24,810 research outputs found
The Underlying Event in Hard Scattering Processes
We study the behavior of the "underlying event" in hard scattering
proton-antiproton collisions at 1.8 TeV and compare with the QCD Monte-Carlo
models. The "underlying event" is everything except the two outgoing hard
scattered "jets" and receives contributions from the "beam-beam remnants" plus
initial and final-state radiation. The data indicate that neither ISAJET or
HERWIG produce enough charged particles (with PT > 0.5 GeV/c) from the
"beam-beam remnant" component and that ISAJET produces too many charged
particles from initial-state radiation. PYTHIA which uses multiple parton
scattering to enhance the "underlying event" does the best job describing the
data.Comment: RevTex4, 18 pages, 29 figures, contribution to Snowmass 200
Using Collider Event Topology in the Search for the Six-Jet Decay of Top Quark-Antiquark Pairs
We investigate the use of the event topology as a tool in the search for the
six-jet decay of top-pair production in proton-antiproton collisions at 1.8
TeV. Modified Fox-Wolfram "shape" variables, H_i, are employed to help
distinguish the top-pair signal from the ordinary QCD multi-jet background. The
H's can be constructed directly from the calorimeter cells or from jets. Events
are required to lie in a region of H-space defined by L_i < H_i < R_i for
i=1,...,,6, where the left, L_i, and right, R_i, cuts are determined by a
genetic algorithm (GA) procedure to maximize the signal over the square root of
the background. We are able to reduce the background over the signal to less
than a factor of 100 using purely topological methods without using jet
multiplicity cuts and without the aid of b-quark tagging.Comment: LaTeX, 19 pages, 13 figure
Interaction of a Modulated Electron Beam with a Plasma
The results of a theoretical and experimental investigation of the high-frequency interaction of an electron beam with a plasma are reported. An electron beam, modulated at a microwave frequency, passes through a uniform region of a mercury arc discharge after which it is demodulated. Exponentially growing wave amplification along the electron beam was experimentally observed for the first time at a microwave frequency equal to the plasma frequency. Approximate theories of the effects of 1) plasma-electron collision frequencies, 2) plasma-electron thermal velocities and 3) finite beam diameter, are given. In a second experiment the interaction between a modulated electron beam and a slow electrostatic wave on a plasma column has been studied. A strong interaction occurs when the velocity of the electron beam is approximately equal to the velocity of the wave and the interaction is essentially the same as that which occurs in traveling-wave amplifiers, except that here the plasma colum replaces the usual helical slow-wave circuit. The theory predicting rates of growth is presented and compared with the experimental results
The automated multi-stage substructuring system for NASTRAN
The substructuring capability developed for eventual installation in Level 16 is now operational in a test version of NASTRAN. Its features are summarized. These include the user-oriented, Case Control type control language, the automated multi-stage matrix processing, the independent direct access data storage facilities, and the static and normal modes solution capabilities. A complete problem analysis sequence is presented with card-by-card description of the user input
Bioengineering Lantibiotics for Therapeutic Success
peer-reviewedSeveral examples of highly modified antimicrobial peptides have been described.
While many such peptides are non-ribosomally synthesized, ribosomally synthesized
equivalents are being discovered with increased frequency. Of the latter group, the
lantibiotics continue to attract most attention. In the present review, we discuss the
implementation of in vivo and in vitro engineering systems to alter, and even enhance,
the antimicrobial activity, antibacterial spectrum and physico-chemical properties,
including heat stability, solubility, diffusion and protease resistance, of these compounds.
Additionally, we discuss the potential applications of these lantibiotics for use as
therapeutics.DF,CH,PC,RR are supported by the Irish Government under the National Development Plan, through a Science Foundation Ireland (SFI) Technology and Innovation Development Award
(TIDA14/TIDA/2286) to DF, a SFI Investigator awards to CH and RR (10/IN.1/B3027),SFI-PIfunding(11/PI/1137) to PDC and the Alimentary Pharmabiotic Centre under Grant Number SFI/12/RC/2273
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Neural processing of imminent collision in humans
Detecting a looming object and its imminent collision is imperative to survival. For most humans, it is a fundamental aspect of daily activities such as driving, road crossing and participating in sport, yet little is known about how the brain both detects and responds to such stimuli. Here we use functional magnetic resonance imaging to assess neural response to looming stimuli in comparison with receding stimuli and motion-controlled static stimuli. We demonstrate for the first time that, in the human, the superior colliculus and the pulvinar nucleus of the thalamus respond to looming in addition to cortical regions associated with motor preparation. We also implicate the anterior insula in making timing computations for collision events
QCD corrections to stoponium production at hadron colliders
If the lighter top squark has no kinematically allowed two-body decays that
conserve flavor, then it will live long enough to form hadronic bound states.
The observation of the diphoton decays of stoponium could then provide a
uniquely precise measurement of the top squark mass. In this paper, we
calculate the cross section for the production of stoponium in a hadron
collider at next-to-leading order (NLO) in QCD. We present numerical results
for the cross section for production of stoponium at the LHC and study the
dependence on beam energy, stoponium mass, and the renormalization and
factorization scale. The cross-section is substantially increased by the NLO
corrections, counteracting a corresponding decrease found earlier in the NLO
diphoton branching ratio.Comment: 24 page
Production of large transverse momentum dileptons and photons in , and collisions by photoproduction processes
The production of large dileptons and photons originating from
photoproduction processes in , and collisions is calculated. We
find that the contribution of dileptons and photons produced by photoproduction
processes is not prominent at RHIC energies. However, the numerical results
indicate that the modification of photoproduction processes becomes evident in
the large region for , and collisions at LHC energies.Comment: 10 figure
Jets associated with Z^0 boson production in heavy-ion collisions at the LHC
The heavy ion program at the LHC will present unprecedented opportunities to
probe hot QCD matter, that is, the quark gluon plasma (QGP). Among these
exciting new probes are high energy partons associated with the production of a
Z^0 boson, or Z^0 tagged jets. Once produced, Z^0 bosons are essentially
unaffected by the strongly interacting medium produced in heavy-ion collisions,
and therefore provide a powerful signal of the initial partonic energy and
subsequent medium induced partonic energy loss. When compared with theory,
experimental measurements of Z^0 tagged jets will help quantify the jet
quenching properties of the QGP and discriminate between different partonic
energy loss formalisms. In what follows, I discuss the advantages of tagged
jets over leading particles, and present preliminary results of the production
and suppression of Z^0 tagged jets in relativistic heavy-ion collisions at LHC
energies using the Guylassy-Levai-Vitev (GLV) partonic energy loss formalism.Comment: To appear in the proceedings of the 2010 Winter Workshop on Nuclear
Dynamics, which was held in Ocho Rios, Jamaica, mon
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