# Presentation: 239652

## COMMISSIONINGTHE pp POLARIMETER

- JET in the IR

- Alessandro Bravar
- et al.

## Recoil spectrometer

- 2004 RUN
- WILL INSTALL
- 6 DETECTORS
- ON BLUE BEAM
- ONLY

- will have “design”
- azimuthal coverage
- one Si layer only
-  smaller energy range
-  reduced bkg rejection
-      power

## The road to Pbeam

- Requires several independent measurements
- 0 target polarization Ptarget (Breit-Rabi polarimeter)
- 1 AN for elastic *pp* in CNI region: AN = 1 / Ptarget N’
- 2 Pbeam = 1 / AN N”
- 	1 & 2 can be combined in a single measurement: Pbeam / Ptarget = - N’ / N”
- 3 *CALIBRATION*: ANpC for *pC* CNI polarimeter in detector kinematical range:
- 	ANpC = 1 / Pbeam N”’
- 	(1 +) 2 + 3 measured almost simultaneously alternating *p* and *C* CNI polarimeters
- 4 BEAM POLARIZATION: Pbeam = 1 / ANpC N”” to experiments
- at each step pick-up some measurement errors:

- transfer    calibration     measurement

- requires
- < 107 *pp*
- CNI events

## Rates for pp CNI events (old estimates)

| beam intensity | target density |
| --- | --- |
| 21011 p / bunch
112 bunches
78 kHz | 
51011 atoms / cm2 |

- Rates for *pp* CNI events (old estimates)

| |t| range (GeV2) | 110-3 –
     210-2 |
| --- | --- |
|  
(cm2) | 3  10-27 |
|  AN  | 0.03 |
| F. o. M. | 2.710-30  |

**L** = 21011 112  78103  51011 ~ 1030 cm-2s-1 (1b-1s-1)
-                                                    ~ 1028 cm-2s-1 / bunch
**N** = **L**    *acc *(=30**0**/2)  *eff *(50%) ~ 125 Hz
-  						        ~    1 Hz / bunch
- in 12 hours (i.e. 1 machine fill)
- 			can collect ~ 5 **** 106 *pp* CNI events

- acceptance ~ 1/12 of azimuth (~300)

- 21012

- 1

- 55

## Bring the JET to full operational status

**3 - 4 days JET installation in tunnel (IP12)**
**1/2-1 week to fine tune the jet beam parameters and attain a stable running condition. This could be done parasitically with RHIC beam tuning.**
**Tune the dissociator for maximum intensity**
**Measure the intensity in chamber 7 by pressure rise**
**Turn on the holding field magnet, RF systems, and BRP gauge and measure the jet polarization **_**without beam**_**.**
- Measurements in November indicated the jet beam polarization to be 99% of the theoretical maximum (this depends on the holding field magnet setting)
**Repeat the Jet polarization measurement with beam** (dedicated)
- Assess if we suffer any beam depolarization from the bunched beam (and intensity). Our expectation is no effect if running with 56 bunches. This has to do with the uniformity of the holding field magnet.
**It does not matter if the beam is at injection or at store. However, it is of interest to do the same with the 200 Mhz system on.**
**The two RHIC beams should be separated by at least 1 cm horizontally;  one beam centered [vertically] in the JET chamber (BPMs and profile measurements)**

## Commissioning pp polarimeter steps

- 1	Energy calibration with  source (Am) and time calibration
- 	of Si detectors
- 2A	Identification of elastic *pp* events
- 		energy – position correlations
- 		inelastic backgrounds
- 		energy and time resolution (200 MHz system on)
- 		MX resolution
- 2B	FE & receiving electronics and DAQ setup / debugging
- 		online waveform analysis
- 		self-triggering
- 		synchronization with RHIC clocks
- 		event building
- RUNNING  AN *pp* and AN *pC* in CNI region
- 	different running conditions (one beam vs both beams, etc.)
- 	polarized and  unpolarized beams and target
- 	 collect > 107 events at 100 GeV
-  collect a sizable sample also at 24 GeV

- first 2 – 3 weeks
- “parasitic mode”

- week 4
- dedicated

## Identifying elastic pp events

## Si detector design

- p+ implants

- n+ implants

- field shaping
- electrodes
- (instead of
- p+ implants)

- Vbias
- (+200 V)

- DC coupled

- AC coupled

- Vfield
- (+180 V)

- double sided readout (opt.)
- 72  64 mm2
- thickness 500 microns
- p+ side pitch 1 mm
-      readout pitch 4 mm
- n+ side pitch 4 mm
- C  80 pF / readout ch.

- p+ implants
- ~0.15  deep

- to minimize entrance window:
- 1. no SiO2
- 2. replaced Al electrode
-     with thin wires
- 3. shallow implants
- dead layer < 200 nm (cfr. 3 m!)
-     almost no energy loss for
-     recoil protons in CNI range

## Si performance

- PMT
- trigger

- Si response to MIPs
- CD ~ 80 pF

- R ~ 25 - 30 ns

- S / N ~ 4

- MIP signals before shaping (full bandwidth)
- NB slowest recoil protons > 3 MIPs

- final detectors will have lower leakage currents => expect better S / N

## Running scheme

*pC* CNI

*pC* CNI

*pp* JET

*pp* JET

- multiplexer

- WFD

- alternate measurements with *pp* CNI (JET) and pC CNI polarimeters
- 							about each hour
*pp* measurement: 	only fraction of whole statistics
- pC measurement:	> 2 107 events (full measurement)

- Same WFD code for pC CNI and JET polarimeters

- Share the same set
- of WFD for all RHIC
- polarimeters
- (total 96 ch.)