Coherent psi (2S) photo-production in ultra-peripheral Pb-Pb collisions at root s(NN)=2.76TeV

We have performed the first measurement of the coherent psi(2S) photo-production cross section in ultraperipheral Pb-Pb collisions at the LHC. This charmonium excited state is reconstructed via the psi(2S) -> l(+)l(-) and ->(2S) -> J/psi pi(+)pi(-) decays, where the J/psi decays into two leptons. The analysis is based on an event sample corresponding to an integrated luminosity of about 22 mu b(-1). The cross section for coherent psi(2S) production in the rapidity interval -0.9 <y <0.9is d sigma(coh)(psi(2S))/dy = 0.83 +/- 0.19 (stat+syst) mb. The psi(2S) to J/psi coherent cross section ratio is 0.34(-0.07)(+0.08)(stat+syst). The obtained results are compared to predictions from theoretical models. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V.Peer reviewe

Energy dependence of ϕ meson production at forward rapidity in pp collisions at the LHC

The production of $\phi$ mesons has been studied in pp collisions at LHC energies with the ALICE detector via the dimuon decay channel in the rapidity region $2.5< y < 4$. Measurements of the differential cross section $\mathrm{d}^2\sigma /\mathrm{d}y \mathrm{d}p_{\mathrm {T}}$ are presented as a function of the transverse momentum ($p_{\mathrm {T}}$) at the center-of-mass energies $\sqrt{s}=5.02$, 8 and 13 TeV and compared with the ALICE results at midrapidity. The differential cross sections at $\sqrt{s}=5.02$ and 13 TeV are also studied in several rapidity intervals as a function of $p_{\mathrm {T}}$, and as a function of rapidity in three $p_{\mathrm {T}}$ intervals. A hardening of the $p_{\mathrm {T}}$-differential cross section with the collision energy is observed, while, for a given energy, $p_{\mathrm {T}}$ spectra soften with increasing rapidity and, conversely, rapidity distributions get slightly narrower at increasing $p_{\mathrm {T}}$. The new results, complementing the published measurements at $\sqrt{s}=2.76$ and 7 TeV, allow one to establish the energy dependence of $\phi$ meson production and to compare the measured cross sections with phenomenological models. None of the considered models manages to describe the evolution of the cross section with $p_{\mathrm {T}}$ and rapidity at all the energies.publishedVersio

ϒ production in p–Pb collisions at sNN=8.16 TeV

ϒproduction in p–Pbinteractions is studied at the centre-of-mass energy per nucleon–nucleon collision √sNN=8.16TeV with the ALICE detector at the CERN LHC. The measurement is performed reconstructing bottomonium resonances via their dimuon decay channel, in the centre-of-mass rapidity intervals 2.03 &lt;3.53and −4.46 &lt;−2.96, down to zero transverse momentum. In this work, results on the ϒ(1S) production cross section as a function of rapidity and transverse momentum are presented. The corresponding nuclear modification factor shows a suppression of the ϒ(1S) yields with respect to ppcollisions, both at forward and backward rapidity. This suppression is stronger in the low transverse momentum region and shows no significant dependence on the centrality of the interactions. Furthermore, the ϒ(2S) nuclear modification factor is evaluated, suggesting a suppression similar to that of the ϒ(1S). A first measurement of the ϒ(3S) has also been performed. Finally, results are compared with previous ALICE measurements in p–Pbcollisions at √sNN=5.02TeV and with theoretical calculations

Measurement of charged jet production cross sections and nuclear modification in p-Pb collisions at root s(NN)=5.02 TeV

Charged jet production cross sections in p-Pb collisions at root s(NN) = 5.02 TeV measured with the ALICE detector at the LHC are presented. Using the anti-k(T) algorithm, jets have been reconstructed in the central rapidity region from charged particles with resolution parameters R = 0.2 and R = 0.4. The reconstructed jets have been corrected for detector effects and the underlying event background. To calculate the nuclear modification factor, R-pPb, of charged jets in p-Pb collisions, a pp reference was constructed by scaling previously measured charged jet spectra at root s = 7 TeV. In the transverse momentum range 20Peer reviewe

Two-particle differential transverse momentum and number density correlations in p-Pb collisions at 5.02 TeV and Pb-Pb collisions at 2.76 TeV at the CERN Large Hadron Collider

We present measurements of two-particle differential number correlation functions R2 and transverse momentum correlation functions P2, obtained from p-Pb collisions at 5.02 TeV and Pb-Pb collisions at 2.76 TeV. The results are obtained by using charged particles in the pseudorapidity range |\u3b7|<1.0 and transverse momentum range 0.2<2.0 GeV/c as a function of pair separation in pseudorapidity, |\u394\u3b7|, azimuthal angle \u394\u3c6, and for several charged-particle multiplicity classes. Measurements are carried out for like-sign and unlike-sign charged-particle pairs separately and combined to obtain charge-independent and charge-dependent correlation functions. We study the evolution of the width of the near-side peak of these correlation functions with collision centrality. Additionally, we study Fourier decompositions of the correlators in \u394\u3c6 as a function of pair separation |\u394\u3b7|. Significant differences in the dependence of their harmonic coefficients on multiplicity classes are found. These differences can be exploited, in theoretical models, to obtain further insight into charged-particle production and transport in heavy-ion collisions. Moreover, an upper limit of nonflow contributions to flow coefficients vn measured in Pb-Pb collisions based on the relative strength of Fourier coefficients measured in p-Pb interactions is estimated

Systematic studies of correlations between different order flow harmonics in Pb-Pb collisions at root s(NN)=2.76 TeV

The correlations between event-by-event fluctuations of anisotropic flow harmonic amplitudes have been measured in Pb-Pb collisions at root s(NN) = 2.76 TeV with the ALICE detector at the Large Hadron Collider. The results are reported in terms of multiparticle correlation observables dubbed symmetric cumulants. These observables are robust against biases originating from nonflow effects. The centrality dependence of correlations between the higher order harmonics (the quadrangular v(4) and pentagonal v(5) flow) and the lower order harmonics (the elliptic v(2) and triangular v(3) flow) is presented. The transverse momentum dependences of correlations between v(3) and v(2) and between v(4) and v(2) are also reported. The results are compared to calculations from viscous hydrodynamics and a multiphase transport (AMPT) model calculations. The comparisons to viscous hydrodynamic models demonstrate that the different order harmonic correlations respond differently to the initial conditions and the temperature dependence of the ratio of shear viscosity to entropy density (eta/s). Asmall average value of eta/s is favored independent of the specific choice of initial conditions in the models. The calculations with the AMPT initial conditions yield results closest to the measurements. Correlations among the magnitudes of v(2), v(3), and v(4) show moderate p(T) dependence in midcentral collisions. This might be an indication of possible viscous corrections to the equilibrium distribution at hadronic freeze-out, which might help to understand the possible contribution of bulk viscosity in the hadronic phase of the system. Together with existing measurements of individual flow harmonics, the presented results provide further constraints on the initial conditions and the transport properties of the system produced in heavy-ion collisions

Probing the chiral magnetic wave with charge-dependent flow measurements in Pb-Pb collisions at the LHC

The Chiral MagneticWave (CMW) phenomenon is essential to provide insights into the strong interaction in QCD, the properties of the quark-gluon plasma, and the topological characteristics of the early universe, offering a deeper understanding of fundamental physics in high-energy collisions. Measurements of the charge-dependent anisotropic flow coefficients are studied in Pb-Pb collisions at center-of-mass energy per nucleon-nucleon collision v sNN = 5.02TeV to probe the CMW. In particular, the slope of the normalized difference in elliptic (v2) and triangular (v3) flow coefficients of positively and negatively charged particles as a function of their event-wise normalized number difference, is reported for inclusive and identified particles. The slope rNorm 3 is found to be larger than zero and to have a magnitude similar to rNorm 2, thus pointing to a large background contribution for these measurements. Furthermore, rNorm 2 can be described by a blast wave model calculation that incorporates local charge conservation. In addition, using the event shape engineering technique yields a fraction of CMW (fCMW) contribution to this measurement which is compatible with zero. This measurement provides the very first upper limit for fCMW, and in the 10-60% centrality interval it is found to be 26% (38%) at 95% (99.7%) confidence level

Measurement of electrons from semileptonic heavy-flavor hadron decays in p

The p(T)-differential production cross section of electrons from semileptonic decays of heavy-flavor hadrons has been measured at midrapidity in proton-proton collisions at root s = 2.76 TeV in the transverse momentum range 0.5 < p(T) < 12 GeV/c with the ALICE detector at the LHC. The analysis was performed using minimum bias events and events triggered by the electromagnetic calorimeter. Predictions from perturbative QCD calculations agree with the data within the theoretical and experimental uncertainties

Measurement of non-prompt D0-meson elliptic flow in Pb–Pb collisions at sqrt{s_NN} = 5.02 TeV

The elliptic flow (v2) of D mesons from beauty-hadron decays (non-prompt D) was measured in midcentral (30–50%) Pb–Pb collisions at a centre-of-mass energy per nucleon pair sNN=5.02 TeV with the ALICE detector at the LHC. The D mesons were reconstructed at midrapidity (| y| &lt; 0.8) from their hadronic decay D → K -π + , in the transverse momentum interval 2 &lt; pT&lt; 12 GeV/c. The result indicates a positive v2 for non-prompt D mesons with a significance of 2.7 σ . The non-prompt D -meson v2 is lower than that of prompt non-strange D mesons with 3.2 σ significance in 2&lt;8GeV/c , and compatible with the v2 of beauty-decay electrons. Theoretical calculations of beauty-quark transport in a hydrodynamically expanding medium describe the measurement within uncertainties

Accessing the strong interaction between Λ baryons and charged kaons with the femtoscopy technique at the LHC

The interaction between Lambda baryons and kaons/antikaons is a crucial ingredient for the strangeness S= 0 and S= -2 sector of the meson-baryon interaction at low energies. In particular, the Lambda(K) over bar might help in understanding the origin of states such as the Xi(1620), whose nature and properties are still under debate. Experimental data on Lambda-K and Lambda-(K) over bar systems are scarce, leading to large uncertainties and tension between the available theoretical predictions constrained by such data. In this Letter we present the measurements of Lambda-K+ circle plus (Lambda) over bar -K- and Lambda-K- circle plus (Lambda) over bar -K+ correlations obtained in the high-multiplicity triggered data sample in pp collisions at root s= 13TeV recorded by ALICE at the LHC. The correlation function for both pairs is modeled using the Lednicky-Lyuboshits analytical formula and the corresponding scattering parameters are extracted. The Lambda-K- circle plus (Lambda) over bar -K+ correlations show the presence of several structures at relative momenta k* above 200 MeV/c, compatible with the Omega baryon, the Xi(1690), and Xi(1820) resonances decaying into Lambda-K- pairs. The low k* region in the Lambda-K- circle plus (Lambda) over bar -K+ also exhibits the presence of the Xi(1620) state, expected to strongly couple to the measured pair. The presented data allow to access the Lambda K+ and Lambda K- strong interaction with an unprecedented precision and deliver the first experimental observation of the Xi(1620) decaying into Lambda K-. (c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP3