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Georgios Choudalakis

Publications and source records attributed to Georgios Choudalakis.

11 recordsLinked to original sources
arXiv2018

Plotting the Differences Between Data and Expectation

This article proposes a way to improve the presentation of histograms where data are compared to expectation. Sometimes, it is difficult to judge by eye whether the difference between the bin content and the theoretical expectation (provided by either a fitting function or another histogram) is just due to statistical fluctuations. More importantly, there could be statistically significant deviations which are completely invisible in the plot. We propose to add a small inset at the bottom of the plot, in which the statistical significance of the deviation observed in each bin is shown. Even though the numerical routines which we developed have only illustration purposes, it comes out that they are based on formulae which could be used to perform statistical inference in a proper way. An implementation of our computation is available at https://github.com/dcasadei/psde .

physics.data-an↗
arXiv2012

Fully Bayesian Unfolding

Bayesian inference is applied directly to the problem of unfolding. The outcome is a posterior probability density for the spectrum before smearing, defined in the multi-dimensional space of all possible spectra. Regularization consists in choosing a non-constant prior. Despite some similarity, the fully bayesian unfolding (FBU) method, presented here, should not be confused with D'Agostini's iterative method.

physics.data-an↗
arXiv2011

How to Use Experimental Data to Compute the Probability of Your Theory

This article is geared towards theorists interested in estimating parameters of their theoretical models, and computing their own limits using available experimental data and elementary Mathematica code. The examples given can be useful also to experimentalists who wish to learn how to use Bayesian methods. A thorough introduction precedes the practical part, to make clear the advantages and shortcomings of the method, and to prevent its abuse. The goal of this article is to help bridge the gap between theory and experiment.

hep-ph↗
arXiv2011

Dijet Searches for New Physics in ATLAS

The latest results are presented of the search for new physics in inclusive dijet events recorded with the ATLAS detector. The search for resonances in the dijet mass spectrum is updated with 0.81 fb^-1 of 2011 data. The latest analysis of dijet angular distributions, with 36 pb^-1 of 2010 data, is also presented. In-depth information is provided about the model-independent search for resonances. Limits are provided for excited quarks, axigluons, scalar color octets, and to Gaussian signals that allow to set approximate limits in a model-independent way.

hep-ex↗
arXiv2011

Early Searches with Jets with the ATLAS Detector at the LHC

We summarize the analysis of high-pT jets in early pp collisions recorded with the ATLAS detector. Two searches for new physics are presented: One for dijet resonances, and one for quark contact interactions. The first search sets the most stringent current limit on the mass of a hypothetical excited quark.

hep-ex↗
arXiv2011

Unfolding in ATLAS

These proceedings present the unfolding techniques used so far in ATLAS. Two representative examples are discussed in detail; one using bin-by-bin correction factors, and the other iterative unfolding.

hep-ex↗
arXiv2011

On hypothesis testing, trials factor, hypertests and the BumpHunter

A detailed presentation of hypothesis testing is given. The "look elsewhere" effect is illustrated, and a treatment of the trials factor is proposed with the introduction of hypothesis hypertests. An example of such a hypertest is presented, named BumpHunter, which is used in the recent ATLAS dijet resonance search, and in an earlier version in the CDF Global Search, to look for exotic phenomena in high energy physics. As a demonstration, the BumpHunter is used to address Problem 1 of the Banff Challenge.

physics.data-an↗
arXiv2008

Model Independent Search For New Physics At The Tevatron

This thesis is a global, model-independent search for new physics, performed with CDF Run II data. The Standard Model prediction is implemented in all final states simultaneously, and an array of statistical probes is employed to search for significant discrepancies between data and prediction. The probes (also known as "Vista", "Sleuth" and "Bump Hunter") are sensitive to population discrepancies, shape disagreements in distributions of kinematic variables, excesses of events of high total transverse momentum, and local excesses of data suggesting resonant production of new massive particles. The result of this search, first in 1 fb-1 and then in 2 fb-1, is null, namely no considerable evidence of new physics was found.

hep-ex↗
arXiv2007

Sleuth at CDF, a quasi-model-independent search for new electroweak scale physics

These proceedings describe Sleuth, a quasi-model-independent search strategy targeting new electroweak scale physics, and its application to 927 pb^-1 of CDF II data. Exclusive final states are analyzed for an excess of data beyond the Standard Model prediction at large summed scalar transverse momentum. This analysis of high-pT data represents one of the most encompassing searches so far conducted for new physics at the energy frontier.

hep-ex↗
arXiv2004

Non-oscillating neutrinos in vacuum

Demonstration of how matter effects can result into non-oscillating neutrinos in vacuum, after they have passed through an appropriate distribution of matter. A brief discussion about matter effects in neutrinos oscillation is also made.

hep-ph↗