1,721,011 research outputs found
uBoost: a boosting method for producing uniform selection efficiencies from multivariate classifiers
Get PDFThe use of multivariate classifiers, especially neural networks and decision trees, has become commonplace in particle physics. Typically, a series of classifiers is trained rather than just one to enhance the performance; this is known as boosting. This paper presents a novel method of boosting that produces a uniform selection efficiency in a selected multivariate space. Such a technique is well suited for amplitude analyses or other situations where optimizing a single integrated figure of merit is not what is desired.United States. Dept. of Energy (Cooperative Research Agreement DE-FG02-94ER-40818)United States. Dept. of Energy (Early Career Award DE-SC0010497
Isolation of flow and nonflow correlations by two- and four-particle cumulant measurements of azimuthal harmonics in √s[subscript NN] = 200 GeV Au+Au collisions
No full textA data-driven method was applied to Au+Au collisions a t√s[subscript NN] = 200 GeV made with the STAR detector at RHIC to isolate pseudorapidity distance Δη-dependent and Δη-independent correlations by using two- and four-particle azimuthal cumulant measurements. We identified a Δη-independent component of the correlation, which is dominated by anisotropic flow and flow fluctuations. It was also found to be independent of η within the measured range of pseudorapidity |η| 0.7.Brookhaven National LaboratoryUnited States. Dept. of Energy. Office of Nuclear PhysicsUnited States. Dept. of Energy. Office of High Energy PhysicsNational Science Foundation (U.S.
Jet-Hadron Correlations in √s[subscript NN] = 200 GeV p + p and Central Au + Au Collisions
No full textAzimuthal angular correlations of charged hadrons with respect to the axis of a reconstructed (trigger) jet in Au + Au and p + p collisions at √s[subscript NN] = 200 GeV in STAR are presented. The trigger jet population in Au + Au collisions is biased toward jets that have not interacted with the medium, allowing easier matching of jet energies between Au + Au and p + p collisions while enhancing medium effects on the recoil jet. The associated hadron yield of the recoil jet is significantly suppressed at high transverse momentum (p[assoc over T]) and enhanced at low p[assoc over T] in 0%–20% central Au + Au collisions compared to p + p collisions, which is indicative of medium-induced parton energy loss in ultrarelativistic heavy-ion collisions.United States. Dept. of Energy. Office of Nuclear PhysicsUnited States. Dept. of Energy. Office of High Energy PhysicsNational Science Foundation (U.S.
Beam-Energy Dependence of Charge Separation Along the Magnetic Field in Au + Au Collisions at RHIC
No full textLocal parity-odd domains are theorized to form inside a quark-gluon plasma which has been produced in high-energy heavy-ion collisions. The local parity-odd domains manifest themselves as charge separation along the magnetic field axis via the chiral magnetic effect. The experimental observation of charge separation has previously been reported for heavy-ion collisions at the top RHIC energies. In this Letter, we present the results of the beam-energy dependence of the charge correlations in Au + Au collisions at midrapidity for center-of-mass energies of 7.7, 11.5, 19.6, 27, 39, and 62.4 GeV from the STAR experiment. After background subtraction, the signal gradually reduces with decreased beam energy and tends to vanish by 7.7 GeV. This implies the dominance of hadronic interactions over partonic ones at lower collision energies.Brookhaven National LaboratoryLawrence Berkeley National LaboratoryUnited States. Dept. of Energy. Office of Nuclear PhysicsUnited States. Dept. of Energy. Office of High Energy PhysicsNational Science Foundation (U.S.
Beam-Energy Dependence of the Directed Flow of Protons, Antiprotons, and Pions in Au+Au Collisions
No full textRapidity-odd directed flow (v[subscript 1]) measurements for charged pions, protons, and antiprotons near midrapidity (y = 0) are reported in √s[subscript NN] = 7.7, 11.5, 19.6, 27, 39, 62.4, and 200 GeV Au+Au collisions as recorded by the STAR detector at the Relativistic Heavy Ion Collider. At intermediate impact parameters, the proton and net-proton slope parameter dv1/dy|[subscript y=0] shows a minimum between 11.5 and 19.6 GeV. In addition, the net-proton dv1/dy|[subscript y=0] changes sign twice between 7.7 and 39 GeV. The proton and net-proton results qualitatively resemble predictions of a hydrodynamic model with a first-order phase transition from hadronic matter to deconfined matter, and differ from hadronic transport calculations.United States. Dept. of Energy. Office of Nuclear PhysicsUnited States. Dept. of Energy. Office of High Energy PhysicsNational Science Foundation (U.S.
Observation of D[superscript 0] Meson Nuclear Modifications in Au + Au Collisions at √s[subscript NN] = 200 GeV
No full textWe report the first measurement of charmed-hadron (D[superscript 0]) production via the hadronic decay channel (D[superscript 0] → K[superscript −] + π[superscript +]) in Au + Au collisions at √s[subscript NN] =200 GeV with the STAR experiment. The charm production cross section per nucleon-nucleon collision at midrapidity scales with the number of binary collisions, N[subscript bin], from p + p to central Au + Au collisions. The D[superscript 0] meson yields in central Au + Au collisions are strongly suppressed compared to those in p + p scaled by N[subscript bin], for transverse momenta p[subscript T] > 3 GeV/c, demonstrating significant energy loss of charm quarks in the hot and dense medium. An enhancement at intermediate p[subscript T] is also observed. Model calculations including strong charm-medium interactions and coalescence hadronization describe our measurements.Brookhaven National LaboratoryLawrence Berkeley National LaboratoryUnited States. Dept. of Energy. Office of Nuclear PhysicsUnited States. Dept. of Energy. Office of High Energy PhysicsUnited States. Dept. of Energy. Office of ScienceNational Science Foundation (U.S.
Dielectron Mass Spectra from Au + Au Collisions at √s[subscript NN] = 200 GeV
No full textWe report the STAR measurements of dielectron (e[superscript +]e[superscript −]) production at midrapidity (|y[subscript ee]| < 1) in Au + Au collisions at √s[subscript NN] = 200 GeV. 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/c[superscript 2]. 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.Brookhaven National LaboratoryLawrence Berkeley National LaboratoryUnited States. Dept. of Energy. Office of Nuclear PhysicsUnited States. Dept. of Energy. Office of High Energy PhysicsNational Science Foundation (U.S.
J/ψ Production at Low p[subscript T] in Au + Au and Cu + Cu Collisions at √s[subscript NN] = 200 GeV with the STAR Detector
No full textThe J/ψ p[subscript T] spectrum and nuclear modification factor (R[subscript AA]) are reported for p[subscript T] < 5GeV/c and |y| < 1 from 0% to 60% central Au + Au and Cu + Cu collisions at √s[subscript NN] = 200 GeV at STAR. A significant suppression of p[subscript T]-integrated J/ψ production is observed in central Au + Au events. The Cu + Cu data are consistent with no suppression, although the precision is limited by the available statistics. R[subscript AA] in Au + Au collisions exhibits a strong suppression at low transverse momentum and gradually increases with p[subscript T]. The data are compared to high-p[subscript T] STAR results and previously published BNL Relativistic Heavy Ion Collider results. Comparing with model calculations, it is found that the invariant yields at low p[subscript T] are significantly above hydrodynamic flow predictions but are consistent with models that include color screening and regeneration.Brookhaven National LaboratoryLawrence Berkeley National LaboratoryUnited States. Dept. of Energy. Office of Nuclear PhysicsUnited States. Dept. of Energy. Office of High Energy PhysicsNational Science Foundation (U.S.
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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