Note:
The analysis presented here follows closely
Alex P. Suaide analysis for Barrel EMC
So far the event sample is 7 Mevents big and spans days 120 (Apr 30, 2003) through 148 (May 28, 2003).
L3 TPC tracks
The L3 TPC tracks with at least Npoints=20 in the track are shown in the two plots below. The left one shows tracks for all STAR triggers and the right one only the ones associated with EEMC triggers (ETH1 and ETH2). The red polygones show our dE/dx and p cut used to select electron candidates. The thick red line corresponds to a "tight" dE/dx cut (approximately 0.36<dE/dx<0.44 keV/cm) and the thin red line corresponds to a "loose" dE/dx cut (approximately 0.34<dE/dx<0.46 keV/cm). The black box shows the "background" region used for comparison to the electron sample.
L3 TPC tracks for all STAR triggers (min. points in the track 20) | L3 TPC tracks for EEMC triggers only (min. points in the track 20) |
L3 tracks dE/dx distributions
The plots below show the dE/dx distribution for the tracks with at least Npoints (15,20,25,30) and with 1.5 GeV < p < 10.0 GeV for the two trigger conditions mentioned above (all STAR and EEMC only). What is actually plotted is a log((dE/dx)/BB), where the dE/dx is taken from L3 track info and the BB stands for the Bethe-Bloch dE/dx prediction for an electron with a given momentum.
A "tri-gaussian" fit to the log((dE/dx)/BB) distribution was then performed
( min points requirement was varied from 15 to 30).
On the plots below: the blue gaussian bell denotes electron candidates, the black and green ones
- background events and the red one the overall fit.
The dE/dx cuts ("tight" and "loose") mentioned in the previous section are shown as thick blue solid vertical bars. The upper two plots show the tight cut -0.05 < log((dE/dx)/BB) < +0.15 and the lower two plots show the loose cut -0.10 < log((dE/dx)/BB) < +0.20.
The backround events were chosen with a -0.60 < log((dE/dx)/BB) < -0.20; cut (thin black solid bars)
L3 tracks dE/dx distribution tight dE/dx cut, all STAR triggers |
L3 tracks dE/dx distribution tight dE/dx cut, EEMC triggers only |
L3 tracks dE/dx distribution loose dE/dx cut, all STAR triggers |
L3 tracks dE/dx distribution loose dE/dx cut, EEMC triggers only |
Electron Sample
Based on the gaussian fits above one can calculate the following quantities:"Tight" dE/dx cut
All STAR triggers | EEMC triggers only | |||||
min points | Ne | Pe [%] | Ee [%] | Ne | Pe [%] | Ee [%] |
15 | 24746 | 35.38 | 70.95 | 3040 | 36.78 | 75.59 |
20 | 14660 | 45.22 | 73.12 | 1589 | 44.06 | 78.77 |
25 | 9325 | 49.25 | 79.13 | 907 | 44.91 | 83.42 |
30 | 7659 | 58.01 | 79.14 | 842 | 64.41 | 82.94 |
"Loose" dE/dx cut
All STAR triggers | EEMC triggers only | |||||
min points | Ne | Pe [%] | Ee [%] | Ne | Pe [%] | Ee [%] |
15 | 31410 | 25.53 | 90.05 | 3744 | 26.08 | 93.09 |
20 | 18351 | 31.24 | 91.53 | 1919 | 29.49 | 95.12 |
25 | 11194 | 33.29 | 94.99 | 1056 | 29.02 | 97.10 |
30 | 9187 | 40.66 | 94.92 | 982 | 43.11 | 96.75 |
Calibration Constant
The electron (and background) track candidates were selected according to the critetria described above.
For the tracks with a matching EEMC tower values of momentum/energy were histogrammed.
The momenta (p) were taken from L3 TPC tracks and
the energies (E) were taken from the EEMC data according to the following formula:
E = ( ADC - PED ) * g * k
where
The thick solid blue histogram shows electron candidate events and the thin black one the background candidates (upper left below). The background histogram was normalized to the electron one requiring that the number of events for 2.5 < p/E < 10.0 be the same. The upper left plot show the "electron - (normalized)background" histogram. Gaussian fits were performed for both "electron" and "electron-background" histograms (solid red line). The lower left distribution is eta versus p/E for the electron candidates and the lower right one shows all the matched L3 tracks that fulfill the minimum Npoints and trigger conditions.
p/E distribution tight dE/dx cut, all STAR triggers |
p/E distribution tight dE/dx cut, EEMC triggers only |
p/E distribution loose dE/dx cut, all STAR triggers |
p/E distribution loose dE/dx cut, EEMC triggers only |
Calibration Constant (chan/GeV)
Finally the the mean values of the gaussian fits to the p/E distributions were converted to the absolute calibration
constants k = 50.0 / mean , where mean is the mean value of the gaussian fit. A table containing the
resulting calibration constants is presented below:
"Tight" dE/dx cut
All STAR triggers | EEMC triggers only | |||
Npoints | no background subtraction | with background subtraction | no background subtraction | with background subtraction |
15 | 53.05 +/- 2.86 | 56.39 +/- 2.65 | 59.53 +/- 4.66 | 57.86 +/- 3.58 |
20 | 55.58 +/- 5.54 | 57.53 +/- 5.61 | 70.94 +/- 16.08 | 71.41 +/-14.69 |
25 | poor fit | poor fit | poor fit | poor fit |
30 | poor fit | poor fit | poor fit | poor fit |
"Loose" dE/dx cut
All STAR triggers | EEMC triggers only | |||
Npoints | no background subtraction | with background subtraction | no background subtraction | with background subtraction |
15 | 48.84 +/- 2.25 | 52.98 +/- 2.08 | 57.03 +/- 5.00 | 53.11 +/- 3.19 |
20 | 51.21 +/- 3.45 | 54.81 +/- 3.98 | 61.90 +/- 9.18 | 61.21 +/- 7.71 |
25 | poor fit | poor fit | poor fit | poor fit |
30 | poor fit | poor fit | poor fit | poor fit |
A graphical presentation of the above table is below
Conclusions
To be written