Input: PLUTO simulation gen2
For the following investigations I have selected events from the PLUTO simulation DST,
which contain exactly
TWO primary lepton tracks originating from the same mother particle created in PLUTO event generator.
The reason for this selection was to keep
the algorithm for the following investigations as simple as possible.
The selected sample contains lepton tracks originating
from different decays e.g. pi0, eta,... and conversion as well. The tracks have to produce signal at least in RICH and inner MDC and
somewhere behind the magnetic field (requirement on PidTrackCandidate; I do not require full reconstruction of the tracks). Since I'd like
to separate "close pairs" and "open pairs" and look into detector signals for these two cases, the selection is correct.
In the following I separate my sample into pairs, where:
- both partners contribute to a single ring or to two rings with some overlap region double-track rings
- both partners build two well defined and well separated rings with NO overlap single-track rings
Properties of selected tracks
In the selected sample of 1.8M events only 205k primary e+/e- pairs from following decays can be found (at the most one pair per event):
Process |
Generator Info |
Pairs |
gamma conversion from pi0 |
7001 |
90766 |
pi0 Dalitz |
7051 |
38462 |
eta Dalitz |
17051 |
37912 |
Delta Dalitz |
34051 |
37798 |
On the following picture the e+/e- pair opening angle distribution for above mentioned sources of e+/e- pairs is depicted. The
displayed range is set to 0 degrees to 25 degrees, which corresponds the to the calculation of the angle to the closest candidate in the
inner MDC.
|
e+e- opening angle distribution for different sources |
In the following I compare the true opening angle (left) distribution and distribution of the angle to the closest lepton candidate (right)
as measured by the inner MDC. The distributions are plotted for single- (
blue) and double- (
red)
track rings. and for all e+e- sources. For the dot-filled spectra, an additional momentum cut p > 50MeV/c on both legs of the pair was applied.
|
|
True opening angle distribution for single and double track rings |
Angle to closest lepton track for single and double track rings |
|
All pairs |
After momentum cut |
Double track rings |
164379 |
147512 |
Single track rings |
2677 |
21840 |
The momentum distributions of double- (left) and single- (right) track rings are displayed on the following two pictures. The black lines
highlight the p = 50 MeV/c border.
|
|
Momentum distribution for double track rings |
Momentum distribution for single track rings |
Comparing the distribution of the angle to the closest lepton candidate for both legs of the pair agrees in 85% for double-track rings
and in 93% for single track ring. The disagreement is visible mainly at small angles, even for cases, when both partners are in different
MDC cells.
|
|
Angle to closest lepton candidate for double-track rings |
Angle to closest lepton candidate for single-track rings |
On the following two pictures the inner MDC chi2 distribution is depicted. For double track rings both track of the pair
share the same MDC segment in 54%. Out of this amount only in 47% cases the segment is not fitted, the rest has passed the fit procedure.
For the single-track rings the situation looks better. Only in 42 cases out of 26.7k pairs both legs share the same segment, but in all
cases this segment was unfitted. In only 4.5% cases on of the legs has unfitted segment, while applying the 50 MeV/c momentum cut on both
legs, this number is reduced by factor of 2.
|
|
Inner MDC chi2 distribution for double-track rings |
Inner MDC chi2 distribution for single-track rings |
The true opening angle distributions including the segment fit information are displayed on the following two pictures for single- and
double- track rings. The inner MDC chi2 cut tend to select tracks with small opening angle. Unfortunately a not negligible amount of
track with small opening angle and same MDC segment survive this cut.
|
|
Opening angle distribution for double-track rings for different inner MDC cuts |
Opening angle distribution for single-track rings for different inner MDC cuts |
RICH signal
On the following pictures I plot RICH ring properties each other. They are:
- pattern matrix (PM)
- average charge (AV_charge)
- number of pads (npads)
- ring centroid (centroid)
In the following, different ring properties are displayed for double- (left) and single- (right) track rings. There is no additional cut
on the quality of the track applied.
|
|
Ring properties for double-track rings |
Ring properties for single-track rings |
Comparing the both cases one can see, that the distributions are similar except of the number of pads distribution.
The 1D distribution is on the following picture. The number of pads distributions for single- (blue) and double- (red) track rings are selected the
exactly the same way as all the distributions before. The brown dashed distribution had in addition to the double-track ring selection a cut
on inner MDC chi2 applied. It select rings, which at least one leg of the pair has negative chi2.
|
Number of pads for double (red) and single (blue) rings |
Yields for several cuts on number of pads are in the following table:
|
Total |
<20 |
<25 |
<30 |
Double-track rings |
164370 |
30% |
52% |
73% |
Double-track rings with at least 1 unfitted segment |
56267 |
24% |
45% |
67% |
Single-track rings |
26677 |
65% |
86% |
96% |
--
MartinJurkovic - 15 Oct 2007