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Register a new userMeasurement of $B^+$, $B^0$ and $Lambda_b^0$ production in $pmkern 1mumathrm{Pb}$ collisions at $sqrt{s_mathrm{NN}}=8.16,{rm TeV}$
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The production of $B^+$, $B^0$ and $Lambda_b^0$ hadrons is studied in proton-lead collisions at a centre-of-mass energy per nucleon pair of $sqrt{s_mathrm{NN}}=8.16,{rm TeV}$ recorded with the LHCb detector at the LHC. The measurement uses a dataset corresponding to an integrated luminosity of $12.2pm0.3,mathrm{nb}^{-1}$ for the case where the proton beam is projected into the LHCb detector (corresponding to measuring hadron production at positive rapidity) and $18.6pm0.5,mathrm{nb}^{-1}$ for the lead beam projected into the LHCb detector (corresponding to measuring hadron production at negative rapidity). Nuclear effects are probed through double-differential cross-sections, forward-to-backward cross-section ratios and nuclear modification factors of the beauty hadrons. The double-differential cross-sections are measured as a function of the beauty-hadron transverse momentum and rapidity in the nucleon-nucleon centre-of-mass frame. Forward-to-backward cross-section ratios and nuclear modification factors indicate a significant nuclear suppression at positive rapidity. The ratio of $Lambda_b^0$ over $B^0$ production cross-sections is reported and is consistent with the corresponding measurement in $pp$~collisions.
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The production of $Upsilon(nS)$ mesons ($n=1,2,3$) in $p$Pb and Pb$p$ collisions at a centre-of-mass energy per nucleon pair $sqrt{s_{NN}}=8.16$ TeV is measured by the LHCb experiment, using a data sample corresponding to an integrated luminosity of 31.8 nb$^{-1}$. The $Upsilon(nS)$ mesons are reconstructed through their decays into two opposite-sign muons. The measurements comprise the differential production cross-sections of the $Upsilon(1S)$ and $Upsilon(2S)$ states, their forward-to-backward ratios and nuclear modification factors, performed as a function of the transverse momentum pt and rapidity in the nucleon-nucleon centre-of-mass frame $y^*$ of the $Upsilon(nS)$ states, in the kinematic range $p_{rm{T}}<25$ GeV/$c$ and $1.5<y^*<4.0$ ($-5.0<y^*<-2.5$) for $p$Pb (Pb$p$) collisions. In addition, production cross-sections for $Upsilon(3S)$ are measured integrated over phase space and the production ratios between all three $Upsilon(nS)$ states are determined. The measurements are compared to theoretical predictions and suppressions for quarkonium in $p$Pb collisions are observed.
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 of J/$psi$ mesons is studied in proton-lead collisions at the centre-of-mass energy per nucleon pair $sqrt{s_{text{NN}}}=8.16$ TeV with the LHCb detector at the LHC. The double differential cross-sections of prompt and nonprompt J/$psi$ production are measured as functions of the J/$psi$ transverse momentum and rapidity in the nucleon-nucleon centre-of-mass frame. Forward-to-backward ratios and nuclear modification factors are determined. The results are compared with theoretical calculations based on collinear factorisation using nuclear parton distribution functions, on the colour glass condensate or on coherent energy loss models.
This Letter reports the first measurement of prompt $chi_{c1}$ and $chi_{c2}$ charmonium production in nuclear collisions at Large Hadron Collider energies. The cross-section ratio $sigma(chi_{c2}) / sigma(chi_{c1})$ is measured in $p$Pb collisions at $sqrt{s_{NN}}$ = 8.16 TeV, collected with the LHCb experiment. The $chi_{c1,2}$ states are reconstructed via their decay to a $rm{J}/psi$ meson, subsequently decaying into a pair of oppositely charged muons, and a photon, which is reconstructed in the calorimeter or via its conversion in the detector material. The cross-section ratio is consistent with unity in the two considered rapidity regions. Comparison with a corresponding cross-section ratio previously measured by the LHCb collaboration in $pp$ collisions suggests that $chi_{c1}$ and $chi_{c2}$ states are similarly affected by nuclear effects occurring in $p$Pb collisions.
Heavy quarks, i.e. charm and beauty, are produced on a shorter time scale with respect to the strongly-interacting matter produced in high-energy heavy-ion collisions. Therefore, they are unique probes to study the mechanisms of parton energy loss, hadronisation and thermalization in the hot and dense state of matter. The nuclear modification factor ($R_{rm AA}$) and the elliptic flow ($v_{2}$) are two of the main experimental observables that allow us to investigate the interaction strength of heavy quarks with the medium. The most recent results on heavy-flavour production and elliptic flow measured by the ALICE collaboration in Pb--Pb collisions at $sqrt{s_mathrm{NN}}$ = 2.76 TeV will be discussed.
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