Bunch-by-bunch (relative) polarization measurements using inner annuli of STAR BBC

Andrew GordonApril 4, 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

Require

East-West coincidence

Top and bottom of inner tiles clean to reduce dilution of asymmetry

Keeps ~5% of all bunch crossings.

Keeps 20% of the 5%=1% of all crossings pass both requirements.

Typical numbers on the order of

~3M events per bunch per hour

~3.5 (statistical) measurement of polarization per bunch per hour

Use tiles 5+6 for Left, tiles 2+3 for Right

(Backgrounds from single beam accidentals less than ~1% of sample after this requirement.)

4

Yellow(east BBC)

Blue(west BBC)

sig

sig

Sigbx=

Statistical uncertainties only

(|Pbx|-<|Pbx|>)bx

Width=1.220.15

Width=1.050.12

5

Yellow

Blue

sig

sig

Sigbx=

Statistical uncertainties only

(|Pbx|-<|Pbx|>)bx

Width=1.120.14

Width=0.910.09

6

Yellow

Blue

sig

sig

Sigbx=

Statistical uncertainties only

(|Pbx|-<|Pbx|>)bx

Width=1.160.13

Width=0.790.08

7

Yellow

Blue

sig

sig

Sigbx=

Statistical uncertainties only

(|Pbx|-<|Pbx|>)bx

Width=1.060.16

Width=0.840.07

8Conclusions

We can see the relative polarization per bunch at a rate of several measurements per fill.

Polarization is largely consistent across bunches.

Can be extended to all Run 8 fills.

Measurement requires calibration to determine polarization at STAR.

To do