1,579 research outputs found
Charm fragmentation fractions and c-cbar cross section in p–Pb collisions at sqrt(sNN)=5.02 TeV
No full textThe total charm-quark production cross section per unit of rapidity dσ (cc)/dy, and the fragmentation fractions of charm quarks to different charm-hadron species f (c → hc), are measured for the first time in p–Pb collisions at √sNN = 5.02 TeV at midrapidity (−0.96 < y < 0.04 in the centre-of-mass frame) using data collected by ALICE at the CERN LHC.
The results are obtained based on all the available measurements of prompt production of ground-state charm-hadron species: D0 , D+, D+s , and J/ψ mesons, and Lambda+c and Csi0c baryons. The resulting cross section is dσ (cc)/dy = 219.6 ± 6.3 (stat.) +10.5−11.8 (syst.) +8.3−2.9 (extr.) ± 5.4 (BR) ±4.6 (lumi.)±19.5 (rapidity shape)+15.0 (Omega0c ) mb, which is consistent with a binary scaling of pQCD calculations from pp collisions. The measured fragmentation fractions are compatible with those measured in pp collisions at √s = 5.02 and 13 TeV, showing an increase in the relative production rates of charm baryons with respect to charm mesons in pp and
p–Pb collisions compared with e+e− and e−p collisions. The pT -integrated nuclear modification factor of charm quarks, RpPb(cc) = 0.91 ± 0.04 (stat.)+0.08−0.09 (syst.)+0.05−0.03 (extr.) ±0.03 (lumi.), is found to be consistent with unity and with theoretical predictions including nuclear modifications of the
parton distribution functions
Differential phase tracking applied to Bragg gratings in multi-core fibre for high accuracy curvature measurement
No full textHigh resolution quasi-static and dynamic curvature measurements are made by differential interferometric phase measurement of fibre Bragg gratings in separate cores of a multi-core fibre. A DC curvature stability of 1 X 10(-3) m(-1) and an AC curvature resolution of 1 X 10(-4) m(-1)/Hz(1/2) are reported
Measurement of the production cross section of prompt baryons in p–Pb collisions at TeV
No full textThe transverse momentum (pT) differential production cross section of the promptly produced charm strange
baryon Csi_0c (and its charge conjugate anti_Csi_0c) is measured at midrapidity via its hadronic decay into π+ Sigma-
in p–Pb collisions at a centre-of-mass energy per nucleon–nucleon collision √sNN = 5.02 TeV with the ALICE detector at the LHC.
The Csi_0c nuclear modification factor (RpPb), calculated
from the cross sections in pp and p–Pb collisions, is
presented and compared with the RpPb of
+c
baryons. The
ratios between the pT-differential production cross section of
0c
baryons and those of D0 mesons and
+c
baryons are also
reported and compared with results at forward and backward
rapidity from the LHCb Collaboration. Themeasurements of
the production cross section of prompt 0c
baryons are compared
with a model based on perturbative QCD calculations
of charm-quark production cross sections, which includes
only cold nuclear matter effects in p–Pb collisions, and underestimates
the measurement by a factor of about 50. This discrepancy
is reduced when the data is compared with a model
that includes string formation beyond leading-colour approximation
or in which hadronisation is implemented via quark
coalescence. The pT-integrated cross section of prompt
0c
-baryon production at midrapidity extrapolated down to
pT = 0 is also reported. These measurements offer insights
and constraints for theoretical calculations of the hadronisation
process. Additionally, they provide inputs for the calculation
of the charm production cross section in p–Pb collisions
at midrapidity
Measurement of the Cross Sections of Ξ0 c and Ξ+ c Baryons and of the Branching-Fraction Ratio BRðΞ0 c → Ξ− e + νeÞ=BRðΞ0 c → Ξ− π + Þ in pp Collisions at ffiffi s p = 13 TeV
No full textThe pT-differential cross sections of prompt charm-strange baryons Ξ0c and Ξ+c were measured at midrapidity (|y|<0.5) in proton-proton (pp) collisions at a center-of-mass energy √s=13 TeV with the ALICE detector at the LHC. The Ξ0c baryon was reconstructed via both the semileptonic decay (Ξ−e+νe) and the hadronic decay (Ξ−π+) channels. The Ξ+c baryon was reconstructed via the hadronic decay (Ξ−π+π+) channel. The branching-fraction ratio BR(Ξ0c→Ξ−e+νe)/BR(Ξ0c→Ξ−π+)=1.38±0.14(stat)±0.22(syst) was measured with a total uncertainty reduced by a factor of about 3 with respect to the current world average reported by the Particle Data Group. The transverse momentum (pT) dependence of the Ξ0c- and Ξ+c-baryon production relative to the D0 meson and to the Σ0,+,++c- and Λ+c-baryon production are reported. The baryon-to-meson ratio increases toward low pT up to a value of approximately 0.3. The measurements are compared with various models that take different hadronization mechanisms into consideration. The results provide stringent constraints to these theoretical calculations and additional evidence that different processes are involved in charm hadronization in electron-positron (e+e−) and hadronic collisions
Measurement of the production cross section of prompt Xi(0)(c) baryons at midrapidity in pp collisions at root s=5.02 TeV
No full textTwo-particle Azimuthal correlations are measured with the ALICE apparatus in pp collisions at s=13 TeV to explore strangeness- and multiplicity-related effects in the fragmentation of jets and the transition regime between bulk and hard production, probed with the condition that a strange meson (KS0) or baryon (Λ) with transverse momentum pT> 3 GeV/c is produced. Azimuthal correlations between kaons or Λ hyperons with other hadrons are presented at midrapidity for a broad range of the trigger (3<20 GeV/c) and associated particle pT (1 GeV/
Dielectron production in proton-proton collisions at root s=7 TeV
No full textCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFINEP - FINANCIADORA DE ESTUDOS E PROJETOSFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOThe first measurement of e(+)e(-) pair production at mid-rapidity (vertical bar eta vertical bar(e) < 0.8) in pp collisions at root s = 7TeV with ALICE at the LHC is presented. The dielectron production is studied as a function of the invariant mass (m(ee )< 3.3 GeV/c(2)), the pair transverse momentum (p(T,ee) < 8 GeV/c), and the pair transverse impact parameter (DCA(ee)), i.e., the average distance of closest approach of the reconstructed electron and positron tracks to the collision vertex, normalised to its resolution. The results are compared with the expectations from a cocktail of known hadronic sources and are well described when PYTHIA is used to generate the heavy-flavour contributions. In the low-mass region (0.14 < m(ee) < 1.1 GeV/c(2)), prompt and non-prompt e(+)e(-) sources can be separated via the DCA(ee). In the intermediate-mass region (1.1 < m(ee) < 2.7 GeV/c(2)), a double-differential fit to the data in m(ee) and p(T,ee) and a fit of the DCA(ee) distribution allow the total cc and bb cross sections to be extracted. Two different event generators, PYTHIA and POWHEG, can reproduce the shape of the two-dimensional m(ee) and p(T,ee) spectra, as well as the shape , of the DCA(ee) distribution, reasonably well. However, differences in the c (c) over bar and b (b) over bar cross sections are observed when using the generators to extrapolate to full phase space. Finally, the ratio of inclusive to decay photons is studied via the measurement of virtual direct photons in the transverse-momentum range 1 < p(T) < 8 GeV/c. This is found to be unity within the statistical and systematic uncertainties and consistent with expectations from next-to-leading order perturbative quantum chromodynamic calculations.9147CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFINEP - FINANCIADORA DE ESTUDOS E PROJETOSFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFINEP - FINANCIADORA DE ESTUDOS E PROJETOSFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOSem informaçãoSem informaçãoSem informaçãoAgências de fomento estrangeiras apoiaram essa pesquisa, mais informações acesse artig
Dielectron production at midrapidity at low transverse momentum in peripheral and semi-peripheral Pb–Pb collisions at √sNN = 5.02 TeV
No full textThe first measurement of the e+e− pair production at low lepton pair transverse momentum (p T,ee) and low invariant mass (m ee) in non-central Pb–Pb collisions at sNN = 5.02 TeV at the LHC is presented. The dielectron production is studied with the ALICE detector at midrapidity (|η e | < 0.8) as a function of invariant mass (0.4 ≤ m ee < 2.7 GeV/c 2) in the 50–70% and 70–90% centrality classes for p T,ee < 0.1 GeV/c, and as a function of p T,ee in three m ee intervals in the most peripheral Pb–Pb collisions. Below a p T,ee of 0.1 GeV/c, a clear excess of e+e− pairs is found compared to the expectations from known hadronic sources and predictions of thermal radiation from the medium. The m ee excess spectra are reproduced, within uncertainties, by different predictions of the photon–photon production of dielectrons, where the photons originate from the extremely strong electromagnetic fields generated by the highly Lorentz-contracted Pb nuclei. Lowest-order quantum electrodynamic (QED) calculations, as well as a model that takes into account the impact-parameter dependence of the average transverse momentum of the photons, also provide a good description of the p T,ee spectra. The measured 〈pT,ee2〉 of the excess p T,ee spectrum in peripheral Pb–Pb collisions is found to be comparable to the values observed previously at RHIC in a similar phase-space region. [Figure not available: see fulltext.]
Measurement of isolated prompt photon production in pp and p–Pb collisions at the LHC
No full textThis paper presents the measurement of the iso-
lated prompt photon inclusive production cross section in pp
and p–Pb collisions by the ALICE Collaboration at the LHC.
The measurement is performed in p–Pb collisions at centre-
of-mass energies per nucleon pair of √sNN = 5.02 TeV and
8.16 TeV, as well as in pp collisions at √s = 5.02 TeV
and 8 TeV. The cross section is obtained at midrapidity
(|y| < 0.7) using a charged-track based isolation momen-
tum piso, ch
T < 1.5 GeV/c in a cone with radius R = 0.4.
The data for both collision systems are well reproduced by
perturbative QCD (pQCD) calculations at next-to-leading
order (NLO) using recent parton distribution functions for
free (PDF) and bound (nPDF) nucleons. Furthermore, the
nuclear modification factor RpA for both collision energies
is consistent with unity for pT > 20 GeV/c. However, devia-
tions from unity (RpA < 1) of up to 20% are observed for pT
< 20 GeV/c with limited significance, indicating the possi-
ble presence of nuclear effects in the initial state of the col-
lision. The suppression increases with decreasing pT with a
significance of 2.3σ for a non-zero slope and yields RpA < 1
with a significance of 1.8σ at √sNN = 8.16 TeV for pT
< 20 GeV/c. In addition, a significance of 1.1σ is observed
for RpA < 1 at the lower collision energy √sNN = 5.02 TeV
for pT < 14 GeV/c. The magnitude and shape of the sup-
pression are consistent with pQCD predictions at NLO using
nPDFs that incorporate nuclear shadowing effects in the Pb
nucleus
Λ c+ production in Pb–Pb collisions at √sNN = 5.02 TeV
No full textA measurement of the production of prompt +c baryons in Pb–Pb collisions at √sNN = 5.02 TeV with the ALICE detector at the LHC is reported. The +c and −c were reconstructed at midrapidity (|y| < 0.5) via the hadronic decay channel +c →pK0S (and charge conjugate) in the transverse momentum and centrality intervals 6 < pT < 12 GeV/c and 0–80%. The +c /D0 ratio, which is sensitive to the charm quark hadronisation mechanisms in the medium, is measured and found to be larger than the ratio measured in minimum-bias pp collisions at √s = 7 TeV and in p–Pb collisions at √sNN = 5.02 TeV. In particular, the values in p–Pb and Pb–Pb collisions differ by about two standard deviations of the combined statistical and systematic uncertainties in the common pT interval covered by the measurements in the two collision systems. The +c /D0 ratio is also compared with model calculations including different implementations of charm quark hadronisation. The measured ratio is reproduced by models implementing a pure coalescence scenario, while adding a fragmentation contribution leads to an underestimation. The +c nuclear modification factor, RAA, is also presented. The measured values of the RAA of +c , D+s and non-strange D mesons are compatible within the combined statistical and systematic uncertainties. They show, however, a hint of a hierarchy ( R D0 < R D+s < R +c ), conceivable with a contribution from coalescence mechanisms to charm hadron formation in the medium
A(+)c production in pp and in p-Pb collisions at root sNN=5.02 TeV
No full textThe production cross section of prompt Λc+ charm baryons was measured with the ALICE detector at the LHC at midrapidity in proton-proton (pp) and proton-lead (p-Pb) collisions at a center-of-mass energy per nucleon pair of sNN=5.02TeV. The Λc+ and Λ ̄c- baryons were reconstructed in the hadronic decay channels Λc+→pK-π+ and Λc+→pKS0 and respective charge conjugates. The measured differential cross sections as a function of transverse momentum (pT) and the pT-integrated Λc+ production cross section in pp and in p-Pb collisions are presented. The Λc+ nuclear modification factor (RpPb), calculated from the cross sections in pp and in p-Pb collisions, is presented and compared with the RpPb of D mesons. The Λc+/D0 ratio is also presented and compared with the light-flavor baryon-to-meson ratios p/π and Λ/KS0, and measurements from other LHC experiments. The results are compared to predictions from model calculations and Monte Carlo event generators
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