We demonstrate that megaton-mass neutrino telescopes are able to observe the signal from long-lived particles beyond the Standard Model, in particular the stau, the supersymmetric partner of the tau ...lepton. Its signature is an excess of charged particle tracks with horizontal arrival directions and energy deposits between 0.1 and 1 TeV inside the detector. We exploit this previously-overlooked signature to search for stau particles in the publicly available IceCube data. The data shows no evidence of physics beyond the Standard Model. We derive a new lower limit on the stau mass of 320 GeV (95% C.L.) and estimate that this new approach, when applied to the full data set available to the IceCube collaboration, will reach word-leading sensitivity to the stau mass (mτ˜=450GeV).
A symbolic handling of Sheffer polynomials Di Nardo, E.; Niederhausen, H.; Senato, D.
Annali di matematica pura ed applicata,
09/2011, Letnik:
190, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We revisit the theory of Sheffer sequences by means of the formalism introduced in Rota and Taylor (SIAM J Math Anal 25(2):694–711, 1994) and developed in Di Nardo and Senato (Umbral nature of the ...Poisson random variables. Algebraic combinatorics and computer science, pp 245–256, Springer Italia, Milan, 2001, European J Combin 27(3):394–413, 2006). The advantage of this approach is twofold. First, this new syntax allows us noteworthy computational simplification and conceptual clarification in several topics involving Sheffer sequences, most of the open questions proposed in Taylor (Comput Math Appl 41:1085–1098, 2001) finds answer. Second, most of the results presented can be easily implemented in a symbolic language. To get a general idea of the effectiveness of this symbolic approach, we provide a formula linking connection constants and Riordan arrays via generalized Bell polynomials, here defined. Moreover, this link allows us to smooth out many results involving Bell Polynomials and Lagrange inversion formula.
The well-known relationship between linear functionals and Sheffer sequences is extended to the case of piecewise functional conditions, where one functional determines the beginning, and a second ...functional shapes the remainder of a the sequence. The concept of Sheffer sequences is generalized from the Roman-Rota approach.
The ARIANNA experiment seeks to observe the diffuse flux of neutrinos in the 108–1010GeV energy range using a grid of radio detectors at the surface of the Ross Ice Shelf of Antarctica. The detector ...measures the coherent Cherenkov radiation produced at radio frequencies, from about 100MHz–1GHz, by charged particle showers generated by neutrino interactions in the ice. The ARIANNA Hexagonal Radio Array (HRA) is being constructed as a prototype for the full array. During the 2013–14 austral summer, three HRA stations collected radio data which was wirelessly transmitted off site in nearly real-time. The performance of these stations is described and a simple analysis to search for neutrino signals is presented. The analysis employs a set of three cuts that reject background triggers while preserving 90% of simulated cosmogenic neutrino triggers. No neutrino candidates are found in the data and a model-independent 90% confidence level Neyman upper limit is placed on the all flavor ν+ν¯ flux in a sliding decade-wide energy bin. The limit reaches a minimum of 1.9×10-23GeV-1cm-2s-1sr-1 in the 108.5–109.5GeV energy bin. Simulations of the performance of the full detector are also described. The sensitivity of the full ARIANNA experiment is presented and compared with current neutrino flux models.
Random walks in octants, and related structures Niederhausen, Heinrich
Journal of statistical planning and inference,
11/2005, Letnik:
135, Številka:
1
Journal Article, Conference Proceeding
Recenzirano
A diffusion walk in
Z
2
is a (random) walk with unit step vectors
→
,
↑
,
←
, and
↓
. Particles from different sources with opposite charges cancel each other when they meet in the lattice. This ...cancellation principle is applied to enumerate diffusion walks in shifted half-planes, quadrants, and octants (a three-dimensional version is also considered). Summing over time we calculate expected numbers of visits and first passage probabilities. Comparing those quantities to analytically obtained expressions leads to interesting identities, many of them involving integrals over products of Chebyshev polynomials of the first and second kind. We also explore what the expected number of visits means when the diffusion in an octant is bijectively mapped onto other combinatorial structures, like pairs of non-intersecting Dyck paths, vicious walkers, bicolored Motzkin paths, staircase polygons in the second octant, and
{
→
↑
}
-paths confined to the third hexadecant enumerated by left turns.
We enumerate two-dimensional walks inside a band parallel to an axis of symmetry, using an algebraic approach. The restrictions along the boundary lines can be more complicated than just initial ...values of zeroes; we consider
recursive initial values prescribing which predecessors a position at the boundary can have. More general, the initial conditions are expressed by certain linear operators which vanish along the axis of symmetry.
We propose a novel approach to the detection of point-like sources of high-energy neutrinos. Motivated by evidence for emerging sources in existing data, we focus on the characterisation and ...interpretation of these sources. The hierarchical Bayesian model is implemented in the Stan platform, enabling computation of the posterior distribution with Hamiltonian Monte Carlo. We simulate a population of weak neutrino sources detected by the IceCube experiment and use the resulting data set to demonstrate and validate our framework. We show that even for the challenging case of sources at the threshold of detection and using limited prior information, it is possible to correctly infer the source properties. Additionally, we demonstrate how modelling flexible connections between similar sources can be used to recover the contribution of sources that would not be detectable individually, going beyond what is possible with existing stacking methods.
We consider certain systems of linear operator equations where the
nth-order solution is made unique by an initial value taken from the preceding solution. Such conditions arise in the enumeration of ...lattice paths with weighted left turns, if the paths are restricted by a lower linear barrier of integer slope.
Sources of astrophysical neutrinos can potentially be discovered through the detection of neutrinos in coincidence with electromagnetic counterparts. Real-time alerts generated by IceCube play an ...important role in this search, acting as triggers for follow-up observations with instruments sensitive to electromagnetic signals in various wavelengths. In previous studies, we investigated the treatment of the systematic uncertainties on the reconstruction method currently used in IceCube's real-time program, concluding that a new approach, more robust against systematic variations, is needed. Here we present the state-of-the-art of these analyses, and discuss a modification to an already-existing and reliable reconstruction method that results in an improved solution under many metrics. The proposed reconstruction method is faster, more precise, and significantly less influenced by systematic uncertainties, than the current one. This system provides a more robust estimate of angular uncertainties than the previous algorithm, making it a solid benchmark for real-time event analyses.
We count lattice paths that are confined to the first quadrant by the nature of their step vectors. If no further restrictions apply, a path can go from any point to infinitely many others, but each ...point on the path has only finitely many predecessors. By “ further restrictions” we mean a boundary line above which the paths may have to stay. Access privilege to the boundary line itself is granted from certain lattice points in the form of a special access step set, which itself may be infinite. We also count the number of paths that contact the weak boundary a given number of times. We approach explicit solutions of such enumeration problems via Sheffer polynomials and functionals, using results of the Umbral Calculus.
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