21 research outputs found
Measurement of Jets and Jet Suppression in sqrt(s_NN)=2.76 TeV Lead-Lead Collisions with the ATLAS detector at the LHC
The first results of single jet observables in Pb+Pb collisions at
sqrt(s_NN)=2.76 TeV measured with the ATLAS detector at the LHC are presented.
Full jets are reconstructed with the anti-kt algorithm with R= 0.2 and 0.4,
using an event-by-event subtraction procedure to correct for the effects of the
underlying event including elliptic flow. The geometrically-scaled ratio of jet
yields in central and peripheral events,Rcp, indicates a clear suppression of
jets with ET >100 GeV. The transverse and longitudinal distributions of jet
fragments is also presented. We find little no substantial change to the
fragmentation properties and no significant change in the level of suppression
when moving to the larger jet definition.Comment: 5 pages, 6 figures, proceedings for Quark Matter 2011, Annecy,
France, May 23-28, 201
Transport Theoretical Description of Collisional Energy Loss in Infinite Quark-Gluon Matter
We study the time evolution of a high-momentum gluon or quark propagating
through an infinite, thermalized, partonic medium utilizing a Boltzmann
equation approach. We calculate the collisional energy loss of the parton,
study its temperature and flavor dependence as well as the the momentum
broadening incurred through multiple interactions. Our transport calculations
agree well with analytic calculations of collisional energy-loss where
available, but offer the unique opportunity to address the medium response as
well in a consistent fashion.Comment: 12 pages, updated with additional references and typos correcte
Particle Production at Large Transverse Momentum with ALICE
We present transverse momentum distributions of inclusive charged particles
and identified hadrons in and Pb--Pb collisions at \rs= 2.76 TeV,
measured by ALICE at the LHC. The Pb--Pb data are presented in intervals of
collision centrality and cover transverse momenta up to 50 GeV/. Nuclear
medium effects are studied in terms of the nuclear modification factor \raa.
The results indicate a strong suppression of high- particles in Pb--Pb
collisions, consistent with a large energy loss of hard-scattered partons in
the hot, dense and long-lived medium created at the LHC. We compare the
preliminary results for inclusive charged particles to previous results from
RHIC and calculations from energy loss models. Furthermore, we compare the
nuclear modification factors of inclusive charged particles to those of
identified , , K, and .Comment: Talk given at Quark Matter 2011 conferenc
Evolution of mechanism of parton energy loss with transverse momentum at RHIC and LHC in relativistic collision of heavy nuclei
We analyze the suppression of particle production at large transverse momenta
in ( most) central collisions of gold nuclei at
200 GeV and lead nuclei at 2.76 TeV. Full
next-to-leading order radiative corrections at , and
nuclear effects like shadowing and parton energy loss are included. The parton
energy loss is implemented in a simple multiple scattering model, where the
partons lose an energy per collision, where
is their mean free path. We take for a treatment
which is suggestive of the Bethe Heitler (BH) mechanism of incoherent
scatterings, for LPM mechanism, and
constant for a mechanism which suggests that the rate of energy loss ()
of the partons is proportional to total path length () of the parton in the
plasma, as the formation time of the radiated gluon becomes much larger than
.
We find that while the BH mechanism describes the nuclear modification factor
for 5 GeV/ (especially at RHIC energy), the LPM
and more so the constant mechanism provides a good description at
larger . This confirms the earlier expectation that the energy loss
mechanism for partons changes from BH to LPM for ,
where 1 fm and 1 GeV is the average
transverse kick-squared received by the parton per collision. The energy loss
per collision at the =2.76 TeV is found to be about
twice of that at 0.2 TeV.Comment: Discussion expanded, additional references added, 14 pages, 6
figures, To appear in Journal of Physics
Quark Matter 2006: high-pT and jets
An overview of new experimental results on high-\pT{} particle production and
jets in heavy ion collisions from the Quark Matter 2006 conference is
presented.Comment: Presented at Quark Matter 200
The theory and phenomenology of perturbative QCD based jet quenching
The study of the structure of strongly interacting dense matter via hard jets
is reviewed. High momentum partons produced in hard collisions produce a shower
of gluons prior to undergoing the non-perturbative process of hadronization. In
the presence of a dense medium this shower is modified due to scattering of the
various partons off the constituents in the medium. The modified pattern of the
final detected hadrons is then a probe of the structure of the medium as
perceived by the jet. Starting from the factorization paradigm developed for
the case of particle collisions, we review the basic underlying theory of
medium induced gluon radiation based on perturbative Quantum Chromo Dynamics
(pQCD) and current experimental results from Deep Inelastic Scattering on large
nuclei and high energy heavy-ion collisions, emphasizing how these results
constrain our understanding of energy loss. This review contains introductions
to the theory of radiative energy loss, elastic energy loss, and the
corresponding experimental observables and issues. We close with a discussion
of important calculations and measurements that need to be carried out to
complete the description of jet modification at high energies at future high
energy colliders.Comment: 78 pages, 24 figures, submitted to prog. part. nucl. phy
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
Comparison of Jet Quenching Formalisms for a Quark-Gluon Plasma "Brick"
We review the currently available formalisms for radiative energy loss of a
high-momentum parton in a dense strongly interacting medium. The underlying
theoretical framework of the four commonly used formalisms is discussed and the
differences and commonalities between the formalisms are highlighted. A
quantitative comparison of the single gluon emission spectra as well as the
energy loss distributions is given for a model system consisting of a uniform
medium with a fixed length of L=2 fm and L=5 fm (the `Brick'). Sizable
quantitative differences are found. The largest differences can be attributed
to specific approximations that are made in the calculation of the radiation
spectrum.Comment: 30 pages, 24 figures update version2: added curves with large x to
Figure 14, Higher Twist curves to Figs 19, 20, plus some changes in the text
(introduction/summary, discussion of Fig 14 and HT section
Recent high-pt results from STAR
We present selected recent results of multi-hadron correlation measurements
in azimuth and pseudorapidity at intermediate and high \pt{} in Au+Au
collisions at GeV, from the STAR experiment at RHIC. At
intermediate \pt, measurements are presented that attempt to determine the
origin of the associated near-side (small \dphi) yield at large pseudo-rapidity
difference \deta{} that is found to be present in heavy ion collisions. In
addition, results are reported on new multi-hadron correlation measures at
high-\pt{} that use di-hadron triggers and multi-hadron cluster triggers with
the goal to constrain the underlying jet kinematics better than in the existing
measurements of inclusive spectra and di-hadron correlations.Comment: 6 pages, 8 figures. Prepared for 3rd International Conference on Hard
and Electro- Magnetic Probes of High-Energy Nuclear Collisions (Hard Probes
2008), submitted to EPJ
Centrality dependence of charged particle production at large transverse momentum in Pb-Pb collisions at TeV
The inclusive transverse momentum () distributions of primary
charged particles are measured in the pseudo-rapidity range as a
function of event centrality in Pb-Pb collisions at
TeV with ALICE at the LHC. The data are presented in the range
GeV/ for nine centrality intervals from 70-80% to 0-5%.
The Pb-Pb spectra are presented in terms of the nuclear modification factor
using a pp reference spectrum measured at the same collision
energy. We observe that the suppression of high- particles strongly
depends on event centrality. In central collisions (0-5%) the yield is most
suppressed with at -7 GeV/. Above
GeV/, there is a significant rise in the nuclear modification
factor, which reaches for GeV/. In
peripheral collisions (70-80%), the suppression is weaker with almost independently of . The measured nuclear
modification factors are compared to other measurements and model calculations.Comment: 17 pages, 4 captioned figures, 2 tables, authors from page 12,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/284