Look For New Physics Research Articles

Searching for heavy neutral leptons at a future muon collider

As the planning stages for a high energy muon collider enter a more concrete era, an important question arises as to what new physics could be uncovered. A TeV-scale muon collider is also a vector boson fusion (VBF) factory with a very clean background, and as such it is a promising environment to look for new physics that couples to the electroweak (EW) sector. In this paper, we explore the ability of a future TeV-scale muon collider to search for Majorana and Dirac heavy neutral leptons (HNLs) produced via EW bosons. Employing a model-independent, conservative approach, we present an estimation of the production and decay rate of HNLs over a mass range between 200 GeV and 9.5 TeV in two benchmark collider proposals with s=3, 10 TeV, as well as an estimation of the dominant Standard Model (SM) background. We find that exclusion limits for the mixing between the HNLs and SM neutrinos can be as low as O(10−6). Additionally, we demonstrate that a TeV-scale muon collider allows for the ability to discriminate between Majorana and Dirac type HNLs for a large range of mixing values. Published by the American Physical Society 2024

Does spacetime have memories? Searching for gravitational-wave memory in the third LIGO-Virgo-KAGRA gravitational-wave transient catalogue

Gravitational-wave memory is a non-linear effect predicted by general relativity that remains undetected. We apply a Bayesian analysis framework to search for gravitational-wave memory using binary black hole mergers in LIGO-Virgo-KAGRA’s third gravitational-wave transient catalogue. We obtain a Bayes factor of ln⁡BF=0.01 , in favour of the no-memory hypothesis, which implies that we are unable to measure memory with currently available data. This is consistent with previous work, suggesting that a catalogue of O(2000) binary black hole mergers is needed to detect memory. We look for new physics by allowing the memory amplitude to deviate from the prediction of general relativity by a multiplicative factor A. We obtain an upper limit of A < 23 (95% credibility).

Parity-odd and even trispectrum from axion inflation

The four-point correlation function of primordial scalar perturbations has parity-even and parity-odd contributions and the parity-odd signal in cosmological observations is opening a novel window to look for new physics in the inflationary epoch. We study the distinct parity-odd and even prediction from the axion inflation model, in which the inflaton couples to a vector field via a Chern-Simons interaction, and the vector field is considered to be either approximately massless (mA ≪ Hubble scale H) or very massive (mA ∼ H). The parity-odd signal arises due to one transverse mode of the vector field being predominantly produced during inflation. We adopt the in-in formalism to evaluate the correlation functions. Considering the vector field mode function to be dominated by its real part up to a constant phase, we simplify the formulas for numerical computations. The numerical studies show that the massive and massless vector fields give significant parity-even signals, while the parity-odd contribution is about one to two orders of magnitude smaller.

Coherent elastic neutrino-nucleus scattering

Since its prediction in 1974, the measurement of the coherent elastic neutrino-nucleus scattering (CE υNS) has been a great challenge for many experimentalists. One of the main factors is the small recoil energies of the nucleus produced by this interaction, which is dominant for energies ≾ 50 MeV, for medium target masses. The detection was finally achieved by the COHERENT experiment in 2017 and several other experiments are currently close to performing this measurement for different neutrino energies and sources, thanks to the development of very low threshold and background detectors. Measuring CEυNS opens up new possibilities to test the Standard Model and to look for new physics beyond it. The purpose of this contribution is to provide a brief overview of the state-of-the-art on this subject, with a focus on some of the latest experimental results and future perspectives.

Transition neutrino magnetic moments in CEvNS

Coherent Elastic Neutrino Nucleus Scattering (CEυNS) is a novel technique to look for new physics beyond the Standard Model. We study the prospects of probing a transition magnetic moment in CEvNS experiments. Showing the NUCLEUS experiment as an example, we demonstrate that properties of a potential sterile neutrino can be deduced.

Exploring the role of new physics in $b \to u \tau \bar \nu$ decays

Abstract The recent measurements on $R_D$, $R_{D^*}$, and $R_{J/\psi}$ by three pioneering experiments, BaBar, Belle, and LHCb, indicate that the notion of lepton flavor universality is violated in weak charged-current processes, mediated through $b \to c \ell \bar \nu_\ell$ transitions. These intriguing results, which delineate a tension with their Standard Model predictions at the level of (2–3)$\sigma$, have triggered many new physics propositions in recent times, and are generally attributed to the possible implication of new physics in $ b \to c \tau \bar \nu$ transitions. This, in turn, opens up another avenue, i.e., $ b \to u \tau \bar \nu$ processes, to look for new physics. Since these processes are doubly Cabibbo suppressed, the impact of new physics could be significant enough, leading to sizable effects in some of the observables. In this work, we investigate in detail the role of new physics in $B \to (\pi,\rho,\omega)\tau \bar \nu$ and $B_s \to (K,K^*) \tau \bar \nu$ processes considering a model-independent approach. In particular, we focus on standard observables like branching fraction, the lepton flavor non-universality (LNU) parameter, forward–backward asymmetry, and polarization asymmetries. We find significant deviations in some of these observables, which can be explored by the currently running experiments, LHCb and Belle-II. We also briefly comment on the impact of the scalar leptoquark $R_2(3,2,7/6)$ and vector leptoquark $U_1(3,1,2/3)$ on these decay modes.

Radiative three-body D-meson decays in and beyond the standard model

We study radiative charm decays D rightarrow P_1 P_2 gamma , P_{1,2}=pi ,K in QCD factorization at leading order and within heavy hadron chiral perturbation theory. Branching ratios including resonance contributions are around sim 10^{-3} for the Cabibbo-favored modes into K pi gamma and sim 10^{-5} for the singly Cabibbo-suppressed modes into pi ^+ pi ^- gamma , K^+ K^- gamma , and thus in reach of the flavor factories BES III and Belle II. Dalitz plots and forward–backward asymmetries reveal significant differences between the two QCD frameworks; such observables are therefore ideally suited for a data-driven identification of relevant decay mechanisms in the standard-model dominated D rightarrow K pi gamma decays. This increases the potential to probe new physics with the D rightarrow pi ^+ pi ^- gamma and D rightarrow K^+ K^- gamma decays, which are sensitive to enhanced dipole operators. CP asymmetries are useful to test the SM and look for new physics in neutral |Delta C|=1 transitions. Cuts in the Dalitz plot enhance the sensitivity to new physics due to the presence of both s- and t, u-channel intermediate resonances.

Implication of family non-universal Z′ model to rare exclusive $b \to s(l\bar l,\nu\bar\nu)$ transitions

We have investigated $B \to (K,K^*)(l\bar l,\nu\bar\nu)$ decay channels and predicted some form factor dependent observables (e.g. branching ratio, forward-backward asymmetry and lepton polarization asymmetry) considering new physics contribution from non-universal $Z'$ model. We have found that there is appreciable difference between the standard model and $Z'$ model predictions. Recently, the lepton flavour non-universality parameters $R_K$ and $R_{K^*}$ have been measured by the LHCb collaboration and are found to be different from their standard model predictions. These deviations provide the hint of flavor non-universality in lepton sector and motivate our research to look for new physics beyond the standard model. The $R_K$ and $R_{K^*}$ anomalies may be due to new physics in either electron or muon sector or both. In our work, we have shown that the experimental results of $R_K$ and $R_{K^*}$ could be achieved in non-universal $Z'$ model considering the new physics couplings to muon sector only.

Physics at the SPS.

The CERN Super Proton Synchrotron (SPS) has delivered a variety of beams to a vigorous fixed target physics program since 1978. In this paper, we restrict ourselves to the description of a few illustrative examples in the ongoing physics program at the SPS. We will outline the physics aims of the COmmon Muon Proton Apparatus for Structure and Spectroscopy (COMPASS), north area 64 (NA64), north area 62 (NA62), north area 61 (NA61), and advanced proton driven plasma wakefield acceleration experiment (AWAKE). COMPASS studies the structure of the proton and more specifically of its spin. NA64 searches for the dark photon A', which is the messenger for interactions between normal and dark matter. The NA62 experiment aims at a 10% precision measurement of the very rare decay K+ → π+νν. As this decay mode can be calculated very precisely in the Standard Model, it offers a very good opportunity to look for new physics beyond the Standard Model. The NA61/SHINE experiment studies the phase transition to Quark Gluon Plasma, a state in which the quarks and gluons that form the proton and the neutron are de-confined. Finally, AWAKE investigates proton-driven wake field acceleration: a promising technique to accelerate electrons with very high accelerating gradients. The Physics Beyond Colliders study at CERN is paving the way for a significant and diversified continuation of this already rich and compelling physics program that is complementary to the one at the big colliders like the Large Hadron Collider.

Spin Gyroscope is Ready to Look for New Physics

Spin Gyroscope is Ready to Look for New Physics

LHC collider phenomenology of minimal universal extra dimensions

We discuss the collider phenomenology of the model of Minimal Universal Extra Dimensions (MUED) at the Large hadron Collider (LHC). We derive analytical results for all relevant strong pair-production processes of two level 1 Kaluza–Klein partners and use them to validate and correct the existing MUED implementation in the fortran version of the Pythia event generator. We also develop a new implementation of the model in the C++ version of Pythia. We use our implementations in conjunction with the Checkmate package to derive the LHC bounds on MUED from a large number of published experimental analyses from Run 1 at the LHC. Program summaryProgram title:Pythia6 MUED and Pythia8 MUEDProgram Files doi:http://dx.doi.org/10.17632/fkvcgdw9j6.1Licensing provisions: CC0 1.0Programming language: Fortran and C++Journal reference of previous version: Comput. Phys. Comm. 181 (2010) 122–127Does the new version supersede the previous version?: YesReasons for new version: The Minimal Universal Extra Dimension (MUED) model was implemented in the Pythia6 event generator from version 6.4.18 onwards. The new version now allows for different masses for various level 1 KK excitations, modified and corrected subroutines to handle the kinematics and squared matrix elements. A new production process has been added. Additionally the model is now made available in the Pythia8 event generator.Summary of revisions: The Minimal Universal Extra Dimension (MUED) model implementation in the Pythia6 event generator now allows for different masses for various level 1 KK excitations. These may appear both in the final states and in the propagators of t∕u channel contributions. Routines handling the kinematics and squared matrix elements are suitably modified to incorporate correct kinematics and ensure proper interferences of diagrams. For some processes, corrections in the expressions for the existing squared matrix elements have been made. A new subprocess qq̄→g1∗g1∗ has been added. A couple of production modes (which originally had some subprocesses lumped together) are now split to handle different masses of doublet and singlet KK excitations.Nature of problem: The ongoing run of the Large Hadron Collider (LHC) at CERN continues to look for new physics Beyond the Standard Model (BSM). For many years, the only complete models which were seriously investigated by the LHC collaborations, were different versions of low energy supersymmetry: mSUGRA, gauge-mediated SUSY, anomaly-mediated SUSY, etc. The MUED model provides an interesting and motivated alternative to supersymmetry, with unique and challenging collider phenomenology. In order to study the MUED model, it was implemented in the fortran version Pythia6 general purpose event generator from version 6.4.18 onwards. The MUED model is not available in the C++ version of Pythia8.Solution method: The new implementation validates and fixes the backward compatibility and some issues in the current Pythia6 version. The model has now been implemented in the Pythia8 event generator.

Status of the COMET experiment

The COMET experiment, currently under construction at J-PARC, is designed to search for the the neutrinoless flavour-changing charged-lepton process μ- + A → e- + A, which is a promising channel to look for new physics. The experiment will make use of the high-power proton beam available at the J-PARC Main Ring to achieve a sensitivity orders of magnitude better than the current limits. The experiment will be staged, with ‘Phase-I’ scheduled to begin commissioning soon while the ‘Phase-II’ design is refined in parallel. A description the design of both Phases is presented, along with the latest developments.

Search for Charged Lepton Flavour Violation at CMS

Lepton flavour is a conserved quantity in the standard model of particle physics, but it does not follow from an underlying gauge symmetry. After the discovery of neutrino oscillation, it has been established that lepton flavour is not conserved in the neutral sector. Thus the lepton sector is an excellent place to look for New Physics, and in this perspective the Charged Lepton Flavour Violation is interesting. Various extensions of the standard model predict lepton flavour violating decays that can be observed at LHC. This report summarises several searches for lepton flavour violation with data collected by the CMS detector.

Study of the rare decays

We investigate the effect of scalar leptoquarks and family non-universal bosons on the rare leptonic decays of mesons, mediated by the flavour-changing neutral-current transitions . They are sensitive to a variety of new physics operators as opposed to the leptonic modes and, hence, can provide an ideal testing ground to look for new physics beyond the Standard Model (SM). We work out the constraint on new physics parameter space using the measured branching ratios of processes and the mixing data. Using the constrained parameters we estimate the branching ratios of processes. We find that the branching ratios are reasonably enhanced from their corresponding SM values in the leptoquark model and are expected to be within the reach of Run II/III of Large Hadron Collider experiments.

Hong Kong Scientists and Students Joined ATLAS Team at LHC, CERN

A team of physicists from Hong Kong has formally joined the ATLAS Collaboration at CERN since June, 2014. In 2012, the ATLAS Collaboration – along with the CMS Collaboration – co-discovered the Higgs boson. The discovery of the Higgs boson is widely regarded as a major step towards understanding the fundamental structure of matter and other mysteries of our universe. The admission of the Hong Kong team into ATLAS means, all these exciting opportunities of unveiling an era of new breakthroughs in fundamental physics, are now opened up to scientists and students from Hong Kong. The Hong Kong team plans to take up both hardware and software tasks on the muon detecting system and analysis of data to look for new physics.

Leading effects beyond the standard model

Using the predictive power of the effective field theory approach, we present a physical parametrization of the leading effects beyond the standard model (BSM), which gives us at present the best way to constrain heavy new physics at low energies. We show that other BSM effects are not independent from these ones, and we provide the explicit correlations. This information is useful to know where to primarily look for new physics in future experiments, and to know how this new physics is related to previous measurements, most importantly in electroweak symmetry breaking processes or Higgs physics.

Lepton Flavor Violation beyond the MSSM

Most extensions of the Standard Model lepton sector predict large lepton flavor violating rates. Given the promising experimental perspectives for lepton flavor violation in the next few years, this generic expectation might offer a powerful indirect probe to look for new physics. In this review we will cover several aspects of lepton flavor violation in supersymmetric models beyond the Minimal Supersymmetric Standard Model. In particular, we will concentrate on three different scenarios: high-scale and low-scale seesaw models as well as models withR-parity violation. We will see that in some cases the LFV phenomenology can have characteristic features for specific scenarios, implying that dedicated studies must be performed in order to correctly understand the phenomenology in nonminimal supersymmetric models.

Finding physics signals with shower deconstruction

We introduce shower deconstruction, a method to look for new physics in a hadronic environment. The method aims to be a full information approach using small jets. It assigns to each event a number chi that is an estimate of the ratio of the probability for a signal process to produce that event to the probability for a background process to produce that event. The analytic functions we derive to calculate these probabilities mimic what full event generators like Pythia or Herwig do and can be depicted in a diagrammatic way. As an example, we apply this method to a boosted Higgs boson produced in association with a Z-boson and show that this method can be useful to discriminate this signal from the Z+jets background.

STUDY OF CP VIOLATION IN $\Lambda_c^+$ DECAY

In this paper, we study CP violation in [Formula: see text] and [Formula: see text] decays, where B, P and V denote a light spin-½ baryon, pseudoscalar and a vector meson respectively. In these processes the T odd CP violating triple-product (TP) correlations are examined. The genuine CP violating observables which are composed of the helicity amplitudes occurring in the angular distribution are constructed. Experimentally, by performing a full angular analysis it is shown how one may extract the helicity amplitudes and then obtain the TP asymmetries. We estimate the TP asymmetries in [Formula: see text] decays to be negligible in the Standard Model making these processes an excellent place to look for new physics. Taking a two-Higgs doublet model, as an example of new physics, we show that large TP asymmetries are possible in these decays. Finally, we discuss how BES-III and super τ-charm experiments will be sensitive to these CP violating signals in [Formula: see text] decays.

Dark Matter Search with the ANTARES Neutrino Telescope

Neutrino telescopes are a promising tool for Astroparticle Physics. Neutrinos are neutral, stable and weakly interacting, so these telescopes will open a new window to observe astrophysical objects like AGNs, GRBs or micro-quasars and will allow to look for new Physics, such as dark matter candidates. WIMPs, weakly interacting massive particles, are a possible constituent of dark matter. WIMPs can scatter and become gravitationally trapped in massive objects like the Sun, the Earth or the Galactic Center. Supersymmetry offers several candidates for WIMPs. In the Minimal Supersymmetric Standard Model (MSSM), the lightest supersymmetric particle is stable in most scenarios because of R-parity conservation. In many MSSM models, the favorite candidate is the lightest neutralino. Their annihilation could give rise to detectable rates of high energy neutrinos. Other possible WIMPs, like the lightest Kaluza-Klein (LKK) particle occuring in scenarios with extra-dimensions, can also be investigated. Neutrino telescopes have complementary potential with respect to direct searches, particularly in the range of large neutralino masses. In this paper we will discuss the prospects for dark matter searches with the ANTARES neutrino telescope that is presently under construction in the Mediterranean Sea.