322 research outputs found
Transverse masses and kinematic constraints: from the boundary to the crease
We re-examine the kinematic variable m_T2 and its relatives in the light of
recent work by Cheng and Han. Their proof that m_T2 admits an equivalent, but
implicit, definition as the `boundary of the region of parent and daughter
masses that is kinematically consistent with the event hypothesis' is
far-reaching in its consequences. We generalize their result both to simpler
cases (m_T, the transverse mass) and to more complex cases (m_TGen). We further
note that it is possible to re-cast many existing and unpleasant proofs (e.g.
those relating to the existence or properties of "kink" and "crease" structures
in m_T2) into almost trivial forms by using the alternative definition. Not
only does this allow us to gain better understanding of those existing results,
but it also allows us to write down new (and more or less explicit) definitions
of (a) the variable that naturally generalizes m_T2 to the case in which the
parent or daughter particles are not identical, and (b) the inverses of m_T and
m_T2 -- which may be useful if daughter masses are known and bounds on parent
masses are required. We note the implications that these results may have for
future matrix-element likelihood techniques
Weighing wimps with kinks at colliders: invisible particle mass measurements from endpoints
We consider the application of endpoint techniques to the problem of mass
determination for new particles produced at a hadron collider, where these
particles decay to an invisible particle of unknown mass and one or more
visible particles of known mass. We also consider decays of these types for
pair-produced particles and in each case consider situations both with and
without initial state radiation. We prove that, in most (but not all) cases,
the endpoint of an appropriate transverse mass observable, considered as a
function of the unknown mass of the invisible particle, has a kink at the true
value of the invisible particle mass. The co-ordinates of the kink yield the
masses of the decaying particle and the invisible particle. We discuss the
prospects for implementing this method at the LHC
The Case for Future Hadron Colliders From Decays
Recent measurements in decays are somewhat
discrepant with Standard Model predictions. They may be harbingers of new
physics at an energy scale potentially accessible to direct discovery. We
estimate the sensitivity of future hadron colliders to the possible new
particles that may be responsible for the anomalies: leptoquarks or
s. We consider luminosity upgrades for a 14 TeV LHC, a 33 TeV LHC,
and a 100 TeV collider such as the FCC-hh. Coverage of models
is excellent: for narrow particles, with perturbative couplings that may
explain the -decay results for masses up to 20 TeV, a 33 TeV 1
ab LHC is expected to cover most of the parameter space up to 8 TeV in
mass, whereas the 100 TeV FCC-hh with 10 ab will cover all of it. A
smaller portion of the leptoquark parameter space is covered by future
colliders: for example, in a di-leptoquark search, a 100 TeV 10
ab collider has a projected sensitivity up to leptoquark masses of 12
TeV (extendable to 21 TeV with a strong coupling for single leptoquark
production), whereas leptoquark masses up to 41 TeV may in principle explain
the anomalies.Comment: 24 pages, 10 figures. v2: Improved discussion and references added,
version submitted to JHE
Gluon Correlators in the Kogan-Kovner Model
The Lorentz-invariant gluon correlation functions, corresponding to scalar
and pseudo-scalar glueballs, are calculated for Kogan's and Kovner's
variational ansatz for the pure SU(N) Yang-Mills wavefunctional.
One expects that only one dynamical mass scale should be present in QCD; the
ansatz generates the expected scale for both glueballs, as well as an
additional scale for the scalar glueball. The additional mass scale must
therefore vanish, or be close to the expected one. This is shown to constrain
the nature of the phase transition in the Kogan-Kovner ansatz.Comment: 9 pages, no figure
Polynomials, Riemann surfaces, and reconstructing missing-energy events
We consider the problem of reconstructing energies, momenta, and masses in
collider events with missing energy, along with the complications introduced by
combinatorial ambiguities and measurement errors. Typically, one reconstructs
more than one value and we show how the wrong values may be correlated with the
right ones. The problem has a natural formulation in terms of the theory of
Riemann surfaces. We discuss examples including top quark decays in the
Standard Model (relevant for top quark mass measurements and tests of spin
correlation), cascade decays in models of new physics containing dark matter
candidates, decays of third-generation leptoquarks in composite models of
electroweak symmetry breaking, and Higgs boson decay into two tau leptons.Comment: 28 pages, 6 figures; version accepted for publication, with
discussion of Higgs to tau tau deca
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Anatomy of the ATLAS diboson anomaly
We perform a general analysis of new physics interpretations of the recent
ATLAS diboson excesses over Standard Model expectations in LHC Run I
collisions. Firstly, we estimate a likelihood function for the true signal in
the , , and channels, finding that the maximum has zero events in
the channel, though the likelihood is sufficiently flat to allow other
scenarios. Secondly, we survey the possible effective field theories containing
the Standard Model plus a new resonance that could explain the data, finding
just two possibilities, viz., a vector that is either a left- or right-handed
triplet. Finally, we compare these models with other experimental data
and determine the parameter regions in which they provide a consistent
explanation.This work has been partially supported by STFC grant ST/L000385/1. We thank M. Redi, J. Tattersall, J. Thaler, A. Wulzer and members of the Cambridge SUSY Working Group for discussions. BG acknowledges MIAPP and King's College, Cambridge. DS acknowledges the support of Emmanuel College, Cambridge.This is the author accepted manuscript. The final version is available from APS via http://dx.doi.org/10.1103/PhysRevD.92.05500
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