1,940 research outputs found

    Theoretical uncertainty in sin 2beta: An update

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    The source of theoretical uncertainty in the extraction of sin 2beta from the measurement of the golden channel Bd -> J/psi K0 is briefly reviewed. An updated estimate of this uncertainty based on SU(3) flavour symmetry and the measurement of the decay Bd -> J/psi pi0 is also presented.Comment: 8 pages, 2 figures, 3 tables, Proceedings of CKM2010, the 6th International Workshop on the CKM Unitarity Triangle, University of Warwick, UK, 6-10 September 201

    Model Inference with Reference Priors

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    We describe the application of model inference based on reference priors to two concrete examples in high energy physics: the determination of the CKM matrix parameters rhobar and etabar and the determination of the parameters m_0 and m_1/2 in a simplified version of the CMSSM SUSY model. We show how a 1-dimensional reference posterior can be mapped to the n-dimensional (n-D) parameter space of the given class of models, under a minimal set of conditions on the n-D function. This reference-based function can be used as a prior for the next iteration of inference, using Bayes' theorem recursively.Comment: Proceedings of PHYSTAT1

    Study the effect of beam energy spread and detector resolution on the search for Higgs boson decays to invisible particles at a future e+^+e−^- circular collider

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    We study the expected sensitivity to measure the branching ratio of Higgs boson decays to invisible particles at a future circular \epem collider (FCC-ee) in the process e+e−→HZe^+e^-\to HZ with Z→ℓ+ℓ−Z\to \ell^+\ell^- (ℓ=e\ell=e or ÎŒ\mu) using an integrated luminosity of 3.5 ab−1^{-1} at a center-of-mass energy s=240\sqrt{s}=240 GeV. The impact of the energy spread of the FCC-ee beam and of the resolution in the reconstruction of the leptons is discussed. %Two different detector concepts are considered: a detector corresponding to the CMS reconstruction performances and the expected design of the ILC detector. The minimum branching ratio for a 5σ5\sigma observation after 3.5ab−1^{-1} of data taking is 1.7±0.1%(stat+syst)1.7\pm 0.1\%(stat+syst) . The branching ratio exclusion limit at 95\% CL is 0.63±0.22%((stat+syst))0.63 \pm 0.22\%((stat+syst)).Comment: 17 pages, submitted to EPJ

    The light stop window

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    We show that a right-handed stop in the 200-400 GeV mass range, together with a nearly degenerate neutralino and, possibly, a gluino below 1.5 TeV, follows from reasonable assumptions, is consistent with present data, and offers interesting discovery prospects at the LHC. Triggering on an extra jet produced in association with stops allows the experimental search for stops even when their mass difference with neutralinos is very small and the decay products are too soft for direct observation. Using a razor analysis, we are able to set stop bounds that are stronger than those published by ATLAS and CMS.Comment: 21 pages, 9 figures. v2: fig. 9b has been updated and revised at large values of the stop/neutralino mass splitting. The discussion of stop co-annihilations has been upgraded including Sommerfeld enhancement

    Variational Autoencoders for New Physics Mining at the Large Hadron Collider

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    Using variational autoencoders trained on known physics processes, we develop a one-sided threshold test to isolate previously unseen processes as outlier events. Since the autoencoder training does not depend on any specific new physics signature, the proposed procedure doesn't make specific assumptions on the nature of new physics. An event selection based on this algorithm would be complementary to classic LHC searches, typically based on model-dependent hypothesis testing. Such an algorithm would deliver a list of anomalous events, that the experimental collaborations could further scrutinize and even release as a catalog, similarly to what is typically done in other scientific domains. Event topologies repeating in this dataset could inspire new-physics model building and new experimental searches. Running in the trigger system of the LHC experiments, such an application could identify anomalous events that would be otherwise lost, extending the scientific reach of the LHC.Comment: 29 pages, 12 figures, 5 table

    Automated visual inspection of CMS HGCAL silicon sensor surface using an ensemble of a deep convolutional autoencoder and classifier

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    More than a thousand 8" silicon sensors will be visually inspected to look for anomalies on their surface during the quality control preceding assembly into the High-Granularity Calorimeter for the CMS experiment at CERN. A deep learning-based algorithm that pre-selects potentially anomalous images of the sensor surface in real time has been developed to automate the visual inspection. The anomaly detection is done by an ensemble of independent deep convolutional neural networks: an autoencoder and a classifier. The performance is evaluated on images acquired in production. The pre-selection reduces the number of images requiring human inspection by 85%, with recall of 97%. Data gathered in production can be used for continuous learning to improve the accuracy incrementally

    Adversarially Learned Anomaly Detection on CMS Open Data: re-discovering the top quark

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    We apply an Adversarially Learned Anomaly Detection (ALAD) algorithm to the problem of detecting new physics processes in proton-proton collisions at the Large Hadron Collider. Anomaly detection based on ALAD matches performances reached by Variational Autoencoders, with a substantial improvement in some cases. Training the ALAD algorithm on 4.4 fb-1 of 8 TeV CMS Open Data, we show how a data-driven anomaly detection and characterization would work in real life, re-discovering the top quark by identifying the main features of the t-tbar experimental signature at the LHC.Comment: 16 pages, 9 figure

    The Global Electroweak and Higgs Fits in the LHC era

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    We update the global fit to electroweak precision observables, including the effect of the latest measurements at hadron colliders of the WW and top-quark masses and the effective leptonic weak mixing angle. We comment on the impact of these measurements in terms of constraints on new physics. We also update the bounds derived from the fit to the Higgs-boson signal strengths, including the observables measured at the LHC Run 2, and compare the improvements with respect to the 7 and 8 TeV results.Comment: 5+1 pages, 3 figures, 2 tables. Prepared for the Proceedings of the 5th LHCP Conference -Shanghai, May 2017- and the EPS-HEP 2017 Conference -Venice, July 2017. (LHCP version.

    Higgs look-alikes at the LHC

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    The discovery of a Higgs particle is possible in a variety of search channels at the LHC. However the true identity of any putative Higgs boson will at first remain ambiguous, until one has experimentally excluded other possible assignments of quantum numbers and couplings. We quantify to what degree one can discriminate a Standard Model Higgs boson from "look-alikes" at, or close to, the moment of discovery at the LHC. We focus on the fully-reconstructible "golden" decay mode to a pair of Z bosons and a four-lepton final state, simulating sPlot-weighted samples of signal and background events. Considering both on-shell and off-shell Z's, we show how to utilize the full decay information from the events, including the distributions and correlations of the five relevant angular variables. We demonstrate how the finite phase space acceptance of any LHC detector sculpts the decay distributions, a feature neglected in previous studies. We use likelihood ratios to discriminate a Standard Model Higgs from look-alikes with other spins or nonstandard parity, CP, or form factors. For a benchmark resonance mass of 200 GeV/c^2, we achieve a median expected discrimination significance of 3 sigma with as few as 19 events, and even better discrimination for the off-shell decays of a 145 GeV/c^2 resonance.Comment: 39 pages, 55 figures, typos fixed, figures added, and minor clarification