Proton Polarimetry for the EIC

Transcription

1 Electron Ion Collider Users Meeting June 24-27, 2014 at Stony Brook University Proton Polarimetry for the EIC Andrei Poblaguev Brookhaven National Laboratory EIC Users Meeting 1

2 Outline Proton Polarimetry at RHIC Discussion of systematic errors Projection to erhic EIC Users Meeting 2

3 Polarizaed beams at RHIC Siberian Snakes Hydrogen Jet Polarimeter Carbon Polarimeters PHENIX STAR Spin Flipper Spin Rotators Siberian Snakes Polarized Source Tune Jump Quads Helical Partial Snake 200 MeV Polarimeter LINAC BOOSTER AGS Strong Snake RF Dipole AGS pc Polarimeter AGS Internal Polarimeter EIC Users Meeting 3

4 Polarimeters at RHIC Complex Linac absolute 200 MeV polarimeter - counting of protons scattered at 12 and 16 degrees in scintillator counters - absolute Polarization measurements - every second bunch is measured AGS relative pcarbon Polarimeter - detection of kev recoil Carbons in 96 Si strips. - monitoring of the beam polarization extracted to RHIC - a tool for beam development studies - statistical accuracy - detection of kev recoil Carbons in 96 Si strips. - monitoring of the beam polarization extracted to RHIC δδpp 2 3% per a few minute measurement. About 4,000 measurements per RHIC run. 4 RHIC relative pcarbon Polarimeters (two per RHIC beam) - detection of kev recoil Carbons in 72 Si strips (each polarimeter). - monitoring of polarization profiles, polarization decays, bunch by bunch and fill by fill polarization in both RHIC beams. - few 1 minute measurements per RHIC store. RHIC absolute Polarized Hydrogen Jet Target Polarimeter (measures both beams) - detection of 1-5 MeV recoil protons in 96 Si strips - the jet (target) polarization 92%. - continuous measurement of average beam polarization - statistical errors δδpp 3% per 8-hour store. Local relative polarimeters at STAR (BBC) and Phenix (ZDC) - monitoring transverse component of the polarization after rotators EIC Users Meeting 4

5 Polarization Measurement Schema in the pcarbon and H-Jet Spin dependent amplitude: Rate in the detector: Beam polarization P can be measured from the production asymmetry a: If average analyzing power is known To suppress systematic errors the asymmetry is calculated as In the pcarbon we use predefine analyzing power A N (E) In the H-Jet, A N is internally measured: EIC Users Meeting 5

6 Polarization in Collision Experiments Intensity and Polarizations profiles, I(x,y) and P(x,y), are needed for the analysis Gaussian Approximation: (similar for y coordinate). Average Beam Polarization (measured by polarimeter): In the pcarbon polarimeters, x- and y- profiles may be measured using moving target (vertical and horizontal, respectively). In a fixed target run, the Pmax is measured. In the H-Jet polarimeter, average beam polarization is measured. Average Polarization in experiment: (single spin) A model dependence between <P> and R: (W. Fischer and A. Bazilevsky, Phys.Rev.ST Accel.Beams 15 (2012) ) If the development of polarization profiles it the primary reason for the reduction of the average polarization : P 0 = P source is zero-emittance polarization EIC Users Meeting 6

7 Square Root Formula L + - R Number of events in a detector: If physics, acceptance, and intensity asymmetries are uncorrelated then Exact solution a polarization asymmetry ε acceptance asymmetry λ intensity asymmetry There is no systematic errors in measurement of asymmetry aa EIC Users Meeting 7

8 Possible correlation between asymmetries It was evaluated in analysis of the AGS pcarbon data: Actually δ ε, δ ±, δ LR are systematic errors in measurements of the a, ε, and λ, respectively WCM Above the δδδδ~ level, errors in calculation of average analyzing power are the only sources of polarization systematic errors EIC Users Meeting 8

9 AGS p-carbon Detectors: Rate Corrections Rate corrections are non-linear effect which was not accounted by the asymmetry correlations. Rate corrections are essential only for the AGS polarimeter. Run In a single Si strip, rate per bunch is r (depends on intensity, emittance, target, ) The Data Acquisition may take only one events per bunch. No good event may be detected even if both coincide signals are good. The measured Polarization is underestimated: In Run13, the average rate correction is 6% (for RHIC ref. runs). Uncertainty in the parameter k propagates to a ~ 1% uncertainty in the measured polarization. The parameter k may be evaluated using experimental data (separately for each detector) with accuracy about 20%: ONLINE the value of k=1 is used (consistent with previous runs) Polarization in RHIC reference runs Horizontal Polarization Profile EIC Users Meeting 9

10 Sources of the systematic errors in pcarbon Analyzing power AA NN EE used in data analysis. Errors in measurement of signal amplitude (e.g. due to (RF) noise) Energy Calibration Background, 1% < δδδδ<0 Energy losses in the target, 1% < δδδδ<0 Rate Corrections, δδδδ 1% EIC Users Meeting 10

11 AGS pcarbon: Analyzing power For data analysis we use Analyzing Power theoretically derived from the E950 (21 GeV/c). We can measure A N (t) up to a scaling factor. Results of measurements are well reproducible. Discrepancy between theoretical and measured analyzing powers may be caused by wrong energy calibration. Measured Analyzing Power ( <P> is determined with theor. A N (t) ) Analyzing Power A N (t) 2012 Analyzing Power A N (t) 2013 Analyzing Power A N (t) 2014 For relative measurements : δδpp ssssssss /PP EIC Users Meeting 11

12 Standalone measurements with FADC250. (Superimposed signal waveforms) RF noise Prompt Carbon Scattering pulse RF noise In regular measurements, signal amplitude and time are calculated in the 8-bit, 140x3 MHz WFD firmware. A simple algorithm assume a flat base time. In RHIC pcarbons we suppress RF noise by reducing cavity voltage during the measurement For AGS pcarbon, the RF noise is a problem which affects time and amplitude measurements and may corrupt the energy calibration. Improving of the RF shielding is needed. At minimum, RF noise should be monitored and properly accounted in measurements EIC Users Meeting 12

13 AGS p-carbon: Energy Calibration Since A N =A N (E), energy calibration is crucial for the polarization measurement δp/p δe/e From experimental data, can find the dependence between measured time and amplitude: If t 0 is known, we can calibrate detector in a model independent way: ADC gain is calibrated using α-source 241 Am : E dep = αa Energy losses may be accounted : EE kkkkkk AA = ααaa + EE llllllll (EE kkkkkk, xx DDDD ) A dead-layer approximation: Stopping range: Dead Layer A dead-layer condition: Using MSTAR parameterization for the de/dx, we can determine t 0 and x DL from the data fit EIC Users Meeting 13

14 Comments about Dead-Layer based calibration This calibration is very sensitive to small variations of the stopping power and dead-layer model. Comparison of the standard and modified calibrations t m is measured time t A is time derived from the measured amplitude Normalized stopping range L 0 (E) = L MSTAR (E) / x DL Fit function: L(E t ) L(αA) = 1 The modified stopping range L(E) = p 0 L 0 (E) + p 1 L 02 (E) fits data much better. Energy calibrations are significantly different. Better fit does not garantee better calibration. This example shows why there is a a concern about reliability of the energy calibration. More reliable method is needed. Determination of t 0 may solve the problem EIC Users Meeting 14

15 Calibration using fast (punch through) protons Carbons Bethe-Bloch formula: Fast Protons The method worked well only in few channels. Results are affected by induced pulse. Extension of the WFD range may solve the problem EIC Users Meeting 15

16 RHIC p-carbon: Target in Beam Ultra-thin (55 μμμμ/cccc 22 ) Carbon ribbon target thickness 30 nnnn width 10 μμμμ Beam heats up the target to glow Targets graphitize from operation Target is electrostatically attracted to the beam Mechanical stress on target, can break need replacement Material in beam is hard to control Induced charge from wake field on target ends Change to insulated ladder construction Targets are broken often Target attraction to beam can affect the results of profile measurement EIC Users Meeting 16

17 Polarized Hydrogen Jet Polarimeter (H-Jet) 255 GeV/c proton beams. 6 detectors (98 channels) Ran with two beam simultaneously separated vertically by 3-4 mm dictated by the machine beam-beam requirements. Alpha-source runs were taken separately from physics runs. Full waveform was recorded for every triggered event Recoil protons were selected within energy range 1 5 MeV Recoil proton asymmetry relative to the beam and jet polarization was mesured simultaneously a Beam = A N (t) P Beam & a Jet = A N (t) P Jet P Beam = (a Beam /a Jet ) P Jet EIC Users Meeting 17

18 Systematic Errors in H-Jet The Breit-Rabi polarimeter measures only polarization (96%) of atomic hydrogen. Average polarization of the jet (including molecular hydrogen) is about 92%. The admixture of the molecular hydrogen in the jet is not monitored continuously. We consider this as a biggest contribution to the systematic error of polarization measurement. Systematic errors due to background - scattering on beam gas - inelastic pp scattering can be studied using acquired data. Elastic pp Beam gas background pp 250 GeV Elastic pp + mπ Elastic pp EIC Users Meeting 18

19 Plans for RHIC Run15 Upgrade of the H-Jet: New detectors: - larger acceptance - extended energy range of detected protons (0.5 9 MeV) - factor 4 effective gain in statistics New DAQ : - based on 12 bit, 250 MHz FADC250 (JLab) - expect improvement in background suppression - study for future upgrade of the p-carbon DAQ The upgrade of the H-Jet may help us to resolve some problems discussed above EIC Users Meeting 19

20 erich The erhic proton beam conditions are likely similar to the current in that the bunch spacing is still 114 nsec, but shorter bunches, but reduced bunch intensity (factor 5-10) factor 10 smaller emittance resulting factor 3 smaller transverse beam size σσ xx, yy~200 μμμμ at polarimeter location. shorter bunches, σσ = 5 cccc = 170 pppp Desirable accuracy of absolute polarization measurement δδδδ PP = 2% EIC Users Meeting 20

21 H-Jet at erich For reduced beam intensity, statistical accuracy of measurements is expected to be about 10% per 8-hour store. very long time will be needed to achieve required statistical accuracy stability of p-carbon performance becomes very important possible solutions: o add unpolarized hydrogen jet target (factor 10 higher jet density) o new Si detectors which will be tested in RHIC Run 15 may effectively increased statistics by factor 4. Continuous molecular hydrogen component measurements has to be implemented. p-carbon at erich Rate at p-carbon detectors will be reduced by factor ~3. We may consider increasing of target thickness by factor 3. Polarization profile (transverse) measurements will still be available. To measure longitudinal polarization profile, the time resolution should be better than σσ 50 pppp. Such a resolution could be provided by FADC250. Due to noise, time resolution is constrained by a value of about σσ~ 500 pppp. Energy resolution should be of order of 10 3 since (δδδδ tt = δδδδ 2EE) It is unlikely to measure longitudinal polarization profile with existing Si detectors EIC Users Meeting 21

22 3 He 2+ beam at erich Yousef Makdisi, EIC14, March 20, EIC Users Meeting 22

23 Summary Based on experience with proton polarimetry at RHIC, a 2% accuracy of absolute polarization measurement of proton beam at erich seems to be achievable with existing detectors, but significant improvements are needed including continuous monitoring of molecular hydrogen component in H-Jet improving of the carbon targets for RHIC p-carbon reducing and monitoring of the RF noise reliable energy calibration for p-carbon detectors upgrading of the DAQ It is expected that p-carbon polarimeters can be used for relative polarization measurements of the 3 He 2+ beam. More study is needed to find a solution for absolute polarization measurement of the 3 He 2+ beam EIC Users Meeting 23

24 Backup EIC Users Meeting 24

25 Absolute Proton Beam Polarimeter at 200 MeV The polarimeter is based on the elastic proton-carbon scattering at 16.2 degree angle, where analyzing power is closed to 100% and is measured with a high accuracy. Inelastic protons background is suppressed by 41 mm Cu absorber The high rate inclusive 12 degree polarimeter is calibrated using the 16.2 degree measurements EIC Users Meeting 25

26 AGS pcarbon Polarimeter (Run 2013 configuration) Every detector consists of 12 Si strips. Right Left Carbon target foils: Thickness: 27 nm Width: 50 and 125 µm (Vertical) 75 and 125 µm (Horizontal) outer inner The polarimeter is employed for 1. Monitoring of the polarization extracted to the RHIC 2. Monitoring the polarization in the beam development studies. A regular measurement (40M events) takes few minutes and allows to determine the polarization with statistical accuracy of about 2-3%. About 4000 measurements per RHIC run EIC Users Meeting 26

27 AGS pcarbon: Polarization Measurements Event selection Ramp Fixed Target Moving Target (Profile meas.) Polarization flips at integer values of GGγγ EIC Users Meeting 27

28 AGS pcarbon: Analyzing power For data analysis we use Analyzing Power theoretically derived from the E950 (21 GeV/c). We can measure A N (t) up to a scaling factor. Results of measurements are well reproducible. Discrepancy between theoretical and measured analyzing powers may be caused by wrong energy calibration. Measured Analyzing Power ( <P> is determined with theor. A N (t) ) Analyzing Power A N (t) 2012 Analyzing Power A N (t) 2013 Analyzing Power A N (t) 2014 For relative measurements : δδpp ssssssss /PP EIC Users Meeting 28

29 RHIC pcarbon Polarimeters EIC Users Meeting 29

30 Target in Beam Beam heats up the target to glow Targets graphitize from operation Target is electrostatically attracted to the beam Mechanical stress on target, can break need replacement Material in beam is hard to control Induced charge from wake field on target ends Change to insulated ladder EIC Users construction Meeting 30

31 Polarization Profile Intensity Significant polarization profiles are observed RR = σσ II 2 σσ PP Polarization in units of intensity σσ xx,yy EIC Users Meeting 31

32 Polarization Decay Polarization losses are correlated to acceleration emittance profile Polarization P (%) injection Provide experiments with PP = PP 0 + dddd dddd tt R = RR 0 + dddd dddd tt Profile R Typical values: dddd dddd = 1%/h ddrr dddd = 5%/h EIC Users Meeting 32

33 Fill Pattern Raw asymmetry per bunch Confirm bunch fill pattern reliably Blue beam PP Averaged over all measurements in a fill PP Example Fill Yellow beam PP PP EIC Users Meeting 33

34 The H-jet polarimeter includes three major parts: polarized Atomic Beam source (ABS), scattering chamber, and Breit-Rabi polarimeter. The polarimeter axis is vertical and the recoil protons are detected in the horizontal plane. The common vacuum system is assembled from nine identical vacuum chambers 50 cm diameter, which provide nine stages of differential pumping each at 1000 l/s Flip jet polarization every 300 sec The Jet beam is focused to 6 mm FWHM so it sees the full beam polarization profile Thickness: 1.2 x10 12 atoms / cm 2 Jet polarization ~ 92% EIC Users Meeting 34

35 Running conditions (2013) 255 GeV/c proton beams. 6 detectors (98 channels) Ran with two beam simultaneously separated vertically by 3-4 mm dictated by the machine beam-beam requirements. Alpha-source runs were taken separately from physics runs. Full waveform was recorded for every triggered event Recoil protons were selected within energy range 1 5 MeV Recoil proton asymmetry relative to the beam and jet polarization was mesured simultaneously a Beam = A N (t) P Beam & a Jet = A N (t) P Jet P Beam = (a Beam /a Jet ) P Jet EIC Users Meeting 35

36 Analyzing Power Used for polarization measurements pp- CNI 24 GeV: PRD 79, (2009) 31 GeV: Preliminary 100 GeV: PLB 638 (2006) GeV: Preliminary Average Analyzing Power in Run 13: 255 GeV Variations of the measured value of A N are less than 1% EIC Users Meeting 36

37 Polarization measurement in the H-Jet in Run 13 Preliminary Analysis: Fills (Run13 Lattice) Fills (Run12 Lattice) Fills (Run12 Lattice) EIC Users Meeting 37

38 Systematic Errors in the H-Jet Measurements Jet Polarization: there are 2 hydrogen components in the jet: - atomic with (measured) polarization P BR 96% - molecular (unpolarized) The admixture of molecular hydrogen was measured to be ε 3% but, but systematic errors of this measurement is not well known. The average polarization P jet = (1- ε) P BR should be used in analysis Background: r ~ 5% is background level For Jet asymmetry α=0. For beam asymmetry α is unknown and may be as large as 1 (e.g for beam gas protons). (some previous experimental estimates gave α 0) In ONLINE analysis the value of P jet = 92% was used EIC Users Meeting 38

39 Calibration methods used in HJet EE GGGG = MeV EE AAAA = MeV α-particles from 241 Am and 148 Gd (α, x DL ) high energy (low amplitude) prompt particles (t 0 ) geometry based calibration (t 0 and α* ) EIC Users Meeting 39

40 Estimation of background effect. For elastic pp-scattering: z-profile of the jet (smeared by Si strip size) is approximated by : Background may be expected to be the same in all strips strip s The method is not verified yet! Two methods for background subtraction - from the fit - average background The peak position is associated with well known (from geometry) energy. In such a calibration t 0 may be determined with accuracy of about 200 ps, and proton energy may be calibrated with accuracy better than 2% By product detector geometry may be aligned. α-particles and prompt indicated more complicated background EIC Users Meeting 40