1,921 research outputs found

### Phenomenology of Universal Extra Dimensions

In this proceeding, the phenomenology of Universal Extra Dimensions (UED), in
which all the Standard Model fields propagate, is explored. We focus on models
with one universal extra dimension, compactified on an $S_1/Z_2$ orbifold. We
revisit calculations of Kaluza-Klein (KK) dark matter without an assumption of
the KK mass degeneracy including all possible coannihilations. We then contrast
the experimental signatures of low energy supersymmetry and UED.Comment: 4 pages, 6 figures, to appear in Proceedings of SUSY06, the 14th
International Conference on Supersymmetry and the Unification of Fundamental
Interactions, UC Irvine, California, 12-17 June 200

### A general method for determining the masses of semi-invisibly decaying particles at hadron colliders

We present a general solution to the long standing problem of determining the
masses of pair-produced, semi-invisibly decaying particles at hadron colliders.
We define two new transverse kinematic variables, $M_{CT_\perp}$ and
$M_{CT_\parallel}$, which are suitable one-dimensional projections of the
contransverse mass $M_{CT}$. We derive analytical formulas for the boundaries
of the kinematically allowed regions in the $(M_{CT_\perp},M_{CT_\parallel})$
and $(M_{CT_\perp},M_{CT})$ parameter planes, and introduce suitable variables
$D_{CT_\parallel}$ and $D_{CT}$ to measure the distance to those boundaries on
an event per event basis. We show that the masses can be reliably extracted
from the endpoint measurements of $M_{CT_\perp}^{max}$ and $D_{CT}^{min}$ (or
$D_{CT_\parallel}^{min}$). We illustrate our method with dilepton $t\bar{t}$
events at the LHC.Comment: thoroughly revised; all new figures; new results on pages 3 and 4;
new illustrative example; includes detector simulation. 4 pages, 6 figures,
uses revtex and axodra

### Higgs and Z-boson Signatures of Supersymmetry

In supersymmetric theories of nature the Higgsino fermionic superpartner of
the Higgs boson can arise as the lightest standard model superpartner depending
on the couplings between the Higgs and supersymmetry breaking sectors. In this
letter the production and decay of Higgsino pairs to the Goldstone fermion of
supersymmetry breaking and the Higgs boson, h, or gauge bosons, Z or $\gamma$
are considered. Relatively clean di-boson final states, hh, $h \gamma$, hZ, $Z
\gamma$, or ZZ, with a large amount of missing energy result. The latter
channels provide novel discovery modes for supersymmetry at high energy
colliders since events with Z bosons are generally rejected in supersymmetry
searches. In addition, final states with real Higgs bosons can potentially
provide efficient channels to discover and study a Higgs signal at the Fermilab
Tevatron Run II.Comment: 11 pages, LaTeX, 3 figure

### How to prove that the LHC did not discover dark matter

If the LHC is able to produce dark matter particles, they would appear at the
end of cascade decay chains, manifesting themselves as missing transverse
energy. However, such "dark matter candidates" may decay invisibly later on. We
propose to test for this possibility by studying the effect of particle widths
on the observable invariant mass distributions of the visible particles seen in
the detector. We consider the simplest non-trivial case of a two-step two-body
cascade decay and derive analytically the shapes of the invariant mass
distributions, for generic values of the widths of the new particles. We
demonstrate that the resulting distortion in the shape of the invariant mass
distribution can be significant enough to measure the width of the dark matter
"candidate", ruling it out as the source of the cosmological dark matter.Comment: 5 pages, 5 figure

### Light Axion within the Next-to-Minimal Supersymmetric Standard Model

We analyze the Higgs sector in the Next-to-Minimal Supersymmetric Standard
Model, emphasizing the possibility of a light CP-odd scalar (axion) in the
spectrum. We compute the coupling of the Standard-Model-like Higgs boson to a
pair of axions, and show that it can be large enough to modify the Higgs
branching fractions, with a significant impact on the Higgs searches. We
delineate the range of parameters relevant for this scenario, and also derive
analytic expressions for the scalar masses and couplings in two special cases -
a decoupling limit where all scalars other than the axion are heavier than the
Standard-Model-like Higgs boson, and the large tan beta limit.Comment: 28 pages, 6 figure

### Focus Point Supersymmetry: Proton Decay, Flavor and CP Violation, and the Higgs Boson Mass

In focus point supersymmetry, all squarks and sleptons, including those of
the third generation, have multi-TeV masses without sacrificing naturalness. We
examine the implications of this framework for low energy constraints and the
light Higgs boson mass. Undesirable contributions to proton decay and electric
dipole moments, generic in many supersymmetric models, are strongly suppressed.
As a result, the prediction for alpha_s in simple grand unified theories is 3
to 5 standard deviations closer to the experimental value, and the allowed
CP-violating phases are larger by one to two orders of magnitude. In addition,
the very heavy top and bottom squarks of focus point supersymmetry naturally
produce a Higgs boson mass at or above 115 GeV without requiring heavy
gauginos. We conclude with an extended discussion of issues related to the
definition of naturalness and comment on several other prescriptions given in
the literature.Comment: 31 pages, 10 figures, references added, version to appear in Phys.
Rev.

### Re-interpreting the Oxbridge stransverse mass variable MT2 in general cases

We extend the range of possible applications of MT2 type analyses to decay
chains with multiple invisible particles, as well as to asymmetric event
topologies with different parent and/or different children particles. We
advocate two possible approaches. In the first, we introduce suitably defined
3+1-dimensional analogues of the MT2 variable, which take into account all
relevant on-shell kinematic constraints in a given event topology. The second
approach utilizes the conventional MT2 variable, but its kinematic endpoint is
suitably reinterpreted on a case by case basis, depending on the specific event
topology at hand. We provide the general prescription for this
reinterpretation, including the formulas relating the measured MT2 endpoint (as
a function of the test masses of all the invisible particles) to the underlying
physical mass spectrum. We also provide analytical formulas for the shape of
the differential distribution of the doubly projected MT2(perp) variable for
the ten possible event topologies with one visible particle and up to two
invisible particles per decay chain. We illustrate our results with the example
of leptonic chargino decays, (chargino to lepton, neutrino and LSP) in
supersymmetry.Comment: 36 pages, 9 figures, Preprint typeset in JHEP styl

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