# Presentation: 717208

## JET 2004 data – preliminary Beam Polarization

## The Elastic Process: Kinematics

- internal targets 
- fixed target mode
****s ~ 14 GeV

- recoil proton
- or Carbon

- (polarized)
- proton beam

- scattered
- proton

- polarized
- proton target
- or Carbon target

- essentially 1 free parameter:
- 	momentum transfer *t* = (p3 – p1)2 = (p4 – p2)2 <0
- 	+ center of mass energy *s* = (p1 + p2)2 = (p3 – p4)2
- 	+ azimuthal angle if polarized !
-  elastic *pp* kinematics fully constrained by recoil proton only !

- ANbeam (*t *) ANtarget (*t *)
- for elastic scattering only!
- Pbeam = Ptarget . Nbeam / Ntarget

## Recoil Si spectrometer

- 6 Si detectors covering
- the blue beam =>
- MEASURE
-    energy             (res. ~ 60 keV)
-    time of flight   (res. ~ 3 ns)
-    scattering angle (res. ~ 2 mrad)
- of recoil protons from
*pp*  *pp* elastic scattering

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

- Ptarget ~ 0.924 ± 0.018

## pp elastic data collected

- Hor. pos. of Jet 10000 cts. = 2.5 mm

- Number of elastic *pp* events

- FWHM ~ 6 mm
- as designed

-  recoil protons unambiguously identified !
-  100 GeV ~ 1.8  106 events for 1.5  10–3 < **-***t* < 1.0  10–2 GeV2
-    24 GeV ~ 300 k events

- CNI peak AN
- 1 < E REC < 2 MeV

- prompt events
- and beam-gas

-  source
- calibration

- recoil protons
- elastic pp pp
- scattering

- background
- 118 cts. subtracted

- JET Profile: measured selecting pp
- elastic events

- ToF vs EREC correlation
- Tkin= 1⁄2 MR(dist/ToF)2

-  ToF <  8 ns

## Missing Mass MX2 @ 100 GeV

- not corrected for the
- magnetic field

- MX2 [GeV2]

- Mp2

- inelastic
- threshold

- number of events (a. u.)

- FWHM ~ 0.1 GeV2

- M2X (GeV2)

- proton

- M2X distribution
- 80 cm from target
- convoluted with
- spectrometer
- Resolution
- M2X~ 0.1 GeV2

- Missing Mass MX2 @ 100 GeV

- M2X

- simulations

## Event selections & Backgrounds

- Strip distribution for energy interval: 1250 – 1750 keV

- visually implement the energy / angle correlation in selecting elastic *pp* events
- 	typically, for each energy bin, select 3 to 4 strips per detector
- Background only from selected channels not from whole detector (4 – 5  smaller !)
- Total Backgrounds < 8 %:  source < 4%, “interaction” backgrounds < 4 %
-  ANsys ~ 0.0015 (~ 3% relative)

- Si #2

- signal

- background

- Si #6

## From N to PBEAM

*raw* asymmetry

- Analyzing Power

- if second term = 0, then

- on run by run basis
- averaging over all runs (PT) and all fills (PB)
- works also if ANN = 0

## AN for pp  pp @ 100 GeV

- AN for *p******p ****** pp* @ 100 GeV

- source of systematic errors:
- 	1  PTARGET = 2 % (normalization error)
- 	2 from backgrounds <  0.0015
- 	3 false asymmetries: small

- statistical errors only

- preliminary

## B / T :

- Data Used:
***t*** range: protons fully absorbed (0.0015 < -***t*** < 0.01 GeV2)
-  90 runs (~100 hours of live DAQ), 1.8  106 events
-  43 runs pC polarimeter run in “event” mode, 0.9  106 events

- 90 runs
- ratio B / T

- reduced 2 ~ 1

- 90 runs: 0.424  0.022
- 43 runs: 0.418  0.031

## PBEAM ...

- all 90 runs
- PBEAM = 0.392  0.021 (stat)  0.008 ( PTARGET)  0.014 (sys) = 0.392  0.026
-   PBEAM / PBEAM = 6.6 %
- 43 runs - SPIN 2004
- PBEAM = 0.386  0.029 (stat)  0.008 ( PTARGET)  0.014 (sys) = 0.386  0.033
- PBEAM / PBEAM = 8.5 %

- tot sys = 0.016

## The Road to Pbeam with the JET target

- Requires several independent measurements
- 0 JET 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”
- 	“self calibration” works for elastic scattering only
- 3 CALIBRATION: ANpC for *pC* CNI polarimeter in covered kinematical range:
- 	ANpC = 1 / Pbeam N”’
- 	(1 +) 2 + 3 measured simultaneously with several insertions of carbon target
- 4 BEAM POLARIZATION: Pbeam = 1 / ANpC N”” to experiments
- at each step pick-up some measurement errors:

- transfer    calibration     measurement

- expected
- precision

## AN for pC  pC @ 100 GeV

- no hadronic
- spin-flip

- with hadronic
- spin-flip

- “forbidden” asymmetries

- systematic
- uncertainty

- best fit with
- hadronic spin-flip
- Kopeliovich –
- Truemann model
- PRD**64 **(01) 034004
- hep-ph/0305085

- preliminary

- statistical errors only

- 2 major sources
- of systematic
- uncertainties:
-  beam polarization
-  energy scale
-   (dead layer)

## 2005 Forecast

- measure both beams in *t* range of 1  10–3 < **-***t* < 1.0  10–2 GeV2
- similar acceptance as for the data shown
- will use one detector centered w.r.t. to the target
- reduce error on  PBEAM / PBEAM by ~ 2
-  increase statistics:
-  4  more running time (based on 2004 ~ 1 month)
- and / or
-  more beam in RHIC (in 2004 had ~ 40  1011 p)
-  higher beam polarization
-  reduce systematic error by 2
-  more background running (at least 10 % of data)
- pC systematics
-  better PBEAM determination
-  energy scale and “dead layer”
-  new grounding scheme and AC coupling
-  repeat calibration several times