Local Polarimetry for Proton Beamswith STAR ZDC Calorimeters

David GrosnickValparaiso University

for the STAR collaboration

Division of Nuclear Physics Meeting25 October 2008

Local Polarimeters at STAR• Currently, beam-beam counters used as local polarimeter

at STAR for

• At higher beam energies, BBCs may have decreasinganalyzing power insufficient polarization measurement

• Need detector located at larger distance from intersectionpoint Zero-Degree Calorimeters

• Detects forward (< 2 mrad) neutral particles

GeV200=s

!

!

ZDCsBBC BBC

Zero-Degree Calorimeters (ZDC) at STAR

Shower Max

Detector

Beam

Samplingcalorimeter

Shower Max Detector

8 horizontal slats (4 strips)

7 vertical slats (3 strips)

Available Data from Dedicated Runs

• Determine feasibility of using ZDC SMDs as localpolarimeter

• Small data sample from limited no. dedicated runs

• Limited quality of data: not all spin states presentand not all spin rotator states available

• Method: gain-match and pedestal-subtract ADCvalues from each vertical and horizontal SMD slat

• Good hits are used to calculate left-right and up-down asymmetries for beam spin states in eacheast and west ZDC

• Used square-root asymmetries

ZDC Shower Max Detector Data

Plot of raw ADC values for given slat index

Slat

Inde

x

East Vertical

East Horizontal

West Vertical

West Horizontial

ZDC Shower Max Detector Data

Plot of corrected ADC values for given slat index

Slat

Inde

x

East Vertical

East Horizontal

West Vertical

West Horizontial

SMD Hit Patterns – East and West ZDC

East ZDC7 Horizontal Slats

West ZDC7 Horizontal Slats

East ZDC8 Vertical Slats

West ZDC8 Vertical Slats

Spin Patterns in Bunches Per Spill

Corrected spin patterns in bunch

No. Events in ZDC perbunch crossing

Note:missing spinpatterns

Can still measure physicsasymmetry with limitedpolarization states

Physics Asymmetry Calculation

Differences in beam polarizations (U,D) and analyzing powers (L,R) entercalculation as higher-order corrections

!

"phys

e=

NLe

##N

Re

$$% N

Le

$$N

Re

##

NLe

## NRe

$$+ N

Le

$$ NRe

##

=PYA

f e% P

BAbe

1+ PYPBANN ,e

+ higher% order terms

Calculated assuming that only 2 of 4 usual spin states are available

where

!

PY

= 12(P

Y

"+ P

Y

#)

PB

= 12(P

B

"+ P

B

#)

Average beampolarizations

!

Af e

= 12(A

L f e+ A

R f e)

Abe

= 12(A

Lbe+ A

Rbe)

ANN ,e

= 12(A

NN ,L e+ A

NN ,R e)

Average analyzingpowers and 2-spin

parameter

Calculated Asymmetries from ZDC SMDs

Luminosity Asymmetry:LRe = -0.0911 +/- 0.0012UDe = -0.0918 +/- 0.0013LRw = -0.0986 +/- 0.0013UDw = -0.0955 +/- 0.0012

Physics Asymmetry:LRe = 0.0137 +/- 0.0012UDe = 0.0049 +/- 0.0013LRw = 0.0140 +/- 0.0013UDw = -0.0039 +/- 0.0012

Used square-root asymmetries:

L,R = left, rightU, D = up, downe,w = east, west; = spins up, down!",

Slat-by-Slat Physics Asymmetry

Higher-order terms above are second-order in small quantities, ratherthan fourth-order in square-root asymmetry

Calculated assuming that only 2 of 4 usual spin states are available

!

"phys,i

e=N

Le,i

##$ RN

Le,i

%%

NLe,i

##+ RN

Le,i

%%

=PYAL f ,i

$ PBALb ,i

1+ PYPBANN ,Li

+ higher$ order terms

&N

Le,i

##/L## $ N

Le,i

%%/L%%

NLe,i

##/L## + N

Le,i

%%/L%%

where

!

R =1+ "

lum

1# "lum

$L%%

L&&

Ratio ofluminosities

Individual Slat AsymmetriesAsymmetry for Vertical Slats East X

-0.0600

-0.0400

-0.0200

0.0000

0.0200

0.0400

0.0600

1 2 3 4 5 6 7

Slat Number

Ph

ysic

s A

sym

metr

y

Asymmetry for Vertical Slats West X

-0.0600

-0.0400

-0.0200

0.0000

0.0200

0.0400

0.0600

1 2 3 4 5 6 7

Slat Number

Ph

ysic

s A

sym

metr

y

Nonzero asymmetryAsymmetry for Horizontal Slats East Y

-0.0600

-0.0400

-0.0200

0.0000

0.0200

0.0400

0.0600

1 2 3 4 5 6 7 8

Slat Number

Ph

ysic

s A

sym

metr

y

Asymmetry for Horizontal Slats West Y

-0.0600

-0.0400

-0.0200

0.0000

0.0200

0.0400

0.0600

1 2 3 4 5 6 7 8

Slat Number

Ph

ysic

s A

sym

metr

y

Consistent with zero

STAR Preliminary

Definition of the Phi Asymmetry

SMD Bin Map for Phi Asymmetry

Form “left-right” asymmetries from opposite bins as function of angle φ

SMD X Slat No.

SMD

Y S

lat N

o.

Phi Asymmetry of Neutral Particles

East ZDC PhiAsymmetry Distribution

West ZDC PhiAsymmetry Distribution

Asymmetry of sum ofvertical and horizontal slatsfor given SMD bin

STAR Preliminary

Summary

• ZDCs tested for feasibility as local polarimeter atSTAR

• Limited data sample analyzed using dedicated runs

• Results:

• Future: need further studies at high energies

Observe significant L-R physics asymmetry

Small U-D asymmetry - consistent with beamproton spins both up or down

Results similar to other experiments