New Results on Hard Probes in Heavy-Ion Collisions with ALICE

Hard probes - final state particles related to an interaction with large momentum transfer or mass scale - play a distinguished role in the discovery and the study of the Quark-Gluon Plasma (QGP), a phase of deconfined quarks and gluons reached at high temperatures in heavy ion collisions. In heavy ion collisions, parton scatterings with a large momentum transfer ($1/Q \ll 1$ fm/$c$) occur prior to QGP formation and thus provide a source of coloured probe particles for the QGP created in the later stage of the reaction. The hard scattered partons and the subsequent parton shower interact strongly with the QGP and its constituents via elastic and radiative processes before hadronization into jets of observable particles. Thus, the comparison to jet and high-$p_T$ observables in pp (vacuum) potentially probes their modification due to medium effects. One of the key observables in the discovery and investigation of these jet modifications has been the nuclear modification factor $R_{AA}$, for which new results on charged particle production in different colliding systems are presented and the question of apparant suppression in peripheral Pb-Pb collisions is addressed. Fore more differential studies of the jet sub-structure and hence the parton shower evolution in the medium, recent results on jet grooming in heavy ion colisions are presented.Comment: Dedicated to Oliver Busch (1976-2018), 6 pages, 4 figures, proceedings of the Sixth Annual Conference on Large Hadron Collider Physics LHCP 2018, Bologn

Geometrical Scaling of Direct-Photon Production in Hadron Collisions from RHIC to the LHC

We consider pp, dAu and AuAu production of photons at RHIC energies, and PbPb collisions at LHC energy. We show that the inclusive spectrum of photons in the transverse momentum range of 1 GeV < pT <= 4 GeV satisfies geometric scaling. Geometric scaling is a property of hadronic interactions predicted by theories of gluon saturation, and expresses rates in terms of dimensionless ratios of the transverse momentum to saturation momentum. We show excellent agreement with geometric scaling with the only input being the previously measured dependence of the saturation momentum upon Bjorken x and centrality.Comment: 12 pages, 4 figure

ALICE in Public Outreach and Bricks

In the last two years various existing public outreach activities in ALICE have been adapted for online usage, this includes the well established particle physics masterclasses but also virtual visits to ALICE. Based on these foundations a six month online workshop was carried out in 2021 with the goal to design a LEGO model of the ALICE detector at the LHC at the scale of a typical minifigure (ca. 1:40) and to motivate young people for a long term online collaboration in a particle physics project. The design stage of the model took half a year with regular online design sessions accompanied by input on 3D construction, detector technology, the physics questions of ALICE, virtual ALICE visits, and particle physics masterclasses. This stage provided first-hand experience on the dynamics of working on different sub-projects in a research collaboration and resulted in a model with more than 16 000 parts that was assembled by the participants during one weekend in an in-person workshop. The experience gained during this construction has been used further by the young designers to optimise the model over the period of another year.Comment: 6 Pages, 4 Figures, Proceedings for the ICHEP Conference 202

Jet and High \pT Measurement with the ALICE Experiment

Since the beginning of 2010 the LHC provides p+p collisions at the highest center of mass energies to date, allowing to study high \pT particle production and jet properties in a new energy regime. For a clear interpretation and the quantification of the medium influence in heavy-ion collisions on high \pT observables a detailed understanding of these elementary reactions is essential. We present first results on the observation of jet-like properties with the ALICE experiment and discuss the performance of jet reconstruction in the first year of data taking.Comment: 6 Pages, 3 Figures, Proceedings for the Workshop "Jets in Proton-Proton and Heavy-Ion Collisions" Prague August 201

Systematic study of high-pTp_T hadron and photon production with the PHENIX experiment

The suppression of hadrons with large transverse momentum ($p_{\rm T}$) in central Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV compared to a binary scaled p+p reference is one of the major discoveries at RHIC. To understand the nature of this suppression PHENIX has performed detailed studies of the energy and system-size dependence of the suppression pattern, including the first RHIC measurement near SPS energies. An additional source of information is provided by direct photons. Since they escape the medium basically unaffected they can provide a high $p_{\rm T}$ baseline for hard-scattering processes. An overview of hadron production at high $p_{\rm T}$ in different colliding systems and at energies from $\sqrt{s_{\rm NN}} = 22.4 - 200$ GeV will be given. In addition, the latest direct photon measurements by the PHENIX experiment shall be discussed.Comment: 6 pages, 3 figures, Proceeding for the Conference Strangeness in Quark Matter, Levoca, Slovakia, June 24-29, 200

Centrality evolution of the charged-particle pseudorapidity density over a broad pseudorapidity range in Pb-Pb collisions at root s(NN)=2.76TeV

Peer reviewe

The ALICE experiment at the CERN LHC

ALICE (A Large Ion Collider Experiment) is a general-purpose, heavy-ion detector at the CERN LHC which focuses on QCD, the strong-interaction sector of the Standard Model. It is designed to address the physics of strongly interacting matter and the quark-gluon plasma at extreme values of energy density and temperature in nucleus-nucleus collisions. Besides running with Pb ions, the physics programme includes collisions with lighter ions, lower energy running and dedicated proton-nucleus runs. ALICE will also take data with proton beams at the top LHC energy to collect reference data for the heavy-ion programme and to address several QCD topics for which ALICE is complementary to the other LHC detectors. The ALICE detector has been built by a collaboration including currently over 1000 physicists and engineers from 105 Institutes in 30 countries. Its overall dimensions are 161626 m3 with a total weight of approximately 10 000 t. The experiment consists of 18 different detector systems each with its own specific technology choice and design constraints, driven both by the physics requirements and the experimental conditions expected at LHC. The most stringent design constraint is to cope with the extreme particle multiplicity anticipated in central Pb-Pb collisions. The different subsystems were optimized to provide high-momentum resolution as well as excellent Particle Identification (PID) over a broad range in momentum, up to the highest multiplicities predicted for LHC. This will allow for comprehensive studies of hadrons, electrons, muons, and photons produced in the collision of heavy nuclei. Most detector systems are scheduled to be installed and ready for data taking by mid-2008 when the LHC is scheduled to start operation, with the exception of parts of the Photon Spectrometer (PHOS), Transition Radiation Detector (TRD) and Electro Magnetic Calorimeter (EMCal). These detectors will be completed for the high-luminosity ion run expected in 2010. This paper describes in detail the detector components as installed for the first data taking in the summer of 2008

New Results on Hard Probes in Heavy-Ion Collisions with ALICE

Hard probes - final state particles related to an interaction with large momentum transfer or mass scale - play a distinguished role in the discovery and the study of the Quark-Gluon Plasma (QGP), a phase of deconfined quarks and gluons reached at high temperatures in heavy ion collisions. In heavy ion collisions, parton scatterings with a large momentum transfer ($1/Q \ll 1$ fm/$c$) occur prior to QGP formation and thus provide a source of coloured probe particles for the QGP created in the later stage of the reaction. The hard scattered partons and the subsequent parton shower interact strongly with the QGP and its constituents via elastic and radiative processes before hadronization into jets of observable particles. Thus, the comparison to jet and high-$p_T$ observables in pp (vacuum) potentially probes their modification due to medium effects. One of the key observables in the discovery and investigation of these jet modifications has been the nuclear modification factor $R_{AA}$, for which new results on charged particle production in different colliding systems are presented and the question of apparant suppression in peripheral Pb-Pb collisions is addressed. Fore more differential studies of the jet sub-structure and hence the parton shower evolution in the medium, recent results on jet grooming in heavy ion colisions are presented.Hard probes - final state particles related to an interaction with largemomentum transfer or mass scale - play a distinguished role in the discoveryand the study of the Quark-Gluon Plasma (QGP), a phase of deconfined quarks andgluons reached at high temperatures in heavy ion collisions. In heavy ioncollisions, parton scatterings with a large momentum transfer ($1/Q \ll 1$fm/$c$) occur prior to QGP formation and thus provide a source of colouredprobe particles for the QGP created in the later stage of the reaction. Thehard scattered partons and the subsequent parton shower interact strongly withthe QGP and its constituents via elastic and radiative processes beforehadronization into jets of observable particles. Thus, the comparison to jetand high-$p_T$ observables in pp (vacuum) potentially probes their modificationdue to medium effects. One of the key observables in the discovery andinvestigation of these jet modifications has been the nuclear modificationfactor $R_{AA}$, for which new results on charged particle production indifferent colliding systems are presented and the question of apparantsuppression in peripheral Pb-Pb collisions is addressed. Fore more differentialstudies of the jet sub-structure and hence the parton shower evolution in themedium, recent results on jet grooming in heavy ion colisions are presented