50,812 research outputs found
Jets and threshold summation in Deductor
We explore jet physics in hadron collisions using the parton shower event
generator Deductor. Of particular interest is the one jet inclusive cross
section dsigma/dpT for jets of very high pT. Compared to the Born level, the
cross section decreases substantially because of pT loss from the jet during
showering. We compare to the same effect in Pythia and Dire. The cross section
then increases substantially because of the summation of threshold logarithms
included in Deductor.
We also study the cross section to have a gap with no jets between two hard
jets that are widely separated in rapidity. Here we compare Deductor with
virtuality based ordering with Deductor with kT ordering and we check whether
adding an underlying event and hadronization has a significant effect beyond
that found with just a parton shower.Comment: 47 pages, 11 figures, published versio
Revisiting Radiation Patterns in Collisions
We propose four simple event-shape variables for semi-inclusive -jet events. The observables and cuts are designed to be especially sensitive
to subleading aspects of the event structure, and allow to test the reliability
of phenomenological QCD models in greater detail. Three of them, ,
, and , focus on soft emissions off three-jet topologies
with a small opening angle, for which coherence effects beyond the leading QCD
dipole pattern are expected to be enhanced. A complementary variable,
, measures the ratio of the hemisphere masses in 4-jet events with
a compressed scale hierarchy (Durham ), for which subleading
splitting effects are expected to be enhanced. We consider several
different parton-shower models, spanning both conventional and dipole/antenna
ones, all tuned to the same reference data, and show that a
measurement of the proposed observables would allow for additional significant
discriminating power between the models.Comment: 27 pages, 10 figure
One Universal Extra Dimension in Pythia
The Universal Extra Dimensions model has been implemented in the Pythia
generator from version 6.4.18 onwards, in its minimal formulation with one
inverse-TeV-sized extra dimension. The additional possibility of
gravity-mediated decays, through a variable number of inverse-eV-sized extra
dimensions into which only gravity extends, is also available. The
implementation covers the lowest-lying Kaluza-Klein (KK) excitations of
Standard Model particles, except for the excitations of the Higgs fields, with
the mass spectrum calculated at one loop. 2 -> 2 tree-level production cross
sections and KK number conserving 2-body decays are included. Mixing between
iso-doublet and -singlet KK excitations is neglected thus far, and is expected
to be negligible for all but the top sector.Comment: 11 page
The underlying event and fragmentation
A good fit to the CDF underlying event is obtained in the multiple parton
scattering picture using HERWIG, after modifying the cluster hadronization
algorithm as suggested by our previous study and adopting a larger maximum
cluster size. The number of scatters per event is generated simply as a Poisson
distribution. If our picture is correct, the baryon yield should be enhanced in
the underlying event. This effect may be studied by measuring the
proton-to-pion ratio.Comment: 23 pages, 8 figure
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