Measurement of identified charged hadron spectra with the ALICE experiment at the LHC

The ALICE experiment features multiple particle identification systems. The measurement of the identified charged hadron $p_{t}$ spectra in proton-proton collisions at $\sqrt{s}=900$ GeV will be discussed. In the central rapidity region ($|\eta|<0.9$) particle identification and tracking are performed using the Inner Tracking System (ITS), which is the closest detector to the beam axis, the Time Projection Chamber (TPC) and a dedicated time-of-flight system (TOF). Particles are mainly identified using the energy loss signal in the ITS and TPC. In addition, the information from TOF is used to identify hadrons at higher momenta. Finally, the kink topology of the weak decay of charged kaons provides an alternative method to extract the transverse momentum spectra of charged kaons. This combination allows to track and identify charged hadrons in the transverse momentum ($p_{t}$) range from 100 MeV/c up to 2.5 GeV/$c$. Mesons containing strange quarks (\kos, $\phi$) and both singly and doubly strange baryons (\lam, \lambar, and \xip + \xim) are identified by their decay topology inside the TPC detector. Results obtained with the various identification tools above described and a comparison with theoretical models and previously published data will be presented.Comment: 11 pages, 14 figures, contribution to conference proceedings of the 27th Winter Workshop on Nuclear Dynamic

Identified charged hadron production in Pb-Pb collisions at the LHC with the ALICE Experiment

Identified particle spectra represent a crucial tool to understand the behavior of the matter created in high-energy heavy-ion collisions. The transverse momentum p_T distributions of identified hadrons contain informations about the transverse expansion of the system and constrain the freezeout properties of the matter created. The ALICE experiment has good particle identification performance over a broad p_T range. In this contribution the results for identified pions, kaons and protons in heavy-ion collisions at 2.76 TeV center-of-mass energy are presented. These results are compared with other identified particle measurements obtained by previous experiments, and discussed in terms of the thermal and hydrodynamic pictures. The status of extensions of this analysis, with the study of identified particles as a function of event-by-event flow in Pb-Pb collisions, is also discussed.Comment: Quark Matter 2012 proceedings, 4 pages, 2 figure

Transverse momentum spectra of hadrons identified with the ALICE Inner Tracking System

The Inner Tracking System is the ALICE detector closest to the beam axis. It is composed of six layers of silicon detectors: two innermost layers of Silicon Pixel Detectors (SPD), two intermediate layers of Silicon Drift Detectors (SDD) and two outermost layers of Silicon Strip Detectors (SSD). The ITS can be used as a standalone tracker in order to recover tracks that are not reconstructed by the Time Projection Chamber (TPC) and to reconstruct low momentum particles with $p_{t}$ down to 100 MeV/c. Particle identification in the ITS is performed by measuring the energy loss signal in the SDD and SSD layers. The ITS allows to extend the charged particle identification capability in the ALICE central rapidity region at low $p_{t}$: it is possible to separate $\pi/K$ in the range 100 MeV/c $< p_{t} <$ 500 MeV/c and $K/p$ in the range 200 MeV/c $< p_{t} <$ 800 MeV/c. The identification of hadron in the ITS will be discussed in detail, different methods used to extract the $p_{t}$ spectra of $\pi, K$ and $p$ will also be described.Comment: 2 pages, 2 figures, submitted as contribution to PLHC2011 conference proceeding

Two-particle correlations in p-Pb collisions at the LHC with ALICE

The double ridge structure previously observed in Pb-Pb collisions has also been recently observed in high-multiplicity p-Pb collisions at sqrt(s_NN) = 5.02 TeV. These systems show a long-range structure (large separation in Delta_eta) at the near- (Delta_phi ~ 0) and away-side (Delta_phi ~ pi) of the trigger particle. In order to understand the nature of this effect the two-particle correlation analysis has been extended to identified particles. Particles are identified up to transverse momentum pT values of 4 GeV/c using the energy loss signal in the Time Projection Chamber detector, complemented with the information from the Time of Flight detector. This measurement casts a new light on the potential collective (i.e. hydrodynamic) behaviour of particle production in p-Pb collisions.Comment: 4 pages, 3 figures, Proceedings of Strangeness in Quark Matter 2013 conference, 21-27 July 201

Uncovering the physics of flapping flat plates with artificial evolution

We consider an experiment in which a rectangular flat plate is flapped with two degrees of freedom, and a genetic algorithm tunes its trajectory parameters so as to achieve maximum average lift force, thus evolving a population of trajectories all yielding optimal lift forces. We cluster the converged population by defining a dynamical formation number for a flapping flat plate, thus showing that optimal unsteady force generation is linked to the formation of a leading-edge vortex with maximum circulation. Force and digital particle image velocimetry measurements confirm this result

Decomposition Based Search - A theoretical and experimental evaluation

In this paper we present and evaluate a search strategy called Decomposition Based Search (DBS) which is based on two steps: subproblem generation and subproblem solution. The generation of subproblems is done through value ranking and domain splitting. Subdomains are explored so as to generate, according to the heuristic chosen, promising subproblems first. We show that two well known search strategies, Limited Discrepancy Search (LDS) and Iterative Broadening (IB), can be seen as special cases of DBS. First we present a tuning of DBS that visits the same search nodes as IB, but avoids restarts. Then we compare both theoretically and computationally DBS and LDS using the same heuristic. We prove that DBS has a higher probability of being successful than LDS on a comparable number of nodes, under realistic assumptions. Experiments on a constraint satisfaction problem and an optimization problem show that DBS is indeed very effective if compared to LDS.Comment: 16 pages, 8 figures. LIA Technical Report LIA00203, University of Bologna, 200