Semileptonic Processes Research Articles

A light-cone QCD sum rule approach for the Ξ baryon electromagnetic form factors and the semileptonic decay Ξc → Ξe+νe

The electromagnetic form factors of the Ξ baryons and the semileptonic decay process Ξc → Ξe+νe are investigated in the frame work of the light-cone QCD sum rule method with Ioffe-type interpolating currents. Our estimates on the magnetic moments are and . The decay width of the semileptonic process is expected to be Γ(Ξc → Ξe+νe) = (6.17+2.24− 2.48) × 10−14 GeV. The results show that the adoption of this type of interpolating current improves the calculations of the magnetic form factors and gives more reliable prediction for the analysis of the semileptonic decay process.

Bulk viscosity of spin-one color superconducting strange quark matter

The bulk viscosity in spin-one color-superconducting strange quark matter is calculated by taking into account the interplay between the nonleptonic and semi-leptonic week processes. In agreement with previous studies, it is found that the inclusion of the semi-leptonic processes may result in non-negligible corrections to the bulk viscosity in a narrow window of temperatures. The effect is generally more pronounced for pulsars with longer periods. Compared to the normal phase, however, this effect due to the semi-leptonic processes is less pronounced in spin-one color superconductors. Assuming that the critical temperature of the phase transition is much larger than 40 keV, the main effect of spin-one color superconductivity in a wide range of temperatures is an overall increase of the bulk viscosity with respect to the normal phase. The corresponding enhancement factor reaches up to about 9 in the polar and A-phases, about 25 in the planar phase and about 29 in the CSL phase. This factor is determined by the suppression of the nonleptonic rate in color-superconducting matter and, therefore, may be even larger if all quark quasiparticles happen to be gapped.

Semileptonic decays of light quarks beyond the Standard Model

We describe non-standard contributions to semileptonic processes in a model independent way in terms of an SU ( 2 ) L × U ( 1 ) Y invariant effective lagrangian at the weak scale, from which we derive the low-energy effective lagrangian governing muon and beta decays. We find that the deviation from Cabibbo universality, Δ CKM ≡ | V u d | 2 + | V u s | 2 + | V u b | 2 − 1 , receives contributions from four effective operators. The phenomenological bound Δ CKM = ( − 1 ± 6 ) × 10 − 4 provides strong constraints on all four operators, corresponding to an effective scale Λ > 11 TeV (90% CL). Depending on the operator, this constraint is at the same level or better then the Z pole observables. Conversely, precision electroweak constraints alone would allow universality violations as large as Δ CKM = − 0.01 (90% CL). An observed Δ CKM ≠ 0 at this level could be explained in terms of a single four-fermion operator which is relatively poorly constrained by electroweak precision measurements.

A unified formalism for the basic nuclear matrix elements in semi-leptonic processes

A general compact formalism, appropriate for the description of transition amplitudes in semi-leptonic processes involving lepton–nucleus interactions, is presented. Closed analytic expressions for the reduced matrix elements of all the basic tensor operators originating from a multipole expansion of the relevant hadronic current density and the use of harmonic oscillator basis are derived. The method improves over the well-known Horie–Sasaki formalism used the last decades as well as over other similar methods employed in nuclear many-body calculations. As a concrete application, we present results of differential cross sections for the neutral-current neutrino–nucleus reaction Mo 98 ( ν , ν ′ ) Mo ∗ 98 obtained with state-by-state calculations in the context of the quasi-particle random phase approximation (QRPA).

Multiparameter approach toR-parity violating supersymmetric couplings

We introduce and implement a new, extended approach to placing bounds on trilinear R-parity violating couplings. We focus on a limited set of leptonic and semi-leptonic processes involving neutrinos, combining multidimensional plotting and cross-checking constraints from different experiments. This allows us to explore new regions of parameter space and to relax a number of bounds given in the literature. We look for qualitatively different results compared to those obtained previously using the assumption that a single coupling dominates the R-parity violating contributions to a process (SCD). By combining results from several experiments, we identify regions in parameter space where two or more parameters approach their maximally allowed values. In the same vein, we show a circumstance where consistency between independent bounds on the same combinations of trilinear coupling parameters implies mass constraints among slepton or squark masses. Though our new bounds are in most cases weaker than the SCD bounds, the largest deviations we find on individual parameters are factors of two, thus indicating that a conservative, order of magnitude bound on an individual coupling is reliably estimated by making the SCD assumption.

Erratum:Bmeson semileptonic form factors from unquenched lattice QCD [Phys. Rev. D73, 074502 (2006)

The semileptonic process, B --> \pi l \nu, is studied via full QCD Lattice simulations. We use unquenched gauge configurations generated by the MILC collaboration. These include the effect of vacuum polarization from three quark flavors: the $s$ quark and two very light flavors ($u/d$) of variable mass allowing extrapolations to the physical chiral limit. We employ Nonrelativistic QCD to simulate the $b$ quark and a highly improved staggered quark action for the light sea and valence quarks. We calculate the form factors $f_+(q^2)$ and $f_0(q^2)$ in the chiral limit for the range 16 GeV$^2 \leq q^2 < q^2_{max}$ and obtain $\int^{q^2_{max}}_{16 GeV^2} [d\Gamma/dq^2] dq^2 / |v_{ub}|^2 = 1.46(35) ps^{-1}$. Combining this with a preliminary average by the Heavy Flavor Averaging Group (HFAG'05) of recent branching fraction data for exclusive B semileptonic decays from the BaBar, Belle and CLEO collaborations, leads to $|V_{ub}| = 4.22(30)(51) \times 10^{-3}$. PLEASE NOTE APPENDIX B with an ERRATUM, to appear in Physical Review D, to the published version of this e-print (Phys.Rev.D 73, 074502 (2006)). Results for the form factor $f_+(q^2)$ in the chiral limit have changed significantly. The last two sentences in this abstract should now read; "We calculate the form factor $f_+(q^2)$ and $f_0(q^2)$ in the chiral limit for the range 16 Gev$^2 \leq q^2 < q^2_{max}$ and obtain $\int^{q^2_{max}}_{16 GeV^2} [d\Gamma/dq^2] dq^2 / |V_{ub}|^2 = 2.07(57)ps^{-1}$. Combining this with a preliminary average by the Heavy Flavor Averagibg Group (HFAG'05) of recent branching fraction data for exclusive B semileptonic decays from the BaBar, Belle and CLEO collaborations, leads to $|V_{ub}| = 3.55(25)(50) \times 10^{-3}$."

Bmeson semileptonic form factors from unquenched lattice QCD

The semileptonic process, $B\ensuremath{\rightarrow}\ensuremath{\pi}l\ensuremath{\nu}$, is studied via full QCD lattice simulations. We use unquenched gauge configurations generated by the MILC Collaboration. These include the effect of vacuum polarization from three quark flavors: the $s$ quark and two very light flavors ($u/d$) of variable mass allowing extrapolations to the physical chiral limit. We employ nonrelativistic QCD to simulate the $b$ quark and a highly improved staggered quark action for the light sea and valence quarks. We calculate the form factors ${f}_{+}({q}^{2})$ and ${f}_{0}({q}^{2})$ in the chiral limit for the range $16\text{ }\text{ }{\mathrm{GeV}}^{2}\ensuremath{\le}{q}^{2}l{q}_{\mathrm{max}}^{2}$ and obtain ${\ensuremath{\int}}_{16\text{ }\text{ }{\mathrm{GeV}}^{2}}^{{q}_{\mathrm{max}}^{2}}[d\ensuremath{\Gamma}/d{q}^{2}]d{q}^{2}/|{V}_{ub}{|}^{2}=1.46(35)\text{ }\text{ }{\mathrm{ps}}^{\ensuremath{-}1}$. Combining this with a preliminary average by the Heavy Flavor Averaging Group (HFAG'05) of recent branching fraction data for exclusive $B$ semileptonic decays from the BABAR, Belle and CLEO Collaborations leads to $|{V}_{ub}|=4.22(30)(51)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$.

Improved Calculation of Electroweak Radiative Corrections and the Value ofVud

A new method for computing hadronic effects on electroweak radiative corrections to low-energy weak interaction semileptonic processes is described. It employs high order perturbative QCD results originally derived for the Bjorken sum rule along with a large QCD-motivated interpolating function that matches long- and short-distance loop contributions. Applying this approach to the extraction of the Cabibbo-Kobayashi-Maskawa (CKM) matrix element Vud from superallowed nuclear beta decays reduces the theoretical loop uncertainty by about a factor of 2 and gives Vud=0.97377(11)(15)(19). Implications for CKM unitarity are briefly discussed.

Piecewise moments method: Generalized Lanczos technique for nuclear response surfaces

For some years Lanczos moments methods have been combined with large-scale shell-model calculations in evaluations of the spectral distributions of certain operators. This technique is of great value because the alternative, a state-by-state summation over final states, is generally not feasible. The most celebrated application is to the Gamow-Teller operator, which governs beta decay and neutrino reactions in the allowed limit. The Lanczos procedure determines the nuclear response along a line q=0 in the (omega,q) plane, where omega and q are the energy and three-momentum transfered to the nucleus. However, generalizing such treatments from the allowed limit to general electroweak response functions at arbitrary momentum transfers seems considerably more difficult: the response function must be determined over the entire (omega,q) plane for an operator O(q) that is not fixed, but depends explicitly on q. Such operators arise in any semileptonic process where the momentum transfer is comparable to (or larger than) the inverse nuclear size. Here we show, for Slater determinants built on harmonic oscillator basis functions, that the nuclear response for any multipole operator O(q) can be determined efficiently over the full response plane by a generalization of the standard Lanczos moments method. We describe the Piecewise Moments Method and thoroughly explore its convergence properties for the test case of electromagnetic responses in a full sd-shell calculation of 28Si. We discuss possible extensions to a variety of electroweak processes, including charged- and neutral-current neutrino scattering.

Estimating the [formula omitted]Kπ interaction in D decay

Heavy flavour decay to light hadrons is the key to understanding many aspects of the Standard Model from CP violation to strong dynamics. It is often presumed in line with the simple quark spectator model of D decay to Kππ that the Kπ system has only I=1/2. E791 have recently presented an analysis of their results on D+→(K−π+)π+ using a generalised isobar picture of two body interactions. While higher Kπ waves are described by sums of known resonances, the S-wave amplitude and phase are determined bin-by-bin in Kπ mass. The phase variation is found not to be that of K−π+ elastic scattering. This hints at a different mixture of I=1/2 and I=3/2S-wave interactions than in elastic scattering. Applying Watson's theorem to this generalised isobar model allows us to estimate the I=3/2Kπ S-wave component. We indeed find that this is larger than in hadronic scattering or semileptonic processes.

Radiative corrections in weak semi-leptonic processes at low energy: a two-step matching determination*

We focus on the chiral Lagrangian couplings describing radiative corrections to weak semi-leptonic decays and relate them to the decay amplitude of a lepton, computed by Braaten and Li at one loop in the standard model. For this purpose, we follow a two-step procedure. A first matching, from the standard model to Fermi theory, yields a relevant set of counterterms. The latter are related to chiral couplings thanks to a second matching, from Fermi theory to the chiral Lagrangian, which is performed using the spurion method. We show that the chiral couplings of physical relevance obey integral representations in a closed form, expressed in terms of QCD chiral correlators and vertex functions. We deduce exact relations among the couplings, as well as numerical estimates which go beyond the usual $\log(M_Z/M_\rho)$ approximation.

KLOE RESULTS AT THE FRASCATI ϕ-FACTORY DAΦNE

The KLOE experiment at the Frascati ϕ-factory DAΦNE has collected about 0.5 fb-1 of data till the end of the year 2002. These data allow to perform a wide physics program, ranging from the physics of charged and neutral kaons to radiative ϕ-decays. Results are presented for the KL lifetime and the semileptonic processes KS,L→πeν. From the light meson spectroscopy program, results on the decays ϕ→f0(980)γ, a0(980)γ as well as ϕ→ηγ, η′γ are presented.

Measurement of lepton momentum moments in the decayB¯→Xlν¯and determination of the heavy quark expansion parameters and|Vcb|

We measure the primary lepton momentum spectrum in B-bar to X l nu decays, for p_l > 1.5 GeV/c in the B rest frame. From this, we calculate various moments of the spectrum. In particular, we find R_0 = [int(E_l>1.7) (dGam/dE_sl)*dE_l] / [int(E_l>1.5) (dGam/dE_sl)*dE_l] = 0.6187 +/- 0.0014_stat +/- 0.0016_sys and R_1 = [int(E_l>1.5) E_l(dGam/dE_sl)*dE_l] / [int(E_l>1.5) (dGam/dE_sl)*dE_l] = (1.7810 +/- 0.0007_stat +/- 0.0009_sys) GeV. We use these moments to determine non-perturbative parameters governing the semileptonic width. In particular, we extract the Heavy Quark Expansion parameters Lambda-bar = (0.39 +/- 0.03_stat +/- 0.06_sys +/- 0.12_th) GeV and lambda_1 = (-0.25 +/- 0.02_stat +/- 0.05_sys +/- 0.14_th) GeV^2. The theoretical constraints used are evaluated through order 1/M_B^3 in the non-perturbative expansion and beta_0*alpha__s^2 in the perturbative expansion. We use these parameters to extract |V_cb| from the world average of the semileptonic width and find |V_cb| = (40.8 +/- 0.5_Gam-sl +/- 0.4_(lambda_1,Lambda-bar)-exp +/- 0.9_th) x 10^-3. In addition, we extract the short range b-quark mass m_b^1S = (4.82 +/- 0.07_exp +/- 0.11_th) GeV/c^2. Finally, we discuss the implications of our measurements for the theoretical understanding of inclusive semileptonic processes.

First measurement of branching ratio and [formula omitted] of the neutral cascade hyperon using final state polarization

The KTeV collaboration has made a first observation of neutral cascade beta decay ( Ξ 0 → Σ + e − ν ). We present measurements of the branching ratio and form factors for this semi leptonic process. The results agree well with the Cabibbo SU(3) f theory and do not favor attempts to include symmetry breaking effects.

QCD corrections to [formula omitted] at LEP2 and the next linear collider: CC10 at O( αs)

QCD one-loop corrections to the semileptonic process e +e − → μ − ν μ u d are computed. We compare the exact calculation with a “naive” approach to strong radiative corrections which has been widely used in the literature and discuss the phenomenological relevance of QCD contributions for LEP2 and NLC physics.

Semileptonic Decays of B Meson into Charmed Higher Resonances in the Heavy Quark Effective Theory

Heavy quark effective theory is applied to semileptonic decays of B mesons into charmed higher resonances D X , where subscript X denotes various spin-parity states of resonances. We calculate the differential decay rates and branching ratios of the decay B → D X lν t . We find that the largest fraction of the semileptonic process B → D X lν t other than D(1869) and D*(2010) is D 2 *(1P state) whose value is 0.11%. It is also estimated that among the unidentified modes in the semileptonic decays of B meson other than D(1896) and D*(2010) the total contribution of exclusive higher resonance modes to the branching ratios is 0.3%. The results are compared to the recent experimental data and the other theoretical analyses

The birth of strange matter from two-flavor quark matter in a neutron star

The phase transition of two-flavor quark matter into strange matter in the interior of a neutron star is studied. It is shown that the timescale of the transition is below 0.1 ωs and the s-quark semileptonic processes are of significance in neutrino emissions during the transition. Owing to these processes, the transition in a young neutron star of 1.4 M ⊙ mass will liberate more than 3×10 51 erg of energy as a neutrino burst.

PHASE TRANSITION OF NONSTRANGE-STRANGE QUARK MATTER IN THE INTERIOR OF A NEUTRON STAR

The phase transition of two-flavor quark matter into strange matter in the interior of a neutron star is studied. It is shown that the timescale of the transition is less than 0.1μs and the s-quark semileptonic processes are of significance in neutrino emission during the transition. Owing to these processes, the transition in a whole neutron star will liberate several 1051 erg of energy as a neutrino burst.

How good is the factorization approach in charm decays?

An analysis of the factorization approach in charm hadronic decays is carried out by using the spectral-functions method and by exploiting the updated information on the semileptonic processes of both the $D$ meson and the $\ensuremath{\tau}$ lepton. Not only the two-body but also the multiparticle exclusive decays can be computed for the first time. While for some channels agreement with experiment is somewhat acceptable, within a factor of 2, much larger variance is found for other modes: ${D}^{0}\ensuremath{\rightarrow}{K}^{\ensuremath{-}}{a}_{1}^{+}(1260)$ ${D}^{0}\ensuremath{\rightarrow}{K}^{\ensuremath{-}*}{\ensuremath{\pi}}^{+}$, ${D}^{0}\ensuremath{\rightarrow}{K}^{\ensuremath{-}}\ensuremath{\pi}\ensuremath{\pi}\ensuremath{\pi}\ensuremath{\pi}$.

Chiral perturbation theory for hadrons containing a heavy quark. The sequel

Charm and bottom mesons and baryons are incorporated into a low energy chiral lagrangian. Interactions of the heavy hadrons with light octet Goldstone bosons are studied in a framework which represents a synthesis of chiral perturbation theory and the heavy quark effective theory. The differential decay rate for the semileptonic process Λ b 0→Σ c ++ + œ −+ ν e + π − is calculated at the zero recoil point using this hybrid formalism.