The triggers of interest are
HLT_Ele15_LW_L1R
hltL1sRelaxedSingleEgammaEt8
hltL1NonIsoHLTNonIsoSingleElectronLWEt15PixelMatchFilter
HLT_Photon10_L1R
hltL1sRelaxedSingleEgammaEt5
hltL1NonIsoHLTNonIsoSinglePhotonEt10HcalIsolFilter
Monte Carlo samples used in the study of electron trigger efficiencies are listed in Table 1.
TABLE 1 | Sample | Location of PAT Files |
---|---|---|
ttbar | TTbarJets-madgraph-7TeV | /castor/cern.ch/user/c/chadwick/TopAna/CMSSW_3_3_1/TTbarJets-madgraph-7TeV |
More information about the sample is detailed here.
Two separate sets of cuts were used.
The plot overflow has been transferred to the last bin in the histogram.
All efficiency plots were generated by defining a TGraphAsymmErrors
in ROOT, and calling the member function BayesDivide()
. This function takes two histograms (one the numerator and the other the denominator) and computes the efficiencies, while assigning suitable asymmetric errors using Bayesian statistics. Information about the TGraphAsymmErrors
class can be found here, and a paper explaining the computation of the errors (which goes beyond normal binomial distribution errors) can be found here.
Each efficiency plot is fitted with the following function:
In the plots below, p0 = A, p1 = and p2 = s. p0 corresponds to the high limit of the efficiency, the midpoint of the slope, and s the gradient of the slope at .
HLT_Ele15_LW_L1R
, Loose Cut
The fit for has been performed only on data points above 12, ignoring the "wiggle" at low . Reading off the value of p0 from the fits, we have at high transverse momentum
TABLE 2 | Efficiencies from fit |
---|---|
0.9895 | |
0.9796 | |
0.9663 |
We should expect that . From Table 2, we obtain .
Comparing the plots shown above, we see that the slopes of the trigger efficiency for the L1 seed and the HLT begin at different transverse momenta: around 5 GeV for the former and 12 GeV for the latter. This accounts for the wiggle that we see in the plot of : at low transverse momentum, both the L1 seed and the HLT have similar efficiencies with respect to all PAT electrons. But between 5 and 12 GeV, the L1 seed is increasingly likely to pass electrons, while the HLT still has the same efficiency as before, leading to a dip in .
In bin 6 and 35 out of 40 bins in the efficiency histograms, ROOT reports that is greater than , which is anomalous.
HLT_Photon10_L1R
, Loose Cut
See the HLT_Ele15_LW_L1R section for a discussion of the common features shared by the plots for both triggers.
Reading off the value of p0 from the fits, we have at high transverse momentum
TABLE 2 | Efficiencies from fit |
---|---|
0.9918 | |
0.9996 | |
0.9914 |
We should expect that . From Table 2, we obtain .
Many of the efficiency data points in the graph of were above 1, and are not plotted in the figure. Stricter electron cuts should eliminate this problem.
Again in bin 6 and 35 out of 40 bins in the histogram, the efficiency exceeds 1, and are not displayed.
HLT_Ele15_LW_L1R
, Tight Cut
TABLE 3 | Barrel | Endcap |
---|---|---|
All electrons | ||
L1 Seed to Electrons Efficiency | ||
HLT to Electrons Efficiency | ||
HLT to L1 Seed Efficiency |
The last plot ends prematurely as all the higher transverse momentum efficiencies exceed 1, and are not shown in the plot. This suggests that there are some electrons in the sample which are considered to match an HLT object, but not an L1 seed.
The eta distribution of such electrons (obtained over all events) are shown below:
The problem electrons are confined to an absolute value of eta of about 2.1, which explains why the barrel efficiencies are alright, while the endcap efficiencies are problematic. After removing all electrons between an eta of 2.0 and 2.25, we get the following more reasonable plots:
TABLE 4 | Barrel | Endcap |
---|---|---|
All electrons | ||
L1 Seed to Electrons Efficiency | ||
HLT to Electrons Efficiency | ||
HLT to L1 Seed Efficiency |
-- HongwanLiu - 10-Jun-2010
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