3,135 research outputs found
Quantum Monte Carlo simulation of spin-polarized tritium
The ground-state properties of spin-polarized tritium T at zero
temperature are obtained by means of diffusion Monte Carlo calculations. Using
an accurate {\em ab initio} T-T interatomic potential
we have studied its liquid phase, from the spinodal point until densities above
its freezing point. The equilibrium density of the liquid is significantly
higher and the equilibrium energy of K significantly lower than in
previous approximate descriptions. The solid phase has also been studied for
three lattices up to high pressures, and we find that hcp lattice is slightly
preferred. The liquid-solid phase transition has been determined using the
double-tangent Maxwell construction; at zero temperature, bulk tritium freezes
at a pressure of bar.Comment: 8 page
Collisional energy transfer in two-component plasmas
The friction in plasmas consisting of two species with different temperatures
is discussed together with the consequent energy transfer. It is shown that the
friction between the two species has no effect on the ion acoustic mode in a
quasi-neutral plasma. Using the Poisson equation instead of the
quasi-neutrality reveals the possibility for an instability driven by the
collisional energy transfer. However, the different starting temperatures of
the two species imply an evolving equilibrium. It is shown that the relaxation
time of the equilibrium electron-ion plasma is, in fact, always shorter than
the growth rate time, and the instability can thus never effectively take
place. The results obtained here should contribute to the definite
clarification of some contradictory results obtained in the past
Search for new phenomena in dijet events using 37 fb−1 of pp collision data collected at √s=13 TeV with the ATLAS detector
Dijet events are studied in the proton-proton collision data set recorded at s=13 TeV with the ATLAS detector at the Large Hadron Collider in 2015 and 2016, corresponding to integrated luminosities of 3.5 fb-1 and 33.5 fb-1 respectively. Invariant mass and angular distributions are compared to background predictions and no significant deviation is observed. For resonance searches, a new method for fitting the background component of the invariant mass distribution is employed. The data set is then used to set upper limits at a 95% confidence level on a range of new physics scenarios. Excited quarks with masses below 6.0 TeV are excluded, and limits are set on quantum black holes, heavy W′ bosons, W∗ bosons, and a range of masses and couplings in a Z′ dark matter mediator model. Model-independent limits on signals with a Gaussian shape are also set, using a new approach allowing factorization of physics and detector effects. From the angular distributions, a scale of new physics in contact interaction models is excluded for scenarios with either constructive or destructive interference. These results represent a substantial improvement over those obtained previously with lower integrated luminosity
Search for supersymmetry in final states with missing transverse momentum and multiple b-jets in proton-proton collisions at √s=13 TeV with the ATLAS detector
A search for supersymmetry involving the pair production of gluinos decaying via third-generation squarks into the lightest neutralino χ˜10 is reported. It uses LHC proton-proton collision data at a centre-of-mass energy s=13 TeV with an integrated luminosity of 36.1 fb−1 collected with the ATLAS detector in 2015 and 2016. The search is performed in events containing large missing transverse momentum and several energetic jets, at least three of which must be identified as originating from b-quarks. To increase the sensitivity, the sample is divided into subsamples based on the presence or absence of electrons or muons. No excess is found above the predicted background. For χ˜10 masses below approximately 300 GeV, gluino masses of less than 1.97 (1.92) TeV are excluded at 95% confidence level in simplified models involving the pair production of gluinos that decay via top (bottom) squarks. An interpretation of the limits in terms of the branching ratios of the gluinos into third-generation squarks is also provided. These results improve upon the exclusion limits obtained with the 3.2 fb−1 of data collected in 2015
Search for new phenomena in high-mass final states with a photon and a jet from pp collisions at √s = 13 TeV with the ATLAS detector
A search is performed for new phenomena in events having a photon with high transverse momentum and a jet collected in 36.7fb-1 of proton–proton collisions at a centre-of-mass energy of s = 13 TeV recorded with the ATLAS detector at the Large Hadron Collider. The invariant mass distribution of the leading photon and jet is examined to look for the resonant production of new particles or the presence of new high-mass states beyond the Standard Model. No significant deviation from the background-only hypothesis is observed and cross-section limits for generic Gaussian-shaped resonances are extracted. Excited quarks hypothesized in quark compositeness models and high-mass states predicted in quantum black hole models with extra dimensions are also examined in the analysis. The observed data exclude, at 95% confidence level, the mass range below 5.3 TeV for excited quarks and 7.1 TeV (4.4 TeV) for quantum black holes in the Arkani-Hamed–Dimopoulos–Dvali (Randall–Sundrum) model with six (one) extra dimensions
On electrostatic modes in multi-ion and pair-ion collisional plasmas
The physics of plasmas containing positive and negative ions is discussed
with special attention to the recently produced pair-ion plasma containing ions
of equal mass and opposite charge. The effects of the density gradient in the
direction perpendicular to the ambient magnetic field vector, observed in the
experiment, are discussed. In addition, the possible presence of electrons is
discussed in the context of plasma modes propagating at an angle with respect
to the magnetic field vector. The electrons may either be added to the plasma
or enter the plasma attached to negative ions and then become released from the
ions as a result of collisions. It is shown that the electron plasma mode in a
cold plasma may become a backward mode in the presence of a density gradient,
and this behavior may be controlled either by the electron number density or
the mode number in the perpendicular direction. In plasmas with hot electrons
an instability may develop, driven by the combination of electron collisions
and the density gradient, and in the regime when the ions' response is similar
to a sound mode, i.e., for un-magnetized ions, implying mode frequencies much
above the ion gyro-frequency or mode wave-lengths shorter than the ion
gyro-radius. In the case of a pure pair-ion plasma, for lower frequencies and
for parameters close to those used in the recent experiments, the perturbed
ions may feel the effects of the magnetic field. In this case the plasma mode
also becomes backward, resembling features of an experimentally observed but
yet unexplained backward mode.Comment: 17 pages plus 5 figure
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