Search For New Physics Research Articles

Electroweak and QCD corrections to Z -boson production with one b jet in a massive five-flavor scheme

We compute the $O(\alpha_s \alpha^2)$ and $O(\alpha_s^2 \alpha)$ contributions to the production cross section of a $Z$ boson with one $b$ jet at the Large Hadron Collider (LHC), and study their phenomenological relevance for LHC physics. The accurate prediction of hadronic $Z+b$-jet production is needed to control a background that greatly affects both the measurement of Higgs-boson properties and searches of new physics at the LHC. At the same time it could enable the first precise measurement of the $b$-quark parton distribution function. In this context $b$-quark mass effects become relevant and need to be studied with care, both at the level of the hard process and at the level of the initial- and final-state parton evolution. It is the aim of this paper to explore some of these issues in the framework of a massive 5 Flavor Scheme and to assess the need for both the inclusion of electroweak corrections, in addition to QCD corrections, and $b$-quark mass effects in the prediction of total and differential cross sections for hadronic $Z+b$-jet production.

Upgrade of the ATLAS detectors and trigger for the High Luminosity LHC: Tracking and timing for pile-up suppression

The High Luminosity-Large Hadron Collider is expected to start data-taking in 2026 and to provide an integrated luminosity of 3000 fb −1 , giving a factor 10 more data than that will be collected by 2023. This high statistics will make it possible to perform precise measurements in the Higgs sector and improve searches of new physics at the TeV scale. The peak luminosity is expected to be 7.5 × 10 34 cm −2 s −1 , corresponding to about 200 proton–proton interactions per event (pile-up), which will increase the rates at each level of the trigger and degrade the reconstruction performance. To cope with such a harsh environment many sub-detectors of the ATLAS experiment will be upgraded and some completely substituted. The Trigger-DAQ system will be upgraded. In this talk an overview of two new sub-detectors enabling powerful pile-up suppression, a new Inner Tracker and a High Granularity Timing Detector, will be given, describing the two technologies, their performance, and their interplay. Emphasis will also be given to the possibility of using tracking and timing information at the earliest, hardware based, ATLAS trigger stage. • Pileup suppression techniques for jets reconstruction at HL-LHC. • Tracking and Timing detectors of ATLAS detector at HL-LHC. • Tracking for Trigger at HL-LHC.

BESIII Latest Results

Since 2009 the BESIII spectrometer, which operates at the IHEP of Beijing, China, collected the world largest data sample of J/ψ, ψ(2S) and ψ(3770). Its excellent performances allowed to access a wide physics program, which includes deep investigation of the Standard Model, spectroscopy studies of the charmonium states, and search for new physics. An overview of the main experimental innovations and of the latest performed investigations will be here discussed.

Exploiting the WH/ZH symmetry in the search for new physics

We suggest to isolate the loop-induced gluon-initiated component (ggrightarrow ZH) for associated ZH production by using the similarity of the Drell–Yan-like component for ZH production to the WH process. We argue that the cross-section ratio of the latter two processes can be predicted with high theoretical accuracy. Comparing it to the experimental ZH/WH cross-section ratio should allow to probe for new physics in the ggrightarrow ZH component at the HL-LHC. We consider typical BSM scenarios in order to exemplify the effect they would have on the proposed observable.

Analysis Preservation and Systematic Reinterpretation within the ATLAS experiment

The LHC data analysis software used in order to derive and publish experimental results is an important asset that is necessary to preserve in order to fully exploit the scientific potential of a given measurement. An important use-case is the re-usability of the analysis procedure in the context of new scientific studies such as the reinterpretation of searches for new physics in terms of signal models that not studied in the original publication (RECAST). We present the usage of the graph-based workflow description language yadage to drive the reinterpretation of preserved HEP analyses. The analysis software is preserved using Docker containers, while the workflow structure is preserved using plain JSON documents. This allows the re-execution of complex analysis workflows on modern distributed container orchestration systems and enables a systematic reinterpretation service based on such preserved analysis.

Search for new physics in dijet angular distributions using proton\u2013proton collisions at sqrt{s}=13hbox {TeV} and constraints on dark matter and other models

A search is presented for physics beyond the standard model, based on measurements of dijet angular distributions in proton–proton collisions at sqrt{s}=13hbox {TeV}. The data collected with the CMS detector at the LHC correspond to an integrated luminosity of 35.9,text {fb}^{-1}. The observed distributions, corrected to particle level, are found to be in agreement with predictions from perturbative quantum chromodynamics that include electroweak corrections. Constraints are placed on models containing quark contact interactions, extra spatial dimensions, quantum black holes, or dark matter, using the detector-level distributions. In a benchmark model where only left-handed quarks participate, contact interactions are excluded at the 95% confidence level up to a scale of 12.8 or 17.5TeV, for destructive or constructive interference, respectively. The most stringent lower limits to date are set on the ultraviolet cutoff in the Arkani–Hamed–Dimopoulos–Dvali model of extra dimensions. In the Giudice–Rattazzi–Wells convention, the cutoff scale is excluded up to 10.1TeV. The production of quantum black holes is excluded for masses below 5.9 and 8.2TeV, depending on the model. For the first time, lower limits between 2.0 and 4.6TeVare set on the mass of a dark matter mediator for (axial-)vector mediators, for the universal quark coupling g_{mathrm {mathrm {q}}} =1.0.

Connection between diphoton and triboson channels in new physics searches

Diphoton channel provides a clean signature in searches for new physics. In this paper, we discuss a connection between the diphoton channel (γγ) and triboson channels (Zγγ, ZZγ, WWγ) imposed by the SU(2)L×U(1)Y symmetry of the Standard Model (SM) in certain classes of models. To illustrate this idea we choose a simple model that has all these channels. In this model, the same physics can give rise to γ+MET instead of γγ and 2 bosons plus missing energy instead of 3-boson channels. We analyze existing constraints and previous searches and show that channels WWγ and especially Zγ+MET have a potential to discover new physics at the LHC.

Testing physics beyond the standard model through additional clock transitions in neutral ytterbium

We study the prospects of using transitions from the ytterbium ground state to metastable states $^3{\rm P}^{\rm o}_2$ at $E=19\,710.388~$cm$^{-1}$ and $4f^{13}5d6s^2\,(J=2)$ at $E=23\,188.518~$cm$^{-1}$ as clock transitions in an optical lattice clock. Having more than one clock transition in Yb could benefit the search for new physics beyond the Standard Model via studying the non-linearity of King's plot or the time-variation of the ratio of the frequencies of two clock transitions. We calculate the lifetime of the states, relevant transition amplitudes, systematic shifts, and the sensitivities of the clock transitions to a variation of the fine structure constant and to the gravitational potential. We find that both transitions can probably support ultra-high accuracy, similar to what is already achieved for the $^1$S$_0$ - $^3$P$^{\rm o}_0$ clock transition.

Establishing a search for b \u2192 s\u2113+\u2113\u2212 anomalies at the LHC

One of the fundamental predictions of the Standard Model is Lepton Flavour Universality. Any deviation from this prediction would indicate the existence of physics beyond the Standard Model. Recent LHCb measurements present a pattern of deviations from this prediction in rare B-meson decays. While not yet statistically significant (currently 2.2−2.6σ), these measurements show an imbalance in the ratio of B-meson decays to a pair of muons in association with a Kaon and decays to a pair of electrons in association with a Kaon. If the measured deviations are indeed present in nature, new physics may mediate interactions involving a pair of same flavour leptons, a b- and an s-quark. We present the prospect for a search of new physics in this type of interactions at the LHC, in a process that involves an s-quark, and a final state with two leptons and a b-jet. The proposed search can improve the sensitivity to new physics in these processes by a factor of four compared to current searches with in the total dataset expected at the LHC.

On the systematic uncertainties in DUNE and their role in New Physics studies

In the recent years experiments have established the existence of neutrino oscillations and most of the oscillation parameters have been measured with a good accuracy. The search for New Physics in neutrino oscillation will be an experimental concrete possibility in the next future. In this paper we investigate the ability of the DUNE facility to search for Non Standard Interaction (NSI) in neutrino propagation in matter, emphasizing the role of different assumptions on the shape and absolute normalization errors of both νe and νμ signals. We also study in detail the effects of NSI and systematics in the extraction of standard oscillation parameters.

The origin of baryonic matter in the Universe

The origin of the matter-antimatter asymmetry in the Universe is a long-standing cosmological puzzle remaining to be solved. This slight excess of the baryonic matter is a key input to the big bang nucleosynthesis and therefore is responsible for the generation of the light elements in the early universe and finally the formation of stars and galaxies at a later time. This excess has been measured in several different ways. In particular, the value of this number has been precisely measured from studies of the temperature an-isotropies in the cosmic microwave background radiation by the Planck collaboration. Despite the concordance of the experimental measurements of this excess from different independent studies, none of the theoretical explanation of this problem is satisfactory and well accepted. The theoretical explanations of the baryon asymmetry are reviewed in this article. While there are many baryogenesis mechanisms, we focus on the mechanism of electroweak baryogenesis, which is a highly testable scenario and is within the reach of current high energy colliders. The physical picture of the mechanism of electroweak baryogenesis is then discussed. This is an interdisciplinary research area closely related to cosmology and the fundamental theory governing the particle physics. Therefore solutions to this cosmological problem may shed light on the searches for new physics governing particle interactions at the high energy frontier as well as the low energy intensity frontier. In particular, the necessity of going beyond the standard model of particle physics is discussed, due to the incapability of the standard model to generate the observed baryon asymmetry, with the solution of resorting to new physics capable of incorporating a new source of CP-violation and a Higgs potential that can accommodate a strongly first order electroweak phase transition. These requirements call for new particle interactions beyond the standard model and therefore can provide additional insight on new physics searches at high energy colliders and low energy precision measurements such as the searches for electric dipole moments of electrons, neutrons, protons and atoms. Also briefly discussed is the physical opportunities associated with the stochastic gravitational waves generated from a first order electroweak phase transition, which is another emerging window for probing the mechanism of electroweak symmetry breaking and therefore can provide another independent test of the mechanism of electroweak baryogenesis. The possibility of primordial black hole formation from the first order phase transition, which can serve as a non-particle candidate for the dark matter, and its possible detection with gravitational waves is also briefly introduced.

The SPES radioactive ion beam facility at the Legnaro National Laboratories and the EDM search

Radioactive ions can be used to amplify the sensitivity to symmetry violations. An example is the time reversal (T-) violation connected, assuming the charge conjugation, the parity and time reversal (CPT) symmetry, to the CP-violation. This is linked to the question of the role that CP violation plays in explaining the cosmological matter-antimatter asymmetry and the search for new physics beyond the Standard Model (SM). One of the most direct probes of such symmetry violation is the existence of a permanent electric dipole moment (EDM) of a particle or system. Octupole-deformed nuclei with high Z and A are expected to be among the best candidates for testing the limit of existence of EDM. The production, extraction and characterization of such unstable systems is part of the scientific program of the new SPES radioactive ion beam facility which is presently under construction at the Legnaro National Laboratories of INFN. In the following I will discuss the present status of the SPES facility and the scientific program foreseen for those studies.

Search for new physics with atoms and molecules

This article reviews recent developments in tests of fundamental physics using atoms and molecules, including the subjects of parity violation, searches for permanent electric dipole moments, tests of the CPT theorem and Lorentz symmetry, searches for spatiotemporal variation of fundamental constants, tests of quantum electrodynamics, tests of general relativity and the equivalence principle, searches for dark matter, dark energy and extra forces, and tests of the spin-statistics theorem. Key results are presented in the context of potential new physics and in the broader context of similar investigations in other fields. Ongoing and future experiments of the next decade are discussed.

Anomalous triple-gauge-boson interactions in vector-boson pair production with Recola2

Diboson production at the LHC is a process of great importance both in the context of tests of the SM and for direct searches for new physics. In this paper we present a phenomenological study of mathrm {W}mathrm {W} (rightarrow mathrm {e^+}nu _{mathrm {e}}mathrm {mu ^-}bar{nu }_{mu }), mathrm {W}mathrm {Z} (rightarrow mathrm {e^-}overline{nu }_{mathrm{e}} mu ^+ mu ^-), and mathrm {Z}mathrm {Z} (rightarrow mathrm {e^+}mathrm {e^-}mu ^+ mu ^-) production considering event selections of interest for the anomalous triple-gauge-boson-coupling searches at the LHC: we provide theoretical predictions within the Standard Model at NLO QCD and NLO EW accuracy and study the effect of the anomalous triple-gauge-boson interactions at NLO QCD. For mathrm {W}mathrm {W} and mathrm {Z}mathrm {Z} the contribution of the loop-induced mathrm {g}mathrm {g}rightarrow mathrm {W}^+mathrm {W}^- and mathrm {g}mathrm {g}rightarrow mathrm {Z}mathrm {Z} processes is included. Anomalous triple-gauge-boson interactions are parametrized in the EFT framework. This paper is the first application of Recola2 in the EFT context.

Search for new physics in events with two soft oppositely charged leptons and missing transverse momentum in proton–proton collisions at [formula omitted

A search is presented for new physics in events with two low-momentum, oppositely charged leptons (electrons or muons) and missing transverse momentum in proton-proton collisions at a centre-of-mass energy of 13 TeV. The data collected using the CMS detector at the LHC correspond to an integrated luminosity of 35.9fb−1. The observed event yields are consistent with the expectations from the standard model. The results are interpreted in terms of pair production of charginos and neutralinos (χ˜1± and χ˜20) with nearly degenerate masses, as expected in natural supersymmetry models with light higgsinos, as well as in terms of the pair production of top squarks (t˜ ), when the lightest neutralino and the top squark have similar masses. At 95% confidence level, wino-like χ˜1±/χ˜20 masses are excluded up to 230 GeV for a mass difference of 20 GeV relative to the lightest neutralino. In the higgsino-like model, masses are excluded up to 168 GeV for the same mass difference. For t˜ pair production, top squark masses up to 450 GeV are excluded for a mass difference of 40 GeV relative to the lightest neutralino.

Weak vector boson production with many jets at the LHCs=13 TeV

Signatures with an electroweak vector boson and many jets play a crucial role at the Large Hadron Collider, both in the measurement of Standard-Model parameters and in searches for new physics. Precise predictions for these multi-scale processes are therefore indispensable. We present next-to-leading order QCD predictions for $W^\pm/Z$+jets at $\sqrt{s}=13$ TeV, including up to five/four jets in the final state. All production channels are included and leptonic decays of the vector bosons are considered at the amplitude level. We assess theoretical uncertainties arising from renormalization- and factorization-scale dependence by considering fixed-order dynamical scales based on the $H_{\rm T}$ variable as well as on the MiNLO procedure. We also explore uncertainties associated to different choices of parton-distribution functions. We provide event samples that can be explored through publicly available $n$-tuple sets, generated with BlackHat in combination with SHERPA.

Search for new physics in final states with an energetic jet or a hadronically decaying W or Z boson and transverse momentum imbalance at s=13 TeV

A search for new physics using events containing an imbalance in transverse momentum and one or more energetic jets arising from initial-state radiation or the hadronic decay of W or Z bosons is presented. A data sample of proton-proton collisions at $\sqrt{s} = $ 13 TeV, collected with the CMS detector at the LHC and corresponding to an integrated luminosity of 35.9 fb$^{-1}$, is used. The observed data are found to be in agreement with the expectation from standard model processes. The results are interpreted as limits on the dark matter production cross section in simplified models with vector, axial-vector, scalar, and pseudoscalar mediators. Interpretations in the context of fermion portal and nonthermal dark matter models are also provided. In addition, the results are interpreted in terms of invisible decays of the Higgs boson and set stringent limits on the fundamental Planck scale in the Arkani-Hamed, Dimopoulos, and Dvali model with large extra spatial dimensions.

The HiggsTools handbook: a beginners guide to decoding the Higgs sector

This report summarises some of the activities of the HiggsTools initial training network working group in the period 2015–2017. The main goal of this working group was to produce a document discussing various aspects of state-of-the-art Higgs physics at the large hadron collider (LHC) in a pedagogic manner. The first part of the report is devoted to a description of phenomenological searches for new physics (NP) at the LHC. All of the available studies of the couplings of the new resonance discovered in 2012 by the ATLAS and CMS experiments (Aad et al (ATLAS Collaboration) 2012 Phys. Lett. B 716 1–29; Chatrchyan et al (CMS Collaboration) 2012 Phys. Lett. B 716 30–61) conclude that it is compatible with the Higgs boson of the standard model (SM) within present precision. So far the LHC experiments have given no direct evidence for any physical phenomena that cannot be described by the SM. As the experimental measurements become more and more precise, there is a pressing need for a consistent framework in which deviations from the SM predictions can be computed precisely. Such a framework should be applicable to measurements in all sectors of particle physics, not only LHC Higgs measurements but also electroweak precision data, etc. We critically review the use of the κ-framework, fiducial and simplified template cross sections, effective field theories, pseudoobservables and phenomenological Lagrangians. Some of the concepts presented here are well known and were used already at the time of the large electron–positron collider (LEP) experiment. However, after years of theoretical and experimental development, these techniques have been refined, and we describe new tools that have been introduced in order to improve the comparison between theory and experimental data. In the second part of the report, we propose as a new and complementary observable for studying Higgs boson production at large transverse momentum in the case where the Higgs boson decays to two photons. The variable depends on measurements of the angular directions and rapidities of the two Higgs decay products rather than the energies, and exploits the information provided by the calorimeter in the detector. We show that, even without tracking information, the experimental resolution for is better than that of the transverse momentum of the photon pair, particularly at low transverse momentum. We make a detailed study of the phenomenology of the variable, contrasting the behaviour with the Higgs transverse momentum distribution using a variety of theoretical tools including event generators and fixed order perturbative computations. We consider the theoretical uncertainties associated with both and distributions. Unlike the transverse momentum distribution, the distribution is well predicted using the Higgs effective field theory in which the top quark is integrated out—even at large values of —thereby making this a better observable for extracting the parameters of the Higgs interaction. In contrast, the potential of the distribution as a probe of NP is rather limited, since although the overall rate is affected by the presence of additional heavy fields, the shape of the distribution is relatively insensitive to heavy particle thresholds.

Search for new physics in events with a leptonically decaying Z boson and a large transverse momentum imbalance in proton\u2013proton collisions at sqrt{s} = 13,text {TeV}

A search for new physics in events with a Z boson produced in association with large missing transverse momentum at the LHC is presented. The search is based on the 2016 data sample of proton-proton collisions recorded with the CMS experiment at sqrt{s} = 13,text {TeV} , corresponding to an integrated luminosity of 35.9,text {fb}^{-1}. The results of this search are interpreted in terms of a simplified model of dark matter production via spin-0 or spin-1 mediators, a scenario with a standard-model-like Higgs boson produced in association with the Z boson and decaying invisibly, a model of unparticle production, and a model with large extra spatial dimensions. No significant deviations from the background expectations are found, and limits are set on relevant model parameters, significantly extending the results previously achieved in this channel.

Multi-jet merged top-pair production including electroweak corrections

We present theoretical predictions for the production of top-quark pairs in association with jets at the LHC including electroweak (EW) corrections. First, we present and compare differential predictions at the fixed-order level for tbar{t} and tbar{t}+text {jet} production at the LHC considering the dominant NLO EW corrections of order {{mathcal {O}}}(alpha _mathrm {s}^2 alpha ) and {{mathcal {O}}}(alpha _mathrm {s}^3 alpha ) respectively together with all additional subleading Born and one-loop contributions. The NLO EW corrections are enhanced at large energies and in particular alter the shape of the top transverse momentum distribution, whose reliable modelling is crucial for many searches for new physics at the energy frontier. Based on the fixed-order results we motivate an approximation of the EW corrections valid at the percent level, that allows us to readily incorporate the EW corrections in the MePs@Nlo framework of Sherpa combined with OpenLoops. Subsequently, we present multi-jet merged parton-level predictions for inclusive top-pair production incorporating NLO QCD + EW corrections to tbar{t} and tbar{t}+text {jet}. Finally, we compare at the particle-level against a recent 8 TeV measurement of the top transverse momentum distribution performed by ATLAS in the lepton + jet channel. We find very good agreement between the Monte Carlo prediction and the data when the EW corrections are included.