5 Search Results

A measurement of inclusive, prompt, and non-prompt J/ψ production in p-Pb collisions at a nucleon-nucleon centre-of-mass energy √^sNN = 5.02 TeV is presented. The inclusive J/ψ mesons are reconstructed in the dielectron decay channel at midrapidity down to a transverse momentum p_T = o. The inclusive J/ψ nuclear modification factor R_pPb is calculated by comparing the new results in p-Pb collisions to a recently measured proton-proton reference at the same centre-of-mass energy. Non-prompt J/ψ mesons, which originate from the decay of beauty hadrons, are separated from promptly produced J/ψ on a statistical basis for p_T larger than 1.0 GeV/c. Thesemore » results are based on the data sample collected by the ALICE detector during the 2016 LHC p-Pb run, corresponding to an integrated luminosity L_int = 292 ± 11 μb^–1, which is six times larger than the previous publications. The total uncertainty on the p_T-integrated inclusive J/ψ and non-prompt J/ψ cross section are reduced by a factor 1.7 and 2.2, respectively. The measured cross sections and R_pPb are compared with theoretical models that include various combinations of cold nuclear matter effects. From the non-prompt J/ψ production cross section, the bb¯ production cross section at midrapidity, dσ_bb¯/dy, and the total cross section extrapolated over full phase space, σ_bb¯, are derived.« less

Annihilation dynamics plays a fundamental role in the baryon–antibaryon interaction ($$B–\bar{B}$$) at low-energy and its strength and range are crucial in the assessment of possible baryonic bound states. Experimental data on annihilation cross sections are available for the $$p–\bar{p}$$ system but not in the low relative momentum region. Data regarding the $$B–\bar{B}$$ interaction with strange degrees of freedom are extremely scarce, hence the modeling of the annihilation contributions is mainly based on nucleon–antinucleon ($$N–\bar{N}$$) results, when available. In this letter we present a measurement of the $$p–\bar{p}$$, $$p–\bar{Λ}$$⊕$$p–{Λ}$$ and $$Λ–\bar{Λ}$$ interaction using correlation functions in the relative momentum space inmore » high-multiplicity triggered pp collisions at $$\sqrt{s}$$=13 TeV recorded by ALICE at the LHC. In the $$p–\bar{p}$$ system the couplings to the mesonic channels in different partial waves are extracted by adopting a coupled-channel approach with recent χEFT potentials. The inclusion of these inelastic channels provides good agreement with the data, showing a significant presence of the annihilation term down to zero momentum. Predictions obtained using the Lednický–Lyuboshits formula and scattering parameters obtained from heavy-ion collisions, hence mainly sensitive to elastic processes, are compared with the experimental $$p–\bar{Λ}$$⊕$$p–{Λ}$$ and $$Λ–\bar{Λ}$$ correlations. The model describes the $$Λ–\bar{Λ}$$ data and underestimates the $$p–\bar{Λ}$$⊕$$p–{Λ}$$ data in the region of momenta below 200 MeV/c. The observed deviation indicates a different contribution of annihilation channels to the two systems containing strange hadrons.« less

In quantum scattering processes between two particles, aspects characterizing the strong and Coulomb forces can be observed in kinematic distributions of the particle pairs. The sensitivity to the interaction potential reaches a maximum at low relative momentum and vanishing distance between the two particles. Ultrarelativistic heavy-ion collisions at the LHC provide an abundant source of many hadron species and can be employed as a measurement method of scattering parameters that is complementary to scattering experiments. This study confirms that momentum correlations of particles produced in Pb–Pb collisions at the LHC provide an accurate measurement of kaon–proton scattering parameters at lowmore » relative momentum, allowing precise access to the K^–p $$\rightarrow$$ K^–p process. This work also validates the femtoscopic measurement in ultrarelativistic heavy-ion collisions as an alternative to scattering experiments and a complementary tool to the study of exotic atoms with comparable precision. In this work, the first femtoscopic measurement of momentum correlations of K^–p (K⁺$$\bar{p}$$) and K⁺p (K^–$$\bar{p}$$) pairs in Pb–Pb collisions at centre-of-mass energy per nucleon pair of $$\sqrt{s_{NN}}$$ =5.02 TeV registered by the ALICE experiment is reported. The components of the K^–p complex scattering length are extracted and found to be $$\mathfrak{R}$$f₀ = -0.91±0.03(stat)$$^{+0.17}_{-0.03}$$(syst) and $$\mathfrak{T}$$f₀ =0.92±0.05(stat)$$^{+0.12}_{-0.33}$$(syst). The results are compared with chiral effective field theory predictions as well as with existing data from dedicated scattering and exotic kaonic atom experiments.« less

The ALICE Collaboration reports the first fully-corrected measurements of the N-subjettiness observable for track-based jets in heavy-ion collisions. This study is performed using data recorded in pp and Pb-Pb collisions at centre-of-mass energies of $$\sqrt{s}$$= 7 TeV and $$\sqrt{s{NN}}$$ = 2.76 TeV, respectively. In particular the ratio of 2-subjettiness to 1-subjettiness, τ₂/τ₁, which is sensitive to the rate of two-pronged jet substructure, is presented. Energy loss of jets traversing the strongly interacting medium in heavy-ion collisions is expected to change the rate of two-pronged substructure relative to vacuum. The results are presented for jets with a resolution parameter of Rmore » = 0.4 and charged jet transverse momentum of 40 ≤ pτ,_jet ≤ 60 GeV/c, which constitute a larger jet resolution and lower jet transverse momentum interval than previous measurements in heavy-ion collisions. This has been achieved by utilising a semi-inclusive hadron-jet coincidence technique to suppress the larger jet combinatorial background in this kinematic region. No significant modification of the τ₂/τ₁ observable for track-based jets in Pb-Pb collisions is observed relative to vacuum PYTHIA6 and PYTHIA8 references at the same collision energy. The measurements of τ₂/τ₁, together with the splitting aperture angle ΔR, are also performed in pp collisions at $$\sqrt{s}$$ = 7 TeV for inclusive jets. These results are compared with PYTHIA calculations at $$\sqrt{s}$$ = 7 TeV, in order to validate the model as a vacuum reference for the Pb-Pb centre-of-mass energy. The PYTHIA references for τ₂/τ₁ are shifted to larger values compared to the measurement in pp collisions. This hints at a reduction in the rate of two-pronged jets in Pb-Pb collisions compared to pp collisions.« less