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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Ground-state and isomeric-state cross sections for 181 Ta( n , 2 n ) 180 Ta between 8 and 15 MeV

Using the activation technique, the cross section for the reaction 181 Ta(n,2n) 180g Ta was measured from 8 to 15 MeV in small energy steps to resolve inconsistencies in the existing database. The 93.4 keV γ ray from the decay of the 180g Ta ground state was recorded with a high-purity germanium (HPGe) detector. The monitor reactions 27 Al(n,α) 24 Na and 197 Au(n,2n) 196 Au were used for neutron fluence determination. The ENDF VII.1 and TENDL 2011 evaluations are in considerable disagreement with the present data, which in turn agree very well with the majority of the existing data in the 14 MeV energy region. Furthermore, a detailed analysis using the code TALYS was performed to describe the present data and to predict the (n,2n) cross section to the isomeric state of 180 Ta.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Observation of γ-vibrations and alignments built on non-ground-state configurations in ¹⁵⁶Dy

The exact nature of the lowest K π =2⁺ rotational bands in all deformed nuclei remains obscure. Traditionally they are assumed to be collective vibrations of the nuclear shape in the γ degree of freedom perpendicular to the nuclear symmetry axis. Very few such γ-bands have been traced past the usual back-bending rotational alignments of high-j nucleons. We have investigated the structure of positive-parity bands in the N=90 nucleus ¹⁵⁶Dy, using the ¹⁴⁸Nd(¹²C,4n)¹⁵⁶Dy reaction at 65 MeV, observing the resulting γ-ray transitions with the Gammasphere array. The even- and odd-spin members of the π =2⁺ γ-band are observed to 32⁺ and 31⁺ respectively. This rotational band faithfully tracks the ground-state configuration to the highest spins. The members of a possible γ-vibration built on the aligned yrast S-band are observed to spins 28⁺ and 27⁺. An even-spin positive-parity band, observed to spin 24⁺, is a candidate for an aligned S-band built on the seniority-zero configuration of the 0₂⁺ state at 676 keV. As a result, the crossing of this band with the 0₂⁺ band is at hw c = 0.28(1) MeV and is consistent with the configuration of the 0₂⁺ band not producing any blocking of the monopole pairing.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2019

Search for vectorlike leptons in multilepton final states in proton-proton collisions at s = 13 TeV

A search for vector-like leptons in multilepton final states is presented. The data sample corresponds to an integrated luminosity of 77.4 fb$^{-1}$ of proton-proton collisions at a center-of-mass energy of 13 TeV collected by the CMS experiment at the LHC in 2016 and 2017. Events are categorized by the multiplicity of electrons, muons, and hadronically decaying $\tau$ leptons. The missing transverse momentum and the scalar sum of the lepton transverse momenta are used to distinguish the signal from background. The observed results are consistent with the expectations from the standard model hypothesis. The existence of a vector-like lepton doublet, coupling to the third generation standard model leptons in the mass range of 120-790 GeV, is excluded at 95% confidence level. These are the most stringent limits yet on the production of a vector-like lepton doublet, coupling to the third generation standard model leptons.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Measurement of the asymmetry in angular distributions of leptons produced in dilepton t t ¯ final states in p p ¯ collisions at s = 1.96 TeV

We present measurements of asymmetries in angular distributions of leptons produced in ttbar events in proton-antiproton collisions at the Fermilab Tevatron Collider. We consider final states where the W bosons from top quark and antiquark decays both decay into l nu (l=e, mu) resulting in oppositely charged dilepton final states with accompanying jets. Using 9.7 fb -1 of integrated luminosity collected with the D0 detector, we find the asymmetries in lepton pseudorapidity compatible with predictions based on the standard model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Observation of a new charged charmoniumlike state in B ¯ 0 → J / ψ K – π + decays

We present the results of an amplitude analysis of B¯ 0 → J/ψK – π + decays. A new charged charmoniumlike state Z c (4200) + decaying to J/ψπ + is observed with a significance of 6.2σ. The mass and width of the Z c (4200) + are 4196$^{+31+17}_{–29–13}$ MeV/c 2 and 370$^{+70+70}_{–70–132}$ MeV, respectively; the preferred assignment of the quantum numbers is J P = 1 + . In addition, we find evidence for Z c (4430) + → J/ψπ + . In conclusion, the analysis is based on a 711 fb –1 data sample collected by the Belle detector at the asymmetric-energy e + e – collider KEKB.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Measurement of e + e – → γ χ c J via initial state radiation at Belle

The process e + e – → γχ cJ (J = 1, 2) is studied via initial state radiation using 980 fb –1 of data at and around the Υ(nS) (n = 1, 2, 3, 4, 5) resonances collected with the Belle detector at the KEKB asymmetric-energy e + e – collider. Here, no significant signal is observed except from ψ(2S) decays. Upper limits on the cross sections between √s = 3.80 and 5.56 GeV are determined at the 90% credibility level, which range from a few pb to a few tens of pb. We also set upper limits on the decay rate of the vector charmonium [ψ(4040), ψ(4160), and ψ(4415)] and charmoniumlike [Y(4260), Y(4360), and Y(4660)] states to γχ cJ .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Measurement of initial-state–final-state radiation interference in the processes e + e – → μ + μ – γ and e + e – → π + π – γ [Measurement of ISR-FSR interference in the processes e + e – → μ + μ – γ and e + e – → π + π – γ ]

Charge asymmetry in the processes e + e – → μ + μ – γ and e + e – → π + π – γ is measured using 232 fb –1 of data collected with the BABAR detector at e + e – center-of-mass energies near 10.58 GeV. An observable is introduced and shown to be very robust against detector asymmetries while keeping a large sensitivity to the physical charge asymmetry that results from the interference between initial- and final-state radiation (FSR). The asymmetry is determined as a function of the invariant mass of the final-state tracks from production threshold to a few GeV/c 2 . It is compared to the expectation from QED for e + e – → μ + μ – γ, and from theoretical models for e + e – → π + π – γ. A clear interference pattern is observed in e + e – → π + π – γ, particularly in the vicinity of the f 2 (1270) resonance. As a result, the inferred rate of lowest-order FSR production is consistent with the QED expectation for e + e – → μ + μ – γ, and is negligibly small for e + e – → π + π – γ.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Directional detection of dark matter in universal bound states

It has been suggested that several small-scale structure anomalies in Λ CDM cosmology can be solved by strong self-interaction between dark matter particles. It was shown in Ref. [1] that the presence of a near threshold S-wave resonance can make the scattering cross section at nonrelativistic speeds come close to saturating the unitarity bound. This can result in the formation of a stable bound state of two asymmetric dark matter particles (which we call darkonium). Ref. [2] studied the nuclear recoil energy spectrum in dark matter direct detection experiments due to this incident bound state. Here we study the angular recoil spectrum, and show that it is uniquely determined up to normalization by the S-wave scattering length. Furthermore, observing this angular recoil spectrum in a dark matter directional detection experiment will uniquely determine many of the low-energy properties of dark matter independent of the underlying dark matter microphysics.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Studies of charmed strange baryons in the Λ D final state at Belle

In this report, we discuss the discovery of Ξ c ( 3055 ) 0 , observed by its decay into the final-state Λ D 0 , and present the first observation and evidence of the decays of Ξ c ( 3055 ) + and Ξ c ( 3080 ) + into Λ D + . Furthermore, we perform a combined analysis of the Λ D + with the Σ c + + K - and Σ c * + + K - decay modes to measure the ratios of branching fractions, masses and widths with improved accuracy. We measure the ratios of branching fractions B ( Ξ c ( 3055 ) + → Λ D + ) / B ( Ξ c ( 3055 ) + → Σ c + + K - ) = 5.09 ± 1.01 ± 0.76 , B ( Ξ c ( 3080 ) + → Λ D + ) / B ( Ξ c ( 3080 ) + → Σ c + + K - ) = 1.29 ± 0.30 ± 0.15 , and B ( Ξ c ( 3080 ) + → Σ c * + + K - ) / B ( Ξ c ( 3080 ) + → Σ c + + K - ) = 1.07 ± 0.27 ± 0.04 , where the uncertainties are statistical and systematic. The analysis is performed using a 980 fb - 1 data sample collected with the Belle detector at the KEKB asymmetric-energy e + e - collider.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Measurement of the t t ¯ production cross section in the τ + jets final state in p p collisions at s = 8 TeV using the ATLAS detector

A measurement of the inclusive p p → t $\bar{t}$ + X production cross section in the τ + jets final state using only the hadronic decays of the τ lepton is presented. The measurement is performed using 20.2 fb -1 of proton-proton collision data recorded at a center-of-mass energy of √ s = 8 TeV with the ATLAS detector at the Large Hadron Collider. The cross section is measured via a counting experiment by imposing a set of selection criteria on the identification and kinematic variables of the reconstructed particles and jets, and on event kinematic variables and characteristics. The production cross section is measured to be σ t $\bar{t}$ = 239 ± 29 pb , which is in agreement with the measurements in other final states and the theoretical predictions at this center-of-mass energy.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗