Search for a W��� Boson Coupling to Third Generation Fermions with Semi-Leptonic Final States in Proton-Proton Collisions

The Standard Model of fundamental particles and their interactions (SM) has accurately pre- dicted a large expanse of experimental phenomena since it was introduced in the 1970���s. A recent instance is the discovery of the Higgs boson in 2012, whose existence and other properties were predicted by the SM [1] [2]. However, the Standard Model is far from a complete theory and currently does not have explanations or predictions for neutrino masses, the presence of dark mat- ter, the matter-antimatter asymmetry in the universe, and other pressing questions. Perhaps a hint to understand the deficiencies of the Standard Model lies on those experiments whose results are in tension with the Standard Model predictions. One such experiment compares the decay of B mesons to the different leptons, B ��� D���l��l, and evaluates the ratio R(D), which is a test of lep- ton universality in the B sector. The published results [3] indicate a deviation from the Standard Model prediction. This deviation can be explained by the introduction of another particle, the W���, which shares similar properties with its Standard Model counterpart, the W boson, but couples exclusively to c b t quarks, and �� ���� leptons. This dissertation presents a search for a W��� coupling exclusively to b and t quarks. Production of such a W��� can occur most copiously as an intermediate step in the decay products of top quark pair production in association with an initial state b-quark. This search is performed on datasets of proton-proton collision at a center of mass energy of 13 TeV collected with the Compact Muon Solenoid (CMS) detector at the Large Hadron Collider. The signal extraction is enhanced by the development of a kinematic fitter that significantly im- prove the reach of the search, allowing strong upper limits on the cross-section of such a W��� in the mass region of 300 GeV to 1100 GeV. This is the first limit in the record set on a W��� of mass lower than 1000 GeV

Front-running Attack in Sharded Blockchains and Fair Cross-shard Consensus

Sharding is a prominent technique for scaling blockchains. By dividing the network into smaller components known as shards, a sharded blockchain can process transactions in parallel without introducing inconsistencies through the coordination of intra-shard and cross-shard consensus protocols. However, we observe a critical security issue with sharded systems: transaction ordering manipulations can occur when coordinating intra-shard and cross-shard consensus protocols, leaving the system vulnerable to attack. Specifically, we identify a novel security issue known as finalization fairness, which can be exploited through a front-running attack. This attack allows an attacker to manipulate the execution order of transactions, even if the victim's transaction has already been processed and added to the blockchain by a fair intra-shard consensus. To address the issue, we offer Haechi, a novel cross-shard protocol that is immune to front-running attacks. Haechi introduces an ordering phase between transaction processing and execution, ensuring that the execution order of transactions is the same as the processing order and achieving finalization fairness. To accommodate different consensus speeds among shards, Haechi incorporates a finalization fairness algorithm to achieve a globally fair order with minimal performance loss. By providing a global order, Haechi ensures strong consistency among shards, enabling better parallelism in handling conflicting transactions across shards. These features make Haechi a promising solution for supporting popular smart contracts in the real world. To evaluate Haechi's performance, we implemented the protocol using Tendermint and conducted extensive experiments on a geo-distributed AWS environment. Our results demonstrate that Haechi achieves finalization fairness with little performance sacrifice compared to existing cross-shard consensus protocols

Measurement of t(t)over-bar normalised multi-differential cross sections in pp collisions at root s=13 TeV, and simultaneous determination of the strong coupling strength, top quark pole mass, and parton distribution functions

Peer reviewe

An embedding technique to determine ττ backgrounds in proton-proton collision data

An embedding technique is presented to estimate standard model tau tau backgrounds from data with minimal simulation input. In the data, the muons are removed from reconstructed mu mu events and replaced with simulated tau leptons with the same kinematic properties. In this way, a set of hybrid events is obtained that does not rely on simulation except for the decay of the tau leptons. The challenges in describing the underlying event or the production of associated jets in the simulation are avoided. The technique described in this paper was developed for CMS. Its validation and the inherent uncertainties are also discussed. The demonstration of the performance of the technique is based on a sample of proton-proton collisions collected by CMS in 2017 at root s = 13 TeV corresponding to an integrated luminosity of 41.5 fb(-1).Peer reviewe

MUSiC : a model-unspecific search for new physics in proton-proton collisions at root s=13TeV

Results of the Model Unspecific Search in CMS (MUSiC), using proton-proton collision data recorded at the LHC at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb(-1), are presented. The MUSiC analysis searches for anomalies that could be signatures of physics beyond the standard model. The analysis is based on the comparison of observed data with the standard model prediction, as determined from simulation, in several hundred final states and multiple kinematic distributions. Events containing at least one electron or muon are classified based on their final state topology, and an automated search algorithm surveys the observed data for deviations from the prediction. The sensitivity of the search is validated using multiple methods. No significant deviations from the predictions have been observed. For a wide range of final state topologies, agreement is found between the data and the standard model simulation. This analysis complements dedicated search analyses by significantly expanding the range of final states covered using a model independent approach with the largest data set to date to probe phase space regions beyond the reach of previous general searches.Peer reviewe

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

Measurement of prompt open-charm production cross sections in proton-proton collisions at root s=13 TeV

The production cross sections for prompt open-charm mesons in proton-proton collisions at a center-of-mass energy of 13TeV are reported. The measurement is performed using a data sample collected by the CMS experiment corresponding to an integrated luminosity of 29 nb(-1). The differential production cross sections of the D*(+/-), D-+/-, and D-0 ((D) over bar (0)) mesons are presented in ranges of transverse momentum and pseudorapidity 4 < p(T) < 100 GeV and vertical bar eta vertical bar < 2.1, respectively. The results are compared to several theoretical calculations and to previous measurements.Peer reviewe

Azimuthal separation in nearly back-to-back jet topologies in inclusive 2-and 3-jet events in pp collisions at root s=13TeV

A measurement for inclusive 2- and 3-jet events of the azimuthal correlation between the two jets with the largest transverse momenta, Delta phi(12), is presented. The measurement considers events where the two leading jets are nearly collinear ("back-to-back") in the transverse plane and is performed for several ranges of the leading jet transverse momentum. Proton-proton collision data collected with the CMS experiment at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 35.9 fb(-1) are used. Predictions based on calculations using matrix elements at leading-order and next-to-leading-order accuracy in perturbative quantum chromodynamics supplemented with leading-log parton showers and hadronization are generally in agreement with themeasurements. Discrepancies between the measurement and theoretical predictions are as large as 15%, mainly in the region 177 degrees <Delta phi(12) <180 degrees. The 2- and 3-jet measurements are not simultaneously described by any of models.Peer reviewe

Measurement of the t(t)over-bar production cross section, the top quark mass, and the strong coupling constant using dilepton events in pp collisions at root s=13TeV

A measurement of the top quark-antiquark pair production cross section sigma(t (t) over bar) in proton-proton collisions at a centre-of-mass energy of 13 TeV is presented. The data correspond to an integrated luminosity of 35.9 fb(-1), recorded by the CMS experiment at the CERN LHC in 2016. Dilepton events (e(+/-) mu(-/+), mu(+) mu(-), e(+) e(-)) are selected and the cross section is measured from a likelihood fit. For a top quark mass parameter in the simulation of m(t)(MC) = 172.5 GeV the fit yields a measured cross section sigma(t (t) over bar) = 803 +/- 2 (stat) +/- 25 (syst) +/- 20 (lumi) pb, in agreement with the expectation from the standard model calculation at next-to-next-to-leading order. A simultaneous fit of the cross section and the top quark mass parameter in the POWHEG simulation is performed. The measured value of m(t)(MC) = 172.33 +/- 0.14 (stat)(-0.72)(+0.66) (syst) GeV is in good agreement with previous measurements. The resulting cross section is used, together with the theoretical prediction, to determine the top quark mass and to extract a value of the strong coupling constant with different sets of parton distribution functions.Peer reviewe

Measurement of electroweak WZ boson production and search for new physics in WZ + two jets events in pp collisions at √s=13TeV

A measurement of WZ electroweak (EW) vector boson scattering is presented. The measurement is performed in the leptonic decay modes WZ→ℓνℓ′ℓ′, where ℓ,ℓ′=e,μ. The analysis is based on a data sample of proton-proton collisions at √s=13 TeV at the LHC collected with the CMS detector and corresponding to an integrated luminosity of 35.9 fb−1. The WZ plus two jet production cross section is measured in fiducial regions with enhanced contributions from EW production and found to be consistent with standard model predictions. The EW WZ production in association with two jets is measured with an observed (expected) significance of 2.2 (2.5) standard deviations. Constraints on charged Higgs boson production and on anomalous quartic gauge couplings in terms of dimension-eight effective field theory operators are also presented