Search results for "coupling constant"
showing 10 items of 262 documents
Measurement of proton and nitrogen polarization in ammonia and a test of equal spin temperature
1998
The 1996 data taking of the SMC experiment used polarized protons to measure the spin-dependent structure function g(1) of the proton. Three liters of solid granular ammonia were irradiated at the Bonn electron linac in order to create the paramagnetic radicals which are needed for polarizing the protons. Proton polarizations of +/- (90 +/- 2.5)% were routinely reached. An analysis based on a theoretical line shape for spin-1. systems with large quadrupolar broadening was developed which allowed the nitrogen polarization in the ammonia to be determined with a 10% relative error. The measured quadrupolar coupling constant of N-14 agrees well with earlier extrapolated values. The polarization…
Absorptive effects inK+Λphotoproduction on nucleons and nuclei
1989
Incorporating final state correlation effects, we have reinvestigated the ..gamma.. /sup 1/H..-->..K/sup +/..lambda.. elementary process. Our model not only resolves the persisting trouble of the small KN..lambda.. coupling constant, but also yields agreement with cross section data at higher energies. Using our amplitudes, we calculate angular distributions for the reaction /sup 16/O(..gamma..,K/sup +/)/sub ..lambda..//sup 16/N . While the forward cross section increases with increasing energy, the total cross section is almost constant from E/sub ..gamma../ = 1.2 GeV through 2 GeV, suggesting that rather low photon energies hold promise for exploration of hypernuclear excitations.
Probing the quenching of gA by single and double beta decays
2013
Abstract Ground-state-to-ground-state two-neutrino double beta ( 2 ν β β ) decays and single beta (EC and β − ) decays are studied for the A = 100 (100Mo 100Tc 100Ru), A = 116 (116Cd 116In 116Sn) and A = 128 (128Te 128I 128Xe) nuclear systems by using the proton–neutron quasiparticle random-phase approximation exploiting realistic effective interactions in very large single-particle bases. The aim of this exercise is to see if both the single-beta and double-beta decay observables related to the ground states of the initial, intermediate and final nuclei participant in the decays can be described simultaneously by changing the value of the axial-vector coupling constant g A . In spite of th…
Commutators of second-class axial currents with normal weak currents and consequences for particle decays
1981
Second-class weak axial currents are studied in the framework of normal weak and electromagnetic currents. Equal time commutators between normal and abnormal axial currents and the isoscalar electromagnetic current are postulated and their consequences are worked out. A number of predictions for masses, coupling constants and decay properties are derived and are compared to available data.
A model for dark matter, naturalness and a complete gauge unification
2015
We consider dark matter in a minimal extension of the Standard Model (SM) which breaks electroweak symmetry dynamically and leads to a complete unification of the SM and technicolor coupling constants. The unification scale is determined to be $M_{\rm U} \approx 2.2 \times 10^{15}$ GeV and the unified coupling $\alpha_{\rm U} \approx 0.0304$. Moreover, unification strongly suggest that the technicolor sector of the model must become strong at the scale of ${\cal O}$(TeV). The model also contains a tightly constrained sector of mixing neutral fields stabilized by a discrete symmetry. We find the lightest of these states can be DM with a mass in the range $m_{\rm DM} \approx 30-800$ GeV. We f…
Lattice Calculation of the Decay of Primordial Higgs Condensate
2015
We study the resonant decay of the primordial Standard Model Higgs condensate after inflation into $SU(2)$ gauge bosons on the lattice. We find that the non-Abelian interactions between the gauge bosons quickly extend the momentum distribution towards high values, efficiently destroying the condensate after the onset of backreaction. For the inflationary scale $H = 10^8$ GeV, we find that 90% of the Higgs condensate has decayed after $n \sim 10$ oscillation cycles. This differs significantly from the Abelian case where, given the same coupling strengths, most of the condensate would persist after the resonance.
Hadronic τ Decays as New Physics Probes in the LHC Era
2019
We analyze the sensitivity of hadronic tau decays to non-standard interactions within the model-independent framework of the Standard Model Effective Field Theory (SMEFT). Both exclusive and inclusive decays are studied, using the latest lattice data and QCD dispersion relations. We show that there are enough theoretically clean channels to disentangle all the effective couplings contributing to these decays, with the $\tau \to \pi\pi\nu_\tau$ channel representing an unexpected powerful New Physics probe. We find that the ratios of non-standard couplings to the Fermi constant are bound at the sub-percent level. These bounds are complementary to the ones from electroweak precision observable…
Isolated photon production in proton-nucleus collisions at forward rapidity
2018
We calculate isolated photon production at forward rapidities in proton-nucleus collisions in the Color Glass Condensate framework. Our calculation uses dipole cross sections solved from the running coupling Balitsky-Kovchegov equation with an initial condition fit to deep inelastic scattering data. For comparison, we also update the results for the nuclear modification factor for pion production in the same kinematics. We present predictions for future forward RHIC and LHC measurements at $\sqrt{s_{NN}}=200$ GeV and $\sqrt{s_{NN}}=8$ TeV.
Unraveling exciton dynamics in amorphous silicon dioxide: Interpretation of the optical features from 8 to 11 eV.
2011
Physical review / B 83, 174201 (2011). doi:10.1103/PhysRevB.83.174201
From correlation-consistent to polarization-consistent basis sets estimation of NMR spin–spin coupling constant in the B3LYP Kohn–Sham basis set limit
2008
Abstract Based on B3LYP spin–spin coupling constants (SSCC) of several molecules calculated with cc-pV x Z, cc-pCV x Z, cc-pCV x Z-sd and cc-pCV x Z-sd+ t basis sets, a reasonably fit, using the two-parameter formula, to the Kohn–Sham complete basis set limit (CBS) is shown. Improvement in the CBS values going from cc-pV x Z to the most elaborated cc-pCV x Z-sd+ t basis set family is observed: standard deviation for all data drops from 33.7 to 23.1, and from 6.0 to 4.8 Hz after excluding problematic 1 J (F,H) and 1 J (F,C). Calculation of water’s 1 J (OH) using B3LYP/cc-pCV x Z and B3LYP/pcJ- n significantly improved the FC term convergence.