Персона: Алексеев, Игорь Геннадьевич
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Институт ядерной физики и технологий
Цель ИЯФиТ и стратегия развития - создание и развитие научно-образовательного центра мирового уровня в области ядерной физики и технологий, радиационного материаловедения, физики элементарных частиц, астрофизики и космофизики.
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Алексеев
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Игорь Геннадьевич
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104 results
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Теперь показываю 1 - 10 из 104
- ПубликацияТолько метаданныеGlobal and local polarization of A hyperons in Au plus Au collisions at 200 GeV from STAR(2019) Niida, T.; Adam, J.; Adamczyk, L.; Adams, J. R.; Alekseev, I.; Brandin, A. V.; Kochenda, L.; Kravtsov, P.; Nigmatkulov, G.; Okorokov, V. A.; Strikhanov, M.; Taranenko, A.; Алексеев, Игорь Геннадьевич; Брандин, Андрей Владимирович; Нигматкулов, Григорий Александрович; Окороков, Виталий Алексеевич; Стриханов, Михаил Николаевич; Тараненко, Аркадий ВладимировичNew results on global polarization of A hyperons in Au+Au collisions at root s(NN) = 200 GeV reveal non-zero signal on the order of a few tenths of a percent. Compared with lower energy results, the current measurement shows that the polarization decreases at higher collision energy, the trend being well reproduced by theoretical calculations. The polarization is found to be larger in more peripheral collisions, as well as in the in-plane than in the out-of-plane direction. The signal seems to depend on the asymmetry between positive and negative charge in each event, which may indicate an influence of the axial current induced by the magnetic field. In addition, the first measurement of a local polarization along the beam direction was performed. The results show a quadrupole modulation relative to the second-order event plane, as expected from the elliptic flow.
- ПубликацияТолько метаданныеUpsilon measurements in Au plus Au collisions at root S-NN=200 GeV with the STAR experiment(2019) Wang, P. F.; Adam, J.; Adamczyk, L.; Adams, J. R.; Alekseev, I.; Brandin, A. V.; Kochenda, L.; Kravtsov, P.; Nigmatkulov, G.; Okorokov, V. A.; Strikhanov, M.; Taranenko, A.; Алексеев, Игорь Геннадьевич; Брандин, Андрей Владимирович; Нигматкулов, Григорий Александрович; Окороков, Виталий Алексеевич; Стриханов, Михаил Николаевич; Тараненко, Аркадий ВладимировичWe present the latest measurements of Upsilon production in Au+Au collisions at root S-NN = 200 GeV via both di-muon and di-electron decay channels by the STAR experiment at RHIC. With the addition of the 2016 data set to those taken in 2011 and 2014, the precision of Upsilon measurements is significantly improved compared to previous preliminary results, especially for the excited Upsilon states. The nuclear modification factors for the ground and excited Upsilon states are shown as a functions of transverse momentum or centrality, and are compared to results from the LHC as well as to theoretical calculations.
- ПубликацияТолько метаданныеMeasurements of open charm production in Au plus Au collisions at root s(NN)=200 GeV with the STAR experiment at RHIC(2019) Radhakrishnan, S.; Adam, J.; Adamczyk, L.; Adams, J. R.; Alekseev, I.; Brandin, A. V.; Kochenda, L.; Kravtsov, P.; Nigmatkulov, G.; Okorokov, V. A.; Strikhanov, M.; Taranenko, A.; Алексеев, Игорь Геннадьевич; Брандин, Андрей Владимирович; Нигматкулов, Григорий Александрович; Окороков, Виталий Алексеевич; Стриханов, Михаил Николаевич; Тараненко, Аркадий ВладимировичWe report in these proceedings on the measurements of collision centrality and transverse momentum (p(T)) dependences of the Lambda(+/-)(c) production in Au+Au collisions at root s(NN) = 200 GeV, using the STAR Heavy Flavor Tracker (HFT). The Lambda(+/-)(c) signal significance is greatly improved with the addition of the high-statistics data set collected in 2016 and the use of a supervised machine learning method for topological reconstruction of the decay vertices. The measured Lambda(+/-)(c)/D-0 ratio shows a significant enhancement compared to the PYTHIA prediction for p+p collisions, across the measured p(T) range. We also report on the updated measurements of D-0 nuclear modification factors R-AA and R-CP using the 2014 data with the HFT. The measured D-0 R-AA in central collisions is lower than unity across the p(T) interval of the measurement. The D-0 yields show strong suppression at high p(T) (> 6 GeV/c) in central collisions, consistent with that of light flavor hadrons. The c (c) over bar production cross section per binary nucleon collision at midrapidity in Au+Au collisions at 200 GeV is extracted based on the various charm hadron measurements by STAR. It is observed that while the charm hadrochemistry is significantly modified in Au+Au collisions compared to p+p collisions, the c (c) over bar production cross section at midrapidity remains consistent between Au+Au and p+p collisions.
- ПубликацияТолько метаданныеThe STAR BES-II and Forward Rapidity Physics and Upgrades(2019) Yang, Q.; Adam, J.; Adamczyk, L.; Adams, J. R.; Alekseev, I.; Brandin, A. V.; Kochenda, L.; Kravtsov, P.; Nigmatkulov, G.; Okorokov, V. A.; Strikhanov, M.; Taranenko, A.; Алексеев, Игорь Геннадьевич; Брандин, Андрей Владимирович; Нигматкулов, Григорий Александрович; Окороков, Виталий Алексеевич; Стриханов, Михаил Николаевич; Тараненко, Аркадий ВладимировичThe second phase of the Beam Energy Scan at RHIC, BES-II, is scheduled to start in 2019 and will explore the high baryon density region of the QCD phase diagram with precision measurements. The detector upgrades will enhance some of the key measurements by extending STAR's kinematic reach, like the kurtosis of net-protons distribution which could pinpoint the position of a critical point. The upgrades currently under way comprise: the replacement of the inner TPC sectors, the Event Plane Detector (EPD) and the end-cap TOR Building on these upgrades STAR is planning to further enhance its detector capabilities by installing a Forward Calorimeter System (FCS) integrating an electromagnetic and hadronic calorimeter and a Forward Tracking System (FTS) combining 3 Silicon mini-strip disks and 4 Small-Strip Thin Gap Chamber (sTGC) wheels. The forward upgrades are motivated by studying the initial state of nucleons and nuclei and the exploration of cold QCD physics in the very high and low x regions. This contribution will highlight these upgrades and some of the physics opportunities that they allow.
- ПубликацияТолько метаданныеBeam energy dependence of net-Lambda fluctuations measured by the STAR experiment at the BNL Relativistic Heavy Ion Collider(2020) Adam, J.; Adamczyk, L.; Adams, J. R.; Adkins, J. K.; Alekseev, I.; Brandin, A. V.; Khyzhniak, Y. V.; Kochenda, L.; Kravtsov, P.; Nigmatkulov, G.; Okorokov, V. A.; Strikhanov, M.; Taranenko, A.; Алексеев, Игорь Геннадьевич; Брандин, Андрей Владимирович; Нигматкулов, Григорий Александрович; Окороков, Виталий Алексеевич; Стриханов, Михаил Николаевич; Тараненко, Аркадий ВладимировичThe measurements of particle multiplicity distributions have generated considerable interest in understanding the fluctuations of conserved quantum numbers in the quantum chromodynamics (QCD) hadronization regime, in particular near a possible critical point and near the chemical freeze-out. Net-protons and net-kaons have been used as proxies for the net-baryon number and net-strangeness, respectively. We report the measurement of efficiency- and centrality-bin width-corrected cumulant ratios (C-2/C-1,C-3/C-3) of net-A distributions, in the context of both strangeness and baryon number conservation, as a function of collision energy, centrality, and rapidity. The results are for Au + Au collisions at five beam energies (root s(NN) = 19.6, 27, 39, 62.4, and 200 GeV) recorded with the Solenoidal Tracker at RHIC (STAR). We compare our results to the Poisson and negative binomial (NBD) expectations, as well as to ultrarelativistic quantum molecular dynamics (UrQMD) and hadron resonance gas (HRG) model predictions. Both NBD and Poisson baselines agree with data within the statistical and systematic uncertainties. UrQMD describes the measured net-A C-1 and C-3 at 200 GeV reasonably well but deviates from C-2, and the deviation increases as a function of collision energy. The ratios of the measured cumulants show no features of critical fluctuations. The chemical freeze-out temperatures extracted from a recent HRG calculation, which was successfully used to describe the net-proton, net-kaon, and net-charge data, indicate A freeze-out conditions similar to those of kaons. However, large deviations are found when comparing with temperatures obtained from net-proton fluctuations. The net-A cumulants show a weak but finite dependence on the rapidity coverage in the acceptance of the detector, which can be attributed to quantum number conservation.
- ПубликацияТолько метаданныеBeam-energy dependence of the directed flow of deuterons in Au+Au collisions(2020) Adam, J.; Adamczyk, L.; Adams, J. R.; Adkins, J. K.; Alekseev, I.; Brandin, A. V.; Khyzhniak, Y. V.; Kochenda, L.; Kravtsov, P.; Nigmatkulov, G.; Okorokov, V. A.; Strikhanov, M.; Taranenko, A.; Алексеев, Игорь Геннадьевич; Брандин, Андрей Владимирович; Нигматкулов, Григорий Александрович; Окороков, Виталий Алексеевич; Стриханов, Михаил Николаевич; Тараненко, Аркадий Владимирович© 2020 American Physical Society.We present a measurement of the first-order azimuthal anisotropy v1 of deuterons from Au+Au collisions at sNN=7.7, 11.5, 14.5, 19.6, 27, and 39 GeV recorded with the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The energy dependence of the v1(y) slope, dv1/dy|y=0, for deuterons, where y is the rapidity, is extracted for semicentral collisions (10%-40% centrality) and compared with that of protons. While the v1(y) slopes of protons are generally negative for sNN>10GeV, those for deuterons are consistent with zero, a strong enhancement of the v1(y) slope of deuterons is seen at the lowest collision energy (the largest baryon density) at sNN=7.7GeV. In addition, we report the transverse momentum dependence of v1 for protons and deuterons. The experimental results are compared with transport and coalescence models.
- ПубликацияТолько метаданныеMeasurement of inclusive J/ψ polarization in p+p collisions at s =200 GeV by the STAR experiment(2020) Adam, J.; Adamczyk, L.; Adams, J. R.; Adkins, J. K.; Alekseev, I.; Brandin, A. V.; Khyzhniak, Y. V.; Kochenda, L.; Kravtsov, P.; Nigmatkulov, G.; Okorokov, V. A.; Strikhanov, M.; Taranenko, A.; Алексеев, Игорь Геннадьевич; Брандин, Андрей Владимирович; Нигматкулов, Григорий Александрович; Окороков, Виталий Алексеевич; Стриханов, Михаил Николаевич; Тараненко, Аркадий Владимирович© 2020 authors.We report on new measurements of inclusive J/ψ polarization at midrapidity in p+p collisions at s=200 GeV by the STAR experiment at the Relativistic Heavy Ion Collider. The polarization parameters, λθ, λφ, and λθφ, are measured as a function of transverse momentum (pT) in both the helicity and Collins-Soper (CS) reference frames within pT<10 GeV/c. Except for λθ in the CS frame at the highest measured pT, all three polarization parameters are consistent with 0 in both reference frames without any strong pT dependence. Several model calculations are compared with data, and the one using the Color Glass Condensate effective field theory coupled with nonrelativistic QCD gives the best overall description of the experimental results, even though other models cannot be ruled out due to experimental uncertainties.
- ПубликацияТолько метаданныеMeasurement of inclusive charged-particle jet production in Au plus Au collisions ats root S-NN=200 GeV(2020) Adam, J.; Adamczyk, L.; Adams, J. R.; Adkins, J. K.; Alekseev, I.; Brandin, A. V.; Khyzhniak, Y. V.; Kochenda, L.; Kravtsov, P.; Nigmatkulov, G.; Okorokov, V. A.; Strikhanov, M.; Taranenko, A.; Алексеев, Игорь Геннадьевич; Брандин, Андрей Владимирович; Нигматкулов, Григорий Александрович; Окороков, Виталий Алексеевич; Стриханов, Михаил Николаевич; Тараненко, Аркадий ВладимировичThe STAR Collaboration at the Relativistic Heavy Ion Collider reports the first measurement of inclusive jet production in peripheral and central Au+Au collisions at root S-NN = 200 GeV. Jets are reconstructed with the anti-k(T) algorithm using charged tracks with pseudorapidity vertical bar n vertical bar < 1.0 and transverse momentum 0.2 < p(T,jet)(ch) < 30 GeV/c, with jet resolution parameter R = 0.2, 0.3, and 0.4. The large background yield uncorrelated with the jet signal is observed to be dominated by statistical phase space, consistent with a previous coincidence measurement. This background is suppressed by requiring a high-transverse-momentum (high-p(T)) leading hadron in accepted jet candidates. The bias imposed by this requirement is assessed, and the p(T) region in which the bias is small is identified. Inclusive charged-particle jet distributions are reported in peripheral and central Au+Au collisions for 5 < p(T,jet)(ch) < 25 GeV/c and 5 < p(T,jet)(ch) < 30 GeV/c, respectively. The charged-particle jet inclusive yield is suppressed for central Au+Au collisions, compared to both the peripheral Au+Au yield from this measurement and to the pp yield calculated using the PYTHIA event generator. The magnitude of the suppression is consistent with that of inclusive hadron production at high p(T) and that of semi-inclusive recoil jet yield when expressed in terms of energy loss due to medium-induced energy transport. Comparison of inclusive charged-particle jet yields for different values of R exhibits no significant evidence for medium-induced broadening of the transverse jet profile for R <0.4 in central Au+Au collisions. The measured distributions are consistent with theoretical model calculations that incorporate jet quenching.
- ПубликацияТолько метаданныеStrange hadron production in Au+Au collisions at sNN =7.7, 11.5, 19.6, 27, and 39 GeV(2020) Adam, J.; Adamczyk, L.; Adams, J. R.; Adkins, J. K.; Alekseev, I.; Brandin, A. V.; Khyzhniak, Y. V.; Kochenda, L.; Kravtsov, P.; Nigmatkulov, G.; Okorokov, V. A.; Strikhanov, M.; Taranenko, A.; Алексеев, Игорь Геннадьевич; Брандин, Андрей Владимирович; Нигматкулов, Григорий Александрович; Окороков, Виталий Алексеевич; Стриханов, Михаил Николаевич; Тараненко, Аркадий Владимирович© 2020 American Physical Society. We present STAR measurements of strange hadron (KS0, Λ, Λ, Ξ-, Ξ+, ω-, ω+, and φ) production at midrapidity (|y|<0.5) in Au+Au collisions at sNN = 7.7-39 GeV from the Beam Energy Scan Program at the Relativistic Heavy Ion Collider (RHIC). Transverse-momentum spectra, averaged transverse mass, and the overall integrated yields of these strange hadrons are presented versus the centrality and collision energy. Antibaryon-to-baryon ratios (Λ/Λ, Ξ+/Ξ-, ω+/ω-) are presented as well and used to test a thermal statistical model and to extract the temperature normalized strangeness and baryon chemical potentials at hadronic freeze-out (μB/Tch and μS/Tch) in central collisions. Strange baryon-to-pion ratios are compared to various model predictions in central collisions for all energies. The nuclear modification factors (RCP) and antibaryon-to-meson ratios as a function of transverse momentum are presented for all collision energies. The KS0 RCP shows no suppression for pT up to 3.5 GeV/c at energies of 7.7 and 11.5 GeV. The Λ/KS0 ratio also shows baryon-to-meson enhancement at intermediate pT (≈2.5 GeV/c) in central collisions at energies above 19.6 GeV. Both observations suggest that there is likely a change of the underlying strange quark dynamics at collision energies below 19.6 GeV.
- ПубликацияТолько метаданныеMeasurement of away-side broadening with self-subtraction of flow in Au plus Au collisions at root S-NN = 200 GeV(2020) Adam, J.; Adamczyk, L.; Adams, J. R.; Adkins, J. K.; Alekseev, I.; Brandin, A. V.; Khyzhniak, Y. V.; Kochenda, L.; Kravtsov, P.; Nigmatkulov, G.; Okorokov, V. A.; Strikhanov, M.; Taranenko, A.; Алексеев, Игорь Геннадьевич; Брандин, Андрей Владимирович; Нигматкулов, Григорий Александрович; Окороков, Виталий Алексеевич; Стриханов, Михаил Николаевич; Тараненко, Аркадий ВладимировичHigh transverse momentum (p(T)) particle production is suppressed owing to the parton (jet) energy loss in the hot dense medium created in relativistic heavy-ion collisions. Redistribution of energy at low-to-modest p(T) has been difficult to measure, owing to large anisotropic backgrounds. We report a data-driven method for background evaluation and subtraction, exploiting the away-side pseudorapidity gaps, to measure the jetlike correlation shape in Au+Au collisions at root S-NN = 200 GeV in the STAR experiment. The correlation shapes, for trigger particles p(T) > 3 GeV/c and various associated particle p(T) ranges within 0.5 < p(T) < 10Gev/c, are consistent with Gaussians, and their widths increase with centrality. The results indicate jet broadening in the medium created in central heavy-ion collisions.