RHIC pC Polarimeters in Run9: Performance and Issues A.Bazilevsky for the RHIC CNI Group Polarimetry Worshop BNL, July 31, 2009

pC: goals/strategy Polarization measurements for experiments Target Scan mode Provides polarization at beam center, polarization profile, average polarization over profile 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) Ultra thin Carbon ribbon Target (5  g/cm 2 ) Si strip detectors (TOF, E C ) 18cm

pC in Run9 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 detectors (blue2) Test Detector2:“Hamamatsu single”: 2 pads in each of detector (yellow2) Ultra thin Carbon ribbon Target (5  g/cm 2 ) Si strip detectors (TOF, E C ) 18cm

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

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

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

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

Response to Alphas 241Am: MeV Example: Blue1 FebAprMayJunJul On the average, energy calibration (response to alphas) is stable within <2%

Response to Carbon M  E  tof 2 ToF vs E Up to 20% drop in Run9! ~10% drop in Run8

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

“Dead Layer” Run5:  g/cm 2 Run6:  g/cm 2 Run8:  g/cm 2 Run9:  g/cm 2

T0 ToF offset drifts by ~3-6 ns! 1 ns change is equivalent to “DeadLayer”~5  g/cm 2 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

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)

pC Monitoring with pulser Generator pulses Carbon Ekin ToF Blue1

pC Monitoring with pulser Low rate example: kHz/strip High rate example: kHz/strip Pulse ToF vs time Event rate vs time Pulse rate vs time Pulse amplitude vs time

pC Monitoring with pulser Run kHz/strip High RateNo Rate Pulser Amplitude distribution

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

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

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

Pol1 vs Pol2  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  s=200 GeV

Systematic effects in pC SourceEffectMonitoring Si radiation damageDead Layer increase?Change in Energy measurements  lower reconstructed C-mass “After rest” (~ a few days) Dead Layer decrease?Change in Energy measurements  higher reconstructed C-mass ??T0 driftFrom fit of E vsToF Rate effectDead Time Shift in energy measurements Event overlap Rate, dead time and shift in energy measurements (from gen. pulses), reconstructed C- mass TargetEnergy loss in targetComparison of 90 degree and 45 degree detectors? ??Pol1/Pol2 inconsistency???

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?

Backups

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

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

Hjet vs pC-Blue, 250 GeV

Hjet vs pC-Yellow, 250 GeV

Hjet vs pC, 250 GeV

Pol1 vs Pol2: 250 GeV