499 research outputs found
Light (anti)nuclei production in Pb-Pb collisions at sNN=5.02Â TeV
The measurement of the production of deuterons, tritons and 3 He and their antiparticles in Pb-Pb collisions
at âs NN = 5.02 TeV is presented in this article. The measurements are carried out at midrapidity (|y| <
0.5) as a function of collision centrality using the ALICE detector. The pT -integrated yields, the coalescence
parameters and the ratios to protons and antiprotons are reported and compared with nucleosynthesis models. The
comparison of these results in different collision systems at different center-of-mass collision energies reveals a
suppression of nucleus production in small systems. In the Statistical Hadronisation Model framework, this can
be explained by a small correlation volume where the baryon number is conserved, as already shown in previous
fluctuation analyses. However, a different size of the correlation volume is required to describe the proton yields
in the same data sets. The coalescence model can describe this suppression by the fact that the wave functions
of the nuclei are large and the fireball size starts to become comparable and even much smaller than the actual
nucleus at low multiplicities
Inclusive and multiplicity dependent production of electrons from heavy-flavour hadron decays in pp and p-Pb collisions
Measurements of the production of electrons from heavy-flavour hadron decays in pp collisions at root s = 13 TeV at midrapidity with the ALICE detector are presented down to a transverse momentum (p(T)) of 0.2 GeV/c and up to p(T) = 35 GeV/c, which is the largest momentum range probed for inclusive electron measurements in ALICE. In p-Pb collisions, the production cross section and the nuclear modification factor of electrons from heavy-flavour hadron decays are measured in the p(T) range 0.5 < p(T) < 26 GeV/c at root s(NN) = 8.16 TeV. The nuclear modification factor is found to be consistent with unity within the statistical and systematic uncertainties. In both collision systems, first measurements of the yields of electrons from heavy-flavour hadron decays in different multiplicity intervals normalised to the multiplicity-integrated yield (self-normalised yield) at midrapidity are reported as a function of the self-normalised charged-particle multiplicity estimated at midrapidity. The self-normalised yields in pp and p-Pb collisions grow faster than linear with the self-normalised multiplicity. A strong p(T) dependence is observed in pp collisions, where the yield of high-p(T) electrons increases faster as a function of multiplicity than the one of low-p(T) electrons. The measurement in p-Pb collisions shows no p(T) dependence within uncertainties. The self-normalised yields in pp and p-Pb collisions are compared with measurements of other heavy-flavour, light-flavour, and strange particles, and with Monte Carlo simulations
Production of pions, kaons, and protons as a function of the relative transverse activity classifier in pp collisions at = 13 TeV
Abstract: The production of ϱ, K±, and ( p )p is measured in pp collisions at âs = 13 TeV
in different topological regions of the events. Particle transverse momentum (pT) spectra are
measured in the âtowardâ, âtransverseâ, and âawayâ angular regions defined with respect
to the direction of the leading particle in the event. While the toward and away regions
contain the fragmentation products of the near-side and away-side jets, respectively, the
transverse region is dominated by particles from the Underlying Event (UE). The relative
transverse activity classifier, RT = NT/ăNTă, is used to group events according to their UE
activity, where NT is the measured charged-particle multiplicity per event in the transverse
region and ăNTă is the mean value over all the analysed events. The first measurements
of identified particle pT spectra as a function of RT in the three topological regions are
reported. It is found that the yield of high transverse momentum particles relative to the
RT-integrated measurement decreases with increasing RT in both the toward and the away
regions, indicating that the softer UE dominates particle production as RT increases and
validating that RT can be used to control the magnitude of the UE. Conversely, the spectral
shapes in the transverse region harden significantly with increasing RT. This hardening
follows a mass ordering, being more significant for heavier particles. Finally, it is observed
that the pT-differential particle ratios (p + p )/(Ï+ + Ïâ) and (K+ + Kâ)/(Ï+ + Ïâ) in
the low UE limit (RT â 0) approach expectations from Monte Carlo generators such as
PYTHIA 8 with Monash 2013 tune and EPOS LHC, where the jet-fragmentation models
have been tuned to reproduce e+eâ results
First measurement of Îc+ production down to pT=0 in pp and p-Pb collisions at sNN=5.02 TeV
The production of prompt Lambda+c baryons has been measured at midrapidity in the transverse momentum interval 0 < pT < 1 GeV/c for the first time, in pp and pâPb collisions at a center-of-mass energy per nucleon-nucleon
collision âs NN = 5.02 TeV. The measurement was performed in the decay channel Lambda+c â pK0S by applying new decay reconstruction techniques using a Kalman-Filter vertexing algorithm and adopting a machine-learning
approach for the candidate selection. The pT -integrated Lambda+c production cross sections in both collision systems were determined and used along with the measured yields in PbâPb collisions to compute the pT -integrated
nuclear modification factors R pPb and R AA of Lambda+c baryons, which are compared to model calculations that
consider nuclear modification of the parton distribution functions. The Lambda+c /D0 baryon-to-meson yield ratio is
reported for pp and pâPb collisions. Comparisons with models that include modified hadronization processes are
presented, and the implications of the results on the understanding of charm hadronization in hadronic collisions
are discussed. A significant (3.7Ï ) modification of the mean transverse momentum of Lambda+c baryons is seen in pâPb collisions with respect to pp collisions, while the pT -integrated Lambda+c /D0 yield ratio was found to be consistent between the two collision systems within the uncertainties
Measurement of the non-prompt D-meson fraction as a function of multiplicity in proton-proton collisions at = 13 TeV
The fractions of non-prompt (i.e. originating from beauty-hadron decays) D0
and D+ mesons with respect to the inclusive yield are measured as a function of the
charged-particle multiplicity in proton-proton collisions at a centre-of-mass energy of âs =
13 TeV with the ALICE detector at the LHC. The results are reported in intervals of
transverse momentum (pT) and integrated in the range 1 < pT < 24 GeV/c. The fraction
of non-prompt D0 and D+ mesons is found to increase slightly as a function of pT in
all the measured multiplicity intervals, while no significant dependence on the charged-
particle multiplicity is observed. In order to investigate the production and hadronisation
mechanisms of charm and beauty quarks, the results are compared to PYTHIA 8 as well
as EPOS 3 and EPOS 4 Monte Carlo simulations, and to calculations based on the colour
glass condensate including three-pomeron fusion
First measurement of prompt and non-prompt Dâ+ vector meson spin alignment in pp collisions at s=13 TeV
This letter reports the first measurement of spin alignment, with respect to the helicity axis, for D*+ vector mesons and their charge conjugates from charm-quark hadronisation (prompt) and from beauty-meson decays (non-prompt) in hadron collisions. The measurements were performed at midrapidity (|y| D0 (-> K- pi+) pi+ decay products, in the D*+ rest frame, with respect to the D*+ momentum direction in the pp centre of mass frame. The rho_00 value for prompt D*+ mesons is consistent with 1/3, which implies no spin alignment. However, for non-prompt D*+ mesons an evidence of rho_00 larger than 1/3 is found. The measured value of the spin density element is in the interval, which is consistent with a Pythia 8 Monte Carlo simulation coupled with the EvtGen package, which implements the helicity conservation in the decay of D*+ meson from beauty mesons. In non-central heavy-ion collisions, the spin of the D*+ mesons may be globally aligned with the direction of the initial angular momentum and magnetic field. Based on the results for pp collisions reported in this letter it is shown that alignment of non-prompt D*+ mesons due to the helicity conservation coupled to the collective anisotropic expansion may mimic the signal of global spin alignment in heavy-ion collisions
Accessing the strong interaction between Î baryons and charged kaons with the femtoscopy technique at the LHC
The interaction between Î baryons and kaons/antikaons is a crucial ingredient for the strangeness S=0 and S=-2 sector of the mesonâbaryon interaction at low energies. In particular, the Lambda-Kbar might help in understanding the origin of states such as the Csi(1620), whose nature and properties are still under debate. Experimental data on Lambda-K and Lambda-Kbar systems are scarce, leading to large uncertainties and tension between the available theoretical predictions constrained by such data. In this Letter we present the measurements of ÎâKKâ and ÎâKK+ correlations obtained in the high-multiplicity triggered data sample in pp collisions at sqrt(s) = 13 TeV recorded by ALICE at the LHC. The correlation function for both pairs is modeled using the LednickĂœâLyuboshits analytical formula and the corresponding scattering parameters are extracted. The ÎâKK+ correlations show the presence of several structures at relative momenta k* above 200 MeV/c, compatible with the Ω baryon, the , and resonances decaying into ÎâKâ pairs. The low k* region in the ÎâKK+ also exhibits the presence of the state, expected to strongly couple to the measured pair. The presented data allow to access the ÎK+ and ÎKâ strong interaction with an unprecedented precision and deliver the first experimental observation of the decaying into ÎKâ
Enhanced Deuteron Coalescence Probability in Jets
: The transverse-momentum (p_{T}) spectra and coalescence parameters B_{2} of (anti)deuterons are measured in p-p collisions at sqrt[s]=13ââTeV for the first time in and out of jets. In this measurement, the direction of the leading particle with the highest p_{T} in the event (p_{T}^{lead}>5ââGeV/c) is used as an approximation for the jet axis. The event is consequently divided into three azimuthal regions, and the jet signal is obtained as the difference between the toward region, that contains jet fragmentation products in addition to the underlying event (UE), and the transverse region, which is dominated by the UE. The coalescence parameter in the jet is found to be approximately a factor of 10 larger than that in the underlying event. This experimental observation is consistent with the coalescence picture and can be attributed to the smaller average phase-space distance between nucleons in the jet cone as compared with the underlying event. The results presented in this Letter are compared to predictions from a simple nucleon coalescence model, where the phase-space distributions of nucleons are generated using pythia8 with the Monash 2013 tuning, and to predictions from a deuteron production model based on ordinary nuclear reactions with parametrized energy-dependent cross sections tuned on data. The latter model is implemented in pythia8.3. Both models reproduce the observed large difference between in-jet and out-of-jet coalescence parameters, although the almost flat trend of the B_{2}^{Jet} is not reproduced by the models, which instead give a decreasing trend
TNF-mediated macrophage activation in the target organ is critical for clinical manifestation of uveitis
Clinically available anti-tumour necrosis factor (TNF) biologics, which inhibit both soluble (sTNF) and transmembrane forms (tmTNF) of TNF, eliminating all TNF signalling, have successfully treated autoimmune diseases including uveitis. These have potentially serious side effects such as reactivation of latent Mycobacterium tuberculosis and, therefore, more specific inhibition of TNF signalling pathways may maintain clinical efficacy while reducing adverse effects. To determine the effects of specific pharmacological inhibition of sTNF on macrophage activation and migration, we used a mouse model of uveitis (experimental autoimmune uveoretinitis; EAU). We show that selective inhibition of sTNF is sufficient to suppress EAU by limiting inflammatory CD11b(+) macrophages and CD4(+) T cell migration into the eye. However, inhibition of both sTNF and tmTNF is required to inhibit interferon-Îł-induced chemokine receptor 2, CD40, major histocompatibility complex class II and nitric oxide (NO) up-regulation, and signalling via tmTNF is sufficient to mediate tissue damage. In confirmation, intravitreal inhibition of sTNF alone did not suppress disease, and inflammatory cells that migrated into the eye were activated, generating NO, thus causing structural damage to the retina. In contrast, intravitreal inhibition of both sTNF and tmTNF suppressed macrophage activation and therefore disease. We conclude that sTNF is required for inflammatory cell infiltration into target tissue, but at the tissue site inhibition of both sTNF and tmTNF is required to inhibit macrophage activation and to protect from tissue damage
High-efficiency bypass of DNA damage by human DNA polymerase Q
Endogenous DNA damage arises frequently, particularly apurinic (AP) sites. These must be dealt with by cells in order to avoid genotoxic effects. DNA polymerase Ξ is a newly identified enzyme encoded by the human POLQ gene. We find that POLQ has an exceptional ability to bypass an AP site, inserting A with 22% of the efficiency of a normal template, and continuing extension as avidly as with a normally paired base. POLQ preferentially incorporates A opposite an AP site and strongly disfavors C. On nondamaged templates, POLQ makes frequent errors, incorporating G or T opposite T about 1% of the time. This very low fidelity distinguishes POLQ from other A-family polymerases. POLQ has three sequence insertions between conserved motifs in its catalytic site. One insert of âŒ22 residues into the tip of the polymerase thumb subdomain is predicted to confer considerable flexibility and additional DNA contacts to affect enzyme fidelity. POLQ is the only known enzyme that efficiently carries out both the insertion and extension steps for bypass of AP sites, commonly formed as endogenous genomic lesions
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