After close to 20 years of preparation, the dedicated heavy ion experiment ALICE took first data with proton collisions at the LHC starting in November 2009. This article summarizes initial operation and performance of ALICE at the LHC as well as first results from collisions at 900 GeV and 7 TeV.
Deconfined strongly interacting QCD matter is produced in the laboratory at the highest energy densities in heavy-ion collisions at the LHC. A selection of recent results from ALICE is presented, spanning observables from the soft sector (bulk particle production and correlations), the hard probes (charmed hadrons and jets) and signatures of possible collective effects in pp and p-Pb collisions with high multiplicity. Finally, the perspectives after the detectors upgrades, taking place in the period 2019-2020, are presented.
ALICE is the CERN LHC experiment optimised for the study of the strongly interacting matter produced in heavy-ion collisions and devoted to the characterisation of the quark-gluon plasma. To achieve the physics program for LHC Run 3, a major upgrade of the experimental apparatus is ongoing. A key element of the upgrade is the substitution of the Inner Tracking System (ITS) with a completely new silicon-based detector (ITS 2) whose features will allow the reconstruction of rare physics channels not accessible with the previous layout. The enabling technology for such a performance boost is the …
ALICE is the CERN LHC experiment optimised for the study of the strongly interacting matter produced in heavy-ion collisions and devoted to the characterisation of the quark-gluon plasma. To achieve the physics program for LHC Run 3, a major upgrade of the experimental apparatus is ongoing. A key element of the upgrade is the substitution of the Inner Tracking System (ITS) with a completely new silicon-based detector whose features will allow the reconstruction of rare physics channels, not accessible with the previous layout. The enabling technology for such a performance boost is the adoptio…
ALICE (A Large Ion Collider Experiment) is the CERN LHC experiment optimized for the study of the strongly interacting matter produced in heavy-ion collisions and devoted to the characterization of the Quark-Gluon Plasma. To achieve the physics program for LHC Run 3 and 4, ALICE is undergoing a major upgrade of the experimental apparatus during the ongoing second long LHC shutdown. A key element of the ALICE upgrade is the substitution of the Inner Tracking System (ITS) with a completely new silicon-based detector whose features will allow the reconstruction of rare physics channels which coul…
Particle identification (PID) is one of the main strengths of the ALICE experiment at the LHC. It is a crucial ingredient for detailed studies of the strongly interacting matter formed in ultrarelativistic heavy-ion collisions. ALICE provides PID information via various experimental techniques, allowing for the identification of particles over a broad momentum range (from around 100 MeV/$c$ to around 50 GeV/$c$). The main challenge is how to combine the information from various detectors effectively. Therefore, PID represents a model classification problem, which can be addressed using Machine…
The ALICE experiment at CERN is undergoing a major upgrade during the Long Shutdown 2 (LS2) of the LHC during 2019-2020. The key elements regarding the central barrel are the installation of a new Inner Tracking System (ITS) and the upgrade of the large Time Projection Chamber (TPC). The TPC is currently being upgraded with a new readout system, including new GEM-based Readout Chambers and new front-end electronics enabling us to operate it in continuous mode. The new ITS based on CMOS Monolithic Active Pixel Sensors will significantly improve the impact parameter resolution and the tracking e…
Precision measurements of jet substructure are used as a probe of fundamental QCD processes. The primary Lund jet plane density is a two-dimensional visual representation of the radiation off the primary emitter within the jet that can be used to isolate different regions of the QCD phase space. A new measurement of the primary Lund plane density for inclusive charged-particle jets in the transverse momentum range of 20 and 120 GeV/$c$ in pp collisions at $\sqrt{s} = $ 13 TeV with the ALICE detector will be presented. This is the first measurement of the Lund plane density in an intermediate j…
Heavy quarks are useful probes to investigate the properties of the Quark-Gluon Plasma (QGP) produced in heavy-ion collisions at the LHC, since they are produced in initial hard scattering processes. To single out the signals that are characteristic of the QGP, it is nevertheless crucial to understand the primordial heavy-quark production in vacuum, and to disentangle hot from cold nuclear matter effects. Moreover, observations of collective effects in high-multiplicity pp and p-Pb collisions show surprising similarities with those in heavy-ion collisions. Heavy-flavour production in such coll…
Charm and beauty quark production measurement represents a fundamental means to access the initial stage of hadronic collisions. Being produced almost exclusively in initial hard partonic scatterings due to their large masses, $m_{\text{c}}=$ 1.3 $ \text{GeV}/c^2$ and $m_{\text{b}} =$ 4.1 $ \text{GeV}/c^2$, charm and beauty quarks are ideal tools to investigate various QCD aspects. In addition, the corresponding measurements in pp collisions represent a baseline for cold nuclear matter studies in p--A collisions as well as for the characterization of the hot and dense interacting nuclear matte…
The high integration density of MAPS, with silicon sensor and readout electronics implemented in the same device, allows very thin structures with a greatly reduced material budget. Thicknesses of $\mathcal{O}$(50~$μ$m), values at which silicon chips become flexible, are readily used in many applications. In addition, MAPS can be produced in sensors of wafer size by a process known as stitching. This in turn allows to build detector elements that are large enough to cover full tracker half-layers with single bent sensors. The ALICE ITS~3 project is planning to build a new vertex tracker based …
Studies of open-charm hadron production in pp and \pPb collisions are performed by the ALICE Collaboration at the LHC to investigate charm-quark hadronization mechanisms. Recent measurements of charm meson (${\rm D^0}$, ${\rm D^+}$, ${\rm D^+_{\rm s}}$, and ${\rm D^{*+}}$) and baryon ($Λ^+_{\rm c}$, $Ξ^{0,+}_{\rm c}$, $Σ^{0,++}_{\rm c}$, and $Ω^0_{\rm c}$) production in pp collisions at $\sqrt{s}$ = 5.02 TeV and $\sqrt{s}$ = 13 TeV allow the determination of the charm cross section and the fragmentation fractions at $\sqrt{s}$ = 5.02 TeV with unprecedented precision. The measurements show that…
Jet quenching has been one of the most important indicators that ultra-relativistic heavy-ion collisions produce a deconfined state of quarks and gluons, known as the Quark-Gluon Plasma. While the quenching of jets traditionally refers to the energy loss of high-momentum partons, the study of jet quenching has grown into a multi-pronged field where the measurement of jets and their modification in heavy-ion collisions is used as an important tool to study many aspects of QCD deconfinement. This contribution reviews the current experimental status of jets at the LHC and RHIC, and reports recent…
A Large Ion Collider Experiment (ALICE) is one of the four big experiments installed at the CERN Large Hadron Collider (LHC) and it is suited to study pp, p--Pb and Pb--Pb collisions. It aims to study the strongly interacting matter at extreme conditions of temperature and density under which the quarks decouple to form a new state of matter called the Quark Gluon Plasma (QGP). Such a state of matter existed a few microseconds after the Big Bang in which the universe was created. Several experimental observables, sensitive to the evolution of the system after the nuclear collisions, reveal imp…
The CMS Collaboration is preparing to build replacement endcap calorimeters for the HL-LHC era. The new high-granularity calorimeter (HGCAL) is, as the name implies, a highly-granular sampling calorimeter with approximately six million silicon sensor channels (approx. 1.1cm2 or 0.5cm2 cells) and about 250 thousand channels of scintillator tiles readout with on-tile silicon photomultipliers. The calorimeter is designed to operate in the harsh radiation environment at the HL-LHC, where the average number of interactions per bunch crossing is expected to exceed 140. Besides measuring energy and p…