1,138 research outputs found
photon+jet event rate estimation for the gluon distribution determination at the Tevatron Run II
Since a lot of theoretical predictions on the production of new particles
(Higgs, SUSY) at the Tevatron are based on model estimations of the proton
gluon density behavior at low and high values of a transfered momentum Q^2,
the study of a possibility of a measurement of the gluon density in this
kinematic region directly in Tevatron experiments is obviously of a big
interest [1].
Basing on the selection criteria proposed ealier in [1,2], the background
events suppression factors and corresponding signal events selection
efficiencies are determined here. The estimation of the number of photon+jet
events suitable for measurement of gluon distribution in different x and Q^2
intervals at Tevatron Run II is also done.
It is shown that with integrated luminosity L_{int}=3 fb^-1 it would be
possible to collect about one million of these events. This number would allow
to cover a new kinematical region, 10^-3 < x < 1.0 with 1.6*10^3 < Q^2 < 2*10^4
(GeV/c)^2, not studied in any previous experiment. This area includes the
values of Q^2 that are, on the average, by about one order of magnitude higher
than those reached at HERA now. The rates of g c-> photon + jet events are also
obtained.Comment: 10 page
Photons and jets at the Tevatron
Presented are the Run II QCD preliminary results of D0 and CDF Collaborations on the measurements of inclusive jet cross sections as well as recently published results on the inclusive and di-photon cross sections
Separation of a single photon and products of the meson neutral decay channels in the CMS electromagnetic calorimeter using neural network
The artificial neural network approach is used for separation of signals from
a single photon and products of the meson neutral
decay channels on the basis of the data from the CMS electromagnetic
calorimeter alone. Rejection values for the three types of mesons as a function
of single photon selection efficiencies are obtained for two Barrel and one
Endcap pseudorapidity regions and initial \Et of 20, 40, 60 and 100 GeV.Comment: 16 pages, uses cernrep.cls style fil
Measuring Hall Viscosity of Graphene's Electron Fluid
Materials subjected to a magnetic field exhibit the Hall effect, a phenomenon
studied and understood in fine detail. Here we report a qualitative breach of
this classical behavior in electron systems with high viscosity. The viscous
fluid in graphene is found to respond to non-quantizing magnetic fields by
producing an electric field opposite to that generated by the classical Hall
effect. The viscous contribution is large and identified by studying local
voltages that arise in the vicinity of current-injecting contacts. We analyze
the anomaly over a wide range of temperatures and carrier densities and extract
the Hall viscosity, a dissipationless transport coefficient that was long
identified theoretically but remained elusive in experiment. Good agreement
with theory suggests further opportunities for studying electron
magnetohydrodynamics.Comment: 18 pages, 9 figure
Negative local resistance caused by viscous electron backflow in graphene
Graphene hosts a unique electron system in which electron-phonon scattering
is extremely weak but electron-electron collisions are sufficiently frequent to
provide local equilibrium above liquid nitrogen temperature. Under these
conditions, electrons can behave as a viscous liquid and exhibit hydrodynamic
phenomena similar to classical liquids. Here we report strong evidence for this
transport regime. We find that doped graphene exhibits an anomalous (negative)
voltage drop near current injection contacts, which is attributed to the
formation of submicrometer-size whirlpools in the electron flow. The viscosity
of graphene's electron liquid is found to be ~0.1 m /s, an order of
magnitude larger than that of honey, in agreement with many-body theory. Our
work shows a possibility to study electron hydrodynamics using high quality
graphene
Giant oscillations in a triangular network of one-dimensional states in marginally twisted graphene
The electronic properties of graphene superlattices have attracted intense
interest that was further stimulated by the recent observation of novel
many-body states at "magic" angles in twisted bilayer graphene (BLG). For very
small ("marginal") twist angles of 0.1 deg, BLG has been shown to exhibit a
strain-accompanied reconstruction that results in submicron-size triangular
domains with the Bernal stacking. If the interlayer bias is applied to open an
energy gap inside the domain regions making them insulating, marginally-twisted
BLG is predicted to remain conductive due to a triangular network of chiral
one-dimensional (1D) states hosted by domain boundaries. Here we study electron
transport through this network and report giant Aharonov-Bohm oscillations
persisting to temperatures above 100 K. At liquid helium temperatures, the
network resistivity exhibits another kind of oscillations that appear as a
function of carrier density and are accompanied by a sign-changing Hall effect.
The latter are attributed to consecutive population of the flat minibands
formed by the 2D network of 1D states inside the gap. Our work shows that
marginally twisted BLG is markedly distinct from other 2D electronic systems,
including BLG at larger twist angles, and offers a fascinating venue for
further research.Comment: 11 pages, 8 figure
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