Limit Of Cross Section Research Articles

Ξ* photoproduction from threshold to W=3.3GeV

The doubly strange Ξ baryons provide an effective way to study a puzzle called the missing-baryons problem where both quark models and lattice gauge theory predict more baryon excited states than are seen experimentally. However, few of these excited states have been observed with any certainty. Here, high-mass Ξ* states have been searched for in photoproduction with the detector of the CLAS Collaboration, and upper limits for the total cross sections have been established from threshold to W=3.3GeV. In addition, the total cross sections of the ground-state Ξ−(1320) and first excited state Ξ−(1530) are presented, extending significantly the center-of-mass energy range of previous data.Received 5 September 2018DOI:https://doi.org/10.1103/PhysRevC.98.062201©2018 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasParticle interactionsPhotonuclear reactionsQCD in nuclear reactionsQuark modelNuclear Physics

Search strategy using LHC pileup interactions as a zero bias sample

Due to a limited bandwidth and a large proton-proton interaction cross section relative to the rate of interesting physics processes, most events produced at the Large Hadron Collider (LHC) are discarded in real time. A sophisticated trigger system must quickly decide which events should be kept and is very efficient for a broad range of processes. However, there are many processes that cannot be accommodated by this trigger system. Furthermore, there may be models of physics beyond the standard model (BSM) constructed after data taking that could have been triggered, but no trigger was implemented at run time. Both of these cases can be covered by exploiting pileup interactions as an effective zero bias sample. At the end of high-luminosity LHC operations, this zero bias dataset will have accumulated about $1\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of data from which a bottom line cross section limit of $\mathcal{O}(1)\text{ }\text{ }\mathrm{fb}$ can be set for BSM models already in the literature and those yet to come.

Search for decays of stopped exotic long-lived particles produced in proton-proton collisions at sqrt{s}=13 TeV

A search is presented for the decays of heavy exotic long-lived particles (LLPs) that are produced in proton-proton collisions at a center-of-mass energy of 13 TeV at the CERN LHC and come to rest in the CMS detector. Their decays would be visible during periods of time well separated from proton-proton collisions. Two decay scenarios of stopped LLPs are explored: a hadronic decay detected in the calorimeter and a decay into muons detected in the muon system. The calorimeter (muon) search covers a period of sensitivity totaling 721 (744) hours in 38.6 (39.0) fb−1 of data collected by the CMS detector in 2015 and 2016. The results are interpreted in several scenarios that predict LLPs. Production cross section limits are set as a function of the mean proper lifetime and the mass of the LLPs, for lifetimes between 100 ns and 10 days. These are the most stringent limits to date on the mass of hadronically decaying stopped LLPs, and this is the first search at the LHC for stopped LLPs that decay to muons.

Ruling out dark matter interpretation of the galactic GeV excess by gamma-ray data of galaxy clusters

Recently, some very tight constraints of annihilating dark matter have been obtained from gamma-ray data of the Milky Way and Milky Way dwarf spheroidal satellite galaxies. In this article, we report that there are two excellent galaxy clusters (A2877 and Fornax) which can provide interesting constraints for annihilating dark matter. The lower limits of the dark matter mass for the thermal relic annihilation cross section are 25 GeV, 6 GeV, 130 GeV and 100 GeV respectively for the e+e−, μ+μ−, τ+τ− and bbar{b} channels. For some configuration of our working assumptions, our results improve the Fermi-LAT upper limits of annihilation cross sections by a factor of 1.3 − 1.8 for wide ranges of dark matter mass for e+e−, μ+μ− and bbar{b} channels, and a factor of 1.2–1.8 for τ+τ− channel with dark matter mass ≤100 GeV. These limits basically rule out most of the existing popular dark matter interpretation of the GeV excess in the Milky Way.

Results from the CMS collaboration on the search of heavy dilepton and diphoton resonances

A survey of the results on the search of new heavy resonances decaying into muon, electron, or photon pairs in the CMS experiment at proton beams of the LHC in the run of 2015 for the total center of mass energy √s = 13 TeV is presented. The limits for heavy resonance production cross sections are set. Excess of diphoton events in the region of mass spectra near 750 GeV with a local statistical significance of 3.4 σ and a global statistical significance of 1.6 σ is observed.

First measurement of coherent double neutral-pion photoproduction on the deuteron at incident energies below 0.9 GeV

The total cross sections were measured for coherent double neutral-pion photoproduction on the deuteron at incident energies below 0.9 GeV for the first time. No clear resonance-like behavior is observed in the excitation function for Wγd=2.38–2.61 GeV, where the d⁎(2380) dibaryon resonance observed at COSY is expected to appear. The measured excitation function is consistent with the existing theoretical calculation for this reaction. The upper limit of the total cross section is found to be 0.034 μb for the dibaryon resonance at Wγd=2.37 GeV (90% confidence level) in the γd→π0π0d reaction.

Search for massive resonances decaying into WW, WZ or ZZ bosons in proton-proton collisions at sqrt{s}=13 TeV

A search is presented for new massive resonances decaying to WW, WZ or ZZ bosons in ell nu qoverline{q} and qoverline{q}qoverline{q} final states. Results are based on data corresponding to an integrated luminosity of 2.3-2.7 fb−1 recorded in proton-proton collisions at sqrt{s}=13 TeV with the CMS detector at the LHC. Decays of spin-1 and spin-2 resonances into two vector bosons are sought in the mass range 0.6-4.0 TeV. No significant excess over the standard model background is observed. Combining the results of the ell nu qoverline{q} and qoverline{q}qoverline{q} final states, cross section and mass exclusion limits are set for models that predict heavy spin-1 and spin-2 resonances. This is the first search for a narrow-width spin-2 resonance at sqrt{s}=13 TeV.

Spin-Dependent Weakly-Interacting-Massive-Particle-Nucleon Cross Section Limits from First Data of PandaX-II Experiment.

New constraints are presented on the spin-dependent weakly-interacting-massive-particle–- (WIMP-)nucleon interaction from the PandaX-II experiment, using a data set corresponding to a total exposure of 3.3×10^{4} kg day. Assuming a standard axial-vector spin-dependent WIMP interaction with ^{129}Xe and ^{131}Xe nuclei, the most stringent upper limits on WIMP-neutron cross sections for WIMPs with masses above 10 GeV/c^{2} are set in all dark matter direct detection experiments. The minimum upper limit of 4.1×10^{-41} cm^{2} at 90%confidence level is obtained for a WIMP mass of 40 GeV/c^{2}. This represents more than a factor of 2 improvement on the best available limits at this and higher masses. These improved cross-section limits provide more stringent constraints on the effective WIMP-proton and WIMP-neutron couplings.

Absorption of a Massive Scalar Field by Wormhole Space-Times

In this paper we consider the problem of the test massive scalar field propagating in the background of a class of wormhole space-times. Basing on the quantum scattering theory, we analyze the Schrodinger-type scalar wave equation and compute transmission coefficients for arbitrary coupling of the field to the background geometry with the WKB approximation. We numerically investigate its absorption cross section and analyze them in the high frequency regime. We find that the absorption cross section oscillates about the geometric optical value and the limit of absorption cross section is uniform in the high frequency regime.

Search for η-mesic [formula omitted] in the [formula omitted] and [formula omitted] reactions with the WASA-at-COSY facility

The search for He4-η bound states was performed with the WASA-at-COSY facility via the measurement of the excitation function for the dd→He3nπ0 and dd→He3pπ− processes. The deuteron beam momentum was varied continuously between 2.127 GeV/c and 2.422 GeV/c, corresponding to the excess energy for the dd→He4η reaction ranging from Q=−70 MeV to Q=30 MeV. The luminosity was determined based on the dd→He3n reaction and the quasi-free proton–proton scattering via dd→ppnspectatornspectator reactions. The excitation functions, determined independently for the measured reactions, do not reveal a structure which could be interpreted as a narrow mesic nucleus. Therefore, the upper limits of the total cross sections for the bound state production and decay in dd→(He4-η)bound→He3nπ0 and dd→(He4-η)bound→He3pπ− processes were determined taking into account the isospin relation between the both of the considered channels. The results of the analysis depend on the assumptions of the N⁎(1535) momentum distribution in the anticipated mesic-He4. Assuming, as in the previous works, that this is identical with the distribution of nucleons bound with 20 MeV in He4, we determined that (for the mesic bound state width in the range from 5 MeV to 50 MeV) the upper limits at 90% confidence level are about 3 nb and about 6 nb for nπ0 and pπ− channels, respectively. However, based on the recent theoretical findings of the N⁎(1535) momentum distribution in the N⁎-He3 nucleus bound by 3.6 MeV, we find that the WASA-at-COSY detector acceptance decreases and hence the corresponding upper limits are 5 nb and 10 nb for nπ0 and pπ− channels respectively.

The origin of the background radioactive isotope 127Xe in the sample of Xe enriched in 124Xe

The results of investigation of 127Xe radioactive isotope production in the xenon sample enriched in 124Xe, 126Xe, 128Xe are presented. The isotope is supposed to be the source of the background events in the low-background experiment on search for 2K-capture of 124Xe. In this work we consider two channels of 127Xe production: the neutron knock-out from 128Xe nucleus by cosmogenic muons and the neutron capture by 126Xe nucleus. For the first channel the upper limit of the cross section of 127Xe production was found to be σ ≤ 0.007 × 10−24 cm2 at 95% C.L. For the second channel the value obtained for the cross section was found to be equal to σ = (2.74 ± 0.4) × 10−24 cm2, which coincides well, within the statistical error, with reference value.

Radiation Hard Contactless Angular Position Sensor Based on Hall Effect

The results of the total ionizing dose (TID) and single event effect (SEE) tests on the contactless angular position sensor based on Hall effect are presented. The TID testing reveals that the devices are resistant to the gamma radiation exhibiting only a slight increase in the supply current, not more than 1 % of the initial values. In general, both the serial peripheral interface (SPI) output errors and analog output errors have recovered to their initial values after annealing at high temperatures. Only the biased sample with magnet showed a significant increase of the analog output error at higher radiation levels and did not return to its initial value, it remained about a 56 % higher. Nevertheless, the error is still within the limits for space application of the sensor. SEE tests were performed up to linear energy transfer (LET) levels of 67.7 MeV $\cdot $ cm2/mg and the sensors experienced neither single event latch-up (SEL) nor single event transient (SET). The upper limit of cross section for single event functional interrupt (SEFI) was found by Weibull fit as being $3.53\cdot 10^{\mathrm {-6}}$ cm2 and the LET threshold was 15.1 MeV $\cdot $ cm2/mg. The SEFI rates were calculated by means of the CREME96 for geostationary orbit (GEO) and the orbit of the International Space Station (ISS). Calculations were performed for minimum solar and peak 5 minutes environment, and in the case of the ISS orbit also trapped particles and magnetic weather conditions were included.

Associated production of a quarkonium and a Z boson at one loop in a quark-hadron-duality approach

In view of the large discrepancy about the associated production of a prompt $J/\psi$ and a $Z$ boson between the ATLAS data at $\sqrt{s}=8$ TeV and theoretical predictions for Single Parton Scattering (SPS) contributions, we perform an evaluation of the corresponding cross section at one loop accuracy (Next-to-Leading Order, NLO) in a quark-hadron-duality approach, also known as the Colour-Evaporation Model (CEM). This work is motivated by (i) the extremely disparate predictions based on the existing NRQCD fits conjugated with the absence of a full NLO NRQCD computation and (ii) the fact that we believe that such an evaluation provides a likely upper limit of the SPS cross section. In addition to these theory improvements, we argue that the ATLAS estimation of the Double Parton Scattering (DPS) yield may be underestimated by a factor as large as 3 which then reduces the size of the SPS yield extracted from the ATLAS data. Our NLO SPS evaluation also allows us to set an upper limit on $\sigma_{\rm eff}$ driving the size of the DPS yield. Overall, the discrepancy between theory and experiment may be smaller than expected, which calls for further analyses by ATLAS and CMS, for which we provide predictions, and for full NLO computations in other models. As an interesting side product of our analysis, we have performed the first NLO computation of $d\sigma / dP_T$ for prompt single-$J/\psi$ production in the CEM from which we have fit the CEM non-pertubative parameter at NLO using the most recent ATLAS data.

Galactic dark matter search via phenomenological astrophysics modeling

Previous searches for the γ-ray signatures of annihilating galactic dark matter used predefined spatial templates to describe the background of γ-ray emission from astrophysical processes like cosmic ray interactions. In this work, we aim to establish an alternative approach, in which the astrophysical components are identified solely by their spectral and morphological properties. To this end, we adopt the recent reconstruction of the diffuse γ-ray sky from Fermi data by the D3PO algorithm and the fact that more than 90% of its flux can be represented by only two spectral components, resulting form the dense and dilute interstellar medium. Under these presumptions, we confirm the reported DM annihilation-like signal in the inner Galaxy and derive upper limits for dark matter annihilation cross sections. We investigate whether the DM signal could be a residual of the simplified modeling of astrophysical emission by inspecting the morphology of the regions, which favor a dark matter component. The central galactic region favors strongest for such a component with the expected spherically symmetric and radially declining profile. However, astrophysical structures, in particular sky regions which seem to host most of the dilute interstellar medium, obviously would benefit from a DM annihilation-like component {as well}. Although these regions do not drive the fit, they warn that a more detailed understanding of astrophysical γ-ray emitting processes in the galactic center region are necessary before definite claims about a DM annihilation signal can be made. The regions off the Galactic plane actually disfavor the best fit DM annihilation cross section from the inner Galactic region unless the radial decline of the Galactic DM density profile in the outer regions is significantly steeper than that usually assumed.

The Limit of the Total Scattering Cross Section of Electrically Large Stirrers in a Reverberation Chamber

The total scattering cross section (TSCS) has been proven to be an effective quantity to characterize the performance of stirrers in a reverberation chamber (RC). It is shown in this letter that the maximum TSCS is a quarter of the stirring surface area, and it is equal to the absorption cross section (ACS) of the same area with perfect radio absorbers. The mathematical proof is presented and measurements are performed to validate this limit. It is also shown that the TSCS and ACS are statistical dual quantities; related dual quantities are also given. The TSCS can be used to characterize how well a stirrer is designed or how close an RC is to a perfect RC.

Search for the production of an excited bottom quark decaying to tW in proton-proton collisions at s = 8 $$ \sqrt{s}=8 $$ TeV

A search is presented for a singly produced excited bottom quark (b*) decaying to a top quark and a W boson in the all-hadronic, lepton + jets, and dilepton final states in proton-proton collisions at sqrt(s) = 8 TeV recorded by the CMS experiment at the CERN LHC. Data corresponding to an integrated luminosity of 19.7 inverse femtobarns are used. No significant excess of events is observed with respect to standard model expectations. We set limits at 95% confidence on the product of the b* quark production cross section and its branching fraction to tW. The cross section limits are interpreted for scenarios including left-handed, right-handed, and vector-like couplings of the b* quark and are presented in the two-dimensional coupling plane based on the production and decay coupling constants. The masses of the left-handed, right-handed, and vector-like b* quark states are excluded at 95% confidence below 1390, 1430, and 1530 GeV, respectively, for benchmark couplings. This analysis gives the most stringent limits on the mass of the b* quark to date.

Searching forη-mesic Helium with WASA-at-COSY facility

The search for the 4 He-η and 3 He-η bound states was performed with the WASA-at-COSY facility using a ramped beam technique in 2008, 2010 and 2014, respectively. The 2008 and 2010 data analyses has already been completed and resulted in the upper limits for the total cross sections for the η -mesic 4 He production in dd → 3 Henπ 0 and dd → 3 Hepπ − processes. No narrow structure which could be interpreted as a bound state was observed. The experiment carried out in 2014 collected the largest data sample for 3 He-η in the world. The data analysis is in progress. This article presents results of the 2010 data analysis and preliminary results of the 2014 data analysis.

Near-threshold charged kaon pair production in two protons collisions

The pp → ppK + K − reaction was measured near threshold at excess energy Q = 4.5 MeV using the COSY-11 detection system installed at the COSY-Juelich accelerator. Preliminary value of upper limit of the total cross section was determined. This limit indicates that an enhancement of the total cross section close to the threshold, caused by the final state interaction, is smaller than suggested by extrapolation of data measured at higher energies.

Upper Limits for the Production of the $\eta $-mesic Helium in the $dd\rightarrow ^{3}$He$n\pi ^0$ and $dd\rightarrow ^3$He$p\pi ^-$ Reactions

We performed a search for 4He-eta bound state in dd -> 3Henpi0 and dd -> 3Heppi- reactions with the WASA-at-COSY facility using a ramped beam technique. The measurement was carried out with high statistics and high acceptance. The signature of eta-mesic nuclei was searched for by the measurement of the excitation functions in the vicinity of the eta production threshold for each of the considered channels. We did not observe the narrow structure which could be interpreted as a bound state. The preliminary upper limits of the total cross sections for the bound state production and decay varies from 21 nb to 36 nb for the dd -> 3Henpi0 channel, and from 5 nb to 9 nb for the dd -> 3Heppi- channel for the bound state width ranging from 5 to 50 MeV.

Nuclear structure aspects of spin-independent WIMP scattering off xenon

We study the structure factors for spin-independent WIMP scattering off xenon based on state-of-the-art large-scale shell-model calculations, which are shown to yield a good spectroscopic description of all experimentally relevant isotopes. Our results are based on the leading scalar one-body currents only. At this level and for the momentum transfers relevant to direct dark matter detection, the structure factors are in very good agreement with the phenomenological Helm form factors used to give experimental limits for WIMP-nucleon cross sections. In contrast to spin-dependent WIMP scattering, the spin-independent channel, at the one-body level, is less sensitive to nuclear structure details. In addition, we explicitly show that the structure factors for inelastic scattering are suppressed by ~ 10^{-4} compared to the coherent elastic scattering response. This implies that the detection of inelastic scattering will be able to discriminate clearly between spin-independent and spin-dependent scattering. Finally, we provide fits for all calculated structure factors.