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Hard-photon-triggered jets in p − p and A − A collisions
No full textAn investigation of high-transverse-momentum (high-) photon-triggered jets in proton-proton (−) and ion-ion (−) collisions at √=0.2 and 5.02TeV is carried out, using the multistage description of in-medium jet evolution. Monte Carlo simulations of hard scattering and energy loss in heavy-ion collisions are performed using parameters tuned in a previous study of the nuclear modification factor () for inclusive jets and high-hadrons. We obtain a good reproduction of the experimental data for photon-triggered jet , as measured by the ATLAS detector, the distribution of the ratio of jet to photon (), measured by both CMS and ATLAS, and the photon-jet azimuthal correlation as measured by CMS. We obtain a moderate description of the photon-triggered jet , as measured by STAR. A noticeable improvement in the comparison is observed when one goes beyond prompt photons and includes bremsstrahlung and decay photons, revealing their significance in certain kinematic regions, particularly at >1. Moreover, azimuthal angle correlations demonstrate a notable impact of bremsstrahlung photons on the distribution, emphasizing their role in accurately describing experimental results. This work highlights the success of the multistage model of jet modification to straightforwardly predict (this set of) photon-triggered jet observables. This comparison, along with the role played by bremsstrahlung photons, has important consequences on the inclusion of such observables in a future Bayesian analysis
Effects of hadronic reinteraction on jet fragmentation from small to large systems
No full textWe investigate the impact of the hadronic phase on jet quenching in nuclear collider experiments, an open question in heavy-ion physics. Previous studies in a simplified setup suggest that hadronic interactions could have significant effects, but a systematic analysis is needed. Using the X-SCAPE event generator with the SMASH afterburner, we study the role of hadronic rescattering on jet fragmentation hadrons. Applying this framework to e+ + e− collisions, we demonstrate that even in small systems with limited particle production, hadronic interactions lead to measurable modifications in final-state hadronic and jet observables by comparing scenarios with and without after-burner rescattering
Charge density waves and structural phase transition in the high- T4 superconducting quantum crystal
No full text
Measurement of the inclusive isolated-photon production cross section in pp and Pb–Pb collisions at TeV
No full textThe ALICE Collaboration at the CERN LHC has measured the inclusive production cross section of isolated photons at midrapidity as a function of the photon transverse momentum (), in Pb–Pb collisions in different centrality intervals, and in pp collisions, at centre-of-momentum energy per nucleon pair of TeV. The photon transverse momentum range is between 10–14 and 40–140 GeV/, depending on the collision system and on the Pb–Pb centrality class. The result extends to lower than previously published results by the ATLAS and CMS experiments at the same collision energy. The covered pseudorapidity range is . The isolation selection is based on a charged particle isolation momentum threshold GeV/ within a cone of radii and 0.4. The nuclear modification factor is calculated and found to be consistent with unity in all centrality classes, and also consistent with the HG-PYTHIA model, which describes the event selection and geometry biases that affect the centrality determination in peripheral Pb–Pb collisions. The measurement is compared to next-to-leading order perturbative QCD calculations and to the measurements of isolated photons and Z bosons from the CMS experiment, which are all found to be in agreement
Multiplicity-dependent jet modification from di-hadron correlations in pp collisions at = 13 TeV
No full textShort-range correlations between charged particles are studied via two-particle angular correlations in pp collisions at = 13 TeV. The correlation functions are measured as a function of the relative azimuthal angle and the pseudorapidity separation for pairs of primary charged particles within the pseudorapidity interval < 0.9 and the transverse-momentum range 1 < p< 8 GeV/c. Near-side ( < 1.3) peak widths are extracted from a generalised Gaussian fitted over the correlations in full pseudorapidity separation (< 1.8), while the per-trigger associated near-side yields are extracted for the short-range correlations ( < 1.3). Both are evaluated as a function of charged-particle multiplicity obtained by two different event activity estimators. The width of the near-side peak decreases with increasing multiplicity, and this trend is reproduced qualitatively by the Monte Carlo event generators PYTHIA 8, AMPT, and EPOS. However, the models overestimate the width in the low transverse-momentum region (p< 3 GeV/c). The per-trigger associated near-side yield increases with increasing multiplicity. Although this trend is also captured qualitatively by the considered event generators, the yield is mostly overestimated by the models in the considered kinematic range. The measurement of the shape and yield of the short-range correlation peak can help us understand the interplay between jet fragmentation and event activity, quantify the narrowing trend of the near-side peak as a function of transverse momentum and multiplicity selections in pp collisions, and search for final-state jet modification in small collision systems
First observation of strange baryon enhancement with effective energy in pp collisions at the LHC
No full textGSI-2026-0020
First polarisation measurement of coherently photoproduced in ultra-peripheral Pb–Pb collisions at = 5.02 TeV
No full textThe first measurement of the polarisation of coherently photoproduced mesons in ultra-peripheral Pb–Pb collisions, using data at = 5.02 TeV, is presented. The meson is measured via its dimuon decay channel in the forward rapidity interval −4.0 < <−2.5 using the ALICE detector at the CERN LHC. An event sample corresponding to an integrated luminosity of 750 5% (syst) is analysed. Hadronic activity is highly suppressed since the interaction is mediated by a photon. The polar and azimuthal angle distributions of the decay muons are measured, and the polarisation parameters are extracted. The analysis is carried out in the helicity frame. The results are found to be consistent with a transversely polarised . These values are compared with previous measurements by the H1 and ZEUS experiments. The polarisation parameters of coherent photoproduction in Pb–Pb collisions are found to be consistent with the s-channel helicity conservation hypothesis
Dielectron production in central Pb-Pb collisions at = 5.02TeV
No full textThe first measurement of the ee pair production at midrapidity and low invariant mass in central Pb-Pb collisions at =5.02TeV at the Large Hadron Collider is presented. The yield of ee pairs is compared with a cocktail of expected hadronic decay contributions in the invariant mass (m) and pair transverse momentum () ranges m < 3.5 GeV/c and p <8 GeV/c. For 0.18 < m < 0.5 GeV/c the ratio of data to the cocktail of hadronic contributions amounts to 1.40±0.11(stat.)±0.23(syst.)±0.16(cocktail) and 1.42±0.11(stat.)±0.23(syst.)−0.29+0.24(cocktail), including or not including medium effects in the estimation of the heavy-flavor background, respectively. It is consistent with predictions from two different models for an additional contribution of thermal ee pairs from the hadronic and partonic phases. In the intermediate-mass range (1.2 < m < 2.6 GeV/c), the pair transverse impact parameter of the ee pairs (DCAee, where “DCA” denotes “distance of closest approach”) is used for the first time in Pb-Pb collisions to separate displaced dielectrons from heavy-flavor hadron decays from a possible (thermal) contribution produced at the interaction point. The data are consistent with a suppression of ee pairs from and an additional prompt component. Finally, the first direct-photon measurement in the 10% most central Pb-Pb collisions at = 5.02TeV is reported via the study of virtual direct photons in the transverse momentum range 1 < p < 5 GeV/c. A model including prompt photons, as well as photons from the preequilibrium and fluid-dynamic phases, can reproduce the result, while being at the upper edge of the data uncertainties
Exploring nuclear structure with multiparticle azimuthal correlations at the LHC
No full textDetails of the nuclear structure of Xe, such as the quadrupole deformation and the nuclear diffuseness, are studied by extensive measurements of anisotropic-flow-related observables in Xe–Xe collisions at a centre-of-mass energy per nucleon pair = 5.44 TeV with the ALICE detector at the LHC. The results are compared with those from Pb–Pb collisions at = 5.02 TeV for a baseline, given that the Pb nucleus exhibits a very weak deformation. Furthermore, comprehensive comparisons are performed with a state-of-the-art hybrid model using IP-Glasma+MUSIC+UrQMD. It is found that among various IP-Glasma+MUSIC+UrQMD calculations with different values of nuclear parameters, the one using a nuclear diffuseness parameter of a = 0.492 and a nuclear quadrupole deformation parameter of β = 0.207 provides a better description of the presented flow measurements. These studies represent the first systematic exploration of nuclear structure at TeV energies, utilizing a comprehensive set of anisotropic flow observables. The measurements serve as a critical experimental benchmark for rigorously testing the interplay between nuclear structure inputs and heavy-ion theoretical models