Large Recoil Research Articles

Transformation of the multipolar components of gravitational radiation under rotations and boosts

We study the transformation of multipolar decompositions of gravitational radiation under rotations and boosts. Rotations to the remnant black hole's frame simplify the waveforms from the merger of generic spinning black hole binaries. Boosts may be important to get an accurate gravitational-wave phasing, especially for configurations leading to large recoil velocities of the remnant. As a test of the formalism we revisit the classic problem of point particles falling into a Schwarzschild black hole. Then we highlight by specific examples the importance of choosing the right frame in numerical simulations of unequal mass, spinning binary black-hole mergers.

CP asymmetries in B̄ → K̄*( → K̄π)l̄land untagged B̄s,Bs→ ϕ( →K+K−)l̄ldecays at NLO

The decay → *( → π)l offers great opportunities to explore the physics at and above the electroweak scale by means of an angular analysis. We investigate the physics potential of the seven CP asymmetries plus the asymmetry in the rate, working at low dilepton mass using QCD factorization at next-to leading order (NLO). The b → s CP asymmetries are doubly Cabibbo-suppressed ≲1% in the Standard Model and its extensions where the CKM matrix is the only source of CP violation. Three CP asymmetries are T-odd, and can be (1) in the presence of non-standard CP violation. The T-even asymmetries can reach (0.1), limited by the small strong phases in the large recoil region. We furthermore point out an easy way to measure CP phases from time-integrated, untagged d, Bd → K*( → K0π0)l and s, Bs → ϕ( → K+K−)l decays. Analyses of these CP asymmetries can rule out, or further support the minimal description of CP violation through the CKM mechanism. Experimental studies are promising for (super) flavor factories and at hadron colliders.

A Simply Modified Single Pole Scenario For B → K* Form Factors

We revisit the form factors of B → K* by using the heavy quark limit and large energy limit, assuming that the form factors have single pole forms near the zero recoil. The deviation from the single pole model is taken into account by adding a term proportional to (v·v′-1)2. On the other hand, we require the form factors to obey the large recoil symmetry relationships when v · v′ becomes very large. A self-consistent set of B → K* form factors is found. This set of form factors is checked to be consistent with the experimental data about B → K*ll modes.

Further insight into gravitational recoil

We test the accuracy of our recently proposed empirical formula to model the recoil velocity imparted to the merger remnant of spinning, unequal-mass black-hole binaries. We study three families of black-hole binary configurations, all with mass ratio $q=3/8$ (to nearly maximize the unequal-mass contribution to the kick) and spins aligned (or counter-aligned) with the orbital angular momentum, two with spin configurations chosen to minimize the spin-induced tangential and radial accelerations of the trajectories, respectively, and a third family where the trajectories are significantly altered by spin-orbit coupling. We find good agreement between the measured and predicted recoil velocities for the first two families, and reasonable agreement for the third. We also reexamine our original generic binary configuration that led to the discovery of extremely large spin-driven recoil velocities and inspired our empirical formula, and find rough agreement between the predicted and measured recoil speeds.

SCET sum rules forB→PandB→Vtransition form factors

We investigate sum rules for heavy-to-light transition form factors at large recoil derived from correlation functions with interpolating currents for light pseudoscalar or vector fields in soft-collinear effective theory (SCET). We consider both, factorizable and nonfactorizable contributions at leading power in the {Lambda}/m{sub b} expansion and to first order in the strong coupling constant {alpha}{sub s}, neglecting contributions from 3-particle distribution amplitudes in the B-meson. We pay particular attention to various sources of parametric and systematic uncertainties. We also discuss certain form factor ratios where part of the hadronic uncertainties related to the B-meson distribution amplitude and to logarithmically enhanced {alpha}{sub s} corrections cancel.

B → K Transition Form Factor with Tensor Current within the kTFactorization Approach

We apply the kT factorization approach to deal with the B → K transition form factor with tensor current in the large recoil regions. Main uncertainties for the estimation are discussed and we obtain FTB→K(0) = 0.25 ± 0.01 ± 0.02, where the first error is caused by the uncertainties from the pionic wavefunctions and the second is from that of the B-meson wavefunctions. This result is consistent with the light-cone sum rule results obtained in the literature.

Angular distributions of B̄ →Kl̄ldecays

We model-independently analyze the angular distributions of → Kl decays, l = e,μ, for low dilepton mass using QCD factorization. Besides the decay rate, we study the forward-backward asymmetry AlFB and a further observable, FlH, which gives rise to a flat term in the angular distribution. We find that in the Standard Model FlH∝ml2, hence vanishing FeH and FμH of around 2% (exact value depends on cuts) with a very small theoretical uncertainty of a few percent. We also give predictions for RK, the ratio of → Kμ to → Kēe decay rates. We analytically show using large recoil symmetry relations that in the Standard Model RK equals one up to lepton mass corrections of the order 10−4 including αs and subleading 1/E power corrections. The New Physics reach of the observables from the → Kl angular analysis is explored together with RK and the s → l and → Xsl branching ratios for both l = e and l = μ. We find substantial room for signals from (pseudo-) scalar and tensor interactions beyond the Standard Model. Experimental investigations of the → Kμ angular distributions are suitable for the LHC environment and high luminosity B factories, where also studies of the electron modes are promising.

B→K transition form factor up to $\mathcal{O}(1/m^2_b)$ within the kT factorization approach

We apply the k(T) factorization approach to deal with the B-->K transition form factor F-+,0(B-->K) (q(2)) in the large recoil regions. The B-meson wave functions Psi(B) and Psi(B) that include the 3-particle Fock states' contributions are adopted to give a consistent PQCD analysis of the form factor up to O(1/m(b)(2)). It has been found that the two wave functions Psi(B) and Psi(B) can give sizable contributions to the form factor and should be kept for a better understanding of the B-meson decays. Next the contributions from different twist structures of the kaon wave function are discussed, including SUf(3)-breaking effects. A sizable contribution from the twist-3 wave function Psi(p) is found, whose model dependence is discussed by taking two groups of parameters that are determined by different distribution amplitude moments obtained in the literature. It is also shown that F-+,0(B-->K) (0) = 0.30 +/- 0.04 and [F-+,0(B-->K) (0)/F-+,0(B-->pi) (0)] = 1.13 +/- 0.02, which are more reasonable and consistent with the light-cone sum rule results in the large recoil regions.

Retaining Black Holes with Very Large Recoil Velocities

Recent numerical simulations of binary black hole mergers show the possibility of producing very large recoil velocities (> 3000 km/s). Kicks of this magnitude should be sufficient to eject the final black hole from virtually any galactic potential. This result has been seen as a potential contradiction with observations of supermassive black holes residing in the centers of most galaxies in the local universe. Using an extremely simplified merger tree model, we show that, even in the limit of very large ejection probability, after a small number of merger generations there should still be an appreciable fraction (>50%) of galaxies with supermassive black holes today. We go on to argue that the inclusion of more realistic physics ingredients in the merger model should systematically increase this retention fraction, helping to resolve a potential conflict between theory and observation. Lastly, we develop a more realistic Monte Carlo model to confirm the qualitative arguments and estimate occupation fractions as a function of the central galactic velocity dispersion.

Large Merger Recoils and Spin Flips from Generic Black Hole Binaries

We report the first results from evolutions of a generic black-hole binary, i.e. a binary containing unequal mass black holes with misaligned spins. Our configuration, which has a mass ratio of 2:1, consists of an initially non-spinning hole orbiting a larger, rapidly spinning hole (specific spin a/m = 0.885), with the spin direction oriented -45 degrees with respect to the orbital plane. We track the inspiral and merger for ~2 orbits and find that the remnant receives a substantial kick of 454 km/s, more than twice as large as the maximum kick from non-spinning binaries. The remnant spin direction is flipped by 103 degrees with respect to the initial spin direction of the larger hole. We performed a second run with anti-aligned spins, a/m = +-0.5 lying in the orbital plane that produces a kick of 1830 km/s off the orbital plane. This value scales to nearly 4000 km/s for maximally spinning holes. Such a large recoil velocity opens the possibility that a merged binary can be ejected even from the nucleus of a massive host galaxy.

Light-cone sum rules: A SCET-based formulation

We describe the construction of light-cone sum rules (LCSRs) for exclusive B -meson decays into light energetic hadrons from correlation functions within soft-collinear effective theory (SCET). As an example, we consider the SCET sum rule for the B → π transition form factor at large recoil, including radiative corrections from hard-collinear loop diagrams at first order in the strong coupling constant.

Heavy-to-light form factors for non-relativistic bound states

We investigate transition form factors between non-relativistic QCD bound states at large recoil energy. Assuming the decaying quark to be much heavier than its decay product, the relativistic dynamics can be treated according to the factorization formula for heavy-to-light form factors obtained from the heavy-quark expansion in QCD. The non-relativistic expansion determines the bound-state wave functions to be Coulomb-like. As a consequence, one can explicitly calculate the so-called ``soft-overlap'' contribution to the transition form factor.

Multifragmentation of Au induced by 14.6 GeVHe4

The multifragmentation reaction channel was investigated in 14.6 GeV $^{4}\mathrm{He}$+Au interactions. The experimental setup enabled event-by-event analysis. An internal correlation study suggests a nearly simultaneous emission of fragments. The velocities ($V{}_{\mathrm{c.m.}}$) of the center-of-mass system of correlated fragments were calculated. The transverse component of $V{}_{c.m.}$ with respect to the beam direction has higher values than the longitudinal one, which corresponds to large recoil angles of the source. The angular distributions of fragments are sideways peaked. The peak angle is dependent on the atomic number of fragment and multiplicity. Our results show that the heaviest fragment in one event corresponds, on average, to the largest emission angle, the second heaviest fragment corresponds to the second largest emission angle, and so on.

Form factor for B→Dlν˜ in the light-cone sum rules with chiral current correlator

Within the framework of QCD light-cone sum rules (LCSR), we calculate the form factor for B -> Dl (v) over tilde transitions with chiral current correlator. The resulting form factor depends on the distribution amplitude (DA) of the D-meson. We try to use three kinds of DA models of the D-meson. C In the velocity transfer region 1.14 Dl (v) over tilde, within the error. In the large recoil region 1.35 Dl (v) over tilde transitions. (c) 2006 Elsevier B.V. All rights reserved.

Defect generation by radioactive decay of light elements in n-type silicon

Defects created by the decay of radioactive sodium, potassium and magnesium isotopes in n-type Si are studied by capacitance spectroscopy. In particular, we were interested in the creation of defects due to the large recoil energies involved in the radioactive decay. No evidence was found for an enhanced defect generation with concentrations exceeding those of the implanted mother isotopes. In our samples only defects are formed which contain mother or daughter isotopes and vacancies. The decay of 24Na isotopes results in two Mg-related defect levels. After implantation of radioactive 42K we observe one K-related acceptor at E c - 0.269 eV . The decay to the stable isotope 42Ca generates the A-center in concentrations comparable to the K-related center. In the decay series of 28Mg via 28Al to 28Si a new level was detected which is thermally unstable at room temperature and converts to the A-center.

Symmetry relations for heavy-to-light meson form factors at large recoil

The description of large-recoil heavy-to-light meson form factors is reviewed in the framework of soft-collinear effective theory. At leading power in the heavy-quark expansion, three classes of approximate symmetry relations arise. The relations are compared to experimental data for D → K* and Ds → φ form factors, and to light-cone QCD sum rule predictions for B → π and B → ρ form factors. Implications for the extraction of |Vub| from semileptonic B → ρ decays are discussed.

Single ionization of the water molecule by electron impact: Angular distributions at low incident energy

Recent experimental results of Milne-Brownlie et al. on the ionization of the water molecule by low-energy electron (250 eV) have been compared to theoretical predictions performed in the distorted-wave first Born model [Phys. Rev. A 69, 032701 (2004)]. It was found that this theory was unable to predict the very large recoil scattering observed experimentally. In this work, more sophisticated theoretical models are investigated in order to better understand the water ionization process at the multidifferential level and to reproduce the experimental observations.

Liquid metal expulsion during laser spot welding of 304 stainless steel

During laser spot welding of many metals and alloys, the peak temperatures on the weld pool surface are very high and often exceed the boiling points of materials. In such situations, the equilibrium pressure on the weld pool surface is higher than the atmospheric pressure and the escaping vapour exerts a large recoil force on the weld pool surface. As a consequence, the molten metal may be expelled from the weld pool surface. The liquid metal expulsion has been examined both experimentally and theoretically for the laser spot welding of 304 stainless steel. The ejected metal droplets were collected on the inner surface of an open ended quartz tube which was mounted perpendicular to the sample surface and co-axial with the laser beam. The size range of the ejected particles was determined by examining the interior surface of the tube after the experiments. The temperature distribution, free surface profile of the weld pool and the initiation time for liquid metal expulsion were computed based on a three-dimensional transient heat transfer and fluid flow model. By comparing the vapour recoil force with the surface tension force at the periphery of the liquid pool, the model predicted whether liquid metal expulsion would take place under different welding conditions. Expulsion of the weld metal was also correlated with the depression of the liquid metal in the middle of the weld pool due to the recoil force of the vapourized material. Higher laser power density and longer pulse duration significantly increased liquid metal expulsion during spot welding.

Heavy-to-light meson form factors at large recoil

Heavy-to-light meson form factors at large recoil can be described using the same techniques as for hard exclusive processes involving only light hadrons. Two competing mechanisms appear in the large-recoil regime, describing so-called ``soft-overlap'' and ``hard-scattering'' components of the form factors. It is shown how existing experimental data from B and D decays constrain the relative size of these components, and how lattice data can be used to study properties such as the energy scaling laws obeyed by the individual components. Symmetry relations between different form factors (F_+, F_0 and F_T), and between different heavy initial-state mesons (B and D), are derived in the combined heavy-quark and large-recoil limits, and are shown to generalize corresponding relations valid at small recoil. Form factor parameterizations that are consistent with the large-recoil limit are discussed.

Heavy-to-light B meson form factors at large recoil energy—spectator-scattering corrections

We complete the investigation of loop corrections to hard spectator-scattering in exclusive B meson to light meson transitions by computing the short-distance coefficient (jet-function) from the hard-collinear scale. Adding together the two coefficients from matching QCD → SCET I → SCET II, we investigate the size of loop effects on the ratios of heavy-to-light meson form factors at large recoil. We find the corrections from the hard and hard-collinear scales to be of approximately the same size, and significant, but the perturbative expansions appear to be well-behaved. Our calculation provides a non-trivial verification of the factorization arguments. We observe considerable differences between the predictions based on factorization in the heavy-quark limit and current QCD sum rule calculations of the form factors. We also include the hard-collinear correction in the B → π π tree amplitudes, and find an enhancement of the colour-suppressed amplitude relative to the colour-allowed amplitude.