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

iterative midpoint cone algorithm with a cone size of Rη,φ = 0.7. Jets must satisfy quality criteria
which suppress background from leptons, photons, and detector noise effects. The measured jet
energy is corrected (different to 4 ) for the energy response of the calorimeter, energy showering in
and out the jet cone, and additional energy from event pile-up and multiple proton interactions.
The plot b) of Fig. 2 shows the values of σeff which were extracted in three intervals
< 20 GeV, 20 < pjet2 < 25 GeV and
of the second jet transverse momentum: 15 < p jet2
T
25 < p jet2
T < 30 GeV 5 by comparing the number of the observed DP γ+ 3 jets events occurring
in one p¯p collision to the number of DI γ+ 3 jets. The knowledge of cross section of inelastic
non-diffractive (hard) p¯p interactions σhard was needed also. It was found by extrapolation of
the values σhard, measured by CDF and D0, up to √ s = 1.96 TeV.
The fraction of DP events is determined by using a set of ∆Sφ , ∆SpT , and ∆S p ′ T variables
sensitive to the kinematic configurations of the two independent scatterings of parton pairs,
specifically to the difference between the pT imbalance of the two object pairs in DP and SP
γ+ 3jets events. The ∆SpT ,∆S p ′ T variables are used in 2,4 , while the ∆Sφ is first proposed in 5
measurement. The extracted values of DP fraction are shown in Fig.2, c). It is seen that the
DP fraction, measured by 5 in three (of equal width) intervals of the second (ordered in pT) jet
transverse momentum p jet2
T , gives an essential contribution to total cross section (from about
47% down to 24%) within the 15 < p jet2
T
a)
S
Δ
/d
3j
γ
σ
) d
3j
γ
σ
(1/
Data / Theory
1
-1
10
-1
DØ, L = 1.0 fb
γ
Data
50 < p < 90 GeV
T
Pythia, tune A
jet1
p > 30 GeV
Pythia, tune DW T
jet2
Pythia, tune S0 15 < p < 30 GeV
T
jet3
Pythia, tune P0 p > 15 GeV
T
Sherpa, with MPI
Pythia, no MPI
Sherpa, no MPI
Total uncertainty
1.4 1.40
0.5 1 1.5 2 2.5 3
1.2
1
0.8
0.6
0.4
0 0.5 1 1.5 2 2.5 3
Δ S (rad)
b)
φ
Δ
/d
(1/ σγ2j)
dσγ2j
Data / Theory
10
1
-1
10
-2
10
-1
DØ, L = 1.0 fb
Data
Pythia, tune A
Pythia, tune DW
Pythia, tune S0
Pythia, tune P0
Sherpa, with MPI
Pythia, no MPI
Sherpa, no MPI
Total uncertainty
γ
50 < p < 90 GeV
T
jet1
p > 30 GeV
T
jet2
15 < p < 20 GeV
T
1.4 1.40
0.5 1 1.5 2 2.5 3
1.2
1
0.8
0.6
0.4
0 0.5 1 1.5 2 2.5 3
Δ φ (rad)
< 30 GeV range.
c)
φ
Δ
/d
(1/ σγ2j)
dσγ2j
Data / Theory
10
1
-1
10
-2
10
-1
DØ, L = 1.0 fb
Data
Pythia, tune A
Pythia, tune DW
Pythia, tune S0
Pythia, tune P0
Sherpa, with MPI
Pythia, no MPI
Sherpa, no MPI
Total uncertainty
γ
50 < p < 90 GeV
T
jet1
p > 30 GeV
T
jet2
20 < p < 25 GeV
T
1.4 1.40
0.5 1 1.5 2 2.5 3
1.2
1
0.8
0.6
0.4
0 0.5 1 1.5 2 2.5 3
Δ φ (rad)
d)
T
φ
Δ
/d
(1/ σγ2j)
dσγ2j
Data / Theory
10
1
-1
10
-2
10
-1
DØ, L = 1.0 fb
Data
Pythia, tune A
Pythia, tune DW
Pythia, tune S0
Pythia, tune P0
Sherpa, with MPI
Pythia, no MPI
Sherpa, no MPI
Total uncertainty
γ
50 < p < 90 GeV
T
jet1
p > 30 GeV
T
jet2
25 < p < 30 GeV
T
1.6 1.60
1.4
1.2
1
0.8
0.6
0.5 1 1.5 2 2.5 3
0.4
0 0.5 1 1.5 2 2.5 3
Δ φ (rad)
Figure 3: a) The (1/σγ3j)dσγ3j/d∆S cross sections in data and MC models and Data/Theory (only models
including MPI) ratios for the bin 15 < p jet2
T < 30 GeV; b) The (1/σγ2j)dσγ2j/d∆φ cross sections in data and MC
models and Data/Theory (only models including MPI) ratios for the bin 15 < p jet2
T < 20 GeV; c) Same as in b),
but for the bin 20 < p jet2
T < 25 GeV; d) Same as in b), but for the bin 25 < pjet2
T < 30 GeV.
Plots a) - c) in Fig.3 present the four D0 measurements of differential cross sections (with
respect to ∆S- and ∆φ- angle variables, shown correspondingly in the plots b) and c) of Fig.2)
(1/σγ3j)dσγ3j/d∆S in a single p jet2
T bin (15−30 GeV) for γ+3 jet events and (1/σγ2j)dσγ2j/d∆φ in
three p jet2
T bins (15 − 20, 20 − 25, and 25 − 30 GeV) for γ + 2 jet events. The differential distributions
decrease by two order of magnitude when moving from ∆S (∆φ) ≈ π to 0 and have
a total uncertainty (δtot) between 7 and 30%, which is dominated by systematics (δsyst). They
are compared to predictions from a few multipal parton interactions (MPI) models implemented
in pythia and sherpa. For completeness, predictions from SP models in pythia and sherpa
(sherpa-1 model) are also shown here. From these plots in Fig.3 one can see that the considered
variables, ∆S and ∆φ, are very sensitive to the models, with predictions varying significantly
and differing from each other by up to a factor 2.5 at the small ∆S and ∆φ angles, i.e. right in
the place where the relative DP contribution is expected to be the highest. It is seen also that
that (a) the predictions derived from SP models differ significantly from the measurements; (b)
the data favor mostly the predictions done with new pythia MPI models, S0 and Perugia and
also sherpa with its MPI model; while (c) the predictions from old MPI models, tune A and
DW, are much less favored. Among the considered new MPI models, agreement with data is a
little worse for the S0 and P-soft models 6 .