Recoil Region Research Articles

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.

Consistent analysis of theB→πtransition form factor in the whole physical region

In the paper, we show that the $B\to\pi$ transition form factor can be calculated by using the different approach in the different $q^2$ regions and they are consistent with each other in the whole physical region. For the $B\to\pi$ transition form factor in the large recoil regions, one can apply the PQCD approach, where the transverse momentum dependence for both the hard scattering part and the non-perturbative wavefunction, the Sudakov effects and the threshold effects are included to regulate the endpoint singularity and to derive a more reliable PQCD result. Pionic twist-3 contributions are carefully studied with a better endpoint behavior wavefunction for $\Psi_p$ and we find that its contribution is less than the leading twist contribution. Both the two wavefunctions $\Psi_B$ and $\bar\Psi_B$ of the B meson can give sizable contributions to the $B\to\pi$ transition form factor and should be kept for a better understanding of the B decays. The present obtained PQCD results can match with both the QCD light-cone sum rule results and the extrapolated lattice QCD results in the large recoil regions.

Exclusive rareB→K*ℓ+ℓ−decays at low recoil: Controlling the long-distance effects

We present a model-independent description of the exclusive rare decays $\overline{B}\ensuremath{\rightarrow}{K}^{*}{e}^{+}{e}^{\ensuremath{-}}$ in the low recoil region (large lepton invariant mass ${q}^{2}\ensuremath{\sim}{m}_{b}^{2}$). In this region the long-distance effects from quark loops can be computed with the help of an operator product expansion in $1/Q$, with $Q={{m}_{b},\sqrt{{q}^{2}}}$. Nonperturbative effects up to and including terms suppressed by $\ensuremath{\Lambda}/Q$ and ${m}_{c}^{2}/{m}_{b}^{2}$ relative to the short-distance amplitude can be included in a model-independent way. Based on these results, we propose an improved method for determining the Cabibbo-Kobayashi-Maskawa matrix element $|{V}_{ub}|$ from a combination of rare and semileptonic $B$ and $D$ decays near the zero recoil point. The residual theoretical uncertainty from long-distance effects in this $|{V}_{ub}|$ determination comes from terms in the operator product expansion of order ${\ensuremath{\alpha}}_{s}(Q)\ensuremath{\Lambda}/{m}_{b}$, ${\ensuremath{\alpha}}_{s}^{2}(Q)$, ${m}_{c}^{4}/{m}_{b}^{4}$, and duality violations, and is estimated to be below 10%.

B → K* ℓ+ ℓ- DECAYS WITH POLARIZED K*

We study the exclusive decays of B → K* ℓ+ ℓ- within the framework of the PQCD. We obtain the form factors for the B → K* transition in the large recoil region, where the PQCD for heavy B meson decays is reliable. We find that the form factors at q2 = 0 are consistent with those from the large energy effective theory combined with the heavy quark effective theory and the experiment of B → K*γ. Via the decay chain of B → K* (Kπ) ℓ+ ℓ-, we can study many physical observables which are related to the different helicity combinations of B → K* ℓ+ ℓ-, such as the forward-backward asymmetries (FBAs). In particular, we can study the T violating effect which is small in the standard model but can be up to 10% in models with new physics.

Analysis of [formula omitted] decays at large recoil region

We study the exclusive decays of B→K ∗ℓ +ℓ − within the framework of the perturbative QCD (PQCD). We obtain the form factors for the B→K ∗ transition in the large recoil region, where the PQCD for heavy B meson decays is reliable. We find that our results for the form factors at q 2=0 are consistent with those from most of the other QCD models in the literature. Via the decay chain of B→K ∗(Kπ)ℓ +ℓ − , we obtain many physical observables related to the different helicity combinations of B→K ∗ℓ +ℓ − . In particular, we point out that the T-violating effect suppressed in the standard model can be up to O(10%) in some CP violating models with new physics.

Annihilation decayBc−→η′l−ν¯

We first investigate the semileptonic annihilation decay ${B}_{c}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\eta}}^{\ensuremath{'}}{l}^{\ensuremath{-}}\overline{\ensuremath{\nu}}$ in QCD. We find the ${\ensuremath{\eta}}^{\ensuremath{'}}$ momentum distribution is peaked within its small recoil region as a result of loop effects. The branching ratio is estimated to be $\mathcal{B}{(B}_{c}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\eta}}^{\ensuremath{'}}{l}^{\ensuremath{-}}\overline{\ensuremath{\nu}})=1.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ for $l=\ensuremath{\mu},e,$ which is accessible at CERN LHC.

Second-order effects in (e, 2e) excitation-ionization of helium to ( n = 2)

First and second Born (e, 2e) calculations are presented for excitation-ionization of ground-state helium to . Results for ionization to the ground-state ion (1s) are also given. The physical content of the approximations is discussed, in particular, the two-step mechanism which appears in the second-order term for excitation-ionization. The second Born term is calculated in the closure approximation using a new numerical method based on prolate spheroidal coordinates. Comparison is made with absolute experimental data from Paris and Rome in very asymmetric coplanar geometry - scattered electron energies of 5500, 1500 and 570 eV and ejected electron energies of 5, 10, 20, 40 and 75 eV. For excitation-ionization the second Born approximation generally gives improved agreement with the experimental data in the recoil region and second-order effects are found to be still significant at 5500 eV. The importance of the second-order term decreases with increasing ejected energy for the cases studied here.

Triple differential cross sections for electron impact ionisation of alkali like ion Mg +

Triple differential cross sections (TDCS) of alkali-like ion Mg + in its ground state are studied theoretically by fast electron impact for coplanar asymmetric geometry, using the correlated three Coulomb wavefunction for the final state which satisfies the asymptotic three body boundary condition. The long range Coulomb attraction is also taken into account in the initial channel. The Mg + ion is treated in a model potential approach. The main feature noticed in the TDCS curve is the presence or an intense recoil peak for lower incident energies even larger than the binary one. Secondary structures are found in both binary and recoil regions.

Perturbative QCD study of B-->D(*) decays.

We compute various form factors involved in $B\to D^{(*)}$ transitions based on the perturbative QCD formalism, which includes Sudakov effects from the resummation of large radiative corrections in a heavy-light system. A two-parameter model wave function for $D^{(*)}$ mesons is fixed using data of the nonleptonic decays $B\to D^{(*)}\pi$, from which the ratio of the decay constants $f_{D^*}/f_D=0.92$ is obtained. We then derive the spectrum of the semileptonic decay $B\to D^{*}\ell\nu$ in the fast recoil region of the $D^*$ meson, and extract the CKM matrix element $|V_{cb}|=0.043\times(0.12 {\rm GeV}/f_B)\times(0.14 {\rm GeV}/f_D)$, $f_B$ and $f_D$ being the $B$ and $D$ meson decay constants, respectively. Here we adopt the convention with the pion decay constant $f_\pi=93$ MeV. With these outcomes, we evaluate the decay rate of $B\to DD_s$, and estimate the ratio $f_{D_s}/f_D=0.98$ from data. Contributions of internal $W$-emission and $W$-exchange diagrams are briefly discussed.

Validity of the Coulomb-Born approximation for (e,2e) reactions.

The Coulomb-Born approximation (CBA) is tested against experiment and against the distorted-wave Born approximation (DWBA) for target inner-shell ionization by fast electrons. It is found that the CBA is fairly accurate in the binary region for the heavy systems when relativistic effects play a minor role. However, CBA underestimates the cross sections in the recoil region for the heavy targets, but also in the binary region for light targets. This is caused by an inappropriate representation of the electronic wave functions, and is neither a deficiency of a first-order theory nor due to lack of orthogonality in the present form of the CBA. \textcopyright{} 1996 The American Physical Society.

PQCD analysis of exclusive charmless B meson decay spectra

We apply the perturbative QCD formalism, including Sudakov effects, to exclusive charmless semi-leptonic B meson decays. Predictions for both the charged lepton and lepton pair invariant mass spectra of the B → πℓ ν and B → ϱℓ ν decays in the large recoil region are presented. After combining soft pionn results, we extract | V ub | ≤ 4.5 × 10 −3 from curren data. With our predictions, future data will not only provide a more precise extraction of | V ub |, but also test perturbative QCD in B meson decays.

Observation of anisotropic PCI effects at high excess energies

A coplanar electron coincidence spectrometer has been used to measure Auger lineshapes in coincidence with the scattered electron produced after electron impact ionization of the 2p shell in argon. The coincident lineshapes have been measured at an excess energy which is close to the nominal Auger energy. The L3-M23M23(1D2) lineshape was measured for two different emission angles, -95' and 132', of the Auger electron. The angles chosen correspond to the recoil and binary regions, respectively, of the triple differential cross section for 2p ionization of argon. Additional structure was observed in the coincidence Auger lineshape at one angle (-95'), consistent with an angular dependence of the post collision interaction.

Correlations in the autoionising region of He measured by the (e, 2e) technique

Results are presented for the triple differential (e, 2e) cross sections in helium in the region encompassing the (2s2)1S, (2s2p)3P, (2p2)1D and (2s2p)1P resonances at incident energies of 100, 200, and 400 eV for scattering angles of 13' at 100 and 200 eV and 3' and 16' at 400 eV. Measurements were taken with an energy resolution of 150 meV over an extended angular range for the ejected electrons, encompassing both the binary ( phi e- phi s= pi ) and recoil ( phi e- phi s=0) regions. The data are analysed in terms of Shore's parametrisation to obtain direct (e, 2e) cross sections fr and resonance parameters ar and br for the (2s2)1S, (2p2)1D and (2s2p)1P resonances as a function of ejected electron momentum. The data show very strong correlations between the resonance amplitudes and the direct ionisation amplitudes.

(e,2e) Studies of Atoms ? Some Recent Developments

Some recent work on (e,2e) collisions in atoms is reported. The first (e,2e) results on an excited target and also on an oriented target are discussed. Sodium atoms are pumped to the m/ = +1 state of the excited 3p state by 0"+ light from a laser. The (e,2e) measurements are then performed on this excited state. The results are in excellent agreement with the momentum density profile given by the 3p(m/ = 1) Hartree-Fock wavefunction. High resolution electron momentum spectroscopy measurements are reported for argon. The first momentum profiles for excited Ar ion states belonging to the 2po and 20e manifolds are obtained. The latter are entirely due to initial state correlations. Comparison is made with several many-body calculations. The importance of core quadrupole (10) excitations is demonstrated. Although the 2se manifold is dominated by final state correlations, the momentum profile to the 4s 2S ion state in the 2Se manifold also shows the influenee of initial state correlation effects. The third series of measurements examines correlations in the autoionising region of helium, encompassing the (2s2)1 S, (2s2p)3p, (2p2)! 0 and (2s2p)! P resonances, at 100, 200 and 400 eV incident electron energies. Measurements, with an energy resolution of 150 meV, were taken at a number of scattered electron angles over an extended range of ejected electron angles, encompassing both the binary and recoil regions. The data show very strong correlations between the resonance amplitudes and the direct ionisation amplitudes.

A Monte Carlo simulation of fast neutron beams used for radiotherapy: II. Cyclotron based beams

For part I see ibid vol.34, p.965-82, 1989. The codes NCF and MCCND which have been previously tested on the (d, t) beam are applied here to unfiltered cyclotron based neutron beams using 16 and 50 MeV deuterons and 55 MeV protons on Be targets having a range of thicknesses. The collimator material is assumed to be high density polythene having the dimensions necessary to give a circular field equivalent in area to 7 cm*7 cm at the phantom surface with values of SSD that are commonly used in clinical practice. The phantom is again assumed to be standard man tissue equivalent. Calculations were made of the dose per neutron, the depths of the maximum and 50% maximum dose, the ratio of gamma to total dose, the dose: LET distributions and the dose- and track-averaged LET. The averaged LETs were found to be mostly constant with depth, except in the build-up region where, in the case of the higher energy beams, a significant reduction takes place between the surface and the dose maximum. In the distribution of dose between three broad LET regions, the authors' calculations show that the (d, t) beam has the highest fraction in the range 88-240 keV mu m-1 with the highest mean energy beam, p(55)Be(10), showing the highest fraction in the heavy recoil region, 240-1250 keV mu m-1.

2H(p,2p)n at 508 MeV: Recoil momenta

Differential cross sections for the reaction $^{2}(\mathit{p}$,2p)n at ${T}_{p}$=507 and 508 MeV are presented. The kinematics selected included two quasi-free angle pairs: 41.5\ifmmode^\circ\else\textdegree\fi{}-41.4\ifmmode^\circ\else\textdegree\fi{} and 30.1\ifmmode^\circ\else\textdegree\fi{}-53.75\ifmmode^\circ\else\textdegree\fi{}; in addition, data away from the quasi-free condition were obtained in four symmetric angle pairs: 38.1\ifmmode^\circ\else\textdegree\fi{}-38.0\ifmmode^\circ\else\textdegree\fi{}, 44.1\ifmmode^\circ\else\textdegree\fi{}-44.0\ifmmode^\circ\else\textdegree\fi{}, 47.1\ifmmode^\circ\else\textdegree\fi{}-47.0\ifmmode^\circ\else\textdegree\fi{}, and 50.0\ifmmode^\circ\else\textdegree\fi{}-50.0\ifmmode^\circ\else\textdegree\fi{}, and five asymmetric angles pairs: 30.1\ifmmode^\circ\else\textdegree\fi{}-37.0\ifmmode^\circ\else\textdegree\fi{}, 30.1\ifmmode^\circ\else\textdegree\fi{}-44.0\ifmmode^\circ\else\textdegree\fi{}, 30.1\ifmmode^\circ\else\textdegree\fi{}-61.0\ifmmode^\circ\else\textdegree\fi{}, 30.1\ifmmode^\circ\else\textdegree\fi{}-68.0\ifmmode^\circ\else\textdegree\fi{}, and 41.5\ifmmode^\circ\else\textdegree\fi{}-50.0\ifmmode^\circ\else\textdegree\fi{}. The data range over an energy window 100 MeV wide on one of the proton energies, the second energy being defined by the kinematic condition of a single neutron recoiling. The data are compared with the impulse approximation prediction and with the results of a nonrelativistic calculation of the six lowest-order Feynman diagrams describing the reaction. A previously known missing strength for the reaction in the small neutron recoil region is confirmed with much smaller experimental uncertainty; the missing strength persists up to 150 MeV/c neutron recoil. The onset of a systematic cross section excess relative to the impulse approximation near neutron recoil momentum 200 MeV/c is explored in detail.

Relativistic and delta effects in the 2H(p, 2p)n cross section at intermediate energies

A calculation of the 2H(p, 2p)n differential cross section, which includes virtual delta excitation and impulse approximation diagrams, is presented and compared with data at 507 MeV in the large neutron recoil region. A main theoretical results is that specific relativistic target effects are large if the usual local five-term representation is used for the NN amplitude.