Along with the direct searches of new particles at the LHC, low-energy phenomenology offers many complementary ways to search for physics beyond the Standard Model. The low-energy searches, however, are often hindered by the insufficiently precise knowledge of hadronic contributions. The last decade has witnessed tremendous progress towards ab-initio and model-independent determinations of these contributions. The purpose of this meeting is to cross-examine the empirical and theoretical progress in this field and the implications in beyond-the-SM physics.
The main website of the 2nd Edition of Hadronic Contributions to New Physics searches (HC2NP 2019) can be found here.
In this talk I will discuss the main open questions in neutrino physics, and the experimental path that we will follow to address them in the future. I will focus on new physics searches in the neutrino sector, paying particular attention to those observables where a more precise knowledge of hadronic contributions could be key in order to distinguish a possible signal of new physics.
The analysis of neutrino experiments requires a quite precise knowledge of the weak interaction with hadrons. In this talk, I will present a few selected developments in this area. I will also show how the neutrino data open new opportunities in our research of hadronic Physics (axial structure, corrections to GT relations, ChPT LECS,..).
The majority of the mass content of the universe is composed by dark matter, whose specific nature is not known. Among the best motivated dark matter candidates are WIMPs, which can interact with atomic nuclei. Direct dark matter detection experiments aim to observe the scattering of WIMPs off nuclei.
The interpretation of direct detection experiments naturally depends on nuclear structure input that needs to be calculated from nuclear theory. In addition, nuclear theory can also provide a hierarchy between WIMP-nucleon interactions: first, realizing that only selected nuclear responses receive a coherent enhancement by the contribution from all or several nucleons in the nucleus; second, identifying which interactions are expected to be dominant according to the symmetries of QCD, via the chiral effective field theory (EFT) power counting.
My talk will discuss nuclear structure factors for all nuclear targets used in direct detection experiments. I will consider the WIMP-nucleon interactions expected to dominate spin-independent and spin-dependent WIMP-nucleus scattering up to third order in chiral EFT.
Loop-induced meson decays are rare in the standard model, but much more likely in the presence of light new particles. In this talk, we will explore the potential to find such particles in final states with missing energy or displaced lepton pairs. At low-energy experiments such as BELLE-II and NA62, we can expect a high sensitivity to hidden particles. I will discuss the discovery prospects for simple renormalizable models and compare them with high-energy searches at the LHC and far-distance detectors.
The purely leptonic FCNC decays $B_{s,d} \to \ell^+ \ell^-$ are powerful probes of the CKM picture of the SM and due to helicity suppression are very sensitive to NP contributions. The hadronic uncertainties are under exceptionally good control due to lattice calculations, allowing theoretical control at the percent level thereby neglecting currently QED corrections. This gap can be closed for this particularly simple decay into muons. We present the calculation of the leading power-enhanced structure-dependent virtual QED corrections and their combination with real radiation from first principles for the case when the energy of the undetected photons is small compared to the QCD binding energy and the muon mass. The QED logarithms that involve the process-specific scales are factorized and resummed with the help of soft-collinear effective theory (SCET).
An NLO computation of the $B_{u,d,s}\to \gamma$ form factor in light-cone sum rules will be presented. I will compare aspects of the computation to more familiar $B_s\to \phi $ form factor computations and give a physical interpretation of the photon distribution amplitude. I will discuss the extraction of the inverse moment of the $B$-meson distribution amplitude but most likely not present a definite number yet.
We present a formalism to extend the well-know Minimal Flavour Violation approach for physics beyond the Standard Model. As a guideline for the flavour pattern we adopt a Froggatt-Nielsen inspired power counting. We study the phenomenological implications when taking into account the spurions associated with a $U_1$ vector leptoquark and their compatibility with flavour data and the anomalies in $B$ decays. As a result of our analysis we observe that leptonic $B$ decays constitute an important test to probe these scenarios.
The recent hints of deviations from the SM in low-energy flavour-changing processes have shaken many prejudices about physics beyond the SM, opening new directions in model building. In this talk I will highlight some of these new directions, emphasising the key role of flavour physics, both at low and at high energies.
The decays of $b$-hadrons offer a unique laboratory to test SM predictions and potentially reveal hints of new physics.
Results and prospects in Flavour from ATLAS and CMS are presented, showing the role and the capability of the general purpose LHC experiments in the low $p_T$ investigation and the bridge to the high $p_T$ searches in view of a coherent physics picture of possible beyond standard model scenarios.
A traditional approach to study flavour is at the high-intensity frontier, where we copiously produce hadrons made of different flavours and examine their properties. In this talk, I will discuss alternative avenues to probe flavour dynamics. High-energy frontier is the most promising direction given the expected luminosity in the coming years at the LHC. Another somewhat radical avenue is to look in the sky for gravitational waves.
I plan to discuss the interplay between Higgs phenomena in high-$p_T$ measurements and low-energy searches. Topics that may be covered are determinations of light-quark Yukawa couplings, bounds on CP-violating or flavour-violating Higgs couplings from searches for electric dipole moments, and more if time permits.
Precision measurements of CP violating observables in the decays of $b$ and $c$ hadrons are powerful probes to search for physics beyond the Standard Model. The most recent results on CP violation in the decay, mixing and interference of both $b$ and $c$ hadrons obtained by the LHCb Collaboration with Run I and part of Run II data are presented, including the first observation of CP violation in the charm system. We also discuss prospects for future sensitivities.
We review recent progress in increasing the precision of SM flavour observables, like heavy hadron lifetimes or $B$-mixing. The latter observable turns out to be a severe constraint on BSM models that try to explain the recently observed anomalies in the flavour sector.
Techniques from Bayesian generative statistical modeling can be applied to uncover hidden features in jet substructure observables that discriminate between different a priori unknown underlying physical processes in multi-jet events. In particular, I will discuss a mixed membership model known as Latent Dirichlet Allocation to build data-driven unsupervised jet taggers. I will compare this proposal to existing traditional and machine learning approaches to top jet tagging, and employ a toy vector-scalar boson model as a benchmark, to demonstrate the potential for discovering New Physics signatures in multi-jet events in a model independent and unsupervised way.
Compositeness due to a new confining gauge force may play roles in several sectors of physics beyond the Standard Model, including composite dark matter and composite Higgs bosons. Given the strongly-coupled nature of the new confining interaction, lattice gauge theory is the appropriate calculational technique. I will briefly review recent progress in this area, focusing on recent studies of light composite scalars (i.e. Higgs bosons) and the search for a low energy effective theory.
Long-distance charm effects in $b\to s\ell\ell$ decays are the main obstacle in the interpretation of measurements of the $B\to K^*\mu\mu$ angular distribution. Given the theoretical difficulty of predicting such a contribution, the natural avenue for progress is to use data to disentangle it from New Physics. In this talk, I will present the latest measurements and plans for unbinned analyses at LHCb, which aim to fit the hadronic contributions and Wilson coefficients simultaneously.
Theory predictions for exclusive $b\to sll$ amplitudes require the evaluation of local and non-local form factors. I will discuss the calculation of local form factors beyond the narrow-width limit, as well as the perturbative and non-perturbative aspects of the non-local form factors, which include the charm-loop effect.
Flavour Changing Neutral Currents (FCNC) are an excellent probe for the search of New Physics. Therefore, LHCb has put a particular care in the study of $B$ decays mediated by FCNC. Tensions between present data and Standard Model predictions have been found in some of these channels, hinting at a possible violation of Lepton Flavour Universality. I will review the status of these tensions after the latest result presented at Moriond 2019, assessing with particular care the theoretical cleanness of the observables displaying such tensions. Then, I'll discuss the possible explanations for such a pattern of anomalies both within and beyond the Standard Model. I will do so employing a model independent EFT framework, and focussing in particular on how a different handling of hadronic uncertainties might yield to different NP interpretations of these anomalies.
I will first discuss a possible parametrisation of the contribution of two-particle intermediate $\bar c c$ states (open charm threshold) to the $B^+ \to K^+ \mu^+ \mu^-$ differential decay rate. Motivated by $B$ anomalies, whose combined explanation calls for large New Physics in the $b \to s \tau^{+} \tau^{-}$ transition, I will then comment on the possibility of extracting a bound on this contribution from the $B^+ \to K^+ \mu^+ \mu^-$ spectrum.
There is a persisting discrepancy of more than three standard deviations between the experimental measurement and the Standard Model prediction of the anomalous magnetic moment of the muon. In this talk, the different contributions to the theory prediction of $g-2$ are reviewed, with main emphasis on the hadronic contributions, especially the hadronic vacuum polarisation corrections determined from hadronic cross section data using the dispersive approach.
The magnetic moments of the charged leptons have long served as an important test of our models of fundamental particles. The well known tension in the anomalous magnetic moment of the muon observed in the E821 experiment at Brookhaven National Laboratory motivated the creation of the new Muon $g-2$ Experiment (E989), now taking place at Fermi National Accelerator Laboratory, which aims to achieve a precision of 140 ppb, more than a three-fold improvement over E821. In this talk, I will report on the status and progress of the new experiment, which has now completed two years of production data collection.
Measurements of the fine-structure constant are powerful tests of the consistency of theory and experiment across physics. We have measured the recoil frequency of cesium-133 atoms in an atom interferometer to measure $\hbar/M$, the ratio of the Planck constant and the mass of the atom, from which we derive the most accurate measurement of the fine-structure constant to date: $\alpha$ = 1/137.035999046(27). This measurement has a 2.5$\sigma$ tension with the value obtained from the electron gyromagnetic anomaly; the tension has the opposite sign as the famous tension between the muon magnetic moment and the standard model. We will present our measurement and some of these implications, as well as our plans to improve the measurement further.
I will review the status of lattice calculations of the hadronic contributions to the muon anomalous magnetic moment, including vacuum polarization and light-by-light scattering.
The experimental measurement of the anomalous contribution to the muon magnetic moment, $a_\mu=(g_\mu-2)/2$, has shown a persistent discrepancy of over 3 standard deviations with the standard model prediction since the early 2000s. At present theoretical and experimental uncertainties are close in size. However, a new experiment underway at Fermilab is aiming to reduce the uncertainty on the measurement of $a_\mu$ by a factor 4 and should release a first set of results this fall. I will present a lattice QCD calculation of the hadronic vacuum polarization contribution to this quantity that, together with the hadronic light-by-light contribution, most limits the precision of its standard model prediction.
The appearance of data-driven approaches to improve the Standard Model prediction of the anomalous magnetic moment of the muon $a_\mu$ has motivated the BESIII collaboration to embark on a dedicated experimental program. The high statistics data samples collected with the BESIII experiment in $e^+e^-$ collisions in the $\tau$-charm region are analyzed exploiting the initial state radiation technique in order to measure hadronic cross sections needed in the dispersive analysis of the hadronic Vacuum Polarization contribution to $a_\mu$. The same data enable investigations of two-photon collisions. These allow the determination of the momentum dependence of transition form factors of light mesons in the relevant kinematic region, which dominate the hadronic Light-by-Light contribution to $a_\mu$. The current status and ongoing investigations will be discussed.
True muonium is the currently unobserved bound state of a muon and anti-muon. The potential of the LHCb experiment to make a discovery of the $1^3S_1$ state, which dominantly decays to $e^+e^-$, is discussed here. It is shown that a search for $\eta\rightarrow\gamma\mathcal{TM}$, $\mathcal{TM}\rightarrow e^+e^-$ can exceed a significance of 5 standard deviations with the expected luminosity during Run-III. Both an inclusive search for the $e^+e^-$ vertex and an exclusive search, including the photon and reconstructing the $\eta$, are possible at LHCb.
I give a short review of the low-energy extensions of the Standard Model (such as axions, dark photons, dark Higgses and sterile neutrinos), and present a short summary of existing bounds and theoretical challenges.
In view of the current $3-4 \sigma$ deviation between theoretical and experimental values for the muon’s anomalous magnetic moment, I will review the ongoing efforts in constraining the hadronic light-by-light contribution to $(g-2)_\mu$ by using dispersive techniques.
The evaluation of the hadronic light-by-light contribution to the $(g-2)_{\mu}$ is hindered by our limited knowledge of nonperturbative physics. Different hadronic models have been introduced in the past to estimate its different contributions, where contact with QCD is achieved by fulfilling a varying number of short-distance constraints. It is not clear, however, which are the most relevant constraints to be fulfilled and whether the analytic form of the hadronic models is compatible with them. In particular, the so-called Melnikov-Vainshtein (MV) constraint is thought to have a substantial impact on the HLbL, yet hadronic models do not naturally implement it. In this talk I will study the interplay between resonance exchange and short-distance constraints using a toy model in a 5-dimensional setup. This toy model provides a full-fledged realization of large-$N_c$ QCD with full analytic control over correlators, and helps clarify the subtleties associated with the MV limit. With it, I will also revisit the (dominant) pion and axial exchange contributions to HLbL.
A model-independent dispersive framework for the evaluation of hadronic light-by-light (HLbL) scattering in the anomalous magnetic moment of the muon $(g-2)_\mu$ was recently developed. It is based on the general principles of analyticity, unitarity, and crossing symmetry to attribute the contributions to on-shell form factors and scattering amplitudes accessible from experiment, complementary to lattice QCD calculations of HLbL scattering. Within this framework, we focus on the recent work on the pion-pole contribution to HLbL scattering in the $(g-2)_\mu$, which is fully determined by the doubly-virtual pion transition form factor. The previous analysis of the singly-virtual transition form factor is generalised to the doubly-virtual kinematics in light of the available data for the $\pi^0\to\gamma \gamma$ decay width, $e^+e^-\to 3\pi$ cross section, and the space-like singly-virtual form factor from $e^+e^-\to e^+e^-\pi^0$. The form factor is reconstructed using a dispersive representation that accounts for all the low-lying singularities and incorporates the asymptotic behavior obtained from perturbative QCD. This detailed study accumulates to the first dispersive determination of the pion-pole contribution to the muon $(g-2)_\mu$, $a_\mu^{\pi^0 \text{-pole}}=62.6^{+3.0}_{-2.5}\times 10^{-11}$ [1,2], where its uncertainty can be reduced further owing to more precise singly-virtual measurements in the future.
[1] M. Hoferichter, B.-L. Hoid, B. Kubis, S. Leupold and S. P. Schneider, Phys. Rev. Lett. 121 (2018) 112002, [arXiv:1805.01471 [hep-ph]]
[2] M. Hoferichter, B.-L. Hoid, B. Kubis, S. Leupold and S. P. Schneider, JHEP 1810 (2018) 141, [arXiv:1808.04823 [hep-ph]]
Neutrinos are the most abundant matter particle and yet one of the most elusive. New results and new experiments, in particular in light of the discovery of neutrino mass, are changing the landscape of particle physics. As neutrino experiments have become both larger and higher precision, a better understanding of neutrino interactions is being realized. Many of these same experiments are searching for new physics – both new particles and new phenomena. A review of new and upcoming results will be presented.
In this talk I will discuss searches for neutrinoless double beta decay as a probe of lepton number violation. After a general introduction, I will discuss an “end-to-end” effective field theory approach to neutrinoless double beta decay based on the Standard Model EFT at high scales and on chiral effective theory at hadronic and nuclear scales. In this framework, I will discuss various sources of lepton number violation, ranging from light Majorana neutrino exchange to TeV-scale mechanisms.
I will discuss the recently proposed dark matter interpretation of the neutron lifetime discrepancy. The difference between bottle and beam neutron lifetime measurements is explained by the existence of a neutron dark decay channel with a branching fraction 1%. Phenomenologically consistent particle physics models of this type can be constructed; they involve either a strongly self-interacting dark sector or a repulsive dark matter-baryon interaction. I will elaborate on the theoretical developments around this idea and describe the efforts undertaken to verify it experimentally. In general, the proposed neutron dark decay need not be linked to the neutron lifetime discrepancy and can occur at a smaller rate, giving rise to new theoretical and experimental avenues of investigation.
Lattice QCD provides the most precise non-perturbative inputs needed for the theoretical predictions of many observables relevant for the current quark flavor physics program. Recent results for those lattice inputs related to $B$-meson flavor observables will be summarized, and future prospects for the improvement of key quantities will be discussed.
The nucleon axial coupling, $g_A$, is ubiquitous in nuclear physics. It also plays an important role in our understanding of thee first row of the CKM Matrix and the search for new physics. With lattice QCD, we have a theoretical determination of $g_A$ with a $1%$ uncertainty, which already places the most stringent constraint on right-handed BSM currents. A theoretical uncertainty of $0.2%$ would allow for a theoretical prediction of the neutron lifetime with an uncertainty matching the size of the uncertainty on the lifetime measurements that currently leads to a $4\sigma$ discrepancy between the beam and bottle experiments. At $0.4%$, there are newly (re?) discovered QED corrections which become relevant for extracting the QCD value of $g_A$ from the experimental measurements. I will discuss the current status of lattice QCD determinations of $g_A$, ongoing calculations, and prospects for incorporating these electromagnetic corrections and aiming for a theoretical uncertainty of $0.2%$.
The amplitudes of the rare kaon decays $K\to\pi\ell^+\ell^-$, $(K,\pi) = (K^+,\pi^+), (K_S , \pi^0)$, $\ell = e , \mu$, are dominated by their long-distance component. The latter is given by the exchange of a virtual photon between the lepton pair and the four-quark operators of the $\Delta S =1$ weak effective Lagrangian. The corresponding $K - \pi - \gamma^*$ form factor is described as a sum of three contributions. At large Euclidian virtualities, it behaves as powers of the logarithm of the photon momentum squared. The one-loop correction of this type is easily computed, and the two-loop one is almost entirely determined by a renormalization-group argument combined with existing calculations of the two-loop anomalous dimensions of the $\Delta S =1$ four-quark operators. At long distances, the form factor is written as an unsubtracted dispersion relation. The absorptive part, when restricted to two-pion intermediate states, is given by the product of the electromagnetic form factor of the pion times the $P$-wave projection of the amplitude for $K\pi\to\pi^+\pi^-$ scattering. Finally, the intermediate region is described by an infinite sum of zero-width resonances, with residues tuned such as to reproduce the correct short-distance behaviour. Predictions of the amplitudes based on this description are presented and compared to experiment. Possibilities to improve this phenomenological description are also discussed.
An approach is presented for the calculation of hadron-lepton and hadron-hadron interactions at large momentum transfer in the presence of Lorentz-violating background fields affecting quarks. Cross sections for deep inelastic scattering and the Drell-Yan process are calculated at leading order for minimal and nonminimal Lorentz violation using the Standard-Model Extension, an effective field theory characterizing general Lorentz-violating effects for the Standard Model fields and General Relativity. Estimated bounds are placed using sidereal-time analyses of existing HERA, LHC, and future US-based electron-ion collider data.
I will review the status of the kaon physics programme of the RBC-UKQCD collaborations as well as prospects for its future. The talk will focus on CP-violation in $K\to\pi\pi$ decays and the evaluation of $\varepsilon'/\varepsilon$, the computation of the $K_L-K_S$ mass difference and the study of rare kaon decays.
The NA62 Experiment, installed in the CERN North Area, studies the physics of the $K^+$ meson.
Its main purpose is to measure the branching ratio of the ultra-rare decay $K^+\rightarrow\pi^+\nu\bar\nu$ with a $10\%$ precision, in order to strictly test the Standard Model, that gives for that physics quantity a very precise prediction: $BR(K^+\rightarrow\pi^+\nu\bar\nu) = (0.84 \pm 0.10) \times 10^{-10}$.
After the full detector installation, completed in 2016, NA62 collected data in the years 2016, 2017 and 2018.
On the 2016 data sample, that corresponds to $2\%$ of the total NA62 statistics in the period 2016-2018, one signal candidate has been observed, leading to the upper limit: $BR(K^+\rightarrow\pi^+\nu\bar\nu) < 14 \times 10^{-10}$ @ $95\%$ C.L.
The analysis of the 2017 data sample (10 times the 2016 statistics) is ongoing, and preliminary results, together with future perspectives, will be presented.
The NA62 physics program also covers the searches for exotic and forbidden Kaon decays: the most recent results on searches for lepton number violating $K^+$ decays ($K^+\rightarrow\pi^- e^+ e^+$ and $K^+\rightarrow\pi^- \mu^+ \mu^+$) and for production of an invisible dark photon in $\pi^0$ decays ($K^+\rightarrow\pi^+ \pi^0, \pi^0 \rightarrow A' \gamma$) will be shown.
The quantity $\varepsilon^\prime/\epsilon$ measures direct CP violation in Kaon decays. SM predictions show a 2.9$\sigma$ tension with data, with the theoretical uncertainty dominating. As rapid progress on the lattice is bringing nonperturbative long-distance effects under control, a more precise knowledge of short-distance contributions is needed. We describe the first NNLO results for $\varepsilon^\prime/\varepsilon$ and discuss future prospects, as well as issues of scheme dependence and the separation of perturbative and nonperturbative effects.
In this contribution, I'm going to provide an overview of current/future kaon physics in light of searching for physics beyond the standard model. The main topics are (1) two $CP$ violations in $K\to \pi \pi$ ($\varepsilon_K$ and $\varepsilon^{\prime}/\varepsilon$) and their new physics implications, (2) $CP$ violation in $K \to \bar{\mu} \mu$ and its new physics sensitivity, and (3) $K \to \pi \bar{\nu} \nu$ and the related searches. These channels are interesting and entangling in light of future precise lattice calculations, and future precision measurements by LHCb, NA62, and KOTO experiments. Besides, these correlations could distinguish the new physics models.
The recent release of improved lattice data has revived again the interest on precise theoretical predictions for the direct CP-violation ratio $\varepsilon'/\varepsilon$. We present a complete update of the Standard Model prediction, including a new re-analysis of isospin-breaking corrections which are of vital importance in the theoretical determination of this observable. Contrary to recent claims, the Standard Model prediction turns out to be in good agreement with the experimental measurement. In addition, we analyse the prospects for future improvements on the current uncertainty, which is dominated by our current ignorance about $1/N_C$-suppressed contributions to some chiral-perturbation theory low-energy constants.
Given the increasing experimental accuracy in the measurement of several weak decay rates and in the calculation of the corresponding hadronic amplitudes, in order to make further progress in the determination of the CKM matrix and in the exploration of the limits of the Standard Model in flavour physics it is necessary to include electromagnetic effects and isospin breaking contributions. In this talk the recent progress in the ab-initio, non-perturbative lattice QCD calculation of the electromagnetic corrections to the leptonic and semi-leptonic decay rates will be reviewed.
Recently, forward dispersion relations were applied to the calculation of the radiative $\gamma W$-box correction to neutron and nuclear $\beta$-decay. These new developments allowed to almost halve the hadronic uncertainty in $V_{ud}$. Taken at its face value, it lead to a significant shift in the extracted value of $V_{ud}$ and raised tension with the top-row CKM unitarity, $\Delta_{CKM}=-0.0016\pm0.0004$. On the other hand, the application of this new technique to nuclear decays indicated that nuclear uncertainties may have been underestimated and further efforts from nuclear theory are welcome to clarify this situation. Recent high-precision measurements of the asymmetries in free neutron decay together with plans to improve the measurements of the neutron lifetime promote free neutron decay as a valid alternative to superallowed nuclear decays as a source of precise information on the value of $V_{ud}$.
We review recent high-precision results for different nucleon matrix elements based on a dispersive low-energy pion-nucleon scattering amplitude analysis using Roy-Steiner equations.
In particular, we focus on the phenomenological determination of the pion-nucleon $\sigma$-term, derived in combination with modern precision data on pionic atoms. We also discuss recent applications to the isovector spectral functions of the nucleon electromagnetic form factors and the nucleon matrix elements of the antisymmetric quark tensor.
We present recent results of baryon matrix elements from lattice QCD simulations with $N_f=2+1$ non-perturbatively Wilson fermions (CLS ensembles). We also discuss octet baryon masses and sigma terms.
The evaluation of so-called disconnected diagrams in Lattice Quantum Chromodynamics (QCD) calculations of hadronic processes has been computationally challenging and expensive. These disconnected diagrams, which are fermionic Wick contraction diagrams involving quark propagators beginning and ending at the same time coordinates, are noisy and the extraction of lattice information from them is difficult. We show how effective field theory (EFT) can be used to understand the quantitative influence and relevance of these disconnected contributions in important lattice calculations of hadronic processes. We use Partially Quenched Chiral Perturbation Theory (PQChPT) to separate the connected and disconnected contributions for, firstly, pion-pion scattering, and then combine it with Lüscher's formalism to relate the theoretical predictions to lattice data. We then show how this technique can be applied towards a better understanding of the pion-nucleon sigma term, which is a crucial element in numerous new physics searches and experiments.