253 research outputs found
Spectral Analysis of Jet Substructure with Neural Networks: Boosted Higgs Case
Jets from boosted heavy particles have a typical angular scale which can be
used to distinguish them from QCD jets. We introduce a machine learning
strategy for jet substructure analysis using a spectral function on the angular
scale. The angular spectrum allows us to scan energy deposits over the angle
between a pair of particles in a highly visual way. We set up an artificial
neural network (ANN) to find out characteristic shapes of the spectra of the
jets from heavy particle decays. By taking the Higgs jets and QCD jets as
examples, we show that the ANN of the angular spectrum input has similar
performance to existing taggers. In addition, some improvement is seen when
additional extra radiations occur. Notably, the new algorithm automatically
combines the information of the multi-point correlations in the jet.Comment: 18 pages, 12 figures, published in JHEP. A cut-based analysis is
adde
Identifying a new particle with jet substructures
We investigate a potential of measuring properties of a heavy resonance X,
exploiting jet substructure techniques. Motivated by heavy higgs boson
searches, we focus on the decays of X into a pair of (massive) electroweak
gauge bosons. More specifically, we consider a hadronic Z boson, which makes it
possible to determine properties of X at an earlier stage. For of O(1)
TeV, two quarks from a Z boson would be captured as a "merged jet" in a
significant fraction of events. The use of the merged jet enables us to
consider a Z-induced jet as a reconstructed object without any combinatorial
ambiguity. We apply a conventional jet substructure method to extract
four-momenta of subjets from a merged jet. We find that jet substructure
procedures may enhance features in some kinematic observables formed with
subjets. Subjet momenta are fed into the matrix element associated with a given
hypothesis on the nature of X, which is further processed to construct a matrix
element method (MEM)-based observable. For both moderately and highly boosted Z
bosons, we demonstrate that the MEM with current jet substructure techniques
can be a very powerful discriminator in identifying the physics nature of X. We
also discuss effects from choosing different jet sizes for merged jets and
jet-grooming parameters upon the MEM analyses.Comment: 36 pages, 11 figures, published in JHE
Mapping Dark Matter in the Milky Way using Normalizing Flows and Gaia DR3
We present a novel, data-driven analysis of Galactic dynamics, using
unsupervised machine learning -- in the form of density estimation with
normalizing flows -- to learn the underlying phase space distribution of 6
million nearby stars from the Gaia DR3 catalog. Solving the collisionless
Boltzmann equation with the assumption of approximate equilibrium, we calculate
-- for the first time ever -- a model-free, unbinned, fully 3D map of the local
acceleration and mass density fields within a 3 kpc sphere around the Sun. As
our approach makes no assumptions about symmetries, we can test for signs of
disequilibrium in our results. We find our results are consistent with
equilibrium at the 10% level, limited by the current precision of the
normalizing flows. After subtracting the known contribution of stars and gas
from the calculated mass density, we find clear evidence for dark matter
throughout the analyzed volume. Assuming spherical symmetry and averaging mass
density measurements, we find a local dark matter density of . We fit our results to a generalized NFW, and find a
profile broadly consistent with other recent analyses.Comment: 19 pages, 13 figures, 3 table
The 750 GeV Diphoton Excess May Not Imply a 750 GeV Resonance
We discuss non-standard interpretations of the 750 GeV diphoton excess
recently reported by the ATLAS and CMS Collaborations which do not involve a
new, relatively broad, resonance with a mass near 750 GeV. Instead, we consider
the sequential cascade decay of a much heavier, possibly quite narrow,
resonance into two photons along with one or more invisible particles. The
resulting diphoton invariant mass signal is generically rather broad, as
suggested by the data. We examine three specific event topologies - the antler,
the sandwich, and the 2-step cascade decay, and show that they all can provide
a good fit to the observed published data. In each case, we delineate the
preferred mass parameter space selected by the best fit. In spite of the
presence of invisible particles in the final state, the measured missing
transverse energy is moderate, due to its anti- correlation with the diphoton
invariant mass. We comment on the future prospects of discriminating with
higher statistics between our scenarios, as well as from more conventional
interpretations.Comment: Discussion about the ATLAS Moriond EW2016 added. Matched to PRL
accepted versio
GalaxyFlow: Upsampling Hydrodynamical Simulations for Realistic Gaia Mock Catalogs
Cosmological N-body simulations of galaxies operate at the level of "star
particles" with a mass resolution on the scale of thousands of solar masses.
Turning these simulations into stellar mock catalogs requires "upsampling" the
star particles into individual stars following the same phase-space density. In
this paper, we demonstrate that normalizing flows provide a viable upsampling
method that greatly improves on conventionally-used kernel smoothing algorithms
such as EnBiD. We demonstrate our flow-based upsampling technique, dubbed
GalaxyFlow, on a neighborhood of the Solar location in two simulated galaxies:
Auriga 6 and h277. By eye, GalaxyFlow produces stellar distributions that are
smoother than EnBiD-based methods and more closely match the Gaia DR3 catalog.
For a quantitative comparison of generative model performance, we introduce a
novel multi-model classifier test. Using this classifier test, we show that
GalaxyFlow more accurately estimates the density of the underlying star
particles than previous methods.Comment: 17 pages, 11 figure
Monojet signatures from heavy colored particles: future collider sensitivities and theoretical uncertainties
In models with colored particle Q that can decay into a dark matter candidate X, the relevant collider process pp → QQ¯ → X X¯ + jets gives rise to events with significant transverse momentum imbalance. When the masses of Q and X are very close, the relevant signature becomes monojetlike, and Large Hadron Collider (LHC) search limits become much less constraining. In this paper, we study the current and anticipated experimental sensitivity to such particles at the High-Luminosity LHC at √s = 14 TeV with L = 3 ab−1 of data and the proposed High-Energy LHC at √s = 27 TeV with L = 15 ab−1 of data. We estimate the reach for various Lorentz and QCD color representations of Q. Identifying the nature of Q is very important to understanding the physics behind the monojet signature. Therefore, we also study the dependence of the observables built from the pp → QQ¯ + j process on Q itself. Using the state-of-theart Monte Carlo suites MadGraph5_aMC@NLO+Pythia8 and Sherpa, we find that when these observables are calculated at NLO in QCD with parton shower matching and multijet merging, the residual theoretical uncertainties are comparable to differences observed when varying the quantum numbers of Q itself. We find, however, that the precision achievable with NNLO calculations, where available, can resolve this dilemma
OPTIMASS: A Package for the Minimization of Kinematic Mass Functions with Constraints
Reconstructed mass variables, such as , , , and
, play an essential role in searches for new physics at hadron
colliders. The calculation of these variables generally involves constrained
minimization in a large parameter space, which is numerically challenging. We
provide a C++ code, OPTIMASS, which interfaces with the MINUIT library to
perform this constrained minimization using the Augmented Lagrangian Method.
The code can be applied to arbitrarily general event topologies and thus allows
the user to significantly extend the existing set of kinematic variables. We
describe this code and its physics motivation, and demonstrate its use in the
analysis of the fully leptonic decay of pair-produced top quarks using the
variables.Comment: 39 pages, 12 figures, (1) minor revision in section 3, (2) figure
added in section 4.3, (3) reference added and (4) matched with published
versio
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