Reweighting of the form factors in exclusive B --> X ell nu decays

A form factor reweighting technique has been elaborated to permit relatively easy comparisons between different form factor models applied to exclusive B --> X l nu decays. The software tool developped for this purpose is described. It can be used with any event generator, three of which were used in this work: ISGW2, PHSP and FLATQ2, a new powerful generator. The software tool allows an easy and reliable implementation of any form factor model. The tool has been fully validated with the ISGW2 form factor hypothesis. The results of our present studies indicate that the combined use of the FLATQ2 generator and the form factor reweighting tool should play a very important role in future exclusive |Vub| measurements, with largely reduced errors.Comment: accepted for publication by EPJ

On-Board Sensor-Based NO x Emissions from Heavy-Duty Diesel Vehicles

Real-world nitrogen oxides (NOx) emissions were estimated using on-board sensor readings from 72 heavy-duty diesel vehicles (HDDVs) equipped with a Selective Catalytic Reduction (SCR) system in California. The results showed that there were large differences between in-use and certification NOx emissions, with 12 HDDVs emitting more than three times the standard during hot-running and idling operations in the real world. The overall NOx conversion efficiencies of the SCR system on many vehicles were well below the 90% threshold that is expected for an efficient SCR system, even when the SCR system was above the optimum operating temperature threshold of 250 °C. This could potentially be associated with SCR catalyst deterioration on some engines. The Not-to-Exceed (NTE) requirements currently used by the heavy-duty in-use compliance program were evaluated using on-board NOx sensor data. Valid NTE events covered only 4.2–16.4% of the engine operation and 6.6–34.6% of the estimated NOx emissions. This work shows that low cost on-board NOx sensors are a convenient tool to monitor in-use NOx emissions in real-time, evaluate the SCR system performance, and identify vehicle operating modes with high NOx emissions. This information can inform certification and compliance programs to ensure low in-use NOx emissions

Right-handed currents in rare exclusive B -> (K, K*) nu bar{nu} decays

The effects of possible right-handed weak hadronic currents in rare exclusive semileptonic decays B -> (K, K*) nu bar{nu} are investigated using a lattice-constrained dispersion quark model for the calculation of the relevant mesonic form factors. The results obtained for the branching ratios and the missing energy spectra are presented and the sensitivity of various observables to long-distance physics is investigated. It is shown that the asymmetry of transversely polarized K*(T) mesons as well as the K / K*(T) production ratio are only slightly sensitive to long-distance contributions and mostly governed by the relative strength and phase of right-handed currents. In particular, within the Standard Model the production of right-handed K*(T) mesons turns out to be largely suppressed with respect to left-handed ones, thanks to the smallness of the final to initial meson mass ratio. Therefore, the measurement of produced right-handed K*(T) mesons in rare B -> K* nu bar{nu} decays offers a very interesting tool to investigate right-handed weak hadronic currents.Comment: latex, 10 pp., 4 figures with epsfig.st

ρ\rho Polarization and `Model Independent' Extraction of ∣Vub∣/∣Vcd∣|V_{ub}|/|V_{cd}| from D→ρℓνD\to\rho\ell\nu and B→ρℓνB\to\rho\ell\nu

We briefly discuss the predictions of the heavy quark effective theory for the semileptonic decays of a heavy pseudoscalar to a light one, or to a light vector meson. We point out that measurement of combinations of differential helicity decay rates at Cleo-c and the $B$ factories can provide a model independent means of extracting the ratio $|V_{ub}|/|V_{cd}|$. We briefly discuss the corrections to this prediction.Comment: 8 pages, LaTeX, 1 figur

Semileptonic decays B→(π,ρ)eνB\to(\pi,\rho)e\nu in relativistic quark model

Quark model results for the $B\to \pi,\rho$ decays are analysed, making use of the dispersion formulation of the model: The form factors at $q^2>0$ are expressed as relativistic invariant double spectral representation over invariant masses of the initial and final mesons through their light--cone wave functions. The dependence of the results on the quark model parameters is studied. For various versions of the quark model the ranges $\Gamma(\bar B^0\to\pi^+e\bar\nu)=(7\pm2)\times10^{12}|V_{ub}|^2\; s^{-1}$, $\Gamma(\bar B^0\to\rho^+e\bar\nu)/\Gamma(\bar B^0\to\pi^+e\bar\nu)=1.45\pm0.1$, and $\Gamma_L/\Gamma_T=0.7\pm0.08$ are found. The effects of the constituent quark transition form factor are briefly discussed.Comment: latex, 8 pages, 2 figure

On Some rare weak decays of vector mesons

Some semileptonic weak decays of vector mesons are considered in the framework of the most popular quark models. The predicted branching ratios are unfortunately too small to make a study of these decays realistic at meson factories under construction.Comment: 14 pages, LaTeX. Some typos correcte

The Lambda_b lifetime in the light front quark model

The enhancement of the Lambda_b decay width relative to B decay one due to the difference of Fermi motion effects in Lambda_b and B is calculated in the light--front quark model with the simplifying assumption that Lambda_b consists of the heavy quark and light scalar diquark. In order to explain the large deviation from unity in the experimental result for tau(Lambda_b)/tau(B), it is necessary that diquark be light and the ratio of the squares of the Lambda_b and B wave functions at the origin be \le 1.Comment: final journal version to appear in JETP Letter

BB Intermeson Potentials in the Quark Model

In this paper we derive quark model results for scattering amplitudes and equivalent low energy potentials for heavy meson pairs, in which each meson contains a heavy quark. This "BB" system is an attractive theoretical laboratory for the study of the nuclear force between color singlets; the hadronic system is relatively simple, and there are lattice gauge theory (LGT) results for V_BB(r) which may be compared to phenomenological models. We find that the quark model potential (after lattice smearing) has qualitative similarities to the LGT potential in the two B*B* channels in which direct comparison is possible, although there is evidence of a difference in length scales. The quark model prediction of equal magnitude but opposite sign for I=0 and I=1 potentials also appears similar to LGT results at intermediate r. There may however be a discrepancy between the LGT and quark model I=1 BB potentials. A numerical study of the two-meson Schrodinger equations in the (bqbar)(bqbar) and (cqbar)(cqbar) sectors with the quark model potentials finds a single "molecule", in the I=0 BB* sector. Binding in other channels might occur if the quark model forces are augmented by pion exchange.Comment: 30 pages, 5 figures, revtex and epsfig. Submitted to Phys. Rev.

Flux Tube Zero-Point Motion, Hadronic Charge Radii, and Hybrid Meson Production Cross Sections

Flux tube zero-point motion produces quark displacements transverse to the flux tube which make significant contributions to hadronic charge radii. In heavy quark systems, these contributions can be related by Bjorken's sum rule to the rates for semileptonic decay to hybrid mesons. This connection can be generalized to other leptoproduction processes, where transverse contributions to elastic form factor slopes are related to the cross sections for the production of the associated hybrid states. I identify the flux tube overlap integral responsible for these effects as the strong QCD analogue of the Sudakov form factor of perturbative QCD.Comment: 16 pages, revised to clarify some points and to improve and correct the notation for the flux tube wave function

Hadronic Charmed Meson Decays Involving Tensor Mesons

Charmed meson decays into a pseudoscalar meson P and a tensor meson T are studied. The charm to tensor meson transition form factors are evaluated in the Isgur-Scora-Grinstein-Wise (ISGW) quark model. It is shown that the Cabibbo-allowed decay $D_s^+\to f_2(1270)\pi^+$ is dominated by the W-annihilation contribution and has the largest branching ratio in $D\to TP$ decays. We argue that the Cabibbo-suppressed mode $D^+\to f_2(1270)\pi^+$ should be suppressed by one order of magnitude relative to $D_s^+\to f_2(1270)\pi^+$. When the finite width effect of the tensor resonances is taken into account, the decay rate of $D\to TP$ is generally enhanced by a factor of $2\sim 3$. Except for $D_s^+\to f_2(1270)\pi^+$, the predicted branching ratios of $D\to TP$ decays are in general too small by one to two orders of magnitude compared to experiment. However, it is very unlikely that the $D\to T$ transition form factors can be enhanced by a factor of $3\sim 5$ within the ISGW quark model to account for the discrepancy between theory and experiment. As many of the current data are still preliminary and lack sufficient statistic significance, more accurate measurements are needed to pin down the issue.Comment: 11 page