3,131 research outputs found
Time-integrated measurements and prospects for the CKM angle gamma at LHCb
The status and prospects of time-integrated measurements of the CKM angle
gamma at LHCb, the LHC's dedicated flavor physics experiment, are reviewed.
Yields obtained from early data taking are presented and extrapolations are
made to estimate what can be expected to be obtained from the 2011 data. The
conclusions drawn from these extrapolations are that LHCb will produce the
world's best measurement of gamma by the end of 2011 and that the long-term
outlook is excellent.Comment: Proceedings of CKM2010, the 6th International Workshop on the CKM
Unitarity Triangle, University of Warwick, UK, 6-10 September 201
A novel approach to the bias-variance problem in bump hunting
This study explores various data-driven methods for performing
background-model selection, and for assigning uncertainty on the
signal-strength estimator that arises due to the choice of background model.
The performance of these methods is evaluated in the context of several
realistic example problems. Furthermore, a novel strategy is proposed that
greatly simplifies the process of performing a bump hunt when little is assumed
to be known about the background. This new approach is shown to greatly reduce
the potential bias in the signal-strength estimator, without degrading the
sensitivity by increasing the variance, and to produce confidence intervals
with valid coverage properties.Comment: 26 pages, 17 figure
Searching for a particle of unknown mass and lifetime in the presence of an unknown non-monotonic background
Many extensions to the Standard Model of particle physics hypothesize the
existence of new low-mass particles. Typically there are few theoretical
constraints on the mass or lifetime of such particles. This requires the
experimentalist to perform a search in which both the mass and lifetime of the
particle are unknown. Such searches for low-mass particles are complicated by
the possible presence of resonances and other non-monotonic backgrounds. This
paper presents a simple and fast approach to assigning significance and setting
limits in such searches
uBoost: A boosting method for producing uniform selection efficiencies from multivariate classifiers
The use of multivariate classifiers, especially neural networks and decision
trees, has become commonplace in particle physics. Typically, a series of
classifiers is trained rather than just one to enhance the performance; this is
known as boosting. This paper presents a novel method of boosting that produces
a uniform selection efficiency in a user-defined multivariate space. Such a
technique is ideally suited for amplitude analyses or other situations where
optimizing a single integrated figure of merit is not what is desired
Efficient, reliable and fast high-level triggering using a bonsai boosted decision tree
High-level triggering is a vital component in many modern particle physics
experiments. This paper describes a modification to the standard boosted
decision tree (BDT) classifier, the so-called "bonsai" BDT, that has the
following important properties: it is more efficient than traditional cut-based
approaches; it is robust against detector instabilities, and it is very fast.
Thus, it is fit-for-purpose for the online running conditions faced by any
large-scale data acquisition system.Comment: 10 pages, 2 figure
Angular correlations between LBQS and APM: Weak Lensing by the Large Scale Structure
We detect a positive angular correlation between bright, high-redshift QSOs
and foreground galaxies. The QSOs are taken from the optically selected LBQS
Catalogue, while the galaxies are from the APM Survey. The correlation
amplitude is about a few percent on angular scales of over a degree. It is a
function of QSO redshift and apparent magnitude, in a way expected from weak
lensing, and inconsistent with QSO-galaxy correlations being caused by physical
associations, or uneven obscuration by Galactic dust. The correlations are
ascribed to the weak lensing effect of the foreground dark matter, which is
traced by the APM galaxies. The amplitude of the effect found here is compared
to the analytical predictions from the literature, and to the predictions of a
phenomenological model, which is based on the observed counts-in-cells
distribution of APM galaxies. While the latter agree reasonably well with the
analytical predictions (namely those of Dolag & Bartelmann 1997, and Sanz et
al. 1997), both under-predict the observed correlation amplitude on degree
angular scales. We consider the possible ways to reconcile these observations
with theory, and discuss the implications these observations have on some
aspects of extragalactic astronomy.Comment: 9 pages; MNRAS, in pres
Coupling QCD-scale axion-like particles to gluons
We present a novel data-driven method for determining the hadronic
interaction strengths of axion-like particles (ALPs) with QCD-scale masses.
Using our method, it is possible to calculate the hadronic production and decay
rates of ALPs, along with many of the largest ALP decay rate to exclusive final
states. To illustrate the impact on QCD-scale ALP phenomenology, we consider
the scenario where the ALP-gluon coupling is dominant over the ALP coupling to
photons, electroweak bosons, and all fermions for GeV. We emphasize, however, that our method can easily be
generalized to any set of ALP couplings to SM particles. Finally, using the
approach developed here, we provide calculations for the branching fractions of
decays, i.e. decays into two vector mesons, which are
consistent with the known experimental values.Comment: 19 pages, 7 figures; v3 Fig 4 updated to account for a small change
in the limit taken from [1903.03586
Nonparametric Regression using the Concept of Minimum Energy
It has recently been shown that an unbinned distance-based statistic, the
energy, can be used to construct an extremely powerful nonparametric
multivariate two sample goodness-of-fit test. An extension to this method that
makes it possible to perform nonparametric regression using multiple
multivariate data sets is presented in this paper. The technique, which is
based on the concept of minimizing the energy of the system, permits
determination of parameters of interest without the need for parametric
expressions of the parent distributions of the data sets. The application and
performance of this new method is discussed in the context of some simple
example analyses.Comment: 10 pages, 4 figure
- …