Search

We present detailed analysis of the $T$-even lepton angular distribution in the Drell-Yan process including $\gamma/Z^0$ gauge boson exchange and using perturbative QCD based on the collinear factorization scheme at leading order in the $\alpha_s$ expansion. We focus on the study of the transverse momentum $Q_T$ dependence of the corresponding hadronic structure functions and angular coefficients up to next-next-to-leading order in the $Q_T^2/Q^2$ expansion. We analyze $Q_T$ dependence numerically and compare $T$-even angular coefficients integrated over rapidity with available data of the ATLAS Collaboration at LHC. Additionally, we present our results for the forward-backward asymmetry and compare it with data., Comment: 26 pages, 9 figures, journal version

We consider the possibility of discovering a light pseudoscalar particle $a$, which could the axion or an axion-like particle (ALP), interacting mainly with quarks using the electron and photon scattering reaction chain $e + Z \rightarrow e + \gamma + Z$; $\gamma + Z \rightarrow a + Z$ on nuclei in the NA64 experiment at the CERN SPS. New bounds on the coupling strengths of the axion/ALP with quarks and of pseudoscalar mesons $P = \pi, \eta, \eta'$ with dark fermions are obtained by using existing upper bounds on invisible decay modes of $P$s including those recently derived by NA64. We also study a scenario when the $a$ plays the role of a messenger in the communication between our world and the dark sector., Comment: 17 pages, 1 figure

We calculate the perturbative $T$-odd contributions to the lepton angular distribution in the Drell-Yan process. Using collinear factorization, we work at the first order in QCD perturbation theory where these contributions appear, ${\cal O}(\alpha_s^2)$, and address both $W^\pm$ and $\gamma/Z^0$ boson exchange. A major focus of our calculation is on the regime where the boson's transverse momentum $Q_T$ is much smaller than its mass $Q$. We carefully expand our results up to next-to-next-to-leading power in $Q_T/Q$. Our calculation provides a benchmark for studies of $T$-odd contributions that employ transverse-momentum dependent parton distribution functions. In the neutral-current case we compare our results for the $T$-odd structure functions to available ATLAS data., Comment: 34 pages, 10 figures

We consider an experiment to search for dark sector particles in dark photon kinetic mixing model by analyze invisible and semi-invisible decays of neutral mesons $M^0 = \pi^0$, $\eta$, $\eta'$, $\omega$, $f_2(1270)$, produced in the NA64 experiment at the CERN SPS. The approach proposed in Ref.~\cite{Gninenko:2014sxa} is to use the charge-exchange reactions $\pi^- + (A, Z) \to M^0 + (A,Z-1); M^0 \to$ invisible or semi-invisible of high-energy pions (or kaons) at a nuclei target as a source of $M^0$s, which subsequently decay invisibly into dark sector. This reaction chain would lead to a striking signature of the signal event - the complete disappearance of the beam energy in the setup. Using data obtained from the study of charge-exchange reactions at IHEP (Protvino) and Fermilab (Batavia) we show that the integral cross sections $\sigma$ for production of the neutral mesons $M^0$ are slightly deviate from phenomenological formula $\sigma \sim Z^{2/3}$, where $Z$ is the nuclei charge. In particular, we present the formulas for the differential and integral sections that explicitly depend on the Mandelstam and $Z$ variables. Derived formulas are used to predict the cross sections as a function of beam energy for several target nuclei, and to estimate the projection sensitivity for the proposed search for the $M^0\to$ semi-invisible and $M^0\to$ invisible decays through the vector portal to dark sector. Sensitivity to different semi-invisible decay modes of neutral pseudoscalar mesons is studied., Comment: 14 pages, 10 figures

We test a novel idea of using a $\pi^-$ beam in the fixed-target experiments to search for New Physics in the events with missing energy. Bounds for invisible vector $\rho$ meson decay were derived, analyzed, and compared with the current limits on searching Dark Matter in the accelerator based experiments. We demonstrate that the new approach can be effective tool to probe sub-GeV Dark Matter parameter space., Comment: 8 pages,, 5 figures and 1 Table

We study possible impact of dark photons on lepton flavor phenomenology. We derive the constraints on non-diagonal dark photon couplings with leptons by analyzing corresponding contributions to lepton anomalous magnetic moments, rare lepton decays and the prospects of fixed-target experiments aiming for search for light dark matter based on missing energy/momentum techniques., Comment: 9 pages, 9 Figs

We study the non-abelian $SU(2)_D$ extension of the $U(1)_D$ Stueckelberg portal, which plays a role of the mediator between the Standard Model (SM) and Dark Sector (DS). This portal is specified by the Stueckelberg mechanism for generation of dark gauge boson masses. Proposed $U(1)_D\times SU(2)_D$ Stueckelberg portal has a connection with SM matter fields in analogy with Familon Model. We derive bounds on the couplings of dark portal bosons and SM particles, which govern diagonal and non-diagonal flavor transitions of quarks and leptons., Comment: 12 pages, 4 figures, journal version

The link between ordinary Standard model (SM) photon and both dark photon and axion like particle (ALP) can be introduced through the dark axion portal coupling. Given the dark axion portal setup, in the present paper we refer the dark photon as the mediator between SM and dark matter (DM) particles, implying that it decays predominantly into pair of DM fermions. Furthermore, we discuss in detail the implication of the dark axion portal scenario for the lepton (electron and muon) fixed target experiments. In particular, for the specific fixed target facility we study the missing energy signatures of the dark photon production followed by its invisible decay into stable DM particles. We investigated the potential to probe dark axion portal vertices with regarding signatures and derive the expected sensitivities of NA64$e$, NA64$\mu$, LDMX and $\mbox{M}^3$. Moreover, we estimated the expected reach of NA64$e$ from the projected statistics of the $J/\psi$ vector meson invisible decays. We also recasted BaBar monophoton bounds for the specific dark axion portal scenario. In addition, we modified the dark axion portal setup by including in the model both the hadron and lepton specific ALP couplings. As the result, we obtain the bounds on the combination of fermion-specific couplings of ALP from the fixed target experiments. We discuss the implication of the modified dark axion portal scenario for the electric dipole moments (EDM) of SM fermions. In addition, we derived the novel constraints on the combination of the $CP$-violating neutron-specific ALP couplings from the existing bounds on neutron EDM by taking into account the neutron anomalous magnetic moment., Comment: 17 pages, 15 figures

We discuss new ideas for consideration of loop diagrams and angular integrals in $D$-dimensions in QCD. In case of loop diagrams, we propose the covariant formalism of expansion of tensorial loop integrals into the orthogonal basis of linear combinations of external momenta. It gives a very simple presentation for the final results and is more convenient for calculations on computer algebra systems. In case of angular integrals we demonstrate how to simplify the integration of differential cross sections over polar angles. Also we derive the recursion relations, which allow to reduce all occurring angular integrals to a short set of basic scalar integrals. All order $\epsilon$-expansion is given for all angular integrals with up to two denominators based on the expansion of the basic integrals and using recursion relations. A geometric picture for partial fractioning is developed which provides a new rotational invariant algorithm to reduce the number of denominators., Comment: 134 pages, 8 figures

We discuss constraints on soft CP-violating couplings of axion-like particles with photon and fermions by using data on electric dipole moments of Standard Model particles. In particular, for the ALP leptophilic scenario we derive bounds on CP-odd ALP-photon-photon coupling from data of the {\tt ACME} Collaboration on electron EDM. We also discuss prospects of the Storage Ring experiment to constrain the ALP-photon-photon coupling from data on proton EDM for the simplified hadrophilic interactions of ALP. The regarding constraints from experimental bounds on the muon and neutron EDMs are weak. We set constraint on the CP-odd ALP coupling with electron and derive bounds on combinations of coupling constants, which involve soft CP-violating terms., Comment: 12 pages, 2 figures, journal reference corrected

We analyze contributions to the electric dipole (EDM) and Schiff (SFM) moments of deuteron induced by the CP-violating three-pseudoscalar meson couplings using phenomenological Lagrangian approach involving nucleons and pseudoscalar mesons $P=\pi, K, \eta, \eta'$. Deuteron is considered as a proton-neutron bound state and its properties are defined by one- and two-body forces. One-body forces correspond to a picture there proton and neutron are quasi free constituents of deuteron and their contribution to the deuteron EDM (dEDM) is simply the sum of proton and neutron EDMs. Two-body forces in deuteron are induced by one-meson exchange between nucleons. They produce a contribution to the dEDM, which is estimated using corresponding potential approach. From numerical analysis of nucleon and deuteron EDMs we derive stringent limits on CP-violating hadronic couplings and $\bar\theta$ parameter. We showed that proposed measurements of proton and deuteron EDMs at level of $\sim 10^{-29}$ by the Store Ring EDM and JEDI Collaborations will provide more stringent upper limits on the CP violating parameters.

We discuss new physics phenomenology of hidden scalar ($S$), pseudoscalar ($P$), vector ($V$) and axial-vector ($A$) particles coupled to nucleons and leptons, which could give contributions to proton charge radius, $(g-2)_\mu$, $^8$Be-$^4$He anomaly and electric dipole moment (EDM) of Standard Model (SM) particles. In particular, we estimate sensitivity of NA64$\mu$ experiment to observe muon missing energy events involving hidden scalar and vector particles. That analysis is based on {\tt GEANT4} Monte Carlo simulation of the signal process of muon scattering off target nuclei $\mu N \to \mu N S(V)$ followed by invisible boson decay into Dark Matter (DM) particles, $S(V)\to \chi \chi$. The existence of light sub-GeV bosons could possibly explain the muon $(g-2)$ anomaly observed. We also summarize existing bounds on ATOMKI $X17(J^P=0^-, 1^\pm)$ boson coupling with neutron, proton and electron. We implement these constraints to estimate the contribution of $P$, $V$ and $A$ particles to proton charge radius via direct 1-loop calculation of Sachs form factors. The analysis reveals the corresponding contribution is negligible. We also calculate bounds on dark axion portal couplings of dimension-five operators, which contribute to the EDMs of leptons and neutron., Comment: 12 pages, 4 figures, version accepted for publication in PRD

We complete our derivation of upper limits on the CP violating $\eta\pi\pi$ and $\eta'\pi\pi$ couplings from an analysis of their two-loop contributions to the neutron electric dipole moment (nEDM). We use a phenomenological Lagrangian approach which is formulated in terms of hadronic degrees of freedom - nucleons and pseudoscalar mesons. The essential part of the Lagrangian contains the CP violating couplings between $\eta(\eta')$ and pions. Previously, we included photons using minimal substitution in case of the proton and charged pions. Now we extend our Lagrangian by adding the nonminimal couplings, i.e. anomalous magnetic couplings of nucleons with the photon. The obtained numerical upper limits for the $\eta\pi\pi$ and $\eta'\pi\pi$ couplings $|f_{\eta\pi\pi}(M_\eta^2)|<4.4 \times10^{-11}$ and $|f_{\eta^\prime\pi\pi}(M_{\eta'}^2)|<3.8 \times10^{-11}$ can be useful for the related, planned experiments at the JLab Eta Factory. Using present experimental limits on the nEDM, we derive upper limits on the CP violating $\bar\theta$ parameter of $\bar{\mathrm{\theta}}<4.7 \times 10^{-10}$., Comment: 6 pages, 2 figures

We provide model-independent bounds on the rates of rare decays $\eta (\eta^\prime) \to \pi\pi$ based on experimental limits on the neutron electric dipole moment (nEDM). Starting from phenomenological $\eta(\eta^\prime) \pi\pi$ couplings, the nEDM arises at two loop level. The leading-order relativistic ChPT calculation with the minimal photon coupling to charged pions and a proton inside the loops leads to a finite, counter term-free result. This is an improvement upon previous estimates which used approximations in evaluating the two loop contribution and were plagued by divergences. While constraints on the $\eta(\eta^\prime) \pi\pi$ couplings in our phenomenological approach are somewhat milder than in the picture with the QCD $\theta$-term, our calculation means that whatever the origin of these couplings, The decays $\eta (\eta') \to 2 \pi$ will remain unobservable in the near future., Comment: 8 hages, 3 figures

We study the Lepton Flavor Violating (LFV) $e(\mu)-\tau$ conversion in Deep Inelastic Scattering (DIS) of electron (muon) on fixed-target nuclei. Our model-independent analysis is based on the set of the low-energy effective four-fermion LFV operators composed of leptons and quarks with the corresponding mass scales $\Lambda_{k}$ for each operator. Using the estimated sensitivity of the search for this LFV process in events with large missing energy in the NA64 experiment at the CERN SPS, we derive lower limits for $\Lambda_{k}$ and compared them with the corresponding limits existing in the literature. We show that the DIS $e(\mu)-\tau$ conversion is able to provide a plenty of new limits as yet non-existing in the literature. We also analyzed the energy spectrum of the final-state $\tau$ and discussed viability of the observation of this process in the NA64 experiment and ones akin to it. The case of polarized beams and targets is also discussed., Comment: 18 pages