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Systematic Errors Studies in the RHIC/AGS Proton-Carbon CNI Polarimeters

Systematic Errors Studies in the RHIC/AGS Proton-Carbon CNI Polarimeters. Andrei Poblaguev Brookhaven National Laboratory The RHIC/AGS Polarimetry Group: I. Alekseev, E. Aschenauer, G. Atoian , A. Bazilevsky , A. Dion, H. Huang,

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Systematic Errors Studies in the RHIC/AGS Proton-Carbon CNI Polarimeters

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  1. Systematic Errors Studies in the RHIC/AGS Proton-Carbon CNI Polarimeters Andrei Poblaguev Brookhaven National Laboratory The RHIC/AGS Polarimetry Group: I. Alekseev, E. Aschenauer, G. Atoian, A. Bazilevsky, A. Dion, H. Huang, Y. Makdisi, A.Poblaguev, W. Schmidke, D. Smirnov, D. Svirida, K. Yip, A. Zelenski PSTP 2011, St. Petersburg

  2. BRAHMS(p) Absolute Polarimeter (H jet) RHIC pC Polarimeters Siberian Snakes Spin flipper PHENIX (p) STAR (p) Spin Rotators (longitudinal polarization) Spin Rotators (longitudinal polarization) Solenoid Partial Siberian Snake LINAC BOOSTER Helical Partial Siberian Snake Pol. H- Source AGS 200 MeV Polarimeter AGS pC Polarimeter Strong AGS Snake Layout of the RHIC facility • H jet (pp) polarimeter provides absolute polarization measurements at RHIC • RHIC pCpolarimeters provide polarization monitoring including polarization profile measurements • AGS pCpolarimeter provides polarization monitoring (mainly used for technical control and special beam studies) PSTP 2011, St. Petersburg

  3. Proton-Carbon Polarimeter kinematics Plan view Event selection in RHIC/BNL pC polarimeters: PSTP 2011, St. Petersburg

  4. Polarization Measurement Spin dependent amplitude: Rate in the detector: 1. Spin Flip (one detector): A theoretical model for AN(t) (a fit to the BNL E950 data) 2. Left-right asymmetry (two detectors) Square-root formula: Combining “spin flip” and “left/right asymmetry” methods allows us to strongly suppress systematic errors PSTP 2011, St. Petersburg

  5. AGS CNI Polarimeter 2011 3 different detector types: 1,8 - Hamamatsu, slow preamplifiers Larger length (50 cm) 2,3,6,7 - BNL, fast preamplifiers Regular length (30 cm) 4,5 - Hamamatsu, fast preamplifiers Silicon Strip Detectors: Dead Layer Strip orientation 90 degree detectors (2,3,6,7) 45 degree detectors (1,4,5,8) PSTP 2011, St. Petersburg

  6. Schema of Mesurements WFD α-source measurements (241Am , 5.486 MeV) “Banana fit” t-t0 = tA(xDL,αA) PSTP 2011, St. Petersburg

  7. An example of data selection If t0 is known, a model independent calibration can be done Wrong determination of mean time It must be a vertical line if detector is properly calibrated PSTP 2011, St. Petersburg

  8. The AGS pC polarimeter is succesfully used for the relative measurements Beam Intensity, I Polarization profile measuremens (jump quads study) Study of Polarization dependence on beam intensity PSTP 2011, St. Petersburg

  9. Is absolute polarization measurement possible with a proton-Carbon polarimeter ? • A systematic errors study is necessary to answer this question. • Are results dependent on detector configuration ? • Do we know the Analyzing Power AN(t) ? • Could we properly calibrate detectors ? • Do we understand energy losses in the target ? • Can we control rate dependence of polarization measurements ? • … PSTP 2011, St. Petersburg

  10. Polarization dependence on detector type Polarization vs Beam Intensity (Late CBM),Vertical Target3, all 2011 runs Polarization measured by all 3 types of detectors is consistent within 1-2% accuracy ! Can we explain slope difference for 90 and 45 degree detectors by rate effect ? All 2011 data was included in the fit. Results of the fit should be used for comparison only Polarization, P(1.2) , is given for intensity 1.2×1011 PSTP 2011, St. Petersburg

  11. Polarization dependence on detector type Hamamatsu (45 degree) vs. BNl (90 degree) detectors No visible variations of the polarization ratio during 4-month Run 2011! PSTP 2011, St. Petersburg

  12. Analyzing Power AN(t) AN measurement for assumed 65% polarization • Poor consistency between theory and measurements • Wrong energy calibration and energy losses in the • target may contribute to the discrepancy • Results depend on the target (rate ?, energy losses ?) Potentially, analyzing power may be measured by the pC polarimeter (up to a normalization constant) PSTP 2011, St. Petersburg

  13. Enrgy Calibration Dead-Layer corrections L0 is stopping range derived from MSTAR dE/dx (used in “standard” calibration) Stopping range parametrization: “standard parametrization”, p=1/d constant energy loss, p=Eloss polinomial Carbon Energy from measured amplitude: PSTP 2011, St. Petersburg

  14. Enrgy Calibration Inverse task: If E(αA) is known then we can determine L(E) and dE/dx If t0 is know then we can measure Carbon energy as a function of the amplitude αA A model independent calibration of the amplitude and thus we can measure dE/dx (in deadlayer length units) WARNING: In such a way we measure effectivedE/dx which may be different from ionization lossesdE/dx. If t0 is unknown we can make a fit, that is to try all possible t0and select one which provides best data consistency. It might provide us with value of t0 and calibration of the measured amplitude ECarbon = E(αA) . WARNING: the fit may work incorrectly if parameterization of stopping range L(p, αA) can not approach well true effective dE/dx. PSTP 2011, St. Petersburg

  15. New calibration method vs standard one • The function L(E) = p0L0(E) + p1L02(E) fits data much better then “standard” calibration function p0L0(E) • Significant difference in the value of t0 • Significant difference (up to 15% ) in the energy scale Better fit of data does not guarantee better calibration ! PSTP 2011, St. Petersburg

  16. Comments about t0 determination in the fit Including t0 to the fit: (τis time of flight for 1 MeV carbon ) If then (good calibration) However, if may be approximated by variations of the then result of the calibration is unpredictable may be masked by faked correction PSTP 2011, St. Petersburg

  17. Rate effect An estimate of the rate effect Simplified example Only one carbon signal may be taken by the DAQ Detection efficiency: where r is average rate per bunch. More realistic example is rate of good events is total DAQ rate - is a strip pair number - is average rate per strip (millions events per spill) - is rate in strip i (events per bunch), n = 0.0528 - is relative rate in the strip I assume factor k is the same for all strips Rate contribution Machine contribution PSTP 2011, St. Petersburg

  18. Rate effect Vertical Target3, all 2011 runs: Strip Pairs The measured value of the rate effect factor agrees well with a pileup based estimate Polarization dependence on beam intensity (averaged over all 2011 runs) : PSTP 2011, St. Petersburg

  19. Enrgy losses in the target Target dependence of the Polarization measurements Polarization vs intensity, Horiz. target #1, JQ-on Polarization vs intensity, Vertical target#3, JQ-on AGS pol., during H-jet meas. at injection Intensity -1.5 • Slope difference is consistent with our estimates • We can explain 4±1 % of polarization difference • by rate effect. Where the rest 4.6±1.7% come • from? PSTP 2011, St. Petersburg

  20. Enrgy losses in the target Energy losses in the target 125 μm target Target φ Beam (d ~ 30 nm) Measured/True Polarization dE/dx Calculation • Effect of energy losses in the target • may be significant • may be unpredictable AN(t) Results are independent on target width ! Energy range 400-900 keV PSTP 2011, St. Petersburg

  21. Summary • Different types of detectors were tested in the Run 2011 • Results of polarization measurements were consistent within 1-2% accuracy • No significant variation of the results of measurements were observed during the whole 4 month run. • The polarimeter has a capability to measure analyzing power up to the arbitrary normalization factor, but accurate study of the systematic errors is needed for that. • Standard energy calibration method was found to be unreliable, new method of calibration are suggested but more development is still needed. • Experimental evaluation of the rate effect is consistent with estimation of pileup contribution. • More accurate control of energy losses in the target is needed. PSTP 2011, St. Petersburg

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