New articles on hep-ex


[1] 2008.05198

All-hadronic HHZ production at 3 TeV CLIC

In this note, $\mathrm{ZHH}$ production in the all-hadronic final state is studied in $\mathrm{e}^{+}\mathrm{e}^{-}$ collisions at the Compact Linear Collider at the 3 TeV stage. At this stage this Higgs boson pair production mode is sub-leading to the $\mathrm{W}^{+}\mathrm{W}^{-}$ fusion production cross-section of $\mathrm{e}^{+}\mathrm{e}^{-}\rightarrow\mathrm{HH}\nu\nu$. The events are characterised by a topology of six jets, where the masses of the three pair-wise combinations of two jets are compatible with originating from two $\mathrm{H}$ and one $\mathrm{Z}$ bosons. The event selection concentrates on the dominant $\mathrm{H}$ boson decays into two b-quarks by requiring a presence of multiple b-jets. The study is based on full simulation using the CLICdet model, including beam-induced backgrounds from $\gamma\gamma\rightarrow\mathrm{hadrons}$. Results on the measurement of the total $\mathrm{ZHH}$ cross section are given.


[2] 2008.05355

Measurement of light-by-light scattering and search for axion-like particles with 2.2 nb$^{-1}$ of Pb+Pb data with the ATLAS detector

This paper describes a measurement of light-by-light scattering based on Pb+Pb collision data recorded by the ATLAS experiment during Run 2 of the LHC. The study uses $2.2$ nb$^{-1}$ of integrated luminosity collected in 2015 and 2018 at $\sqrt{s_\mathrm{NN}}=5.02$ TeV. Light-by-light scattering candidates are selected in events with two photons produced exclusively, each with transverse energy $E_{\mathrm{T}}^{\gamma} > 2.5$ GeV, pseudorapidity $|\eta_{\gamma}| < 2.37$, diphoton invariant mass $m_{\gamma\gamma} > 5$ GeV, and with small diphoton transverse momentum and diphoton acoplanarity. The integrated and differential fiducial cross sections are measured and compared with theoretical predictions. The diphoton invariant mass distribution is used to set limits on the production of axion-like particles. This result provides the most stringent limits to date on axion-like particle production for masses in the range 6-100 GeV. Cross sections above 2 to 70 nb are excluded at the 95% CL in that mass interval.


[3] 2008.05029

Shedding New Light on Sterile Neutrinos from XENON1T Experiment

The XENON1T collaboration recently reported the excess of events from recoil electrons, possibly giving an insight into new area beyond the Standard Model (SM) of particle physics. We try to explain this excess by considering effective interactions between the sterile neutrinos and the SM particles. In this paper, we present an effective model based on one-particle-irreducible interaction vertices at low energies that are induced from the SM gauge symmetric four-fermion operators at high energies. The effective interaction strength is constrained by the SM precision measurements, astrophysical and cosmological observations. We introduce a novel effective electromagnetic interaction between sterile neutrinos and SM neutrinos, which can successfully explain the XENON1T event rate through inelastic scattering of the sterile neutrino dark matter from Xenon electrons. We find that sterile neutrinos with masses around $90$ keV and specific effective coupling can fit well with the XENON1T data where the best fit points preserving DM constraints and possibly describe the anomalies in other experiments.


[4] 2008.05062

Prediction of Tunable Spin-Orbit Gapped Materials for Dark Matter Detection

New ideas for low-mass dark matter direct detection suggest that narrow band gap materials, such as Dirac semiconductors, are sensitive to the absorption of meV dark matter or the scattering of keV dark matter. Here we propose spin-orbit semiconductors - materials whose band gap arises due to spin-orbit coupling - as low-mass dark matter targets owing to their ~10 meV band gaps. We present three material families that are predicted to be spin-orbit semiconductors using Density Functional Theory (DFT), assess their electronic and topological features, and evaluate their use as low-mass dark matter targets. In particular, we find that that the tin pnictide compounds are especially suitable having a tunable range of meV-scale band gaps with anisotropic Fermi velocities allowing directional detection. Finally, we address the pitfalls in the DFT methods that must be considered in the ab initio prediction of narrow-gapped materials, including those close to the topological critical point.


[5] 2008.05080

Sensitivity of direct detection experiments to neutrino magnetic dipole moments

With large active volume sizes dark matter direct detection experiments are sensitive to solar neutrino fluxes. Nuclear recoil signals are induced by $^8$B neutrinos, while electron recoils are mainly generated by the pp flux. Measurements of both processes offer an opportunity to test neutrino properties at low thresholds with fairly low backgrounds. In this paper we study the sensitivity of these experiments to neutrino magnetic dipole moments assuming 1, 10 and 40 tonne active volumes (representative of XENON1T, XENONnT and DARWIN), 0.3 keV and 1 keV thresholds. We show that with nuclear recoil measurements alone a 40 tonne detector could be as competitive as Borexino, TEXONO and GEMMA, with sensitivities of order $8.0\times 10^{-11}\,\mu_B$ at the $90\%$ CL after one year of data taking. Electron recoil measurements will increase sensitivities way below these values allowing to test regions not excluded by astrophysical arguments. Using electron recoil data and depending on performance, the same detector will be able to explore values down to $4.0\times 10^{-12}\mu_B$ at the $90\%$ CL in one year of data taking. By assuming a 200-tonne liquid xenon detector operating during 10 years, we conclude that sensitivities in this type of detectors will be of order $10^{-12}\,\mu_B$. Reducing statistical uncertainties may enable improving sensitivities below these values.


[6] 2008.05208

Charmed and $φ$ meson decay constants from 2+1-flavor lattice QCD

On a lattice with 2+1-flavor dynamical domain-wall fermions at the physical pion mass, we calculate the decay constants of $D_{s}^{(*)}$, $D^{(*)}$ and $\phi$. The lattice size is $48^3\times96$, which corresponds to a spatial extension of $\sim5.5$ fm with the lattice spacing $a\approx 0.114$ fm. For the valence light, strange and charm quarks, we use overlap fermions at several mass points close to their physical values. Our results at the physical point are $f_D=213(5)$ MeV, $f_{D_s}=249(7)$ MeV, $f_{D^*}=234(6)$ MeV, $f_{D_s^*}=274(7)$ MeV, and $f_\phi=241(9)$ MeV. The couplings of $D^*$ and $D_s^*$ to the tensor current ($f_V^T$) can be derived, respectively, from the ratios $f_{D^*}^T/f_{D^*}=0.91(4)$ and $f_{D_s^*}^T/f_{D_s^*}=0.92(4)$, which are the first lattice QCD results. We also obtain the ratios $f_{D^*}/f_D=1.10(3)$ and $f_{D_s^*}/f_{D_s}=1.10(4)$, which reflect the size of heavy quark symmetry breaking in charmed mesons. The ratios $f_{D_s}/f_{D}=1.16(3)$ and $f_{D_s^*}/f_{D^*}=1.17(3)$ can be taken as a measure of SU(3) flavor symmetry breaking.


[7] 2008.05342

Simultaneous extraction of fragmentation functions of light charged hadrons with mass corrections

Achieving the highest possible precision for theoretical predictions at the present and future high-energy lepton and hadron colliders requires a precise determination of fragmentation functions (FFs) of light and heavy charged hadrons from a global QCD analysis with great accuracy. We describe a simultaneous determination of unpolarized FFs of charged pions, charged kaons and protons/antiprotons from single-inclusive hadron production in electron-positron annihilation (SIA) data at next-to-leading order and next-to-next-to-leading order accuracy in perturbative QCD. A new set of FFs, called {\tt SGKS20}, is presented. We include data for identified light charged hadrons ($\pi^\pm, K^\pm$ and $p/\bar{p}$) as well as for unidentified light charged hadrons, $h^\pm$. We examine the inclusion of higher-order perturbative QCD corrections and finite-mass effects. We compare the new {\tt SGKS20} FFs with other recent FFs available in the literature and find in general reasonable agreement, but also important differences for some parton species. We show that theoretical predictions obtained from our new FFs are in very good agreement with the analyzed SIA data, especially at small values of $z$. The {\tt SGKS20} FF sets presented in this work are available via the {\tt LHAPDF} interface.


[8] 2008.05351

Transverse moments of TMD parton densities and ultraviolet divergences

I review some open questions relating to the large transverse momentum divergences in transverse moments of transverse momentum dependent (TMD) parton correlation functions. I also explain, in an abbreviated and summarized form, recent work that shows that the resulting violations of a commonly used integral relation are not perturbatively suppressed. I argue that this implies a need for more precise definitions for the correlation functions used to describe transverse moments.


[9] 2008.05434

Invisible Higgs search through Vector Boson Fusion: A deep learning approach

Vector boson fusion, originally proposed as an alternative channel for finding heavy Higgs, has now established itself as a crucial search scheme to probe different properties of Higgs or for new physics. We explore the merit of deep-learning entirely from the low-level calorimeter data searching for invisibly decaying Higgs, as a choice to supersede decades-old faith on its salient underlying event structure produced in vector boson fusion. We investigate among different neural network architectures considering both low-level and high-level input variables as a detailed comparative analysis. To have a consistent comparison with existing techniques, we closely follow a recent experimental study of CMS search on invisible Higgs with 36 fb$^{-1}$ data. We find that sophisticated deep-learning techniques have the impressive capability to improve the bound on invisible branching ratio by a factor of three, utilising the same amount of data. Without relying on any exclusive event reconstruction, this novel technique can provide the most stringent bounds on the invisible branching ratio of the SM-like Higgs boson. Such an outcome has the ability to constraint many different BSM models severely.


[10] 2008.05467

Interference Effect in LNV and LNC Meson Decays for Left Right Symmetric Model

We study the effect of interference on the lepton number violating~(LNV) and lepton number conserving~(LNC) three-body meson decays $M_1^{+}\to\ell_i^{+}\ell_j^{\pm}\pi^{\mp}$, that arise in a TeV scale Left Right Symmetric model~(LRSM) with nearly degenerate right handed~(RH) neutrinos. LRSM contains three RH neutrinos and a RH gauge boson. The RH neutrinos of masses in the MeV-few GeV range can give resonant enhancement in the semi-leptonic LNV and LNC meson decays. In the case, where only one RH neutrino contributes to these decays, the predicted branching ratio of semi-leptonic LNV and LNC meson decays $M_1^{+}\to\ell_i^{+}\ell_j^{+}\pi^{-}$ and $M_1^{+}\to\ell_i^{+}\ell_j^{-}\pi^{+}$ are the same. However, we find, that with at least two RH neutrinos contributing to the process, the LNV and LNC decay rates can differ. Depending on the RH neutrino mixing angles and $CP$ violating phases, the branching ratios for the decay channels $M_1^{+}\to\ell_i^{+}\ell_j^{+}\pi^{-}$ or $M_1^{+}\to\ell_i^{+}\ell_j^{-}\pi^{+}$ can be either enhanced or suppressed.


[11] 2008.05470

The Sivers Asymmetry in Hadronic Dijet Production

We study the single spin asymmetry in the back-to-back dijet production in transversely polarized proton-proton collisions. Such an asymmetry is generated by the Sivers functions in the incoming polarized proton. We propose a QCD formalism in terms of the transverse momentum dependent parton distribution functions, which allow us to resum the large logarithms that arise in the perturbative calculations. We make predictions for the Sivers asymmetry of hadronic dijet production at the kinematic region that is relevant to the experiment at the Relativistic Heavy Ion Collider~(RHIC). We further compute the spin asymmetries in the selected positive and negative jet charge bins, to separate the contributions from $u$- and $d$-quark Sivers functions. We find that both the sign and size of our numerical results are roughly consistent with the preliminary results from the STAR collaboration at the RHIC.