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We present measurements of two-particle differential number correlation functions R2 and transverse momentum correlation functions P2, obtained from p-Pb collisions at 5.02 TeV and Pb-Pb collisions at 2.76 TeV. The results are obtained using charged particles in the pseudorapidity range |η|< 1.0, and transverse momentum range 0.2<pT<2.0 GeV/c as a function of pair separation in pseudorapidity, |Δη|, azimuthal angle, Δφ, and for several charged-particle multiplicity classes. Measurements are carried out for like-sign and unlike-sign charged-particle pairs separately and combined to obtain charge-independent and charge-dependent correlation functions. We study the evolution of the width of the near-side peak of these correlation functions with collision centrality. Additionally, we study Fourier decompositions of the correlators in Δφ as a function of the pair separation |Δη|. Significant differences in the dependence of their harmonic coefficients on multiplicity classes are found. These differences can be exploited, in theoretical models, to obtain further insight into charged-particle production and transport in heavy-ion collisions. Moreover, an upper limit of non-flow contributions to flow coefficients vn measured in Pb-Pb collisions based on the relative strength of Fourier coefficients measured in p-Pb interactions is estimated.
Transverse momentum (pT) spectra of charged particles at mid-pseudorapidity in Xe-Xe collisions at sNN−−−√ = 5.44 TeV measured with the ALICE apparatus at the Large Hadron Collider are reported. The kinematic range 0.15<pT<50 GeV/c and |η|<0.8 is covered. Results are presented in nine classes of collision centrality in the 0-80% range. For comparison, a pp reference at the collision energy of s√ = 5.44 TeV is obtained by interpolating between existing \pp measurements at s√ = 5.02 and 7 TeV. The nuclear modification factors in central Xe-Xe collisions and Pb-Pb collisions at a similar center-of-mass energy of sNN−−−√ = 5.02 TeV, and in addition at 2.76 TeV, at analogous ranges of charged particle multiplicity density ⟨dNch/dη⟩ show a remarkable similarity at pT>10 GeV/c. The centrality dependence of the ratio of the average transverse momentum ⟨pT⟩ in Xe-Xe collisions over Pb-Pb collision at s√ = 5.02 TeV is compared to hydrodynamical model calculations.
In this work we provided additional insights into our understanding of bulk QCD matter through the study of the transport coeffcients which govern the non-equilibrium microscopical processes of statistical ensembles. Specically, we focused on the low energy regime corresponding to the hadron gas, as the properties of this region of the phase diagram are still relatively unknown, and existing calculations for the transport coeffcients are either scarce, contradictory, or somewhat limited in scope; this thesis' main goal was thus to shed some light on this by providing new independent calculations of these quantities.
We subsequently presented two formalisms which can be used to calculate transport coeffcients. The first one (which also was the main tool we used in the following chapters to produce our results) relies on the development of so-called Green-Kubo formulas, which relate non-equilibrium dissipative fluctuations with transport coeffcients; notably, the off-diagonal components of the energy-momentum tensor are shown to be related to the shear viscosity, its diagonal components to the bulk viscosity and fluctuations in the electric current can be related to the electric conductivity. We additionally introduced two new conductivities, namely the baryon-electric and strange electric conductivities, which we dubbed, together with the already known electric one, the "cross-conductivity", which encodes information about how electric fluctuations are correlated to changes in electric, baryonic or strange currents, or vice-versa. The second way of calculating transport coeffcient which we discussed consists in linearizing the collision term of the Boltzmann equation through the Chapman-Enskog formalism. While in principle providing direct semi-analytical results for the transport coeffcients, this approach is complicated to implement when more than a few species are considered, and as such was then mostly used as a tool to calibrate our Green-Kubo calculations.
The hadron gas model that we used for all calculations, namely the transport approach SMASH, was then presented. The main features of the model were explained, such as the collision criterion, the considered degrees of freedom and the specific way in which they microscopically interact with each other. It was verified that SMASH does reproduce analytical results of the Boltzmann equation in an expanding universe scenario, thus showing the equivalence of this transport approach and the associated kinetic theory results. A special care was taken to detail the ways in which a state of thermal and chemical equilibrium (which is necessary for Green-Kubo relations to be valid) can be reached and described using SMASH.
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ALICE (A Large Ion Collider Experiment) is preparing for a major upgrade of the detector, readout and computing systemsfor LHC Run 3. A new facility called O2 (Online-Offline) will play a major role in data compression and event processing. To efficiently operate the experiment, we are designing a monitoring subsystem, which will provide a complete overview of the O2 overall health, detect performance degradation and component failures. The monitoring subsystem will receive and collect up to 600 kHz of performance metrics. It consists of a custom monitoring library and a server-side, distributed software covering five main functional tasks: parameter collection and processing, storage, visualisation and alarms. To select the most appropriate tools for these tasks, we evaluated three options: “Modular Stack”, Zabbix and the currently used ALICE Grid monitoring tool called MonALISA. The former one consists of a toolkit including collectd, Apache Flume, Apache Spark, InfluxDB, Grafana and Riemann. This paper describes the monitoring subsystem functional architecture. It goes through a complete evaluation of the three considered options, the selection process, risk assessment and justification for the final decision. The in-depth comparison includes functional features and throughput measurement to ensure the required processing and storage performance.
HADES (High Acceptance DiElectron Spectrometer), located at GSI, is a versatile detector for precise spectroscopy of e+ e- pairs and charged hadrons produced on a fixed target in a 1 to 3.5 AGeV kinetic beam energy region. The main experimental goal is to investigate properties of dense nuclear matter created in heavy ion collisions and learn about in-medium hadron properties.
In the HADES set-up 24 Mini Drift Chambers (MDC) allow for track reconstruction and determining the particle momentum by exploiting charged particle deflection in a magnetic field. In addition, the drift chambers contribute to particle identification by measuring the energy loss. The read-out concept foresees each sensing wire to be equipped with a preamplifier, analog pulse shaper and discriminator. In the current front-end electronics, the ASD-8 ASIC comprises the above modules. Due to limitations of the current on-board time to digital converters (TDC), especially regarding higher reaction rates expected at the future FAIR facility (HADES at SIS-100), the electronics need to be replaced by new board featuring multi-hit TDCs. Whereas ASD-8 chips cannot be procured anymore, a promising replacement candidate is the PASTTREC ASIC, developed by JU Krakow, which was tested w.r.t. suitability for MDC read-out in a variety of set-ups and, where possible, in direct comparison to ASD-8.
The timing precision, being the most crucial performance parameter of the joint system of detector and read-out electronics, was assessed in two different set-ups, i.e. a cosmic muon tracking set-up and a beam test at the COSY accelerator at Juelich using a minimum ionizing proton beam.
The beam test results were reproduced and can thus be quantitatively explained in a three dimensional GARFIELD simulation of a HADES MDC drift cell. In particular, the simulation is able to describe the characteristic dependence of the time precision on the track position within the cell.
A circuit simulation (SPICE) was used to closely model the time development of a raw drift chamber pulse, measured as a response to X-rays from a 55 Fe source. The insights gained from this model were used for attributing realistic charge values to the time over threshold values measured with the read-out ASICs in a charge calibration set-up. Furthermore, a high-level circuit simulation of the PASTTREC shaper is implemented to serve as a demonstration of the effect of the individual shaping and tail cancellation stages which are present in both ASICs.
Charmonia with different transverse momentum pT usually comes from different mechanisms in the relativistic heavy ion collisions. This work tries to review the theoretical studies on quarkonium evolutions in the deconfined medium produced in p-Pb and Pb-Pb collisions. The charmonia with high pT are mainly from the initial hadronic collisions, and therefore sensitive to the initial energy density of the bulk medium. For those charmonia within 0.1 < pT < 5 GeV/c at the energies of Large Hadron Collisions (LHC), They are mainly produced by the recombination of charm and anti-charm quarks in the medium. In the extremely low pT ∼ 1/RA (RA is the nuclear radius), additional contribution from the coherent interactions between electromagnetic fields generated by one nucleus and the target nucleus plays a non-negligible role in the J/ψ production even in semi-central Pb-Pb collisions.
The Projectile Spectator Detector (PSD) of the CBM experiment at the future FAIR facility is a compensating lead-scintillator calorimeter designed to measure the energy distribution of the forward going projectile nucleons and nuclei fragments (reaction spectators) produced close to the beam rapidity. The detector performance for the centrality and reaction plane determination is reviewed based on Monte-Carlo simulations of gold-gold collisions by means of four different heavy-ion event generators. The PSD energy resolution and the linearity of the response measured at CERN PS for the PSD supermodule consisting of 9 modules are presented. Predictions of the calorimeter radiation conditions at CBM and response measurement of one PSD module equipped with neutron irradiated MPPCs used for the light read out are discussed.
In high multiplicity nucleus-nucleus collisions baryon-antibaryon annihilation and regeneration occur during the final hadronic expansion phase, thus distorting the initial equilibrium multiplicity ratios. We quantify the modifications employing the hybrid UrQMD transport model and apply them to the grand canonical partition functions of the Statistical Hadronization Model(SHM). We analyze minimum bias and central Pb+Pb collision data at SPS and LHC energy. We explain the Pion to Proton ratio puzzle. We also reproduce the deuteron to proton ratio at LHC energy by the SHM, and by UrQMD after attaching a phase space coalescence process. We discuss the resulting (T,μB) diagram.
We present the first measurement of the proton–Ω correlation function in heavy-ion collisions for the central (0–40%) and peripheral (40–80%) Au + Au collisions at √sNN = 200 GeV by the STAR experiment at the Relativistic Heavy-Ion Collider (RHIC). Predictions for the ratio of peripheral collisions to central collisions for the proton–Ω correlation function are sensitive to the presence of a nucleon– bound state. These predictions are based on the proton– interaction extracted from (2 + 1)-flavor lattice QCD calculations at the physical point. The measured ratio of the proton–Ω correlation function between the peripheral (small system) and central (large system) collisions is less than unity for relative momentum smaller than 40 MeV/c. Comparison of our measured correlation ratio with theoretical calculation slightly favors a proton– bound system with a binding energy of ∼ 27 MeV.
We investigate the role of the Pauli Exclusion Principle (PEP) for light nuclei, at the examples of 12C and 16O. We show that ignoring the PEP does lead not only to a too dense spectrum at low energy but also to a wrong grouping into bands. Using a geometrical mapping, a triangular structure for 12C and a tetrahedral structure in 16O in the ground state is obtained by using the indistinguishably of the α-particles.