Run 8 Polarization measurements from STAR BBC

Andrew GordonSeptember 12, 2008

2

} {East-West Coincidence

Bunch Crossing (7-bits){

Hank’s Scaler Boards

}

24-bit word is histogrammed every clock cycle

Inner tiles of BBC accumulated every clock cycle

Discriminated phototube outputs

3

Requirements:

Outer left and right phototubes of small tiles have no hits.

Left Hit=Hit in 2 or 3 AND no hit in 5 and 6

Right Hit=Hit in 5 or 6 AND no hit in 2 and 3

Polarization:

p

NL NR

up down

NR NL

up down

-

NL NR

up down

NR NL

up down

+=

For effective analyzing power use final Run 6 polarizations and Run 6

BBC data:Yellow Polarization (%)=p(East)/(6.9±0.1(stat))x10-5

Blue Polarization (%)=p(West)/(7.1±0.1(stat))x10-5

See also J. Kiryluk (STAR) ArXiv:hep-ex/0501072v1, 28 Jan 2005

and C.A.Whitten (STAR), Proceedings PSTP 2007, p. 390.

Effective Analyzing PowerBBC Polarimeter

• Analysis from available run-6 data more complete analysis still to do

• Event data suggests BBC very similar year to year assume same effective analyzing power for run 8

5

Example: Rates for start of Fill 9949East-West Coincidence Rates for each crossing

100 Yellow

filled & Blue

filled crossings

7 Yellow Empty

& Blue Filled

bunches

7 Yellow Filled &

Blue Empty bunches

Yellow Background ~ 0.1%

Blue Background ~ 0.2%

<Instantaneous BBC Rate>

~0.5 MHz

Star preliminary

6

Background level from abort gaps low

Yellow filled & Blue empty

Yellow empty & Blue empty

Yellow empty & Blue filled

Yellow filled & Blue filled

<Blue Empty & Yellow Filled>

<Blue Filled & Yellow Filled>

Yellow beam Background fraction

=

<Blue Filled & Yellow Empty>

<Blue Filled & Yellow Filled>

Blue beam Background fraction

=

Star preliminary

Example: Background for Fills 9949 and 9951

Note change

of scale on y-

axis

Background

fractions low and

relatively stable,

except for event in

blue beam at around

3 hours.

Time=midpoint of run relative to start of fill, <run time> ~ 10 minutes Star preliminary

Example: Multiplicity for Fills 9949 and 9951

Average number of

BBC phototubes with

hits is relatively

stable. (Event in blue

beam 9949 not

detectable.)

East BBC

West BBC

Star preliminary

9

Sample polarization time dependenceDecline visible in fill 9949, but 9951 more stable.

Time=midpoint of run relative to start of fill, <run time> ~ 10 minutes Star preliminary

Flat line fits shown Flat line fits shown

10Polarization dependence not always smooth decay

Star preliminary

11Polarization dependence not always smooth decay

Star preliminary

12

Effective decay rates of polarization vs Fill

Polarization of each fill fitted to

P = A e-t

separately for each beam.

Yellow beam decay rate more consistently non-zero than blue beam.

Star preliminary

Comparing to Whitten PSTP 2007, roughly same rates as for Run 6.

Polarization in units of percent. The values for are the y-axis values divided by 100.

<100>=1.7±0.1

<100>=0.7±0.1

13

Fill averaged polarizationsRun 6 calibration of BBC asymmetries applied to Run 8 data.

Star preliminary

Comparison of Polarization to CNI results

For each fill calculate

STAR/pC

Error bars are uncorrelated errors only.

pC data from Sasha, September 12, 2008. Uncertainties dominated by pC uncertainty estimates.

Mean=1.026±0.023

Mean=0.929±0.012

15Conclusions

Absolute polarization can be derived from Run 6 calibration.

Polarization shows dependence on time.

•Some fills show a step downward in middle of fill

•Stronger for the yellow beam

STAR can measure polarization at relatively small time steps.