467 research outputs found
Transverse mass and invariant mass observables for measuring the mass of a semi-invisibly decaying heavy particle
Formulae are derived for the positions of end-points in the invariant mass
and transverse mass distributions obtained from the products of heavy states
decaying to pairs of semi-invisibly decaying lighter states. Formulae are
derived both for the special case where the two decay chains are identical and
the more general case where they are different. The formulae are tested with a
simple case study of heavy SUSY higgs particles decaying to gauginos at the
LHC.Comment: 13 pages, 8 eps figure
The Analysis of Multijet Events Produced at High Energy Hadron Colliders
We define and discuss a set of (4N - 4) parameters that can be used to
analyse events in which N jets have been produced in high energy hadron-hadron
collisions. These multijet variables are the multijet mass and (4N - 5)
independent dimensionless parameters. To illustrate the use of the variables
QCD predictions are presented for events with up to five jets produced at the
Fermilab Tevatron Proton-Antiproton Collider. These QCD predictions are
compared with the predictions of a model in which multijet events uniformly
populate the N-body phase-space
Sqrt{shat}_{min} resurrected
We discuss the use of the variable sqrt{shat}_{min}, which has been proposed
in order to measure the hard scale of a multi parton final state event using
inclusive quantities only, on a SUSY data sample for a 14 TeV LHC. In its
original version, where this variable was proposed on calorimeter level, the
direct correlation to the hard scattering scale does not survive when effects
from soft physics are taken into account. We here show that when using
reconstructed objects instead of calorimeter energy and momenta as input, we
manage to actually recover this correlation for the parameter point considered
here. We furthermore discuss the effect of including W + jets and t tbar+jets
background in our analysis and the use of sqrt{shat}_{min} for the suppression
of SM induced background in new physics searches.Comment: 23 pages, 9 figures; v2: 1 figure, several subsections and references
as well as new author affiliation added. Corresponds to published versio
Effect of friction on disoriented chiral condensate formation
We have investigated the effect of friction on the DCC domain formation. We
solve the Newton equation of motion for the O(4) fields, with quenched initial
condition. The initial fields are randomly distributed in a Gaussian form. In
one dimensional expansion, on the average, large DCC domains can not be formed.
However, in some particular orbits, large instabilities may occur. This
possibility also greatly diminishes with the introduction of friction. But, if
the friction is large, the system may be overdamped and then, there is a
possibility of large DCC domain formation in some events.Comment: 9 pages, including figure
How to Make Large Domains of Disoriented Chiral Condensate
Rajagopal and Wilczek have proposed that relativistic nuclear collisions can
generate domains in which the chiral condensate is disoriented. If sufficiently
large ({\it i.e.} nucleus sized), such domains can yield measurable
fluctuations in the number of neutral and charged pions. However, by numerical
simulation of the zero-temperature two-flavor linear sigma model, we find that
domains are essentially {\it pion} sized. Nevertheless, we show that large
domains can occur if the effective mesons masses are much lighter.Comment: 6 pages and 2 postscript figures, BNL-GGP-
Hadronic Total Cross-sections Through Soft Gluon Summation in Impact Parameter Space
The Bloch-Nordsieck model for the parton distribution of hadrons in impact
parameter space, constructed using soft gluon summation, is investigated in
detail.
Its dependence upon the infrared structure of the strong coupling constant
is discussed, both for finite as well as singular, but integrable,
. The formalism is applied to the prediction of total proton-proton
and proton-antiproton cross-sections, where screening, due to soft gluon
emission from the initial valence quarks, becomes evident.Comment: 20 pages, Latex2e, input FEYNMAN,12 postscipt figures. Submitted to
PR
A fundamental test of the Higgs Yukawa coupling at RHIC in A+A collisions
Searches for the intermediate boson, , the heavy quantum of the Weak
Interaction, via its semi-leptonic decay, , in the 1970's instead
discovered unexpectedly large hadron production at high , notably ,
which provided a huge background of from internal and external
conversions. Methods developed at the CERN ISR which led to the discovery of
direct-single- in 1974, later determined to be from the semi-leptonic
decay of charm which had not yet been discovered, were used by PHENIX at RHIC
to make precision measurements of heavy quark production in p-p and Au+Au
collisions, leading to the puzzle of apparent equal suppression of light and
heavy quarks in the QGP. If the Higgs mechanism gives mass to gauge bosons but
not to fermions, then a proposal that all 6 quarks are nearly massless in a
QGP, which would resolve the puzzle, can not be excluded. This proposal can be
tested with future measurements of heavy quark correlations in A+A collisionsComment: 12 pages, 16 figures, 26th Winter Workshop on Nuclear Dynamics, Ocho
Rios, Jamaica WI, January 2-9, 2010. Corrected citation of 1974 direct single
lepton discover
Fully differential W' production and decay at next-to-leading order in QCD
We present the fully differential production and decay of a W' boson, with
arbitrary vector and axial-vector couplings, to any final state at
next-to-leading order in QCD. We demonstrate a complete factorization of
couplings at next-to-leading order in both the partial width of the W' boson,
and in the full two-to-two cross section. We provide numerical predictions for
the contribution of a W' boson to single-top-quark production, and separate
results based on whether the mass of the right-handed neutrino (nu_R) is light
enough for the leptonic decay channel to be open. The single-top-quark analysis
will allow for an improved direct W' mass limit of 525-550 GeV using data from
run I of the Fermilab Tevatron. We propose a modified tolerance method for
estimating parton distribution function uncertainties in cross sections.Comment: 23 pages, revtex3, 13 ps fig
Transverse momentum distributions and their forward- backward correlations in the percolating colour string approach
The forward-backward correlations in the distributions, which present a
clear signature of non-linear effects in particle production, are studied in
the model of percolating colour strings. Quantitative predictions are given for
these correlations at SPS, RHIC and LHC energies. Interaction of strings also
naturally explains the flattening of distributions and increase of
with energy and atomic number for nuclear collisionsComment: 6 pages in LaTex, 3 figures in Postscrip
Jet Quenching in the Opposite Direction of a Tagged Photon in High-Energy Heavy-Ion Collisions
We point out that events associated with large direct photons in
high-energy heavy-ion collisions can be used to study jet energy loss in dense
matter. In such events, the spectrum of charged hadrons from jet
fragmentation in the opposite direction of the tagged photon is estimated to be
well above the background which can be reliably subtracted at moderately large
. We demonstrate that comparison between the extracted fragmentation
function in and collisions can be used to determine the jet energy
loss and the interaction mean-free-path in the dense matter produced in
high-energy heavy-ion collisions.Comment: 4 pages in RevTex twocolumn with embedded psfigure
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