# JetEtmissApproved2011PileupOffsetAndJVF

[Jet Offset in data (I)]
Calorimeter jet p_{T} as a function of number of reconstructed primary vertices (N_{PV}), for the central pseudo-rapidity region. Calorimeter jets reconstructed at the EM scale are associated to track jets in bins of p_{T}. Each point shows the most probable value of calorimeter jet p_{T}, for a specific p_{T} (track jet) range and NPV.
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[Jet Offset in data (II)]
a p_{T}-independent pile-up correction based on simulation (MC11a) is applied to calorimeter jets, and is found to greatly reduce the pile-up contribution. Note that by construction, the pile-up correction is close to zero at the average number of primary vertices, N_{PV} = 5.4.
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[Jet Offset at high luminosity]
A data set with an integrated luminosity of 0.4 pb^{-1} and approximately 30 interactions per bunch crossing. Reconstructed tracks originating from the chosen primary vertex were matched within &DeltaR < 0.6 to anti-k_{t} R = 0.6 topo-cluster jets. The sum of the p_{T} of the matched tracks is insensitive to pile-up and correlated with the true jet p_{T}. In each bin of matched track p_{T}, we see clearly the dependence of the calorimeter jet p_{T} on in-time pile-up, as described by the number of reconstructed primary vertices (N_{PV}). This dependence remains linear up to at least N_{PV} = 30, and it is in quantitative agreement with the results of similar studies performed in 2011 data with significantly less pile-up.
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[Jet Vertex Fraction Discriminant]
The jet vertex fraction (JVF) quantifies
the fraction of track transverse momentum associated
to a jet from the hard-scattering interaction.
Discrimination between jets produced in
the hard-scatter and those originating in pile-up using the JVF
in events simulated at L=2×10^{33}cm^{-‐2}s^{‐1} and
25 ns bunch spacing. Monte Carlo truth information is
used to separate jets from pile-up with
p_{T} > 20 GeV in the central region of the
detector, and the JVF discriminant is shown for each class of jets.
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[Jet Vertex Fraction Distribution in Z events]
The jet vertex fraction (JVF) distribution in data and Monte Carlo
simulation for jets in in Z → ll (l = e, μ) events. Events must contain at
least one primary vertex consisting of 3 or more tracks and are then
required to contain exactly two leptons (which are oppositely signed in
the case of muons) with p_{T} > 20 GeV and |η| < 2.5 which form an
invariant mass 76 < m_{ll} < 106 GeV. Jets are reconstructed using an
anti‐kt algorithm with distance parameter R = 0.4 and are required to
have p_{T} > 25 GeV and |η| < 2.5. The Monte Carlo overestimates the
number of jets at low values of JVF, where the jets have a large
contribution from vertices coming from additional proton-proton
interactions (“pile-up”).
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[Jet Vertex Fraction performance in Z events]
The average number of jets, N_{jet}, before (black) and after (red) a cut
on the jet vertex fraction, |JVF|>0.75, as a function of the number of
primary vertices (containing at least 3 tracks) in data and Monte Carlo
simulation for jets in Z → ll (l = e, μ) events. Events are required to
contain exactly two leptons (which are oppositely signed in the case of
muons) with p_{T} > 20 GeV and |η| < 2.5 which form an invariant mass 76 <
m_{ll} < 106 GeV. Jets are reconstructed using an anti-k_{t} algorithm with
distance parameter D = 0.4 and are required to have p_{T} > 2 GeV and
|η| < 2.5. Before the JVF cut, increases with the number of
primary vertices, as expected due to the additional proton-proton
interactions (“pile-up”). This increase is faster in the Monte Carlo,
suggesting the number of pile-up jets is overestimated in the
simulation. After the cut, N_{jet} is constant with the number of primary
vertices and reasonably well described by the Monte Carlo.
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**Major updates**:

-- ArielSchwartzman - 04-Jan-2012

Responsible: ArielSchwartzman

Subject: public