COT primary track multiplicity comparisons can be used to set the mean number of extra MBR interactions to be added to Monte Carlo. Addition of 0.13 extra interactions is motivated by comparing mean from data to means from simulation (for 0 and 1 extra interaction).
Table of mean (Nav) of COT primary track multiplicity (from Heather):
MC with no extra MBR: Nav = 10.59
MC with one extra MBR: Nav = 18.32
Pre-Jan 03 Data: Nav = 11.33
Post-Jan 03 Data: Nav = 12.04
N(vtx)<=1 Data: Nav = 9.89 (3687 events)
N(vtx)>1 Data: Nav = 16.01 (1465 events)
In order to achieve the same Nav as the data (11.63 for the average of 2002-2003 data), one calculates (11.63-10.59)/(18.32-10.59) = 0.13 extra MBR events to be added to MC.
Another way to estimate the number of extra MB interactions is to count the number of Z->ee events with more than one vertex. Ignoring vertexing inefficiency and fake rate, this yields Nav = 0.34.
It is also instructive to compare to the first-principles calculation:
Nmb = L_inst * time between the bunch crossings * sigma_inelastic
Substituting the numbers:
Nmb = 1.6*10^31 * 396*10^-9 * 60*10^-27 = 0.4
(L_inst reported by Pasha Murat)
Agreement of Plug electron ID variables requires more extraneous energy flow, achieved by adding 1 extra MB. Since this is quite inconsistent with the COT track multiplicity and vertexing measures, it suggests another source of extraneous energy flow in the forward direction - perhaps beam halo secondary interactions.
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Primary COT Track Multiplicity in Z->ee Events Tracks satisfy >2 axial, > 2 stereo superlayers with >4 hits and beam-corrected |d0| < 3 mm. Simulation is pure Z->ee Pythia MC with Rick-Field-tune of underlying event (blue) and the same with average one (poisson-distributed) extra MBR event superposed (red). current release = pre-Jan03shutdown data next release = post-Jan03shutdown data post-shutdown data appear to have slightly higher instantaneous luminosity than pre-shutdown data. (plots from Heather Gerberich) |
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Primary COT Track Multiplicity in Z->ee Events Track requirements and simulation as above. current release = data selected with one primary vertex next release = data selected with more than one primary vertex Track multiplicity is consistent with one and two interactions respectively (although some deficit is observed in the data at very high multiplicities). This shows that the COT primary track multiplicity is a reasonable measure of the number of extra interactions. (plots from Heather Gerberich) |
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Overlaying one extra MB interaction gives good results for plug simulation. Primary COT track multiplicity (see above) suggests ~0.13 extra interactions. Plug may be seeing effects of secondary interactions (perhaps induced by beam halo) which are not simulated. |
Plug ID efficiencies Tail of PEM chi^2 distribution is sensitive to energy flow in the calorimeter. N-1 efficiency of PEM chi^2 cut is significantly over-estimated with pure Z->ee event, and is consistent with these data when average of one MB event is overlaid. Isolation and Had/EM cut efficiencies are not very sensitive. Total Plug electron ID efficiency was 89 +- 0.6 (stat) % in the Z-ee data, MC without extra min-bias predicts 94.2 +- 0.1 (stat) %, and MC with average one extra MB predicts 90.0 +- 0.6 (stat) % (table from Heather Gerberich) |
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consistent with above |
Central ID Efficiencies Cut efficiencies of central ID variables are not very sensitive to extra interactions. The top table shows the total and N-1 efficiencies measured in the data, compared to Z-ee MC with and without extra MB interactions simulated. The bottom table confirms this with Z-ee data split into events with one and more than one primary vertex. (table from Heather Gerberich) |
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Distributions of Plug ID Variables current release = no extra MB interactions overlaid on Z-ee MC next release = average one extra MB interactions overlaid on Z-ee MC (plots from Heather Gerberich) |
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Distribution of Plug PEM chi^2 current release = no extra MB interactions overlaid on Z-ee MC next release = average one extra MB interactions overlaid on Z-ee MC Tail of PEM chi^2 distribution is sensitive to energy flow in the calorimeter. Overlaying one extra MB interaction gives a better description of the tail. (plot from Heather Gerberich) |
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