Limit Of Cross Section Research Articles

Gamma-ray signal from ZN≥3 dark matter-companion models

In Ref. [10], we proposed to replace the final dark matter (DM) particle in the semi-annihilation mode DM+DM→antiDM+Higgs boson with its ZN≥3 companion, thus reducing DM number density without DM-nucleon scattering. In this work, we study the indirect detection signals from DM annihilation, the Higgs boson pair with one of them from the companion decay being on- or off- shell, depending on the DM-companion mass splitting. We generate the photon spectrum by using PYTHIA8 and study the properties of the spectrum, to find that the hard part of the spectrum in our model is mainly shaped by the direct Higgs boson and thus does not differ much from that of the conventional semi-annihilation mode. Using the Fermi-LAT data of dwarf spheroidal galaxies, we derive the current limit of the DM annihilation cross section for DM+DM→companion⁎+Higgs boson, and for the relatively light DM, it reaches the typical thermal cross section. However, for the TeV scale DM, we have to rely on the Cherenkov Telescope Array, which is able to rule out the whole parameter space except for the coannihilation region.

Impact of a nearby subhalo on the constraint of dark matter annihilation from cosmic ray antiprotons* *Supported by the Science & Technology Development Fund of Tianjin Education Commission for Higher Education (2020KJ003).

Numerous simulations indicate that a large number of subhalos should be hosted by the Milky Way. The potential existence of a nearby subhalo could have important implications for our understanding of dark matter (DM) annihilation. In this study, we investigate the hypothetical presence of a nearby subhalo and set the upper limits on the DM annihilation cross section by analyzing the cosmic-ray antiproton spectrum. By presenting the ratios of annihilation cross section limits for scenarios with and without a nearby subhalo, we can quantitatively evaluate the potential impact of the nearby subhalo on the limits of the DM annihilation cross section. The impacts of the concentration model and the subhalo probability distribution have been considered. We explore the antiproton contribution of the potential nearby DM subhalo accounting for the DAMPE spectrum at TeV and find that the current AMS-02 antiproton results do not limit this contribution.

Anisotropic flow and the valence quark skeleton of hadrons

We study transverse momentum anisotropies, in particular, the elliptic flow v2 due to the interference effect sourced by valence quarks in high-energy hadron-hadron collisions. Our main formula is derived as the high-energy (eikonal) limit of the impact-parameter dependent cross section in quantum field theory, which agrees with that in terms of the impact parameter in the classical picture. As a quantitative assessment of the interference effect, we calculate v2 in the azimuthal distribution of gluons at a comprehensive coverage of the impact parameter and the transverse momentum in high-energy pion-pion collisions. In a broad range of the impact parameter, a sizable amount of v2, comparable with that produced due to saturated dense gluons or final-state interactions, is found to develop. This is in contrast with similar studies in heavy-ion collisions using classical color charge distributions in which such a contribution from geometric correlations was found to be small and has, hence, been ignored in recent studies. In our calculations, the valence sector of the pion wave function is obtained numerically from the Basis Light-Front Quantization, a non-perturbative light-front Hamiltonian approach. And our formalism is generic and can be applied to other small collision systems like proton-proton collisions.

Search for the double-charmonium state with ηcJ/ψ at Belle

We measure the cross section of e+e− → ηcJ/ψ at the Υ(nS)(n = 1–5) on-resonance and 10.52 GeV off-resonance energy points using the full data sample collected by the Belle detector with an integrated luminosity of 955 fb−1. We also search for double charmonium production in e+e− → ηcJ/ψ via initial state radiation near the ηcJ/ψ threshold. No evident signal of the double charmonium state is found, but evidence for the e+e−→ ηcJ/ψ process is found with a statistical significance greater than 3.3σ near the ηcJ/ψ threshold. The average cross section near the threshold is measured and upper limits of cross sections are set for other regions.

Weakly interacting massive particle cross section limits from LOFAR observations of dwarf spheroidal galaxies

Context. Weakly interacting massive particles (WIMPs) can self-annihilate, thus providing us with a way to indirectly detect dark matter (DM). Dwarf spheroidal (dSph) galaxies are excellent places to search for annihilation signals because they are rich in DM and background emission is low. If O(0.1–10 μG) magnetic fields in dSph galaxies exist, the particles produced in DM annihilation emit synchrotron radiation in the radio band. Aims. We used the non-detection of 150 MHz radio continuum emission from dSph galaxies with the LOw Frequency ARray (LOFAR) to derive constraints on the annihilation cross section of WIMPs in electron–positron pairs. Our main underlying assumption is that the transport of the cosmic rays can be described by the diffusion approximation, which necessitates the existence of magnetic fields. Methods. We used observations of six dSph galaxies in the LOFAR Two-metre Sky Survey (LoTSS). The data were reimaged, and a radial profile was generated for each galaxy. We also used stacking to increase the sensitivity. In order to derive upper limits on the WIMP cross section, we injected fake Gaussian sources into the data, which were then detected with 2σ significance in the radial profile. These sources represent the lowest emission we would have been able to detect. Results. We present limits from the observations of individual galaxies as well as from stacking. We explored the uncertainty due to the choice of diffusion and magnetic field parameters by constructing three different model scenarios: optimistic (OPT), intermediate (INT), and pessimistic (PES). Assuming monochromatic annihilation into electron–positron pairs, the limits from the INT scenario exclude thermal WIMPs (⟨σv⟩≈2.2 × 10−26 cm3 s−1) below 20 GeV, and the limits from the OPT scenario even exclude thermal WIMPs below 70 GeV. The INT limits can compete with limits set by Fermi-LAT using γ-ray observations of multiple dwarf galaxies, and they are especially strong for low WIMP masses.

Electron-impact ionization of the 4p6 subshell in strontium

Electron-impact ionization of the 4p6 subshell in Sr atoms has been studied by observing the excitation dynamics of the electron spectra arising from the Auger decay of the 4p states. The measurements were carried out in the energy range of incident electrons from the 4p6 ionization threshold at 26.92 to 600 eV. At near-threshold impact energies, the effect of post-collision interaction was found for most of the Auger lines. The identification of 21 lines observed between 10 and 14 eV electron energy showed that the 4p6 Auger spectrum of Sr atoms is completely described by the configurations 4p54d5s, 4p55s2 and 4p54d2. The cross sections for the lowest quartet and doublet states in 4p54d5s and 4p55s2 configurations have been obtained with the maximum values of ( cm2 at 52 eV for the (4p54d5s)4P state and ( cm2 at 112 eV for the (4p55s2)2P state. Configuration interaction and excitation-autoionization processes determine the energy behavior of the excitation cross sections of doublet states. The lower limit of the total ionization cross section of the 4p6 subshell in Sr has been obtained with the maximum value of ( cm2 at 92 eV.

Exotic Dark Matter Search with the CDEX-10 Experiment at China’s Jinping Underground Laboratory

A search for exotic dark matter (DM) in the sub-GeV mass range has been conducted using 205kg day data taken from a p-type point contact germanium detector of the CDEX-10 experiment at China's Jinping underground laboratory. New low-mass dark matter searching channels, neutral current fermionic DM absorption (χ+A→ν+A) and DM-nucleus 3→2 scattering (χ+χ+A→ϕ+A), have been analyzed with an energy threshold of 160eVee. No significant signal was found; thus new limits on the DM-nucleon interaction cross section are set for both models at the sub-GeV DM mass region. A cross section limit for the fermionic DM absorption is set to be 2.5×10^{-46} cm^{2} (90%C.L.) at DM mass of 10 MeV/c^{2}. For the DM-nucleus 3→2 scattering scenario, limits are extended to DM mass of 5 and 14 MeV/c^{2} for the massless dark photon and bound DM final state, respectively.

Direct Observation and Quantitative Measurement of OH Radical Desorption During the Ultraviolet Photolysis of Liquid Nonanoic Acid.

Ultraviolet (UV) photolysis of fatty acid surfactants─which cover the surfaces of atmospheric liquid aerosols and are found in the oceans─such as nonanoic acid (NA) has recently been suggested as a source of hydroxyl (OH) radicals in the troposphere. We used laser-induced fluorescence to directly observe OH radicals desorbed from the surface of neat liquid NA as a primary photoproduct following 213 nm irradiation. The upper limit of photoreaction cross section for the OH radical desorption was estimated to be 9.0(4.1) × 10-22 cm2, which is only 1.2 ± 0.8% of the photoreaction cross section established for the photolysis of gas-phase acetic acid monomers. Vibrational sum-frequency generation spectroscopy for liquid NA revealed the hydrogen-bonded, cyclic, dimer structure of the NA molecules at the liquid surface. This dimerization can inhibit the formation of OH radicals and lead the present low photochemical reactivity of liquid NA.

Searches for invisible scalar decays at CLIC

The Compact Linear Collider (CLIC) is a proposed TeV-scale high-luminosity electron-positron collider at CERN. The first CLIC running stage, at 380 GeV, will focus on precision Higgs boson and top quark studies while the main aim of the subsequent high-energy stages, at 1.5 TeV and 3 TeV, is to extend the sensitivity of CLIC to different Beyond the Standard Model (BSM) scenarios. We studied the prospects for measuring invisible Higgs boson and additional heavy scalar decays using CLIC data at 380 GeV and 1.5 TeV. The analysis is based on the Whizard event generator, with fast simulation of the CLIC detector response parametrised by the Delphes package. We present the expected limits for the invisible decays of the 125 GeV Higgs boson, the cross section limits for production of an additional neutral Higgs scalar, assuming its invisible decays, and limits on the mixing angle between the SM-like Higgs boson and the new scalar of the "dark sector" in the framework of the vector-fermion dark matter model.

Limiting capabilities of two-dimensional plasmonics in electromagnetic wave detection

Plasmons in two-dimensional electron systems (2DESs) feature ultrastrong confinement and are expected to efficiently mediate the interactions between light and charge carriers. Despite these expectations, the electromagnetic detectors exploiting 2D plasmon resonance have been so far inferior to their nonresonant counterparts. Here, we theoretically analyze the origin of these failures, and suggest a proper niche for 2D plasmonics in electromagnetic wave detection. We find that a confined 2DES supporting plasmon resonance has an upper limit of absorption cross section, which is identical to that of simple metallic dipole antenna. Small size of plasmonic resonators implies their weak dipole moments and impeded coupling to free-space radiation. Achieving the ``dipole limit'' of the absorption cross section in isolated 2DES is possible either at unrealistically long carrier momentum relaxation times, or at resonant frequencies below units of terahertz. We further show that amendment of even small metal contacts to 2DES promotes the coupling and reduces the fundamental mode frequency. The contacted resonators can still have deep-subwavelength size. They can be merged into compact arrays of detectors responding resonantly to multiple frequencies. Such arrays may find applications in multichannel wireless communications, hyper-spectral imaging, and energy harvesting.

Quantitative Determination of the Complex Polarizability of Individual Nanoparticles by Scanning Cavity Microscopy

The complex polarizability describes the complete optical properties of a nanoobject in the Rayleigh limit, including its absorption, scattering, and dispersion. A large range of applications would benefit from the capability to infer the polarizability on a single-particle level; however, it requires two complementary measurements to fully determine this quantity, and the smallness of the signals makes this highly challenging. Here we use signal enhancement in a tunable high finesse fiber cavity and apply noise-rejecting differential measurement techniques to simultaneously obtain the extinction cross section and the dispersion of individual gold nanospheres, which allows us to quantitatively obtain the real and imaginary part of the polarizability with high precision. We achieve a detection limit for extinction cross sections of 1.8 nm2 and for the polarizability of α/ϵ0 = (28 000 + 200i) nm3. Our method opens the way to a full characterization of the optical properties of individual nanosystems, with applications ranging from nanomaterial science to biology.

Sensitivity to invisible scalar decays at CLIC

We studied the possibility of constraining production of new scalar particles at CLIC running at 380 GeV and 1.5 TeV, assuming the associated production of Higgs-like neutral scalar with mathrm{Z}{}{} boson and its invisible decays. The analysis is based on the Whizard event generation and fast simulation of the CLIC detector response with Delphes. We considered {mathrm{e}{}{}}^{+} {mathrm{e}{}{}}^{-} background processes but also relevant upgamma {}{} upgamma {}{} and upgamma {}{} mathrm{e}{}{} ^{pm } interactions. The approach consisting of a two-step analysis was used to optimise separation between signal and background processes. First, a set of preselection cuts was applied; then, multivariate analysis methods were employed to optimise the significance of observations. We first estimated the expected limits on the invisible decays of the 125 GeV Higgs boson, which were then extended to the cross section limits for production of an additional neutral scalar, assuming its invisible decays, as a function of its mass. Extracted model-independent branching ratio and cross section limits were then interpreted in the framework of the Higgs-portal models to set limits on the mixing angle between the SM-like Higgs boson and the new scalar of the “dark sector”.

Determination of the absorption cross sections of higher-order iodine oxides at 355 and 532 nm

Abstract. Iodine oxides (IxOy) play an important role in the atmospheric chemistry of iodine. They are initiators of new particle formation events in the coastal and polar boundary layers and act as iodine reservoirs in tropospheric ozone-depleting chemical cycles. Despite the importance of the aforementioned processes, the photochemistry of these molecules has not been studied in detail previously. Here, we report the first determination of the absorption cross sections of IxOy, x=2, 3, 5, y=1–12 at λ=355 nm by combining pulsed laser photolysis of I2∕O3 gas mixtures in air with time-resolved photo-ionization time-of-flight mass spectrometry, using NO2 actinometry for signal calibration. The oxides selected for absorption cross-section determinations are those presenting the strongest signals in the mass spectra, where signals containing four iodine atoms are absent. The method is validated by measuring the absorption cross section of IO at 355 nm, σ355nm,IO= (1.2±0.1) ×10-18 cm2, which is found to be in good agreement with the most recent literature. The results obtained are σ355nm,I2O3<5×10-19 cm2 molec.−1, σ355nm,I2O4= (3.9±1.2)×10-18 cm2 molec.−1, σ355nm,I3O6= (6.1±1.6)×10-18 cm2 molec.−1, σ355nm,I3O7= (5.3±1.4)×10-18 cm2 molec.−1, and σ355nm,I5O12= (9.8±1.0)×10-18 cm2 molec.−1. Photodepletion at λ=532 nm was only observed for OIO, which enabled determination of upper limits for the absorption cross sections of IxOy at 532 nm using OIO as an actinometer. These measurements are supplemented with ab initio calculations of electronic spectra in order to estimate atmospheric photolysis rates J(IxOy). Our results confirm a high J(IxOy) scenario where IxOy is efficiently removed during daytime, implying enhanced iodine-driven ozone depletion and hindering iodine particle formation. Possible I2O3 and I2O4 photolysis products are discussed, including IO3, which may be a precursor to iodic acid (HIO3) in the presence of HO2.

Photoproduction of three jets in the CGC: gluon TMDs and dilute limit

We study the process γA → qoverline{q}g + X in the Color Glass Condensate (CGC) effective theory. After obtaining the cross section, we consider two kinematic limits which are encompassed in our result. In the so-called correlation limit, the vector sum of the transverse momenta of the three outgoing particles is small with respect to the individual transverse momenta; the cross section then simplifies considerably and can be written in a factorized form, sensitive to both the unpolarized and linearly-polarized Weizsäcker-Williams transverse momentum dependent gluon distribution function (gluon TMD). The second limit of the CGC cross section that we consider is the dilute limit, which we obtain after performing a weak-field expansion; we recover a typical linear-regime expression, involving a single unintegrated gluon distribution function. Using numerical simulations of the small-x QCD evolution of the TMDs, we investigate the rapidity dependence of the cross section in the correlation limit.

Search for η^{'} Bound Nuclei in the ^{12}C(γ,p) Reaction with Simultaneous Detection of Decay Products.

We measured missing mass spectrum of the ^{12}C(γ,p) reaction for the first time in coincidence with potential decay products from η^{'} bound nuclei. We tagged an (η+p) pair associated with the η^{'}N→ηN process in a nucleus. After applying kinematical selections to reduce backgrounds, no signal events were observed in the bound-state region. An upper limit of the signal cross section in the opening angle cosθ_{lab}^{ηp}<-0.9 was obtained to be 2.2 nb/sr at the 90%confidence level. It is compared with theoretical cross sections, whose normalization ambiguity is suppressed by measuring a quasifree η^{'} production rate. Our results indicate a small branching fraction of the η^{'}N→ηN process and/or a shallow η^{'}-nucleus potential.

Tip-Enhanced Infrared Imaging with Sub-10 nm Resolution and Hypersensitivity.

Here we demonstrate sub-10 nm spatial resolution sampling of a volume of ∼360 molecules with a strong field enhancement at the sample-tip junction by implementing noble metal substrates (Au, Ag, Pt) in photoinduced force microscopy (PiFM). This technique shows the versatility and robustness of PiFM and is promising for application in interfacial studies with hypersensitivity and super spatial resolution.

Annual modulation search by XMASS-I with 2.7 years of data

In this work, we conducted annual modulation search for dark matter with 2.7 years of data taking with the XMASS-I detector. A total exposure was 800 live days times 832 kg. When we assume Weakly Interacting Massive Particle (WIMP) dark matter elastically scattering on the xenon target, the exclusion upper limit of the WIMP-nucleon cross section was 1.9×10−41cm2 at 8 GeV/c2. For model independent case, without assuming any specific dark matter model, we did not find any modulation signal with a p-value of 0.11 in the 1-20 keV energy region for the null hypothesis.

Search for α decay of Te104 with a novel recoil-decay scintillation detector

A search for superallowed α decay of N=Z nuclei Te104 and Xe108 was carried out using a novel recoil-decay scintillator detector at the tandem accelerator facility at the Japan Atomic Energy Agency (JAEA). Inorganic crystal scintillation material YAP:Ce (yttrium aluminum perovskite) coupled to a position-sensitive photomultiplier tube (PSPMT) was implemented for the first time in a radioactive decay experiment. Residues from the fusion-evaporation reaction Ni58+Fe54→Xe∗112 were separated by the JAEA Recoil Mass Separator (RMS) and implanted into the YAP:Ce crystal. α decays of neutron-deficient tellurium isotopes were identified and proton emission of I109 was observed. The α-decay chain Xe109→Te105→Sn101 was recorded with a time interval of 960 ns between two α pulses. Position localization in the crystal for decays and ions in the energy range from hundreds of keV to 60 MeV was achieved with an accuracy of 0.67 mm, proving that this detector is capable of making temporal and spatial correlations for fast decay events. No conclusive evidence was found for the decay chain Xe108→Te104→Sn100 within 3 days of experiment. However, two events were observed with properties consistent with the reported observation at the Fragment Mass Analyzer (FMA), but with a separation between signals of less than 4 ns. The cross section limit of 130 pb was obtained for production of two events of Xe108, about an order of magnitude below the expectation based on earlier cross section measurements and the hivap fusion-evaporation code.

Search for supersymmetry in final states with photons and missing transverse momentum in proton-proton collisions at 13 TeV

Results are reported of a search for supersymmetry in final states with photons and missing transverse momentum in proton-proton collisions at the LHC. The data sample corresponds to an integrated luminosity of 35.9 fb−1 collected at a center-of-mass energy of 13 TeV using the CMS detector. The results are interpreted in the context of models of gauge-mediated supersymmetry breaking. Production cross section limits are set on gluino and squark pair production in this framework. Gluino masses below 1.86 TeV and squark masses below 1.59 TeV are excluded at 95% confidence level.

Search for resonant production of second-generation sleptons with same-sign dimuon events in proton\u2013proton collisions at sqrt{s} = 13,text {TeV}

A search is presented for resonant production of second-generation sleptons (widetilde{mu } _{mathrm {L}}, widetilde{nu }_{mu }) via the R-parity-violating coupling {lambda ^{prime }_{211}} to quarks, in events with two same-sign muons and at least two jets in the final state. The smuon (muon sneutrino) is expected to decay into a muon and a neutralino (chargino), which will then decay into a second muon and at least two jets. The analysis is based on the 2016 data set of proton-proton collisions at sqrt{s}=13,text {TeV} recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 35.9,text {fb}^{-1}. No significant deviation is observed with respect to standard model expectations. Upper limits on cross sections, ranging from 0.24 to 730,text {fb}, are derived in the context of two simplified models representing the dominant signal contributions leading to a same-sign muon pair. The cross section limits are translated into coupling limits for a modified constrained minimal supersymmetric model with {lambda ^{prime }_{211}} as the only nonzero R-parity violating coupling. The results significantly extend restrictions of the parameter space compared with previous searches for similar models.