Azimuthal Anisotropy of Heavy-Flavor Decay Electrons in p -Pb Collisions at s N N = 5.02 TeV
Not Available
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Engineering topics
Bellini, F.
Publications and source records attributed to Bellini, F..
Direct photon production at low transverse momentum in proton-proton collisions at s = 2.76 and 8 TeV
Not Available
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurement of dielectron production in central Pb-Pb collisions at s NN = 2.76 TeV
The first measurement of dielectron (e + e - ) production in central (0–10%) Pb–Pb collisions at $\sqrt{s}$$_{NN}$ = 2.76 TeV at the LHC is presented. The dielectron invariant-mass spectrum is compared to the expected contributions from hadron decays in the invariant-mass range 0 < m ee < 3.5 GeV /$c$ 2 . The ratio of data and the cocktail of hadronic contributions without vacuum ρ0 is measured in the invariant-mass range 0.15 < m ee < 0.7 GeV /$c$ 2 , where an excess of dielectrons is observed in other experiments, and its value is 1.40 ± 0.28 (stat.) ± 0.08 (syst.) ± 0.27 (cocktail). The dielectron spectrum measured in the invariant mass range 0 < m ee < 1 GeV /$c$ 2 is consistent with the predictions from two theoretical model calculations that include thermal dielectron production from both partonic and hadronic phases with in-medium broadened ρ 0 meson. The fraction of direct virtual photons over inclusive virtual photons is extracted for dielectron pairs with invariant mass 0.1 < m ee < 0.3 GeV /$c$ 2 and in the transverse-momentum intervals 1 < $p{_T}_{,ee}$ < 2 GeV/$c$ and 2 < $p{_T}_{,ee}$ < 4 GeV /$c$. The measured fraction of virtual direct photons is consistent with the measurement of real direct photons by ALICE and with the expectations from previous dielectron measurements at RHIC within the experimental uncertainties.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
p − p , p − Λ , and Λ − Λ correlations studied via femtoscopy in p p reactions at s = 7 TeV
Not Available
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Suppression of Λ ( 1520 ) resonance production in central Pb-Pb collisions at s NN = 2.76 TeV
The production yield of the Λ(1520) baryon resonance is measured at midrapidity in Pb-Pb collisions at $\sqrt{s}$$_{NN}$ = 2.76 TeV with the ALICE detector at the Large Hadron Collider (LHC). The measurement is performed in the Λ(1520) → pK - (and charge conjugate) hadronic decay channel as a function of the transverse momentum (p T ) and collision centrality. The ratio of the p T -integrated production of Λ(1520) baryons relative to baryons in central collisions is suppressed by about a factor of 2 with respect to peripheral collisions. This is the first observation of the suppression of a baryonic resonance at the LHC and the first 3σ evidence of Λ(1520) suppression within a single collision system. The measured Λ(1520)/Λ ratio in central collisions is smaller than the value predicted by the statistical hadronization model calculations. The shape of the measured p T distribution and the centrality dependence of the suppression are reproduced by the EPOS3 Monte Carlo event generator. The measurement adds further support to the formation of a dense hadronic phase in the final stages of the evolution of the fireball created in heavy-ion collisions, lasting long enough to cause a significant reduction in the observable yield of short-lived resonances.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Multiplicity dependence of light-flavor hadron production in p p collisions at s = 7 TeV
Comprehensive results on the production of unidentified charged particles, $π^±, K^±, K^0_S, K^*(892)^0, p,$ $\bar{p}$, $\phi$ (1020), Λ, $\bar{Λ}$, $\Xi^-$, $\bar{\Xi}^+$, $Ω^-$, and $\bar{Ω}^+$ hadrons in proton-proton ($pp$) collisions at $\sqrt{s}$ = 7 TeV at midrapidity ($|y|$ < 0.5) as a function of charged-particle multiplicity density are presented. In order to avoid autocorrelation biases, the actual transverse momentum ($p$ T ) spectra of the particles under study and the event activity are measured in different rapidity windows. In the highest multiplicity class, the charged-particle density reaches about 3.5 times the value measured in inelastic collisions. While the yield of protons normalized to pions remains approximately constant as a function of multiplicity, the corresponding ratios of strange hadrons to pions show a significant enhancement that increases with increasing strangeness content. Furthermore, all identified particle-to-pion ratios are shown to depend solely on charged-particle multiplicity density, regardless of system type and collision energy. The evolution of the spectral shapes with multiplicity and hadron mass shows patterns that are similar to those observed in $p$-Pb and Pb-Pb collisions at Large Hadron Collider energies. The obtained $p$ T distributions and yields are compared to expectations from QCD-based $pp$ event generators as well as to predictions from thermal and hydrodynamic models. These comparisons indicate that traces of a collective, equilibrated system are already present in high-multiplicity $pp$ collisions.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Study of J/ ψ azimuthal anisotropy at forward rapidity in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV
The second ( v 2 ) and third ( v 3 ) flow harmonic coefficients of J/ ψ mesons are measured at forward rapidity (2.5 < y < 4.0) in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV with the ALICE detector at the LHC. Results are obtained with the scalar product method and reported as a function of transverse momentum, p T , for various collision centralities. A positive value of J/ ψ v 3 is observed with 3.7σ significance. The measurements, compared to those of prompt D 0 mesons and charged particles at mid-rapidity, indicate an ordering with v n (J/ ψ ) < v n (D 0 ) < v n (h ± ) (n = 2, 3) at low and intermediate p T up to 6GeV/ c and a convergence with v 2 (J/ ψ ) ≈ v 2 (D 0 ) ≈ v 2 (h ± ) at high p T above 6–8 GeV/ c . In semi-central collisions (5–40% and 10–50% centrality intervals) at intermediate p T between 2 and 6 GeV/ c , the ratio v 3 / v 2 of J/ ψ mesons is found to be significantly lower (4.6σ) with respect to that of charged particles. In addition, the comparison to the prompt D 0 -meson ratio in the same p T interval suggests an ordering similar to that of the v 2 and v 3 coefficients. The J/ ψ v 2 coefficient is further studied using the Event Shape Engineering technique. The obtained results are found to be compatible with the expected variations of the eccentricity of the initial-state geometry.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Direct photon elliptic flow in Pb–Pb collisions at s NN = 2.76 TeV
The elliptic flow of inclusive and direct photons was measured at mid-rapidity in two centrality classes 0–20% and 20–40% in Pb–Pb collisions at s NN =2.76 TeV by ALICE. Photons were detected with the highly segmented electromagnetic calorimeter PHOS and via conversions in the detector material with the e + e - pairs reconstructed in the central tracking system. The results of the two methods were combined and the direct-photon elliptic flow was extracted in the transverse momentum range 0.9 < p T < 6.2 GeV/ c . A comparison to RHIC data shows a similar magnitude of the measured direct-photon elliptic flow. Hydrodynamic and transport model calculations are systematically lower than the data, but are found to be compatible.
Acharya, S.↗
Dielectron and heavy-quark production in inelastic and high-multiplicity proton–proton collisions at s = 13 TeV
Not Available
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Charged jet cross section and fragmentation in proton-proton collisions at s = 7 TeV
Not Available
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Centrality and pseudorapidity dependence of the charged-particle multiplicity density in Xe–Xe collisions at s NN = 5.44 TeV
In this Letter, the ALICE Collaboration presents the first measurements of the charged-particle multiplicity density, dN ch /dη and total charged-particle multiplicity, N$tot\atop{ch}$, in Xe–Xe collisions at a centre-of-mass energy per nucleon–nucleon pair of $ \sqrt{s_{NN}}$=5.44TeV. The measurements are performed as a function of collision centrality over a wide pseudorapidity range of -3.5<η<5. The values of dN ch /dη at mid-rapidity and N$tot\atop{ch}$ for central collisions, normalised to the number of nucleons participating in the collision (N part ) as a function of $ \sqrt{s_{NN}}$ follow the trends established in previous heavy-ion measurements. The same quantities are also found to increase as a function of Npart, and up to the 5% most central collisions the trends are the same as the ones observed in Pb–Pb at a similar energy. For more central collisions, the Xe–Xe scaled multiplicities exceed those in Pb–Pb for a similar N part . The results are compared to phenomenological models and theoretical calculations based on different mechanisms for particle production in nuclear collisions. All considered models describe the data reasonably well within 15%.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
CUORE: The first bolometric experiment at the ton scale for rare decay searches
Here, the Cryogenic Underground Observatory for Rare Events (CUORE) is the first bolometric experiment searching for neutrinoless double beta decay that has been able to reach the 1-ton scale. The detector consists of an array of 988 TeO 2 crystals arranged in a cylindrical compact structure of 19 towers. The construction of the experiment and, in particular, the installation of all towers in the cryostat was completed in August 2016 and data taking started in spring 2017. In this contribution the achievement of the commissioning phase and the performance of the detector and the cryostat during the first physics run will be presented.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
Transverse momentum spectra and nuclear modification factors of charged particles in pp, p-Pb and Pb-Pb collisions at the LHC
We report the measured transverse momentum ($p_T$) spectra of primary charged particles from pp, p-Pb and Pb-Pb collisions at a center-of-mass energy $\sqrt{s}$$_{NN}$ = 5.02 TeV in the kinematic range of 0.15 < $p_T$ < 50 GeV/$c$ and |$η$| < 0.8. A significant improvement of systematic uncertainties motivated the reanalysis of data in pp and Pb-Pb collisions at $\sqrt{s}$$_{NN}$ = 2.76 TeV, as well as in p-Pb collisions at $\sqrt{s}$$_{NN}$ = 5.02 TeV, which is also presented. Spectra from Pb-Pb collisions are presented in nine centrality intervals and are compared to a reference spectrum from pp collisions scaled by the number of binary nucleon-nucleon collisions. For central collisions, the $p_T$ spectra are suppressed by more than a factor of 7 around 6–7 GeV/$c$ with a significant reduction in suppression towards higher momenta up to 30 GeV/$c$. The nuclear modification factor $R_p$Pb, constructed from the pp and p-Pb spectra measured at the same collision energy, is consistent with unity above 8 GeV/$c$. While the spectra in both pp and Pb-Pb collisions are substantially harder at $\sqrt{s}$$_{NN}$ = 5.02 TeV compared to 2.76 TeV, the nuclear modification factors show no significant collision energy dependence. The obtained results should provide further constraints on the parton energy loss calculations to determine the transport properties of the hot and dense QCD matter.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurement of D 0 , D + , D$^{*+}$ and D$_s^+$ production in Pb-Pb collisions at $\sqrt{{\mathrm{s}}_{\mathrm{NN}}}=5.02$ TeV
We report measurements of the production of prompt D 0 , D + , D$^{*+}$ and D$_s^+$ mesons in Pb–Pb collisions at the centre-of-mass energy per nucleon-nucleon pair $\sqrt{s}$$_{NN}$ = 5.02 TeV, in the centrality classes 0–10%, 30–50% and 60–80%. The D-meson production yields are measured at mid-rapidity (|$y$| < 0.5) as a function of transverse momentum ($p_T$). The $p_T$ intervals covered in central collisions are: 1 < $p_T$ < 50 GeV/$c$ for D$^0$, 2 < $p_T$ < 50 GeV/$c$ for D$^+$, 3 < $p_T$ < 50 GeV/$c$ for D$^{*+}$, and 4 < $p_T$ < 16 GeV/$c$ for D$_s^+$ mesons. The nuclear modification factors ($R_{AA}$) for non-strange D mesons (D$^0$, D$^+$, D$^{*+}$) show minimum values of about 0.2 for $p_T$ = 6–10 GeV/$c$ in the most central collisions and are compatible within uncertainties with those measured at $\sqrt{{\mathrm{s}}_{\mathrm{NN}}}$ = 2.76 TeV. For D$_s^+$ mesons, the values of $R_{AA}$ are larger than those of non-strange D mesons, but compatible within uncertainties. In central collisions the average $R_{AA}$ of non-strange D mesons is compatible with that of charged particles for $p_T$ > 8 GeV/$c$, while it is larger at lower $p_T$. The nuclear modification factors for strange and non-strange D mesons are also compared to theoretical models with different implementations of in-medium energy loss.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Medium modification of the shape of small-radius jets in central Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV
We present the measurement of a new set of jet shape observables for track-based jets in central Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV. The set of jet shapes includes the first radial moment or angularity, g; the momentum dispersion, pTD; and the difference between the leading and sub-leading constituent track transverse momentum, LeSub. These observables provide complementary information on the jet fragmentation and can constrain different aspects of the theoretical description of jet-medium interactions. The jet shapes were measured for a small resolution parameter R = 0.2 and were fully corrected to particle level. The observed jet shape modifications indicate that in-medium fragmentation is harder and more collimated than vacuum fragmentation as obtained by PYTHIA calculations, which were validated with the measurements of the jet shapes in proton-proton collisions at $\sqrt{s}=7$ TeV. The comparison of the measured distributions to templates for quark and gluon-initiated jets indicates that in-medium fragmentation resembles that of quark jets in vacuum. We further argue that the observed modifications are not consistent with a totally coherent energy loss picture where the jet loses energy as a single colour charge, suggesting that the medium resolves the jet structure at the angular scales probed by our measurements (R = 0.2). Furthermore, we observe that small-R jets can help to isolate purely energy loss effects from other effects that contribute to the modifications of the jet shower in medium such as the correlated background or medium response.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Neutral pion and η meson production at midrapidity in Pb-Pb collisions at s NN = 2.76 TeV
Not Available
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Measurements of low-$p_T$ electrons from semileptonic heavy-flavour hadron decays at mid-rapidity in pp and Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV
Transverse-momentum ($p_T$) differential yields of electrons from semileptonic heavy-flavour hadron decays have been measured in the most central (0–10%) and in semi-central (20–40%) Pb–Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV. The corresponding production cross section in pp collisions has been measured at the same energy with substantially reduced systematic uncertainties with respect to previously published results. The modification of the yield in Pb–Pb collisions with respect to the expectation from an incoherent superposition of nucleon-nucleon collisions is quantified at mid-rapidity (|$y$| < 0.8) in the $p_T$ interval 0.50-3 GeV/$c$ via the nuclear modi cation factor, $R_{AA}$. This paper extends the $p_T$ reach of the $R_{AA}$ measurement towards significantly lower values with respect to a previous publication. In Pb–Pb collisions the $p_T$-differential measurements of yields at low $p_T$ are essential to investigate the scaling of heavy-flavour production with the number of binary nucleon-nucleon collisions. Heavy-quark hadronization, a collective expansion and even initial-state effects, such as the nuclear modification of the Parton Distribution Function, are also expected to have a significant effect on the measured distribution.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗