31 research outputs found
Evolution variable dependence of jet substructure
Studies on jet substructure have evolved significantly in recent years. Jet
substructure is essentially determined by QCD radiations and non-perturbative
effects. Predictions of jet substructure are usually different among Monte
Carlo event generators, and are governed by the parton shower algorithm
implemented. For leading logarithmic parton shower, even though one of the core
variables is the evolution variable, its choice is not unique. We examine
evolution variable dependence of the jet substructure by developing a parton
shower generator that interpolates between different evolution variables using
a parameter . Jet shape variables and associated jet rates for quark
and gluon jets are used to demonstrate the -dependence of the jet
substructure. We find angular ordered shower predicts wider jets, while
relative transverse momentum () ordered shower predicts narrower
jets. This is qualitatively in agreement with the missing phase space of
ordered showers. Such difference can be reduced by tuning other
parameters of the showering algorithm, especially in the low energy region,
while the difference tends to increase for high energy jets.Comment: 16 pages, 7 figure
Quark-gluon discrimination in the search for gluino pair production at the LHC
We study the impact of including quark- and gluon-initiated jet
discrimination in the search for strongly interacting supersymmetric particles
at the LHC. Taking the example of gluino pair production, considerable
improvement is observed in the LHC search reach on including the jet
substructure observables to the standard kinematic variables within a
multivariate analysis. In particular, quark and gluon jet separation has higher
impact in the region of intermediate mass-gap between the gluino and the
lightest neutralino, as the difference between the signal and the standard
model background kinematic distributions is reduced in this region. We also
compare the predictions from different Monte Carlo event generators to estimate
the uncertainty originating from the modelling of the parton shower and
hadronization processes.Comment: 22 pages, 8 figures, 1 table; v2: statistical treatment improved and
figures update
Associated jet and subjet rates in light-quark and gluon jet discrimination
We show that in studies of light quark- and gluon-initiated jet
discrimination, it is important to include the information on softer
reconstructed jets (associated jets) around a primary hard jet. This is
particularly relevant while adopting a small radius parameter for
reconstructing hadronic jets. The probability of having an associated jet as a
function of the primary jet transverse momentum () and radius, the minimum
associated jet and the association radius is computed upto next-to-double
logarithmic accuracy (NDLA), and the predictions are compared with results from
Herwig++, Pythia6 and Pythia8 Monte Carlos (MC). We demonstrate the improvement
in quark-gluon discrimination on using the associated jet rate variable with
the help of a multivariate analysis. The associated jet rates are found to be
only mildly sensitive to the choice of parton shower and hadronization
algorithms, as well as to the effects of initial state radiation and underlying
event. In addition, the number of subjets of an anti- jet is found
to be an observable that leads to a rather uniform prediction across different
MC's, broadly being in agreement with predictions in NDLA, as compared to the
often used number of charged tracks observable.Comment: 25 pages, 12 figures; v2: Figures of 2D joint distributions included,
additions to text and Refs., version to appear in JHE
New physics searches at the ILC positron and electron beam dumps
We study capability of the ILC beam dump experiment to search for new
physics, comparing the performance of the electron and positron beam dumps. The
dark photon, axion-like particles, and light scalar bosons are considered as
new physics scenarios, where all the important production mechanisms are
included: electron-positron pair-annihilation, Primakoff process, and
bremsstrahlung productions. We find that the ILC beam dump experiment has
higher sensitivity than past beam dump experiments, with the positron beam dump
having slightly better performance for new physics particles which are produced
by the electron-positron pair-annihilation.Comment: 26 pages, 7 figure