4,068 research outputs found
Multiple Parton Interactions with ALICE: from pp to p-Pb
The study of multiplicity dependent di-hadron angular correlations allows us
to assess the contribution of multiple-parton interactions to particle
production. We will review these measurements in pp and p-Pb collisions with
the ALICE detector at the LHC and discuss the results in the context of
centrality determination and other multiplicity dependent observables in p-Pb.Comment: 9 pages, 10 figures; Invited talk presented at the 30th Winter
Workshop on Nuclear Dynamics (WWND 2014), Galveston, Texas, USA, April 6-12,
201
p-Pb Results from ALICE with an Emphasis on Centrality Determination
New ALICE results concerning particle production at low and intermediate
transverse momenta in p-Pb collisions at a centre of mass energy of 5.02 TeV
per nucleon pair are briefly discussed. Emphasis is given to the determination
of centrality in p-Pb and their implications for binary scaling of hard
processes.Comment: 5 pages, 5 figures, talk given at Strangeness in Quark Matter SQM
2013, 22nd - 27th July 2013 Birmingham, United Kingdo
Results on Jet Spectra and Structure from ALICE
Full jet reconstruction in ALICE uses the combined information from charged
and neutral particles. Essentially all jet constituents can be measured with
large efficiency down to very low transverse momenta (pT > 150 MeV/c). This has
the advantage to introduce a minimum bias on the jet fragmentation, in
particular for low jet momenta and in the presence of quenching. In this
article, we present preliminary results from reconstruction of charged jets in
Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV. The inclusive charged jet spectrum,
the jet nuclear modification factors (R_AA, R_CP), the ratio of spectra
measured with different resolution parameters and hadron-jet correlations are
discussed. For pp data at the same center of mass energy, the inclusive
spectrum of fully reconstructed jets and its resolution parameter dependence
are reported.Comment: 8 pages, 11 figures; to be published in the Proceedings of Quark
Matter 201
Simulation in ALICE
ALICE, the experiment dedicated to the study of heavy ion collisions at the
LHC, uses an object-oriented framework for simulation, reconstruction and
analysis (AliRoot) based on ROOT. Here, we describe the general ALICE
simulation strategy and those components of the framework related to
simulation. Two main requirements have driven the development of the simulation
components. First, the possibility to run different transport codes with the
same user code for geometry and detector response has led to the development of
the Virtual Monte Carlo concept. Second, simulation has to provide tools to
efficiently study events ranging from low-multiplicity pp collisions to Pb-Pb
collisions with up to 80000 primary particles per event. This has led to the
development of a variety of collaborating generator classes and specific
classes for event merging.Comment: Talk from the 2003 Computing in High Energy and Nuclear Physics
(CHEP03), La Jolla, Ca, USA, March 2003, 6 pages, LaTeX, 5 eps figures. PSN
TUMT00
Absence of jet quenching in peripheral nucleus-nucleus collisions
Medium effects on the production of high- particles in
nucleus-nucleus (AA) collisions are generally quantified by the nuclear
modification factor (), defined to be unity in absence of nuclear
effects. Modeling particle production including a nucleon-nucleon impact
parameter dependence, we demonstrate that at midrapidity in
peripheral AA collisions can be significantly affected by event selection and
geometry biases. Even without jet quenching and shadowing, these biases cause
an apparent suppression for in peripheral collisions, and are
relevant for all types of hard probes and all collision energies. Our studies
indicate that calculations of jet quenching in peripheral AA collisions should
account for the biases, or else they will overestimate the relevance of parton
energy loss. Similarly, expectations of parton energy loss in light-heavy
collision systems based on comparison with apparent suppression seen in
peripheral should be revised. Our interpretation of the peripheral
data would unify observations for lighter collision systems or
lower energies where significant values of elliptic flow are observed despite
the absence of strong jet quenching.Comment: 13 pages, 4 captioned figures (the 4th is not in the published
version); our code for HG-PYTHIA was ported in 2019 by Austin Baty to run on
top of a default PYTHIA installation and can be found at
https://github.com/abaty/HGPythi
Structure for the breathing mode of the nucleon from high energy p-p scattering
Spectra of p-p and pi-p scattering at beam momenta between 6 and 30 GeV/c
have been reanalysed. These show strong excitation of N* resonances, the
strongest one corresponding to the "scalar" P11 excitation (breathing mode) at
m_o= 1400+-10 MeV with Gamma= 200+-25 MeV. The result of a strong scalar
excitation is supported by a large longitudinal amplitude S_1/2 extracted from
e-p scattering. From exclusive data on p+p=>p p pi+ pi- a large 2pi-N decay
branch for the P_11 resonance of B_2pi= 75+-20 % has been extracted.
The differential cross sections were described in a double folding approach,
assuming multi-gluon exchange as the dominant part of the effective interaction
between the constituents of projectile and target. First, the parameters of the
interaction were fitted to elastic scattering; then with this interaction the
inelastic cross sections were described in the distorted wave Born
approximation. A good description of the data requires a surface peaked
transition density, quite different from that of a pure radial mode. In
contrast, the electron scattering amplitude S_1/2 is quite well described by a
breathing mode transition density with radial node. This large difference
between charge and matter transition density suggests, that in p-p scattering
the coupling to the multi-gluon field is much more important than the coupling
to the valence quarks. A multi-gluon (or sea-quark) transition density is
derived, which shows also breathing, indicating a rather complex multi-quark
structure of N and N* including multi-glue (or q^2n qbar ^-2n) creation out of
the g.s. vacuum.Comment: 18 pages with 7 figure
- …