3,414 research outputs found
First LHC results on coherent J/psi photoproduction in ultra-peripheral Pb-Pb collisions at sqrt{s_NN} = 2.76 TeV
The first LHC measurement on ultra-peripheral heavy-ion collisions was
carried out with the ALICE experiment. In this paper, ALICE results on
exclusive J/psi studies in Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV, in the
rapidity region -3.6 < y < -2.6, are given. The coherent J/psi cross section
was found to be dsigma/dy_coh_J/\psi = 1.00 +/- 0.18 (stat) +0.24 -0.26 (syst)
mb. These studies favour theoretical models that include strong modifications
to the nuclear gluon density, also known as nuclear gluon shadowing.Comment: Presented at DIFFRACTION 2012: International Workshop on Diffraction
in High-Energy Physics. Puerto del Carmen, Canary Islands, 10-15 September
201
Prospects for meson production in pp collisions at the ALICE experiment
The ALICE experiment at the CERN Large Hadron Collider (LHC) will allow the
study of resonance production in nucleus-nucleus and proton-proton collisions.
This paper presents results based on physics performance studies to discuss
prospects in ALICE for (1020) meson production in pp interactions during
the LHC startup.Comment: To appear in the proceedings of International Conference on
Strangeness in Quark Matter (SQM 2007), Levoca, Slovakia, 24-29 Jun 2007.
Submitted to J.Phys.
Mass dependence of vector meson photoproduction off protons and nuclei within the energy-dependent hot-spot model
We study the photoproduction of vector mesons off proton and off nuclear
targets. We work within the colour dipole model in an approach that includes
subnucleon degrees of freedom, so-called hot spots, whose positions in the
impact-parameter plane change event-by-event. The key feature of our model is
that the number of hot spots depends on the energy of the photon--target
interaction. Predictions are presented for exclusive and dissociative
production of , , and off protons, as
well as for coherent and incoherent photoproduction of off nuclear
targets, where Xe, Au, and Pb nuclei are considered. We find that the mass
dependence of dissociative production off protons as a function of the energy
of the interaction provides a further handle to search for saturation effects
at HERA, the LHC and future colliders. We also find that the coherent
photonuclear production of is sensitive to fluctuations in the
subnucleon degrees of freedom at RHIC and LHC energies.Comment: 19 pages, 4 figures. Typo in legend of figs. 1 and 2 correcte
Quantum tomography for collider physics: Illustrations with lepton pair production
Quantum tomography is a method to experimentally extract all that is
observable about a quantum mechanical system. We introduce quantum tomography
to collider physics with the illustration of the angular distribution of lepton
pairs. The tomographic method bypasses much of the field-theoretic formalism to
concentrate on what can be observed with experimental data, and how to
characterize the data. We provide a practical, experimentally-driven guide to
model-independent analysis using density matrices at every step. Comparison
with traditional methods of analyzing angular correlations of inclusive
reactions finds many advantages in the tomographic method, which include
manifest Lorentz covariance, direct incorporation of positivity constraints,
exhaustively complete polarization information, and new invariants free from
frame conventions. For example, experimental data can determine the
of the production process, which is a
model-independent invariant that measures the degree of coherence of the
subprocess. We give reproducible numerical examples and provide a supplemental
standalone computer code that implements the procedure. We also highlight a
property of that guarantees in a least-squares type fit
that a local minimum of a statistic will be a global minimum: There
are no isolated local minima. This property with an automated implementation of
positivity promises to mitigate issues relating to multiple minima and
convention-dependence that have been problematic in previous work on angular
distributions.Comment: 25 pages, 3 figure
Applying Quantum Tomography to Hadronic Interactions
A proper description of inclusive reactions is expressed with density matrices. Quantum tomography reconstructs density matrices from experimental observables. We review recent work that applies quantum tomography to practical experimental data analysis. Almost all field-theoretic formalism and modeling used in a traditional approach is circumvented with great efficiency. Tomographically-determined density matrices can express information about quantum systems which cannot in principle be expressed with distributions defined by classical probability. Topics such as entanglement and von Neumann entropy can be accessed using the same natural language where they are defined. A deep relation exists between {\it separability}, as defined in quantum information science, and {\it factorization}, as defined in high energyphysics. Factorization acquires a non-perturbative definition when expressed in terms of a conditional form of separability. An example illustrates how to go from data for momentum 4-vectors to a density matrix while bypassing almost all the formalism of the Standard Model
Event-shape engineering for inclusive spectra and elliptic flow in Pb-Pb collisions at √ s NN = 2.76 TeV
We report on results obtained with the event-shape engineering technique applied to Pb-Pb collisions at √sNN=2.76 TeV. By selecting events in the same centrality interval, but with very different average flow, different initial-state conditions can be studied. We find the effect of the event-shape selection on the elliptic flow coefficient v2 to be almost independent of transverse momentum pT, which is as expected if this effect is attributable to fluctuations in the initial geometry of the system. Charged-hadron, -pion, -kaon, and -proton transverse momentum distributions are found to be harder in events with higher-than-average elliptic flow, indicating an interplay between radial and elliptic flow
The ALICE trigger electronics
The ALICE trigger system (TRG) consists of a Central Trigger Processor (CTP) and up to 24 Local Trigger Units (LTU) for each sub-detector. The CTP receives and processes trigger signals from trigger detectors and the outputs from the CTP are 3 levels of hardware triggers: L0, L1 and L2. The 24 sub-detectors are dynamically partitioned in up to 6 independent clusters. The trigger information is propagated through the LTUs to the Front-end electronics (FEE) of each sub-detector via LVDS cables and optical fibres. The trigger information sent from LTU to FEE can be monitored online for possible errors using the newly developed TTCit board. After testing and commissioning of the trigger system itself on the surface, the ALICE trigger electronics has been installed and tested in the experimental cavern with appropriate ALICE experimental software. Testing the Alice trigger system with detectors on the surface and in the experimental cavern in parallel is progressing very well. Currently one setup is used for testing on the surface; another is installed in experimental cavern. This paper describes the current status of ALICE trigger electronics, online error trigger monitoring and appropriate software for this electronics
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