10/21/2003 Andrei Nomerotski  

Can we use even looser muons than now?

We use the following cuts on muon candidates - they are referred below as "usual cuts"
1) nseg > 1
2) chi^2 local >-0.5 (i.e. converged fit exists)
3) CFT and SMT hits
4) central rank = 1 (this is obsolete in p14 and is not used in the below)
5) lepton Pt>2 GeV, Ptotal >3 GeV

after Sergey's D* loose selections here is what we have in <6 pb^-1 with usual cuts. Note that not all data files were used so the sample
is a bit smaller wrt what has been shown before for 6 pb^-1.   The plot is the mass difference between D* and D0 candidates.

D* with usual loose cuts

next plots will show the same sample but looser cuts exploring the currently unused areas of the parameter space

1) same as usual cuts but nseg = 0 (those are MTC aka calorimetric muons)



2) same as usual cuts but nseg = 1 (have associated Layer A hits only)



3) same as usual cuts but nseg = 3 and chi^2 local = -1 (fit did not converge)



4) same as usual cuts but lepton Pt < 2 GeV or P < 3 GeV



at last the full sample with looser cuts (any muon candidate from reco with Pt > 1.5 GeV and P > 2 GeV. For comparison
the histogram with usual cuts is also shown.



 selection
entries
 signal
S/B
total usual
2635
 642
 11
nseg = 0
 1544
 89
 2.6
nseg = 1
 292
 36
 4.3
nseg = 3, no fit
 72
 3
 2.3
small P
 213
 16
 3.1
total looser cuts
 5055
 805
 6.7

S/B is defined as ratio of signal and background heights in the center of the mass peak Bottom line of the above is that
the loosiest cuts we can think of increase the D* sample by (805-642)/642 = 25 % at expense of  (11-6.7)/11 = 39 %
decrease in S/B ratio.

another thing we checked was what happens if we use tight muons as defined by muon  ID group. here they are



compared to the usual cuts (note that these two plots had different number of processed files compared to the plots above)



the ratio of signal events is ~95% and bkg is practically the same. so tighter muons do not improve S/B.
this is may be not a surprise since most of the events came from single muon trigger which required a muon that is
similar to "tight" definition at L3.

Comparison of "tight" D0 for usual and tight muons shows (may be) a little improvement which still needs to be quantified, see below.
Red histogram is usual muon cuts, black histogram is tight muon cuts.