Current and Future Transverse Spin at PHENIX

Yousef Makdisi Spin 2008 October 6-11, 2008

Towards Improved Polarimetry at RHIC

Yousef I. MakdisiBrookhaven National LaboratoryForThe RHIC Polarimetry Group

Outline
A brief introduction to the polarimetry components

The P-Carbon CNI polarimeters

Current R&D efforts

Upgrade plans

The Polarized Jet Target issues

Plans for the Jet for Run 9 Summary

The RHIC Polarimetry Complex
Self Calibrating
The Polarized Hydrogen Jet target
Calibrated from the Jet Data
p-Carbon Polarimeters

p-Carbon Polarimeters
(t0,x)Kinematic Fit
E
5.486 MeV (85%)5.443 MeV (12%)

p-Carbon Polarimeters Energy Correction Vipuli
Energy calibration uses alpha sources followed by a fit to TOF/ Energy relation to extract the dead layer thicknessThe average thickness is ~ 80 gm/cm2 >> 25-30 gm/cm2 expected The energy correction in the silicon carbon could be charge dependent !!

R&D Effort At The Tandem Morozov
The BNL Tandem: Carbon beams to scan energies of interest with varying intensities up to 4.106/cm2: 0.3 5 MeV (wider than the current range to reach the Alpha energy from the Americium source) Charge of +1, +2, and +3 This will provide a good energy calibration Will decouple the time and energy dependences Use alpha sources impinging forward and backward to determine the effective silicon thickness and assess potential degradation Use a foil to simulate the polarimeter carbon target

p-Carbon Polarimeters Looking Ahead
Test new Hammamatsu photodiode detectors and array under similar conditionsA factor of 4 energy resolution good for going to lower t We will also test a duel-silicon detector system with a thin 5 m followed by the 300 m detectorsIdentify the carbon charge with the thin detector at energies between 0.3 1 MeV. This then drives the energy loss (dead layer) determination from the earlier dataAn added bonus, the thin detector could provide a trigger. It is blind to minimum ionizing prompts, so less rate dependentTest the existing charge amplifier with a lower shaping timeTest a new low capacitance cable between the detector and preamp

Test a current amplifier concept: better for high capacitance detectors and high rate environment. Are the noise levels acceptable? For high rate we will try to reduce the silicon volume current by reducing area and thickness

Testing in situ w/ New Polarimeter Upgrade
Run 9: install the new detectors in a two arm 450 configuration in one of the duel polarimeters:

Compare its performance to the existing systems under similar beam conditions

Assess resilience to radiation

Include a detector to get a handle on the prompts or t0 timing

Jet Target experienced higher background levels H. Okada

Background Under The Jet Elastic Signal
Studied the contribution fromeach beam separately the incident beam and the displaced beam

If elastics, expected a beam related Asymmetry. None was found

Two beam mode did not show increased background!

With beam incident at the jet FWHM position did not observe lower asymmetry within stats.
Collimators were removed this Run

The Polarized Jet Target Two Beam Mode
x
y
jet
(+10, -10) mm
(0, -1.5) mm
-10
+10
(0, -7) mm

For Run 9
Re-install and survey the collimators albeit with a wider vertical opening for better two-beam acceptance. Re-establish conditions similar to Run6 The two beam mode allows for simultaneous calibration of both the Blue and Yellow p-Carbon polarimeters instead of alternating between them. Use one beam only impinging on the jet center and assess the associated background Use one beam displaced by 10 x 10 mm in x and y respectively and determine the background under the signal if any Use a two beam mode to see if the background is any different Run with the beam at the FWHM position for enough statistics to see if there is any jet beam polarization profile Repeat jet beam depolarization measurements with the two beam mode

Run 9 +
We need to revisit the molecular hydrogen background.This still represents the largest systematic error on the jet measurement

Re-do the electron beam measurement with a time of flight measurement instead of the magnetic measurement of the outgoing products.(A. Belov, INR)

A good statistical measurement and calibration at RHIC injection energy to couple the AGS and RHIC measurements and assure that we do not lose polarization on the RHIC ramp

Summary
We continue to strive for consistent polarimetry measurements from one run to the next We are embarking on a significant R&D effort for better detector performance especially in anticipating higher rate environment

Continued efforts to understand the associated backgrounds and reduce the associated systematic errors

It is gratifying to see the analyses of both the polarimaters and jet data completed in half the earlier times. A testimonial to the analysis maturity and thanks to the diligence of Hiromi Okada (BNL Spin Phys. Group, now at KEK-Jparc) Vipuli Dharmawardane (New Mexico State University)