A Large Ion Collider Experiment

ALICE empty structure after modules removal, during LS2 — ALICE empty structure after modules removal (Image: CERN)

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update on - 18:27:59

ALICE Calendar

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The ALICE Collaboration has built a detector optimized to study the collisions of nuclei at the ultra-relativistic energies provided by the LHC. The aim is to study the physics of strongly interacting matter at the highest energy densities reached so far in the laboratory. In such conditions, an extreme phase of matter - called the quark-gluon plasma - is formed. Our universe is thought to have been in such a primordial state for the first few millionths of a second after the Big Bang, before quarks and gluons were bound together to form protons and neutrons. Recreating this primordial state of matter in the laboratory and understanding how it evolves will allow us to shed light on questions about how matter is organized and the mechanisms that confine quarks and gluons. For this purpose, we are carrying out a comprehensive study of the hadrons, electrons, muons, and photons produced in the collisions of heavy nuclei (²⁰⁸Pb). ALICE is also studying proton-proton and proton-nucleus collisions both as a comparison with nucleus-nucleus collisions and in their own right. In 2021 ALICE is completing a significant upgrade of its detectors to further enhance its capabilities and continue its scientific journey at the LHC for many years to come.

Recent highlights

ALICE’s special: PID - in Xe-Xe!

For the first time, the production of pions, kaons, (anti-)protons and φ mesons at midrapidity has been measured in Xe–Xe collisions: arXiv

Unveiling the strong interaction among hadrons at the LHC

ALICE collaboration shows how pp collisions at the LHC can reveal the strong interaction between the hadrons. https://www.nature.com/articles/s41586-020-3001-6

ALICE’s dark side

Precision measurements of the production and annihilation of light anti-nuclei are sharpening the search for dark matter. https://cerncourier.com/a/alices-dark-side/

Latest ALICE Submissions

First measurement of the ${\mathbf{\|\textit t\|}}$-dependence of coherent $\mathbf{\rm{J/ψ}}$ photonuclear productionThe first measurement of the dependence on $\|t\|$, the square of the momentum transferred between the incoming and outgoing target nucleus, of coherent J/$\psi$ photoproduction is presented. The data were measured with the ALICE detector in ultra-peripheral Pb-Pb collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}} = 5.02$ TeV with the J/$\psi$ produced in the central rapidity region $\|y\| < ~0.8$, which corresponds to the small Bjorken-$x$ range $(0.3-1.4)\times10^{-3}$. The measured $\|t\|$-dependence is not described by computations based only on the Pb nuclear form factor, while the photonuclear cross section is better reproduced by models including shadowing according to the leading-twist approximation, or gluon-saturation effects from the impact-parameter dependent Balitsky-Kovchegov equation. This new observable is therefore a valid tool to constrain the relevant model parameters and to investigate the transverse gluonic structure at very low Bjorken-$x$.	2101.04623
Coherent $\rm{J/ψ}$ and $\rm{ψ'}$ photoproduction at midrapidity in ultra-peripheral Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}~=~5.02$ TeVThe coherent photoproduction of $\rm{J/\psi}$ and $\rm{\psi'}$ mesons was measured in ultra-peripheral Pb-Pb collisions at a center-of-mass energy $\sqrt{s_{\mathrm{NN}}}~=~5.02$ TeV with the ALICE detector. Charmonia are detected in the central rapidity region for events where the hadronic interactions are strongly suppressed. The $\rm{J/\psi}$ is reconstructed using the dilepton ($l^{+} l^{-}$) and proton-antiproton decay channels, while for the $\rm{\psi'}$, the dilepton and the $l^{+} l^{-} \pi^{+} \pi^{-}$ decay channels are studied. The analysis is based on an event sample corresponding to an integrated luminosity of about 233 ${\mu b}^{-1}$. The results are compared with theoretical models for coherent $\rm{J/\psi}$ and $\rm{\psi'}$ photoproduction. The coherent cross section is found to be in a good agreement with models incorporating moderate nuclear gluon shadowing of about 0.65 at a Bjorken-$x$ of around $6\times 10^{-4}$, such as the EPS09 parametrization, however none of the models is able to fully describe the rapidity dependence of the coherent $\rm{J/\psi}$ cross section including ALICE measurements at forward rapidity. The ratio of $\rm{\psi'}$ to $\rm{J/\psi}$ coherent photoproduction cross sections was also measured and found to be consistent with the one for photoproduction off protons.	2101.04577
Long- and short-range correlations and their event-scale dependence in high-multiplicity pp collisions at $\boldsymbol{\sqrt{\textit s}}=13$ TeVTwo-particle angular correlations are measured in high-multiplicity proton-proton collisions at $\sqrt{s} =13$ TeV by the ALICE Collaboration. The yields of particle pairs at short-($\Delta\eta$ $\sim$ 0) and long-range ($1.6 < ~ \|\Delta\eta\| < ~ 1.8$) in pseudorapidity are extracted on the near-side ($\Delta\varphi$ $\sim$ 0). They are reported as a function of transverse momentum ($p_{\mathrm T}$) in the range $1 < ~p_{\mathrm T} < ~ 4$ GeV/$c$. Furthermore, the event-scale dependence is studied for the first time by requiring the presence of high-$p_{\rm T}$ leading particles and jets for varying $p_{\rm T}$ thresholds. The results demonstrate that the long-range "ridge" yield, possibly related to the collective behavior of the system, is present in events with high-$p_{\mathrm T}$ processes. The magnitudes of the short- and long-range yields are found to grow with the event scale. The results are compared to EPOS LHC and PYTHIA 8 calculations, with and without string-shoving interactions. It is found that while both models describe the qualitative trends in the data, calculations from EPOS LHC show a better quantitative agreement, in particular for the $p_{\rm T}$ and event-scale dependencies.	2101.03110
Event-by-event multi-harmonic correlations of different flow amplitudes in Pb-Pb collisions at $\sqrt{s_{_{\rm NN}}}=2.76$ TeVThe genuine event-by-event correlations between three flow amplitudes are measured for the first time in Pb-Pb collisions at $\sqrt{s_{\rm {NN}}} = 2.76$ TeV by the ALICE Collaboration at the Large Hadron Collider. The results are obtained with recently developed observables, the higher order Symmetric Cumulants (SC), in the midrapidity region $\|\eta\| < ~ 0.8$ and the transverse momentum range $0.2 < ~ p_{\mathrm T} < ~ 5.0$ GeV/$c$. These higher order observables show the same robustness against systematic biases arising from nonflow effects as the two-harmonic SC. The new results cannot be interpreted in terms of lower order flow measurements, since they are dominated by different patterns of event-by-event flow fluctuations. The results are compared with expectations from initial state models such as T$_{\rm{R}}$ENTo and next-to-leading order perturbative-QCD+saturation model of initial conditions, followed by iEBE-VISHNU and EKRT viscous hydrodynamic calculations. Model comparisons provide an indication of the development of genuine correlations between the elliptic $v_2$, the triangular $v_3$ and the quadrangular $v_4$ flow amplitudes during the collective evolution of the medium. The comparison with the predictions for the correlations between $v_2$, $v_3$ and the pentagonal flow magnitude $v_5$ illustrate the need for further tuning of model parameterizations. Therefore, these results can provide new and independent constraints for the initial conditions and system properties of nuclear matter created in heavy-ion collisions, complementary to previous flow measurements.	2101.02579
First measurement of coherent $ρ^{0}$ photoproduction in ultra-peripheral Xe-Xe collisions at $\mathbf{\sqrt{s_{\rm {\scriptscriptstyle \mathbf{NN}}}} = 5.44}$ TeVThe first measurement of the coherent photoproduction of $\rho^{0}$ vector mesons in ultra-peripheral Xe-Xe collisions at $\sqrt{s_{\mathrm{\rm NN}}}= 5.44$ TeV is presented. This result, together with previous $\gamma$p and $\gamma$-Pb measurements, describes the atomic number ($A$) dependence of this process, which is particularly sensitive to nuclear shadowing effects and to the approach to the black-disc limit of QCD at a semi-hard scale. The cross section of the ${\rm Xe}+{\rm Xe} \to \rho^{0} + {\rm Xe}+{\rm Xe}$ process, measured at midrapidity through the decay channel $\rho^{0}\to\pi^+\pi^-$, is found to be ${\rm d}\sigma/{\rm d}y=131.5\pm 5.6 {\rm (stat.)} ^{+17.5}_{-16.9} {\rm (syst.)}$ mb. The ratio of the continuum to resonant contributions for the production of pion pairs is also measured. In addition, the fraction of events accompanied by electromagnetic dissociation of either one or both colliding nuclei is reported. The dependence on $A$ of cross section for the coherent $\rho^{0}$ photoproduction at a centre-of-mass energy per nucleon of the $\gamma A$ system of $W_{\gamma A,n}= 65$ GeV is found to be consistent with a power-law behaviour $\sigma (\gamma A\rightarrow \rho^{0} A) \propto A^{\alpha}$ with a slope $\alpha = 0.96 \pm 0.02 {\rm (syst.)}$. This slope signals important shadowing effects, but it is still far from the behaviour expected in the black-disc limit.	2101.02581

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Upcoming Conferences (Next Week)

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Jobs info

Job - Open position in hadronic physics in Saclay (06-01-2021)

Job - Postdoctoral position (3 years) at Louvain (Belgium) in the CMS experiment (05-01-2021)

Job - ATLAS Job offer of PhD position (05-01-2021)

Diversity and Inclusivity in ALICE

The ALICE Collaboration embraces and values the diversity of its team members and colleagues. We are committed to fostering an inclusive environment for all people regardless of their nationality/culture, profession, age/generation, family situation and gender, as well as individual differences such as but not limited to ethnic origin, sexual orientation, belief, disability, or opinions provided that they are consistent with the Organization’s values.

NEWSLETTER

ALICE and COVID-19

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Summary of COVID-19

ALICE secretariat and Covid-19 latest news

News of cards

Installation of Muon Forward Tracker

The new Muon Forward Tracker, one of ALICE’s main sub-detectors, was installed in the cavern in December 2020.

Miniframe Installation

The upgraded ALICE Miniframe was reinstalled in the experimental cavern in November

TPC installation

The refurbished TPC was lowered into the ALICE cavern and installed in the experiment in August 2020.

Calendar Today

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A Large Ion Collider Experiment

Heavy-ion collision

proton-proton collision

ALICE INDICO

ALICE Calendar

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ALICE mission

Recent highlights