arXiv subjects

N. Kersting

Publications and source records attributed to N. Kersting.

18 recordsLinked to original sources

arXiv2011

Improving SUSY Spectrum Determinations at the LHC with Wedgebox Technique

The LHC has the potential not only to discover supersymmetry (SUSY), but also to permit fairly precise measurements of at least a portion of the sparticle spectrum. Proposed mass reconstruction methods rely upon either inverting invariant mass endpoint expressions or upon solving systems of mass-shell equations. These methodologies suffer from the weakness that one certain specific sparticle decay chain is assumed to account for all the events in the sample. Taking two examples of techniques utilizing mass-shell equations, it is found that also applying the wedgebox technique allows for the isolation of a purer event sample, thus avoiding errors, possibly catastrophic, due to mistaken assumptions about the decay chains involved and simultaneously improving accuracy. What is innovative is using endpoint measurements (via the wedgebox technique) to obtain a more homogeneous, well-understood sample set rather than just using said endpoints to constrain the values of the masses (here found by the mass-shell technique). The fusion of different established techniques in this manner represents a highly profitable option for LHC experimentalists who will soon have data to analyze.

hep-ph↗

arXiv2010

Mass Estimation without using MET in early LHC data

Many techniques exist to reconstruct New Physics masses from LHC data, though these tend to either require high luminosity O(100) fb^-1, or an accurate measurement of missing transverse energy (MET) which may not be available in the early running of the LHC. Since in popular models such as SUSY a fairly sharp, triangular dilepton invariant mass spectrum can emerge already at low luminosity O(1) fb^-1, a Decay Kinematics (DK) technique can be used on events near the dilepton mass endpoint to estimate squark, slepton, and neutralino masses without relying on MET. With the first 2 fb^-1 of 7 TeV LHC data SPS1a masses can thus be found to 20% or better accuracy, at least several times better than what has been taken to be achievable.

hep-ph↗

arXiv2009

Neutralino Reconstruction at the LHC from Decay-frame Kinematics

Decay-frame Kinematics (DK) has previously been introduced as a technique to reconstruct neutralino masses from their three-body decays to leptons. This work is an extension to the case of two-body decays through on-shell sleptons, with Monte Carlo simulation of LHC collisions demonstrating reconstruction of neutralino masses for the SPS1a benchmark point.

hep-ph↗

arXiv2009

A Simple Mass Reconstruction Technique for SUSY particles at the LHC

It is often true that an invariant mass constructed from visible decay products of a heavy particle may attain a maximum(or minimum) for a certain kinematic configuration only -- this fact can be used to reconstruct relevant particle masses from observed decay product momenta of events near the invariant mass endpoint. MSSM neutralino and chargino mass reconstruction at the LHC from multi-lepton endstates is illustrated by way of example.

hep-ph↗

arXiv2009

On Measuring Split-SUSY Neutralino and Chargino Masses at the LHC

In Split-Supersymmetry models, where the only non-Standard Model states produceable at LHC-energies consist of a gluino plus neutralinos and charginos, it is conventionally accepted that only mass differences among these latter are measureable at the LHC. The present work shows that application of a simple `Kinematic Selection' technique allows full reconstruction of neutralino and chargino masses from one event, in principle. A Monte Carlo simulation demonstrates the feasibilty of using this technique at the LHC.

hep-ph↗

arXiv2009

Elimination of IR/UV via Gravity in Noncommutative Field Theory

Models of particle physics with Noncommutative Geometry (NCG) generally suffer from a manifestly non-Wilsonian coupling of infrared and ultraviolet degrees of freedom known as the "IR/UV Problem" which would tend to compromise their phenomenological relevance. In this Letter we explicitly show how one may remedy this by coupling NCG to gravity. In the simplest scenario the Lagrangian gets multiplied by a nonconstant background metric; in $ϕ-4$ theory the theorem that $\int d^4 x ϕ\star ϕ= \int d^4 x ϕ^2$ is no longer true and the field propagator gets modified by a factor which depends on both NCG and the variation of the metric. A suitable limit of this factor as the propagating momentum gets asymptotically large then eradicates the IR/UV problem. With gravity and NCG coupled to each other, one might expect anti-symmetric components to arise in the metric. Cosmological implications of such are subsequently discussed.

hep-th↗

arXiv2008

Hidden Thresholds: Reconstructing NP Masses

The Hidden Thresholds technique reconstructs New Physics (NP) masses from two or more simultaneous NP decays at a hadron collider. We show how this works in several MSSM examples: $\widetildeχ_{i}^0 \widetildeχ_{j}^0 \to e^+ e^- μ^+ μ^- \widetildeχ_{1}^0 \widetildeχ_{1}^0$ ($i,j=2,3,4$) and ${\widetildeχ_1}^\pm {\widetildeχ_2}^0 \to {W^\pm}^*(\to \ell^\pm ν) {\widetildeχ_1}^0 ~ {Z^0}^*(\to \ell^\pm \ell^\mp) {\widetildeχ_1}^0 $.

hep-ph↗

arXiv2008

Hidden Thresholds: A Technique for Reconstructing New Physics Masses at Hadron Colliders

We present an improved method of reconstructing New Physics (NP) masses from invariant mass endpoints. While the traditional method focuses on a single NP decay, our method considers the decays of two or more NP particles ($ABC...$) in a grander decay chain: $ anything \to ABC... \to ... \to jets + leptons$. Though the center-of-mass energy $E_{CM}$ of `anything' varies unpredictably at a hadron collider, a sample of many events nonetheless expresses features of threshold production $E_{CM} = m_A + m_B + ...$: invariant masses constructed from the final jet and lepton momenta are correlated in a way that makes their threshold endpoints visually obvious in a scatterplot. We illustrate this technique for the production of two neutralinos in the MSSM: $anything \to \widetildeχ_{i}^0 \widetildeχ_{j}^0$ ($i,j=2,3,4$) which subsequently decay via on- or off-shell sleptons to four leptons. Assuming the relevant SUSY spectrum is below $1 TeV$ and squarks/gluinos eventually decay to neutralinos, our MC study shows that one low-luminosity year at the LHC ($10-30 fb^{-1}$) can quantitatively determine on- versus off-shell decays and find the relevant neutralino and slepton masses to less than 10 percent.

hep-ph↗

arXiv2008

Extracting MSSM Masses From Heavy Higgs Decays to Four Leptons at the LHC

It is well known that finding and measuring the masses of particles in the Minimal Supersymmetric Standard Model (MSSM) at the Large Hadron Collider (LHC) may be possible using invariant mass distributions in exclusive channels containing n_j jets and n_l leptons. We perform this analysis for the (n_j, n_l) = (0,4) decay of heavy Higgs bosons to neutralinos, pp \to H/A \to χ_i χ_j (i,j =2,3,4), which then decay to four leptons and two lightest neutralinos χ_1 via on-shell sleptons. When i=j and the sleptons are degenerate, our Monte Carlo study shows that the LHC will be able to measure the Higgs and relevant neutralino and slepton masses to roughly 30%; however, if one of these is already known within 5%, the other three may be found to equal or better accuracy. This would provide the first accurate measurement of the H/A mass via invariant mass distribution techniques.

hep-ph↗

arXiv2006

The GZK Bound in Discrete Space

The maximum distance bound for ultrahigh energy cosmic rays (UHECR) with energies above the Greisen-Zatsepin-Kuzmich cutoff $\sim 10^{19} eV$ relaxes significantly if there is some mechanism that forces UHECR to propagate in discrete intervals, rather than continuously, through intergalactic space. In particular, intervals as small as a femtometer relax the bound for protons by an order of magnitude and potentially account for the observed excess of UHECR flux.

astro-ph↗

arXiv2005

Pair-produced heavy particle topologies:MSSM neutralino properties at the LHC from gluino/squark cascade decays

Processes of the form $pp\to anything \to X_i X_j \to x\bar{x} + y\bar{y} (+ \slashchar{E})$ are studied via a technique that may be viewed as an adaptation of time-honoured Dalitz plot analyses. $X_i$ and $X_j$ are new heavy states (with $i,j=1...n$), which may be identical or distinct; and $x\bar{x}$ and $y\bar{y}$ are necessarily distinct Standard Model (SM) fermion pairs whose invariant masses can be measured. A Dalitz-like plot of said invariant masses, $M(x\bar{x})$ {\it vs.$$} $M(y\bar{y})$, exhibits a topology connected to the masses and specific decay chains of $X_i$ and $X_j$. Aside from relatively minor details, observed patterns consist of a collection of box and wedge shapes. This collection is model-dependent: comparison of the observed pattern to the possibilities for a specific model yields information on which new particle pair combinations are actually being produced, information beyond that extractable from conventional one-dimensional invariant mass distributions. The technique is illustrated via application to the Minimal Supersymmetric Standard Model (MSSM) process $pp \to \tilde{g}\tilde{g},\tilde{g}\tilde{q},\tilde{q}\tilde{q} \to \widetildeχ_i^0 \widetildeχ_j^0 \to e^+ e^- + μ^+ μ^- (+ \slashchar{E})$. Here the heavy states are neutralinos $\widetildeχ_i^0$ ($i=2,3,4$) -- note $\widetildeχ_1^0$ is excluded -- which are produced in gluino/squark ($\tilde{g}$/$\tilde{q}$) cascade decay chains. Even with fairly modest expectations for the LHC performance during the first few years, this method still provides substantial insight into the neutralino mass spectrum and couplings if gluino/squark masses are relatively low ($\simeq 400 \hbox{GeV}$).

hep-ph↗

arXiv2004

The Higgs Working Group: Summary Report 2003

Theoretical progress in Higgs boson production and background processes is discussed with particular emphasis on QCD corrections at and beyond next-to-leading order as well as next-to-leading order electroweak corrections. The residual theoretical uncertainties of the investigated processes are estimated in detail. Moreover, recent investigations of the MSSM Higgs sector and other extensions of the SM Higgs sector are presented. The potential of the LHC and a high-energy linear e+e- collider for the measurement of Higgs couplings is analyzed.

hep-ph↗

arXiv2003

Nonsymmetric Gravity and Noncommutative Signals

Models in which the space-time metric $g_{μν}$ is not symmetric, $i.e.$ $g_{μν} \ne g_{νμ}$ may make predictions in scattering experiments, for example in a future $e^+e^-$ linear collider, similar to those from noncommutative field theory. We compute the differential cross sections for pair annihilation, Bhabha and M$ø$ller scattering and find that both nonsymmetric gravity theory(NGT) and noncommutative field theory predict a similar dependence of the differential cross section on the azimuthal angle in agreement with all known data, however in NGT Lorentz violation need not be as severe. Astrophysical and cosmological tests may prove very useful in distinguishing these two theories.

hep-ph↗

arXiv2003

Review of the Phenomenology of Noncommutative Geometry

We present a pedagogical review of particle physics models that are based on the noncommutativity of space-time, $[\hat{x}_μ,\hat{x}_ν]=i θ_{μν}$, with specific attention to the phenomenology these models predict in particle experiments either in existence or under development. We summarize results obtained for high energy scattering such as would occur for example in a future $e^+e^-$ linear collider with $\sqrt{s} = 500 GeV$, as well as low energy experiments such as those pertaining to elementary electric dipole moments and other $\cpviolng$ observables, and finally comment on the status of phenomenological work in cosmology and extra dimensions.

hep-ph↗

arXiv2001

g-2 From Noncommutative Geometry

This brief Letter demonstrates that effects from a $\nc$ space-time geometry will measurably affect the value of $(g-2)_μ$ inferred from the decay of the muon to an electron plus two neutrinos. If the scale of noncommutivity is ${\cal O}(TeV)$, the alteration of the $V-A$ structure of the lepton-lepton-W vertex is sufficient to shift the inferred value of $(g-2)_μ$ to one part in $10^8$. This may account for the recently reported $2.6 σ$ discrepancy between the BNL measurement $a_{expt} = 11659202(14)(6) \times 10^{-10}$ and the Standard Model prediction $a_{SM} = 11659159.6(6.7) \times 10^{-10}$.

hep-ph↗

arXiv2001

CP violation from noncommutative geometry

If the geometry of space-time is $\nc$, i.e. $[x_μ,x_ν]=i θ_{μν}$, then $\nc$ $\cpviolng$ effects may be manifest at low energies. For a $\nc$ scale $Λ\equiv θ^{-1/2} \leq 2 TeV$, $\cpviol$ from $\ncg$ is comparable to that from the Standard Model (SM) alone: the $\nc$ contributions to $ε$ and $ε'/ε$ in the $K$-system, may actually dominate over the Standard Model contributions. Present data permit $\ncg$ to be the only source of $\cpviol$. Furthermore the most recent findings for g-2 of the muon are consistent with predictions from $\ncg$. If the geometry of space-time is $\nc$, $i.e.$ $[x_μ,x_ν]=i θ_{μν}$, then $\nc$ $\cpviolng$ effects may be manifest at low energies. For a $\nc$ scale $Λ\equiv θ^{-1/2} \leq 2 TeV$, $\cpviol$ from $\ncg$ is comparable to that from the Standard Model (SM) alone: the $\nc$ contributions to $ε$ and $ε'/ε$ in the K-system, may actually dominate over the Standard Model contributions. Present data permit $\ncg$ to be the only source of $\cpviol$. Furthermore the most recent findings for g-2 of the muon are consistent with predictions from $\ncg$.

hep-ph↗

arXiv2000

Flavor Alignment in SUSY GUTs

A Supersymmetric Grand unified model is constructed based on SO(10)xSO(10) symmetry in which new types of Yukawa matrices couple standard and exotic fermions. Evolution of these couplings from the Grand Unified scale to the electroweak scale causes some of them to be driven to their fixed points. This solves the supersymmetric alignment problem and ensures that there are no observable flavor changing neutral currents mediated by supersymmetric particles. Fermion hierarchy and neutrino mixing constraints are automatically satisfied in this formalism.

hep-ph↗

arXiv2000

Constraining CP Violating Phases of the MSSM

Possible CP violation in supersymmetric (SUSY) extensions of the Standard Model (SM) is discussed. The consequences of CP violating phases in the gaugino masses, trilinear soft supersymmetry-breaking terms and the `mu' parameter are explored. Utilizing the constraints on these parameters from electron and neutron electric dipole moments, possible CP violating effects in B-physics are shown. A set of measurements from the B-system which would overconstrain the above CP violating phases is illustrated.

hep-ph↗