Exploring the effect of current sheet thickness on the high‐frequency Fourier spectrum breakpoint of the solar wind

The magnetic power spectrum of the solar wind at 1 AU exhibits a breakpoint at a frequency of about 0.1–1 Hz, with the spectrum being steeper above the breakpoint than below the breakpoint. Because magnetic discontinuities contain much of the Fourier power in the solar wind, it is suspected that current sheet thicknesses (i.e., discontinuity thicknesses) may play a role in determining the frequency of this breakpoint. Using time series measurements of the solar wind magnetic field from the Wind spacecraft, the effect of current sheet thicknesses on the breakpoint is investigated by time stretching the solar wind time series at the locations of current sheets, effectively thickening the current sheets in the time series. This localized time stretching significantly affects the magnetic power spectral density of the solar wind in the vicinity of the high‐frequency breakpoint: a substantial fraction of the Fourier power at the breakpoint frequency is contained in current sheets that occupy a small fraction of the spatial volume of the solar wind. It is concluded that current sheet thickness appears to play a role in determining the frequency fB of the high‐frequency breakpoint of the magnetic power spectrum of the solar wind. This analysis of solar wind data is aided by comparisons with power spectra generated from artificial time series.Key PointsCurrent‐sheet thicknesses affect the high‐frequency breakpoint frequency of the solar windSolar‐wind current sheets contain substantial magnetic Fourier powerThere are outstanding questions about the solar‐wind current sheet origins and physicsPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/144299/1/jgra52192_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/144299/2/jgra52192.pd

Ion‐driven instabilities in the solar wind: Wind observations of 19 March 2005

Intervals of enhanced magnetic fluctuations have been frequently observed in the solar wind. But it remains an open question as to whether these waves are generated at the Sun and then transported outward by the solar wind or generated locally in the interplanetary medium. Magnetic field and plasma measurements from the Wind spacecraft under slow solar wind conditions on 19 March 2005 demonstrate seven events of enhanced magnetic fluctuations at spacecraft‐frame frequencies somewhat above the proton cyclotron frequency and propagation approximately parallel or antiparallel to the background magnetic field Bo. The proton velocity distributions during these events are characterized by two components: a more dense, slower core and a less dense, faster beam. Observed plasma parameters are used in a kinetic linear dispersion equation analysis for electromagnetic fluctuations at k x Bo = 0; for two events the most unstable mode is the Alfvén‐cyclotron instability driven by a proton component temperature anisotropy T⊥/T|| > 1 (where the subscripts denote directions relative to Bo), and for three events the most unstable mode is the right‐hand polarized magnetosonic instability driven primarily by ion component relative flows. Thus, both types of ion anisotropies and both types of instabilities are likely to be local sources of these enhanced fluctuation events in the solar wind.Key PointsIon temperature anisotropies and proton beam/core flows are sources of enhanced field observationsFor two events Alfven‐cyclotron modes are most unstableFor three events magnetosonic modes are most unstablePeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137412/1/jgra52322.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137412/2/jgra52322_am.pd

Search for first generation leptoquark pair production in the electron + missing energy + jets final state

We present a search for the pair production of first generation scalar leptoquarks (LQ) in data corresponding to an integrated luminosity of 5.4 fb$^{-1}$ collected with the D0 detector at the Fermilab Tevatron Collider in ppbar collisions at $\sqrt{s}=1.96$ TeV. In the channel $LQ \bar{LQ} \rightarrow e\nu_e qq'$, where q, q' are u or d quarks, no significant excess of data over background is observed, and we set a 95% C.L. lower limit of 326 GeV on the leptoquark mass, assuming equal probabilities of leptoquark decays to eq and $\nu_e q'$.Comment: 7 pages, 6 figures, submitted to PRD-R

Azimuthal anisotropy of charged jet production in root s(NN)=2.76 TeV Pb-Pb collisions

We present measurements of the azimuthal dependence of charged jet production in central and semi-central root s(NN) = 2.76 TeV Pb-Pb collisions with respect to the second harmonic event plane, quantified as nu(ch)(2) (jet). Jet finding is performed employing the anti-k(T) algorithm with a resolution parameter R = 0.2 using charged tracks from the ALICE tracking system. The contribution of the azimuthal anisotropy of the underlying event is taken into account event-by-event. The remaining (statistical) region-to-region fluctuations are removed on an ensemble basis by unfolding the jet spectra for different event plane orientations independently. Significant non-zero nu(ch)(2) (jet) is observed in semi-central collisions (30-50% centrality) for 20 <p(T)(ch) (jet) <90 GeV/c. The azimuthal dependence of the charged jet production is similar to the dependence observed for jets comprising both charged and neutral fragments, and compatible with measurements of the nu(2) of single charged particles at high p(T). Good agreement between the data and predictions from JEWEL, an event generator simulating parton shower evolution in the presence of a dense QCD medium, is found in semi-central collisions. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).Peer reviewe

Forward-central two-particle correlations in p-Pb collisions at root s(NN)=5.02 TeV

Two-particle angular correlations between trigger particles in the forward pseudorapidity range (2.5 2GeV/c. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B. V.Peer reviewe

Event-shape engineering for inclusive spectra and elliptic flow in Pb-Pb collisions at root(NN)-N-S=2.76 TeV

Peer reviewe