41 research outputs found
Seeing in Color: Jet Superstructure
A new class of observables is introduced which aims to characterize the
superstructure of an event, that is, features, such as color flow, which are
not determined by the jet four-momenta alone. Traditionally, an event is
described as having jets which are independent objects; each jet has some
energy, size, and possible substructure such as subjets or heavy flavor
content. This description discards information connecting the jets to each
other, which can be used to determine if the jets came from decay of a color
singlet object, or if they were initiated by quarks or gluons. An example
superstructure variable, pull, is presented as a simple handle on color flow.
It can be used on an event-by-event basis as a tool for distinguishing
previously irreducible backgrounds at the Tevatron and the LHC.Comment: 4 pages, 5 figures. Published version. Some clarifications and
references adde
Quark and Gluon Tagging at the LHC
Being able to distinguish light-quark jets from gluon jets on an
event-by-event basis could significantly enhance the reach for many new physics
searches at the Large Hadron Collider. Through an exhaustive search of existing
and novel jet substructure observables, we find that a multivariate approach
can filter out over 95% of the gluon jets while keeping more than half of the
light-quark jets. Moreover, a combination of two simple variables, the charge
track multiplicity and the -weighted linear radial moment (girth), can
achieve similar results. While this pair appears very promising, our study is
only Monte Carlo based, and other discriminants may work better with real data
in a realistic experimental environment. To that end, we explore many other
observables constructed using different jet sizes and parameters, and highlight
those that deserve further theoretical and experimental scrutiny. Additional
information, including distributions of around 10,000 variables, can be found
on this website http://jets.physics.harvard.edu/qvg .Comment: 5 pages, 3 figures. v2 published versio
Testing Bell's Inequality with Cosmic Photons: Closing the Setting-Independence Loophole
We propose a practical scheme to use photons from causally disconnected
cosmic sources to set the detectors in an experimental test of Bell's
inequality. In current experiments, with settings determined by quantum random
number generators, only a small amount of correlation between detector settings
and local hidden variables, established less than a millisecond before each
experiment, would suffice to mimic the predictions of quantum mechanics. By
setting the detectors using pairs of quasars or patches of the cosmic microwave
background, observed violations of Bell's inequality would require any such
coordination to have existed for billions of years --- an improvement of 20
orders of magnitude.Comment: 5 pages, 4 figures. Minor edits to closely match journal version to
be published in Physical Review Letter
Quark and Gluon Jet Substructure
Distinguishing quark-initiated jets from gluon-initiated jets has the potential to significantly improve the reach of many beyond-the-standard model searches at the Large Hadron Collider and to provide additional tests of QCD. To explore whether quark and gluon jets could possibly be distinguished on an event-by-event basis, we perform a comprehensive simulation-based study. We explore a variety of motivated and unmotivated variables with a semi-automated multivariate approach. General conclusions are that at 50% quark jet acceptance efficiency, around 80%-90% of gluon jets can be rejected. Some benefit is gained by combining variables. Different event generators are compared, as are the effects of using only charged tracks to avoid pileup. Additional information, including interactive distributions of most variables and their cut efficiencies, can be found at http://jets.physics.harvard.edu/qvg.Physic
Astronomical random numbers for quantum foundations experiments
Photons from distant astronomical sources can be used as a classical source
of randomness to improve fundamental tests of quantum nonlocality,
wave-particle duality, and local realism through Bell's inequality and
delayed-choice quantum eraser tests inspired by Wheeler's cosmic-scale
Mach-Zehnder interferometer gedankenexperiment. Such sources of random numbers
may also be useful for information-theoretic applications such as key
distribution for quantum cryptography. Building on the design of an
"astronomical random-number generator" developed for the recent "cosmic Bell"
experiment [Handsteiner et al., Phys. Rev. Lett. 118, 060401 (2017)], in this
paper we report on the design and characterization of a device that, with
20-nanosecond latency, outputs a bit based on whether the wavelength of an
incoming photon is greater than or less than 700 nm. Using the one-meter
telescope at the Jet Propulsion Laboratory (JPL) Table Mountain Observatory, we
generated random bits from astronomical photons in both color channels from 50
stars of varying color and magnitude, and from 12 quasars with redshifts up to
. With stars, we achieved bit rates of Hz /
m, limited by saturation for our single-photon detectors, and with quasars
of magnitudes between 12.9 and 16, we achieved rates between and Hz /m. For bright quasars, the resulting bitstreams exhibit
sufficiently low amounts of statistical predictability as quantified by the
mutual information. In addition, a sufficiently high fraction of bits generated
are of true astronomical origin in order to address both the locality and
freedom-of-choice loopholes when used to set the measurement settings in a test
of the Bell-CHSH inequality.Comment: 17 pages, 12 figures. References added and minor edits to match
published versio
Pure Samples of Quark and Gluon Jets at the LHC
Having pure samples of quark and gluon jets would greatly facilitate the
study of jet properties and substructure, with many potential standard model
and new physics applications. To this end, we consider multijet and jets+X
samples, to determine the purity that can be achieved by simple kinematic cuts
leaving reasonable production cross sections. We find, for example, that at the
7 TeV LHC, the pp {\to} {\gamma}+2jets sample can provide 98% pure quark jets
with 200 GeV of transverse momentum and a cross section of 5 pb. To get 10 pb
of 200 GeV jets with 90% gluon purity, the pp {\to} 3jets sample can be used.
b+2jets is also useful for gluons, but only if the b-tagging is very efficient.Comment: 19 pages, 16 figures; v2 section on formally defining quark and gluon
jets has been adde
A Digital Calibration Source for 21cm Cosmology Telescopes
Foreground mitigation is critical to all next-generation radio
interferometers that target cosmology using the redshifted neutral hydrogen 21
cm emission line. Attempts to remove this foreground emission have led to new
analysis techniques as well as new developments in hardware specifically
dedicated to instrument beam and gain calibration, including stabilized signal
injection into the interferometric array and drone-based platforms for beam
mapping. The radio calibration sources currently used in the literature are
broad-band incoherent sources that can only be detected as excess power and
with no direct sensitivity to phase information. In this paper, we describe a
digital radio source which uses Global Positioning Satellite (GPS) derived time
stamps to form a deterministic signal that can be broadcast from an aerial
platform. A copy of this source can be deployed locally at the instrument
correlator such that the received signal from the aerial platform can be
correlated with the local copy, and the resulting correlation can be measured
in both amplitude and phase for each interferometric element. We define the
requirements for such a source, describe an initial implementation and
verification of this source using commercial Software Defined Radio boards, and
present beam map slices from antenna range measurements using the commercial
boards. We found that the commercial board did not meet all requirements, so we
also suggest future directions using a more sophisticated chipset.Comment: 13 pages, 5 figures, published in Journal of Astronomical
Instrumentatio