1938181
Determining SUSY model parameters and masses at the LHC using cross-sections, kinematic edges and other observables.
We address the problem of mass measurements of supersymmetric particles at the Large Hadron Collider, using the ATLAS detector as an example. By using Markov Chain sampling techniques to combine standard measurements of kinematic edges in the invariant mass distributions of decay products with a measurement of a missing pT cross-section, we show that the precision of mass measurements at the LHC can be dramatically improved, even when we do not assume that we have measured the kinematic endpoints precisely, or that we have identified exactly which particles are involved in the decay chain causing the endpoints. The generality of the technique is demonstrated in a preliminary investigation of a non-universal SUGRA model, in which we relax the requirements of mSUGRA by breaking the degeneracy of the GUT scale gaugino masses. The model studied is compatible with the WMAP limits on dark matter relic density.
118552878
Natural gauge mediation with a bino NLSP at the LHC
Natural models of supersymmetry with a gravitino LSP provide distinctive signatures at the LHC. For a neutralino NLSP, sparticles can decay to two high energy photons plus missing energy. We use the ATLAS diphoton search with 4.8 fb of data to place limits in both the stop-gluino and neutralino-chargino mass planes for this scenario. If the neutralino is heavier than 50 GeV, the lightest stop must be heavier than 580 GeV, the gluino heavier than 1100 GeV and charginos must be heavier than approximately 300-470 GeV. This provides the first nontrivial constraints in natural gauge mediation models with a neutralino NLSP decaying to photons, and implies a fine tuning of at least a few percent in such models.
117428092
Constraining the MSSM with Dark Matter indirect detection data
Recently, a claim of possible evidence for Dark Matter in data from the Fermi LAT experiment was made by Goodenough and Hooper [8]. We test the Dark Matter properties consistent with their claim in terms of the MSSM by a 24-dimensional parameter scan using nested sampling, excluding all but a very small region of the MSSM. Although this claim is very preliminary, and not made by the Fermi LAT experiment, our scan shows a possible approach for the analysis of future firm evidence from an indirect detection experiment, and its potential for heavily constraining models.
42216143
Fast supersymmetry phenomenology at the Large Hadron Collider using machine learning techniques
A pressing problem for supersymmetry (SUSY) phenomenologists is how to incorporate Large Hadron Collider search results into parameter fits designed to measure or constrain the SUSY parameters. Owing to the computational expense of fully simulating lots of points in a generic SUSY space to aid the calculation of the likelihoods, the limits published by experimental collaborations are frequently interpreted in slices of reduced parameter spaces. For example, both ATLAS and CMS have presented results in the Constrained Minimal Supersymmetric Model (CMSSM) by fixing two of four parameters, and generating a coarse grid in the remaining two. We demonstrate that by generating a grid in the full space of the CMSSM, one can interpolate between the output of an LHC detector simulation using machine learning techniques, thus obtaining a superfast likelihood calculator for LHC-based SUSY parameter fits. We further investigate how much training data is required to obtain usable results, finding that approximately 2000 points are required in the CMSSM to get likelihood predictions to an accuracy of a few per cent. The techniques presented here provide a general approach for adding LHC event rate data to SUSY fitting algorithms, and can easily be used to explore other candidate physics models.
44117065
NMSSM in disguise: Discovering singlino dark matter with soft leptons at the LHC
Abstract We suggest an NMSSM scenario, motivated by dark matter constraints, that may disguise itself as a much simpler mSUGRA scenario at the LHC. We show how its non-minimal nature can be revealed, and the bino–singlino mass difference measured, by looking for soft leptons.
14135931
Three body kinematic endpoints in SUSY models with non-universal Higgs masses
We derive and present expressions for the kinematic endpoints that arise in the invariant mass distributions of visible decay products of cascade decays featuring a two body decay followed by a three body decay. This is an extension of a current technique that addresses chains of successive two body decays. We then apply these to a supergravity model with Non-Universal Higgs Masses (NUHM), having simulated a data set using the ATLFAST detector simulation. We find that, should such a model be chosen by nature, the endpoints will be visible in ATLAS data, and we discuss the problems associated with mass reconstruction in models with a similar phenomenology.
10342800
Acceleration of Nitrogen Ions to 7.4 Gev in the Princeton Particle Accelerator
Nitrogen ions in charge states N5+ and N6+ have been accelerated in the Princeton Particle Accelerator to 4 and 7.4 billion electron volts (Gev), respectively. An external N5+ beam of 1 x 106 particles per second has been obtained and focused to a 6-millimeter-diameter spot. The N6+ beam was about 2 x 105 particles per second. The total charge-changing collision cross section of N5+ in water vapor was determined as a function of ion energy. The improvement in vacuum necessary to increase the N5+ beam at least tenfold was calculated. The N6+ total cross section is probably smaller than that of N5+ at the higher energies.
125390779
Proton compton scattering and neutral-pion photoproduction at large angles
The differential cross sections for ..gamma..p ..-->.. ..gamma..p and ..gamma..p ..-->.. ..pi../sup 0/p have been measured from abs. value (t) = 0.7 to 4.3 GeV/sup 2/ and for incident energies in the range 2 to 6 GeV. The energy dependence of Compton scattering is well described by parton model ideas. However, the energy dependences of ..pi../sup 0/ photoproduction and the ratio of Compton scattering to ..pi../sup 0/ photoproduction are not consistent with dimensional counting arguments.
118661436
The Princeton-Pennsylvania 3 GeV Proton Accelerator as a Nuclear Tool
I would like to describe the Princeton-Pennsylvania Accelerator as a tool for nuclear research. Some people tend to think of the PPA as being too high in energy for nuclear research and, therefore, regard it as only an elementary particle research tool. While much of our work has, in fact, been related to the study of mesons, especially K-mesons, and to the study of the invariance principles, such as C, P, T, about 15% of the research has been either purely nuclear, or with strong nuclear overtones. As examples of the purely nuclear, I mention spallation reactions at 3 BeV and the study of the resulting neutron deficient nuclei. On the other side of the valley are the baryon stable, neutron rich, light fragments, 19N and 21O, which have been discovered in confirmation of Garvey’s mass formula. Negative pion scattering by twelve different complex nuclei from Be to Au over the energy range 600-1600 MeV has been used to determine optical model potentials. Neutron total cross sections over the momentum range 500-2800 MeV/c are now being studied for a wide variety of target nuclei, including the Physical Review! An especially beautiful experiment, begun as a missing mass search in the reaction p+d → He3+X° not only studied things of interest to elementary particle physics, the so-called ABC region, but simultaneously, and inadvertently, provided a hadronic probe, the proton, at correlation distances far smaller than, ever achieved before.
124181456
Acceleration of Heavy Ions to Relativistic Energies and Their Use in Physics and Biomedicine
109689468
Spallation neutron source (SNS)
The Spallation Neutron Source [1], located at Oak Ridge, TN, is a state-of-the-art neutron-scattering facility presently under construction as a collaborative effort of six national laboratories. The facility is comprised of a high-power particle-accelerator system, a liquid-mercury target-moderator system, and a suite of world-class scientific instruments. One-ms-long negative-hydrogen-ion (H - ) pulses are produced by an ion source. The ion beam is accelerated to 185 MeV by normal conducting (NC) linear accelerator (linac) cavities, and further accelerated to 1 GeV by a superconducting linac [2]. The acceleration is accomplished by means of niobium superconducting radiofrequency (SRF) cavities that operate at 2.1K. The linac beam is stacked in a compressor ring, and 695-ns-long pulses are extracted onto the target at a 60-Hz rate. Neutrons are produced by spallation in the mercury, and their energy is moderated to useable levels, in part by supercritical hydrogen moderators. The simultaneous performance goals of more than one MW of initial proton beam power, 95% facility availability, and the desire for hands-on maintenance capability in the accelerator complex place significant demands on the performance and operational reliability of the technical and conventional systems. An overview of the SNS facility, including its purpose, major components, and a summary of the present status is presented, with particular emphasis on the superconducting linac and the cryogenic moderators.