Complete Photoionization Experiments via Ultrafast Coherent Control with Polarization MultiplexingHockett, P.
doi: 10.1103/PhysRevLett.112.223001pmid: 24949763
Photoelectron angular distributions (PADs) obtained from ionization of potassium atoms using moderately intense femtosecond IR fields ( ∼ 10 12 W cm − 2 ) of various polarization states are shown to provide a route to “complete” photoionization experiments. Ionization occurs by a net three-photon absorption process, driven via the 4 s → 4 p resonance at the one-photon level. A theoretical treatment incorporating the intrapulse electronic dynamics allows for a full set of ionization matrix elements to be extracted from 2D imaging data. 3D PADs generated from the extracted matrix elements are also compared to experimental, tomographically reconstructed, 3D photoelectron distributions, providing a sensitive test of their validity. Finally, application of the determined matrix elements to ionization via more complex, polarization-shaped, pulses is demonstrated, illustrating the utility of this methodology towards detailed understanding of complex ionization control schemes and suggesting the utility of such “multiplexed” intrapulse processes as powerful tools for measurement.
Granular Dynamics During ImpactNordstrom, K. N.; Lim, E.; Harrington, M.; Losert, W.
doi: 10.1103/PhysRevLett.112.228002pmid: 24949789
We study the impact of a projectile onto a bed of 3 mm grains immersed in an index-matched fluid. We vary the amount of prestrain on the sample, strengthening the force chains within the system. We find this affects only the prefactor of the linear depth-dependent term in the stopping force. We propose a simple model to account for the strain dependence of this term, owing to increased pressure in the pile. Interestingly, we find that the presence of the fluid does not affect the impact dynamics, suggesting that dynamic friction is not a factor. Using a laser sheet scanning technique to visualize internal grain motion, we measure the trajectory of each grain throughout an impact. Microscopically, our results indicate that weaker initial force chains result in more irreversible, plastic rearrangements, suggesting static friction between grains does play a substantial role in the energy dissipation.
Longitudinal Coherence in a Holographic Model of Asymmetric CollisionsCasalderrey-Solana, Jorge; Heller, Michal P.; Mateos, David; van der Schee, Wilke
doi: 10.1103/PhysRevLett.112.221602pmid: 24949755
As a model of the longitudinal structure in heavy ion collisions, we simulate gravitational shock wave collisions in anti–de Sitter space in which each shock is composed of multiple constituents. We find that all constituents act coherently, and their separation leaves no imprint on the resulting plasma, when this separation is ≲ 0.26 / T hyd , with T hyd the temperature of the plasma at the time when hydrodynamics first becomes applicable. In particular, the center-of-mass of the plasma coincides with the center-of-mass of all the constituents participating in the collision, as opposed to the center-of-mass of the individual collisions. We discuss the implications for nucleus-nucleus and proton-nucleus collisions.
Value of H 0 in the Inhomogeneous UniverseBen-Dayan, Ido; Durrer, Ruth; Marozzi, Giovanni; Schwarz, Dominik J.
doi: 10.1103/PhysRevLett.112.221301pmid: 24949753
Local measurements of the Hubble expansion rate are affected by structures like galaxy clusters or voids. Here we present a fully relativistic treatment of this effect, studying how clustering modifies the mean distance- (modulus-)redshift relation and its dispersion in a standard cold dark matter universe with a cosmological constant. The best estimates of the local expansion rate stem from supernova observations at small redshifts ( 0.01 < z < 0.1 ). It is interesting to compare these local measurements with global fits to data from cosmic microwave background anisotropies. In particular, we argue that cosmic variance (i.e., the effects of the local structure) is of the same order of magnitude as the current observational errors and must be taken into account in local measurements of the Hubble expansion rate.
Selection Rules for Hadronic Transitions of X Y Z MesonsBraaten, Eric; Langmack, Christian; Smith, D. Hudson
doi: 10.1103/PhysRevLett.112.222001pmid: 24949759
Many of the X Y Z mesons discovered in the last decade can be identified as bound states of a heavy quark and antiquark in Born-Oppenheimer (BO) potentials defined by the energy of gluon and light-quark fields in the presence of static color sources. The mesons include quarkonium hybrids, which are bound states in excited flavor-singlet BO potentials, and quarkonium tetraquarks, which are bound states in BO potentials with light-quark + antiquark flavor. The deepest hybrid potentials are known from lattice QCD calculations. The deepest tetraquark potentials can be inferred from lattice QCD calculations of static adjoint mesons. Selection rules for hadronic transitions are derived and used to identify X Y Z mesons that are candidates for ground-state energy levels in the BO potentials for charmonium hybrids and tetraquarks.