Search For New Physics Research Articles

The SHiP experiment at CERN

The discovery of the Higgs boson has fully confirmed the Standard Model of particles and fields. Nevertheless, there are still fundamental phenomena, like the existence of dark matter and the baryon asymmetry of the Universe, which deserve an explanation that could come from the discovery of new particles. Searches for new physics with accelerators are performed at the LHC, looking for high massive particles coupled to matter with ordinary strength. A new experiment at CERN meant to search for very weakly coupled particles in the few GeV mass domain has been recently proposed. The existence of such particles, foreseen in different theoretical models beyond the Standard Model, is largely unexplored. A beam dump facility using high intensity 400 GeV protons is a copious source of such unknown particles in the GeV mass range. The beam dump is also a copious source of neutrinos and in particular it is an ideal source of tau neutrinos, the less known particle in the Standard Model. Indeed, tau anti-neutrinos have not been directly observed so far. We report the physics potential of such an experiment.

Status of Belle II and Physics Prospects

The Belle II experiment is a new generation B factory experiment at KEK in Japan, whose aim is the search of New Physics in the rare B meson decays. The operation of the SuperKEKB accelerator has just been started and the tuning of the beam condition is in progress. The construction of the Belle II detector is smoothly going on to be prepared for the start of physics run in 2018. The physics program at the Belle II experiment is now being discussed in the framework of Belle II Theory Interface Platform (B2TIP). In this report, the latest status of the SuperKEKB accelerator and the Belle II detector is described. The prospects for the physics at Belle II are shown in the latter part based on the on-going discussion in B2TIP.

Measurements of differential cross sections for associated production of a W boson and jets in proton-proton collisions at s=8 TeV

Differential cross sections for a W boson produced in association with jets are measured in a data sample of proton-proton collisions at a center-of-mass energy of 8 TeV recorded with the CMS detector and corresponding to an integrated luminosity of 19.6 inverse femtobarns. The W bosons are identified through their decay mode W to mu nu. The cross sections are reported as functions of jet multiplicity, transverse momenta, and the scalar sum of jet transverse momenta (HT) for different jet multiplicities. Distributions of the angular correlations between the jets and the muon are examined, as well as the average number of jets as a function of HT and as a function of angular variables. The measured differential cross sections are compared with tree-level and higher-order recent event generators, as well as next-to-leading-order and next-to-next-to-leading-order theoretical predictions. The agreement of the generators with the measurements builds confidence in their use for the simulation of W+jets background processes in searches for new physics at the LHC.

The Belle II imaging Time-of-Propagation (iTOP) detector

High precision flavor physics measurements are an essential complement to the direct searches for new physics at the LHC ATLAS and CMS experiments. Such measurements will be performed using the upgraded Belle II detector that will take data at the SuperKEKB accelerator. With 40x the luminosity of KEKB, the detector systems must operate efficiently at much higher rates than the original Belle detector. A central element of the upgrade is the barrel particle identification system. Belle II has built and installed an imaging-Time-of-Propagation (iTOP) detector. The iTOP uses quartz optics as Cherenkov radiators. The photons are transported down the quartz bars via total internal reflection with a spherical mirror at the forward end to reflect photons to the backward end where they are imaged onto an array of segmented Micro-Channel Plate Photo-Multiplier Tubes (MCP-PMTs). The system is read out using giga-samples per second waveform sampling Application-Specific Integrated Circuits (ASICs). The combined timing and spatial distribution of the photons for each event are used to determine particle species. This paper provides an overview of the iTOP system.

Effective theories of flavor and the nonuniversal MSSM

Flavor symmetries \`{a} la Froggatt-Nielsen~(FN) provide a compelling way to explain the hierarchies of fermionic masses and mixing angles in the Yukawa sector. In Supersymmetric~(SUSY) extensions of the Standard Model where the mediation of SUSY breaking occurs at scales larger than the breaking of flavor, this symmetry must be respected not only by the Yukawas of the superpotential, but by the soft-breaking masses and trilinear terms as well. In this work we show that contrary to naive expectations, even starting with completely flavor blind soft-breaking in the full theory at high scales, the low-energy sfermion mass matrices and trilinear terms of the effective theory, obtained upon integrating out the heavy mediator fields, are strongly non-universal. We explore the phenomenology of these SUSY flavor models after the latest LHC searches for new physics.

Quark-gluon tagging with shower deconstruction: Unearthing dark matter and Higgs couplings

The separation of quark and gluon initiated jets can be an important way to improve the sensitivity in searches for new physics or in measurements of Higgs boson properties. We present a simplified version of the shower deconstruction approach as a novel observable for quark-gluon tagging. Assuming topocluster-like objects as input, we compare our observable with energy correlation functions and find a favorable performance for a large variety of jet definitions. When applied to dark matter searches in mono-jet final states limitations from small signal-to-background ratios can be overcome. We also show that quark-gluon tagging is an alternative way of separating weak boson from gluon-fusion production in the process p + p -> H + jet + jet + X

QCD next-to-leading-order predictions matched to parton showers for vector-like quark models

Vector-like quarks are featured by a wealth of beyond the Standard Model theories and are consequently an important goal of many LHC searches for new physics. Those searches, as well as most related phenomenological studies, however, rely on predictions evaluated at the leading-order accuracy in QCD and consider well-defined simplified benchmark scenarios. Adopting an effective bottom-up approach, we compute next-to-leading-order predictions for vector-like-quark pair production and single production in association with jets, with a weak or with a Higgs boson in a general new physics setup. We additionally compute vector-like-quark contributions to the production of a pair of Standard Model bosons at the same level of accuracy. For all processes under consideration, we focus both on total cross sections and on differential distributions, most these calculations being performed for the first time in our field. As a result, our work paves the way to precise extraction of experimental limits on vector-like quarks thanks to an accurate control of the shapes of the relevant observables and emphasise the extra handles that could be provided by novel vector-like-quark probes never envisaged so far.

Remarks on the Standard Model predictions for R(D) and R(D*)

Semileptonic $b \to c$ transitions, and in particular the ratios $R(D^{(*)}) = \frac{\Gamma(B \rightarrow D^{(*)} \tau \nu )}{\Gamma(B \rightarrow D^{(*)} \ell \nu )}$, can be used to test the universality of the weak interactions. In light of the recent discrepancies between the experimental measurements of these observables by BaBar, Belle and LHCb and the Standard Model predicted values, we study the robustness of the latter. Our analysis reveals that $R(D)$ might be enhanced by lepton mass effects associated to the mostly unknown scalar form factor. In constrast, the Standard Model prediction for $R(D^*)$ is found to be more robust, since possible pollutions from $B^*$ contributions turn out to be negligibly small, which indicates that $R(D^*)$ is a promising observable for searches of new physics.

Search for new physics beyond the Standard Model in final states with jets and leptons+jets at CMS

Searches for new physics beyond the Standard Model performed by the CMS experiment in final states with jets and leptons+jets are presented. The document focuses on a selection of recent results from searches for heavy dijet resonances, leptoquarks, and heavy majorana neutrinos using proton-proton collision data at both √s = 8 and 13 TeV. The novel CMS datascouting technique, used to probe the low-mass region in hadronic final states, is introduced and results from a Run1 analysis are shown. Two searches in the electrons+jets final states showing an excess of events in Run1 data are also discussed.

ATLAS searches for resonances decaying to boson pairs

Many extensions to the Standard Model predict new particles decaying into two bosons (W , Z , photon, or Higgs bosons) making these important signatures in the search for new physics. Searches for such diboson resonances have been performed in final states with different numbers of leptons, photons, jets and b -jets where new jet substructure techniques to disentangle the hadronic decay products in highly boosted configuration are being used. This document summarizes recent ATLAS searches for resonances decaying to diboson final states, VV , VH and HH with LHC Run 2 data collected.

Searches for BSM physics in dilepton, multilepton and lepton+MET final states at CMS

Numerous new physics models, e.g., theories with extra dimensions and various gauge-group extensions of the standard model, predict the existence of new particles decaying to dilepton, multilepton, and lepton+MET final states. This talk presents the recent results from searches for new physics in the leptonic final states at CMS.

V+jets from CMS

The production of vector bosons (V = W, Z, or γ) in association with jets is a stringent test of perturbative QCD and is a background process in searches for new physics. Total and differential cross-section measurements of vector bosons produced in association with jets (and heavy flavour quarks) are presented. The data have been recorded with the CMS detector at the LHC and are compared to next-to(-next-to)-leading-order calculations and event simulations that devise matrix element calculations interfaced with parton showers.

Recent results on search for new physics at BaBar

We present some recent measurements for the search of New Physics using 514 fb−1 of e + e − collisions collected with the BaBar detector at the PEP-II e + e − collider at SLAC. First we present a search for the decay ϒ (1S ) → γA 0 , A 0 → cc , where A 0 is a candidate for the CP-odd Higgs boson of the next-to-minimal supersymmetric standard model. No significant signal is observed and we set 90% confidence-level upper limits on B(ϒ(1S ) → γ A 0 ) × B (A 0 → cc ). We report the search for a light non-Standard Model gauge boson Z ′ coupling only to the second and third lepton families. Our results significantly improve current limits and further constrain the remaining region of the allowed parameter space. Finally, we present a search for a long-lived particle L that is produced in e + e − annihilations and decays into two oppositely charged tracks. We do not observe a significant signal and we and set 90% confidence level upper limits on the product of the L production cross section, branching fraction, and reconstruction efficiency as a function of the L mass. In addition, upper limits are provided on the branching fraction B (B → Xs L ), where Xs is an hadronic system with strangeness -1.

Searches for new physics with heavy flavour at ATLAS

The Flavour Changing Neutral Current processes are sensitive to New Physics contributions, in particular through additional electroweak loop amplitudes. The angular analysis of the decay of B 0 → μ + μ − K* 0 is presented. A number of angular coefficients are measured as a function of the invariant mass squared of the dimuon system using data collected by the ATLAS experiment at the LHC. Comparison is made to theoretical predictions, including for the observable P ′ 5 , for which there has been recent tension between theory and experiment. ATLAS result on the study of the B ( s ) 0 → μ + μ − rare decays is also presented.

Kaon Flavour Physics Strikes Back

In this short presentation I emphasize the increased importance of kaon flavour physics in the search for new physics (NP) that we should witness in the rest of this decade and in the next decade. The main actors will be the branching ratios for the rare decays and , to be measured by NA62 and KOTO, and their correlations with the ratio ε′/ε on which recently progress by lattice QCD and large N dual QCD approach has been made implying a new flavour anomaly. Further correlations of , and ε′/ε with εK, ΔMK, KL → μ+ μ− and will help us to identify indirectly possible NP at short distance scales. This talk summarizes the present highlights of this facinating field including some results from concrete NP scenarios.

The Inverse Bagging Algorithm: Anomaly Detection by Inverse Bootstrap Aggregating

For data sets populated by a very well modeled process and by another process of unknown probability density function (PDF), a desired feature when manipulating the fraction of the unknown process (either for enhancing it or suppressing it) consists in avoiding to modify the kinematic distributions of the well modeled one. A bootstrap technique is used to identify sub-samples rich in the well modeled process, and classify each event according to the frequency of it being part of such sub-samples. Comparisons with general MVA algorithms will be shown, as well as a study of the asymptotic properties of the method, making use of a public domain data set that models a typical search for new physics as performed at hadronic colliders such as the Large Hadron Collider (LHC).

Foundation of a unified physics

Since searches of new physics is not successful till now we need to have new approaches to the fundamental physics as a whole. In this report we exhibit new system of fundamental equations of physics (derived from the first principle) which gives rise to new physics and provides a basis for comparison with current one.

Precise measurement of the Ke2/Kμ2 branching ratio and search for new physics beyond the Standard Model

The E36 experiment recently conducted at J-PARC by the TREK Collaboration will provide a precise mesurement of the decay ratio RK = Γ(K+→e+υe)/Γ(K+→μ+υμ) with the aim of testing lepton universality, a basic assumption of the Standard Model (SM). The SM prediction for the decay ratio RK is highly precise (δRK/RK = 4 × 10−4) and any observed deviation from this prediction would clearly indicate the existence of new physics. The E36 experimental apparatus, designed to offer small systematic errors, was installed at the J-PARC K1.1BR kaon beam line in the fall of 2014, fully commissioned in the spring of 2015, and the production data were collected in the fall of 2015. A scintillating fiber target was used to stop a beam of 1.2 × 106K+ per spill. The K+ decay products were then momentum analyzed by a 12-sector superconducting toroidal spectrometer and charged particles were tracked with high precision by Multi-Wire Proportional Chambers (MWPC) combined with a photon calorimeter with a large solid angle (75% of 4π) and 3 different particle identification systems. Details of the E36 experimental apparatus, as well as the status of the data analysis will be presented.

Search for new physics in final states with two opposite-sign, same-flavor leptons, jets, and missing transverse momentum in pp collisions at s = 13 $$ \sqrt{s}=13 $$ TeV

A search is presented for physics beyond the standard model in final states with two opposite-sign, same-flavor leptons, jets, and missing transverse momentum. The data sample corresponds to an integrated luminosity of 2.3 inverse femtobarns of proton-proton collisions at sqrt(s) = 13 TeV collected with the CMS detector at the LHC in 2015. The analysis uses the invariant mass of the lepton pair, searching for a kinematic edge or a resonant-like excess compatible with the Z boson mass. Both search modes use several event categories in order to increase the sensitivity to new physics. These categories are based on the rapidity of the leptons, the multiplicity of jets and b jets, the scalar sum of jet transverse momenta, and missing transverse momentum. The observations in all signal regions are consistent with the expectations from the standard model, and the results are interpreted in the context of simplified models of supersymmetry.

On methods for correcting for the look-elsewhere effect in searches for new physics

The search for new significant peaks over a energy spectrum often involves a statistical multiple hypothesis testing problem. Separate tests of hypothesis are conducted at different locations over a fine grid producing an ensemble of local p-values, the smallest of which is reported as evidence for the new resonance. Unfortunately, controlling the false detection rate (type I error rate) of such procedures may lead to excessively stringent acceptance criteria. In the recent physics literature, two promising statistical tools have been proposed to overcome these limitations. In 2005, a method to ``find needles in haystacks'' was introduced by Pilla et al. [1], and a second method was later proposed by Gross and Vitells [2] in the context of the ``look-elsewhere effect'' and trial factors. We show that, although the two methods exhibit similar performance for large sample sizes, for relatively small sample sizes, the method of Pilla et al. leads to an artificial inflation of statistical power that stems from an increase in the false detection rate. This method, on the other hand, becomes particularly useful in multidimensional searches, where the Monte Carlo simulations required by Gross and Vitells are often unfeasible. We apply the methods to realistic simulations of the Fermi Large Area Telescope data, in particular the search for dark matter annihilation lines. Further, we discuss the counter-intuitive scenario where the look-elsewhere corrections are more conservative than much more computationally efficient corrections for multiple hypothesis testing. Finally, we provide general guidelines for navigating the tradeoffs between statistical and computational efficiency when selecting a statistical procedure for signal detection.