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Register a new userMeasurement of $mathrm{D}$-meson production as a function of charged-particle multiplicity in proton--proton collisions at $sqrt{s} = 13$ TeV with ALICE at the LHC
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Yoshini Bailung
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Heavy quarks (charm and beauty) are produced in hard-scattering processes and the study of their production in proton--proton (pp) collisions is an important test for calculations based on perturbative Quantum Chromodynamics (pQCD). Heavy-flavor production as a function of charged-particle multiplicity provides insight into the processes occurring at the partonic level and the interplay between the hard and soft particle production mechanisms in pp collisions. In this contribution, measurements of open heavy-flavor production as a function of multiplicity, via the study of the $mathrm{D}$-meson self-normalized yields in pp collisions at the center-of-mass energy of $sqrt{s} = 13$ TeV is presented. The $mathrm{D}$-meson self-normalized yield is found to increase stronger than linearly with increasing charged-particle multiplicity. The measurements are compared to theoretical model calculations, and with the results at $sqrt{s} = 7$ TeV.
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The measurement of the heavy-flavour production cross sections in pp collisions at the LHC will allow to test perturbative QCD calculations in a new energy domain. Moreover, within the physics program of the ALICE experiment, it will provide the reference for the study of medium effects in Pb-Pb collisions, where heavy quarks are regarded as sensitive probes of parton-medium interaction dynamics. We present the status and first preliminary results of charm and beauty production measurements with the ALICE experiment, using hadronic D meson decays and semi-leptonic D and B meson decays, including the first cross section measurement of muons from heavy flavour decays at forward rapidity. We also describe the preliminary cross section measurement for J/psi production, obtained using the di-electron decay channel at central rapidity and the di-muon decay channel at forward rapidity.
Proton-proton (pp) collisions have been used extensively as a reference for the study of interactions of larger colliding systems at the LHC. Recent measurements performed in high-multiplicity pp and proton-lead (p-Pb) collisions have shown features that are reminiscent of those observed in lead-lead (Pb-Pb) collisions. In this context, the study of identified particle spectra and yields as a function of multiplicity is a key tool for the understanding of similarities and differences between small and large systems. We report on the production of pions, kaons, protons, $K^{0}_{rm S}$, $Lambda$, $Xi$, $Omega$ and $K^{*0}$ as a function of multiplicity in pp collisions at $sqrt{s}=$ 7 TeV measured with the ALICE experiment. The work presented here represents the most comprehensive set of results on identified particle production in pp collisions at the LHC. Spectral shapes, studied both for individual particles and via particle ratios as a function of $p_{rm T}$, exhibit an evolution with charged particle multiplicity that is similar to the one observed in larger systems. In addition, results on the production of light flavour hadrons in pp collisions at $sqrt{s}=$ 13 TeV, the highest centre-of-mass energy ever reached in the laboratory, are also presented and compared with previous, lower energy results.
Recent measurements of charm-baryon production in proton--proton (pp) collisions at midrapidity by the ALICE collaboration showed that baryon-to-meson yield ratios are significantly higher than those measured in $rm e^+e^-$ collisions. The charm baryon-to-meson and charm baryon-to-baryon yield ratios provide unique information on hadronization mechanisms since the contributions from parton distribution function and parton--parton scattering terms cancel in the ratios. In this contribution, the first measurement of $rm Omega_{c}^{0}$ production via the hadronic decay channel $rm Omega_{c}^{0} rightarrow Omega^{-}pi^{+}$ (and its charge conjugate) in $2<p_{rm T}<12$ GeV/$c$ performed with the ALICE detector at midrapidity in pp collisions at $sqrt{s}=$ 13 TeV is presented. The $rm Omega_c^0/D^0$ and $rm Omega_c^0/Xi_c^0$ ratios multiplied by the decay branching ratio $rm BR(Omega_{c}^{0} rightarrow Omega^{-}pi^+)$, which is not experimentally measured, are compared to MC generators with fragmentation fractions based on $rm e^+e^-$ measurements and models including hadronization of charm quark via coalescence.
The production cross-sections of B mesons are measured in pp collisions at a centre-of-mass energy of 7 TeV, using data collected with the LHCb detector corresponding to a integrated luminosity of 0.36 fb-1. The B+, B0 and Bs0 mesons are reconstructed in the exclusive decays B+ -> J/psi K+, B0 -> J/psi K*0 and Bs0 -> J/psi phi, with J/psi -> mu+ mu-, K*0 -> K+ pi- and phi -> K+ K-. The differential cross-sections are measured as functions of B meson transverse momentum pT and rapidity y, in the range 0 < pT < 40 GeV/c and 2.0 < y < 4.5. The integrated cross-sections in the same pT and y ranges, including charge-conjugate states, are measured to be sigma(pp -> B+ + X) = 38.9 +- 0.3 (stat.) +- 2.5 (syst.) +- 1.3 (norm.) mub, sigma(pp -> B0 + X) = 38.1 +- 0.6 (stat.) +- 3.7 (syst.) +- 4.7 (norm.) mub, sigma(pp -> Bs0 + X) = 10.5 +- 0.2 (stat.) +- 0.8 (syst.) +- 1.0 (norm.) mub, where the third uncertainty arises from the pre-existing branching fraction measurements.
We report on the measurement of the Central Exclusive Production of charged particle pairs $h^{+}h^{-}$ ($h = pi, K, p$) with the STAR detector at RHIC in proton-proton collisions at $sqrt{s} = 200$ GeV. The charged particle pairs produced in the reaction $ppto p^prime+h^{+}h^{-}+p^prime$ are reconstructed from the tracks in the central detector, while the forward-scattered protons are measured in the Roman Pot system. Differential cross sections are measured in the fiducial region, which roughly corresponds to the square of the four-momentum transfers at the proton vertices in the range $0.04~mbox{GeV}^2 < -t_1 , -t_2 < 0.2~mbox{GeV}^2$, invariant masses of the charged particle pairs up to a few GeV and pseudorapidities of the centrally-produced hadrons in the range $|eta|<0.7$. The measured cross sections are compared to phenomenological predictions based on the Double Pomeron Exchange (DPE) model. Structures observed in the mass spectra of $pi^{+}pi^{-}$ and $K^{+}K^{-}$ pairs are consistent with the DPE model, while angular distributions of pions suggest a dominant spin-0 contribution to $pi^{+}pi^{-}$ production. The fiducial $pi^+pi^-$ cross section is extrapolated to the Lorentz-invariant region, which allows decomposition of the invariant mass spectrum into continuum and resonant contributions. The extrapolated cross section is well described by the continuum production and at least three resonances, the $f_0(980)$, $f_2(1270)$ and $f_0(1500)$, with a possible small contribution from the $f_0(1370)$. Fits to the extrapolated differential cross section as a function of $t_1$ and $t_2$ enable extraction of the exponential slope parameters in several bins of the invariant mass of $pi^+pi^-$ pairs. These parameters are sensitive to the size of the interaction region.
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