arXiv subjects

N. Paver

Publications and source records attributed to N. Paver.

At least 37 records · Page 2Linked to original sources

arXiv2005

Radiative Ke3 decays revisited

Motivated by recent experimental results and ongoing measurements, we review the chiral perturbation theory prediction for radiative Ke3 decays (neutral kaons). Special emphasis is given on the stability of the inner bremsstrahlung-dominated relative branching ratio vs. the Ke3 form factors, and on the separation of the structure dependent amplitude in differential distributions over the phase space. For the structure dependent terms, an assessment of the order p^6 corrections is given. In particular, a full next-to-leading order calculation of the axial component is performed. The experimental analysis of the photon energy spectrum is discussed, and other potentially useful distributions are introduced.

hep-ph↗

arXiv2005

Identification of indirect new physics effects at e^+e^- colliders: the large extra dimensions case

We discuss indirect manifestations of graviton exchange, predicted by large extra dimensions, in fermion-pair production at a high-energy e^+e^- collider. By means of specifically defined asymmetries among integrated angular distributions, the graviton exchange signal can be cleanly distinguished from the effects of either vector-vector contact interactions or heavy scalar exchanges. The role of initial electron and positron beams polarization is also discussed. The method is applied to a quantitative assessment of the sensitivity to the mass cut-off parameter M_H of the KK graviton tower in the ADD scenario, and of the potential identification reach of this mechanism obtainable at the currently planned Linear Collider.

hep-ph↗

arXiv2004

Search and identification of extra spatial dimensions at LHC

We present an analysis, based on the center-edge asymmetry, to distinguish effects of extra dimensions within the Arkani-Hamed-Dimopoulos-Dvali (ADD) and Randall-Sundrum (RS) scenarios from other new physics effects in lepton-pair production at the CERN Large Hadron Collider LHC. Spin-2 and spin-1 exchange can be distinguished up to an ADD cutoff scale, M_H, of about 5 TeV, at the 95% CL. In the RS scenario, spin-2 resonances can be identified in most of the favored parameter space.

hep-ph↗

arXiv2004

Center-Edge Asymmetry at Hadron Colliders

We investigate the possibility of using the center-edge asymmetry to distinguish graviton exchange from other new physics effects at hadron colliders. Specifically, we study lepton-pair production within the ADD and RS scenarios. At the Tevatron, the graviton-Z interference is the most important contribution to the center-edge asymmetry, whereas at the LHC, the dominant contribution comes from gluon fusion via graviton exchange, which has no analogue at e^+ e^- colliders. We find that spin-2 and spin-1 exchange can be distinguished up to an ADD cut-off scale, M_H, of about 5 TeV, at the 95% CL. In the RS scenario, spin-2 resonances can be identified in most of the favored parameter space.

hep-ph↗

arXiv2003

Discriminating graviton exchange effects from other new physics scenarios in e^+e^- collisions

We study the possibility of uniquely identifying the effects of graviton exchange from other new physics in high energy e^+e^- annihilation into fermion-pairs. For this purpose, we use as basic observable a specific asymmetry among integrated differential distributions, that seems particularly suitable to directly test for such gravitational effects in the data analysis.

hep-ph↗

arXiv2003

Model-independent constraints on contact interactions from LEP2 data analysis

We derive model-independent constraints on four-fermion contact interaction-type dynamics from the published preliminary LEP2 experimental data on e^+e^- annihilation into μ^+μ^- and τ^+τ^- pairs, measured at different energies between 130 and 207 GeV. The basic observables are chosen to be the total cross section and the forward-backward asymmetry, and the analysis realistically takes into account data uncertainties and correlations among measurements at the various energies. The combination of data from different energy points plays an important role in the determination of regions allowed for the contact interaction coupling constants. In contrast to the more common one-parameter analyses, we only obtain constraints on pairs of parameters rather than limits on individual ones.

hep-ph↗

arXiv2002

Bhabha vs. Moller scattering as a contact-interaction analyzer at a polarized Linear Collider

We discuss electron-electron contact-interaction searches in the Bhabha and Moller processes at planned Linear Colliders run in the electron-positron and electron-electron modes, with longitudinally polarized beams. Our analysis is based on the measurement, for the two processes, of polarized differential cross sections that allow to disentangle the different, independent, four-fermion couplings. We evaluate by a model-independent analysis the sensitivities to the contact coupling constants, emphasizing the role of the available beam polarization and the complementarity of the two processes in giving the best limits. We also make a comparison with the potential of $e^+e^-\toμ^+μ^-$ at the same energy and beams polarization.

hep-ph↗

arXiv2001

Model independent constraints on contact interactions from polarized Bhabha scattering at LC

We discuss electron-electron contact-interaction searches in the process e^+e^- -->e^+e^- at a future e^+e^- Linear Collider with c.m. energy \sqrt{s}=0.5 TeV and with both beams longitudinally polarized. Our analysis is based on the measurement of the polarized differential cross sections, and allows to simultaneously take into account the general set of contact interaction couplings as independent, non-zero, parameters thus avoiding simplifying, model-dependent, assumptions. We evaluate the corresponding model-independent constraints on the coupling constants, emphasizing the role of beam polarization, and make a comparison with the case of e^+e^- -->μ^+μ^-.

hep-ph↗

arXiv2001

The sigma and rho in D and B decays

We study the D^{+} -> sigma pi^{+}, D^{+} -> rho^0 pi^{+}, B^{-} -> sigma pi^{-}, B^{-} -> rho^0 pi^{-} and \bar{B}^0 -> rho^{\pm} pi^{\mp} decays in a valence quark triangle model, incorporating chiral symmetries. We find a good agreement with recent experimental data for D^{+} -> sigma pi^{+} and for D^{+} -> rho^0 pi^{+}. We point out that a "long-distance" contribution due to the axial vector a_1 meson pole, calculated by using chiral symmetry, can be relevant to explain D^{+}-> rho^0 π^{+} and for lowering the ratio R=Br(\bar{B}^0 -> rho^{\pm} pi^{\mp})/Br(B^{-} -> rho^0 pi^{-}) to be consistent with its phenomenological determination, within the large experimental uncertainity.

hep-ph↗

arXiv2001

New physics signatures at a Linear Collider: model-independent analysis from `conventional' polarized observables

We discuss four-fermion contact-interaction searches in the processes e^+e^-\toμ^+μ^-, c{\bar c} and b{\bar b} at a future e^+e^- Linear Collider with c.m. energy \sqrt{s}=0.5 TeV and with both beams longitudinally polarized. Our analysis is based on the measurements of familiar polarized observables such as the total cross section and the forward-backward/left-right asymmetries, and accounts for the general set of contact interaction couplings as independent, non-zero, parameters thus avoiding simplifying, model-dependent, assumptions. We derive the corresponding model-independent constraints on the above-mentioned coupling constants, and evaluate the corresponding reach at the Linear Collider, emphasizing the role of beam polarization. We compare the results with a model-dependent procedure where only one coupling is varied at a time.

hep-ph↗

arXiv2001

Contact interactions and polarized beams at a Linear Collider

We discuss contact-interaction searches in the processes e^+e^-\to μ^+μ^-, b\bar{b} and c\bar{c} at an e^+e^- Linear Collider with c.m. energy \sqrt{s}=0.5 TeV and with longitudinally polarized beams. The measurement of polarized cross sections allows to study the individual helicity cross sections, and consequently to derive separate, model-independent, constraints on the four-fermion contact interaction couplings. We evaluate the reach on those parameters foreseeable in the case of both electron and positron polarization fixed at some reference values, and compare it with the situation where only electron polarization is available. The analysis is based on polarized integrated cross sections with optimal kinematical cuts that can improve the sensitivity to the relevant couplings. While electron polarization would by itself allow such an analysis, the additional positron polarization (with no loss of beam intensity) and optimization can have a crucial role in improving the sensitivity to the new interactions.

hep-ph↗

arXiv2000

Model independent constraints on contact interactions from LEP2

We quantitatively discuss the possibility of deriving model-independent constraints on the general four-fermion contact interaction couplings, from the currently available data on the two-fermion production processes $e^+e^-\toμ^+μ^-$, $b\bar{b}$ and $c\bar{c}$ with unpolarized initial beams. The method is essentially based on particular, simple, combinations of the measured total cross section and forward-backward asymmetry that allow partial separation of the helicity cross sections, and the combination of experimental data obtained at the different energies of TRISTAN, LEP1 and LEP2.

hep-ph↗

arXiv2000

Contact interaction probes at the Linear Collider with polarized electron and positron beams

For contact-interaction searches at the Linear Collider, we discuss the advantages of polarizing both the electron and the positron beams as compared with polarizing only the electron beam. In particular, for the processes e^+e^-\to μ^+μ^-, τ^+τ^-, b\bar{b} and c\bar{c} at a future e^+e^- collider with \sqrt{s}=0.5 TeV we derive model-independent bounds on the four-fermion contact interaction parameters from studies of the helicity cross sections.

hep-ph↗

arXiv2000

Optimal polarized observables for model-independent new-physics search at e+e- colliders

For the processes e+e-\to μ+μ-, τ+τ-, b\bar{b} and c\bar{c} at a future e+e- collider with \sqrt{s}=0.5 TeV, we examine the sensitivity of the helicity cross sections to four-fermion contact interactions. If longitudinal polarization of the electron beam were available, two polarized integrated cross sections would offer the opportunity to separate the helicity cross sections and, in this way, to derive model-independent bounds on the relevant parameters. The measurement of these polarized cross sections with optimal kinematical cuts could significantly increase the sensitivity of helicity cross sections to contact interaction parameters and could give crucial information on the chiral structure of such new interactions.

hep-ph↗

arXiv1999

Optimal polarized observables for model-independent new physics searches at the linear collider

We discuss the sensitivity to four-fermion contact interactions of the process of fermion-pair production at the e^+ - e^- Linear Collider (LC), with E_{CM}=0.5 TeV and longitudinally polarized electron beam. The analysis is based on polarized integrated cross sections with optimal cuts. Beam polarization and optimization are shown to have a crucial role in the derivation of model-independent constraints on the new interactions from the data.

hep-ph↗

arXiv1999

Analysis of the Three-Body $B \to D^+ D^- π^0$ Decay

The decay process $B\to D^+ D^- π^0$ is an interesting channel for the investigation of CP violating effects in the $b-$ sector. We write down a decay amplitude constrained by a low-energy theorem, which also includes the contribution of resonant $S-$ and $P-$wave beauty and charmed mesons, and we determine the relevant matrix elements in the infinite heavy quark mass limit, assuming the factorization ansatz. We estimate the rate of the decay: ${\cal B}(B \to D^+ D^- π^0)\simeq 1 \times 10^{-3}$. We also analyze the time-independent and time-dependent differential decay distributions, concluding that a signal for this process should be observed at the B-factories. Finally, we give an estimate of the decay rate of the Cabibbo-favoured process $B\to D^+ D^- K_S$.

hep-ph↗

arXiv1998

Polarized observables to probe Z' at the e+e- linear collider

We study the sensitivity to the Z' couplings of the processes $e^+e^-\to l^+l^-,\bar{b}b$ and $\bar{c}c$ at the linear collider with $\sqrt{s}=500 GeV$ with initial beam polarization, for typical extended model examples. To this aim, we use suitable integrated, polarized, observables directly related to the helicity cross sections that carry information on the individual Z' chiral couplings to fermions. We discuss the derivation of separate, model-independent limits on the couplings in the case of no observed indirect Z' signal within the expected experimental accuracy. In the hypothesis that such signals were, indeed, observed we assess the expected accuracy on the numerical determination of such couplings and the consequent range of Z' masses where the individual models can be distinguished from each other as the source of the effect.

hep-ph↗

arXiv1998

Universal Isgur-Wise form factors from QCD sum rules in HQET

We review the role of the universal Isgur-Wise functions parameterizing the $B$ meson semileptonic matrix elements to charm states in the infinite heavy quark mass limit. We also discuss the determination of one of such form factors by QCD sum rules in the framework of the Heavy Quark Effective Theory.

hep-ph↗