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Bellini, F.

Publications and source records attributed to Bellini, F..

At least 217 records · Page 12
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DOE OSTI2019

H Λ 3 and H - Λ - 3 lifetime measurement in Pb–Pb collisions at s NN = 5.02 TeV via two-body decay

An improved value for the lifetime of the (anti-)hypertriton has been obtained using the data sample of Pb–Pb collisions at s NN = 5.02 TeV collected by the ALICE experiment at the LHC. The (anti-)hypertriton has been reconstructed via its charged two-body mesonic decay channel and the lifetime has been determined from an exponential fit to the dN/d(ct) spectrum. The measured value, τ = 242$_{-38}^{+34}$ (stat.) ± 17 (syst.) ps, is compatible with representative theoretical predictions, thus contributing to the solution of the longstanding hypertriton lifetime puzzle.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Production of muons from heavy-flavour hadron decays in pp collisions at s $$ \sqrt{s} $$ = 5.02 TeV

Production cross sections of muons from semi-leptonic decays of charm and beauty hadrons were measured at forward rapidity $(2.5 < y < 4)$ in proton-proton (pp) collisions at a centre-of-mass energy $\sqrt{s} = 5.02 TeV$ with the ALICE detector at the CERN LHC. The results were obtained in an extended transverse momentum interval, $2 < p_T < 20$ GeV/$c$, and with an improved precision compared to previous measurements performed in the same rapidity interval at centre-of-mass energies $\sqrt{s}$ = 2.76 and 7 TeV. The $p_T$- and $y$-differential production cross sections as well as the $p_T$-differential production cross section ratios between different centre-of-mass energies and different rapidity intervals are described, within experimental and theoretical uncertainties, by predictions based on perturbative QCD.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Measurement of the production of charm jets tagged with D 0 mesons in pp collisions at $\sqrt{\mathrm{s}}=7$ TeV

The production of charm jets in proton-proton collisions at a center-of-mass energy of $\sqrt{\mathrm{s}}=7$ TeV was measured with the ALICE detector at the CERN Large Hadron Collider. The measurement is based on a data sample corresponding to a total integrated luminosity of 6.23 nb -1 , collected using a minimum-bias trigger. Charm jets are identified by the presence of a D 0 meson among their constituents. The D 0 mesons are reconstructed from their hadronic decay D 0 → $K^-π^+$. The D 0 -meson tagged jets are reconstructed using tracks of charged particles (track-based jets) with the anti-$k$ T algorithm in the jet transverse momentum range 5 < p T , j e t c h 30 GeV/ c and pseudorapidity |$η$ jet | < 0.5. The fraction of charged jets containing a D 0 -meson increases with p T , j e t c h from 0.042 ± 0.004 (stat) ± 0.006 (syst) to 0.080 ± 0.009 (stat) ± 0.008 (syst). The distribution of D 0 -meson tagged jets as a function of the jet momentum fraction carried by the D 0 meson in the direction of the jet axis ( z &#x2225;<!-- ∥ --> c h ) is reported for two ranges of jet transverse momenta, 5 < p T , j e t c h < 15 GeV/ c and 15 < p T , j e t c h < 30 GeV/ c in the intervals 0.2 < z &#x2016; c h < 1.0 and 0.4 < z &#x2016; c h < 1.0 respectively. The data are compared with results from Monte Carlo event generators (PYTHIA 6, PYTHIA 8 and Herwig 7) and with a Next-to-Leading-Order perturbative Quantum Chromodynamics calculation, obtained with the POWHEG method and interfaced with PYTHIA 6 for the generation of the parton shower, fragmentation, hadronisation and underlying event.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Λ c + production in Pb–Pb collisions at s NN = 5.02 TeV

A measurement of the production of prompt $\Lambda^+_c$ baryons in Pb–Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV with the ALICE detector at the LHC is reported. The $\Lambda^+_c$ and $\Lambda^-_c$ were reconstructed at midrapidity ($\mid{y}\mid < 0.5$) via the hadronic decay channel $\Lambda^+_c$ $\rightarrow {pK^0_s}$ (and charge conjugate) in the transverse momentum and centrality intervals GeV/c and 0–80%. The ratio, which is sensitive to the charm quark hadronisation mechanisms in the medium, is measured and found to be larger than the ratio measured in minimum-bias pp collisions at TeV and in p–Pb collisions at TeV. In particular, the values in p–Pb and Pb–Pb collisions differ by about two standard deviations of the combined statistical and systematic uncertainties in the common interval covered by the measurements in the two collision systems. The ratio is also compared with model calculations including different implementations of charm quark hadronisation. The measured ratio is reproduced by models implementing a pure coalescence scenario, while adding a fragmentation contribution leads to an underestimation. The nuclear modification factor, , is also presented. The measured values of the of , and non-strange D mesons are compatible within the combined statistical and systematic uncertainties. They show, however, a hint of a hierarchy , conceivable with a contribution from coalescence mechanisms to charm hadron formation in the medium.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Calibration of the photon spectrometer PHOS of the ALICE experiment

The procedure for the energy calibration of the high granularity electromagnetic calorimeter PHOS of the ALICE experiment is presented. The methods used to perform the relative gain calibration, to evaluate the geometrical alignment and the corresponding correction of the absolute energy scale, to obtain the nonlinearity correction coefficients and finally, to calculate the time-dependent calibration corrections, are discussed and illustrated by the PHOS performance in proton-proton (pp) collisions at √s = 13 TeV. After applying all corrections, the achieved mass resolutions for π 0 and η mesons for p T > 1.7 GeV/c are σ m π0 = 4.56 ± 0.03 MeV/c 2 and σ m η = 15.3 ± 1.0 MeV/c 2 , respectively.

47 OTHER INSTRUMENTATION↗
DOE OSTI2019

Energy dependence of exclusive $$\mathrm {J}/\psi $$ J / ψ photoproduction off protons in ultra-peripheral p–Pb collisions at $$\sqrt{s_{\mathrm {\scriptscriptstyle NN}}} = 5.02$$ s NN = 5.02 TeV

The ALICE Collaboration has measured the energy dependence of exclusive photoproduction of J / ψ vector mesons off proton targets in ultra–peripheral p–Pb collisions at a centre-of-mass energy per nucleon pair sNN=5.02 TeV. The e + e - and μ + μ - decay channels are used to measure the cross section as a function of the rapidity of the J / ψ in the range - 2.5 < y< 2.7 , corresponding to an energy in the γp centre-of-mass in the interval 40 < W γp < 550 GeV. The measurements, which are consistent with a power law dependence of the exclusive J / ψ photoproduction cross section, are compared to previous results from HERA and the LHC and to several theoretical models. They are found to be compatible with previous measurements.

Acharya, S.↗
DOE OSTI2019

Measurement of ${{\mathrm{D}}^0}$, ${{\mathrm{D}}^+}$, ${{\mathrm{D}}^{*+}}$ and ${{\mathrm{D}}^+_{\mathrm{s}}}$ production in pp collisions at ${\sqrt{{\textit{s}}}~=~5.02~{\text {TeV}}}$ with ALICE

The measurements of the production of prompt D 0 , D + , D *+ , and D$_s^+$ mesons in proton–proton (pp) collisions at $\sqrt{s}$=5.02 TeV with the ALICE detector at the Large Hadron Collider (LHC) are reported. D mesons were reconstructed at mid-rapidity (|y| < 0.5) via their hadronic decay channels D 0 → K - $π$ + , D + → K - $π$ + $π$ + , D *+ → D 0 $π$ + → K - $π$ + $π$ + , D$_s^+$ → Φ$π$ + → K + K - $π$ + , and their charge conjugates. The production cross sections were measured in the transverse momentum interval 0 < $p$T < 36 GeV/$c$ for D 0 , 1 < $p$T < 36 GeV/$c$ for D + and D *+ , and in 2 < $p$T < 24 GeV/$c$ for D$_s^+$ mesons. Thanks to the higher integrated luminosity, an analysis in finer $p$T bins with respect to the previous measurements at $\sqrt{s}$ = 7 TeV was performed, allowing for a more detailed description of the cross-section $p$T shape. The measured $p$T differential production cross sections are compared to the results at √ s = 7 TeV and to four different perturbative QCD calculations. Its rapidity dependence is also tested combining the ALICE and LHCb measurements in pp collisions at $\sqrt{s}$ = 5.02 TeV. This measurement will allow for a more accurate determination of the nuclear modification factor in p–Pb and Pb–Pb collisions performed at the same nucleon– nucleon centre-of-mass energy.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Charged-particle pseudorapidity density at mid-rapidity in p–Pb collisions at $\pmb {\sqrt{s_{\scriptscriptstyle {\mathrm{NN}}}}}$ = 8.16 TeV

The pseudorapidity density of charged particles, d$N$ ch /d$η$, in p–Pb collisions has been measured at a centre-of-mass energy per nucleon–nucleon pair of $\sqrt{s_{NN}}$ = 8.16 TeV at mid-pseudorapidity for non-single-diffractive events. The results cover 3.6 units of pseudorapidity, |$η$| < 1.8. The d$N$ ch /d$η$ value is 19.1 ± 0.7 at |$η$| < 0.5. This quantity divided by (N part )/2 is 4.73 ± 0.20 , where (N part ) is the average number of participating nucleons, is 9.5% higher than the corresponding value for p–Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV. Measurements are compared with models based on different mechanisms for particle production. All models agree within uncertainties with data in the Pb-going side, while HIJING overestimates, showing a symmetric behaviour, and EPOS underestimates the p-going side of the d$N$ ch /d$η$ distribution. Saturation-based models reproduce the distributions well for < -1.3. The d$N$ ch /d$η$ is also measured for different centrality estimators, based both on the charged-particle multiplicity and on the energy deposited in the Zero-Degree Calorimeters. A study of the implications of the large multiplicity fluctuations due to the small number of participants for systems like p–Pb in the centrality calculation for multiplicity-based estimators is discussed, demonstrating the advantages of determining the centrality with energy deposited near beam rapidity.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Jet fragmentation transverse momentum measurements from di-hadron correlations in$\sqrt{\mathrm{s}}=7$ TeV pp and $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV p–Pb collisions

The transverse structure of jets was studied via jet fragmentation transverse momentum ( j T ) distributions, obtained using two-particle correlations in proton-proton and proton-lead collisions, measured with the ALICE experiment at the LHC. The highest transverse momentum particle in each event is used as the trigger particle and the region 3 < p T t < 15GeV/ c is explored in this study. The measured distributions show a clear narrow Gaussian component and a wide non-Gaussian one. Based on Pythia simulations, the narrow component can be related to non-perturbative hadronization and the wide component to quantum chromodynamical splitting. The width of the narrow component shows a weak dependence on the transverse momentum of the trigger particle, in agreement with the expectation of universality of the hadronization process. On the other hand, the width of the wide component shows a rising trend suggesting increased branching for higher transverse momentum. The results obtained in pp collisions at $\sqrt{\mathrm{s}}=7$ TeV and in p–Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV are compatible within uncertainties and hence no significant cold nuclear matter effects are observed. The results are compared to previous measurements from CCOR and PHENIX as well as to Pythia 8 and Herwig 7 simulations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Relative particle yield fluctuations in Pb-Pb collisions at $\sqrt{s_\mathrm{{NN}}} =2.76\hbox { TeV}$

First results on K/$\pi$, p/$\pi$ and K/p fluctuations are obtained with the ALICE detector at the CERN LHC as a function of centrality in Pb-Pb collisions at $\sqrt{s_\mathrm{{NN}}} =2.76\hbox { TeV}$. The observable ν dyn , which is defined in terms of the moments of particle multiplicity distributions, is used to quantify the magnitude of dynamical fluctuations of relative particle yields and also provides insight into the correlation between particle pairs. This study is based on a novel experimental technique, called the Identity Method, which allows one to measure the moments of multiplicity distributions in case of incomplete particle identification. The results for p/$\pi$ show a change of sign in ν dyn from positive to negative towards more peripheral collisions. For central collisions, the results follow the smooth trend of the data at lower energies and ν dyn exhibits a change in sign for p/$\pi$ and K/p.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Measuring K S 0 K ± interactions using pp collisions at s = 7 TeV

We present the first measurements of femtoscopic correlations between the K$^0_S$ and K ± particles in pp collisions at $\sqrt{s}=7$ TeV measured by the ALICE experiment. The observed femtoscopic correlations are consistent with final-state interactions proceeding solely via the a 0 (980) resonance. The extracted kaon source radius and correlation strength parameters for K$^0_S$K - are found to be equal within the experimental uncertainties to those for K$^0_S$K + . Results of the present study are compared with those from identical-kaon femtoscopic studies also performed with pp collisions at $\sqrt{s}=7$ TeV by ALICE and with a K$^0_S$K ± measurement in Pb–Pb collisions at s NN =2.76 TeV. Combined with the Pb–Pb results, our pp analysis is found to be compatible with the interpretation of the a 0 (980) having a tetraquark structure instead of that of a diquark.

Acharya, S.↗
DOE OSTI2019

Event-Shape Engineering for the D-meson elliptic flow in mid-central Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV

The production yield of prompt D mesons and their elliptic flow coefficient $\nu$ 2 were measured with the Event-Shape Engineering (ESE) technique applied to mid-central (10–30% and 30–50% centrality classes) Pb-Pb collisions at the centre-of-mass energy per nucleon pair $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV, with the ALICE detector at the LHC. The ESE technique allows the classification of events, belonging to the same centrality, according to the azimuthal anisotropy of soft particle production in the collision. The reported measurements give the opportunity to investigate the dynamics of charm quarks in the Quark-Gluon Plasma and provide information on their participation in the collective expansion of the medium. D mesons were reconstructed via their hadronic decays at mid-rapidity, | η | < 0.8, in the transverse momentum interval 1 < p T < 24 GeV/ c . The $\nu$ 2 coefficient is found to be sensitive to the event-shape selection confirming a correlation between the D-meson azimuthal anisotropy and the collective expansion of the bulk matter, while the per-event D-meson yields do not show any significant modification within the current uncertainties.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗