Difference: Conversion20070912MartinJurkovic (r6 vs. r5)

Input: PLUTO simulation gen2 Report: Conversion identification and suppression in RICH and MDC0

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
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.

Opening angle for single and double ringsAngle to closest lepton for single and double rings
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.

Single leg momentum distribution for double-track ringSingle leg momentum distribution for single-track ring
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 doublesAngle to closest lepton candidate for singles
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.

Chi2 distribution for double-track ringsChi2 distribution for single-track rings
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.

Opang for doubles and mdc cutopang for singles and mdc 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 ringsRing properties for single-track rings
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 single and double track rings
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 23 Oct 2007

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