263 research outputs found
Multi-jet cross sections at NLO with BlackHat and Sherpa
In this talk, we report on a recent next-to-leading order QCD calculation of
the production of a W boson in association with three jets at hadron colliders.
The computation is performed by combining two programs, BlackHat for the
computation of the virtual one-loop matrix elements and Sherpa for the real
emission part.Comment: 4 pages, contribution to the proceedings of the XLIIIth Rencontres de
Moriond (QCD
Next-to-Leading Order Jet Physics with BlackHat
We present several results obtained using the BlackHat next-to-leading order
QCD program library, in conjunction with SHERPA. In particular, we present
distributions for vector boson plus 1,2,3-jet production at the Tevatron and at
the asymptotic running energy of the Large Hadron Collider, including new
Z+3-jet distributions. The Z+2-jet predictions for the second-jet P_T
distribution are compared to CDF data. We present the jet-emission probability
at NLO in W+2-jet events at the LHC, where the tagging jets are taken to be the
ones furthest apart in pseudorapidity. We analyze further the large left-handed
W polarization, identified in our previous study, for W bosons produced at high
P_T at the LHC.Comment: Presented at RADCOR 2009 - 9th International Symposium on Radiative
Corrections (Applications of Quantum Field Theory to Phenomenology), October
25 - 30 2009, Ascona, Switzerland}, 12 pages, 9 figures, LaTeX, v2 updated
small correction to polarization effect plo
Gaugephobic Higgs Signals at the LHC
The Gaugephobic Higgs model provides an interpolation between three different
models of electroweak symmetry breaking: Higgsless models, Randall-Sundrum
models, and the Standard Model. At parameter points between the extremes,
Standard Model Higgs signals are present at reduced rates, and Higgsless
Kaluza-Klein excitations are present with shifted masses and couplings, as well
as signals from exotic quarks necessary to protect the Zbb coupling. Using a
new implementation of the model in SHERPA, we show the LHC signals which
differentiate the generic Gaugephobic Higgs model from its limiting cases.
These are all signals involving a Higgs coupling to a Kaluza-Klein gauge boson
or quark. We identify the clean signal mediated by a
Kaluza-Klein W, which can be present at large rates and is enhanced for even
Kaluza-Klein numbers. Due to the very hard lepton coming from the W decay, this
signature has little background, and provides a better discovery channel for
the Higgs than any of the Standard Model modes, over its entire mass range. A
Higgs radiated from new heavy quarks also has large rates, but is much less
promising due to very high multiplicity final states.Comment: 16 pages, 8 figure
NLO vector boson production with light jets
In this contribution we present recent progress in the computation of
next-to-leading order (NLO) QCD corrections for the production of an
electroweak vector boson in association with jets at hadron colliders. We focus
on results obtained using the virtual matrix element library BLACKHAT in
conjunction with SHERPA, focusing on results relevant to understanding the
background to top production.Comment: 4+2 epsilon pages, Submitted for the proceedings of TOP2011 - 4th
International Workshop on Top Quark Physics, 25-30th September 2011, Sant
Feliu de Guixols, Spai
Friedel oscillations in a gas of interacting one-dimensional fermionic atoms confined in a harmonic trap
Using an asymptotic phase representation of the particle density operator
in the one-dimensional harmonic trap, the part which describes the Friedel oscillations is extracted. The
expectation value with respect to the interacting
ground state requires the calculation of the mean square average of a properly
defined phase operator. This calculation is performed analytically for the
Tomonaga-Luttinger model with harmonic confinement. It is found that the
envelope of the Friedel oscillations at zero temperature decays with the
boundary exponent away from the classical boundaries. This
value differs from that known for open boundary conditions or strong pinning
impurities. The soft boundary in the present case thus modifies the decay of
Friedel oscillations. The case of two components is also discussed.Comment: Revised version to appear in Journal of Physics B: Atomic, Molecular
and Optical Physic
CalcHEP 3.4 for collider physics within and beyond the Standard Model
We present version 3.4 of the CalcHEP software package which is designed for
effective evaluation and simulation of high energy physics collider processes
at parton level.
The main features of CalcHEP are the computation of Feynman diagrams,
integration over multi-particle phase space and event simulation at parton
level. The principle attractive key-points along these lines are that it has:
a) an easy startup even for those who are not familiar with CalcHEP; b) a
friendly and convenient graphical user interface; c) the option for a user to
easily modify a model or introduce a new model by either using the graphical
interface or by using an external package with the possibility of cross
checking the results in different gauges; d) a batch interface which allows to
perform very complicated and tedious calculations connecting production and
decay modes for processes with many particles in the final state.
With this features set, CalcHEP can efficiently perform calculations with a
high level of automation from a theory in the form of a Lagrangian down to
phenomenology in the form of cross sections, parton level event simulation and
various kinematical distributions.
In this paper we report on the new features of CalcHEP 3.4 which improves the
power of our package to be an effective tool for the study of modern collider
phenomenology.Comment: 82 pages, elsarticle LaTeX, 7 Figures. Changes from v1: 1) updated
reference list and Acknowledgments; 2) 2->1 processes added to CalcHEP; 3)
particles decay (i.e. Higgs boson) into virtual W/Z decays added together
with comparison to results from Hdecay package; 4) added interface with Root
packag
Precise Predictions for W + 3 Jet Production at Hadron Colliders
We report on the first next-to-leading order QCD computation of W + 3-jet
production in hadronic collisions including all partonic subprocesses. We
compare the results with CDF data from the Tevatron, and find excellent
agreement. The renormalization and factorization scale dependence is reduced
substantially compared to leading-order calculations. The required one-loop
matrix elements are computed using on-shell methods, implemented in a numerical
program, BlackHat. We use the SHERPA package to generate the real-emission
contributions and to integrate the various contributions over phase space. We
use a leading-color (large-N_c) approximation for the virtual part, which we
confirm in W + 1,2-jet production to be valid to within three percent. The
present calculation demonstrates the utility of on-shell methods for computing
next-to-leading-order corrections to processes important to physics analyses at
the Large Hadron Collider.Comment: 5 pages, 3 figures, RevTex, v3 small change in values, no changes in
conclusion
Left-Handed W Bosons at the LHC
The production of W bosons in association with jets is an important
background to new physics at the LHC. Events in which the W carries large
transverse momentum and decays leptonically lead to large missing energy and
are of particular importance. We show that the left-handed nature of the W
coupling, combined with valence quark domination at a pp machine, leads to a
large left-handed polarization for both W^+ and W^- bosons at large transverse
momenta. The polarization fractions are very stable with respect to QCD
corrections. The leptonic decay of the W bosons translates the common
left-handed polarization into a strong asymmetry in transverse momentum
distributions between positrons and electrons, and between neutrinos and
anti-neutrinos (missing transverse energy). Such asymmetries may provide an
effective experimental handle on separating W + jets from top quark production,
which exhibits very little asymmetry due to C invariance, and from various
types of new physics.Comment: 32 pages, revtex, 17 figures, 3 tables, v2 minor corrections to ME+PS
results, no changes to conclusions, added reference
Report on Running Channels in iseg 32-Ch HV Power Supplies
We report a study and solution of the so-called "running channel" (RC) phenomenon observed in the iseg 32-channel HV power supplies for the ATLAS Liquid Argon Calorimetry
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