Post on 17-Dec-2015
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