48 research outputs found
Equation of state at FAIR energies and the role of resonances
Two microscopic models, UrQMD and QGSM, are used to extract the effective
equation of state (EOS) of locally equilibrated nuclear matter produced in
heavy-ion collisions at energies from 11.6 AGeV to 160 AGeV. Analysis is
performed for the fixed central cubic cell of volume V = 125 fm**3 and for the
expanding cell that followed the growth of the central area with uniformly
distributed energy. For all reactions the state of local equilibrium is nearly
approached in both models after a certain relaxation period. The EOS has a
simple linear dependence P/e = c_s**2 with 0.12 < c_s**2 < 0.145. Heavy
resonances are shown to be responsible for deviations of the c_s**2(T) and
c_s**2(mu_B) from linear behavior. In the T-mu_B and T-mu_S planes the EOS has
also almost linear dependence and demonstrates kinks related not to the
deconfinement phase transition but to inelastic freeze-out in the system.Comment: SQM2008 proceedings, 6 page
Microscopic models and effective equation of state in nuclear collisions at FAIR energies
Two microscopic models, UrQMD and QGSM, were employed to study the formation
of locally equilibrated hot and dense nuclear matter in heavy-ion collisions at
energies from 11.6 AGeV to 160 AGeV. Analysis was performed for the fixed
central cubic cell of volume V = 125 fm**3 and for the expanding cell which
followed the growth of the central area with uniformly distributed energy. To
decide whether or not the equilibrium was reached, results of the microscopic
calculations were compared to that of the statistical thermal model. Both
dynamical models indicate that the state of kinetic, thermal and chemical
equilibrium is nearly approached at any bombarding energy after a certain
relaxation period. The higher the energy, the shorter the relaxation time.
Equation of state has a simple linear dependence P = a(sqrt{s})*e, where a =
c_s**2 is the sound velocity squared. It varies from 0.12 \pm 0.01 at E_{lab} =
11.6 AGeV to 0.145 \pm 0.005 at E_{lab} = 160 AGeV. Change of the slope in
a(sqrt{s}) behavior occurs at E_{lab} = 40 AGeV and can be assigned to the
transition from baryon-rich to meson-dominated matter. The phase diagrams in
the T - mu_B plane show the presence of kinks along the lines of constant
entropy per baryon. These kinks are linked to the inelastic (i.e. chemical)
freeze-out in the system.Comment: 14 pages, REVTE
Nuclear shadowing in Glauber-Gribov theory with Q2-evolution
We consider deep inelastic scattering off nuclei in the Regge limit within
the Glauber-Gribov model. Using unitarized parton distribution functions for
the proton, we find sizeable shadowing effects on the nuclear total and
longitudinal structure functions, and , in the low-x limit.
Extending a fan-diagram analysis for the large-mass region of coherent
diffraction off nuclei to high Q2, we also find significant shadowing effects
in this kinematical regime. Finally, we discuss shortcomings of our approach
and possible extensions of the model to other kinematical regimes.Comment: 16 pages, 9 figure
Jet Quenching via Jet Collimation
The ATLAS Collaboration recently reported strong modifications of dijet
properties in heavy ion collisions. In this work, we discuss to what extent
these first data constrain already the microscopic mechanism underlying jet
quenching. Simple kinematic arguments lead us to identify a frequency
collimation mechanism via which the medium efficiently trims away the soft
components of the jet parton shower. Through this mechanism, the observed dijet
asymmetry can be accomodated with values of that lie in the
expected order of magnitude.Comment: 6 pages, 4 figure
Charmonium dissociation and recombination at RHIC and LHC
Charmonium production at heavy-ion colliders is considered within the
comovers interaction model. The formalism is extended by including possible
secondary J/psi production through recombination and an estimate of
recombination effects is made with no free parameters involved. The comovers
interaction model also includes a comprehensive treatment of initial-state
nuclear effects, which are discussed in the context of such high energies. With
these tools, the model properly describes the centrality and the rapidity
dependence of experimental data at RHIC energy, = 200 GeV, for both
Au+Au and Cu+Cu collisions. Predictions for LHC, = 5.5 TeV, are
presented and the assumptions and extrapolations involved are discussed.Comment: 16 pages, 5 figure
The physics potential of proton-nucleus collisions at the TeV scale
The LHC brings nuclear collisions to the TeV scale for the first time and the
first data show the qualitative differences of this new regime. The
corresponding phase-space available encompasses completely uncharted regions of
QCD in which high-density or high-temperature domains can be identified.
Proton-nucleus runs are essential for a complete interpretation of the data and
for the study of new regimes dominated by large occupation numbers in the
hadronic wave function. I comment here the physics opportunities for p+Pb runs
at the LHC and d+Au runs at RHIC and the corresponding needs in view of the new
Pb+Pb data from the LHC.Comment: Proceedings of the conference Quark Matter 2011, Annecy (France) May
201
Thermal Dileptons at LHC
We predict dilepton invariant-mass spectra for central 5.5 ATeV Pb-Pb
collisions at LHC. Hadronic emission in the low-mass region is calculated using
in-medium spectral functions of light vector mesons within hadronic many-body
theory. In the intermediate-mass region thermal radiation from the Quark-Gluon
Plasma, evaluated perturbatively with hard-thermal loop corrections, takes
over. An important source over the entire mass range are decays of correlated
open-charm hadrons, rendering the nuclear modification of charm and bottom
spectra a critical ingredient.Comment: 2 pages, 2 figures, contributed to Workshop on Heavy Ion Collisions
at the LHC: Last Call for Predictions, Geneva, Switzerland, 14 May - 8 Jun
2007 v2: acknowledgment include
A Large Hadron Electron Collider at CERN
This document provides a brief overview of the recently published report on
the design of the Large Hadron Electron Collider (LHeC), which comprises its
physics programme, accelerator physics, technology and main detector concepts.
The LHeC exploits and develops challenging, though principally existing,
accelerator and detector technologies. This summary is complemented by brief
illustrations of some of the highlights of the physics programme, which relies
on a vastly extended kinematic range, luminosity and unprecedented precision in
deep inelastic scattering. Illustrations are provided regarding high precision
QCD, new physics (Higgs, SUSY) and electron-ion physics. The LHeC is designed
to run synchronously with the LHC in the twenties and to achieve an integrated
luminosity of O(100) fb. It will become the cleanest high resolution
microscope of mankind and will substantially extend as well as complement the
investigation of the physics of the TeV energy scale, which has been enabled by
the LHC
The Large Hadron-Electron Collider at the HL-LHC
The Large Hadron-Electron Collider (LHeC) is designed to move the field of deep inelastic scattering (DIS) to the energy and intensity frontier of particle physics. Exploiting energy-recovery technology, it collides a novel, intense electron beam with a proton or ion beam from the High-Luminosity Large Hadron Collider (HL-LHC). The accelerator and interaction region are designed for concurrent electron-proton and proton-proton operations. This report represents an update to the LHeC's conceptual design report (CDR), published in 2012. It comprises new results on the parton structure of the proton and heavier nuclei, QCD dynamics, and electroweak and top-quark physics. It is shown how the LHeC will open a new chapter of nuclear particle physics by extending the accessible kinematic range of lepton-nucleus scattering by several orders of magnitude. Due to its enhanced luminosity and large energy and the cleanliness of the final hadronic states, the LHeC has a strong Higgs physics programme and its own discovery potential for new physics. Building on the 2012 CDR, this report contains a detailed updated design for the energy-recovery electron linac (ERL), including a new lattice, magnet and superconducting radio-frequency technology, and further components. Challenges of energy recovery are described, and the lower-energy, high-current, three-turn ERL facility, PERLE at Orsay, is presented, which uses the LHeC characteristics serving as a development facility for the design and operation of the LHeC. An updated detector design is presented corresponding to the acceptance, resolution, and calibration goals that arise from the Higgs and parton-density-function physics programmes. This paper also presents novel results for the Future Circular Collider in electron-hadron (FCC-eh) mode, which utilises the same ERL technology to further extend the reach of DIS to even higher centre-of-mass energies.Peer reviewe
Alignment of the ALICE Inner Tracking System with cosmic-ray tracks
37 pages, 15 figures, revised version, accepted by JINSTALICE (A Large Ion Collider Experiment) is the LHC (Large Hadron Collider) experiment devoted to investigating the strongly interacting matter created in nucleus-nucleus collisions at the LHC energies. The ALICE ITS, Inner Tracking System, consists of six cylindrical layers of silicon detectors with three different technologies; in the outward direction: two layers of pixel detectors, two layers each of drift, and strip detectors. The number of parameters to be determined in the spatial alignment of the 2198 sensor modules of the ITS is about 13,000. The target alignment precision is well below 10 micron in some cases (pixels). The sources of alignment information include survey measurements, and the reconstructed tracks from cosmic rays and from proton-proton collisions. The main track-based alignment method uses the Millepede global approach. An iterative local method was developed and used as well. We present the results obtained for the ITS alignment using about 10^5 charged tracks from cosmic rays that have been collected during summer 2008, with the ALICE solenoidal magnet switched off.Peer reviewe