635 research outputs found
Energy dependence of multiplicity fluctuations in heavy ion collisions
No full textThe energy dependence of multiplicity fluctuations was studied for the most central Pb+Pb collisions at 20A, 30A, 40A, 80A and 158A GeV by the NA49 experiment at the CERN SPS. The multiplicity distribution for negatively and positively charged hadrons is significantly narrower than Poisson one for all energies. No significant structure in energy dependence of the scaled variance of multiplicity fluctuations is observed. The measured scaled variance is lower than the one predicted by the grand-canonical formulation of the hadron-resonance gas model. The results for scaled variance are in approximate agreement with the string-hadronic model UrQMD
Coherent J/psi and psi ' photoproduction at midrapidity in ultra-peripheral Pb-Pb collisions at root s(NN)=5.02 TeV
No full textThe coherent photoproduction of J / ψ and ψ ′ mesons was measured in ultra-peripheral Pb–Pb collisions at a center-of-mass energy sNN=5.02 TeV with the ALICE detector. Charmonia are detected in the central rapidity region for events where the hadronic interactions are strongly suppressed. The J / ψ is reconstructed using the dilepton (l+l-) and proton–antiproton decay channels, while for the ψ ′ the dilepton and the l+l-π+π- decay channels are studied. The analysis is based on an event sample corresponding to an integrated luminosity of about 233 μb - 1. The results are compared with theoretical models for coherent J / ψ and ψ ′ photoproduction. The coherent cross section is found to be in a good agreement with models incorporating moderate nuclear gluon shadowing of about 0.64 at a Bjorken-x of around 6 × 10 - 4, such as the EPS09 parametrization, however none of the models is able to fully describe the rapidity dependence of the coherent J / ψ cross section including ALICE measurements at forward rapidity. The ratio of ψ ′ to J / ψ coherent photoproduction cross sections was also measured and found to be consistent with the one for photoproduction off protons
Dielectron Mass Spectra From Au+au Collisions At Snn =200 Gev
No full textWe report the STAR measurements of dielectron (e+e-) production at midrapidity (|yee|<1) in Au+Au collisions at sNN=200GeV. The measurements are evaluated in different invariant mass regions with a focus on 0.30-0.76 (ρ-like), 0.76-0.80 (ω-like), and 0.98-1.05 (φ-like) GeV/c2. The spectrum in the ω-like and φ-like regions can be well described by the hadronic cocktail simulation. In the ρ-like region, however, the vacuum ρ spectral function cannot describe the shape of the dielectron excess. In this range, an enhancement of 1.77±0.11(stat)±0.24(syst)±0. 33(cocktail) is determined with respect to the hadronic cocktail simulation that excludes the ρ meson. The excess yield in the ρ-like region increases with the number of collision participants faster than the ω and φ yields. Theoretical models with broadened ρ contributions through interactions with constituents in the hot QCD medium provide a consistent description of the dilepton mass spectra for the measurement presented here and the earlier data at the Super Proton Synchrotron energies. © 2014 American Physical Society.1132DOE; National Science Foundation; NSF; National Science Foundation; NSFC; National Science FoundationAdams, J., Aggarwal, M.M., Ahammed, Z., Amonett, J., Anderson, B.D., Arkhipkin, D., Averichev, G.S., Hallman, T.J., Experimental and theoretical challenges in the search for the quark-gluon plasma: The STAR Collaboration's critical assessment of the evidence from RHIC collisions (2005) Nuclear Physics A, 757 (1-2 SPEC. ISS.), pp. 102-183. , DOI 10.1016/j.nuclphysa.2005.03.085, PII S0375947405005294Adcox, K., Adler, S.S., Afanasiev, S., Aidala, C., Ajitanand, N.N., Akiba, Y., Al-Jamel, A., Zajc, W.A., Formation of dense partonic matter in relativistic nucleus-nucleus collisions at RHIC: Experimental evaluation by the PHENIX Collaboration (2005) Nuclear Physics A, 757 (1-2 SPEC. ISS.), pp. 184-283. , DOI 10.1016/j.nuclphysa.2005.03.086, PII S0375947405005300Back, B.B., Baker, M.D., Ballintijn, M., Barton, D.S., Becker, B., Betts, R.R., Bickley, A.A., Zhang, J., The PHOBOS perspective on discoveries at RHIC (2005) Nuclear Physics A, 757 (1-2 SPEC. ISS.), pp. 28-101. , DOI 10.1016/j.nuclphysa.2005.03.084, PII S0375947405005282Arsene, I., Bearden, I.G., Beavis, D., Besliu, C., Budick, B., Boggild, H., Chasman, C., Zgura, I.S., Quark-gluon plasma and color glass condensate at RHIC? The perspective from the BRAHMS experiment (2005) Nuclear Physics A, 757 (1-2 SPEC. ISS.), pp. 1-27. , DOI 10.1016/j.nuclphysa.2005.02.130, PII S0375947405002770Shuryak, E., (1980) Phys. Rep., 61, p. 71. , PRPLCM 0370-1573 10.1016/0370-1573(80)90105-2Rapp, R., (2001) Phys. Rev. C, 63, p. 054907. , PRVCAN 0556-2813 10.1103/PhysRevC.63.054907Rapp, R., Wambach, J., (2000) Adv. Nucl. Phys., 25, p. 1. , 10.1007/0-306-47101-9-1Brown, G.E., Rho, M., (1996) Phys. Rep., 269, p. 333. , PRPLCM 0370-1573 10.1016/0370-1573(95)00067-4Rapp, R., Wambach, J., (1999) Eur. Phys. J. A, 6, p. 415. , EPJAFV 1434-6001 10.1007/s100500050364Porter, R.J., (1997) Phys. Rev. Lett., 79, p. 1229. , (DLS Collaboration),. PRLTAO 0031-9007 10.1103/PhysRevLett.79.1229Agakichiev, G., Agodi, C., Alvarez-Pol, H., Balanda, A., Bertini, D., Bielcik, J., Bellia, G., Bohmer, M., Dielectron production in C12+C12 collisions at 2AGeV with the HADES spectrometer (2007) Physical Review Letters, 98 (5), p. 052302. , http://oai.aps.org/oai?verb=GetRecord&Identifier=oai:aps.org: PhysRevLett.98.052302&metadataPrefix=oai_apsmeta_2, DOI 10.1103/PhysRevLett.98.052302Adamova, G., (2011) Phys. Rev. C, 84, p. 014902. , (HADES Collaboration),. PRVCAN 0556-2813 10.1103/PhysRevC.84.014902Angelis A L, S., (2000) Eur. Phys. J. C, 13, p. 433. , (HELIOS/3 Collaboration),. EPCFFB 1434-6044 10.1007/s100520050707Agakichiev, G., (2003) Phys. Rev. Lett., 91, p. 042301. , (CERES Collaboration), ()PRLTAO 0031-9007 10.1103/PhysRevLett.91.042301Agakichiev, G., Appelshauser, H., Bielcikova, J., Baur, R., Braun-Munzinger, P., Cherlin, A., Damjanovic, S., Yurevich, V., E+ e- -pair production in Pb-Au collisions at 158 GeV per nucleon (2005) European Physical Journal C, 41 (4), pp. 475-513. , DOI 10.1140/epjc/s2005-02272-3Arnaldi, R., Averbeck, R., Banicz, K., Castor, J., Chaurand, B., Cicalo, C., Colla, A., Wohri, H.K., First measurement of the spectral function in high-energy nuclear collisions (2006) Physical Review Letters, 96 (16), p. 162302. , http://oai.aps.org/oai?verb=GetRecord&Identifier=oai:aps.org: PhysRevLett.96.162302&metadataPrefix=oai_apsmeta_2, DOI 10.1103/PhysRevLett.96.162302Arnaldi, R., (2008) Phys. Rev. Lett., 100, p. 022302. , (NA60 Collaboration), ()PRLTAO 0031-9007 10.1103/PhysRevLett.100.022302Arnaldi, R., (2009) Eur. Phys. J. C, 59, p. 607. , (NA60 Collaboration),. EPCFFB 1434-6044 10.1140/epjc/s10052-008-0857-2Adare, A., (2010) Phys. Rev. C, 81, p. 034911. , (PHENIX Collaboration),. PRVCAN 0556-2813 10.1103/PhysRevC.81.034911Van Hees, H., Rapp, R., Comprehensive interpretation of thermal dileptons measured at the CERN super proton synchrotron (2006) Physical Review Letters, 97 (10), p. 102301. , http://oai.aps.org/oai?verb=GetRecord&Identifier=oai:aps.org: PhysRevLett.97.102301&metadataPrefix=oai_apsmeta_2, DOI 10.1103/PhysRevLett.97.102301Van Hees, H., Rapp, R., (2008) Nucl. Phys., A806, p. 339. , NUPBBO 0550-3213 10.1016/j.nuclphysa.2008.03.009Ruppert, J., Gale, C., Renk, T., Lichard, P., Kapusta, J.I., Low mass dimuons produced in relativistic nuclear collisions (2008) Physical Review Letters, 100 (16), p. 162301. , http://oai.aps.org/oai?verb=GetRecord&Identifier=oai:aps.org: PhysRevLett.100.162301&metadataPrefix=oai_apsmeta_2, DOI 10.1103/PhysRevLett.100.162301Renk, T., Ruppert, J., (2008) Phys. Rev. C, 77, p. 024907. , PRVCAN 0556-2813 10.1103/PhysRevC.77.024907Dusling, K., Teaney, D., Zahed, I., (2007) Phys. Rev. C, 75, p. 024908. , PRVCAN 0556-2813 10.1103/PhysRevC.75.024908Linnyk, O., Bratkovskaya, E.L., Ozvenchuk, V., Cassing, W., Ko, C.M., (2011) Phys. Rev. C, 84, p. 054917. , PRVCAN 0556-2813 10.1103/PhysRevC.84.054917Abelev, B.I., (2009) Phys. Rev. C, 79, p. 034909. , (STAR Collaboration),. PRVCAN 0556-2813 10.1103/PhysRevC.79.034909Anderson, M., Berkovitz, J., Betts, W., Bossingham, R., Bieser, F., Brown, R., Burks, M., Zhang, W., The STAR time projection chamber: A unique tool for studying high multiplicity events at RHIC (2003) Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 499 (2-3), pp. 659-678. , DOI 10.1016/S0168-9002(02)01964-2Llope, W.J., (2012) Nucl. Instrum. Methods Phys. Res., Sect. A, 661, pp. S110. , (for the STAR Collaboration),. NIMAER 0168-9002 10.1016/j.nima.2010.07. 086Shao, M., Barannikova, O., Dong, X., Fisyak, Y., Ruan, L., Sorensen, P., Xu, Z., (2006) Nucl. Instrum. Methods Phys. Res., Sect. A, 558, p. 419. , NIMAER 0168-9002 10.1016/j.nima.2005.11.251Adamczyk, L., (2012) Phys. Rev. C, 86, p. 024906. , (STAR Collaboration),. PRVCAN 0556-2813 10.1103/PhysRevC.86.024906http://wwwasdoc.web.cern.ch/wwwasdoc/geant_html3/geantall.html, geant 3.21, CERN program libraryZhao, J., (2013), https://drupal.star.bnl.gov/STAR/theses/phd-32, Ph.D. thesis, Shanghai Institute of Applied PhysicsTang, Z., Xu, Y., Ruan, L., Van Buren, G., Wang, F., Xu, Z., (2009) Phys. Rev. C, 79, p. 051901. , PRVCAN 0556-2813 10.1103/PhysRevC.79.051901Tang, Z.-B., Yi, L., Ruan, L.-J., Shao, M., Li, C., Chen, H.-F., Mohanty, B., Xu, Z.-B., (2013) Chin. Phys. Lett., 30, p. 031201. , CPLEEU 0256-307X 10.1088/0256-307X/30/3/031201Adams, J., (2004) Phys. Rev. Lett., 92, p. 112301. , (STAR Collaboration), ()PRLTAO 0031-9007 10.1103/PhysRevLett.92.112301Abelev, B.I., Aggarwal, M.M., Ahammed, Z., Anderson, B.D., Anderson, M., Arkhipkin, D., Averichev, G.S., Guertin, S.M., Identified baryon and meson distributions at large transverse momenta from Au+Au collisions at sNN=200a GeV (2006) Physical Review Letters, 97 (15), p. 152301. , http://oai.aps.org/oai?verb=GetRecord&Identifier=oai:aps.org: PhysRevLett.97.152301&metadataPrefix=oai_apsmeta_2, DOI 10.1103/PhysRevLett.97.152301Alder, S.S., (2003) Phys. Rev. Lett., 91, p. 072301. , (PHENIX Collaboration), ()PRLTAO 0031-9007 10.1103/PhysRevLett.91. 072301Adler, S.S., Afanasiev, S., Aidala, C., Ajitanand, N.N., Akiba, Y., Alexander, J., Amirikas, R., Hayano, R., Identified charged particle spectra and yields in Au+Au collisions at SNN=200 GeV (2004) Physical Review C - Nuclear Physics, 69 (3), pp. 0349091-03490932. , DOI 10.1103/PhysRevC.69.034909, 034909Adler, S.S., (2007) Phys. Rev. C, 75, p. 024909. , (PHENIX Collaboration),. PRVCAN 0556-2813 10.1103/PhysRevC.75.024909Adams, J., (2005) Phys. Lett. B, 612, p. 181. , (STAR Collaboration),. PYLBAJ 0370-2693 10.1016/j.physletb.2004.12.082Adare, A., Afanasiev, S., Aidala, C., Ajitanand, N.N., Akiba, Y., Al-Bataineh, H., Alexander, J., Al-Jamel, A., J/production versus centrality, transverse momentum, and rapidity in Au+Au collisions at s NN=200 GeV (2007) Physical Review Letters, 98 (23), p. 232301. , http://oai.aps.org/oai?verb=GetRecord&Identifier=oai:aps.org: PhysRevLett.98.232301&metadataPrefix=oai_apsmeta_2, DOI 10.1103/PhysRevLett.98.232301Sjostrand, T., Eden, P., Friberg, C., Lonnblad, L., Miu, G., Mrenna, S., Norrbin, E., High-energy-physics event generation with PYTHIA 6.1 (2001) Computer Physics Communications, 135 (2), pp. 238-259. , DOI 10.1016/S0010-4655(00)00236-8, PII S0010465500002368L. Adamczyk (STAR Collaboration), arXiv:1404.6185Rapp, R., Proc. Sci., 2013 (CPOD2013), p. 008Rapp, R., (private communication)Linnyk, O., Cassing, W., Manninen, J., Bratkovskaya, E.L., Ko, C.M., (2012) Phys. Rev. C, 85, p. 024910. , PRVCAN 0556-2813 10.1103/PhysRevC.85.024910Linnyk, O., (private communication)Cassing, W., Bratkovskaya, E.L., (2009) Nucl. Phys., A831, p. 215. , NUPBBO 0550-3213 10.1016/j.nuclphysa.2009.09.007Bratkovskaya, E.L., Cassing, W., Konchakovski, V.P., Linnyk, O., (2011) Nucl. Phys., A856, p. 162. , NUPHA7 0029-5582 10.1016/j.nuclphysa.2011.03.003Xu, H.J., Chen, H.F., Dong, X., Wang, Q., Zhang, Y.F., (2012) Phys. Rev. C, 85, p. 024906. , PRVCAN 0556-2813 10.1103/PhysRevC.85.024906Vujanovic, G., Young, C., Schenke, B., Jeon, S., Rapp, R., Gale, C., (2013) Nucl. Phys., A904, pp. 557c. , NUPBBO 0550-3213 10.1016/j.nuclphysa.2013.02.075Gujanovic, G., Young, C., Schenke, B., Rapp, R., Jeon, S., Gale, C., (2014) Phys. Rev. C, 89, p. 034904. , PRVCAN 0556-2813 10.1103/PhysRevC.89.034904Heinz, U., Lee, K.S., (1991) Phys. Lett. B, 259, p. 162. , PYLBAJ 0370-2693 10.1016/0370-2693(91)90152-GAdare, A., Afanasiev, S., Aidala, C., Ajitanand, N.N., Akiba, Y., Al-Bataineh, H., Alexander, J., Aphecetche, L., Energy loss and flow of heavy quarks in Au+Au collisions at sNN=200GeV (2007) Physical Review Letters, 98 (17), p. 172301. , http://oai.aps.org/oai?verb=GetRecord&Identifier=oai:aps.org: PhysRevLett.98.172301&metadataPrefix=oai_apsmeta_2, DOI 10.1103/PhysRevLett.98.17230
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
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
Underlying Event measurements in pp collisions at root s=0.9 and 7 TeV with the ALICE experiment at the LHC
No full textWe present measurements of Underlying Event observables in pp collisions at root s = 0 : 9 and 7 TeV. The analysis is performed as a function of the highest charged-particle transverse momentum p(T),L-T in the event. Different regions are defined with respect to the azimuthal direction of the leading (highest transverse momentum) track: Toward, Transverse and Away. The Toward and Away regions collect the fragmentation products of the hardest partonic interaction. The Transverse region is expected to be most sensitive to the Underlying Event activity. The study is performed with charged particles above three different p(T) thresholds: 0.15, 0.5 and 1.0 GeV/c. In the Transverse region we observe an increase in the multiplicity of a factor 2-3 between the lower and higher collision energies, depending on the track p(T) threshold considered. Data are compared to PYTHIA 6.4, PYTHIA 8.1 and PHOJET. On average, all models considered underestimate the multiplicity and summed p(T) in the Transverse region by about 10-30%
Measurement of charm production at central rapidity in proton-proton collisions at ps = 7 TeV
No full textThe p t-differential inclusive production cross sections of the prompt charmed mesons D0, D+, and D*+ in the rapidity range |y| < 0.5 were measured in proton-proton collisions at Ös = 7 TeVs=7TeV at the LHC using the ALICE detector. Reconstructing the decays D0 → K−π+, D+ → K−π+π+, D*+ → D0π+, and their charge conjugates, about 8,400 D0, 2,900 D+, and 2,600 D*+ mesons with 1 < p t < 24 GeV/c were counted, after selection cuts, in a data sample of 3.14 × 108 events collected with a minimum-bias trigger (integrated luminosity L int = 5 nb−1). The results are described within uncertainties by predictions based on perturbative QCD
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
Publisher Correction: Direct observation of the dead-cone effect in quantum chromodynamics (Nature, (2022), 605, 7910, (440-446), 10.1038/s41586-022-04572-w)
No full textIn the version of this article initially published, there was a typographical error in the first sentence following the “Exposing the dead cone” heading, now reading, “The measurements of R(θ), in the three radiator (charmquark) energy intervals 5 &lt; ERadiator &lt; 10 GeV, 10 &lt; ERadiator &lt; 20 GeV and 20 &lt; ERadiator &lt; 35 GeV…,” where “35 GeV” initially appeared as “3 GeV.” The error has been corrected in the HTML and PDF versions of the article. *A list of authors and their affiliations appears online. © The Author(s) 2022
Jet-associated deuteron production in pp collisions at root s=13 TeV
No full textDeuteron production in high-energy collisions is sensitive to the space-time evolution of the collision system, and is typically described by a coalescence mechanism. For the first time, we present results on jet-associated deuteron production in pp collisions at root s = 13 TeV, providing an opportunity to test the established picture for deuteron production in events with a hard scattering. Using a trigger particle with high transverse-momentum (p(T) > 5 GeV/c) as a proxy for the presence of a jet at midrapidity, we observe a measurable population of deuterons being produced around the jet proxy. The associated deuteron yield measured in a narrow angular range around the trigger particle differs by 2.4-4.8 standard deviations from the uncorrelated background. The data are described by PYTHIA model calculations featuring baryon coalescence. (C) 2021 The Author. Published by Elsevier B.V
- …
