ALICE INDICO

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ALICE Calendar

ALICE mission

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

 

Recent highlights

In a recent study, the ALICE Collaboration has studied baryon-to-meson ratios with a new twist: by studying the ratios in two parts of the events separately – inside jets and in the event portion perpendicular to a jet cone. arXiv.
Neutral pion and eta meson production cross sections at midrapidty were measured up to unprecedentedly high transverse momenta in proton-proton (pp) and proton-lead (p-Pb) collisions at √s_NN = 8 and 8.16 TeV, respectively. arXiv.
The beauty-quark production cross section was measured at midrapidity by the ALICE Collaboration in pp collisions at √s = 5.02 TeV through non-prompt D-meson measurements exploiting machine-learning classification techniques arXiv.

Latest ALICE Submissions

Charm-quark fragmentation fractions and production cross section at midrapidity in pp collisions at the LHCRecent $p_{\rm T}$-integrated cross section measurements of the ground-state charm mesons and baryons, D$^{\rm 0}$, D$^+$, D$_{\rm s}^{+}$, $\Lambda_{\rm c}^{+}$, and $\Xi_{\rm c}^0$, are used to evaluate the charm fragmentation fractions and production cross section per unit of rapidity at midrapidity ($|y| < ~0.5$), in pp collisions at $\sqrt{s} = 5.02$ TeV at the LHC. The latter is ${\rm d} \sigma^{\rm c \overline{c}}/{\rm d} y|_{|y| < ~ 0.5}$ =1165 $\pm 44(\rm{stat})^{+134}_{-101}(\rm{syst})$ $\mu b$. These measurements were obtained for the first time in hadronic collisions at the LHC including the charm baryon states, recently measured by ALICE at midrapidity. The charm fragmentation fractions differ significantly from the values measured in e$^+$e$^-$ and ep collisions, providing evidence of the dependence of the parton-to-hadron fragmentation fractions on the collision system, indicating that the assumption of their universality is not supported by the measured cross sections. An increase of a factor of about 3.3 for the fragmentation fraction for the $\Lambda_{\rm c}^{+}$ with a significance of $5\,\sigma$ between the values obtained in pp collisions and those obtained in e$^+$e$^-$ (ep) collisions is reported. The fragmentation fraction for the $\Xi_{\rm c}^0$ was obtained for the first time in any collision system. The measured fragmentation fractions were used to update the $\rm c \overline{c}$ cross sections per unit of rapidity at $|y| < ~0.5$ at $\sqrt{s} = 2.76$ and 7 TeV, which are about 40% higher than the previously published results. The data were compared with perturbative-QCD calculations and lie at the upper edge of the theoretical bands.
2105.06335
Charged-particle multiplicity fluctuations in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeVMeasurements of event-by-event fluctuations of charged-particle multiplicities in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV using the ALICE detector at the CERN Large Hadron Collider (LHC) are presented in the pseudorapidity range $|\eta| < ~0.8$ and transverse momentum $0.2 < ~ p_{\rm T} < ~ 2.0$ GeV/$c$. The amplitude of the fluctuations is expressed in terms of the variance normalized by the mean of the multiplicity distribution. The $\eta$ and $p_{\rm T}$ dependences of the fluctuations and their evolution with respect to collision centrality are investigated. The multiplicity fluctuations tend to decrease from peripheral to central collisions. The results are compared to those obtained from HIJING and AMPT Monte Carlo event generators as well as to experimental data at lower collision energies. Additionally, the measured multiplicity fluctuations are discussed in the context of the isothermal compressibility of the high-density strongly-interacting system formed in central Pb-Pb collisions.
2105.05745
$\Xi^{0}_{c}$ production in semi-leptonic decay channel in pp collisions at 5 TeV The ALICE detector at the Large Hadron Collider (LHC) is optimised for the investigation of the Quark-Gluon Plasma (QGP) created in heavy-ion collisons. Charm quarks are effective probes to elucidate the properties of the QGP. They are dominantly produced at the initial stage of the collisons via hard partonic scattering processes and experience the whole evolution of the system. Charm-baryon measurements provides unique insight into hadronisation prcesses. In particular, the baryon-to-meson ratio is expected to be enhanced if charm quarks hadronise via recombination with the surroudning light quarks in the QGP. Moreover, in such a recombination picture, the baryon-to-meson ratio could further be enhanced in the presence of diquark bound states in the hot and dense QCD medium. Measurements of charm-baryon production in pp collisions are essebtial to establish a baseline for studies in Pb-Pb collisions. In addition, the measuremnt in pp collisons provide critical tests of pQCD calculations and for models of charm hadronisation in vacuum.    In this paper, the $p_{\rm T}$ differential cross section of the $\Xi^{0}_{\rm c}$ baryon measured in the decay channel $\Xi^{0}_{\rm c} \rightarrow e\Xi\nu$ in pp collisions at $\sqrt s = 5.02$ TeV will be shown.
2105.05616
Kaon-proton strong interaction at low relative momentum via femtoscopy in Pb-Pb collisions at the LHCIn quantum scattering processes between two particles, aspects characterizing the strong and Coulomb forces can be observed in kinematic distributions of the particle pairs. The sensitivity to the interaction potential reaches a maximum at low relative momentum and vanishing distance between the two particles. Ultrarelativistic heavy-ion collisions at the LHC provide an abundant source of many hadron species and can be employed as a measurement method of scattering parameters that is complementary to scattering experiments. This study confirms that momentum correlations of particles produced in Pb-Pb collisions at the LHC provide an accurate measurement of kaon-proton scattering parameters at low relative momentum, allowing precise access to the $ {K}^{-} p\rightarrow {K}^{-} p$ process. This work also validates the femtoscopic measurement in ultrarelativistic heavy-ion collisions as an alternative to scattering experiments and a complementary tool to the study of exotic atoms with comparable precision. In this work, the first femtoscopic measurement of momentum correlations of ${K}^{-} p\ ({K}^{+}\overline{p})$ and ${K}^{+}p ({K}^{-}\overline{p})$ pairs in Pb-Pb collisions at centre-of-mass energy per nucleon pair of $\sqrt{s_{\rm NN}} = 5.02$ TeV registered by the ALICE experiment is reported. The components of the ${K}^{-} p$ complex scattering length are extracted and found to be $\Re f_0=-0.91\pm~{0.03}$(stat)$^{+0.17}_{-0.03}$(syst) and $\Im f_0 = 0.92\pm~{0.05}$(stat)$^{+0.12}_{-0.33}$(syst). The results are compared with chiral effective field theory predictions as well as with existing data from dedicated scattering and exotic kaonic atom experiments.
2105.05683
Measurement of K$^{*}$(892)$^{\mathrm{\pm}}$ production in inelastic pp collisions at the LHCThe first results on K$^{*}$(892)$^{\mathrm{\pm}}$ resonance production in inelastic pp collisions at LHC energies of $\sqrt{s} = 5.02$, 8, and 13 TeV are presented. The K$^{*}$(892)$^{\mathrm{\pm}}$ has been reconstructed via its hadronic decay channel K$^{*}$(892)$^{\mathrm{\pm}}$ $\rightarrow$ $\mathrm {K^0_S}$ $~+~\pi^{\pm}$ with the ALICE detector. Measurements of transverse momentum distributions, integrated yields, and mean transverse momenta for charged K$^{*}$(892) are found to be consistent with previous ALICE measurements for neutral K$^{*}$(892) within uncertainties. For $p_{\mathrm{T}} > 1$ GeV/$c$ the K$^{*}$(892)$^{\mathrm{\pm}}$ transverse momentum spectra become harder with increasing centre-of-mass energy from 5.02 to 13 TeV, similar to what previously observed for charged kaons and pions. For $p_{\mathrm{T}} < ~ 1$ GeV/$c$ the K$^{*}$(892)$^{\mathrm{\pm}}$ yield does not evolve significantly and the abundance of K$^{*}$(892)$^{\mathrm{\pm}}$ relative to K is rather independent of the collision energy. The transverse momentum spectra, measured for K$^{*}$(892)$^{\mathrm{\pm}}$ at midrapidity in the interval $0 < ~ p_{\mathrm{T}} < ~ 15$ GeV/$c$, are not well described by predictions of different versions of PYTHIA 6, PYTHIA 8 and EPOS-LHC event generators. These generators reproduce the measured $p_{\mathrm{T}}$-integrated K$^{*\mathrm{\pm}}$/K ratios and describe well the momentum dependence for $p_{\mathrm{T}} < ~ 2$ GeV/$c$.
2105.05760
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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.

ALICE & COVID-19

News of cards

The new ITS Outer Barrel was installed in March 2021.

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

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

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