Search NASA⌕ Search

Engineering topics

Gainer, James S.

Publications and source records attributed to Gainer, James S..

17 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Enhancing the discovery prospects for SUSY-like decays with a forgotten kinematic variable

The lack of a new physics signal thus far at the Large Hadron Collider motivates us to consider how to look for challenging final states, with large Standard Model backgrounds and subtle kinematic features, such as cascade decays with compressed spectra. Adopting a benchmark SUSY-like decay topology with a four-body final state proceeding through a sequence of two-body decays via intermediate resonances, we focus our attention on the kinematic variable Δ 4 which previously has been used to parameterize the boundary of the allowed four-body phase space. We highlight the advantages of using Δ 4 as a discovery variable, and present an analysis suggesting that the pairing of Δ 4 with another invariant mass variable leads to a significant improvement over more conventional variable choices and techniques.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Adding pseudo-observables to the four-lepton experimentalist’s toolbox

Here, the "golden" channel, in which the newly-discovered Higgs boson decays to four leptons by means of intermediate vector bosons, is important for determining the properties of the Higgs boson and for searching for subtle new physics effects. Different approaches exist for parametrizing the relevant Higgs couplings in this channel; here we relate the use of pseudo-observables to methods based on specifying the most general amplitude or Lagrangian terms for the $HVV$ interactions. We also provide projections for sensitivity in this channel in several novel scenarios, illustrating the use of pseudo-observables, and analyze the role of kinematic distributions and (ratios of) rates in such $H\to4\ell$ studies.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Reach of the high-energy LHC for gluinos and top squarks in SUSY models with light Higgsinos

We investigate the top squark (stop) and gluino reach of the proposed 33 TeV energy upgrade of the Large Hadron Collider (LHC33) in the Minimal Supersymmetric Standard Model (MSSM) with light Higgsinos and relatively heavy electroweak gauginos. In our analysis, we assume that stops decay to Higgsinos via t ˜ 1 → t Z ˜ 1 , t ˜ 1 → t Z ˜ 2 , and t ˜ 1 → b W ˜ 1 with branching fractions in the ratio 1 : 1 : 2 (expected if the decay occurs dominantly via the superpotential Yukawa coupling), while gluinos decay via g ˜ → t t ˜ 1 or via three-body decays to third-generation quarks plus Higgsinos. These decay patterns are motivated by models of natural supersymmetry where Higgsinos are expected to be close in mass to m Z , but gluinos may be as heavy as 5–6 TeV, and stops may have masses up to ~ 3 TeV . We devise cuts to optimize the signals from stop and gluino pair production at LHC33. We find that experiments at LHC33 should be able to discover stops with > 5 σ significance if m t ˜ 1 < 2.3 (2.8) [3.2] TeV for an integrated luminosity of 0.3 (1) [ 3 ] ab - 1 . The corresponding reach for gluinos extends to 5 (5.5) [6] TeV. These findings imply that experiments at LHC33 should be able to discover at least one of the stop or gluino pair signals even with an integrated luminosity of 0.3 ab - 1 for natural supersymmetry models with no worse than 3% electroweak fine-tuning and quite likely both gluinos and stops for an integrated luminosity of 3 ab - 1 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Gluino reach and mass extraction at the LHC in radiatively-driven natural SUSY

Radiatively-driven natural SUSY (RNS) models enjoy electroweak naturalness at the 10% level while respecting LHC sparticle and Higgs mass constraints. Gluino and top-squark masses can range up to several TeV (with other squarks even heavier) but a set of light Higgsinos are required with mass not too far above mh ~ 125 GeV. Within the RNS framework, gluinos dominantly decay via g˜ → tt ˜* 1 , t ¯t ˜ 1 → tt ¯Z 1,2 or tb¯W- 1 + c.c., where the decay products of the higgsino-like W ~ 1 and Z ~ 2 are very soft. Gluino pair production is, therefore, signaled by events with up to four hard b-jets and large E T . We devise a set of cuts to isolate a relatively pure gluino sample at the (high-luminosity) LHC and show that in the RNS model with very heavy squarks, the gluino signal will be accessible for m g ˜ < 2400 (2800) GeV for an integrated luminosity of 300 (3000) fb -1 . We also show that the measurement of the rate of gluino events in the clean sample mentioned above allows for a determination of m g ˜ with a statistical precision of 2–5% (depending on the integrated luminosity and the gluino mass) over the range of gluino masses where a 5σ discovery is possible at the LHC.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Detecting kinematic boundary surfaces in phase space: particle mass measurements in SUSY-like events

We critically examine the classic endpoint method for particle mass determination, focusing on difficult corners of parameter space, where some of the measurements are not independent, while others are adversely affected by the experimental resolution. In such scenarios, mass differences can be measured relatively well, but the overall mass scale remains poorly constrained. Using the example of the standard SUSY decay chain q ~ →χ ~ 0 2 →ℓ ~ →χ ~ 0 1 , we demonstrate that sensitivity to the remaining mass scale parameter can be recovered by measuring the two-dimensional kinematical boundary in the relevant three-dimensional phase space of invariant masses squared. We develop an algorithm for detecting this boundary, which uses the geometric properties of the Voronoi tessellation of the data, and in particular, the relative standard deviation (RSD) of the volumes of the neighbors for each Voronoi cell in the tessellation. We propose a new observable, Σ¯ , which is the average RSD per unit area, calculated over the hypothesized boundary. We show that the location of the Σ¯ maximum correlates very well with the true values of the new particle masses. Our approach represents the natural extension of the one-dimensional kinematic endpoint method to the relevant three dimensions of invariant mass phase space.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Measuring the Higgsplosion Yield: Counting Large Higgs Multiplicities at Colliders

Recent work has brought renewed attention to the possibility that the cross section for producing n Higgs bosons grows large with n at a sufficiently energetic hadron collider. In particular, this "Higgsplosion'" mechanism has been suggested as a solution to the hierarchy problem. In this work, we investigate the phenomenology of this scenario. Discovery is trivial, so we consider several variables for use in measuring large Higgs multiplicities and evaluate their effectiveness. We find that a 10% level measurement of the number of Higgs bosons is possible with a handful of events, using the scalar sum of jet transverse momenta, but determining the exact multiplicity may take a few thousand events, depending on the degree of statistical significance desired for the measurement. While this situation may be acceptable given the potentially large cross sections in this scenario, future research to improve the measurement is warranted.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

OPTIMASS: A package for the minimization of kinematic mass functions with constraints

Reconstructed mass variables, such as M 2 , M 2C , M* T , and M T2 W , play an essential role in searches for new physics at hadron colliders. The calculation of these variables generally involves constrained minimization in a large parameter space, which is numerically challenging. We provide a C++ code, Optimass, which interfaces with the Minuit library to perform this constrained minimization using the Augmented Lagrangian Method. The code can be applied to arbitrarily general event topologies, thus allowing the user to significantly extend the existing set of kinematic variables. Here, we describe this code, explain its physics motivation, and demonstrate its use in the analysis of the fully leptonic decay of pair-produced top quarks using M 2 variables.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

The hierarchy solution to the LHC inverse problem

Supersymmetric (SUSY) models, even those described by relatively few parameters, generically allow many possible SUSY particle (sparticle) mass hierarchies. As the sparticle mass hierarchy determines, to a great extent, the collider phenomenology of a model, the enumeration of these hierarchies is of the utmost importance. We therefore provide a readily generalizable procedure for determining the number of sparticle mass hierarchies in a given SUSY model. As an application, we analyze the gravity-mediated SUSY breaking scenario with various combinations of GUT-scale boundary conditions involving different levels of universality among the gaugino and scalar masses. For each of the eight considered models, we provide the complete list of forbidden hierarchies in a compact form. Lastly, our main result is that the complete (typically rather large) set of forbidden hierarchies among the eight sparticles considered in this analysis can be fully specified by just a few forbidden relations involving much smaller subsets of sparticles.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Exploring theory space with Monte Carlo reweighting

Theories of new physics often involve a large number of unknown parameters which need to be scanned. Additionally, a putative signal in a particular channel may be due to a variety of distinct models of new physics. This makes experimental attempts to constrain the parameter space of motivated new physics models with a high degree of generality quite challenging. We describe how the reweighting of events may allow this challenge to be met, as fully simulated Monte Carlo samples generated for arbitrary benchmark models can be effectively re-used. Specifically, we suggest procedures that allow more efficient collaboration between theorists and experimentalists in exploring large theory parameter spaces in a rigorous way at the LHC.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

The Matrix Element Method: Past, Present, and Future

The increasing use of multivariate methods, and in particular the Matrix Element Method (MEM), represents a revolution in experimental particle physics. With continued exponential growth in computing capabilities, the use of sophisticated multivariate methods-- already common-- will soon become ubiquitous and ultimately almost compulsory. While the existence of sophisticated algorithms for disentangling signal and background might naively suggest a diminished role for theorists, the use of the MEM, with its inherent connection to the calculation of differential cross sections will benefit from collaboration between theorists and experimentalists. In this white paper, we will briefly describe the MEM and some of its recent uses, note some current issues and potential resolutions, and speculate about exciting future opportunities.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗