dis 2006 tsukuba, april 21, 2006 alessandro bravar proton polarimetry at rhic alekseev, a. bravar,...

DIS 2006Tsukuba, April 21, 2006

Alessandro Bravar

Proton Polarimetry at RHICProton Polarimetry at RHIC

Alekseev, A. Bravar, G. Bunce, S. Dhawan, R. Gill, W. Haeberli,

H. Huang, O. Jinnouchi, K. Kurita, Y. Makdisi, A. Nass, H. Okada,

N. Saito, H. Spinka, E. Stephenson, D. Svirida, T. Wise, J. Wood, A. Zelenski

1. Provide polarization measurements for accelerator

2. Provide polarization measurements for experiments

DIS 2006 Alessandro Bravar

GNN

NN

PA

BLL

2

1

NN

NN

PA

BN

1

Polarimetry : Impact on RHIC Spin Polarimetry : Impact on RHIC Spin PhysicsPhysics

measured spin asymmetries normalized by PB to extract Physics Spin Observables

RHIC Spin Program requires Pbeam / Pbeam ~ 0.05 normalization scale uncertainty

polarimetric process with large + sizable and known AN

– pC elastic scattering in CNI region, AN ~ 1 – 2 % large statistics > 107 events

– (very) large section fast measurements

– requires absolute calibration polarized gas jet target

Physics AsymmetriesSingle Spin Asymmetries

Double Spin Asymmetries

measurements


RHIC RHIC pppp accelerator complex accelerator complex

BRAHMS & PP2PP

STARPHENIX

AGS

LINACBOOSTER

Pol. Proton Source

Spin Rotators

20% Snake

Siberian Snakes

200 MeV polarimeter Rf Dipoles

RHIC pC “CNI” polarimeters

PHOBOS

RHIC

absolute pHpolarimeter

SiberianSnakes

AGS pC “CNI” polarimeter

5% Snake


How It Works ?How It Works ?

recoilCarbon

polarizedbeam

scatteredproton

Carbontarget

t = (pout – pin)2 < 0

Tkin 2 MC

0.01 < |t| < 0.02 (GeV/c)2

rightleft

rightleft

NB NN

NN

AP

1

Polarimetry:

Requires large F.o.M: AN2 x rate for fast measurement

(not at any price however, i.e. by increasing the rates)

small AN ~ 1 % (far from ideal !)

requires large statistics > 107, for d PB ~ few %

however too large rates (i.e. thick target, detector area, etc.) occupancy and pileup

very difficult operation corrections to measured asymmetries

larger systematic uncertainty

Absolute calibration Polarized Gas Jet target


Setup for Setup for ppC scattering – C scattering – the RHIC the RHIC polarimeterspolarimeters

recoil carbon ions detected with Silicon strip detectors

2 72 channels read out with WFD (increased acceptance by 2)

very large statistics per measurement (~ 20 106 events) allows detailed analysis– bunch by bunch analysis– channel by channel (each channel is an “independent polarimeter”)– 45o detectors: sensitive to vertical and radial components of Pbeam unphysical asymmetries

Ultra thin Carbon ribbon Target

(3.5g/cm2, 10m wide)

beamdirection

1

34

5

6

RHIC 2 rings

2

Si strip detectors(ToF, EC)

36cm

inside RHIC ring @IP12

all Si stripsparallel to beam

Beam direction


Event Selection & PerformanceEvent Selection & Performance

- very clean data, background < 1 % within “banana” cut- good separation of recoil carbon from (C* X) and prompts

may allow going to very high |t| values

- (Tof) < 10 ns ( ~ 1 GeV)

- very high rate: 105 ev / ch / sec

EC, keV

TOF, nsTypical mass reconstruction

Carbon

AlphaC*

PromptsAlpha

Carbon

Prompts

MR, GeV

MR ~ 11 GeV

~ 1 GeV

Tkin= ½ MR(dist/ToF)2

non-relativistic kinematics


ppC Systematics RHIC:C Systematics RHIC:each detector channel covers same t range

72 independent measurements of AN

width ~stat. error

single meas.

channel by channel raw asymmetry

sources of systematic uncertainties:

1 PBEAM = 8.5 % (normalization)

[PBEAM = 0.386 0.029 0.016]

2 energy scale ~ 50 keV for lowest |t| bin (from detector dead layer) NB these are “external” factors

not “intrinsic” limitations

Fit with sine function (phase fixed)Fit with sine function (phase fixed)


DAQ and WFDDAQ and WFD

ADC3140 MHz

synchronized to accelerator clocks

bunch -ing “start” TDC

“online” analysis of waveformperformed beteween consecutive

bunch -ing PH, tot Q, t.o.f.; full waveform (JET)

~50ns

~100mV

FPGA

onboardmemory

t ~ 2 nsE < 50 keV

DAQ PC

20 106 events in 20 seconds deadtimeless DAQ systemcan accept, analyze, and store 1 event / each bunch -ing

Wave Form Digitizer = peak sensing ADC, CFD, …

common to the pC and JET DAQ system


AGS polarization during acceleration AGS polarization during acceleration (ramp)(ramp)

raw

asy

mm

etry

= A

N

PB

12+ 36- 36+G = 1.91 Ebeam

depolarizing

resonances:

intrinsic: G =

imperfection: G = n

each point = 50 MeV step

48-

red line: simulation of polarization losses assuming constant AN


Bunch by BunchBunch by Bunch

110 bunches

typical examplesometime even nicerthan in textbooks


Bunch by Bunch + Spin PatternsBunch by Bunch + Spin Patterns

high statistics28 bunches @ injection

110 bunches@ flattop1011 p / bunch

110 bunches@ flattopwith messedspin pattern


Beam Polarization Profiles …Beam Polarization Profiles …

to avoid target locationdependencies, sweep the target throughthe beam=> “average” bunch polarization

2 mm

intensity profile


Beam EmittanceBeam Emittance

by sweeping the carbontarget through the beam~ 1 sec. measurement


The Road to PThe Road to Pbeam beam with the JET targetwith the JET targetRequires 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:

%6arg

arg

pCpCN

N

ppett

ett

beam

beam

A

A

P

P

P

P

transfer calibration measurement

expectedprecision


JET TargetJET Target

B

ANbeam (t ) AN

target (t )

for elastic scattering only!

Pbeam = Ptarget . Nbeam / N

target


the JET ran with an average intensity of 11017 atoms / sec

the JET thickness of 1 1012 atoms/cm2 record intensity

target polarization cycle+/0/- ~ 500 / 50 / 500 sec

polarization to be scaled

down due to a ~3% H2

background:

Ptarget ~ 0.924 ± 0.018

(current understanding)

no depolarization from beamwake fields observed !

JET target polarization & performanceJET target polarization & performance


pppp elastic data collected elastic data collected

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

Num

ber

of e

last

ic pp

even

ts

FWHM ~ 6 mmas designed

• recoil protons unambiguously identified !

• 100 GeV ~ 1.8 106 events for 1.5 10–3 < -t < 1.0 10–2 GeV2

similar statistics for 1.0 10–2 < -t < 3.0 10–2 GeV2

• 24 GeV ~ 300 k events

CNI peak AN

1 < E REC < 2 MeV prompt eventsand beam-gas

sourcecalibration

recoil protons elastic pp ppscattering

background118 cts. subtracted

JET Profile: measured selecting ppelastic events

ToF vs EREC correlation

Tkin= ½ MR(dist/ToF)2

ToF < 8 ns

T Kin [MeV]


Energy - Position correlationsEnergy - Position correlations

pp elastic events clearly identified !

num

ber

of e

vent

s (a

. u.)

Tkin 2 (i.e. position2)

Ene

rgy

Position

4 - 36 mm

11 – 181 – 8

not u

sed


Event selections & BackgroundsEvent selections & BackgroundsStrip distribution for energy interval: 1250 – 1750 keV

implement the energy / angle correlation in selecting elastic pp eventstypically, 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 %

Si #2

signal

background Si #6


PPBEAMBEAM … …

PBEAM = 0.392 0.021 (stat) 0.008 ( PTARGET) 0.014 (sys) = 0.392 0.026

2004 ERROR: PBEAM / PBEAM = 6.6 %

2005, 2006: in progress D PBEAM / PBEAM < 5 % !

tot sys = 0.016

“self calibrating”

“Target”: T – target asymmetry

average over beam polarization

“Beam”: B – beam asymmetry

average over targetpolarization

Target

BeamTargetBeam PP

ratio B / T

reduced 2 ~ 1


SummarySummary

fast measurements of Pbeam in ~ 30 sec.

provides also information on beam properties

steady progress in understanding and addressing systematic issues

“online” precision ~ 10 % (relative)

absolute normalization with a polarized gas JET

during 2004 run with Jet target precision on beam polarization

PBEAM / PBEAM = 6.6 %

2005 – 2006 (in progress): PBEAM / PBEAM < 5 % !

dis 2006 tsukuba, april 21, 2006 alessandro bravar proton polarimetry at rhic alekseev, a. bravar,...

Documents

large statistics

detector channel

large rates

large f

d pbeam

normalization pbeam

large s sizable

rhic alekseev