decay vs time in a fill • Polarization profile, both vertical and horizontal • Normalized to HJet measurements over many fills • Knowledge on polarization profile in one transverse direction is required • Fill-by-fill polarization • Knowledge on polarization profile in both transverse directions is required • Feedback for accelerator experts • Beam emittance measurements, bunch-by-bunch • Polarization • Polarization profile, both vertical and horizontal • Polarization at injection (and polarization loss in transfer) • Polarization on the ramp (and polarization loss during ramp) Si strip detectors (TOF, EC)

  3. 6 1 2 5 3 4 Ultra thin Carbon ribbon Target (5 mg/cm2) pC in Run9 18cm Two independent polarimeters in each ring (but using the same DAQ) 12 carbon targets in each polarimeter (6 vertical and 6 horizontal) 6 detectors in each polarimeter 3 types of detectors: “BNL strip”: 12 strip in each detector Test Detector1: “Hamamatsu strip”: 12 strip in each of 2 900detectors (blue2) Test Detector2:“Hamamatsu single”: 2 pads in each of 2 900 detector (yellow2) Si strip detectors (TOF, EC)

  4. Overall Performance • Great efforts for polarimeter upgrade led by A.Zelenski finished on time by Run9: two independent polarimeters in each ring • Very important precise cross check for pC measurements (comparison to HJet is much less precise) • ~ Simultaneous measurements of polarization profile in both trans. directions • Twice more targets – enough for the half a year long Spin Run • New detectors tested (see talk by B.Morozov) • No major issues/complains from operation by MCR • Smooth performance • … But encountered serious systematic effects

  5. Hjet / pC-Blue vs fill(online values) s=200 GeV HJet/pC ~ Const Within (large) fill-by-fill stat. errors (of HJet)

  6. Hjet / pC-Yellow vs fill(online values) s=200 GeV HJet/pC ~ Const Within (large) fill-by-fill stat. errors (of HJet)

  7. Hjet / pC vs period(online values) Periods defined by target change in any of polarimeters: HJet Again no problems seen on the level of (still sizable) stat. errors

  8. Response to Alphas 241Am: 5.486 MeV Example: Blue1 Feb Apr May Jun Jul On the average, energy calibration (response to alphas) is stable within <2%

  9. Response to Carbon MEtof2 ToF vs E Up to 20% drop in Run9! ~10% drop in Run8

  10. Energy and ToF correction(before Run9) Fit to kinematical curve for C (C-mass)  energy correction (in terms of “dead layer”) and t0 correction

  11. “Dead Layer” Run5: 40-55 g/cm2 Run6: 70-80 g/cm2 Run8: 75-90 g/cm2 Run9: 55-75 g/cm2

  12. T0 • ToF offset drifts by ~3-6 ns! • 1 ns change is equivalent to “DeadLayer”~5 g/cm2 • Is it just a fit problem (correlation between “DL” and T0)? • If ~20% change in reconstructed C-mass corresponded to shift in energy scale it would mean ~20% change in asymmetry, which is not confirmed by the comparison with Hjet  T0 as measured by the system does drift! • Need to monitor T0 • Simple suggestion (by Gregor Atoyan and Boris Morozov): install photon detector – installed in Run9 but has not been well tested

  13. Rate “problems” s=200 GeV In “banana” cut: Run9-250 GeV: up to 150 kHz/strip Run9-100 GeV: up to 100 kHz/strip Run8-100 GeV: up to 50 kHz/strip Run6-100 GeV: up to 30 kHz/strip Effectively rates are twice higher (in the ToF-Energy window at the entrance of WFD)

  14. pC Monitoring with pulser ToF Generator pulses Blue1 Carbon Ekin

  15. pC Monitoring with pulser Low rate example: 10429.013 20 kHz/strip High rate example: 10346.007 100 kHz/strip Event rate vs time Pulse rate vs time Pulse amplitude vs time Pulse ToF vs time

  16. pC Monitoring with pulser Run 10450.116 110 kHz/strip Pulser Amplitude distribution No Rate High Rate

  17. Rate effects: Mass vs Rate Mass Rate Different correlation patterns  not only rate problems (but also T0 drift etc.)

  18. Rate effects: asymmetry vs bunch Low rate case Detector asymmetry is a function of bunch #: Detector (system) performance may vary vs bunch (after abort gap) and vs detector High rate case

  19. Rate effects: Mass vs bunch Low rate case Det 1 Det 3 4% Det 6 Det 4 Bunch dependence of mass  Bunch dependence of system performance (energy, tof etc.) High rate case

  20. Pol1 vs Pol2 s=200 GeV 10% variation in the Pol1/Pol2 ratio vs fill (20% variation at s=500 GeV) No obvious correlation with “obvious” observables, such as rate, C-mass

  21. Systematic effects in pC

  22. Summary • Upgraded pC polarimeter – many new opportunities • New detectors tested (see talk by B.Morozov) • Crucial cross check from the comparison of Pol1 vs Pol2 • Smooth performance and operation by MCR • Sizable systematic effects observed • Rate effects • “Still unknown” effects • Data analysis ongoing • Expect <10% (<20%) uncertainty in pol. measurements for 100 GeV (250 GeV) beams in Run9 • Considering substantial system modification • Better (thinner and uniform) target production (see talk by A.Zelenski) • More robust detectors, smaller acceptance (see talk by B.Morozov) • Faster preamps • Replace WFD with simple ADC/TDC scheme?

  23. Backups

  24. Rate Run9-250GeV (per 48 strip) Run9-100GeV (per 48 strip) Run6 (per 72 strip) Run8 (per 72 strip)

  25. C-mass Run9-250GeV Run9-100GeV Run8

  26. Hjet vs pC-Blue, 250 GeV

  27. Hjet vs pC-Yellow, 250 GeV

  28. Hjet vs pC, 250 GeV

  29. Pol1 vs Pol2: 250 GeV

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