321 research outputs found
Evidence for a QCD accelerator in relativistic heavy-ion collisions
No full textWe report measurements of forward jets produced in Cu+Au collisions at
GeV at the Relativistic Heavy Ion Collider. The jet-energy
distributions extend to energies much larger than expected by Feynman scaling.
This constitutes the first clear evidence for Feynman-scaling violations in
heavy-ion collisions. Such high-energy particle production has been in models
via QCD string interactions, but so far is untested by experiment. One such
model calls this a hadronic accelerator. Studies with a particular heavy-ion
event generator (HIJING) show that photons and mesons exhibit such very
high-energy production in a heavy-ion collision, so {\it QCD accelerator}
appropriately captures the physics associated with such QCD string
interactions. All models other than HIJING used for hadronic interactions in
the study of extensive air showers from cosmic rays either do not include these
QCD string interactions, or have smaller effects from the QCD accelerator.Comment: As accepted for publication in Phys. Rev.
Cross sections and transverse single-spin asymmetries in forward jet production from proton collisions at s=500 GeV
No full textAbstractMeasurements of the production of forward jets from transversely polarized proton collisions at s=500 GeV conducted at the Relativistic Heavy Ion Collider (RHIC) are reported. Our measured jet cross section is consistent with hard scattering expectations. Our measured analyzing power for forward jet production is small and positive, and provides constraints on the Sivers functions that are related to partonic orbital angular momentum through theoretical models
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
Measurement of the production of high-p(T) electrons from heavy-flavour hadron decays in Pb-Pb collisions at root s(NN)=2.76 TeV
No full textElectrons from heavy-flavour hadron decays (charm and beauty) were measured with the ALICE detector in Pb-Pb collisions at a centre-of-mass of energy root s(NN) = 2.76 TeV. The transverse momentum (pT) differential production yields at mid-rapidity were used to calculate the nuclear modification factor R-AA in the interval 3 < p(T) < 18 GeV/c. The R-AA shows a strong suppression compared to binary scaling of pp collisions at the same energy (up to a factor of 4) in the 10% most central Pb-Pb collisions. There is a centrality trend of suppression, and a weaker suppression (down to a factor of 2) in semi-peripheral (50-80%) collisions is observed. The suppression of electrons in this broad p(T) interval indicates that both charm and beauty quarks lose energy when they traverse the hot medium formed in Pb-Pb collisions at LHC. (C) 2017 The Author. Published by Elsevier B.V
First measurement of Xi(0)(c) production in pp collisions at root s=7 TeV
No full textThe production of the charm-strange baryon Xi(0)(c) is measured for the first time at the LHC via its semileptonic decay into e(+) Xi(-) nu(e) in ppcollisions at root s = 7 TeV with the ALICE detector. The transverse momentum ( p(T)) differential cross section multiplied by the branching ratio is presented in the interval 1 < p(T)< 8 GeV/c at mid-rapidity, vertical bar y vertical bar < 0.5. The transverse momentum dependence of the Xi(0)(c) baryon production relative to the D-0 meson production is compared to predictions of event generators with various tunes of the hadronisation mechanism, which are found to underestimate the measured cross-section ratio. (C) 2018 The Author(s). Published by Elsevier B.V
Centrality dependence of the pseudorapidity density distribution for charged particles in Pb-Pb collisions at root s(NN)=5.02 TeV
No full textWe present the charged-particle pseudorapidity density in Pb-Pb collisions at root s(NN) = 5.02 TeV in centrality classes measured by ALICE. The measurement covers a wide pseudorapidity range from -3.5 to 5, which is sufficient for reliable estimates of the total number of charged particles produced in the collisions. For the most central (0-5%) collisions we find 21 400 +/- 1 300, while for the most peripheral (80-90%) we find 230 +/- 38. This corresponds to an increase of (27 +/- 4)% over the results at root s(NN) = 2.76 TeV previously reported by ALICE. The energy dependence of the total number of charged particles produced in heavy-ion collisions is found to obey a modified power-law like behaviour. The charged-particle pseudorapidity density of the most central collisions is compared to model calculations-none of which fully describes the measured distribution. We also present an estimate of the rapidity density of charged particles. The width of that distribution is found to exhibit a remarkable proportionality to the beam rapidity, independent of the collision energy from the top SPS to LHC energies. (C) 2017 The Author(s). Published by Elsevier B.V
First measurement of the vertical bar t vertical bar-dependence of coherent J/psi photonuclear production
No full textThe first measurement of the cross section for coherent J/Psi photoproduction as a function of vertical bar t vertical bar, the square of the momentum transferred between the incoming and outgoing target nucleus, is presented. The data were measured with the ALICE detector in ultra-peripheral Pb-Pbcollisions at a centre-of-mass energy per nucleon pair root s(NN) = 5.02 TeV with the J/Psi produced in the central rapidity region vertical bar y vertical bar < 0.8, which corresponds to the small Bjorken-xrange (0.3 - 1.4) x 10(-3). The measured vertical bar t vertical bar-dependence is not described by computations based only on the Pb nuclear form factor, while the photonuclear cross section is better reproduced by models including shadowing according to the leading-twist approximation, or gluon-saturation effects from the impact-parameter dependent Balitsky-Kovchegov equation. These new results are therefore a valid tool to constrain the relevant model parameters and to investigate the transverse gluonic structure at very low Bjorken- x. (C) 2021 The Author(s). Published by Elsevier B.V
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
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/)
The role of air pollution in the aetiology of type 2 diabetes
No full textBackground. The public health burden of type 2 diabetes cannot be overestimated. Prevalence of type 2 diabetes is continuously increasing and has caused a great number of deaths and economic losses. Optimal prevention measures for type 2 diabetes entail that more risk factors need to be identified. Air pollution is one of the modifiable environmental risk factors causing health problems, most notably respiratory diseases. Recently there have been indications for a spill-over of its effects into the cardio-metabolic systems. Short-term exposure to air pollution may exert acute or sub-acute inflammatory cardio-metabolic responses which on long-term, sustained exposure could lead to overt cardiovascular diseases and type 2 diabetes. However, it is unclear if long-term exposure to pollutants in the air contributes to the development of type 2 diabetes. This work generates evidence to fill knowledge gaps on the impact of air pollutants on the development of type 2 diabetes and on how different susceptibilities in the general population could contribute to the understanding of the mechanisms involved in this relationship.
Methods. First, this work summarized the existing evidence on the possible relationship between long-term exposure to air pollutants and type 2 diabetes. Furthermore, in the framework of the first follow-up of SAPALDIA- the Swiss Cohort Study on Air Pollution and Lung and Heart Diseases in Adults, this work used indices for long-term exposure air pollution – 10-year mean particulate matter <10μm in diameter [PM10] and nitrogen dioxide [NO2] - assigned to participants’ residences using a combination of Gaussian dispersion and Land-use regression models, participants residential histories and pollutant trends at monitoring stations. It identified diabetes and metabolic syndrome cases in a comprehensive way considering self-reports, blood tests and other physical measures. It additionally identified genetic variants through genotyping on two different arrays – the Human Illumina610quad Bead Chip and the Taqman PCR assay - for 63 type 2 diabetes genetic polymorphisms [towards a diabetes gene score] and a functional polymorphism on the IL6 gene respectively. Based on the above and detailed health socio-demographic and lifestyle characteristics including smoking habits, occupational exposures, alcohol, nutrition, physical activity, body measurements and additional data collected in SAPALDIA, it was ideal to investigate the cross-sectional relationships between air pollutants and diabetes and to explore interactions [based on various susceptibilities] to understand mechanisms involved in the relationship between long-term exposure to air pollutants and type 2 diabetes.
Results. In this work, we found a positive relationship between PM2.5 and NO2 and the risk of T2D in the pooled evidence synthesized from electronic databases. In the frame of SAPALDIA biobank, we found a moderate positive association between long-term exposure to PM10 [and NO2] and prevalent diabetes, and demonstrated a sustained effect of PM10 independent of NO2, while NO2 lost its association on accounting for PM10 in multi-pollutant models. Among the measures of cardio-metabolic function, PM10 impacted most on impairment of glucose homeostasis and least on blood lipoproteins and triglycerides. The relationship between PM10 and impaired fasting glycaemia was more apparent among the physically active. Age also appeared to influence the relationship between PM10 and impaired fasting glycaemia. People at higher polygenic risk for type 2 diabetes were more susceptible to PM10. Genetic risk for insulin resistance and obesity appeared to be more relevant than those for beta-cell function in modifying the effects of PM10, especially among those with some background inflammatory conditions. Carriers of the pro-inflammatory major ‘G’ allele of IL6-572GC, with allele frequency of 93%, were also more susceptible to PM10 in relation to diabetes.
Conclusions. This work has greatly contributed to evidence suggesting the possible role of air pollutants in diabetes aetiology. The reported associations were observed at mean concentrations below current air quality guidelines. PM10 may be a good marker for aspects of air pollution [rather than NO2] relevant for the development of diabetes. In particular, PM10 might act through sub-clinical inflammation and resultant impaired insulin sensitivity. Impairment of insulin secretion may be a less relevant pathway for PM10 action. Physical activity, though beneficial, presented another likely pathway for PM10 effects. These findings, if confirmed, call for the strengthening of air quality policies and adaptation of physical activity promotion to environmental contrasts. Future studies should explore the totality of environmental exposures – exposomics –in a life-course fashion. The mediating role of DNA methylation influencing genetic expression should be further explored. For global generalizability, there is a strong need for evidence replication in developing countries where outdoor and indoor air pollution is quite high and mostly unregulated, and the burden of non-communicable diseases is rapidly growing
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