To enable vertex reconstruction of the pp events with the above topology, the original lmv() code was duplicated and added as a method to the StPrimaryMaker::ppLMV() . Additionally, ppLMV() has built in a cut rejecting all global tracks with too large Zdca to the nominal beam line.
The ((StPrimaryMaker *) chain->GetMaker("primary"))->ppLMVuse(15.);
// cm
method is added for both:
- force the StPrimaryMaker to use
ppLMV() for all events , regardless on track multiplicity ( instead of
lmv() or egr() ) and
- define maximal Zdca value
Performance of ppLMV
ppLMV() was tested with pp nondiffractive minbias
pp events, generated with geometry 'year2001' for MDC4. The vertex
was smeared with sigZ=7.5 cm and sigX=sigY=0.5 mm.
Pythia events were processed using TRS with
pileup added , starting from 0 upto the level of 2% probability
per bunch crossing .
1% of pileup per bunch corresponds approximately
to the luminosity of 4*10**30 1/cm**2 1/s, assuming the
pp nondiffractive cross section of 28 mb and 106 ns separation between
bunches =120 bunches/ring.
| pileup prob.
per bunch X |
total number of
pileups in TPC |
vertex recon
efficiency |DZ vert| <1.5 cm |
RMS-Z ( cm)
using only |DZ vert| <1.5 cm |
RMS-X (cm)
using only |DX vert| <1.5 cm |
CPU/event (sec)
with the MDC4 chain |
| no | 0 | 0.87 +- 0.015 | 0.34 | 0.34 | 23 |
| 1% | 8 | 0.74 +- 0.02 | 0.50 | 0.41 | 69 |
| 2% | 16 | 0.65 +- 0.02 | 0.55 | 0.44 | 120 |
| 3% | 24 | 0.58 +- 0.02 | 0.60 | 0.47 | 173 |
| 5% | 40 | 0.49 +- 0.02 | 0.75 | 0.45 --> sigX | 273 |
| 10% | 80 | 0.37 +- 0.02 |
Fig below shows error of reconstructed vertex
in Z and in X directions for 500 input events without pileup.
Similar plots with pileup probability of
1%
per bunch crossing .500 input events.
Similar plots with pileup probability of
2%
per bunch crossing .500 input events.
imilar plots with pileup probability of
3%
per bunch crossing .500 input events.
imilar plots with pileup probability of
5%
per bunch crossing .500 input events.
imilar plots with pileup probability of
10%
per bunch crossing . 400 input events.
The ppLMV() was added to St_dst_maker in
the CVS repository.