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RHIC pC Polarimeters in Run8

RHIC pC Polarimeters in Run8. A.Bazilevsky For the RHIC CNI Group RSC meeting April 4, 2008. 6. 1. 2. 5. 3. 4. RHIC pC Polarimeter. Carbon target. 90º in Lab frame. Recoil carbon. Polarized proton. Ultra thin Carbon ribbon Target (3.5 m g/cm 2 ). 18cm. Si strip detectors

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RHIC pC Polarimeters in Run8

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  1. RHIC pC Polarimeters in Run8 A.Bazilevsky For the RHIC CNI Group RSC meeting April 4, 2008

  2. 6 1 2 5 3 4 RHIC pC Polarimeter Carbon target 90º in Lab frame Recoil carbon Polarized proton Ultra thin Carbon ribbon Target (3.5mg/cm2) 18cm Si strip detectors (TOF, EC)

  3. Goals • 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) • Polarization measurements for experiments • 4-5 runs per fill • Pol. profile corrected fill-by-fill polarization (different for HJet comparison and for experiments)

  4. What’s new since last pp run • New target mechanism • Vertical-horizontal, blue-yellow • Precision target positioning • 6 vertical targets, 4 horizontal targets in a ring • New Si detectors in blue • New people

  5. Global Performance • Commissioning finished on Feb 14 • Calibration with 241Am  source • Initial “Dead Layer” and T0 for each strip • Online configuration (time gate, energy threshold) • Data reliable after Fill 9866 • Problems with thick target (high rate) • Fill 9942-9948 blue may be non-recoverable • HJet polarizations available for these fills • Change time gate in DAQ • after Fill 9977 • To get rid of beam induced pulses • Hopefully doesn’t have any effect on online polarizations • Requires more accurate offline analysis (banana curves deformed  need to select another safe -t range)

  6. Performance Run 9866.117 (Feb 14) Detector 1: ToF vs Carbon Ekin

  7. Performance Run 9866.117 (Feb 14) Detector 1: Inv. mass distribution

  8. Performance Online panel

  9. pC-online vs HJet “Fast Offline” analysis of HJet!

  10. pC-online / HJet 1.1350.028 1.1290.038

  11. Polarization Profile If there are problems with target position determination  Exclude position from calculations: P(L/Lmax): just an example    R=0.290.07 for Hjet for experiments (assumes equal horiz. and vert. profiles )

  12. Polarization Profile <R> ~ 0.18: <P>/Pmax~ 0.92 <R> ~ 0.30 <P>/Pmax ~0.88 Run5/6: R~ 0.100.15

  13. “Fast offline” Corrected fill-by-fill for pol. profile Normalized to HJet

  14. Thick target  too high event rate (5MHz) pC stability: “Dead Layer”

  15. pC stability: T0 Stable

  16. Issues • Target loss (11 of 20) • 4(H)+1(V) yellow and 2(V) blue – due bad target quality and/or to human error • 2(V) yellow and 2(V) blue due to life time (usual life time – 2 weeks) • Non-gaussian intensity profiles • Due to loose targets? • Our technique of P(L) for pol. profile measurements fully defeats this problem? • Leak current in Si detectors • But surprisingly didn’t spoil polarization measurements (if rates are not tooo high) • High rate problems? • Confusion with normalization • Run4 normalization used (…Run6 normalization changed by ~15%) • Known only after HJet collects enough data • Normalization of pC online values was provided 2 weeks after physics run began; wasn’t reflected in “official” online polarizations • pC measurements take too long (complain from experiments) • Ambitious goals: many operational modes used, many updates in instructions, dynamically changes software …

  17. Solutions • New chamber (see Anatoly’s talk) • Basically two polarimeters per ring, one for vertical scan, another for horizontal – no interference, quick measurements • More targets: longer running without access • More ports to develop/test new detectors • Develop new detectors • Photo diod (by B.Morozov) • Will help to work at higher rates • More controllable “Dead Layer” • Sweep (continuous) scan • Successfully checked and used in the end of Run8 • Faster measurements and safer for targets • Provides everything we need for beam polarization and emittance measurements • Simplify instructions and GUI • Only one mode (sweep scan) for routine operation (all others for experts) • Normlaization • Should discuss…

  18. Summary • Stable reliable polarization measurements • For the first time we do “fast offline” analysis to take into account energy correction (“Dead Layer”) drift and QA • For the first time we provide semi-online results on polarization profile • For the first time we started providing normalized pC measurements after a week of physics running • We learnt a lot from Run8 • Operation in next runs expected to be simpler, faster and smoother • Upgrade program is ongoing • New detectors • New chamber with extended capabilities

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