Search for new particles in events with energetic jets and large missing transverse momentum in proton-proton collisions at root s=13 TeV

A search is presented for new particles produced at the LHC in proton-proton collisions at root s = 13 TeV, using events with energetic jets and large missing transverse momentum. The analysis is based on a data sample corresponding to an integrated luminosity of 101 fb(-1), collected in 2017-2018 with the CMS detector. Machine learning techniques are used to define separate categories for events with narrow jets from initial-state radiation and events with large-radius jets consistent with a hadronic decay of a W or Z boson. A statistical combination is made with an earlier search based on a data sample of 36 fb(-1), collected in 2016. No significant excess of events is observed with respect to the standard model background expectation determined from control samples in data. The results are interpreted in terms of limits on the branching fraction of an invisible decay of the Higgs boson, as well as constraints on simplified models of dark matter, on first-generation scalar leptoquarks decaying to quarks and neutrinos, and on models with large extra dimensions. Several of the new limits, specifically for spin-1 dark matter mediators, pseudoscalar mediators, colored mediators, and leptoquarks, are the most restrictive to date.Peer reviewe

Search for effective Lorentz and CPT violation using ZEUS data

Lorentz and CPT symmetry in the quark sector of the Standard Model are studied in the context of an effective field theory using ZEUS e±p data. Symmetry-violating effects can lead to time-dependent oscillations of otherwise time-independent observables, including scattering cross sections. An analysis using five years of inclusive neutral-current deep inelastic scattering events corresponding to an integrated HERA luminosity of 372 pb-1 at s=318 GeV has been performed. No evidence for oscillations in sidereal time has been observed within statistical and systematic uncertainties. Constraints, most for the first time, are placed on 42 coefficients parametrizing dominant CPT-even dimension-four and CPT-odd dimension-five spin-independent modifications to the propagation and interaction of light quarks

Identification of hadronic tau decays using a deep neural network with the CMS experiment at LHC

Tau leptons are a key ingredient to perform many Standard Model measurements and searches for new physics at LHC. The CMS experiment has released a new algorithm to discriminate hadronic tau lepton decays against jets, electrons, and muons. The algorithm is based on a deep neural network and combines fully connected and convolutional layers. It combines information from all individual reconstructed particles near the tau axis with information about the reconstructed tau candidate and other high-level variables. Many CMS Run 2 analyses have already benefitted from the improvement brought in performance. The algorithm is presented together with its measured performance in CMS Run 2 data

Direct optimization of the discovery significance in machine learning for new physics searches in particle colliders

We introduce two new loss functions designed to directly optimize the statistical significance of the expected number of signal events when training neural networks and decision trees to classify events as signal or background. The loss functions are designed to directly maximize commonly used estimates of the statistical significance, , and the so-called Asimov estimate, Za . We consider their use in a toy search for Supersymmetric particles with 30 fb$^{−1}$ of 14 TeV data collected at the LHC. In the case that the search for this model is dominated by systematic uncertainties, it is found that the loss function based on Za can outperform the binary cross entropy in defining an optimal search region. The same approach is applied to a boosted decision tree by modifying the objective function used in gradient tree boosting

Identification of displaced τ\tau leptons for long-lived τ\tau slepton searches at CMS

Searches for the supersymmetric (SUSY) partner of the tau lepton are of high interest, since scenarios in which the tau slepton (τ) is the next-to-lightest supersymmetric particle can lead to the observed relic density. In gauge mediated symmetry breaking scenarios, τ can have macroscopic lifetime. Direct searches of τ → τχ01, where χ01 is the lightest SUSY particle are limited by the reconstruction efficiency of displaced tau leptons at CMS, which are produced up to 50 cm away from the IP. In addition, the small cross-section of slepton production at the LHC makes such searches challenging. In our study, we explore a new displaced τ lepton tagger using a deep neural network

Search for contact interactions in inclusive ep scattering at HERA

The high-precision HERA data are used to search for Beyond the Standard Model contributions toelectron-quark scattering in the framework of eeqq contact interactions (CI). Combined measurementsof the inclusive deep inelastic cross sections in neutral and charged current ep scattering areconsidered, corresponding to a luminosity of around 1 fb1. The analysis of the inclusive ep datais based on the simultaneous fits of parton distribution functions together with contributions ofCI couplings to ep scattering. Results are presented for different general CI scenarios and heavyleptoquarks with expected 95% C.L. limits on the CI mass scales in the 10 TeV range

Search for effective Lorentz and CPT violation using ZEUS data

Lorentz and CPT symmetry in the quark sector of the Standard Model are studied in the context of an effective field theory using ZEUS $e^{\pm}p$ data. Symmetry-violating effects can lead to time-dependent oscillations of otherwise time-independent observables, including scattering cross sections. An analysis using five years of inclusive neutral-current deep inelastic scattering events corresponding to an integrated luminosity of 372 pb$^{-1}$ at $\sqrt{s} = 318$ GeV has been performed. No evidence for oscillations in sidereal time has been observed within statistical and systematic uncertainties. Constraints, most for the first time, are placed on 42 coefficients parameterising dominant CPT-even dimension-four and CPT-odd dimension-five spin-independent modifications to the propagation and interaction of light quarks

Azimuthal correlations in photoproduction and deep inelastic epep scattering at HERA

Collective behaviour of final-state hadrons, and multiparton interactions are studied in high-multiplicity ep scattering at a centre-of-mass energy $\sqrt(s)$ = 318 GeV with the ZEUS detector at HERA. Two- and four-particle azimuthal correlations, as well as multiplicity, transverse momentum, and pseudorapidity distributions for charged particle multiplicities N$_{ch}$ ≥ 20 are measured. The dependence of two-particle correlations on the virtuality of the exchanged photon shows a clear transition from photoproduction to neutral current deep inelastic scattering. For the multiplicities studied, neither the measurements in photoproduction processes nor those in neutral current deep inelastic scattering indicate significant collective behaviour of the kind observed in high-multiplicity hadronic collisions at RHIC and the LHC. Comparisons of PYTHIA predictions with the measurements in photoproduction strongly indicate the presence of multiparton interactions from hadronic fluctuations of the exchanged photon

Conceptual Design Report for the LUXE Experiment

This Conceptual Design Report describes LUXE (Laser Und XFEL Experiment), an experimental campaign that aims to combine the high-quality and high-energy electron beam of the European XFEL with a powerful laser to explore the uncharted terrain of quantum electrodynamics characterised by both high energy and high intensity. We will reach this hitherto inaccessible regime of quantum physics by analysing high-energy electron-photon and photon-photon interactions in the extreme environment provided by an intense laser focus. The physics background and its relevance are presented in the science case which in turn leads to, and justifies, the ensuing plan for all aspects of the experiment: Our choice of experimental parameters allows (i) effective field strengths to be probed at and beyond the Schwinger limit and (ii) a precision to be achieved that permits a detailed comparison of the measured data with calculations. In addition, the high photon flux predicted will enable a sensitive search for new physics beyond the Standard Model. The initial phase of the experiment will employ an existing 40 TW laser, whereas the second phase will utilise an upgraded laser power of 350 TW. All expectations regarding the performance of the experimental set-up as well as the expected physics results are based on detailed numerical simulations throughout