2011 QCD and High Energy Interactions - Rencontres de Moriond ...

The measurement of the differential cross section with respect to ∆φ and predictions for the
SP contributions to this cross sections in different models was used to determine the fraction
of γ + 2 jet events which originate from DP interactions as a function of the second parton
interaction scale (p jet2
T ) and of the ∆φ angle 6 . Using the uniform distribution for the DP model
template and sherpa-1 as the SP model template, the fit of the ∆φ distributions measured
in data was done to obtain the fraction of DP events with a maximum likelihood fit. The
distributions in data, SP, and DP models, as well as a sum of the SP and DP distributions,
weighted with their respective fractions, are shown in plots a) - c) of Fig.4 for the three p jet2
T
intervals. One can see that the sum of the SP and DP predictions reproduces the data very well.
φ
Δ
/d
2j
γ
σ
) d
2j
γ
σ
(1/
-1
10
-2
10
-1
jet2
Dé, L=1.0 fb 15 < p < 20 GeV
T
1 Data
DP model
SP model
γ2j
γ2j
DP fdp
+ SP(1-f )
dp
γ2j
fdp
= 0.116 ± 0.010
0 0.5 1 1.5 2 2.5 3
a) Δφ
(rad)
φ
Δ
/d
2j
γ
σ
) d
2j
γ
σ
(1/
-1
10
-2
10
-1
jet2
Dé, L=1.0 fb 20 < p < 25 GeV
T
1 Data
DP model
SP model
γ2j
γ2j
DP fdp
+ SP(1-f )
dp
γ2j
fdp
= 0.050 ± 0.012
0 0.5 1 1.5 2 2.5 3
b) Δφ
(rad)
φ
Δ
/d
2j
γ
σ
) d
2j
γ
σ
(1/
-1
10
-2
10
-1
jet2
Dé, L=1.0 fb 25 < p < 30 GeV
T
1 Data
DP model
SP model
γ2j
γ2j
DP fdp
+ SP(1-f )
dp
γ2j
fdp
= 0.022 ± 0.008
0 0.5 1 1.5 2 2.5 3
c) Δφ
(rad)
Fraction of DP events
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
-1
Dé, L=1.0 fb
jet2
15 < p < 20 GeV
T
jet2
20 < p < 25 GeV
T
jet2
25 < p < 30 GeV
T
1.6 1.8 2 2.2 2.4 2.6 2.8 3
d) Δφ
(rad)
max
Figure 4: a) ∆φ distribution in data, SP, and DP models, and the sum of the SP and DP contributions weighted
with their fractions in the bin 15 < p jet2
T < 20 GeV; b) Same as in a), but for the bin 20 < pjet2
T < 25 GeV; c)
Same as in a), but for the bin 25 < p jet2
T < 30 GeV; d) Fractions of DP events (%) with total uncertainties for
0 ≤∆φ ≤ π in the three p jet2
T bins.
From the same plots in Fig.4 one can see that the fraction of DP events is expected to be
higher at smaller ∆φ angles. To determine the fractions as a function of the ∆φ angle, a simple
fit was done in the different ∆φ regions by excluding the bins at high ∆φ values; for example, by
considering the ∆φ regions 0 − 2.85,0 − 2.65,0 − 2.45,0 − 2.15, and 0 − 1.60. The DP fractions
with total uncertainties as functions of the upper limit on ∆φ (∆φmax) for all three p jet2
T bins
are shown in plot d). As expected, they grow significantly for the smaller angles and are higher
for smaller p jet2
T bins.
The found sizable DP contribution can provide an important background for searches of
deviations from Standard Model at Tevatron and it indicates the importance of performing the
analogous measurements of double parton interactions at LHC for searches of Higgs boson and
New Physics signals.
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