Drell-Yan Tails Beyond the Standard Model

We investigate the high-$p_T$ tails of the $pp\to \ell \nu$ and $pp \to \ell \ell$ Drell-Yan processes as probes of New Physics in semileptonic interactions with an arbitrary flavor structure. For this purpose, we provide a general decomposition of the $2\to2$ scattering amplitudes in terms of form-factors that we match to specific scenarios, such as the Standard Model Effective Field Theory (SMEFT), including all relevant operators up to dimension-$8$, as well as ultraviolet scenarios giving rise to tree-level exchange of new bosonic mediators with masses at the TeV scale. By using the latest LHC run-II data in the monolepton ($e\nu$, $\mu\nu$, $\tau\nu$) and dilepton ($ee$, $\mu\mu$, $\tau\tau$, $e\mu$, $e\tau$, $\mu\tau$) production channels, we derive constraints on the SMEFT Wilson coefficients for semileptonic four-fermion and dipole operators with the most general flavor structure, as well as on all possible leptoquark models. For the SMEFT, we discuss the range of validity of the EFT description, the relevance of $\mathcal{O}(1/\Lambda^2)$ and $\mathcal{O}(1/\Lambda^4)$ truncations, the impact of $d=8$ operators and the effects of different quark-flavor alignments. Finally, as a highlight, we extract for several New Physics scenarios the combined limits from high-$p_T$ processes, electroweak pole measurements and low-energy flavor data for the $b\to c\tau\nu$ transition, showing the complementarity between these different observables. Our results are compiled in {\tt HighPT}, a package in {\tt Mathematica} which provides a simple way for users to extract the Drell-Yan tails likelihoods for semileptonic effective operators and for leptoquark models.Comment: 61 pages, 19 figure

HighPT: A Tool for high-pTp_T Drell-Yan Tails Beyond the Standard Model

HighPT is a Mathematica package for the analysis of high-energy data of semileptonic transitions at hadron colliders. It allows to compute high-$p_T$ tail observables for semileptonic processes, i.e. Drell-Yan cross sections, for dilepton and monolepton final states at the LHC. These observables can be calculated at tree level within the Standard Model Effective Field Theory, including the relevant operators up to dimension eight to ensure a consistent description of the cross section including terms of $\mathcal{O}(\Lambda^{-4})$ in the cutoff scale $\Lambda$. For New Physics models with new mediators that can be resolved at LHC energies, HighPT can also account for the full propagation effects of these new bosonic states at tree level. Using the available data from the high-$p_T$ tails in the relevant LHC run-II searches by the ATLAS and CMS collaborations, HighPT can also construct the corresponding likelihoods for all possible flavors of the leptonic final states. As an illustration, we derive and compare constraints on Wilson coefficients at different orders in the Effective Field Theory expansion, and we investigate lepton flavor violation for the $S_3$ leptoquark model. The HighPT code is publicly available at https://github.com/HighPT/HighPT.Comment: 34 page

Probing new physics with polarization components of the tau lepton in quasielastic e−p→Λcτ−e^- p \to \Lambda_c \tau^- scattering process

Kinematics restrict the ability of rare charm decays to explore the charged Lepton Flavor Violation processes mediated by the quark-level $c\to u \ell \tau$ transition. To fill the gap, we propose exploring new physics (NP) through the quasielastic scattering process $e^-p\to \tau^-\Lambda_c$ and the polarization of the $\tau$ lepton. As analyzing modes for the $\tau$ polarization, we consider the decays $\tau^-\to \pi^-\nu_{\tau}$, $\tau^-\to \rho^-\nu_{\tau}$, and $\tau^- \to \ell^-\bar{\nu}_{\ell}\nu_{\tau}$, and show that the $\tau$ polarization components can be extracted from analyzing the kinematics of the $\tau$ visible decay products. In the framework of a general low-energy effective Lagrangian, we then perform a detailed analysis of the polarization components in various aspects and scrutinize possible NP signals. With one upcoming experimental setup, we finally demonstrate promising event rate can be expected for the cascade process and, even in the worst-case scenario -- no signals is observed at all -- it can still provide a competitive potential for constraining the NP, compared with those from the high-$p_T$ dilepton invariant mass tails at high-energy colliders.Comment: 20 pages, 4 figures, 5 table

A Search for Dark Matter Through Invisible Decays of the Higgs Boson With the Atlas Detector at the LHC

Diboson physics provides insight into a wide variety of processes that are produced copiously at the LHC. Of particular interest are events where leptons and neutrinos are produced, strong signatures of electroweak physics. The study of electroweak physics is essential to understanding the Standard Model and in searches for phenomena outside the Standard Model. The most sensitive channels that contributed to the discovery of the Higgs boson searched for decays to dibosons. This thesis will present four analyses that utilize charged leptons and neutrinos whose presence are inferred from the missing transverse momentum. Two measurements of Standard Model cross sections will be presented. The WW cross section is measured using 35 pb-1 of data collected in 2010 and is one of the earliest measurements of diboson processes at the LHC. The ZZ cross section is measured using 4.6 fb-1 of data collected in 2011. A search for the Higgs in the WW decay channel is presented also using 4.6 fb-1 of data collected in 2011. This analysis did not have the sensitivity to discover the Higgs boson, but when data were added in 2012 this channel contributed significantly to its discovery. Finally a search for anomalous invisible decays of the Higgs boson using 4.6 fb-1 of data taken in 2011 and 13.1 fb-1 of data taken in 2012 will be presented. This search is sensitive to new physics that couples to the Higgs boson that would result in an increased rate of decays to invisible particles. One possible scenario is that dark matter couples to the Higgs boson. If the mass of the dark matter particle is less than half of the mass of the Higgs boson decays to dark matter increase its invisible branching fraction. Dark matter is a significant contribution to the makeup of the universe, but very little is known about it. This search provides additional limits on how dark matter can couple to the Standard Model. No excess of events is observed in this search and limits are placed on the allowed invisible branching fraction. These limits are interpreted in the context of simple Higgs portal models to place constraints on the allowed dark matter mass and interaction cross section. The results are compared with current limits on dark matter and place significant restrictions on the allowed dark matter mass and cross section within these models

Expected Performance of the ATLAS Experiment - Detector, Trigger and Physics

A detailed study is presented of the expected performance of the ATLAS detector. The reconstruction of tracks, leptons, photons, missing energy and jets is investigated, together with the performance of b-tagging and the trigger. The physics potential for a variety of interesting physics processes, within the Standard Model and beyond, is examined. The study comprises a series of notes based on simulations of the detector and physics processes, with particular emphasis given to the data expected from the first years of operation of the LHC at CERN

Measurement of the ZZ production cross section and limits on anomalous neutral triple gauge couplings with the ATLAS detector

This thesis presents measurements of the ZZ production cross section in proton-proton collisions at √s = 7 TeV and at √s = 8 TeV, using data recorded by the ATLAS experiment at the LHC in 2011 and 2012. Events are selected which are consistent with two Z bosons decaying to electrons or muons. The cross section is first measured in a fiducial phase-space corresponding closely to the detector acceptance. For the 7 TeV measurement, this phase-space is defined by requiring four electrons or muons with pT > 7 GeV and |eta|<3.16, with a minimum separation between any pair of leptons (electrons or muons) of delta(R)=0.2. The leptons must form two opposite-sign same-flavour pairs, each with invariant mass 66 < m(ll) < 116 GeV. The fiducial cross section times branching ratio to four electrons or muons measured in a dataset corresponding to an integrated luminosity of 4.6 fb−1 is 25.2 +3.3 −3.0 (stat) +1.2 −1.0 (syst) +1.1 −0.9 (lumi) fb. For the 8 TeV measurement, the fiducial phase-space is defined in the same way, except with the lepton pseudo-rapidity requirement tightened to |eta| < 2.7. The fiducial cross section measured in a dataset corresponding to an integrated luminosity of 20 fb−1 is 20.8 +1.3 -1.2 (stat) +1.0 -0.9 (syst) +0.6 -0.6(lumi) fb. Additionally, a fiducial cross section allowing one of the Z bosons to be off shell is measured at √s = 7 TeV by relaxing the mass requirement on one of the lepton pairs to ml−l+ > 20 GeV. This is found to be 27.8 +3.6 -3.4 (stat) +1.8 -1.6 (syst) +1.1 -1.0 (lumi) fb. These results are then used to derive the total cross section for ZZ production with Z bosons in the mass range 66 GeV to 116 GeV, by correcting for the acceptance of the fiducial phase-space and the Z -> ll branching fractions. The total cross section is measured to be 7.0 +0.9 -0.8 (stat) +0.4 -0.3 (syst) +0.3 -0.2 (lumi) pb at √s = 7 TeV and − 7.1 +0.4 -0.4 (stat) +0.4 -0.3 (syst) +0.2 -0.2 (lumi) pb at √s = 8 TeV, which is consistent with the Standard Model expectation of 5.9 +/- 0.2 pb at √s = 7 TeV and 7.2 +/- 0.2 pb at √s = 8 TeV, calculated to next-to-leading order in QCD. The differential cross section in bins of three kinematic variables is also presented. The differential event yield as a function of the transverse momentum of the highest transverse momentum Z boson is used to set limits on the strength of anomalous ZZZ and ZZgamma neutral triple gauge boson couplings, which are forbidden in the Standard Model. The limits obtained with the √s = 8 TeV data are the most constraining to date

CMS Physics Technical Design Report, Volume II: Physics Performance

Este artículo fue en colaboración con otras Universidades en la que participaron alrededor de 2300 autores

CMS physics technical design report, volume II: Physics performance

CMS is a general purpose experiment, designed to study the physics of pp collisions at 14 TeV at the Large Hadron Collider ( LHC). It currently involves more than 2000 physicists from more than 150 institutes and 37 countries. The LHC will provide extraordinary opportunities for particle physics based on its unprecedented collision energy and luminosity when it begins operation in 2007. The principal aim of this report is to present the strategy of CMS to explore the rich physics programme offered by the LHC. This volume demonstrates the physics capability of the CMS experiment. The prime goals of CMS are to explore physics at the TeV scale and to study the mechanism of electroweak symmetry breaking - through the discovery of the Higgs particle or otherwise. To carry out this task, CMS must be prepared to search for new particles, such as the Higgs boson or supersymmetric partners of the Standard Model particles, from the start- up of the LHC since new physics at the TeV scale may manifest itself with modest data samples of the order of a few fb(-1) or less. The analysis tools that have been developed are applied to study in great detail and with all the methodology of performing an analysis on CMS data specific benchmark processes upon which to gauge the performance of CMS. These processes cover several Higgs boson decay channels, the production and decay of new particles such as Z and supersymmetric particles, B-s production and processes in heavy ion collisions. The simulation of these benchmark processes includes subtle effects such as possible detector miscalibration and misalignment. Besides these benchmark processes, the physics reach of CMS is studied for a large number of signatures arising in the Standard Model and also in theories beyond the Standard Model for integrated luminosities ranging from 1 fb(-1) to 30 fb(-1). The Standard Model processes include QCD, B-physics, diffraction, detailed studies of the top quark properties, and electroweak physics topics such as the W and Z(0) boson properties. The production and decay of the Higgs particle is studied for many observable decays, and the precision with which the Higgs boson properties can be derived is determined. About ten different supersymmetry benchmark points are analysed using full simulation. The CMS discovery reach is evaluated in the SUSY parameter space covering a large variety of decay signatures. Furthermore, the discovery reach for a plethora of alternative models for new physics is explored, notably extra dimensions, new vector boson high mass states, little Higgs models, technicolour and others. Methods to discriminate between models have been investigated. This report is organized as follows. Chapter 1, the Introduction, describes the context of this document. Chapters 2-6 describe examples of full analyses, with photons, electrons, muons, jets, missing E-T, B-mesons and taus, and for quarkonia in heavy ion collisions. Chapters 7-15 describe the physics reach for Standard Model processes, Higgs discovery and searches for new physics beyond the Standard Model