# Faculty Publications: January, 2016

Query Results from the Smithsonian/NASA Astrophysics Data System (ADS)

 Title: A perfect proposal Authors: Kleppner, Daniel; Horowitz, Paul Publication: Physics Today, vol. 69, issue 1, pp. 48-52 Publication Date: 01/2016 Origin: CROSSREF DOI: 10.1063/PT.3.3053 Bibliographic Code: 2016PhT....69a..48K

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Not Available

 Title: Improving the Pan-STARRs/2MASS 3-D dust map: Regularization for increased resolution and fidelity. Authors: Finkbeiner, Douglas P.; Green, Gregory; Lee, Albert; Ford Schlafly, Edward Publication: American Astronomical Society, AAS Meeting #227, id.242.06 Publication Date: 01/2016 Origin: AAS Abstract Copyright: (c) 2016: American Astronomical Society Bibliographic Code: 2016AAS...22724206F

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The Green et al. (2015) 3-D map of interstellar dust uses photometry of nearly 1 billion stars from Pan-STARRS1 and 2MASS to infer the distribution of dust in the Milky Way. The current map treats each angular pixel (~ 6 arcmin) independently, and estimates the dust in 30 distance bins. However, dust structures cut across pixels and the fit could be improved by coupling the dust density in neighboring pixels. This also has the advantage that fewer stars would be required per pixel, allowing finer angular resolution. We propose a simple way to do this, and show that it allows the use of smaller angular pixels and produces sharper resolution in the distance direction for a test case in Orion. We intend to incorporate similar regularization into the next full-sky 3-D dust map.

 Title: Dust Reddening Variation in the Milky Way Authors: Lee, Albert; Finkbeiner, Douglas P.; Green, Gregory; Ford Schlafly, Edward Publication: American Astronomical Society, AAS Meeting #227, id.242.07 Publication Date: 01/2016 Origin: AAS Abstract Copyright: (c) 2016: American Astronomical Society Bibliographic Code: 2016AAS...22724207L

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Various studies of dust extinction have shown that reddening curves vary from cloud to cloud. However, most of these results use relatively small numbers of stars in limited regions of interest. We describe a generalized technique for estimating the angular variation in the reddening law across the Milky Way at mid-to-high galactic latitudes, inferred from the photometry of millions of stars from Pan-STARRS 1. We find pixels where stars are primarily extinguished by a single dust-cloud, and determine a most likely de-reddening vector from shifts of the stellar locus in color space. We present maps for some target clouds, and compare a variety of reddening laws with our results.The maps should help us better understand the general properties of dust in the Milky Way, as well as provide more accurate extinction correction in the relevant regions. The stellar locus fitting technique can also corroborate detailed studies of reddening based on APOGEE spectra (Schlafly et al.) and more rigorous analyses of the line-of-sight extinction (Green et al.)

 Title: Milky Way Dust in 3D using Pan-STARRS 1 Authors: Green, Gregory; Ford Schlafly, Edward; Lee, Albert; Finkbeiner, Douglas P. Publication: American Astronomical Society, AAS Meeting #227, id.242.08 Publication Date: 01/2016 Origin: AAS Abstract Copyright: (c) 2016: American Astronomical Society Bibliographic Code: 2016AAS...22724208G

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We present a three-dimensional map of dust reddening in the Milky Way, covering three quarters of the sky out to a distance of several kiloparsecs, at an angular resolution of ~7'. We combine stellar photometry from Pan-STARRS 1 and 2MASS with prior information on the spatial distribution, metallicity and luminosity of stars to infer the distance, reddening and type of 800 million stars. Using this information, we infer how dust reddening increases with distance along 2.4 million sightlines north of δ = -30°.Our map reveals a wealth of structure within the ISM, from angular scales of ~7' to large cloud complexes. Comparison with the 2D Planck reddening maps shows agreement to within 0.05 mag in E(B-V) out to a cumulative reddening of 0.5 mag. We expect this map to have a wide range of applications, from correcting for reddening in observations, to studies of Galactic structure, to distance determinations to molecular clouds in the Milky Way.Our map has now been released, and is available at http://argonaut.skymaps.info. We provide an online tool for exploring the map, an API through which users can query the map remotely, and the full data cube for users who desire access to the entire map.

 Title: Interstellar Extinction and its Variation in the Galaxy Authors: Ford Schlafly, Edward; Rix, Hans-Walter; Finkbeiner, Douglas P.; Green, Gregory; Lee, Albert; Meisner, Aaron M. Publication: American Astronomical Society, AAS Meeting #227, id.242.09 Publication Date: 01/2016 Origin: AAS Abstract Copyright: (c) 2016: American Astronomical Society Bibliographic Code: 2016AAS...22724209F

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Dust reddening is an important diagnostic of the interstellar medium and the dust grain size distribution, as well as a pervasive observational nuisance. Detailed studies of the dust extinction curve and its variation have hithertofore been largely limited to samples of hundreds of specially chosen stars. We use spectroscopy from APOGEE in combination with photometry from Pan-STARRS1, 2MASS, and WISE to characterize the dust extinction curve throughout much of the nearest few kiloparsecs of the Galactic plane using tens of thousands of stars. We make new measurements of the dust extinction curve and its variation, finding that the extinction curve in the optical through infrared is well characterized by a one-parameter family of curves, described, for instance, by R(V). Our data show little evidence of any need for further parameters. The local curvature of the extinction curve increases with decreasing R(V) throughout most of the optical and infrared: the extinction curve in the infrared is not more universal'' than in the optical, in contrast to several widely-used extinction curve parameterizations. We find that the shape of the dust extinction curve is rather uniform, with σ(R(V)) = 0.2, and with less than two percent of sight lines having R(V) > 4. However, significant spatially coherent variations in R(V) do exist. The primary variations are on scales much larger than individual molecular clouds, indicating that grain growth in dense molecular cloud environments is not the primary driver of R(V) variations in dust at large. Indeed, we find no correlation between R(V) and dust column density out to E(B-V) ≈ 2.

 Title: Inference of Dim Gamma-Ray Point Sources Using Probabilistic Catalogues Authors: Daylan, Tansu; Portillo, Stephen; Finkbeiner, Douglas P. Publication: American Astronomical Society, AAS Meeting #227, id.337.08 Publication Date: 01/2016 Origin: AAS Abstract Copyright: (c) 2016: American Astronomical Society Bibliographic Code: 2016AAS...22733708D

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Poisson regression of the Fermi-LAT data in the inner Milky Way reveals an extended gamma-ray excess. The anomalous emission falls steeply away from the galactic center and has an energy spectrum that peaks at 1-2 GeV. An important question is whether the signal is coming from a collection of unresolved point sources, possibly recycled pulsars, or constitutes a truly diffuse emission component. Previous analyses have relied on non-Poissonian template fits or wavelet decomposition of the Fermi-LAT data, which find evidence for a population of dim point sources just below the 3FGL flux limit. In order to be able to make conclusions about such a dim population we propose to sample from the catalogue space of point sources in the inner galaxy, where the model dimensionality, i.e., the number of sources, is unknown. Although being a computationally expensive sampling problem, this approach allows us to infer the number, luminosity and radial distribution of the point source population that is consistent with the data while providing a Bayesian evidence for the point source hypothesis, which is independent of the model indicator. This talk will focus on the method of trans-dimensional sampling using the reversible-jump formalism and its application to the inference of a mock point source population. See the poster by Stephen K. N. Portillo for the inferred catalogue using the high latitude Fermi-LAT data.

 Title: A Probabilistic Catalogue of Unresolved High Latitude Fermi LAT Sources Authors: Portillo, Stephen; Daylan, Tansu; Finkbeiner, Douglas P. Affiliation: AA(Harvard University), AB(Harvard University), AC(Harvard University) Publication: American Astronomical Society, AAS Meeting #227, id.337.09 Publication Date: 01/2016 Origin: AAS Abstract Copyright: (c) 2016: American Astronomical Society Bibliographic Code: 2016AAS...22733709P

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Several groups have identified a highly significant and spatially extended excess of GeV gamma-rays in the Inner Galaxy using data from the Fermi LAT. While this signal's properties are consistent with those expected from dark matter annihilation, another interpretation is that it is the emission from a population of unresolved point sources. Motivated by the point source interpretation, we implement a Bayesian method for producing probabilistic catalogues to constrain the population of point sources below the Fermi LAT detection limit. To validate our method, we apply it to the high latitude Fermi LAT data to confirm that the probabilistic catalogue recovers the resolved sources in the Fermi Collaboration's 3FGL catalogue. Then, we compare our constraints on the unresolved point source population at high latitude to those obtained using non-Poissonian template fitting.

 Title: A proposal for a test of Weak Equivalence Principle with improved accuracy using a cryogenic differential accelerometer installed on a pendulum Authors: Iafolla, V. A.; Fiorenza, E.; Lefevre, C.; Lucchesi, D. M.; Lucente, M.; Magnafico, C.; Nozzoli, S.; Peron, R.; Santoli, F.; Lorenzini, E. C.; Milyukov, V.; Shapiro, I. I.; Glashow, S. Publication: Advances in Space Research, Volume 57, Issue 2, p. 715-723. (AdSpR Homepage) Publication Date: 01/2016 Origin: ELSEVIER Keywords: Weak Equivalence Principle, Differential accelerometer, GReAT, GReAT_G Abstract Copyright: (c) 2016 COSPAR DOI: 10.1016/j.asr.2015.11.013 Bibliographic Code: 2016AdSpR..57..715I

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We present here the concept for a new experimental test of the Weak Equivalence Principle (WEP) carried out in the gravity field of the Sun. The WEP, stating the independence of the gravitational acceleration a body is subject to from its mass and composition, is at the basis of general relativity theory and more in general of metric theories of gravitation. It is therefore very important to test it to the precision allowable by current technology. The experiment here proposed aims at measuring the relative acceleration of two test masses in free fall, searching for a possible violation of the WEP, which would show up as a non-zero acceleration signal. The core of the experiment is constituted by a differential accelerometer with zero baseline, whose central elements are two test masses of different materials. This differential accelerometer is placed on a pendulum, in such a way as to make the common center of mass coincident with the center of mass of the pendulum itself. Ensuring a very precise centering, such a system should provide a high degree of attenuation of the local seismic noise, which - together with an integration time of the order of tens of days - would allow a test of the WEP with an accuracy improved by at least an order of magnitude with respect to the best measurements achieved so far. One of the strengths of this proposal is the know-how acquired from a previous study and technology development (GReAT: General Relativity Accuracy Test) that involved a test of the WEP in the gravity field of the Earth, in free fall inside a co-moving capsule released from a stratospheric balloon. The concept of the experiment is introduced, with particular attention to the differential accelerometer and its accommodation on the pendulum. A preliminary estimate of the attainable precision is given, along with a critical analysis of the associated challenges.

 Title: Initial Performance of BICEP3: A Degree Angular Scale 95 GHz Band Polarimeter Authors: Wu, W. L. K.; Ade, P. A. R.; Ahmed, Z.; ... Kovac, J. M.; ... and 48 coauthors. Publication: eprint arXiv:1601.00125 Publication Date: 01/2016 Origin: ARXIV Keywords: Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - Cosmology and Nongalactic Astrophysics Comment: 7 pages, LTD-16 proceedings; doi:10.1007/s10909-015-1403-x Bibliographic Code: 2016arXiv160100125W

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BICEP3 is a $550~mm$ aperture telescope with cold, on-axis, refractive optics designed to observe at the $95~GHz$ band from the South Pole. It is the newest member of the BICEP/Keck family of inflationary probes specifically designed to measure the polarization of the cosmic microwave background (CMB) at degree-angular scales. BICEP3 is designed to house 1280 dual-polarization pixels, which, when fully-populated, totals to $\sim$9$\times$ the number of pixels in a single Keck $95~GHz$ receiver, thus further advancing the BICEP/Keck program's $95~GHz$ mapping speed. BICEP3 was deployed during the austral summer of 2014-2015 with 9 detector tiles, to be increased to its full capacity of 20 in the second season. After instrument characterization measurements were taken, CMB observation commenced in April 2015. Together with multi-frequency observation data from Planck, BICEP2, and the Keck Array, BICEP3 is projected to set upper limits on the tensor-to-scalar ratio to $r$ $\lesssim 0.03$ at $95\%$ C.L..

 Title: Search for a Low-Mass Neutral Higgs Boson with Suppressed Couplings to Fermions Using Events with Multiphoton Final States Authors: CDF Collaboration; Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... and 393 coauthors. Publication: eprint arXiv:1601.00401 Publication Date: 01/2016 Origin: ARXIV Keywords: High Energy Physics - Experiment Comment: Submitted to Phys. Rev. Lett Bibliographic Code: 2016arXiv160100401C

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A search for a Higgs boson with suppressed couplings to fermions, $h_f$, assumed to be the neutral, lower-mass partner of the Higgs boson discovered at the Large Hadron Collider, is reported. Such a Higgs boson could exist in extensions of the standard model with two Higgs doublets, and could be produced via $p\bar{p} \to H^\pm h_f \to W^* h_f h_f \to 4\gamma + X$, where $H^\pm$ is a charged Higgs boson. This analysis uses all events with at least three photons in the final state from proton-antiproton collisions at a center-of-mass energy of 1.96~TeV collected by the Collider Detector at Fermilab, corresponding to an integrated luminosity of 9.2~${\rm fb}^{-1}$. No evidence of a signal is observed in the data. Values of Higgs-boson masses between 10 and 100 GeV/$c^2$ are excluded at 95\% Bayesian credibility.

 Title: Soft Hair on Black Holes Authors: Hawking, Stephen W.; Perry, Malcolm J.; Strominger, Andrew Publication: eprint arXiv:1601.00921 Publication Date: 01/2016 Origin: ARXIV Keywords: High Energy Physics - Theory Comment: 22 pages 2 figures Bibliographic Code: 2016arXiv160100921H

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It has recently been shown that BMS supertranslation symmetries imply an infinite number of conservation laws for all gravitational theories in asymptotically Minkowskian spacetimes. These laws require black holes to carry a large amount of soft ($i.e.$ zero-energy) supertranslation hair. The presence of a Maxwell field similarly implies soft electric hair. This paper gives an explicit description of soft hair in terms of soft gravitons or photons on the black hole horizon, and shows that complete information about their quantum state is stored on a holographic plate at the future boundary of the horizon. Charge conservation is used to give an infinite number of exact relations between the evaporation products of black holes which have different soft hair but are otherwise identical. It is further argued that soft hair which is spatially localized to much less than a Planck length cannot be excited in a physically realizable process, giving an effective number of soft degrees of freedom proportional to the horizon area in Planck units.

 Title: Liquid jet rebound upon impact on a soft gel Authors: Daniel, Dan; Yao, Xi; Brenner, Michael; Aizenberg, Joanna Publication: eprint arXiv:1601.02065 Publication Date: 01/2016 Origin: ARXIV Keywords: Physics - Fluid Dynamics, Condensed Matter - Soft Condensed Matter Bibliographic Code: 2016arXiv160102065D

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A liquid jet can stably bounce off a sufficiently soft gel, by following the contour of the dimple created due to pressure upon impact. This phenomenon is relatively insensitive to the wetting properties of the liquid and was observed for different liquids over a wide range of surface tensions, $\gamma$ = 24-72 mN/m. In contrast, other jet rebound phenomena are typically sensitive to $\gamma$: jet rebound off a hard solid (e.g. superhydrophobic surface) or another liquid is possible only for high and low $\gamma$ liquids respectively. This is because an air layer must exist between the two interfaces. For a soft gel, no air layer is necessary and jet rebound remains stable even when there is direct liquid-gel contact.

 Title: Self-sustained lift and low friction via soft lubrication Authors: Saintyves, Baudouin; Jules, Théo; Salez, Thomas; Mahadevan, L. Publication: eprint arXiv:1601.03063 Publication Date: 01/2016 Origin: ARXIV Keywords: Condensed Matter - Soft Condensed Matter, Condensed Matter - Materials Science, Physics - Chemical Physics, Physics - Fluid Dynamics Bibliographic Code: 2016arXiv160103063S

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Relative motion between soft wet solids arises in a number of applications in natural and artificial settings, and invariably couples elastic deformation and fluid flow. We explore this in a minimal setting by considering a fluid-immersed negatively-buoyant cylinder moving along a soft inclined wall. Our experiments show that there is a robust steady-state sliding regime of the cylinder with an effective friction that is significantly reduced relative to that of rigid fluid-lubricated contacts. A simple scaling approach that couples the cylinder-induced flow to substrate deformation allows us to explain the emergence of an elastohydrodynamic lift that underlies the self-sustained lubricated motion of the cylinder, consistent with recent theoretical predictions. Our results suggest an explanation for a range of effects such as reduced wear in animal joints and long-runout landslides, and can be couched as a design principle for low-friction interfaces.

 Title: Direct Time-domain Observation of Conformational Relaxation in Gas-phase Cold Collisions Authors: Drayna, Garrett K.; Hallas, Christian; Wang, Kenneth; Domingos, Sérgio R.; Eibenberger, Sandra; Doyle, John M.; Patterson, David Publication: eprint arXiv:1601.03359 Publication Date: 01/2016 Origin: ARXIV Keywords: Physics - Chemical Physics, Physics - Atomic Physics Comment: 7 pages, 6 figures, LaTeX; Withdrawn in accordance with the submission policies of Angewandte Chemie Bibliographic Code: 2016arXiv160103359D

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Cooling molecules in the gas phase is important for precision spectroscopy, cold molecule physics, and physical chemistry. Measurements of conformational relaxation cross sections shed important light on potential energy surfaces and energy flow within a molecule. However, gas-phase conformational cooling has not been previously observed directly. In this work, we directly observe conformational dynamics of 1,2-propanediol in cold (6K) collisions with atomic helium using microwave spectroscopy and buffer-gas cooling. Precise knowledge and control of the collisional environment in the buffer-gas allows us to measure the absolute collision cross-section for conformational relaxation. Several conformers of 1,2-propanediol are investigated and found to have relaxation cross-sections with He ranging from $\sigma=4.7(3.0)\times10^{-18}\:\mathrm{cm}^{2}$ to $\sigma>5\times10^{-16}\:\mathrm{cm}^{2}$. Our method is applicable to a broad class of molecules and could be used to provide information about the potential energy surfaces of previously uninvestigated molecules.

 Title: Measurement of the $B_c^{pm}$ production cross section in $pbar{p}$ collisions at $sqrt{s}=1.96$ TeV Authors: CDF Collaboration; Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... and 393 coauthors. Publication: eprint arXiv:1601.03819 Publication Date: 01/2016 Origin: ARXIV Keywords: High Energy Physics - Experiment Comment: 33 pages, 25 figures, and 20 tables (To be submitted to Phys. Rev. D) Bibliographic Code: 2016arXiv160103819C

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We describe a measurement of the ratio of the cross sections times branching fractions of the $B_c^+$ meson in the decay mode $B_c^+ \rightarrow J/\psi \mu\nu$ to the $B^+$ meson in the decay mode $B^+ \rightarrow J/\psi K^+$ in proton-antiproton collisions at center-of-mass energy $\sqrt{s}=1.96$ TeV. The measurement is based on the complete CDF Run II data set, which comes from an integrated luminosity of $8.7\,{\rm fb}^{-1}$. The ratio of the production cross sections times branching fractions for $B_c^+$ and $B_c^+$ mesons with momentum transverse to the beam greater than $6~\textrm{GeV}/c$ and rapidity magnitude smaller than 0.6 is $0.211\pm 0.012~\mbox{(stat)}^{+0.021}_{-0.020}~\mbox{(syst)}$. Using the known $B^+ \rightarrow J/\psi K^+$ branching fraction, the known $B^+$ production cross section, and a selection of the predicted $B_c^+ \rightarrow J/\psi \mu\nu$ branching fractions, the range for the total $B_c^+$ production cross section is estimated.

 Title: First measurement of electron neutrino appearance in NOvA Authors: Adamson, P.; Ader, C.; Andrews, M.;... Feldman, G. J.;... and 256 coauthors. Publication: eprint arXiv:1601.05022 Publication Date: 01/2016 Origin: ARXIV Keywords: High Energy Physics - Experiment, Physics - Instrumentation and Detectors Comment: 7 pages, 4 figures. Submitted to Phys. Rev. Lett Bibliographic Code: 2016arXiv160105022A

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We report results from the first search for $\nu_\mu\to\nu_e$ transitions by the NOvA experiment. In an exposure equivalent to $2.74\times10^{20}$ protons-on-target in the upgraded NuMI beam at Fermilab, we observe 6 events in the Far Detector, compared to a background expectation of $0.99\pm0.11$ (syst.) events based on the Near Detector measurement. A secondary analysis observes 11 events with a background of $1.07\pm0.14$ (syst.). The $3.3\sigma$ excess of events observed in the primary analysis disfavors $0.1\pi < \delta_{CP} < 0.5\pi$ in the inverted mass hierarchy at the 90% C.L.

 Title: Collective atomic scattering and motional effects in a dense coherent medium Authors: Bromley, Sarah L.; Zhu, Bihui; Bishof, Michael; Zhang, Xibo; Bothwell, Tobias; Schachenmayer, Johannes; Nicholson, Travis L.; Kaiser, Robin; Yelin, Susanne F.; Lukin, Mikhail D.; Rey, Ana Maria; Ye, Jun Publication: eprint arXiv:1601.05322 Publication Date: 01/2016 Origin: ARXIV Keywords: Physics - Atomic Physics Comment: 27 pages, 4 figures Bibliographic Code: 2016arXiv160105322B

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We investigate systematically collective emission from coherently driven ultracold $^{88}$Sr atoms. We perform two sets of experiments, using a strong (weak) transition with natural linewidth of $\Gamma$$=$$32$ MHz ($7.5$ kHz), making it insensitive (sensitive) to atomic motion at one microKelvin. We observe highly directional forward emission with a peak intensity that is enhanced, for the strong transition, by $>$$10^{3} compared to that in the transverse direction. This is accompanied by substantial broadening of spectral lines. For the weak transition, the forward enhancement is substantially reduced due to motion. At the same time, a density-dependent frequency shift of the weak transition (\sim$$0.1\Gamma$) is observed. In contrast, this line shift is suppressed to $<$$0.01\Gamma$ for the strong transition. Along the transverse direction, we observe strong polarization dependences of the fluorescence intensity and line broadening for both transitions. The measurements are reproduced with a theoretical model treating the atoms as coherent, interacting, radiating dipoles.

 Title: Enhanced Thermoelectric Power in Graphene: Violation of the Mott Relation By Inelastic Scattering Authors: Ghahari, Fereshte; Xie, Hong-Yi; Taniguchi, Takashi; Watanabe, Kenji; Foster, Matthew S.; Kim, Philip Publication: eprint arXiv:1601.05859 Publication Date: 01/2016 Origin: ARXIV Keywords: Condensed Matter - Mesoscale and Nanoscale Physics Comment: 5 pages, 4 figures Bibliographic Code: 2016arXiv160105859G

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We report the enhancement of the thermoelectric power (TEP) in graphene with extremely low disorder. At high temperature we observe that the TEP is substantially larger than the prediction of the Mott relation, approaching to the hydrodynamic limit due to strong inelastic scattering among the charge carriers. However, closer to room temperature the inelastic carrier-optical-phonon scattering becomes more significant and limits the TEP below the hydrodynamic prediction. We support our observation by employing a Boltzmann theory incorporating disorder, electron interactions, and optical phonons.

 Title: Measurement of the forward-backward asymmetry in low-mass bottom-quark pairs produced in proton-antiproton collisions Authors: CDF Collaboration; Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.; and 393 coauthors. Publication: eprint arXiv:1601.06526 Publication Date: 01/2016 Origin: ARXIV Keywords: High Energy Physics - Experiment Comment: submitted to Phys. Rev. D Bibliographic Code: 2016arXiv160106526C

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We report a measurement of the forward-backward asymmetry, $A_{FB}$, in $b\bar{b}$ pairs produced in proton-antiproton collisions and identified by muons from semileptonic $b$-hadron decays. The event sample was collected at a center-of-mass energy of $\sqrt{s}=1.96$ TeV with the CDF II detector and corresponds to 6.9 fb$^{-1}$ of integrated luminosity. We obtain an integrated asymmetry of $A_{FB}(b\bar{b})=(1.2 \pm 0.7)$\% at the particle level for $b$-quark pairs with invariant mass, $m_{b\bar{b}}$, down to $40$ GeV/$c^2$ and measure the dependence of $A_{FB}(b\bar{b})$ on $m_{b\bar{b}}$. The results are compatible with expectations from the standard model.

 Title: Continuous probe of cold complex molecules with infrared frequency comb spectroscopy Authors: Spaun, Ben; Changala, P. Bryan; Patterson, David; Bjork, Bryce J.; Heckl, Oliver H.; Doyle, John M.; Ye, Jun Publication: eprint arXiv:1601.07845 Publication Date: 01/2016 Origin: ARXIV Keywords: Physics - Chemical Physics Bibliographic Code: 2016arXiv160107845S

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Cavity-enhanced frequency comb spectroscopy for molecule detection in the mid-infrared powerfully combines high resolution, high sensitivity, and broad spectral coverage. However, this technique, and essentially all spectroscopic methods, is limited in application to relatively small, simple molecules. Here we integrate comb spectroscopy with continuous, cold samples of molecules produced via buffer gas cooling, thus enabling the study of significantly more complex molecules. We report simultaneous gains in resolution, sensitivity, and bandwidth and demonstrate this combined capability with the first rotationally resolved direct absorption spectra in the CH stretch region of several complex molecules. These include nitromethane (CH$_3$NO$_2$), a model system that presents challenging questions to the understanding of large amplitude vibrational motion, as well as several large organic molecules with fundamental spectroscopic and astrochemical relevance, including naphthalene (C$_{10}$H$_8$), adamantane (C$_{10}$H$_{16}$), and hexamethylenetetramine (C$_{6}$N$_4$H$_{12}$). This general spectroscopic tool has the potential to significantly impact the field of molecular spectroscopy, simultaneously improving efficiency, spectral resolution, and specificity by orders of magnitude. This realization could open up new molecular species and new kinetics for precise investigations, including the study of complex molecules, weakly bound clusters, and cold chemistry.

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