Heavy-flavour production and multiplicity dependence in pp and p--Pb collisions with ALICE

The production of heavy quarks in pp collisions provides a precision test of perturbative QCD calculations at the LHC energies. More complex collision systems like p--Pb collisions allow studies of cold nuclear matter effects, such as modifications of the parton distribution functions at small x and of the \kt broadening effect. We present the ALICE results of prompt D-meson production as a function of the charged-particle multiplicity, in pp and p--Pb collisions at $\sqrt{s}=7$ TeV and $\sqrt{s_{NN}}=5.02$ TeV respectively. The per-event yield of D mesons in different multiplicity and \pt intervals are compared for pp and p--Pb collisions to study the contribution of multi-parton interactions to open-charm production. Angular correlations of prompt D mesons and heavy-flavour decay electrons with charged hadrons in pp and p-Pb collisions are also shown in different kinematic ranges and compared to pQCD models. These measurements provide information on the charm fragmentation processes, on cold nuclear matter effects on charm production, and on the participation of charm in the collective motion arising in small collision systems like p-Pb.Comment: Proceedings for the LHCP Conference, 201

Di-jet measurements in heavy-ion collisions at STAR

Jets are produced from hard scatterings in the early stages of heavy-ion collisions. It is expected that these high-$p_T$ partons travel through the hot and dense medium before fragmenting. Therefore they are expected to suffer energy loss in the QGP via gluon radiation and elastic collisions along their path. Measurements of fully reconstructed jets help understand the effect of the energy loss on the jet structure and energy profile. A data-driven characterization of the background in Au+Au is needed in order to compare the results to p+p. The full azimuthal coverage of STAR Time Projection Chamber and Electromagnetic Calorimeter allows measurements of fully reconstructed di-jets, defined by jets that match the online trigger and recoil jets on the away side. A tight selection of the trigger jets allows for a selection of those coming from the surface. Hence, the population of jets on the recoil side is biased towards a maximal energy loss because of the extreme in-medium pathlength. We present measurements of di-jets, exploring their structure and properties in Au+Au and p+p at $\sqrt s_{NN}=$200 GeV in the STAR experiment.Comment: Proceedings for the Jets in Proton-Proton and Heavy-Ion Collisions worksho

D-meson nuclear modification factor and v2_2 in Pb-Pb collisions at the LHC

We present the ALICE results on open heavy flavour, focusing on the exclusive reconstruction of charmed mesons via displaced decay topologies. These measurements benefit from the large Pb-Pb statistics collected in 2011. The results on the nuclear modification factor Raa for D mesons indicate a suppression of their yield in central collisions relative to binary-scaled pp collisions in a large momentum range. The comparison to the Raa of non-prompt J/psi (measured with CMS) indicates a difference in the suppression of charm and beauty, as expected according to the predicted mass hierarchy in energy loss models. The measurement of the azimuthal anisotropy of charmed mesons is also discussed. The observed positive second Fourier harmonic v2 for transverse momentum 2<pT<6 GeV/c in semi-peripheral events is a hint for collective motion of charm quarks. The results discussed above are also compared to theoretical models.Comment: Proceedings for the conference Strangeness in Quark Matter, 201

Open charm reconstruction in ALICE: D+→K−π+π+{\rm D^+\to K^-\pi^+\pi^+}

Open charm mesons produced in high energy A-A interactions are expected to be powerful probes to investigate the medium produced in the collision. In this context it is important to measure the production of as many charmed hadrons as possible, such as D$^0$, D$^+$, D$^+_s$ and $\Lambda_c$, because the measurement of their relative yield can provide information on the hadronization mechanism and is necessary to reduce the systematic error on the absolute cross section. The ALICE experiment at the LHC is designed to perform such measurements at midrapidity down to $p_T$ below 1 GeV/c, mainly by means of the silicon vertex and tracker detector, the time projection chamber and the time of flight detector. One of the main channels for the detection of charm production in ALICE is the exclusive reconstruction of the D$^+$ meson through its three charged body decay $K^-\pi^+\pi^+$ in Pb-Pb ($\sqrt s=5.5$ TeV) and pp ($\sqrt s=14$ TeV) collisions. The selection strategies for this analysis and the results of a feasibility study on Monte Carlo events will be presented together with the perspectives for the study of D$^+$ quenching and azimuthal anisotropy measurements.Comment: 8 pages, Proceeding for the poster presented at Quark Matter 200

Measurements of jet structure and fragmentation from full jet reconstruction in heavy ion collisions at RHIC

Measurements of inclusive hadron suppression and di-hadron azimuthal correlations have provided important insights into jet quenching in hot QCD matter. However, they do not provide access to the energy of the hard scattering and are limited in their sensitivity since they can be affected by biases toward hard fragmentation and small energy loss. Full jet reconstruction in heavy-ion collisions enables a complete study of the modification of jet structure due to energy loss, but is challenging due to the high-multiplicity environment. We present measurements of fully reconstructed di-jets at mid-rapidity in 200 GeV p+p and central Au+Au collisions performed with the STAR detector. We compare fragmentation functions measured in 200 GeV p+p and central Au+Au collisions and assess the systematic uncertainties of their ratio.Comment: Proceedings of Quark Matter 09 Conferenc

Numerical modelling of aerodynamics for applications in sports car engineering

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Measurements of di-jets in p+p and Au+Au in the STAR experiment

Jets are produced from hard scatterings in the early stages of heavy-ion collisions. It is expected that these high-p$_T$ partons travel through the hot and dense medium before fragmenting. Therefore they are expected to suffer energy loss in the QGP via gluon radiation or elastic collisions along their path. Measurements from full jet reconstruction help in the understanding of energy loss and its effect{\ss} on the jet structure and energy profile. A data-driven characterization of the background in Au+Au is needed in order to compare the results to p+p. The large coverage of the STAR detector along with an online trigger also allows for reconstructing di-jets. Suitable selection of trigger jets allows for studying a subset of jets on the recoil side which are biased towards higher energy loss because of a larger, on average, in-medium path length traversed. Trigger jets are also used to study jet-hadron correlations as an independent measurement to assess the effect of energy loss on the recoil side. We present measurements of di-jets and jet-hadron correlations in the presence of reconstructed di-jets in Au+Au and p+p at 200 GeV in the STAR experiment.Comment: Proceedings for Hard Probes 2010 Conferenc

Overview on jet results from STAR

Full jet reconstruction allows access to the parton kinematics over a large energy domain and can be used to constrain the mechanisms of energy loss in heavy-ion collisions. Such measurements are challenging at RHIC, due to the high-multiplicity environments created in heavy-ion collisions. In these proceedings, we report an overview of the results on full jet reconstruction obtained by the STAR experiment. Jet measurements in 200 GeV p+p show that jets are calibrated pQCD probes and provide a baseline for jet measurements in Au+Au collisions. Inclusive differential jet production cross sections and ratios are reported for central 200 GeV Au+Au collisions and compared to p+p. We also present measurements of fully reconstructed di-jets at mid-rapidity, and compare spectra and fragmentation functions in p+p and central Au+Au collisions.Comment: Proceedings for the 26th WWND conferenc