QGP tomography with photon tagged jets in ALICE

$\gamma +$jet events provide a tomographic measurement of the medium formed in heavy ion collisions at LHC energies. Tagging events with a well identified high $p_{T}$ direct photon and measuring the correlation distribution of hadrons emitted oppositely to the photon, allows us to determine, with a good approximation, both the jet fragmentation function and the back-to-back azimuthal misalignement of the direct photon and the jet. Comparing these two observables measured in $pp$ collisions with the ones measured in $AA$ collisions will reveal the modifications of the jet structure induced by the medium formed in $AA$ collisions and consequently will infer the medium properties.Comment: 3 pages, 3 figures, Proceedings for 5th International Conference on Quarks and Nuclear Physic

Imaging constituent quark shape of proton with exclusive vector meson production at HERA

We show within proton hot spot picture that the exclusive vector meson production in electron-proton deeply inelastic scattering is sensitive to the individual width of the constituent quarks of the proton. For comparison, we calculate the exclusive $J/\Psi$ production cross-sections in three cases, $\mathrm{B_u} \geq \mathrm{B_d}$, $\mathrm{B_u} < \mathrm{B_d}$ and $\mathrm{B_u}\neq\mathrm{B^{\prime}_u}\neq\mathrm{B_d}$, where the $\mathrm{B_u}$, $\mathrm{B^{\prime}_u}$ and $\mathrm{B_d}$ denote the widths of two up quarks and down quark. We find that only results calculated with $\mathrm{B_u} \geq \mathrm{B_d}$ can give a reasonable description of the exclusive $J/\Psi$ production cross-section data at HERA. To test that our results are independent of the details of the model, we retain the average width of the three constituent quarks unchanged and compute the exclusive $J/\Psi$ production cross-sections with contribution weight by setting different proportional coefficients ($\mathrm{W_u}$ and $\mathrm{W_d}$) for the up and down quarks, respectively. It shows that the results calculated with $\mathrm{W_u}\geq\mathrm{W_d}$ can well reproduce the exclusive $J/\Psi$ production data at HERA, while the opposite case cannot describe the HERA data. These interesting findings seem to indicate that the up quark has more gluons around it than the down quark at high energy although the spatial distribution of gluons fluctuates event-by-event . To ensure the relevant results independent of the species of the vector meson, we also calculate the $\rho$ production cross-sections with the same group of parameters used in the exclusive $J/\Psi$ production and compare the predictions with the HERA data. It shows that all the results computed in the exclusive $\rho$ productions are consistent with the findings obtained in the exclusive $J/\Psi$ productions.Comment: 12 pages, 6 figure

γ–hadron correlation measurements to study jets fragmentation with ALICE at LHC

The possibility to study the fragmentation function of jets with energies below 50 GeV, which cannot be reconstructed in the heavy-ion environment, is explored. We propose to measure the imbalance distribution between prompt photon and charged hadrons with the ALICE experiment at LHC. In the present article, the case of proton–proton collisions at $\sqrt{s}=14$ TeV is examined with Monte-Carlo simulations. Performances for prompt photon identification and rejection of the π 0 decay photons are presented. We find that the measurement in proton–proton is meaningful with respect to statistical and systematic errors for photon energies larger than 20 GeV

Study of neutron density fluctuation and neutron-proton correlation in Au+Au collisions using PYTHIA8/Angantyr

Utilizing the PYTHIA8 Angantyr model, which incorporates the multiple-parton interactions (MPI) based color reconnection (CR) mechanism, we study the relative neutron density fluctuation and neutron-proton correlation in Au+Au collisions at $\sqrt{s_\text{NN}}$ = 7.7, 11.5, 14.5, 19.6, 27, 39, 62.4, and 200 GeV. In this study, we have not only delved into the dependence of these two remarkable observations on rapidity, centrality, and energy, but also presented an analysis of their interplay with the MPI and CR. Our results have shown that the light nuclei yield ratio of proton, deuteron, and triton, expressed by the elegant expression $N_tN_p/N_d^2$, remains unchanged even as the rapidity coverage and collision centrality increase. Interestingly, we have also revealed that the effect of CR is entirely dependent on the presence of MPI; CR has no impact on the yield ratio if MPI is off. Our findings further demonstrate that the light nuclei yield ratio experiences a slight increase with increasing collision energy as predicted by the PYTHIA8 Angantyr model, but it cannot describe the non-monotonic trend observed by the STAR experiment. Based on the Angantyr model simulation results, it is essential not to overlook the correlation between neutron and proton fluctuations. The Angantyr model is a good baseline for studying collisions in the absence of a Quark-Gluon Plasma (QGP) system, given its lack of flow and jet quenching.Comment: arXiv admin note: text overlap with arXiv:2211.03297 by other author

Point-to-point readout for the ALICE EMCal detector

AbstractIt is anticipated that the LHC will deliver Pb+Pb collisions at a minimum bias interaction rate of about 50kHz after the second long shutdown of the LHC in 2018. This will be roughly two orders of magnitude greater than the current data recording rate capability of the ALICE experiment. Therefore a major upgrade of the ALICE detector is planned for the next shutdown to enable ALICE to record data at the full Pb+Pb minimum bias interaction rate delivered by the LHC. A new point-to-point readout system for the electromagnetic calorimeter (EMCal) of ALICE has been developed, to replace the legacy readout bus, that essentially accomplishes this goal, and is being installed during the current LHC shutdown (2013–2014). The new readout uses the existing EMCal front end electronics yet provides more than an order of magnitude decrease in the readout time, to about 21μs, with modest cost and effort