The shape and dynamics of a heliotropic dusty ringlet in the Cassini Division

The so-called "Charming Ringlet" (R/2006 S3) is a low-optical-depth, dusty ringlet located in the Laplace gap in the Cassini Division. This ringlet is particularly interesting because its radial position varies systematically with longitude relative to the Sun in such a way that the ringlet's geometric center appears to be displaced away from Saturn's center in a direction roughly toward the Sun. In other words, the ringlet is always found at greater distances from the planet's center at longitudes near the sub-solar longitude than it is at longitudes near Saturn's shadow. This "heliotropic" behavior indicates that the dynamics of the particles in this ring are being influenced by solar radiation pressure. In order to investigate this phenomenon, which has been predicted theoretically but has never been observed this clearly, we analyze multiple image sequences of this ringlet obtained by Cassini in order to constrain its shape and orientation. These data can be fit reasonably well with a model in which both the eccentricity and the inclination of the ringlet have "forced" components (that maintain a fixed orientation relative to the Sun) as well as "free" components (that drift around the planet at steady rates determined by Saturn's oblateness). While the magnitude of the forced eccentricity is roughly consistent with theoretical expectations for radiation pressure acting on 10-to-100-micron-wide icy grains, the existence of significant free eccentricities and inclinations poses a significant challenge for models of low-optical-depth dusty rings.Comment: 31 pages, 6 figures, accepted for publication in Icarus. Slight edits made to match various proof correction

Using Subsystem MT2 for Complete Mass Determinations in Decay Chains with Missing Energy at Hadron Colliders

We propose to use the MT2 concept to measure the masses of all particles in SUSY-like events with two unobservable, identical particles. To this end we generalize the usual notion of MT2 and define a new MT2(n,p,c) variable, which can be applied to various subsystem topologies, as well as the full event topology. We derive analytic formulas for its endpoint MT2{max}(n,p,c) as a function of the unknown test mass Mc of the final particle in the subchain and the transverse momentum pT due to radiation from the initial state. We show that the endpoint functions MT2{max}(n,p,c)(Mc,pT) may exhibit three different types of kinks and discuss the origin of each type. We prove that the subsystem MT2(n,p,c) variables by themselves already yield a sufficient number of measurements for a complete determination of the mass spectrum (including the overall mass scale). As an illustration, we consider the simple case of a decay chain with up to three heavy particles, X2 -> X1 -> X0, which is rather problematic for all other mass measurement methods. We propose three different MT2-based methods, each of which allows a complete determination of the masses of particles X0, X1 and X2. The first method only uses MT2(n,p,c) endpoint measurements at a single fixed value of the test mass Mc. In the second method the unknown mass spectrum is fitted to one or more endpoint functions MT2{max}(n,p,c)(Mc,pT) exhibiting a kink. The third method is hybrid, combining MT2 endpoints with measurements of kinematic edges in invariant mass distributions. As a practical application of our methods, we show that the dilepton W+W- and tt-bar samples at the Tevatron can be used for an independent determination of the masses of the top quark, the W boson and the neutrino, without any prior assumptions.Comment: 47 pages, 9 figures. revised version, published in JHEP. Major addition: a new appendix with the complete set of formulas for the MT2 endpoints as functions of the upstream transverse momentum pT and test mass M

Optically bound microscopic particles in one dimension

Counter-propagating light fields have the ability to create self-organized one-dimensional optically bound arrays of microscopic particles, where the light fields adapt to the particle locations and vice versa. We develop a theoretical model to describe this situation and show good agreement with recent experimental data (Phys. Rev. Lett. 89, 128301 (2002)) for two and three particles, if the scattering force is assumed to dominate the axial trapping of the particles. The extension of these ideas to two and three dimensional optically bound states is also discussed.Comment: 12 pages, incl. 5 figures, accepted by Phys. Rev.

The three-dimensional structure of Saturn's E ring

Saturn's diffuse E ring consists of many tiny (micron and sub-micron) grains of water ice distributed between the orbits of Mimas and Titan. Various gravitational and non-gravitational forces perturb these particles' orbits, causing the ring's local particle density to vary noticeably with distance from the planet, height above the ring-plane, hour angle and time. Using remote-sensing data obtained by the Cassini spacecraft in 2005 and 2006, we investigate the E-ring's three-dimensional structure during a time when the Sun illuminated the rings from the south at high elevation angles (> 15 degrees). These observations show that the ring's vertical thickness grows with distance from Enceladus' orbit and its peak brightness density shifts from south to north of Saturn's equator plane with increasing distance from the planet. These data also reveal a localized depletion in particle density near Saturn's equatorial plane around Enceladus' semi-major axis. Finally, variations are detected in the radial brightness profile and the vertical thickness of the ring as a function of longitude relative to the Sun. Possible physical mechanisms and processes that may be responsible for some of these structures include solar radiation pressure, variations in the ambient plasma, and electromagnetic perturbations associated with Saturn's shadow.Comment: 42 Pages, 13 Figures, modified to include minor proof correction

Using kinematic boundary lines for particle mass measurements and disambiguation in SUSY-like events with missing energy

We revisit the method of kinematical endpoints for particle mass determination, applied to the popular SUSY decay chain squark -> neutralino -> slepton -> LSP. We analyze the uniqueness of the solutions for the mass spectrum in terms of the measured endpoints in the observable invariant mass distributions. We provide simple analytical inversion formulas for the masses in terms of the measured endpoints. We show that in a sizable portion of the SUSY mass parameter space the solutions always suffer from a two-fold ambiguity, due to the fact that the original relations between the masses and the endpoints are piecewise-defined functions. The ambiguity persists even in the ideal case of a perfect detector and infinite statistics. We delineate the corresponding dangerous regions of parameter space and identify the sets of "twin" mass spectra. In order to resolve the ambiguity, we propose a generalization of the endpoint method, from single-variable distributions to two-variable distributions. In particular, we study analytically the boundaries of the (m_{jl(lo)}, m_{jl(hi)}) and (m_{ll}, m_{jll}) distributions and prove that their shapes are in principle sufficient to resolve the ambiguity in the mass determination. We identify several additional independent measurements which can be obtained from the boundary lines of these bivariate distributions. The purely kinematical nature of our method makes it generally applicable to any model that exhibits a SUSY-like cascade decay.Comment: 47 pages, 19 figure

\sqrt{s}_min: a global inclusive variable for determining the mass scale of new physics in events with missing energy at hadron colliders

We propose a new global and fully inclusive variable \sqrt{s}_{min} for determining the mass scale of new particles in events with missing energy at hadron colliders. We define \sqrt{s}_{min} as the minimum center-of-mass parton level energy consistent with the measured values of the total calorimeter energy E and the total visible momentum \vec{P}. We prove that for an arbitrary event, \sqrt{s}_{min} is simply given by the formula \sqrt{s}_{min}=\sqrt{E^2-P_z^2}+\sqrt{\met^2+M_{inv}^2}, where M_{inv} is the total mass of all invisible particles produced in the event. We use t\bar{t} production and several supersymmetry examples to argue that the peak in the \sqrt{s}_{min} distribution is correlated with the mass threshold of the parent particles originally produced in the event. This conjecture allows a determination of the heavy superpartner mass scale (as a function of the LSP mass) in a completely general and model-independent way, and without the need for any exclusive event reconstruction. In our SUSY examples of several multijet plus missing energy signals, the accuracy of the mass measurement based on \sqrt{s}_{min} is typically at the percent level, and never worse than 10%. After including the effects of initial state radiation and multiple parton interactions, the precision gets worse, but for heavy SUSY mass spectra remains 10%.Comment: 33 pages, 36 figures, discussion on effect of ISR and MPI adde

Three-body interactions in colloidal systems

We present the first direct measurement of three-body interactions in a colloidal system comprised of three charged colloidal particles. Two of the particles have been confined by means of a scanned laser tweezers to a line-shaped optical trap where they diffused due to thermal fluctuations. Upon the approach of a third particle, attractive three-body interactions have been observed. The results are in qualitative agreement with additionally performed nonlinear Poissson-Boltzmann calculations, which also allow us to investigate the microionic density distributions in the neighborhood of the interacting colloidal particles

Precise reconstruction of sparticle masses without ambiguities

We critically reexamine the standard applications of the method of kinematical endpoints for sparticle mass determination. We consider the typical decay chain in supersymmetry (SUSY) squark -> neutralino -> slepton -> LSP, which yields a jet j and two leptons ln and lf. The conventional approaches use the upper kinematical endpoints of the individual distributions m_{jll}, m_{jl(lo)} and m_{jl(hi)}, all three of which suffer from parameter space region ambiguities and may lead to multiple solutions for the SUSY mass spectrum. In contrast, we do not use m_{jll}, m_{jl(lo)} and m_{jl(hi)}, and instead propose a new set of (infinitely many) variables whose upper kinematic endpoints exhibit reduced sensitivity to the parameter space region. We then outline an alternative, much simplified procedure for obtaining the SUSY mass spectrum. In particular, we show that the four endpoints observed in the three distributions m^2_{ll}, m^2_{jln} U m^2_{jlf} and m^2_{jln}+m^2_{jlf} are sufficient to completely pin down the squark mass and the two neutralino masses, leaving only a discrete 2-fold ambiguity for the slepton mass. This remaining ambiguity can be easily resolved in a number of different ways: for example, by a single additional measurement of the kinematic endpoint of any one out of the many remaining 1-dimensional distributions at our disposal, or by exploring the correlations in the 2-dimensional distribution of m^2_{jln} U m^2_{jlf} versus m^2_{ll}. We illustrate our method with two examples: the LM1 and LM6 CMS study points. An additional advantage of our method is the expected improvement in the accuracy of the SUSY mass determination, due to the multitude and variety of available measurements.Comment: 37 pages, added a new figure in the Appendix, published versio

A lower bound on the local extragalactic magnetic field

Assuming that the hard gamma-ray emission of Cen A is a result of synchrotron radiation of ultra-relativistic electrons, we derive a lower bound on the local extragalactic magnetic field, $B> 10^{-8}$ G. This result is consistent with (and close to) upper bounds on magnetic fields derived from consideration of cosmic microwave background distortions and Faraday rotation measurements.Comment: Includes extensive discussion of particle acceleration above 10^20 eV in the hot spot-like region of Cen

Sparticle masses in deflected mirage mediation

We discuss the sparticle mass patterns that can be realized in deflected mirage mediation scenario of supersymmetry breaking, in which the moduli, anomaly, and gauge mediations all contribute to the MSSM soft parameters. Analytic expression of low energy soft parameters and also the sfermion mass sum rules are derived, which can be used to interpret the experimentally measured sparticle masses within the framework of the most general mixed moduli-gauge-anomaly mediation. Phenomenological aspects of some specific examples are also discussed.Comment: 43 pages, 17 figures, references adde