Suppression of high transverse momentum D mesons in central Pb-Pb collisions at root s(NN)=2.76 TeV

The production of the prompt charm mesons D-0, D+, D*(+), and their antiparticles, was measured with the ALICE detector in Pb-Pb collisions at the LHC, at a centre-of-mass energy root s(NN) = 2.76 TeV per nucleon-nucleon collision. The p(t)-differential production yields in the range 2 < p(t) < 16 GeV/c at central rapidity, vertical bar y vertical bar < 0.5, were used to calculate the nuclear modification factor R-AA with respect to a proton-proton reference obtained from the cross section measured at root s = 7 TeV and scaled to root s = 2.76 TeV. For the three meson species, R-AA shows a suppression by a factor 3-4, for transverse momenta larger than 5 GeV/c in the 20% most central collisions. The suppression is reduced for peripheral collisions.

Measurement of the proton-air cross section at root s=57 TeV with the Pierre Auger Observatory

We report a measurement of the proton-air cross section for particle production at the center-of-mass energy per nucleon of 57 TeV. This is derived from the distribution of the depths of shower maxima observed with the Pierre Auger Observatory: systematic uncertainties are studied in detail. Analyzing the tail of the distribution of the shower maxima, a proton-air cross section of [505 +/- 22(stat)(-36)(+28)(syst)] mb is found.

J/psi production as a function of charged particle multiplicity in pp collisions at root s=7 TeV

The ALICE Collaboration reports the measurement of the relative J/psi yield as a function of charged particle pseudorapidity density dN(ch)/d eta in pp collisions at root s = 7 TeV at the LHC. J/psi particles are detected for p(t) > 0, in the rapidity interval vertical bar y vertical bar < 0.9 via decay into e(+)e(-), and in the interval 2.5 < y < 4.0 via decay into mu(+)/mu(-) pairs. An approximately linear increase of the J/psi yields normalized to their event average (dN(J/psi)/dy)/(dN(J/psi)/dy) with (dN(ch)/c eta)/(dN(ch)/d eta) is observed in both rapidity ranges, where dN(ch)/d eta is measured within vertical bar eta vertical bar < 1 and p(t) > 0. In the highest multiplicity interval with (dN(ch)/d eta)(bin)) = 24.1, corresponding to four times the minimum bias multiplicity density, an enhancement relative to the minimum bias J/psi yield by a factor of about 5 at 2.5 < y <4 (8 at vertical bar y vertical bar < 0.9) is observed. (C) 2012 CERN. Published by Elsevier B.V. All rights reserved.

Light vector meson production in pp collisions at root s=7 TeV ALICE Collaboration

The ALICE experiment has measured low-mass dimuon production in pp collisions at root s = 7 TeV in the dimuon rapidity region 2.5 < y < 4. The observed dimuon mass spectrum is described as a superposition of resonance decays (eta, rho, omega, eta', phi) into muons and semi-leptonic decays of charmed mesons. The measured production cross sections for omega and phi are sigma(omega)(1 < p(t) < 5 GeV/c. 2.5 < y < 4) = 5.28 +/- 0.54(stat) +/- 0.49(syst) mb and sigma(phi)(1 < p(t) < 5 GeV/c. 2.5 < y < 4) = 0.940 +/- 0.084(stat) +/- 0.076(syst) mb. The differential cross sections d(2)sigma/dy dp(t) are extracted as a function of p(t) for omega and phi. The ratio between the rho and omega cross section is obtained. Results for the phi are compared with other measurements at the same energy and with predictions by models. (C) 2012 CERN. Published by Elsevier B.V. All rights reserved.

Alpha cluster structure in 16O.

The alpha cluster phenomenon in the light nuclei structure has been the subject of a longtime investigation since the proposal of the Ikeda diagrams, however the mechanism of the cluster formation is still not completely understood. In fact, if the clusters have a fairly rigid crystal-like or a gas-like structure remains an open question. The interpretation of the Hoyle state as an α condensate brought a renewed interest to this subject, in particular to resonances analogous to the Hoyle state. In this context the study of the experimental evolution of the α-cluster phenomenon through (6Li,d) transfer reactions has been performed in São Paulo. Particularly important are the regions around the nα thresholds where the α-cluster structure states are predicted. The resonant states around the 4α threshold in the nucleus 16O are the focus of the present contribution. The 12C(6Li,d)16O reaction was measured at a bombarding energy of 25.5 MeV employing the São Paulo Pelletron-Enge-Spectrograph facility and the nuclear emulsion detection technique. Resonant states above the α threshold were measured and an energy resolution of 15-30 keV allows to define states previously unresolved. The angular distributions of the absolute cross sections were determined in a range of 4-40 degree in the center of mass system and up to 17 MeV excitation energy. The upper limit for the resonance widths in the crucial region of the 4α threshold was obtained. These values revealed to be at least a factor three smaller than the ones previously reported in the literature, indicating that the α cluster structure information on this region should be revised.

Study of reactions induced by 6He on 9Be

We present the results of experiments using a 6He beam on a 9Be target at energies 7 − 9 times the Coulomb barrier. Angular distributions of the elastic, inelastic scattering (target breakup) and the -particle production in the 6He+9Be collision have been analysed. Total reaction cross sections were obtained from the elastic scattering analyses and a considerable enhancement has been observed by comparing to stable systems.

EE01. Esercizi di esame di Meccanica con risultati.

Esercizi di esame per i corsi di Fisica Generale. I compiti di esame contengono esercizi sorteggiati da questa lista, nell'ultima versione disponibile sul Web 15 giorni prima della data di esame. I punteggi riportati a fianco dei quesiti/esercizi sono calcolati dinamicamente sulla base dei precedenti risultati nelle prove di esame, in modo da rendere il secondo terzile della distribuzione dei voti sul singolo esercizio pari a 3/3. In altre parole il punteggio assegnato al singolo quesito/esercizio è tale da assicurare che un terzo degli studenti che hanno affrontato l'esercizio ottenga la massima valutazione. Il punteggio degli esercizi riportato sul file è indicativo. Esso si modifica dinamicamente a ogni esame, in modo che a ogni esame diviene una valutazione più precisa della difficoltà dell'esercizio (all'aumentare della statistica sperimentale l'errore di misura diminuisce).

EE03. Esercizi di esame di Elettromagnetismo con risultati

Esercizi di esame per i corsi di Fisica Generale. I compiti di esame contengono esercizi sorteggiati da questa lista, nell'ultima versione disponibile sul Web 15 giorni prima della data di esame. I punteggi riportati a fianco dei quesiti/esercizi sono calcolati dinamicamente sulla base dei precedenti risultati nelle prove di esame, in modo da rendere il secondo terzile della distribuzione dei voti sul singolo esercizio pari a 3/3. In altre parole il punteggio assegnato al singolo quesito/esercizio è tale da assicurare che un terzo degli studenti che hanno affrontato l'esercizio ottenga la massima valutazione. Il punteggio degli esercizi riportato sul file è indicativo. Esso si modifica dinamicamente a ogni esame, in modo che a ogni esame diviene una valutazione più precisa della difficoltà dell'esercizio (all'aumentare della statistica sperimentale l'errore di misura diminuisce).

Pattern recognition analysis on heavy ion reaction data

One of the problems in the analysis of nucleus-nucleus collisions is to get information on the value of the impact parameter b. This work consists in the application of pattern recognition techniques aimed at associating values of b to groups of events. To this end, a support vec- tor machine (SVM) classifier is adopted to analyze multifragmentation reactions. This method allows to backtracing the values of b through a particular multidimensional analysis. The SVM classification con- sists of two main phase. In the first one, known as training phase, the classifier learns to discriminate the events that are generated by two different model:Classical Molecular Dynamics (CMD) and Heavy- Ion Phase-Space Exploration (HIPSE) for the reaction: 58Ni +48 Ca at 25 AMeV. To check the classification of events in the second one, known as test phase, what has been learned is tested on new events generated by the same models. These new results have been com- pared to the ones obtained through others techniques of backtracing the impact parameter. Our tests show that, following this approach, the central collisions and peripheral collisions, for the CMD events, are always better classified with respect to the classification by the others techniques of backtracing. We have finally performed the SVM classification on the experimental data measured by NUCL-EX col- laboration with CHIMERA apparatus for the previous reaction.