2,262 research outputs found
Identifying Boosted Objects with N-subjettiness
We introduce a new jet shape -- N-subjettiness -- designed to identify
boosted hadronically-decaying objects like electroweak bosons and top quarks.
Combined with a jet invariant mass cut, N-subjettiness is an effective
discriminating variable for tagging boosted objects and rejecting the
background of QCD jets with large invariant mass. In efficiency studies of
boosted W bosons and top quarks, we find tagging efficiencies of 30% are
achievable with fake rates of 1%. We also consider the discovery potential for
new heavy resonances that decay to pairs of boosted objects, and find
significant improvements are possible using N-subjettiness. In this way,
N-subjettiness combines the advantages of jet shapes with the discriminating
power seen in previous jet substructure algorithms.Comment: 26 pages, 26 figures, 2 tables; v2: references added; v3: discussion
of results extende
The mass area of jets
We introduce a new characteristic of jets called mass area. It is defined so
as to measure the susceptibility of the jet's mass to contamination from soft
background. The mass area is a close relative of the recently introduced
catchment area of jets. We define it also in two variants: passive and active.
As a preparatory step, we generalise the results for passive and active areas
of two-particle jets to the case where the two constituent particles have
arbitrary transverse momenta. As a main part of our study, we use the mass area
to analyse a range of modern jet algorithms acting on simple one and
two-particle systems. We find a whole variety of behaviours of passive and
active mass areas depending on the algorithm, relative hardness of particles or
their separation. We also study mass areas of jets from Monte Carlo simulations
as well as give an example of how the concept of mass area can be used to
correct jets for contamination from pileup. Our results show that the
information provided by the mass area can be very useful in a range of
jet-based analyses.Comment: 36 pages, 12 figures; v2: improved quality of two plots, added entry
in acknowledgments, nicer form of formulae in appendix A; v3: added section
with MC study and pileup correction, version accepted by JHE
Jet Substructure Without Trees
We present an alternative approach to identifying and characterizing jet
substructure. An angular correlation function is introduced that can be used to
extract angular and mass scales within a jet without reference to a clustering
algorithm. This procedure gives rise to a number of useful jet observables. As
an application, we construct a top quark tagging algorithm that is competitive
with existing methods.Comment: 22 pages, 16 figures, version accepted by JHE
E-learning for project management
This paper examines the reasons for the apparent reluctance of civil engineers and other construction professionals to use computer-aided learning on distance-learning programmes and reports on the evaluation of a project-management CD-ROM. It concludes that ‘e-learning’ can be as effective as traditional distance learning and face-to-face teaching, but is best suited to the development of ‘hard’, technically oriented, project management skills than ‘soft’ interpersonal skills
A Definitive Signal of Multiple Supersymmetry Breaking
If the lightest observable-sector supersymmetric particle (LOSP) is charged
and long-lived, then it may be possible to indirectly measure the Planck mass
at the LHC and provide a spectacular confirmation of supergravity as a symmetry
of nature. Unfortunately, this proposal is only feasible if the gravitino is
heavy enough to be measured at colliders, and this condition is in direct
conflict with constraints from big bang nucleosynthesis (BBN). In this work, we
show that the BBN bound can be naturally evaded in the presence of multiple
sectors which independently break supersymmetry, since there is a new decay
channel of the LOSP to a goldstino. Certain regions of parameter space allow
for a direct measurement of LOSP decays into both the goldstino and the
gravitino at the LHC. If the goldstino/gravitino mass ratio is measured to be
2, as suggested by theory, then this would provide dramatic verification of the
existence of multiple supersymmetry breaking and sequestering. A variety of
consistent cosmological scenarios are obtained within this framework. In
particular, if an R symmetry is imposed, then the gauge-gaugino-goldstino
interaction vertices can be forbidden. In this case, there is no bound on the
reheating temperature from goldstino overproduction, and thermal leptogenesis
can be accommodated consistently with gravitino dark matter.Comment: 10 pages, 5 figures, title changed to match the version published in
JHE
Optimal jet radius in kinematic dijet reconstruction
Obtaining a good momentum reconstruction of a jet is a compromise between
taking it large enough to catch the perturbative final-state radiation and
small enough to avoid too much contamination from the underlying event and
initial-state radiation. In this paper, we compute analytically the optimal jet
radius for dijet reconstructions and study its scale dependence. We also
compare our results with previous Monte-Carlo studies.Comment: 30 pages, 11 figures; minor corrections; published in JHE
Jet Dipolarity: Top Tagging with Color Flow
A new jet observable, dipolarity, is introduced that can distinguish whether
a pair of subjets arises from a color singlet source. This observable is
incorporated into the HEPTopTagger and is shown to improve discrimination
between top jets and QCD jets for moderate to high pT.Comment: 8 pages, 6 figures (updated to JHEP version
Higgs friends and counterfeits at hadron colliders
We consider the possibility of "Higgs counterfeits" - scalars that can be
produced with cross sections comparable to the SM Higgs, and which decay with
identical relative observable branching ratios, but which are nonetheless not
responsible for electroweak symmetry breaking. We also consider a related
scenario involving "Higgs friends," fields similarly produced through gg fusion
processes, which would be discovered through diboson channels WW, ZZ, gamma
gamma, or even gamma Z, potentially with larger cross sections times branching
ratios than for the Higgs. The discovery of either a Higgs friend or a Higgs
counterfeit, rather than directly pointing towards the origin of the weak
scale, would indicate the presence of new colored fields necessary for the
sizable production cross section (and possibly new colorless but electroweakly
charged states as well, in the case of the diboson decays of a Higgs friend).
These particles could easily be confused for an ordinary Higgs, perhaps with an
additional generation to explain the different cross section, and we emphasize
the importance of vector boson fusion as a channel to distinguish a Higgs
counterfeit from a true Higgs. Such fields would naturally be expected in
scenarios with "effective Z's," where heavy states charged under the SM produce
effective charges for SM fields under a new gauge force. We discuss the
prospects for discovery of Higgs counterfeits, Higgs friends, and associated
charged fields at the LHC.Comment: 27 pages, 5 figures. References added and typos fixe
Heavy Squarks at the LHC
The LHC, with its seven-fold increase in energy over the Tevatron, is capable
of probing regions of SUSY parameter space exhibiting qualitatively new
collider phenomenology. Here we investigate one such region in which first
generation squarks are very heavy compared to the other superpartners. We find
that the production of these squarks, which is dominantly associative, only
becomes rate-limited at mSquark > 4(5) TeV for L~10(100) fb-1. However,
discovery of this scenario is complicated because heavy squarks decay primarily
into a jet and boosted gluino, yielding a dijet-like topology with missing
energy (MET) pointing along the direction of the second hardest jet. The result
is that many signal events are removed by standard jet/MET anti-alignment cuts
designed to guard against jet mismeasurement errors. We suggest replacing these
anti-alignment cuts with a measurement of jet substructure that can
significantly extend the reach of this channel while still removing much of the
background. We study a selection of benchmark points in detail, demonstrating
that mSquark= 4(5) TeV first generation squarks can be discovered at the LHC
with L~10(100)fb-1
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