134 research outputs found
Influence du nitrate d'hexyle et de la température de l'air admis sur les délais d'inflammation des huiles végétales dans un moteur diesel
Le but de ce travail est de vĂ©rifier l'influence, d'une part, d'u amĂ©liorant d'indice de cĂ©tane - le nitrate d'hexyle -, et d'autre part, de la tempĂ©rature de l'air admis sur les dĂ©lais d'inflammation des huiles vĂ©gĂ©tales dans un moteur diesel Ă chambre de turbulence. Les rĂ©sultats rĂ©vĂšlent que dans un moteur sensible aux conditions rencontrĂ©es par le carburant au moment de l'injection : - 8 % environ de nitrate d'hexyle sont nĂ©cessaires aux huiles vĂ©gĂ©tales courantes pour avoir les mĂȘmes valeurs de dĂ©lai d'inflammation que le gazole, - les huiles prĂ©sentant les dĂ©lais les plus longs, avec une tempĂ©rature d'admission de 25 deg C. retrouvent les valeurs de dĂ©lais du gazole lorsque l'air est admis Ă 105 ÂŒC (+80 deg C
Distinguishing Supersymmetry From Universal Extra Dimensions or Little Higgs Models With Dark Matter Experiments
There are compelling reasons to think that new physics will appear at or
below the TeV-scale. It is not known what form this new physics will take,
however. Although The Large Hadron collider is very likely to discover new
particles associated with the TeV-scale, it may be difficult for it to
determine the nature of those particles, whether superpartners, Kaluza-Klein
modes or other states. In this article, we consider how direct and indirect
dark matter detection experiments may provide information complementary to
hadron colliders, which can be used to discriminate between supersymmetry,
models with universal extra dimensions, and Little Higgs theories. We find
that, in many scenarios, dark matter experiments can be effectively used to
distinguish between these possibilities.Comment: 23 pages, 7 figures, references added in version
Generation of 1.5 Million Beam Loss Threshold Values
CERN's Large Hadron Collider will store an unprecedented amount of energy in its circulating beams. Beamloss monitoring (BLM) is, therefore, critical for machine protection. It must protect against the consequences (equipment damage, quenches of superconducting magnets) of excessive beam loss. About 4000 monitors will be installed at critical loss locations. Each monitor has 384 beam abort thresholds associated; for 12 integrated loss durations (s to 83 s) and 32 energies (450GeV to 7 TeV). Depending on monitor location, the thresholds vary by orders of magnitude. For simplification, the monitors are grouped in 'families'. Monitors of one family protect similar magnets against equivalent loss scenarios. Therefore, they are given the same thresholds. The start-up calibration of the BLM system is required to be within a factor of five in accuracy; and the final accuracy should be a factor of two. Simulations (backed-up by control measurements) determine the relation between the BLM signal, the deposited energy and the critical energy deposition for damage or quench (temperature of the coil). The paper presents the strategy of determining 1.5 million threshold values
Operational Experience with a LHC Collimator Prototype in the CERN SPS
A full-scale prototype of the Large Hadron Collider (LHC) collimator was installed in 2004 in the CERN Super Proton Synchrotron (SPS) and has been extensively used for beam tests, for control tests and also LHC simulation benchmarking during four years of operation. This operational experience has been extremely valuable in view of the final LHC implementation as well as for estimating the LHC operational scenarios, most notably to establish procedures for the beam-based alignment of the collimators with respect to the circulating beam. These studies were made possible by installing in the SPS a first prototype of the LHC beam loss monitoring system. The operational experience gained at the SPS and the lessons learnt for the LHC operation are presented
High energy photon flux prediction from neutralino annihilation in the globular cluster Palomar 13
The distant globular cluster Palomar 13 has been found to have a very high
mass-to-light ratio and its profile can be well fitted either by a King model
with a tail, or with a NFW model. This cluster may be the first case of the
many clumps predicted by CDM simulations that would not be disrupted by the
galactic halo potential. We make the hypothesis that Pal 13 is made of
neutralinos and run the DarkSuspect code to estimate the high-energy photon
flux due to the annihilation of neutralinos through various channels in some
benchmark scenarios. These low fluxes may be used as targets to be reached in
proposals for future ground-based high altitude Cerenkov telescopes.Comment: A 2-page poster to be published in ``Astronomy, Cosmology and
Fundamental Physics'', the proceedings of the ESO-CERN-ESA Symposium, eds. P.
A. Shaver, L. Di Lella, and A. Gimene
Testing Beam-Induced Quench Levels of LHC Superconducting Magnets
In the years 2009-2013 the Large Hadron Collider (LHC) has been operated with
the top beam energies of 3.5 TeV and 4 TeV per proton (from 2012) instead of
the nominal 7 TeV. The currents in the superconducting magnets were reduced
accordingly. To date only seventeen beam-induced quenches have occurred; eight
of them during specially designed quench tests, the others during injection.
There has not been a single beam- induced quench during normal collider
operation with stored beam. The conditions, however, are expected to become
much more challenging after the long LHC shutdown. The magnets will be
operating at near nominal currents, and in the presence of high energy and high
intensity beams with a stored energy of up to 362 MJ per beam. In this paper we
summarize our efforts to understand the quench levels of LHC superconducting
magnets. We describe beam-loss events and dedicated experiments with beam, as
well as the simulation methods used to reproduce the observable signals. The
simulated energy deposition in the coils is compared to the quench levels
predicted by electro-thermal models, thus allowing to validate and improve the
models which are used to set beam-dump thresholds on beam-loss monitors for Run
2.Comment: 19 page
Three heavy jet events at hadron colliders as a sensitive probe of the Higgs sector
Assuming that a non-standard neutral Higgs with an enhanced Yukawa coupling
to a bottom quark is observed at future hadron experiments, we propose a method
for a better understanding of the Higgs sector. Our procedure is based on
"counting" the number of events with heavy jets (where "heavy" stands for a c
or b jet) versus b jets, in the final state of processes in which the Higgs is
produced in association with a single high p_T c or b jet. We show that an
observed signal of the type proposed, at either the Tevatron or the LHC, will
rule out the popular two Higgs doublet model of type II as well as its
supersymmetric version - the Minimal Supersymmetric Standard Model (MSSM), and
may provide new evidence in favor of some more exotic multi Higgs scenarios. As
an example, we show that in a version of a two Higgs doublet model which
naturally accounts for the large mass of the top quark, our signal can be
easily detected at the LHC within that framework. We also find that such a
signal may be observable at the upgraded Tevatron RunIII, if the neutral Higgs
in this model has a mass around 100 GeV and \tan\beta > 50 and if the
efficiency for distinguishing a c jet from a light jet will reach the level of
50%.Comment: Revtex, 11 pages, 4 figures embedded in the text. Main changes with
respect to Version 1: Numerical results re-calculated using the CTEQ5L pdf,
improved discussion on the experimental consequences, new references added.
Conclusions remain unchanged. As will appear in Phys. Rev.
Investigations of the LHC Emittance Blow-Up During the 2012 Proton Run
About 30 % of the potential luminosity performance is lost through the different phases of the LHC cycle, mainly due to transverse emittance blow-up. Measuring the emittance growth is a difficult task with high intensity beams and changing energies. Improvements of the LHC transverse profile instrumentation helped to study various effects. A breakdown of the growth through the different phases of the LHC cycle is given as well as a comparison with the data from the LHC experiments for transverse beam size. In 2012 a number of possible sources and remedies have been studied. Among these are intra beam scattering, 50 Hz noise and the effect of the transverse damper gain. The results of the investigations are summarized in this paper. Requirements for transverse profile instrumentation for post LHC long shutdown operation to finally tackle the emittance growth are given as well
Supersymmetric dark matter in M31: can one see neutralino annihilation with CELESTE?
It is widely believed that dark matter exists within galaxies and clusters of
galaxies. Under the assumption that this dark matter is composed of the
lightest, stable supersymmetric particle, assumed to be the neutralino, the
feasibility of its indirect detection via observations of a diffuse gamma-ray
signal due to neutralino annihilations within M31 is examined. To this end,
first the dark matter halo of the close spiral galaxy M31 is modeled from
observations, then the resultant gamma-ray flux is estimated within
supersymmetric model configurations. We conclude that under favorable
conditions such as the rapid accretion of neutralinos on the central black hole
in M31 and/or the presence of many clumps inside its halo with inner
profiles, a neutralino annihilation gamma-ray signal is marginally detectable
by the ongoing collaboration CELESTE.Comment: Latex, 32 pages, 12 figures, 5 table
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