The study of (anti-)deuteron production in pp collisions has proven to be a powerful tool to inve... more The study of (anti-)deuteron production in pp collisions has proven to be a powerful tool to investigate the formation mechanism of loosely bound states in high-energy hadronic collisions. In this paper the production of $$\text {(anti-)deuterons}$$ (anti-)deuterons is studied as a function of the charged particle multiplicity in inelastic pp collisions at $$\sqrt{s}=13$$ s = 13 TeV using the ALICE experiment. Thanks to the large number of accumulated minimum bias events, it has been possible to measure (anti-)deuteron production in pp collisions up to the same charged particle multiplicity ($${\mathrm {d} N_{ch}/\mathrm {d} \eta } \sim 26$$ d N ch / d η ∼ 26 ) as measured in p–Pb collisions at similar centre-of-mass energies. Within the uncertainties, the deuteron yield in pp collisions resembles the one in p–Pb interactions, suggesting a common formation mechanism behind the production of light nuclei in hadronic interactions. In this context the measurements are compared with the...
Measurements of K * (892) 0 and φ(1020) resonance production in Pb-Pb and pp collisions at √ s NN... more Measurements of K * (892) 0 and φ(1020) resonance production in Pb-Pb and pp collisions at √ s NN = 5.02 TeV with the ALICE detector at the Large Hadron Collider are reported. The resonances are measured at midrapidity (| y| < 0.5) via their hadronic decay channels and the transverse momentum (p T) distributions are obtained for various collision centrality classes up to p T = 20 GeV/c. The p T-integrated yield ratio K * (892) 0 /K in Pb-Pb collisions shows significant suppression relative to pp collisions and decreases towards more central collisions. In contrast, the φ(1020)/K ratio does not show any suppression. Furthermore, the measured K * (892) 0 /K ratio in central Pb-Pb collisions is significantly suppressed with respect to the expectations based on a thermal model calculation, while the φ(1020)/K ratio agrees with the model prediction. These measurements are an experimental demonstration of rescattering of K * (892) 0 decay products in the hadronic phase of the collisions. The K * (892) 0 /K yield ratios in Pb-Pb and pp collisions are used to estimate the time duration between chemical and kinetic freeze-out, which is found to be ∼ 4-7 fm/c for central collisions. The p T-differential ratios of K * (892) 0 /K, φ(1020)/K, K * (892) 0 /π , φ(1020)/π , p/K * (892) 0 and p/φ (1020) are also presented for Pb-Pb and pp collisions at √ s NN = 5.02 TeV. These ratios show that the rescattering effect is predominantly a low-p T phenomenon.
The production of the (1520) baryonic resonance has been measured at midrapidity in inelastic pp ... more The production of the (1520) baryonic resonance has been measured at midrapidity in inelastic pp collisions at √ s = 7 TeV and in p-Pb collisions at √ s NN = 5.02 TeV for non-single diffractive events and in multiplicity classes. The resonance is reconstructed through its hadronic decay channel (1520) → pK − and the charge conjugate with the ALICE detector. The integrated yields and mean transverse momenta are calculated from the measured transverse momentum distributions in pp and p-Pb collisions. The mean transverse momenta follow mass ordering as previously observed for other hyperons in the same collision systems. A Blast-Wave function constrained by other light hadrons (π , K, K 0 S , p,) describes the shape of the (1520) transverse momentum distribution up to 3.5 GeV/c in p-Pb collisions. In the framework of this model, this observation suggests that the (1520) resonance participates in the same collective radial flow as other light hadrons. The ratio of the yield of (1520) to the yield of the ground state particle remains constant as a function of charged-particle multiplicity, suggesting that there is no net effect of the hadronic phase in p-Pb collisions on the (1520) yield.
The ALICE collaboration performed the first rapidity-differential measurement of coherent J/ψ pho... more The ALICE collaboration performed the first rapidity-differential measurement of coherent J/ψ photoproduction in ultra-peripheral Pb-Pb collisions at a center-of-mass energy √ s NN = 5.02 TeV. The J/ψ is detected via its dimuon decay in the forward rapidity region (−4.0 < y < −2.5) for events where the hadronic activity is required to be minimal. The analysis is based on an event sample corresponding to an integrated luminosity of about 750 µb −1. The cross section for coherent J/ψ production is presented in six rapidity bins. The results are compared with theoretical models for coherent J/ψ photoproduction. These comparisons indicate that gluon shadowing effects play a role in the photoproduction process. The ratio of ψ to J/ψ coherent photoproduction cross sections was measured and found to be consistent with that measured for photoproduction off protons.
The production of charm jets in proton-proton collisions at a center-of-mass energy of $$ \sqrt{s... more The production of charm jets in proton-proton collisions at a center-of-mass energy of $$ \sqrt{s}=7 $$ s = 7 TeV was measured with the ALICE detector at the CERN Large Hadron Collider. The measurement is based on a data sample corresponding to a total integrated luminosity of 6.23 nb−1, collected using a minimum-bias trigger. Charm jets are identified by the presence of a D0 meson among their constituents. The D0 mesons are reconstructed from their hadronic decay D0 →K−π+. The D0-meson tagged jets are reconstructed using tracks of charged particles (track-based jets) with the anti-k T algorithm in the jet transverse momentum range $$ 5
The pseudorapidity density of charged particles, dN ch /dη, in p-Pb collisions has been measured ... more The pseudorapidity density of charged particles, dN ch /dη, in p-Pb collisions has been measured at a centreof-mass energy per nucleon-nucleon pair of √ 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 dN ch /dη 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 √ 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 dN ch /dη distribution. Saturation-based models reproduce the distributions well for η > −1.3. The dN ch /dη is also measured for different centrality estimators, based both on the chargedparticle 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.
The production yield of prompt D mesons and their elliptic flow coefficient v 2 were measured wit... more The production yield of prompt D mesons and their elliptic flow coefficient v 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 $$ \sqrt{s_{\mathrm{NN}}}=5.02 $$ s N N = 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 v 2 coefficient is found to be sensitive to the event-shape selection confirming a correlation between the D-m...
The ALICE Collaboration reports the measurement of semi-inclusive distributions of charged-partic... more The ALICE Collaboration reports the measurement of semi-inclusive distributions of charged-particle jets recoiling from a high-transverse momentum trigger hadron in p-Pb collisions at √ s NN = 5.02 TeV. Jets are reconstructed from charged-particle tracks using the anti-k T algorithm with resolution parameter R = 0.2 and 0.4. A data-driven statistical approach is used to correct the uncorrelated background jet yield. Recoil jet distributions are reported for jet transverse momentum 15 < p ch T,jet < 50 GeV/c and are compared in various intervals of p-Pb event activity, based on charged-particle multiplicity and zero-degree neutral energy in the forward (Pb-going) direction. The semi-inclusive observable is self-normalized and such comparisons do not require the interpretation of p-Pb event activity in terms of collision geometry, in contrast to inclusive jet observables. These measurements provide new constraints on the magnitude of jet quenching in small systems at the LHC. In p-Pb collisions with high event activity, the average medium-induced out-of-cone energy transport for jets with R = 0.4 and 15 < p ch T,jet < 50 GeV/c is measured to be less than 0.4 GeV/c at 90% confidence, which is over an order of magnitude smaller than a similar measurement for central Pb-Pb collisions at √ s NN = 2.76 TeV. Comparison is made to theoretical calculations of jet quenching in small systems, and to inclusive jet measurements in p-Pb collisions selected by event activity at the LHC and in d-Au collisions at RHIC.
Transverse momentum spectra and nuclear modification factors of charged particles in Xe-Xe collis... more Transverse momentum spectra and nuclear modification factors of charged particles in Xe-Xe collisions at √ s NN = 5.
The measurement of azimuthal correlations of charged particles is presented for Pb-Pb collisions ... more The measurement of azimuthal correlations of charged particles is presented for Pb-Pb collisions at √ s NN = 2.76 TeV and p-Pb collisions at √ s NN = 5.02 TeV with the ALICE detector at the CERN Large Hadron Collider. These correlations are measured for the second, third and fourth order flow vector in the pseudorapidity region |η| < 0.8 as a function of centrality and transverse momentum p T using two observables, to search for evidence of p T-dependent flow vector fluctuations. For Pb-Pb collisions at 2.76 TeV, the measurements indicate that p T-dependent fluctuations are only present for the second order flow vector. Similar results have been found for p-Pb collisions at 5.02 TeV. These measurements are compared to hydrodynamic model calculations with event-by-event geometry fluctuations in the initial state to constrain the initial conditions and transport properties of the matter created in Pb-Pb and p-Pb collisions.
This is an addendum to the article JHEP 11 (2015) 205 [1]. The figures 3 (right), 4 (right) and 5... more This is an addendum to the article JHEP 11 (2015) 205 [1]. The figures 3 (right), 4 (right) and 5 are updated with published results on non-prompt J/ψ-meson production from the CMS collaboration [2]. ArXiv ePrint: 1506.06604 In [1] the average nuclear modification factor R AA of D 0 , D + and D * + mesons in Pb-Pb collisions at √ s NN = 2.76 TeV measured by ALICE was compared with that of non-prompt J/ψ mesons from B-meson decays measured by the CMS collaboration using 2010 data (7.28 µb −1) [3]. A higher-precision measurement based on 2011 data (152 µb −1) was recently published by the CMS collaboration [2]. The measurement for the p T interval 6.5-30 GeV/c is carried out in three rapidity intervals, including |y| < 1.2, which is more similar to that of D mesons (|y| < 0.5). Figure 1 shows the average of the D 0 , D + and D * + nuclear modification factors as a function of centrality in 8 < p T < 16 GeV/c, compared with the R AA of non-prompt J/ψ mesons with 6.5 < p T < 30 GeV/c [2]. The latter is significantly higher than that of the D mesons in the five centrality intervals from 0-10% to 40-50%. For example, the average difference of the R AA values of D mesons and non-prompt J/ψ mesons in the 0-10% and 10-20% centrality classes is larger than zero with a significance of 3.4 σ, obtained including the systematic uncertainties, and taking into account their correlation between Open Access, Copyright CERN, for the benefit of the ALICE Collaboration. Article funded by SCOAP 3 .
The second and the third order anisotropic flow, V 2 and V 3 , are mostly determined by the corre... more The second and the third order anisotropic flow, V 2 and V 3 , are mostly determined by the corresponding initial spatial anisotropy coefficients, ε 2 and ε 3 , in the initial density distribution. In addition to their dependence on the same order initial anisotropy coefficient, higher order anisotropic flow, V n (n > 3), can also have a significant contribution from lower order initial anisotropy coefficients, which leads to mode-coupling effects. In this Letter we investigate the linear and non-linear modes in higher order anisotropic flow V n for n = 4, 5, 6 with the ALICE detector at the Large Hadron Collider. The measurements are done for particles in the pseudorapidity range |η| < 0.8 and the transverse momentum range 0.2 < p T < 5.0 GeV/c as a function of collision centrality. The results are compared with theoretical calculations and provide important constraints on the initial conditions, including initial spatial geometry and its fluctuations, as well as the ratio of the shear viscosity to entropy density of the produced system.
The measurement of two-particle angular correlations is a powerful tool to study jet quenching in... more The measurement of two-particle angular correlations is a powerful tool to study jet quenching in a p T region inaccessible by direct jet identification. In these measurements pseudorapidity (Δη) and azimuthal (Δφ) differences are used to extract the shape of the nearside peak formed by particles associated with a higher p T trigger particle (1 < p T;trig < 8 GeV=c). A combined fit of the nearside peak and long-range correlations is applied to the data allowing the extraction of the centrality evolution of the peak shape in Pb-Pb collisions at ffiffiffiffiffiffiffi ffi s NN p ¼ 2.76 TeV. A significant broadening of the peak in the Δη direction at low p T is found from peripheral to central collisions, which vanishes above 4 GeV=c, while in the Δφ direction the peak is almost independent of centrality. For the 10% most central collisions and 1 < p T;assoc < 2 GeV=c, 1 < p T;trig < 3 GeV=c a novel feature is observed: a depletion develops around the center of the peak. The results are compared to pp collisions at the same center of mass energy and AMPT model simulations. The comparison to the investigated models suggests that the broadening and the development of the depletion is connected to the strength of radial and longitudinal flow.
The study of (anti-)deuteron production in pp collisions has proven to be a powerful tool to inve... more The study of (anti-)deuteron production in pp collisions has proven to be a powerful tool to investigate the formation mechanism of loosely bound states in high-energy hadronic collisions. In this paper the production of $$\text {(anti-)deuterons}$$ (anti-)deuterons is studied as a function of the charged particle multiplicity in inelastic pp collisions at $$\sqrt{s}=13$$ s = 13 TeV using the ALICE experiment. Thanks to the large number of accumulated minimum bias events, it has been possible to measure (anti-)deuteron production in pp collisions up to the same charged particle multiplicity ($${\mathrm {d} N_{ch}/\mathrm {d} \eta } \sim 26$$ d N ch / d η ∼ 26 ) as measured in p–Pb collisions at similar centre-of-mass energies. Within the uncertainties, the deuteron yield in pp collisions resembles the one in p–Pb interactions, suggesting a common formation mechanism behind the production of light nuclei in hadronic interactions. In this context the measurements are compared with the...
Measurements of K * (892) 0 and φ(1020) resonance production in Pb-Pb and pp collisions at √ s NN... more Measurements of K * (892) 0 and φ(1020) resonance production in Pb-Pb and pp collisions at √ s NN = 5.02 TeV with the ALICE detector at the Large Hadron Collider are reported. The resonances are measured at midrapidity (| y| < 0.5) via their hadronic decay channels and the transverse momentum (p T) distributions are obtained for various collision centrality classes up to p T = 20 GeV/c. The p T-integrated yield ratio K * (892) 0 /K in Pb-Pb collisions shows significant suppression relative to pp collisions and decreases towards more central collisions. In contrast, the φ(1020)/K ratio does not show any suppression. Furthermore, the measured K * (892) 0 /K ratio in central Pb-Pb collisions is significantly suppressed with respect to the expectations based on a thermal model calculation, while the φ(1020)/K ratio agrees with the model prediction. These measurements are an experimental demonstration of rescattering of K * (892) 0 decay products in the hadronic phase of the collisions. The K * (892) 0 /K yield ratios in Pb-Pb and pp collisions are used to estimate the time duration between chemical and kinetic freeze-out, which is found to be ∼ 4-7 fm/c for central collisions. The p T-differential ratios of K * (892) 0 /K, φ(1020)/K, K * (892) 0 /π , φ(1020)/π , p/K * (892) 0 and p/φ (1020) are also presented for Pb-Pb and pp collisions at √ s NN = 5.02 TeV. These ratios show that the rescattering effect is predominantly a low-p T phenomenon.
The production of the (1520) baryonic resonance has been measured at midrapidity in inelastic pp ... more The production of the (1520) baryonic resonance has been measured at midrapidity in inelastic pp collisions at √ s = 7 TeV and in p-Pb collisions at √ s NN = 5.02 TeV for non-single diffractive events and in multiplicity classes. The resonance is reconstructed through its hadronic decay channel (1520) → pK − and the charge conjugate with the ALICE detector. The integrated yields and mean transverse momenta are calculated from the measured transverse momentum distributions in pp and p-Pb collisions. The mean transverse momenta follow mass ordering as previously observed for other hyperons in the same collision systems. A Blast-Wave function constrained by other light hadrons (π , K, K 0 S , p,) describes the shape of the (1520) transverse momentum distribution up to 3.5 GeV/c in p-Pb collisions. In the framework of this model, this observation suggests that the (1520) resonance participates in the same collective radial flow as other light hadrons. The ratio of the yield of (1520) to the yield of the ground state particle remains constant as a function of charged-particle multiplicity, suggesting that there is no net effect of the hadronic phase in p-Pb collisions on the (1520) yield.
The ALICE collaboration performed the first rapidity-differential measurement of coherent J/ψ pho... more The ALICE collaboration performed the first rapidity-differential measurement of coherent J/ψ photoproduction in ultra-peripheral Pb-Pb collisions at a center-of-mass energy √ s NN = 5.02 TeV. The J/ψ is detected via its dimuon decay in the forward rapidity region (−4.0 < y < −2.5) for events where the hadronic activity is required to be minimal. The analysis is based on an event sample corresponding to an integrated luminosity of about 750 µb −1. The cross section for coherent J/ψ production is presented in six rapidity bins. The results are compared with theoretical models for coherent J/ψ photoproduction. These comparisons indicate that gluon shadowing effects play a role in the photoproduction process. The ratio of ψ to J/ψ coherent photoproduction cross sections was measured and found to be consistent with that measured for photoproduction off protons.
The production of charm jets in proton-proton collisions at a center-of-mass energy of $$ \sqrt{s... more The production of charm jets in proton-proton collisions at a center-of-mass energy of $$ \sqrt{s}=7 $$ s = 7 TeV was measured with the ALICE detector at the CERN Large Hadron Collider. The measurement is based on a data sample corresponding to a total integrated luminosity of 6.23 nb−1, collected using a minimum-bias trigger. Charm jets are identified by the presence of a D0 meson among their constituents. The D0 mesons are reconstructed from their hadronic decay D0 →K−π+. The D0-meson tagged jets are reconstructed using tracks of charged particles (track-based jets) with the anti-k T algorithm in the jet transverse momentum range $$ 5
The pseudorapidity density of charged particles, dN ch /dη, in p-Pb collisions has been measured ... more The pseudorapidity density of charged particles, dN ch /dη, in p-Pb collisions has been measured at a centreof-mass energy per nucleon-nucleon pair of √ 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 dN ch /dη 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 √ 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 dN ch /dη distribution. Saturation-based models reproduce the distributions well for η > −1.3. The dN ch /dη is also measured for different centrality estimators, based both on the chargedparticle 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.
The production yield of prompt D mesons and their elliptic flow coefficient v 2 were measured wit... more The production yield of prompt D mesons and their elliptic flow coefficient v 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 $$ \sqrt{s_{\mathrm{NN}}}=5.02 $$ s N N = 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 v 2 coefficient is found to be sensitive to the event-shape selection confirming a correlation between the D-m...
The ALICE Collaboration reports the measurement of semi-inclusive distributions of charged-partic... more The ALICE Collaboration reports the measurement of semi-inclusive distributions of charged-particle jets recoiling from a high-transverse momentum trigger hadron in p-Pb collisions at √ s NN = 5.02 TeV. Jets are reconstructed from charged-particle tracks using the anti-k T algorithm with resolution parameter R = 0.2 and 0.4. A data-driven statistical approach is used to correct the uncorrelated background jet yield. Recoil jet distributions are reported for jet transverse momentum 15 < p ch T,jet < 50 GeV/c and are compared in various intervals of p-Pb event activity, based on charged-particle multiplicity and zero-degree neutral energy in the forward (Pb-going) direction. The semi-inclusive observable is self-normalized and such comparisons do not require the interpretation of p-Pb event activity in terms of collision geometry, in contrast to inclusive jet observables. These measurements provide new constraints on the magnitude of jet quenching in small systems at the LHC. In p-Pb collisions with high event activity, the average medium-induced out-of-cone energy transport for jets with R = 0.4 and 15 < p ch T,jet < 50 GeV/c is measured to be less than 0.4 GeV/c at 90% confidence, which is over an order of magnitude smaller than a similar measurement for central Pb-Pb collisions at √ s NN = 2.76 TeV. Comparison is made to theoretical calculations of jet quenching in small systems, and to inclusive jet measurements in p-Pb collisions selected by event activity at the LHC and in d-Au collisions at RHIC.
Transverse momentum spectra and nuclear modification factors of charged particles in Xe-Xe collis... more Transverse momentum spectra and nuclear modification factors of charged particles in Xe-Xe collisions at √ s NN = 5.
The measurement of azimuthal correlations of charged particles is presented for Pb-Pb collisions ... more The measurement of azimuthal correlations of charged particles is presented for Pb-Pb collisions at √ s NN = 2.76 TeV and p-Pb collisions at √ s NN = 5.02 TeV with the ALICE detector at the CERN Large Hadron Collider. These correlations are measured for the second, third and fourth order flow vector in the pseudorapidity region |η| < 0.8 as a function of centrality and transverse momentum p T using two observables, to search for evidence of p T-dependent flow vector fluctuations. For Pb-Pb collisions at 2.76 TeV, the measurements indicate that p T-dependent fluctuations are only present for the second order flow vector. Similar results have been found for p-Pb collisions at 5.02 TeV. These measurements are compared to hydrodynamic model calculations with event-by-event geometry fluctuations in the initial state to constrain the initial conditions and transport properties of the matter created in Pb-Pb and p-Pb collisions.
This is an addendum to the article JHEP 11 (2015) 205 [1]. The figures 3 (right), 4 (right) and 5... more This is an addendum to the article JHEP 11 (2015) 205 [1]. The figures 3 (right), 4 (right) and 5 are updated with published results on non-prompt J/ψ-meson production from the CMS collaboration [2]. ArXiv ePrint: 1506.06604 In [1] the average nuclear modification factor R AA of D 0 , D + and D * + mesons in Pb-Pb collisions at √ s NN = 2.76 TeV measured by ALICE was compared with that of non-prompt J/ψ mesons from B-meson decays measured by the CMS collaboration using 2010 data (7.28 µb −1) [3]. A higher-precision measurement based on 2011 data (152 µb −1) was recently published by the CMS collaboration [2]. The measurement for the p T interval 6.5-30 GeV/c is carried out in three rapidity intervals, including |y| < 1.2, which is more similar to that of D mesons (|y| < 0.5). Figure 1 shows the average of the D 0 , D + and D * + nuclear modification factors as a function of centrality in 8 < p T < 16 GeV/c, compared with the R AA of non-prompt J/ψ mesons with 6.5 < p T < 30 GeV/c [2]. The latter is significantly higher than that of the D mesons in the five centrality intervals from 0-10% to 40-50%. For example, the average difference of the R AA values of D mesons and non-prompt J/ψ mesons in the 0-10% and 10-20% centrality classes is larger than zero with a significance of 3.4 σ, obtained including the systematic uncertainties, and taking into account their correlation between Open Access, Copyright CERN, for the benefit of the ALICE Collaboration. Article funded by SCOAP 3 .
The second and the third order anisotropic flow, V 2 and V 3 , are mostly determined by the corre... more The second and the third order anisotropic flow, V 2 and V 3 , are mostly determined by the corresponding initial spatial anisotropy coefficients, ε 2 and ε 3 , in the initial density distribution. In addition to their dependence on the same order initial anisotropy coefficient, higher order anisotropic flow, V n (n > 3), can also have a significant contribution from lower order initial anisotropy coefficients, which leads to mode-coupling effects. In this Letter we investigate the linear and non-linear modes in higher order anisotropic flow V n for n = 4, 5, 6 with the ALICE detector at the Large Hadron Collider. The measurements are done for particles in the pseudorapidity range |η| < 0.8 and the transverse momentum range 0.2 < p T < 5.0 GeV/c as a function of collision centrality. The results are compared with theoretical calculations and provide important constraints on the initial conditions, including initial spatial geometry and its fluctuations, as well as the ratio of the shear viscosity to entropy density of the produced system.
The measurement of two-particle angular correlations is a powerful tool to study jet quenching in... more The measurement of two-particle angular correlations is a powerful tool to study jet quenching in a p T region inaccessible by direct jet identification. In these measurements pseudorapidity (Δη) and azimuthal (Δφ) differences are used to extract the shape of the nearside peak formed by particles associated with a higher p T trigger particle (1 < p T;trig < 8 GeV=c). A combined fit of the nearside peak and long-range correlations is applied to the data allowing the extraction of the centrality evolution of the peak shape in Pb-Pb collisions at ffiffiffiffiffiffiffi ffi s NN p ¼ 2.76 TeV. A significant broadening of the peak in the Δη direction at low p T is found from peripheral to central collisions, which vanishes above 4 GeV=c, while in the Δφ direction the peak is almost independent of centrality. For the 10% most central collisions and 1 < p T;assoc < 2 GeV=c, 1 < p T;trig < 3 GeV=c a novel feature is observed: a depletion develops around the center of the peak. The results are compared to pp collisions at the same center of mass energy and AMPT model simulations. The comparison to the investigated models suggests that the broadening and the development of the depletion is connected to the strength of radial and longitudinal flow.
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