A Possible Path Forward Current Polarimeter Upgrades Efforts Based on a proposal by Boris Morozov

1. A Possible Path Forward Current Polarimeter Upgrades EffortsBased on a proposal by Boris Morozov • Our experience this year • New detector test this year • The Proposed Test Plan • - Detectors and Front-End • - Front-End Logic and Digitizer Logic • - Digitizers and Trigger Features

2. Problems we faced lately with the present system RHIC CNI polarimeters • Experienced Large changes in leakage current (> 4μA) • Poor resolution (>50 KeV) • “Dead layer” or other instability during with rate issues • Low dynamic range of the Preamps (~11MeV) • Possible Noise pick up due to long distance (~100m) between Preamp and Shaper • 8-bit WFD limits dynamic range (limits ramp measurement at 250 GeV) • FPGA code limitations: Coupling between the time (T0) and amplitude measurements AGS CNI polarimeter • A significant jump in polarization when new detectors were installed • Some WFD digitizer had strong (and uncontrolled) dependence on the external clock wave form The Jet • Odd calibration data • Can we reduce the background and reach a lower pt?

3. What About the Jet? Significant background specially at low energy! Odd calibration behavior Why do we not see a much cleaner peak before cuts are applied?

4. New Detector TestsAtoian, Gill, Morozov • Compare BNL and Hamamatsu large area (1cm x 1cm) Si and strip PIN photodiode detectors. Results show a several advantages to use these devices instead of the strip detectors • A factor of ~2 better resolution (21 KeV vs. 43 KeV) which allows us to measure elastic carbons at ~ t=-0.005 GeV/c2 at higher analyzing power • ~ 20 times less bias current after 4 months working on the RHIC beam (0.23A vs. 4  A) • Simplify the readout electronics as well as DAQ • Did not experience a timing or mass shifts vs rate

5. 5 The Test Plan • Install two sets of 8-single strip Hamamatsu detectors at the 45 degree location in the AGS polarimeter • Install new 16 channels of commercial amplifier and shaper system • Trigger Circuitry for the ADC gating and TDC start time • A new set of ADC and TDC system read through VME • Cables are already in place need to be terminated • Need a new DAQ system • This represents a prototype for the RHIC p-Carbon CNI polarimeter • Orders have been placed for the components and expect to have them in hand for the AGS polarized proton start up in late January • Install similar single strip detectors in the Jet to replace the equivalent of two Jet detectors • These will be readout in a similar manner to the current Jet system • Allows in situ comparison to the current system • These have to be installed prior to RHIC startup November 20?

6. Ultra thin Carbon ribbon Target (5g/cm2) 6 1 Detectors & FrontEnd Detectors: Hamamtsu Single PIN photodiode for direct detection (S3588-09) Each detector has 30mm x 3mm active area and ~300 μm thickness and placed along the beam axis. The typical dead layer is 60 μg/cm2 8 detectors/per port placed on the existing (+/- 45°) vacuum ports. Front End: Charge sensing Preamps/Shapers (MSI-8 & MSCF-16) connected to the detectors throughthe0.5 m long low capacitance coax. The Shaper has two outputs: Digital (Time,CFD) – min delay 5ns with CFD –Walk: for 30ns input risetime, max 1ns (dynamic range 100:1) Analog – σ = 100 - 400 ns. PZ compensation: range 4 μs - ∞ Dynamic range: - 33 MeV Shaper has remote control capability. 8 Si single PIN detectors 32cm 2 5 12 Si-strips detectors 3 4 Beam axis Target axis

7. Front-End & Digitizer Logic Target Beam

8. Digitizers & Trigger Features • Digitizers: • The Peak sensing ADC(MADC-32) is used for deposit energy measurement • -11 bits • - 0.8 μs dead time • - 10 ns Time Stamp • - VME • The Dead Time-less TDC (V767A) is used for TOF • - 0.6 ns bin width • - 10 ns double pulse resolution • - VME • Triggers: • The Shaper time filtering output with CFD discriminator & fast NIM logic were • used for trigger • - protection against multiple pulsing • - bunch time synchronization • - “Prompt” suppression at the beginning of the bunch.

9. Backup

10. Carbon Spectroscopy range • According to Tandem results one can detect 0.2 MeV carbon recoil by using Hamamtsu PIN Photodiode • with MIPs noise cut (~80 KeV for 300μm). Assuming that, for AGS beam energies the pC -> pC kinematic gives: At recoil angle of 37mrad the literal displacement will be 12mm at 32cm target-detector distance. Hamamatsu S3588 has 3mm X 30mm sensitive area. By setting detector at centre of the target axis , one can cover this angular interval (the recoil energy is ~1.5 MeV) The analyzing power varies from ~ 0.035 to ~0.02 at /t/ range of [0.0045 – 0.0335] (GeV/c)2. It should be noted: - unlike RHIC, there is no T.o.F. limitation at that range; - “prompt” events can be fully rejected at flattop (bunch length ~30ns) and ~45% at injection (140ns); - measurement range can be extended down to ~0.002 (GeV/c)2 by minimizing electronic noises.

11. Angular Straggling due to MS • Another limitation for low /t/ value comes from the Multiple Scattering in carbon target. Ebeam = 24 GeV Errors include AngularStragglin&EnergyResolution The Carbon energy 0.15 MeV has Angular Straggling with σ =14mm for 5μg/cm2 target. For 1 MeV recoil energy the angular straggling is σ = 1.5mm. The Angular Straggling is dominating factor to overall angular spread of low energy carbon recoils. The separated kinematic range elastic-inelastic (the first excited carbon state at 4.4 MeV) is ~0.15 MeV - >1.0 MeV. So, the kinematic restriction shows that the ~0.15 MeV carbon recoil energy (/t/=0.0034 GeV2) is the lowest possible value.

12. Abacus Count Rate Estimation Target: Thickness = 5μg/cm2 Number of nuclei (Nt) = 5*10-6 / 19.9*10-24 = 2.5*1017 /cm2 Full width (Wtarget) = 0.0125 cm Target efficiency (Teff) = Wtarget / Wbeam = 5*10-2 • Beam: • Energy (Ebeam) = 24 GeV • Intensity (Ibunch) = 2.5*1011 protons/bunch • Full width (Wbeam) = 0.25 cm Luminosity: Luminosity (L) = Ibunch x Nt x Teff = 2.5*1011 x 2.5*1017 x 5*10-2 ≈ 3*1027 /cm2/bunch Cross-section pC->pC: Average Cross-section (Selastic) ≈ 3 * 10-24 cm2/(GeV/c)2 at –t = 0.003÷0.03 interval /t/ range (Δt) = 0.03 (GeV/c)2 Angular acceptance: Detector size = (0.3cm X 3cm) Target-Detector distance = 32cm Acceptance (Adet) ≈ 1*10-4 Count Rate: Revolution Time (Trev) = 2.7 μs Ramp Time (Tramp) = 0.450 s Count Rate per detector (Rdet) = L x Selastic x Δt x Adet = 3*1027 x 3*10-24 x 0.03 x 1*10-4 ≈ ≈ 3*10-2 events/bunch/det or ≈ 1*104 events/s/det or ≈ 4.5 *103 events/ramp/det

13. Pile-upand Dead Time Losses Estimation • There are two main drawbacks using conventional ADC: a possible pile-up and dead time losses. • Assume that the rise time of the digitized pulse is ~150 ns (analog output). • Signal to background ratio at ~50% prompts events suppression is ~ 1 (RHIC test results) • So, the total raw rate per detector would be ~ 2*Rdet=20 KHz/det. It gives a pile-up of ~0.3%. • MADC32 has 0.8 μs dead time and one gate for 8 channels. It will give ~6% losses at the rate of 10 KHz/det. • It should be noted that the pile-up reduction is important, because pile-up “introduces” direct systematic shift • to polarization value, while dead time losses increase the measurement time for given statistics only.

14. Cost Estimation Blue – available for test’10 set up

15. Summary • Single SI PIN Photodiode gives good performance in terms of the energy and time resolutions, dead layer uniformity, • rate behavior and noise suppression. It is very robust set up, easy to handle and… also cheap. • The conventional DAQ with modern Peak Sensing ADC (thanks to MADC32) is also simple and well suitable for our • Purpose, especially, if one uses the shaper filtering and prompts noise suppression on the level of the events triggers. • Besides that it is programming without any “magic touch” technique. Estimate less than 0.3 men-year for DAQ • software development. • The detectors set up and DAQ are based completely on commercial available devices. • Summarized main features of the proposed system are: • Good resolution (<25 KeV) • Constant value of Dead Layer • Large dynamic range of Preamps (33 MeV) • Short distance (~2m from Preamps to Shaper) • There are no dependence from detector-to-detector • Large solid angle (~twice more compared to the present setup) • 11-bits dynamic range • Small leakage current (<0.2μA) • Conventional fast ADC with 800ns dead time and dead-time less TDC.