1,156 research outputs found
Determining masses of supersymmetric particles
If supersymmetric particles are produced at the Large Hadron Collider it
becomes very important not only to identify them, but also to determine their
masses with the highest possible precision, since this may lead to an
understanding of the SUSY-breaking mechanism and the physics at some higher
scale. We here report on studies of how such mass measurements are obtained,
and how the precision can be optimized.Comment: 11 pages, contribution to the proceedings "II. Southeastern European
Workshop Challenges Beyond The Standard Model", 19-23 May 2005, Vrnjacka
Banja, Serbi
Mass Determination in Cascade Decays Using Shape Formulas
In SUSY scenarios with invisible LSP, sparticle masses can be determined from
fits to the endpoints of invariant mass distributions. Here we discuss possible
improvements by using the shapes of the distributions. Positive results are
found for multiple-minima situations and for mass regions where the endpoints
do not contain sufficient information to obtain the masses.Comment: 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
Mass ambiguities in cascade decays
We review the use of invariant mass distributions in cascade decays to
measure the masses of New Physics (NP) particles in scenarios where the final
NP cascade particle is invisible. We extend earlier work by exploring further
the problem of multiple solutions for the masses.Comment: 4 pages, 4 figures, to appear in the proceedings of the XXXIII
International Conference on High Energy Physics (ICHEP'06), July 26 - August
2 2006, Mosco
Measurement of SUSY masses via cascade decays for SPS 1a
If R-parity conserving supersymmetry exists below the TeV-scale, new particles will be produced and decay in cascades at the LHC. The lightest supersymmetric particle will escape the detectors, thereby complicating the full reconstruction of the decay chains. In this paper we expand on existing methods for determining the masses of the particles in the cascade from endpoints of kinematical distributions. We perform scans in the mSUGRA parameter space to delimit the region where this method is applicable. From the examination of theoretical distributions for a wide selection of mass scenarios it is found that caution must be exerted when equating the theoretical endpoints with the experimentally obtainable ones. We provide analytic formulae for the masses in terms of the endpoints most readily available. Complications due to the composite nature of the endpoint expressions are discussed in relation to the detailed analysis of two points on the SPS 1a line. Finally we demonstrate how a Linear Collider measurement can improve dramatically on the precision of the masses obtained
Kinematic Edges with Flavor Oscillation and Non-Zero Widths
Kinematic edges in cascade decays provide a probe of the masses of new
particles. In some new physics scenarios the decay chain involves intermediate
particles of different flavors that can mix and oscillate. We discuss the
implication of such oscillation, and in particular its interplay with the
non-zero widths of the particles. We derive explicit formulae for differential
decay rates involving both non-zero widths and oscillation, and show that in
the case where the mass difference between the intermediate particle is of the
order of their widths, both oscillation and width effects are important. An
examination of the physical observables contained in these differential decay
rates is provided. We calculate differential decay rates for cases in which the
intermediate particles are either scalars or fermions.Comment: 28 pages, 6 figure
Using Subsystem MT2 for Complete Mass Determinations in Decay Chains with Missing Energy at Hadron Colliders
We propose to use the MT2 concept to measure the masses of all particles in
SUSY-like events with two unobservable, identical particles. To this end we
generalize the usual notion of MT2 and define a new MT2(n,p,c) variable, which
can be applied to various subsystem topologies, as well as the full event
topology. We derive analytic formulas for its endpoint MT2{max}(n,p,c) as a
function of the unknown test mass Mc of the final particle in the subchain and
the transverse momentum pT due to radiation from the initial state. We show
that the endpoint functions MT2{max}(n,p,c)(Mc,pT) may exhibit three different
types of kinks and discuss the origin of each type. We prove that the subsystem
MT2(n,p,c) variables by themselves already yield a sufficient number of
measurements for a complete determination of the mass spectrum (including the
overall mass scale). As an illustration, we consider the simple case of a decay
chain with up to three heavy particles, X2 -> X1 -> X0, which is rather
problematic for all other mass measurement methods. We propose three different
MT2-based methods, each of which allows a complete determination of the masses
of particles X0, X1 and X2. The first method only uses MT2(n,p,c) endpoint
measurements at a single fixed value of the test mass Mc. In the second method
the unknown mass spectrum is fitted to one or more endpoint functions
MT2{max}(n,p,c)(Mc,pT) exhibiting a kink. The third method is hybrid, combining
MT2 endpoints with measurements of kinematic edges in invariant mass
distributions. As a practical application of our methods, we show that the
dilepton W+W- and tt-bar samples at the Tevatron can be used for an independent
determination of the masses of the top quark, the W boson and the neutrino,
without any prior assumptions.Comment: 47 pages, 9 figures. revised version, published in JHEP. Major
addition: a new appendix with the complete set of formulas for the MT2
endpoints as functions of the upstream transverse momentum pT and test mass
M
Initial determination of the spins of the gluino and squarks at LHC
In principle particle spins can be measured from their production cross
sections once their mass is approximately known. The method works in practice
because spins are quantized and cross sections depend strongly on spins. It can
be used to determine, for example, the spin of the top quark. Direct
application of this method to supersymmetric theories will have to overcome the
challenge of measuring mass at the LHC, which could require high statistics. In
this article, we propose a method of measuring the spins of the colored
superpatners by combining rate information for several channels and a set of
kinematical variables, without directly measuring their masses. We argue that
such a method could lead to an early determination of the spin of gluino and
squarks. This method can be applied to the measurement of spin of other new
physics particles and more general scenarios.Comment: 23 pages, 8 figures, minor change
LHC/ILC Interplay in SUSY Searches
Combined analyses at the Large Hadron Collider and at the International
Linear Collider are important to reveal precisely the new physics model as, for
instance, supersymmetry. Examples are presented where ILC results as input for
LHC analyses could be crucial for the identification of signals as well as of
the underlying model. The synergy of both colliders leads also to rather
accurate SUSY parameter determination and powerful mass constraints even if the
scalar particles have masses in the multi-TeV range.Comment: 5 pages, contribution to the proceedings of EPS0
Measuring superparticle masses at hadron collider using the transverse mass kink
We present a detailed study of the collider observable applied for
pair-produced superparticles decaying to visible particles and a pair of
invisible lightest supersymmetric particles (LSPs). Analytic expressions of the
maximum of over all events () are derived. It is
noticed that if the decay product of each superparticle involves more than one
visible particles, being a function of the {\it trial} LSP
mass has a kink structure at true LSP mass, which can be
used to determine the mother superparticle mass and the LSP mass
simultaneously. To see how well can be constructed from
collider data, a Monte-Carlo analysis of the gluino is performed for
some superparticle spectra.Comment: Typos corrected. A few references added. Figures update
- âŠ