The background is defined as the average number of electrons and positrons hitting PC3
per event. The results for several MVD/nosecone configurations is shown.
In the following table, I have applied a cut requiring pt>200MeV/c on all electrons.
| source of background | old pisa MVD, old pisa nosecone 150 events used (e/event) | current pisa MVD old pisa nosecone 150 events used (e/event) | with MVD removed, "background" from MVD 150 events used (e/event) MVD barrel MCMs, | Power/comm, plenum 0.07+-.02
| 0.63+-.06
| 0.00
| Si in barrel, | rohacell C cages 0.46+-.06
| 0.43+-.06
| 0.01+-.01
| pads+motherboards
| 0.20+-.05
| 0.26+-.08
| 0.00
| MVD enclosure, | frame 0.59+-.09
| 0.48+-.07
| 0.02+-.01
| MVD total
| 1.45+-.13
| 1.87+-.15
| 0.12+-.03
| nosecone
| 1.28+-.12
| 1.18+-.09
| 1.44+-.13
| Dalitz+ | beam pipe 0.89+-.08
| 0.85+-.08
| 0.99+-.08
| total
| 18.97+-.38
| 20.00+-.43
| 18.05+-.39
| events used | in analysis 150
| 150
| 150
| |
In the following table, I have applied a cut requiring pt>200MeV/c on all electrons.
| source of background | current pisa MVD Jan. DC nosecone 150 events used (e/event) | Jan 98 version of new nosecone 480 events used (e/event) | with MVD removed, "background" from MVD 150 events used (e/event) MVD barrel MCMs, | Power/comm, plenum 0.63+-.06
| 0.66+-.04
| 0.00
| Si in barrel, | rohacell C cages 0.43+-.06
| 0.47+-.03
| 0.01+-.01
| pads+motherboards
| 0.26+-.08
| 0.38+-.05
| 0.00
| MVD enclosure, | frame 0.48+-.07
| 0.52+-.05
| 0.02+-.01
| MVD total
| 1.87+-.15
| 2.10+-.09
| 0.12+-.03
| nosecone
| 1.18+-.09
| 1.13+-.06
| 1.44+-.13
| Dalitz+ | beam pipe 0.85+-.08
| 0.90+-.05
| 0.99+-.08
| total
| 20.00+-.43
| 19.82+-.24
| 18.05+-.39
| |
(Postscript) "radiographs" of the MVD based on these calculations are available here. These "radiographs" show the r and z location (first page) and the x and y locations (second page) of the vertex for all of the electrons and positrons hitting PC3. Only th background from the MVD is shown on these plots. A total of 480 pisa events were used to make these plots. All the the vertex locations are marked with black dots. The part of the backgroubd which comes from the MVD electronics (MVD barrel MCMs, Power/comm cables, plenum) is also circled in red. The part of the background which comes from the Silicon in the barrel and from the C-cages is circled in green. The contribution from the pad detectors and their motherboards is circles in dark blue. The contribution from the MVD enclosure and frame is circled in light blue. The first pair of plots requires the electron/positron to have pt>200MeV/c. The second plot pair of plots shows all electrons and positrons, without a pt cut.
When Charlie Maguire does these background calculations, he makes a cut requiring the vertex of the event (i.e. where the primary collision took place) to be abs(Z0).lt.35cm. In the table below I show the effect of this cut on the results for the "Jan 98" version of the nosecone. The error analysis for the average number per event is a little tricky and I have not done it for the case with the cut on Z0. Therefore no uncertainties are given in that column or in the ratio.
| source of background | current pisa MVD, Jan 98 version of new nosecone, no Z0 cut 480 events used (e/event) | current pisa MVD, Jan 98 version of new nosecone, abs(z0).lt.35 446 events used (e/event) | ratio of two previous columns MVD barrel MCMs, | Power/comm, plenum 0.66+-.04
| 0.70
| 1.06
| Si in barrel, | rohacell C cages 0.47+-.03
| 0.50
| 1.07
| pads+motherboards
| 0.38+-.05
| 0.22
| 0.57
| MVD enclosure, | frame 0.52+-.05
| 0.36
| 0.68
| MVD total
| 2.10+-.09
| 1.85
| 0.88
| nosecone
| 1.13+-.06
| 1.00
| 0.88
| Dalitz+ | beam pipe 0.90+-.05
| 0.92
| 1.03
| total
| 19.82+-.24
| 19.94
| 1.01
| |
The following calculation is based on Charlie Maguire's work -- I took an
ntuple from him and did my own analysis using his ntuple. There is one detail
different in his calculation (i.e. the one below) and mine (i.e. the ones above) --
he counts hits on PC2 while I was
counting hits on PC3. Otherwise, the table below is like the table above except
1) I got the ntuple from Charlie instead of creating it myself
2) it is based on hits at PC2 (not PC3)
3) it uses the latest version of the nosecone geometry
4) it uses the latest version of the MVD (which differs from the version
of the MVD above only because the correct radius of the "struts" is
used in the calculation below).
The total background from all sources is lower at PC2 than at PC3. The
MVD background is about the same for PC2 and PC3.
| source of background | current pisa MVD, Feb 98 version of new nosecone, no Z0 cut 316 events used (e/event) | current pisa MVD, Feb 98 version of new nosecone, abs(z0).lt.35 292 events used (e/event) | ratio of two previous columns MVD barrel MCMs, | Power/comm, plenum 0.57+-.04
| 0.61
| 1.06
| Si in barrel, | rohacell C cages 0.38+-.04
| 0.40
| 1.07
| pads+motherboards
| 0.25+-.04
| 0.12
| 0.49
| MVD enclosure, | frame 0.45+-.05
| 0.32
| 0.71
| MVD total
| 1.72+-.09
| 1.53
| 0.89
| nosecone
| 1.11+-.07
| 0.97
| 0.87
| Dalitz+ | beam pipe 0.89+-.06
| 0.92
| 1.03
| total
| 13.13+-.24
| 13.15
| 1.00
| |