1,152 research outputs found
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No full textWe publish here the second part of our spectroscopic survey at high
dispersion of some known and suspected λ Bootis stars with a view
to detecting circumstellar shell features. Eight stars of our sample exhibit
such features. These stars are fast rotators, a result which is in line
with Hohlweger and Rentzsch-Holm's study (1995). The analysis of the
photometric data has allowed us to confirm the exclusion of a few stars
misclassified from the λ Bootis group
Measurement of inclusive charged-particle b-jet production in pp and p-Pb collisions at √sNN = 5.02 TeV
No full textA measurement of the inclusive b-jet production cross section is presented in pp and p-Pb collisions at sNN = 5.02 TeV, using data collected with the ALICE detector at the LHC. The jets were reconstructed in the central rapidity region |η| < 0.5 from charged particles using the anti-kT algorithm with resolution parameter R = 0.4. Identification of b jets exploits the long lifetime of b hadrons, using the properties of secondary vertices and impact parameter distributions. The pT-differential inclusive production cross section of b jets, as well as the corresponding inclusive b-jet fraction, are reported for pp and p-Pb collisions in the jet transverse momentum range 10 ≤ pT,ch jet≤ 100 GeV/c, together with the nuclear modification factor, RpPbb−jet. The analysis thus extends the lower pT limit of b-jet measurements at the LHC. The nuclear modification factor is found to be consistent with unity, indicating that the production of b jets in p-Pb at sNN = 5.02 TeV is not affected by cold nuclear matter effects within the current precision. The measurements are well reproduced by POWHEG NLO pQCD calculations with PYTHIA fragmentation. [Figure not available: see fulltext.]
Measurement of inclusive charged-particle b-jet production in pp and p-Pb collisions at √sNN = 5.02 TeV
No full textA measurement of the inclusive b-jet production cross section is presented in pp and p-Pb collisions at sNN = 5.02 TeV, using data collected with the ALICE detector at the LHC. The jets were reconstructed in the central rapidity region |η| T algorithm with resolution parameter R = 0.4. Identification of b jets exploits the long lifetime of b hadrons, using the properties of secondary vertices and impact parameter distributions. The pT-differential inclusive production cross section of b jets, as well as the corresponding inclusive b-jet fraction, are reported for pp and p-Pb collisions in the jet transverse momentum range 10 ≤ pT,ch jet≤ 100 GeV/c, together with the nuclear modification factor, RpPbb−jet. The analysis thus extends the lower pT limit of b-jet measurements at the LHC. The nuclear modification factor is found to be consistent with unity, indicating that the production of b jets in p-Pb at sNN = 5.02 TeV is not affected by cold nuclear matter effects within the current precision. The measurements are well reproduced by POWHEG NLO pQCD calculations with PYTHIA fragmentation. [Figure not available: see fulltext.]
Investigating the role of strangeness in baryon–antibaryon annihilation at the LHC
No full textAnnihilation dynamics plays a fundamental role in the baryon–antibaryon interaction (B–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–p ̅ system but not in the low relative momentum region. Data regarding the B–B ̅ interaction with strange degrees of freedom are extremely scarce, hence the modeling of the annihilation contributions is mainly based on nucleon–antinucleon (N–N ̅) results, when available. In this letter we present a measurement of the p–p ̅, p–Λ ̅⊕p ̅–Λ and Λ–Λ ̅ interaction using correlation functions in the relative momentum space in high-multiplicity triggered pp collisions at s=13 TeV recorded by ALICE at the LHC. In the p–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–Λ ̅⊕p ̅–Λ and Λ–Λ ̅ correlations. The model describes the Λ–Λ ̅ data and underestimates the p–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
Measuring (KSK +/-)-K-0 interactions using Pb-Pb collisions at root S-NN=2.76 TeV
No full textWe present the first ever measurements of femtoscopic correlations between the K-S(0) and K-+/- particles. The analysis was performed on the data from Pb-Pb collisions at root S-NN = 2.76 TeV measured by the ALICE experiment. The observed femtoscopic correlations are consistent with final-state interactions proceeding via the a(0)(980) resonance. The extracted kaon source radius and correlation strength parameters for (KSK-)-K-0 are found to be equal within the experimental uncertainties to those for (KSK+)-K-0. Comparing the results of the present study with those from published identical-kaon femtoscopic studies by ALICE, mass and coupling parameters for the a(0) resonance are tested. Our results are also compatible with the interpretation of the a(0) having a tetraquark structure instead of that of a diquark. (c) 2017 The Author. Published by Elsevier B.V
A femtoscopic correlation analysis tool using the Schrödinger equation (CATS)
No full textAbstract We present a new analysis framework called “Correlation Analysis Tool using the Schrödinger equation” (CATS) which computes the two-particle femtoscopy correlation function C(k), with k being the relative momentum for the particle pair. Any local interaction potential and emission source function can be used as an input and the wave function is evaluated exactly. In this paper we present a study on the sensitivity of C(k) to the interaction potential for different particle pairs: p–p, p– Λ , K- –p, K+ –p, p– Ξ- and Λ – Λ . For the p–p Argonne v18 and Reid Soft-Core potentials have been tested. For the other pair systems we present results based on strong potentials obtained from effective Lagrangians such as χ EFT for p– Λ , Jülich models for K(K¯) –N and Nijmegen models for Λ – Λ . For the p– Ξ- pairs we employ the latest lattice results from the HAL QCD collaboration. Our detailed study of different interacting particle pairs as a function of the source size and different potentials shows that femtoscopic measurements can be exploited in order to constrain the final state interactions among hadrons. In particular, small collision systems of the order of 1 fm, as produced in pp collisions at the LHC, seem to provide a suitable environment for quantitative studies of this kind
Measurement of inclusive charged-particle b-jet production in pp and p-Pb collisions at root S-NN =5.02 TeV
No full textA measurement of the inclusive b-jet production cross section is presented in pp and p-Pb collisions at root S-NN = 5.02 TeV, using data collected with the ALICE detector at the LHC. The jets were reconstructed in the central rapidity region vertical bar eta vertical bar < 0.5 from charged particles using the anti-kT algorithm with resolution parameter R = 0.4. Identification of b jets exploits the long lifetime of b hadrons, using the properties of secondary vertices and impact parameter distributions. The p(T)-differential inclusive production cross section of b jets, as well as the corresponding inclusive b-jet fraction, are reported for pp and p-Pb collisions in the jet transverse momentum range 10 <= p(T)(,)(ch)( jet) <= 100 GeV/c, together with the nuclear modification factor, R-pPb(b-jet). The analysis thus extends the lower p(T) limit of b-jet measurements at the LHC. The nuclear modification factor is found to be consistent with unity, indicating that the production of b jets in p-Pb at root S-NN = 5.02 TeV is not affected by cold nuclear matter effects within the current precision. The measurements are well reproduced by POWHEG NLO pQCD calculations with PYTHIA fragmentation
First measurement of quarkonium polarization in nuclear collisions at the LHC
No full textThe polarization of inclusive J/psi and Upsilon(1S) produced in Pb-Pb collisions at root s(NN) = 5.02 TeV at the LHC is measured with the ALICE detector. The study is carried out by reconstructing the quarkonium through its decay to muon pairs in the rapidity region 2.5 < y < 4 and measuring the polar and azimuthal angular distributions of the muons. The polarization parameters lambda(theta), lambda(phi) and lambda(theta phi) are measured in the helicity and Collins-Soper reference frames, in the transverse momentum interval 2 < p(T) < 10 GeV/c and p(T) < 15 GeV/c for the J/psi and Upsilon(1S), respectively. The polarization parameters for the J/psi are found to be compatible with zero, within a maximum of about two standard deviations at low p(T), for both reference frames and over the whole p(T) range. The values are compared with the corresponding results obtained for pp collisions at root s = 7 and 8 TeV in a similar kinematic region by the ALICE and LHCb experiments. Although with much larger uncertainties, the polarization parameters for Upsilon(1S) production in Pb-Pb collisions are also consistent with zero. (c) 2021 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/)
Dielectron and heavy-quark production in inelastic and high-multiplicity proton–proton collisions at s=13TeV
No full textThe measurement of dielectron production is presented as a function of invariant mass and transverse momentum (pT) at midrapidity (|ye| <0.8) in proton–proton (pp) collisions at a centre-of-mass energy of √s=13TeV. The contributions from light-hadron decays are calculated from their measured cross sections in pp collisions at √s=7TeV or 13TeV. The remaining continuum stems from correlated semileptonic decays of heavy-flavour hadrons. Fitting the data with templates from two different MC event generators, PYTHIA and POWHEG, the charm and beauty cross sections at midrapidity are extracted for the first time at this collision energy: dσc ̄c/dy|y=0=974 ±138 (stat.) ±140 (syst.) ±214(BR)μb and dσb ̄b/dy|y=0=79 ±14 (stat.) ±11 (syst.) ±5(BR)μb using PYTHIA simulations and dσc ̄c/dy|y=0=1417 ±184 (stat.) ±204 (syst.) ±312(BR)μb and dσb ̄b/dy|y=0=48 ±14 (stat.) ±7 (syst.) ±3(BR)μb for POWHEG. These values, whose uncertainties are fully correlated between the two generators, are consistent with extrapolations from lower energies. The different results obtained with POWHEG and PYTHIA imply different kinematic correlations of the heavy-quark pairs in these two generators. Furthermore, comparisons of dielectron spectra in inelastic events and in events collected with a trigger on high charged-particle multiplicities are presented in various pTintervals. The differences are consistent with the already measured scaling of light-hadron and open-charm production at high charged-particle multiplicity as a function of pT. Upper limits for the contribution of virtual direct photons are extracted at 90% confidence level and found to be in agreement with pQCD calculations
Measurement of strange baryon–antibaryon interactions with femtoscopic correlations
No full textTwo-particle correlation functions were measured for p (p) over bar, p (Lambda) over bar, (p) over bar Lambda, and Lambda(Lambda) over bar pairs in Pb-Pb collisions at root sNN = 2.76 TeV and root sNN = 5.02 TeV recorded by the ALICE detector. From a simultaneous fit to all obtained correlation functions, real and imaginary components of the scattering lengths, as well as the effective ranges, were extracted for combined p (Lambda) over bar and (p) over bar Lambda pairs and, for the first time, for Lambda(Lambda) over bar pairs. Effective averaged scattering parameters for heavier baryon-antibaryon pairs, not measured directly, are also provided. The results reveal similarly strong interaction between measured baryon-antibaryon pairs, suggesting that they all annihilate in the same manner at the same pair relative momentum k*. Moreover, the reported significant non-zero imaginary part and negative real part of the scattering length provide motivation for future baryon-antibaryon bound state searches. (C) 2020 The Author(s). Published by Elsevier B.V
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