3,095 research outputs found
A comment on "Amplification of endpoint structure for new particle mass measurement at the LHC"
We present a comment on the kinematic variable recently proposed in
"Amplification of endpoint structure for new particle mass measurement at the
LHC". The variable is designed to be applied to models such as R-parity
conserving Supersymmetry (SUSY) when there is pair production of new heavy
particles each of which decays to a single massless visible and a massive
invisible component. It was proposed in "Amplification of endpoint structure
for new particle mass measurement at the LHC" that a measurement of the peak of
the distribution could be used to precisely constrain the masses of
the SUSY particles. We show that when Standard Model backgrounds are included
in simulations, the sensitivity of the variable to the SUSY particle
masses is more seriously impacted for than for other previously
proposed variables.Comment: 5 page
The stransverse mass, MT2, in special cases
This document describes some special cases in which the stransverse mass,
MT2, may be calculated by non-iterative algorithms. The most notable special
case is that in which the visible particles and the hypothesised invisible
particles are massless -- a situation relevant to its current usage in the
Large Hadron Collider as a discovery variable, and a situation for which no
analytic answer was previously known. We also derive an expression for MT2 in
another set of new (though arguably less interesting) special cases in which
the missing transverse momentum must point parallel or anti parallel to the
visible momentum sum. In addition, we find new derivations for already known
MT2 solutions in a manner that maintains manifest contralinear boost invariance
throughout, providing new insights into old results. Along the way, we stumble
across some unexpected results and make conjectures relating to geometric forms
of M_eff and H_T and their relationship to MT2.Comment: 11 pages, no figures. v2 corrects minor typos. v3 corrects an
incorrect statement in footnote 8 and inserts a missing term in eq (3.9). v4
and v5 correct minor typos spotted by reader
SUSY and Dark Matter Constraints from the LHC
The ability of the LHC to make statements about the dark matter problem is
considered, with a specific focus on supersymmetry. After reviewing the current
strategies for supersymmetry searches at the LHC (in both CMS and ATLAS), some
key ATLAS studies are used to demonstrate how one could establish that SUSY
exists before going on to measure the relic density of a neutralino WIMP
candidate. Finally, the general prospects for success at the LHC are
investigated by looking at different points in the MSSM parameter space.Comment: Talk given at the XLIrst Rencontres de Moriond session devoted to
Electroweak Interactions And Unified Theories in March 2006, to be published
in the associated proceedings. 10 pages, 8 figure
Supersymmetric particle mass measurement with invariant mass correlations
The kinematic end-point technique for measuring the masses of supersymmetric
particles in R-Parity conserving models at hadron colliders is re-examined with
a focus on exploiting additional constraints arising from correlations in
invariant mass observables. The use of such correlations is shown to
potentially resolve the ambiguity in the interpretation of quark+lepton
end-points and enable discrimination between sequential two-body and three-body
lepton-producing decays. The use of these techniques is shown to improve the
SUSY particle mass measurement precision for the SPS1a benchmark model by at
least 20-30% compared to the conventional end-point technique.Comment: 29 pages, 23 .eps figures, JHEP3 style; v2 adds some references and
small clarifications to text; v3 adds some more clarifications to the tex
Supersymmetric particle mass measurement with the boost-corrected contransverse mass
A modification to the contransverse mass (MCT) technique for measuring the
masses of pair-produced semi-invisibly decaying heavy particles is proposed in
which MCT is corrected for non-zero boosts of the centre-of-momentum (CoM)
frame of the heavy states in the laboratory transverse plane. Lack of knowledge
of the mass of the CoM frame prevents exact correction for this boost, however
it is shown that a conservative correction can nevertheless be derived which
always generates an MCT value which is less than or equal to the true value of
MCT in the CoM frame. The new technique is demonstrated with case studies of
mass measurement with fully leptonic ttbar events and with SUSY events
possessing a similar final state.Comment: 33 pages, 33 .eps figures, JHEP3 styl
Reducing combinatorial uncertainties: A new technique based on MT2 variables
We propose a new method to resolve combinatorial ambiguities in hadron
collider events involving two invisible particles in the final state. This
method is based on the kinematic variable MT2 and on the MT2-assisted-on-shell
reconstruction of invisible momenta, that are reformulated as `test' variables
Ti of the correct combination against the incorrect ones. We show how the
efficiency of the single Ti in providing the correct answer can be
systematically improved by combining the different Ti and/or by introducing
cuts on suitable, combination-insensitive kinematic variables. We illustrate
our whole approach in the specific example of top anti-top production, followed
by a leptonic decay of the W on both sides. However, by construction, our
method is also directly applicable to many topologies of interest for new
physics, in particular events producing a pair of undetected particles, that
are potential dark-matter candidates. We finally emphasize that our method is
apt to several generalizations, that we outline in the last sections of the
paper.Comment: 1+23 pages, 8 figures. Main changes in v3: (1) discussion at the end
of sec. 2 improved; (2) added sec. 4.2 about the method's dependence on mass
information. Matches journal versio
Guide to transverse projections and mass-constraining variables
This paper seeks to demonstrate that many of the existing mass-measurement
variables proposed for hadron colliders (mT, mEff, mT2, missing pT, hT,
rootsHatMin, etc.) are far more closely related to each other than is widely
appreciated, and indeed can all be viewed as a common mass bound specialized
for a variety of purposes. A consequence of this is that one may understand
better the strengths and weaknesses of each variable, and the circumstances in
which each can be used to best effect. In order to achieve this, we find it
necessary first to revisit the seemingly empty and infertile wilderness
populated by the subscript "T" (as in pT) in order to remind ourselves what
this process of transversification actually means. We note that, far from being
simple, transversification can mean quite different things to different people.
Those readers who manage to battle through the barrage of transverse notation
distinguishing mass-preserving projections from velocity preserving
projections, and `early projection' from `late projection', will find their
efforts rewarded towards the end of the paper with (i) a better understanding
of how collider mass variables fit together, (ii) an appreciation of how these
variables could be generalized to search for things more complicated than
supersymmetry, (iii) will depart with an aversion to thoughtless or naive use
of the so-called `transverse' methods of any of the popular computer
Lorentz-vector libraries, and (iv) will take care in their subsequent papers to
be explicit about which of the 61 identified variants of the `transverse mass'
they are employing.Comment: 47 pages, 15 figures. v2: Title change for journal, and minor
typographical correction
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
Measuring Invisible Particle Masses Using a Single Short Decay Chain
We consider the mass measurement at hadron colliders for a decay chain of two
steps, which ends with a missing particle. Such a topology appears as a
subprocess of signal events of many new physics models which contain a dark
matter candidate. From the two visible particles coming from the decay chain,
only one invariant mass combination can be formed and hence it is na\"ively
expected that the masses of the three invisible particles in the decay chain
cannot be determined from a single end point of the invariant mass
distribution. We show that the event distribution in the
vs. invariant mass-squared plane, where , are the transverse
energies of the two visible particles, contains the information of all three
invisible particle masses and allows them to be extracted individually. The
experimental smearing and combinatorial issues pose challenges to the mass
measurements. However, in many cases the three invisible particle masses in the
decay chain can be determined with reasonable accuracies.Comment: 45 pages, 32 figure
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.Comment: 17 pages, 4 figures; EPJC versio
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