The event selection used in this analysis is basically the same as that described in Ref. [3] for the 2010 analysis, except for changes that are either to adapt to the higher instantaneous lu-minosity of the 2011 dataset or to the different detector condi-tions. The event selection proceeds as follows:
1. Events are required to have a primary vertex, as defined in Sect.5.4, with at least five associated tracks (Nvertextracks≥ 5).
10 Any dependence of the MPF response on the jet reconstruction algorithm is introduced solely by the event selection.
hResponseBB_Bin_0__1__1
RMPF
-0.5 0 0.5 1 1.5 2 2.5 3
Events / 0.05
0 200 400 600 800 1000 1200 1400 1600 1800 2000
hResponseBB_Bin_0__1__1 < 45 GeV γ 25 < pT
ATLAS
= 7 TeV, L dt = 4.7 fb-1
s
∫
< 45 GeV
γ
pT
≤ 25
Data 2011 Fit function
| < 1.2 ηdet
|
(a) 25 ≤ pγT< 45 GeV
hResponseBB_Bin_5__1__1 Entries 32296 Mean 0.7452 RMS 0.1041
RMPF
-0.5 0 0.5 1 1.5 2 2.5 3
Events / 0.05
0 1000 2000 3000 4000 5000 6000 7000 8000
hResponseBB_Bin_5__1__1 Entries 32296 Mean 0.7452 RMS 0.1041
ATLAS
= 7 TeV, L dt = 4.7 fb-1
s
∫
< 210 GeV γ T 160 < p
< 210 GeV
γ
pT
≤ 160
Data 2011 Fit function
| < 1.2 ηdet
|
(b) 160 ≤ pγT< 210 GeV
Fig. 21: MPF response distributions in the γ–jet data for(a)25 ≤ pγT< 45 GeV and(b)160 ≤ pγT< 210 GeV when using topo-clusters at the EM scale. The dashed lines represent the fits with a Gaussian function. The mean value from the fit in each pγTbin is the value used as the measured average MPF response.
T
/pγ T
pjet
0 0.5 1 1.5 2 2.5 3 3.5 4
Events / 0.04
0 200 400 600 800 1000 1200 1400 1600 1800
Data 2011 Fit Function = 7 TeV s
L dt ~ 4.7 fb-1
∫
< 45 GeV
γ
25 < pT
| < 1.2 ηdet
|
ATLAS
(a) 25 ≤ pγT< 45 GeV
T
/pγ T
pjet
0 0.5 1 1.5 2 2.5 3
Events / 0.02
0 200 400 600 800 1000 1200 1400
Data 2011 Fit Function = 7 TeV s
L dt ~ 4.7 fb-1
∫
< 210 GeV
γ
160 < pT
| < 1.2 ηdet
|
ATLAS
(b) 160 ≤ pγT< 210 GeV
Fig. 22: Jet response distributions in the γ–jet data for(a)25 ≤ pγT< 45 GeV and(b)160 ≤ pγT< 210 GeV as measured by the DB technique for anti-ktjets with R = 0.6 at the EM+JES scale. The dashed lines represent fits of Gaussian functions, except in the lowest bin (25 ≤ pγT< 45 GeV), where the fit function is a Poisson distribution. The mean value from the fit in each pγTbin is the value used as the measured average jet response in DB.
MPFR
0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00
Data 2011 γ+jet PYTHIA ATLAS
= 7 TeV,
s
∫
L dt = 4.7 fb-1| < 1.2 ηdet
| EM scale
[GeV]
γ
pT
30 40 100 200 300 1000
Data / MC
0.96 0.97 0.980.99 1.001.01 1.021.03 1.04
(a) EM
MPFR
0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00
Data 2011 γ+jet PYTHIA ATLAS
= 7 TeV,
s
∫
L dt = 4.7 fb-1| < 1.2 ηdet
|
LCW scale
[GeV]
γ
pT
30 40 100 200 300 1000
Data / MC
0.96 0.97 0.98 0.99 1.00 1.01 1.02 1.03 1.04
(b) LCW
Fig. 23: Average jet response as determined by the MPF technique in γ–jet events using topo-clusters at the(a)EM and(b)LCW energy scales, for both data and MC simulations, as a function of the photon transverse momentum. The data-to-MC response ratio is shown in the bottom inset of each figure. Only the statistical uncertainties are shown.
Table 4: Table with the approximate number of selected events in each pγTbin.
pγT[GeV] Events pγT[GeV] Events 25–45 20 480 210–260 10 210 45–65 61 220 260–310 4 650 65–85 125 040 310–400 2 770 85–110 262 220 400–500 800 110–160 143 180 500–600 240
160–210 32 300 600–800 100
2. There must be at least one reconstructed photon; the highest-pT(leading) photon is taken as the hard-process photon and must have pγT> 25 GeV.
3. The event is required to pass a single-photon trigger, with trigger pT threshold depending on the pT of the leading photon.
4. The leading photon must pass strict identification criteria [87], meaning that the pattern of energy deposition in the calorimeter is consistent with the expected photon shower-ing behaviour.
5. The leading photon must lie in the pseudorapidity range
|ηγ| < 1.37, meaning it is fully contained within the elec-tromagnetic barrel calorimeter.
6. Jets with high electromagnetic content (e.g., jets fluctuating to a leading π0, with π0→ γγ) may be misidentified as photons. In order to reduce this background, the leading
photon is required to be isolated from other activity in the calorimeter. The isolation variable (ETγ Iso) [87] is computed in a cone of size R = 0.4 around the photon, and corrected for pile-up energy inside the isolation cone. Only photons with ETγ Iso< 3 GeV are selected.
7. The photon reconstruction algorithm attempts to retain pho-tons that have converted into an electron-positron pair. Whi-le clusters without matching tracks are directly classified as “unconverted” photon candidates, clusters matched to pairs of tracks originating from reconstructed conversion vertices are considered as “converted” photon candidates (double-track conversions). To increase the reconstruction efficiency of converted photons, conversion candidates whe-re only one of the two tracks is whe-reconstructed (single-track conversions) are also retained. Jets that are misidentified as photons fall more often in the category of converted pho-tons, because fake photons produce wider showers and have tracks associated to them. To suppress this background fur-ther, the ratio of the transverse energy of the photon can-didate cluster to the scalar sum of the pTof the matching tracks (ETγ cluster/(∑ ptracksT )) is required to be in the range from 0 to 2 for single-track conversions, and from 0.5 to 1.5 for double-track conversions. The fraction of converted photons is ∼ 30% throughout the pγTrange under consider-ation.
8. Only jets with pjetT > 12 GeV are considered. From those, only jets that pass quality criteria designed to reject fake jets originating from noise bursts in the calorimeters or from non-collision background or cosmics (see Sect. 5.3), are
>γ T/pjet T<p
0.85 0.9 0.95 1 1.05
1.1 ATLAS
jets, R = 0.4 anti-kt
EM+JES
= 7 TeV s
| < 1.2 ηdet
|
dt = 4.7 fb-1
∫L Data 2011
+ jet γ PYTHIA
[GeV]
γ
pT
30 40 50 100 200 300 1000
Data / MC
0.97 0.98 0.99 1 1.01 1.02 1.03
(a) R = 0.4, EM+JES
>γ T/pjet T<p
0.85 0.9 0.95 1 1.05
1.1 ATLAS
jets, R = 0.4 anti-kt
LCW+JES
= 7 TeV s
| < 1.2 ηdet
|
dt = 4.7 fb-1
∫L Data 2011
+ jet γ PYTHIA
[GeV]
γ
pT
30 40 50 100 200 300 1000
Data / MC
0.97 0.98 0.99 1 1.01 1.02 1.03
(b) R = 0.4, LCW+JES
>γ T/pjet T<p
0.85 0.9 0.95 1 1.05 1.1
ATLAS jets, R = 0.6 anti-kt
EM+JES
= 7 TeV s
| < 1.2 ηdet
|
dt = 4.7 fb-1
∫L Data 2011
+ jet γ PYTHIA
[GeV]
γ
pT
30 40 50 100 200 300 1000
Data / MC
0.97 0.98 0.99 1 1.01 1.02 1.03
(c) R = 0.6, EM+JES
>γ T/pjet T<p
0.85 0.9 0.95 1 1.05 1.1
ATLAS jets, R = 0.6 anti-kt
LCW+JES
= 7 TeV s
| < 1.2 ηdet
|
dt = 4.7 fb-1
∫L Data 2011
+ jet γ PYTHIA
[GeV]
γ
pT
30 40 50 100 200 300 1000
Data / MC
0.97 0.98 0.99 1 1.01 1.02 1.03
(d) R = 0.6, LCW+JES
Fig. 24: Average jet response as determined by the DB technique in γ–jet events for anti-kt jets with ((a),(b)) R = 0.4 and ((c), (d)) R = 0.6, calibrated with the ((a),(c)) EM+JES scheme and with the ((b),(d)) LCW+JES scheme, for both data and MC simulations, as a function of the photon transverse momentum.
used. After these jet selections, each event is required to have at least one jet.
9. The highest-pT(leading) jet must be in the region |ηjet| <
1.2. This choice is motivated by the small η-intercalibrati-on correctiη-intercalibrati-on below 1.5% in this regiη-intercalibrati-on.
10. To suppress soft radiation that would affect the pTbalance between the jet and the photon, the following two condi-tions are required:
(a) The leading jet must be back-to-back to the photon in the transverse plane (∆ φ (jet, γ) > 2.9 rad).
(b) The pT of the sub-leading jet from the hard process (pjet2T ) must be less than 20% (30%) of the pT of the photon for DB (MPF11). In order to distinguish jets from the hard process against jets from pile-up, the sub-leading jet is defined as the highest-pTjet from the sub-set of non-leading jets that either have JVF > 0.75 or for which JVF could not be computed because they are outside the region covered by the tracking system. See Sect.8.2.3for the explanation of JVF.
11. In the case of DB, the event is rejected if either the lea-ding jet or the sub-lealea-ding jet falls in a region where, for a certain period, the read-out of the EM calorimeter was not functioning. For MPF, the condition is extended to all jets with pjetT > 20 GeV in the event. A similar condition is imposed on the reference photon.
A summary of the event selection criteria is given in Table3.
Table4shows the approximate number of selected events per pγTbin.