Perturbative QCD study on the photonic penguin contributions to the decay B\rightarrow K^* \gamma

Including corrections of order , we present an analysis of photonic penguin contributions to the decay in the perturbative QCD framework. Employing several models of the meson wave functions, we demonstrate that the corrections of are enhanced and will provide substantial contributions to the decay because of the meson wave function being sharply peaked (bound state effect). The numerical predictions for the corrections are about which depend on the non-perturbative inputs such as the meson wave functions and the -quark mass. Received: 8 July 1997 / Published online: 23 February 1998     

Near-threshold production of a0(980)-mesons in the reaction \rm {pp \rightarrow d K^ + \bar{K^0}}

Using an effective Lagrangian approach as well as the Quark-Gluon Strings Model, we analyze near-threshold production of a ₀(980)-mesons in the reaction as well as the background of non-resonant -pair production. We argue that the reaction at an energy release MeV is dominated by the intermediate production of the a ₀(980)-resonance. At larger energies the non-resonant -pair production --where the kaons are produced in a relative P-wave-- becomes important. The effects of final-state interactions are evaluated in a unitarized scattering length approach and found to be in the order of a 20% suppression close to threshold. Thus, in present experiments at the Cooler Synchrotron COSY-Jülich for MeV the a ₀ ⁺ signal can reliably be separated from the non-resonant background.Received: 26 February 2004, Published online: 21 September 2004PACS: 25.10. + s Nuclear reactions involving few-nucleon systems - 13.75.-n Hadron-induced low- and intermediate-energy reactions and scattering (energy GeV)     

Disentangling weak and strong interactions in $$B\rightarrow K^{*}(\rightarrow K\pi )\pi $$ Dalitz-plot analyses

Dalitz-plot analyses of \(B\rightarrow K\pi \pi \) decays provide direct access to decay amplitudes, and thereby weak and strong phases can be disentangled by resolving the interference patterns in phase space between intermediate resonant states. A phenomenological isospin analysis of \(B\rightarrow K^*(\rightarrow K\pi )\pi \) decay amplitudes is presented exploiting available amplitude analyses performed at the BaBar, Belle and LHCb experiments. A first application consists in constraining the CKM parameters thanks to an external hadronic input. A method, proposed some time ago by two different groups and relying on a bound on the electroweak penguin contribution, is shown to lack the desired robustness and accuracy, and we propose a more alluring alternative using a bound on the annihilation contribution. A second application consists in extracting information on hadronic amplitudes assuming the values of the CKM parameters from a global fit to quark flavour data. The current data yields several solutions, which do not fully support the hierarchy of hadronic amplitudes usually expected from theoretical arguments (colour suppression, suppression of electroweak penguins), as illustrated from computations within QCD factorisation. Some prospects concerning the impact of future measurements at LHCb and Belle II are also presented. Results are obtained with the CKMfitter analysis package, featuring the frequentist statistical approach and using the Rfit scheme to handle theoretical uncertainties.     

Forward elastic scattering of light on light, \gamma+\gamma\rightarrow\gamma+\gamma

The forward elastic scattering of light on light, i.e., the reaction in the forward direction, is analyzed utilizing real analytic amplitudes. We calculate , the ratio of the real to the imaginary portion of the forward scattering amplitude, by fitting the total cross section data in the high energy region 5 GeV GeV, assuming a cross section that rises asymptotically as ln² s. We then compare , the ratio of the even portions of the pp and forward scattering amplitudes, as well as to [1], the value for Compton scattering. Within errors, we find that the three -values in the c.m.s. energy region 5 GeV 130 GeV are the same, as predicted by a factorization theorem of Block and Kaidalov [2]. Received: 18 June 2002 / Published online: 9 August 2002     

The $Z \rightarrow \gamma \gamma,\;gg$ decays in the non-commutative standard model

On non-commutative spacetime, the standard model (SM) allows new, usually SM forbidden, triple gauge boson interactions to occur. In this letter we propose the SM strictly forbidden and decay modes coming from the gauge sector of the non-commutative standard model (NCSM) as a place where non-commutativity could be experimentally discovered. Received: 2 July 2002, Revised: 28 February 2003, Published online: 18 June 2003     

Helicity dependence of the \gamma p\rightarrow N \pi channels and multipole analysis in the \Delta region

A high-quality double-polarization data set for the helicity dependence of the total and differential cross-sections for both channels in the region has been obtained in the framework of the GDH experiment. The experiment, performed at the Mainz microtron MAMI, used a 4 detection system, a circularly polarized photon beam, and a longitudinally polarized frozen-spin target. These data are included in the database to perform a multipole analysis to determine the properties of the -resonance. For the resonant (1232) multipoles we find a very good agreement with previous analyses, while the nonresonant ones show significant deviations.Received: 11 July 2003, Revised: 16 January 2004, Published online: 17 August 2004PACS: 13.60.Le Meson production - 14.20.Gk Baryon resonances with S = 0 - 25.20.Lj Photoproduction reactions     

\mu\rightarrow e\gamma decay in the left-right supersymmetric model

We calculate the dipole amplitude for the decay and related processes in the left-right supersymmetric model when parity breaking occurs at a considerably large scale. The low-energy flavor violation in the model originates either from the nonvanishing remnants of the left-right symmetry in the slepton mass matrix or from the direct flavor changing lepton-slepton-neutralino interaction. The result is found to be large and already accessible with current experimental accuracy for supersymmetric masses not far above the electroweak scale. It also provides nontrivial constraints on the lepton mixing in the model. Received: 8 June 1998 / Published online: 15 October 1998