Decays Of Charmed Mesons Research Articles

Search for rare and forbidden decays of charm and charmed-strange mesons to final statesh±e∓e+

We have searched for flavor-changing neutral current decays and lepton-number-violating decays of D^+ and D^+_s mesons to final states of the form h^+- e^-+ e^+, where h is either \pi or K. We use the complete samples of CLEO-c open-charm data, corresponding to integrated luminosities of 818 pb^-1 at the center-of-mass energy E_CM = 3.774 GeV containing 2.4 x 10^6 D^+D^- pairs and 602 pb^-1 at E_CM = 4.170 GeV containing 0.6 x 10^6 D^*+-_s D^-+_s pairs. No signal is observed in any channel, and we obtain 90% confidence level upper limits on branching fractions B(D^+ --> \pi^+ e^+ e^-) < 5.9 x 10^-6, B(D^+ --> \pi^- e^+ e^+) < 1.1 x 10^-6, B(D^+ --> K^+ e^+ e^-) < 3.0 x 10^-6, B(D^+ --> K^- e^+ e^+) < 3.5 x 10^-6, B(D^+_s --> \pi^+ e^+ e^-) < 2.2 x 10^-5, B(D^+_s --> \pi^- e^+ e^+) < 1.8 x 10^-5, B(D^+_s --> K^+ e^+ e^-) < 5.2 x 10^-5, and B(D^+_s --> K^- e^+ e^+) < 1.7 x 10^-5.

Charm hadronic decays and quantum correlations at CLEO-c

Several recent CLEO-c results on hadronic decays of charm mesons are reviewed. Topics include measurements of precision branching fractions for exclusive modes, investigations of inclusive rates, and analyses of Dalitz plots. In addition, the quantum correlations of the DD̄ pairs produced at the ψ(3770) are exploited to measure phase information that is of current interest for both D and B physics.

Two-body hadronic charmed meson decays

We study in this work the two-body hadronic charmed meson decays, including both the PP and VP modes. The latest experimental data are first analyzed in the diagrammatic approach. The magnitudes and strong phases of the flavor amplitudes are extracted from the Cabibbo-favored (CF) decay modes using $\chi^2$ minimization. The best-fitted values are then used to predict the branching fractions of the singly-Cabibbo-suppressed (SCS) and doubly-Cabibbo-suppressed decay modes in the flavor SU(3) symmetry limit. We observe significant SU(3) breaking effects in some of SCS channels. In the case of VP modes, we point out that the $A_P$ and $A_V$ amplitudes cannot be completely determined based on currently available data. We conjecture that the quoted experimental results for both $D_s^+\to\bar K^0K^{*+}$ and $D_s^+\to \rho^+\eta'$ are overestimated. We compare the sizes of color-allowed and color-suppressed tree amplitudes extracted from the diagrammatical approach with the effective parameters $a_1$ and $a_2$ defined in the factorization approach. The ratio $|a_2/a_1|$ is more or less universal among the $D \to {\bar K} \pi$, ${\bar K}^* \pi$ and ${\bar K} \rho$ modes. This feature allows us to discriminate between different solutions of topological amplitudes. For the long-standing puzzle about the ratio $\Gamma(D^0\to K^+K^-)/\Gamma(D^0\to\pi^+\pi^-)$, we argue that, in addition to the SU(3) breaking effect in the spectator amplitudes, the long-distance resonant contribution through the nearby resonance $f_0(1710)$ can naturally explain why $D^0$ decays more copiously to $K^+ K^-$ than $\pi^+ \pi^-$ through the $W$-exchange topology.

Measurement of absolute branching fractions of inclusive semileptonic decays of charm and charmed-strange mesons

We have measured the inclusive semileptonic branching fractions of $D^0$, $D^+$, and $D^+_s$ mesons. For these measurements, we have used the full CLEO-c open-charm data samples, 818 pb$^{-1}$ at $E_\text{CM} = 3.774$ GeV, giving $D^0 \bar{D}^0$ and $D^+ D^-$ events, and 602 pb$^{-1}$ at $E_\text{CM} = 4.170$ GeV, giving $D^{\ast \pm}_s D^\mp_s$ events. We obtain $\mathcal{B}(D^0 \to X e^+ \nu_e) = (6.46 \pm 0.09 \pm 0.11)$%, $\mathcal{B}(D^+ \to X e^+ \nu_e) = (16.13 \pm 0.10 \pm 0.29)$%, and $\mathcal{B}(D^+_s \to X e^+ \nu_e) = (6.52 \pm 0.39 \pm 0.15)$%, where the first uncertainties are statistical and the second are systematic. From these and lifetimes obtained elsewhere, we obtain the ratios of semileptonic decay widths $\Gamma (D^+ \to X e^+ \nu_e) / \Gamma (D^0 \to X e^+ \nu_e) = 0.985 \pm 0.015 \pm 0.024$ and $\Gamma (D^+_s \to X e^+ \nu_e) / \Gamma (D^0 \to X e^+ \nu_e) = 0.828 \pm 0.051 \pm 0.025$. The ratio of $D^+$ and $D^0$ is consistent with the isospin symmetry prediction of unity, and the ratio of $D^+_s$ and $D^0$ differs from unity, as expected.

Can scalar leptoquarks explain the [formula omitted] puzzle?

Motivated by the disagreement between experimental and lattice QCD results on the Ds decay constant we systematically reinvestigate role of leptoquarks in charm meson decays. We consider scalar leptoquarks that transform as a weak interaction triplet, doublet, or singlet in a model independent approach, and also argue that in a particular class of SU(5) GUT models these leptoquark states, contained in the 45-dimensional Higgs representation, could be safe against proton decay bounds. Using the current experimental measurements in τ, kaon and charm sectors, we find that scalar leptoquarks cannot naturally explain the Ds→μν and Ds→τν decay widths simultaneously. While any contributions of the triplet leptoquarks are already excluded, the singlets could only contribute significantly to the Ds→τν width. Finally, a moderate improvement of the experimental upper bound on the D0→μ+μ− decay width could exclude the doublet contribution to the Ds→μν, while present experimental data limits its mass to be below 1.4 TeV. Possible new signatures at present and near future experiments are also briefly discussed.

Atmospheric lepton fluxes at ultrahigh energies

In order to estimate the possibility to observe exotic physics in a neutrino telescope, it is essential to first understand the flux of atmospheric neutrinos, muons and dimuons. We study the production of these leptons by high-energy cosmic rays. We identify three main sources of muons of energy E ⩾ 106 GeV: the weak decay of charm and bottom mesons and the electromagnetic decay of unflavored mesons. Contrary to the standard assumption, we find that η mesons, not the prompt decay of charm hadrons, are the dominant source of atmospheric muons at these energies. We show that, as a consequence, the ratio between the neutrino and muon fluxes is significantly reduced. For dimuons, which may be a background for long-lived staus produced near a neutrino telescope, we find that pairs of E ≈ 107 GeV forming an angle above 10−6 rad are produced through D (80%) or B (10%) meson decay and through Drell-Yan proceses (10%). The frequency of all these processes has been evaluated using the jet code PYTHIA.

The role and detectability of the charm contribution to ultra high energy neutrino fluxes

It is widely believed that charm meson production and decay may play an important role in high energy astrophysical sources of neutrinos, especially those that are baryon-rich, providing an environment conducive to pp interactions. Using slow-jet supernovae (SJS) as an example of such a source, we study the detectability of high-energy neutrinos, paying particular attention to those produced from charmed-mesons. We highlight important distinguishing features in the ultra-high energy neutrino flux which would act as markers for the role of charm in the source. In particular, charm leads to significant event rates at higher energies, after the conventional (π,K) neutrino fluxes fall off. We calculate event rates both for a nearby single source and for diffuse SJS fluxes for an IceCube-like detector. By comparing muon event rates for the conventional and prompt fluxes in different energy bins, we demonstrate the striking energy dependence in the rates induced by the presence of charm. We also show that it leads to an energy dependant flux ratio of shower to muon events, providing an additional important diagnostic tool for the presence of prompt neutrinos. Motivated by the infusion of high energy anti-electron neutrinos into the flux by charm decay, we also study the detectability of the Glashow resonance due to these sources.

Experimental Sensitivities on Searching for Rare and Forbidden Decays of Charm Mesons at BES-III

We discuss the Monte Carlo studies of searching for the rare and forbidden pure-leptonic and semi-leptonic decays of D+,0 and Ds+ mesons, based on a full Monte Carlo simulation for the BES-III detector, with the BES-III Offline Software System. The experimental sensitivities of searching for 36 rare and forbidden charm meson decays are estimated.

Updated constraints on new physics in rare charm decays

Motivated by recent experimental results on charm physics, we investigate implications of the updated constraints of new physics in rare charm meson decays. We first reconsider effects of the minimal supersymmetric standard model (MSSM) in $c\ensuremath{\rightarrow}u\ensuremath{\gamma}$ constrained by the recent experimental evidence on $\ensuremath{\Delta}{m}_{D}$ and find that, due to the dominance of long-distance physics, $D\ensuremath{\rightarrow}V\ensuremath{\gamma}$ decay rates cannot be modified by MSSM contributions. Then we consider effects of the extra heavy up vectorlike quark models on the decay spectrum of ${D}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ and ${D}_{s}^{+}\ensuremath{\rightarrow}{K}^{+}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ decays. We find a possibility for the tiny increase of the differential decay rate in the region of large dilepton mass. The $R$-parity violating supersymmetric model can also modify short distance dynamics in $c\ensuremath{\rightarrow}u{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ decays. We constrain relevant parameters using the current upper bound on the ${D}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ decay rate and investigate the impact of that constraint on the ${D}_{s}^{+}\ensuremath{\rightarrow}{K}^{+}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ differential decay dilepton distribution. Present bounds still allow a small modification of the standard model differential decay rate distribution.

A review of charm semileptonic decays

Several high energy experiments have been actively pursuing the analyses of semileptonic decays of charm mesons, resulting in numerous new results and publications. In this report, we summarize the recent efforts on the topics of pseudoscalar and vector charm semileptonic decays, especially in the area of branching fractions and form factor measurements.

Charm Decays at B Factories

Recent results relating to charm baryon and meson decays from the Belle and BABAR experiments are presented. In addition to recent observations for charm hyperons, evidence for a new charm baryon state, the Λc(2940), observed in its decay to D0p is also reported. No evidence for doubly charmed baryons is seen in e+e- interactions. A measurement of the spin of the Ω- hyperon is made using decays of the [Formula: see text] and [Formula: see text] baryons. On the assumption that the spin of the parent baryons are J = 1/2, the assignment J = 3/2 is confirmed and both J = 1/2 and also higher spins are excluded. New results on rare, Cabibbo-suppressed decays of charm mesons are also presented.

Dependence of the non-photonic electron spectrum on the charmed baryon-to-meson ratio

In this talk I argue that a substantial fraction of the non-photonic electron suppression in Au+Au collisions could arise as a result of an enhanced Λc/D ratio rather than purely from jet-quenching. At intermediate transverse momentum (2<pT<6 GeV/c), the baryon-to-meson ratio in Au+Au collisions is enhanced compared to p+p collisions. Since charm-baryon decays produce electrons less frequently than charm-meson decays, the non-photonic electron spectrum is sensitive to the Λc/D ratio. I show the dependence of the non-photonic electron spectrum on the baryon-to-meson ratio for charm hadrons. As an example, I assume that the Λc/D ratio is the same as the Λ/K0 S ratio. I show that even if the total charm quark yield in Au+Au collisions scales with the number of binary nucleon-nucleon collisions (Nbin), the electron spectrum at 2<pT<5 GeV/c will be suppressed relative to Nbin scaled p+p collisions by as much as 20%.

High energy neutrino yields from astrophysical sources

We calculate the yield and flavour content of high energy neutrinos produced in astrophysical sources with negligible magnetic fields varying their interaction depth. We take into account the scattering of secondaries on background photons as well as the direct production of neutrinos in decays of charm mesons. If multiple scattering of nucleons becomes important, the neutrino spectra from meson and muon decays are strongly modified with respect to transparent sources. Characteristic for neutrino sources containing photons as scattering targets is a strong energy-dependence of the ratio R0 of νμ and νe fluxes at the sources, ranging from R0=ϕμ/ϕe∼0 below threshold to R0∼4 close to the energy where the decay length of charged pions and kaons equals their interaction length on target photons. Above this energy, the neutrino flux is strongly suppressed and depends mainly on charm production.

Suppression of nonphotonic electrons from enhancement of charm baryons in heavy ion collisions

At intermediate transverse momentum (2 < p_T < 6 GeV/c), baryon production in Au+Au collisions is enhanced compared to p+p collisions. Since charm baryon decays produce electrons less frequently than charm meson decays, the non-photonic electron spectrum is sensitive to the Lambda_c/D ratio. In this report we study the dependence of the non-photonic electron spectrum on the baryon-to-meson ratio for charm hadrons. As an example, we take the Lambda_c/D ratio to have the same form as the Lambda/K^0_S ratio. In this case, even if the total charm quark yield in Au+Au collisions scales with the number of binary nucleon-nucleon collisions (N_bin), the electron spectrum at 2 < p_T < 5 GeV/c is suppressed relative to N_bin scaled p+p collisions by as much as 20%.

Charmed-Meson Decay Constants in Three-Flavor Lattice QCD

We present the first lattice QCD calculation with realistic sea quark content of the D+-meson decay constant f(D+). We use the MILC Collaboration's publicly available ensembles of lattice gauge fields, which have a quark sea with two flavors (up and down) much lighter than a third (strange). We obtain f(D+)=201+/-3+/-17 MeV, where the errors are statistical and a combination of systematic errors. We also obtain f(Ds)=249+/-3+/-16 MeV for the Ds meson.

Search for T violation in charm meson decays

Using data from the FOCUS (E831) experiment, we have searched for T violation in charm meson decays using the four-body decay channels D0→K−K+π−π+, D+→KS0K+π−π+, and Ds+→KS0K+π−π+. The T violation asymmetry is obtained using triple-product correlations and assuming the validity of the CPT theorem. We find the asymmetry values to be ATviol(D0)=0.010±0.057(stat.)±0.037(syst.), ATviol(D+)=0.023±0.062(stat.)±0.022(syst.), and ATviol(Ds+)=−0.036±0.067(stat.)±0.023(syst.). Each measurement is consistent with no T violation. New measurements of the CP asymmetries for some of these decay modes are also presented.

Dalitz plot analysis in the FOCUS experiment

The K-matrix formalism has been applied to the charm sector for the .rst time in the FOCUS Dalitz plot analyses of the Ds+ and D+ → π+π−π+ final states. The results, presented here, are extremely encouraging since the same K-matrix description provides a coherent picture of both two-body scattering measurements in light-quark experiments as well as charm meson decay. Such a result was not obvious beforehand. Moreover, the non-resonant component of each decay appears to be described by known two-body S-wave dynamics, without the need to include any three-body constant amplitude contribution.

The PHENIX measurement of heavy flavour via single electrons in pp, d–Au and Au–Au collisions at

The PHENIX experiment at RHIC has measured single electron spectra in proton–proton, deuteron–gold and gold–gold collisions at . The photonic contribution (photon conversions and Dalitz decays) is subtracted from the inclusive spectra resulting in non-photonic single electron spectra. The principal source of non-photonic electrons is the semi-leptonic decay of charm and bottom mesons. The implications for heavy flavour production in hot and cold nuclear systems are discussed.

Light quark spectroscopy and charm decays

Weak decays of charm mesons has been used for studies of light quark spectroscopy, with particular emphasis on the J^{PC}=0^{++} states. Recent results on light scalars are summarized and some conceptual issues are discussed, especially the relation between charm decays and hadronic production.

Recent results on charm meson decays at FOCUS

E831-FOCUS is a photoproduction experiment which collected data during the 1996/1997 fixed target run at Fermilab. More than 1 million charm particles have been reconstructed. Using this sample we measure the lifetimes of all the weakly decaying singly charmed particles, establishing the charm lifetime hierachy. Then we present recent results on semileptonic decays of charm mesons, including the new s-wave inteference phenomena in D+ to K-pi+mu+nu, and high statistics branching ratio and form factor measurements.