Binary Scaling Research Articles

J/ψProduction versus Centrality, Transverse Momentum, andRapidity inAu+AuCollisions atsNN=200 GeV

The PHENIX experiment at the BNL Relativistic Heavy Ion Collider (RHIC) has measured J/psi production for rapidities -2.2<y<2.2 in Au+Au collisions at square root sNN=200 GeV. The J/psi invariant yield and nuclear modification factor RAA as a function of centrality, transverse momentum, and rapidity are reported. A suppression of J/psi relative to binary collision scaling of proton-proton reaction yields is observed. Models which describe the lower energy J/psi data at the CERN Super Proton Synchrotron invoking only J/psi destruction based on the local medium density predict a significantly larger suppression at RHIC and more suppression at midrapidity than at forward rapidity. Both trends are contradicted by our data.

Heavy Flavor Physics in STAR

The STAR experiment at the BNL Relativistic Heavy Ion Collider (RHIC) measured heavy flavor production via two independent channels: hadronic and semileptonic decays. The nonphotonic electron spectrum was measured over a wide range of p T (up to 10 GeV/ c). The low- p T region was constrained by muon measurements. The extracted charm cross section, in p+p, d+Au, and Au+Au collisions, exhibits binary scaling suggestive of charm origins in the early phase of the collision. The nuclear modification factor shows a consistent pattern of suppression at high p T in central heavy-ion collisions not explained by current theoretical models.

Open charm measurements at STAR

We report on the measurements of D0 meson production via direct reconstruction through the hadronic decay channel D0→Kπ in minimum bias d+Au and Au+Au collisions at \(\sqrt{s_{NN}}=200\mathrm{GeV}\) with pT up to ∼3 GeV/c. We derive the charm production total cross-section per nucleon–nucleon collision from a combination of three measurements: the D0 meson spectra, the non-photonic electron spectra from charm semi-leptonic decays obtained in p+p, d+Au, and Au+Au collisions, and the charm-decayed single muon (prompt muon) spectra at low pT in Au+Au collisions. The cross-section is found to follow binary scaling, which is a signature of charm production exclusively at the initial impact. The implications of charm quark energy-loss and thermalization in the strongly interacting matter are discussed.

Measurement of single muon yields from charm semileptonic decay at $\sqrt{s_{NN}}$ =200 GeV Au + Au collisions at STAR

We report on the first measurement of single muon from charm semileptonic decays at low transverse momentum (p(T)) in root s(NN) = 200 GeV Au + Au collisions. Muon identification was obtained using the STAR time projection chamber in conjunction with a time-of-flight detector. The p(T) spectra of electron and muon from charm semileptonic decays are presented. The measured D -> mu + X at p(T) < 0.25 GeV / c greatly constrains the charm total cross section. The charm differential cross section d sigma(cc)/dy is found to be consistent with the number of binary collision scaling.

Open charm production in GeV Au+Au collisions

We report on the measurement of D meson production from the analysis of their hadronic (D0 → Kπ) and semileptonic (D → μ + X, D → e + X) decays in GeV Au+Au collisions. The transverse momentum (pT) spectra and the nuclear modification factors for D0 and for electron/muonThe word ‘muon’ refers to μ+/μ−, ‘electron’ refers to electron/positron throughout this article. from charm semileptonic decays will be presented. The differential cross section dσ/dy is found to be consistent with the number of binary scaling. The blast-wave fit suggests that the charm hadron freeze out earlier than other light flavour hadrons.

Medium modification of heavy flavour production measured by PHENIX in Au + Au collisions at GeV

Charm quarks serve as a probe of matter produced in heavy-ion collisions. Due to the large quark mass, the charm cross section is calculable as a point-like QCD process. Since initial-state effects should be small at RHIC energies, the charm yield should follow binary scaling at mid-rapidity. Heavy quarks are expected to lose less energy in the medium than lighter quarks due to the ‘dead-cone effect’. Heavy flavour production can be investigated in PHENIX via the pT spectra of single electrons. While the total charm yield measured from the Au + Au collisions taken by PHENIX in 2002 scales with the number of binary collisions, single-electron pT spectra suggest a strong suppression of the heavy flavour yield at high pT. We present an analysis of the centrality dependence of the electron spectra from heavy quark decays obtained from the high statistics data sample of Au + Au collisions at GeV taken in 2004.

Identified Baryon and Meson Distributions at Large Transverse Momenta fromAu+AuCollisions atsNN=200 GeV

Transverse momentum spectra of $\pi^{\pm}$, $p$ and $\bar{p}$ up to 12 GeV/c at mid-rapidity in centrality selected Au+Au collisions at $\sqrt{s_{_{NN}}} = 200$ GeV are presented. In central Au+Au collisions, both $\pi^{\pm}$ and $p(\bar{p})$ show significant suppression with respect to binary scaling at $p_T > $ 4 GeV/c. Protons and anti-protons are less suppressed than $\pi^{\pm}$, in the range 1.5 $< p_{T} <$6 GeV/c. The $\pi^-/\pi^+$ and $\bar{p}/p$ ratios show at most a weak $p_T$ dependence and no significant centrality dependence. The $p/\pi$ ratios in central Au+Au collisions approach the values in p+p and d+Au collisions at $p_T >$ 5 GeV/c. The results at high $p_T$ indicate that the partonic sources of $\pi^{\pm}$, $p$ and $\bar{p}$ have similar energy loss when traversing the nuclear medium.

Bennett clocking of quantum-dot cellular automata and the limits to binary logicscaling

We examine power dissipation in different clocking schemes for molecular quantum-dot cellularautomata (QCA) circuits. ‘Landauer clocking’ involves the adiabatic transition of a molecularcell from the null state to an active state carrying data. Cell layout creates devices whichallow data in cells to interact and thereby perform useful computation. We perform directsolutions of the equation of motion for the system in contact with the thermal environmentand see that Landauer’s Principle applies: one must dissipate an energy of at leastkBT per bit only when the information is erased. The ideas of Bennett can be applied to keepcopies of the bit information by echoing inputs to outputs, thus embedding any logicallyirreversible circuit in a logically reversible circuit, at the cost of added circuit complexity. Apromising alternative which we term ‘Bennett clocking’ requires only altering thetiming of the clocking signals so that bit information is simply held in place bythe clock until a computational block is complete, then erased in the reverseorder of computation. This approach results in ultralow power dissipation withoutadditional circuit complexity. These results offer a concrete example in which toconsider recent claims regarding the fundamental limits of binary logic scaling.

Modern developments in hypersonic wind tunnels

AbstractThe development of new methods of producing hypersonic wind-tunnel flows at increasing velocities during the last few decades is reviewed with attention to airbreathing propulsion, hypervelocity aerodynamics and superorbital aerodynamics. The role of chemical reactions in these flows leads to use of a binary scaling simulation parameter, which can be related to the Reynolds number, and which demands that smaller wind tunnels require higher reservoir pressure levels for simulation of flight phenomena. The use of combustion heated vitiated wind tunnels for propulsive research is discussed, as well as the use of reflected shock tunnels for the same purpose. A flight experiment validating shock-tunnel results is described, and relevant developments in shock tunnel instrumentation are outlined. The use of shock tunnels for hypervelocity testing is reviewed, noting the role of driver gas contamination in determining test time, and presenting examples of air dissociation effects on model flows. Extending the hypervelocity testing range into the superorbital regime with useful test times is seen to be possible by use of expansion tube/tunnels with a free piston driver.

Quarkonium production from d + Au to Au + Au collisions

The PHENIX experiment measured J/ $\psi$ production in pp, d + Au and Au + Au reactions at $\sqrt{s_{NN}}$ = 200 GeV over a wide range of rapidity and transverse momentum. The nuclear modification factor obtained by comparing the d + Au and pp cross sections as a function of rapidity, is consistent with shadowing of the gluon distribution functions. J/ $\psi$ production in Au + Au collisions was compared to the production in pp collisions and it was found to be inconsistent with models that predict strong enhancement relative to binary collision scaling.

Production of K0s, ϕ, Λ and Ξ from 200 GeV d+Au collisions at RHIC

We present the preliminary measurement of K0s, ϕ, Λ and Ξ transverse momentum (pt) distribution from GeV d+Au collisions at RHIC. The measured spectra can be described by using a double exponential fit. The centrality dependence of the particle yield with respect to the number of binary collision scaling (RCP) will be presented for a pt up to 6 GeV/c. The particle dependence of the RCP among K0s, ϕ, Λ and Ξ is consistent with expectations from parton recombination models for hadron formation. The Cronin effect and its particle dependence appear not due to initial parton scatterings alone as previously assumed in models.

Nuclear Modification Factors for Hadrons at Forward and Backward Rapidities in Deuteron-Gold Collisions atsNN=200 GeV

We report on charged hadron production in deuteron-gold reactions at sqrt[s(NN)]=200 GeV. Our measurements in the deuteron direction cover 1.4<eta<2.2, referred to as forward rapidity, and in the gold direction -2.0<eta<-1.4, referred to as backward rapidity, and a transverse momentum range p(T)=0.5-4.0 GeV/c. We compare the relative yields for different deuteron-gold collision centrality classes. We observe a suppression relative to binary collision scaling at forward rapidity, sensitive to low momentum fraction (x) partons in the gold nucleus, and an enhancement at backward rapidity, sensitive to high momentum fraction partons in the gold nucleus.

Open Charm Yields ind+AuCollisions atsNN=200 GeV

Midrapidity open charm spectra from direct reconstruction of D0(D0)-->K-/+pi+/- in d+Au collisions and indirect electron-positron measurements via charm semileptonic decays in p+p and d+Au collisions at squareroot[sNN]=200 GeV are reported. The D0(D0) spectrum covers a transverse momentum (pT) range of 0.1<pT<3 GeV/c, whereas the electron spectra cover a range of 1<pT<4 GeV/c. The electron spectra show approximate binary collision scaling between p+p and d+Au collisions. From these two independent analyses, the differential cross section per nucleon-nucleon binary interaction at midrapidity for open charm production from d+Au collisions at BNL RHIC is dsigma(NN)cc/dy=0.30+/-0.04(stat)+/-0.09(syst) mb. The results are compared to theoretical calculations. Implications for charmonium results in A+A collisions are discussed.

Centrality and pseudorapidity dependence of charged hadron production at intermediatepTinAu+Aucollisions atsNN=130GeV

We present STAR measurements of charged hadron production as a function of centrality in Au+Au collisions at sNN=130GeV. The measurements cover a phase space region of 0.2<pT<6.0GeV∕c in transverse momentum and −1<η<1 in pseudorapidity. Inclusive transverse momentum distributions of charged hadrons in the pseudorapidity region 0.5<∣η∣<1 are reported and compared to our previously published results for ∣η∣<0.5. No significant difference is seen for inclusive pT distributions of charged hadrons in these two pseudorapidity bins. We measured dN∕dη distributions and truncated mean pT in a region of pT>pTcut, and studied the results in the framework of participant and binary scaling. No clear evidence is observed for participant scaling of charged hadron yield in the measured pT region. The relative importance of hard scattering processes is investigated through binary scaling fraction of particle production.3 MoreReceived 15 April 2004DOI:https://doi.org/10.1103/PhysRevC.70.044901©2004 American Physical Society

Open charm yields in 200 GeV p+p and d+Au collisions at RHIC

Open charm spectra at mid-rapidity from direct reconstruction of D0 → Kπ and indirect electron/positron measurements via charm semileptonic decay in p+p and d+Au collisions at are reported. The combined spectra cover open charm transverse momentum range 0.1 ⪅ pT ⪅ 6 GeV/c. The electron spectra show approximate binary scaling between p+p and d+Au collisions. From these two independent analyses, the differential cross section per nucleon–nucleon interaction at mid-rapidity for open charm production at RHIC is (syst) mb. The next-to-leading-order pQCD calculation underpredicts the charm yields.

J∕ψproduction inAu-Aucollisions atsNN=200GeV

First results on charm quarkonia production in heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) are presented. The yield of J/psi's measured in the PHENIX experiment via electron-positron decay pairs at midrapidity for Au-Au reactions at roots(NN) = 200 GeV is analyzed as a function of collision centrality. For this analysis we have studied 49.3x10(6) minimum bias Au-Au reactions. We present the J/psi invariant yield dN/dy for peripheral and midcentral reactions. For the most central collisions where we observe no signal above background, we quote 90% confidence level upper limits. We compare these results with our J/psi measurement from proton-proton reactions at the same energy. We find that our measurements are not consistent with models that predict strong enhancement relative to binary collision scaling.

Nuclear profile dependence of elliptic flow from a parton cascade

The transverse profile dependence of elliptic flow is studied in a parton cascade model. We compare results from the binary scaling profile to results from the wounded nucleon scaling profile. The impact parameter dependence of elliptic flow is shown to depend sensitively on the transverse profile of initial particles, however, if elliptic flow is plotted as a function of the relative multiplicity, the nuclear profile dependence disappears. The insensitivity was found previously in a hydrodynamical calculation. Our calculations indicate that the insensitivity is also valid with additional viscous corrections. In addition, the minimum bias differential elliptic flow is demonstrated to be insensitive to the nuclear profile of the system.

Open charm and charmonium production at relativistic energies

We calculate open charm and charmonium production in $Au+Au$ reactions at $\sqrt{s}$ = 200 GeV within the hadron-string dynamics (HSD) transport approach employing open charm cross sections from $pN$ and $\pi N$ reactions that are fitted to results from PYTHIA and scaled in magnitude to the available experimental data. Charmonium dissociation with nucleons and formed mesons to open charm ($D+\bar{D}$ pairs) is included dynamically. The 'comover' dissociation cross sections are described by a simple phase-space model including a single free parameter, i.e. an interaction strength $M_0^2$, that is fitted to the $J/\Psi$ suppression data for $Pb+Pb$ collisions at SPS energies. As a novel feature we implement the backward channels for charmonium reproduction by $D \bar{D}$ channels employing detailed balance. From our dynamical calculations we find that the charmonium recreation is comparable to the dissociation by 'comoving' mesons. This leads to the final result that the total $J/\Psi$ suppression at $\sqrt{s}$ = 200 GeV as a function of centrality is slightly less than the suppression seen at SPS energies by the NA50 Collaboration, where the 'comover' dissociation is substantial and the backward channels play no role. Furthermore, even in case that all directly produced $J/\Psi$ mesons dissociate immediately (or are not formed as a mesonic state), a sizeable amount of charmonia is found asymptotically due to the $D+\bar{D} \to J/\Psi$ + meson channels in central collisions of $Au+Au$ at $\sqrt{s}$ = 200 GeV which, however, is lower than the $J/\Psi$ yield expected from binary scaling of $pp$ collisions.

High momentum particle suppression in AuAu collisions at RHIC

Phenix has measured at mid-rapidity tranverse momentum spectra of charged particles in AuAu collisions at √SNN = 130 [1] and 200 GeV/c. At both energies, in central collisions Phenix observes a suppression of high momentum particles relative to a binary collision scaling of nucleon-nucleon interactions. The evolution with the event centrality has been investigated [2].

Generalized Nonequilibrium Binary Scaling for Shock Standoff on Hypersonic Blunt Bodies

Although numerical codes are available to predict δ, they are expensive for engineering parametric studies and do not yield physical insight and similitude laws needed for experimental design and data interpretation. On the other hand, existing analytical methods may not permit extension to include multitemperature ionization. This paper examines a new analytical theory of shock standoff with a nonequilibrium-dissociated shock layer to demonstrate a generalized binary scaling property for high-altitude hypervelocity flight simulation work.