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Alexey A. Petrov

Publications and source records attributed to Alexey A. Petrov.

88 records · Page 5Linked to original sources
arXiv1999

Charmonium production at neutrino factories

At existing and planned neutrino factories (high energy and high intensity neutrino beam facilities) precision studies of QCD in neutrino-nucleon interactions are a realistic opportunity. We investigate charmonium production in fixed target neutrino experiments. We find that $J/ψ$ production in neutrino-nucleon collision is dominated by the color octet $^3S_1$ NRQCD matrix element in a neutral current process, which is not accessible in photo or leptoproduction. Neutrino experiments at a future Muon Collider will acquire sufficient event rate to accurately measure color octet matrix element contributions. The currently running high energy neutrino experiments, NOMAD and NuTeV could also observe several such events.

hep-ph↗
arXiv1999

Radiative Leptonic B_c Decays in Effective Field Theory

The recent discovery of the B_c meson by the CDF collaboration and proposed new experiments at Fermilab and CERN motivate new theoretical studies of the B_c system. Here we investigate the radiative leptonic decay B_c -> gamma l nu. This process is an important background to the annihilation process B_c -> l nu, which will be used to extract the B_c decay constant. We perform a model-independent calculation, based on QCD, of the partial width and various kinematic distributions. We also examine the decay within the framework of NRQCD, an effective field theory of nonrelativistic quarks, generalizing the NRQCD Lagrangian to include external sources for the weak and electromagnetic currents. Finally, we comment on the role of the B_c* intermediate state for very soft photon energies.

hep-ph↗
arXiv1998

Hybrid Charmonium Production in NRQCD

Using the operator product expansion and nonrelativistic QCD we study the production of charmonium hybrids in B decays. We express the decay rate in terms of a few matrix elements which eventually will be fixed by experimental measurements or calculated on the lattice. While the Fock state expansion is problematic for hybrids, the operator product expansion still provides a model independent framework for phenomenological calculations of hybrid production and decay. We then use a simple flux tube model to estimate the branching ratio B -> psi_g+X, where psi_g is a J^{PC}=0^{+-} hybrid, the large production of which could help resolve the low charm multiplicity observed in B decays.

hep-ph↗
arXiv1998

Hybrid Charmonium Production in B Decays

We study the production of charmonium hybrids in B decays. We use the operator product expansion and nonrelativistic QCD to organize the various contributions to this process. We express the decay rate in terms of a few matrix elements which eventually will be fixed by experimental measurements or calculated on the lattice. While the Fock state expansion is problematic for hybrids, in that there is no perturbative large mass limit, the operator product expansion still provides a model independent framework for phenomenological calculations of hybrid production and decay. We then use a simple flux tube model to estimate the branching ratio B -> psi_g + X, where psi_g is a J^{PC}=0^{+-} hybrid, the large production of which could help resolve the low charm multiplicity and semileptonic branching ratio observed in B decays. We also investigate the possible contributions of tensor charmonium production. We observe that it is unlikely for either effect to be large enough to play a significant role in resolving these problems.

hep-ph↗
arXiv1998

Can Nearby Resonances Enhance D^0 - anti-D^0 Mixing?

We consider the possibility that D^0 - anti-D^0 mixing undergoes resonant enhancement. Various scenarios are explored, including the potential effects of nearby pseudoscalar or scalar quark-antiquark (Q - anti-Q) resonances as well as of hybrid quark-antiquark-gluon Q - anti-Q G states. Assuming reasonable values for the resonance parameters we find relatively sizeable contributions from individual resonances to both Δm_D and ΔΓ_D. We derive a variant of the GIM cancellation mechanism for the resonance amplitudes and show that broken SU(3) can allow for sizeable residual effects. Additional input from meson spectroscopy and lattice gauge simulations will be needed to improve the accuracy of these predictions.

hep-ph↗
arXiv1997

Intrinsic charm of light mesons and CP violation in heavy quark decay

We investigate the impact of the intrinsic heavy quark states on the predicted values of CP asymmetries in the decays of heavy mesons. It is shown that the intrinsic charm contribution, although dynamically suppressed in QCD, is favored by the weak interaction, and therefore it can significantly dilute the predicted values of CP-violating asymmetries. This introduces additional non-perturbative uncertainty into the estimate of direct CP violating effects. We provide a phenomenological estimate of intrinsic charm content of eta and eta' mesons by expanding various amplitudes in terms of the heavy-light quark mixing angle and discuss theoretical uncertainties in the estimates of direct CP-violating asymmetries in B -> eta^(') K^(*).

hep-ph↗
arXiv1997

Dipenguin-like contributions to D0 - anti-D0 mixing

We show that because of the milder GIM suppression, the four-quark dipenguin operator contributes to the short distance piece of the D^0-\bar D^0 mixing amplitude at the same order of magnitude as the box diagram. In addition, we put an upper bound Δm_D^{LDR} \leq 5 \times Δm_D^{box} on a long-distance resonant contribution induced by the penguin mixing.

hep-ph↗
arXiv1997

Final State Interactions and New Physics in B -> pi K Decays

Within the Standard Model, and if one assumes that soft rescattering effects are negligible, the CP asymmetry A^dir_CP (B^\pm -> π^\pm K) is predicted to be very small and the ratio R = BR(B_d -> π^\mp K^\pm)/BR(B^\pm -> π^\pm K) provides a bound on the angle γof the unitarity triangle, sin^2 γ\leq R. We estimate the corrections from soft rescattering effects using an approach based on Regge phenomenology, and find effects of order 10% with large uncertainties. In particular, we conclude that A^dir_CP \sim 0.2 and sin^2 γ\sim 1.2 R could not be taken unambiguously to signal New Physics. Using SU(3) relations, we suggest experimental tests that could constrain the size of the soft rescattering effects thus reducing the related uncertainty. Finally, we study the effect of various models of New Physics on A^dir_CP and on R.

hep-ph↗
arXiv1997

$η'$ production in B-decays: Standard Model vs. New Physics

Standard model factorization can account for the large rate for $B^\pm \to η' K^\pm$. The large rate for $B \to η' X_s$ is more problematic and requires a ``cocktail'' solution. Individual contributions from factorization, $b \to η' s g$, and ``intrinsic charm'' fall significantly short of the observed rate. In contrast, the observed $η'$ yields are easily explained in models with $B(b \to sg) \sim 15%$. Factorization can account for the entire semi-inclusive $η'$ yield without violating rare decay constraints. Implications for CP violation are discussed.

hep-ph↗
arXiv1996

How to trap a non-standard penguin? Isospin Symmetry Violations in B-decays with Enhanced Chromomagnetic Dipole Operator

A recently proposed Non-Standard Model solution to the problem of low semileptonic branching ratio B_{SL} which suggests a large branching ratio for the decay $b \to sg$ is critically examined. It is shown that the effects of the Enhanced Chromomagnetic Dipole Operator might lead to significant violations of isospin symmetry in rare radiative decays of B-mesons.

hep-ph↗
arXiv1996

Factorization in non-leptonic decays of heavy mesons

We propose a QCD-based model for calculation of the non-perturbative corrections to the factorization approximation in the decays of heavy mesons. In the framework of the model, factorization in pseudoscalar transitions holds exactly at the leading order leaving the opportunity to calculate non-leading corrections consistently.

hep-ph↗
arXiv1996

Final state rescattering as a contribution to $B \to ργ$

We provide a new estimate of the long-distance component to the radiative transition $B \to ργ$. Our mechanism involves the soft-scattering of on-shell hadronic products of nonleptonic $B$ decay, as in the chain $B \to ρρ\to ργ$. We employ a phenomenological fit to scattering data to estimate the effect. The specific intermediate states considered here modify the $B \to ργ$ decay rate at roughly the $5 \to 8%$ level, although the underlying effect has the potential to be larger. Contrary to other mechanisms of long distance physics which have been discussed in the literature, this yields a non-negligible modification of the $B^0 \to ρ^0 γ$ channel and hence will provide an uncertainty in the extraction of $V_{td}$. This mechanism also affects the isospin relation between the rates for $B^- \to ρ^-γ$ and $B^0 \to ρ^0 γ$ and may generate CP asymmetries at experimentally observable levels.

hep-ph↗
arXiv1996

Systematics of soft final state interactions in $B$ decay

By using very general and well established features of soft strong interactions we show, contrary to conventional expectations, that (i) soft final state interactions (FSI) do not disappear for large $m_B$, (ii) inelastic rescattering is expected to be the main source of soft FSI phases, and (iii) flavor off-diagonal FSI are suppressed by a power of $m_B$, but are quite likely to be significant at $m_B\simeq 5$~GeV. We briefly discuss the influence of these interactions on tests of CP-violation and on theoretical calculations of weak decays.

hep-ph↗
arXiv1995

Is $B \to X_s γ$ equal to $b \to s γ$ ? Spectator contributions to rare inclusive B decays

In $B \to X_s γ$ there are perturbative $QCD$ corrections at order $α_s$ not only to the single quark line process $ b \to s γ$ but also coming from a set of diagrams where the weak interaction vertex involves a gluon which interacts with the spectator quark in the B hadron. We discuss the impact of the full set of these diagrams. These can influence the decay rate and also the line shape of the photon spectrum as they favor a softer photon energy than does the pure spectator decay $b \to s γ$. A subset of these diagrams generate differences in the decay rates for charged and neutral B's , $B^+ \to X_s γ$ vs. $B^0 \to X_s γ$ which can be searched for experimentally, although our calculation indicates that the effect will be hard to observe. Bound state effects turn out to be required to give rise to spectator corrections to the decay rate at order $α_s$. The resulting contribution to the total rate is rather small (of about $5 \% $ ), although the effect is somewhat larger on portions of the photon spectrum.

hep-ph↗