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J. Milana

Publications and source records attributed to J. Milana.

12 recordsLinked to original sources
arXiv1996

Neutral Meson Photoproduction in $SU_f(3)$ $χ$PT

We present the results for the electric dipole amplitude for $γN \to π^0 N$ at threshold at the $O(p^2)$ level in SU$_f$(3) chiral perturbation theory. We find that the SU$_f$(3) results differ only slightly from the SU$_f$(2) results. At the $O(p^3)$ level one encounters new, unknown counterterms to fix which one is likely to need the threshold photoproduction data themselves, thus losing predictive power. We suggest, instead, that the {\it difference} between the proton and neutron $π^0$ photoproduction amplitudes may provide a test of the convergence properties of the $χ$PT in the present context. We urge that the neutron's electric dipole amplitude be measured.

nucl-th↗
arXiv1995

Double Penguins and the Contribution of Vector Meson--like States to the Decays $B \to K^* γ, \, B \to ργ$

Using perturbative QCD, the contribution at the leading twist, leading $α_s$ level, of charm and up quark loops to the decays $B \rightarrow K^* γ$ and $B \rightarrow ργ$ is presented. In the case of $B \rightarrow ργ$, the relative importance of these contributions depend upon the unknown CKM matrix elements $V_{bu}$ and $V_{td}$. Assuming that the ratio $r = V_{bc}V^*_{cd}/V_{bt}V^*_{td}$ is bounded between $-2.25 \le r \le -.5$ as is suggested by the Particle Data Group, the error in extracting $ |V_{td}/V_{ts}| $ by these decays is estimated.

hep-ph↗
arXiv1995

The Decuplet Revisited in $χ$PT

The paper deals with two issues. First, we explore the quantitiative importance of higher multiplets for properties of the $Δ$ decuplet in chiral perturbation theory. In particular, it is found that the lowest order one--loop contributions from the Roper octet to the decuplet masses and magnetic moments are substantial. The relevance of these results to the chiral expansion in general is discussed. The exact values of the magnetic moments depend upon delicate cancellations involving ill--determined coupling constants. Second, we present new relations between the magnetic moments of the $Δ$ decuplet that are independent of all couplings. They are exact at the order of the chiral expansion used in this paper.

hep-ph↗
arXiv1995

Can Large $u, d$ Quark Masses be Inferred from the $D_s \to n π$ decay rate?

The $D_s \rightarrow n π$ measured branching could lead to information on $u, d$ quark masses if it is dominated by the (helicity suppressed) $D_s \rightarrow u \bar d$ annihilation channel. The data would then suggest anomalously high $m_u \approx m_d \approx 30$MeV masses. We find however that $D_s \rightarrow u {\bar d} g$ can explain $\sum Br(D_s \rightarrow n π)$ with zero up and down quark masses. We also argue that the present $D_s \rightarrow n π$ data may not even convincingly imply any annihilation process whatsoever.

hep-ph↗
arXiv1995

Baryon Mass Splittings in Chiral Perturbation Theory

Baryon masses are calculated in chiral perturbation theory at the one--loop-${\cal O}(p^3)$ level in the chiral expansion and to leading order in the heavy baryon expansion. Ultraviolet divergences occur requiring the introduction of counter--terms. Despite this neccessity, no knowledge of the counter terms is required to determine the violations to the Gell--Mann Okubo mass relation for the baryon octet or to the decuplet equal mass--spacing rule, as all divergences cancel {\it exactly} at this order. For the same reason all reference to an arbitrary scale $μ$ is absent. Neither of these features continue to higher--powers in the chiral expansion. We also discuss critically the absolute neccessity of simultaneously going beyond the leading order heavy baryon expansion, if one goes beyond the one-loop-${\cal O}(p^3)$ level. We point out that these corrections in $1/M_B$ generate new divergences $\propto m^4/M_{10}$. These divergences together with the divergences occuring in one-loop-${\cal O}(p^4)$ graphs of chiral perturbation theory are taken care of by the same set of counter--terms. Because of these unknown counter--terms one cannot predict the baryon mass splittings at the one-loop-${\cal O}(p^4)$ level. We point out another serious problem of going to the one-loop-${\cal O}(p^4)$ level. When the decuplet is off its mass--shell there are additional $πNΔ$ and $πΔΔ$ interaction terms. These interactions contribute not only to the divergent terms $\propto (m^4/M_{10})$, but also to nonanalytic terms such as $\propto (m^4/M_{10}){\rm ln}(m/M_{10})$. Thus without a knowledge of the coupling constants appearing in these interactions one cannot carry out a consistent one-loop-${\cal O}(p^4)$ level calculation.

hep-ph↗
arXiv1994

Non-factorization and the Decays B into J/psi + K(*)

Many known models, which generally use a factorization hypothesis, give a poor account of the decays B into J/psi + K(*). Usually there is a free overall factor, which is fit to the data, so that tests of the models rely upon ratios. The models tend to give too much K* compared to K and too much transverse polarization compared to longitudinal. Our microscopic calculations, which use perturbative QCD, do well for both ratios. A microscopic calculation allows us to see how well factorization, heavy quark symmetry, and other features of various models are working. In the present case, agreement with the experimental ratios is dependent upon a breakdown of factorization for one of the amplitudes.

hep-ph↗
arXiv1994

Penguins leaving the pole: bound-state effects in B decaying to K* + photon

Applying perturbative QCD methods recently seen to give a good description of the two body hadronic decays of the B meson, we address the question of bound-state effects on the decay B into K* + gamma. Consistent with most analyses, we demonstrate that gluonic penguins, with photonic bremsstrahlung off a quark, change the decay rate by only a few percent. However, explicit off-shell b-quark effects normally discarded are found to be large in amplitude, although in the standard model accidents of phase minimize the effect on the rate. Using an asymptotic distribution amplitude for the K* and just the standard model, we can obtain a branching ratio of a few times 10^{-5}, consistent with the observed rate.

hep-ph↗
arXiv1994

Model Independent Extraction of $|V_{\rm bc}|$ Without Heavy Quark Symmetry

A new method to extract $|V_{\rm bc}|$ is proposed based on a sum--rule for semileptonic decays of the $B$ meson. The method relies on much weaker assumptions than previous approaches which are based on heavy--quark symmetry. This sum--rule only relies on the assumption that the virtual $c \overline{c}$ pair content of the $B$ meson can be neglected. The extraction of the CKM matrix element also requires that the sum--rule saturates in the kinematically accessible region.

hep-ph↗
arXiv1994

Systematics of Exclusive B-decays

Systematic analysis of the high recoil decay channels of the B-meson, two body mesonic decay channels in particular. For decays involving D-mesons, all experimentally observed rates are in reasonable accord with our calculations. Noticeable corrections to heavy quark symmetry are found, appearing most prominently when comparing D and D* decay modes. Calculated branching ratios involving the CKM matrix element V_{ub} are all below experimental upper bounds, but not markedly so. Calculated decay rates into charmonium lie a bit on the low side. Where color-suppressed diagrams contribute, they are found to be also suppressed dynamically and explicit calculation shows that the color-suppressed diagrams are ignorable in B to D pi decays.

hep-ph↗
arXiv1993

On the $A$ dependence of $R = σ_L/σ_T$ and the $Q^2$ dependence of Shadowing

A higher--twist nuclear enhancement of $R = σ_L/σ_T$, as might be expected to arise due to fermi motion and whose magnitude is within the error-bars of recent experiment, is shown to lead to a monotonic {\it decrease} in the ratio of nuclear vs. nucleon cross--sections at small Bjorken $x$ for {\it increasing} $Q^2$. This effect at small $x$, comparable in magnitude to those reported for shadowing, is driven mainly by kinematic factors and essentially vanishes for $x > .1$. Its unusual $Q^2$ dependence rather complicates the unravelling from present data in the shadowing region the corresponding dependence in $Q^2$ of the nuclear structure functions, $F_2^{A}(x,Q^2)$.

hep-ph↗