Excited Charm Research Articles

Spectroscopy Results from HERA

HERA is an electron-collider which has terminated its operations in 2007 and is currently processing large amounts of experimental data. This presentation reviews the latest HERA hadronic final state and spectroscopic results as performed by the H1 and ZEUS experiments. It covers more specifically the observation of K s 0 K s 0 states, the excited charm mesons and a survey of the charm pentaquark analyses.

IMPACT OF POSITIVE PARITY HEAVY MESONS ON CHARM MESON DECAYS

We discuss strong decays of positive and negative parity charmed mesons within heavy meson chiral perturbation theory and study the impact of excited charm states on the determination of the effective meson couplings. Motivated by recent experimental results we also reconsider semileptonic D → Plνl and D → Vlνl decays within a model which combines heavy quark symmetry and properties of the chiral Lagrangian. Using limits of soft collinear effective theory and heavy quark effective theory we parametrize the semileptonic form factors. We include excited charm meson states in our Lagrangian and determine their impact on the charm meson semileptonic form factors.

Puzzles of excited charm meson masses

We attempt a comprehensive analysis of the low lying charm meson states which present several puzzles, including the poor determination of masses of several non-strange excited mesons. We use the well-determined masses of the ground states and the strange first excited states to ‘predict’ the mass of the non-strange first excited state in the framework of heavy hadron chiral perturbation theory, an approach that is complementary to the well-known analysis of Mehen and Springer. This approach points to values for the masses of these states that are smaller than the experimental determinations. We provide a critical assessment of these mass measurements and point out the need for new experimental information.

Charm Hadronic Decays

In this paper, we report recent results on charm hadronic decays using data taken at E831/FOCUS experiment which is a photo-production experiment at Fermilab. During its 1996-1997 run, we obtained more than 1 million high quality charm particles. Using this sample we study Dalitz plot analysis of D + and D S + → π + π − π + using K -matrix formalism, high multiplicity charm mesons decays of many bodies and the measurements of excited charm resonant states.

Charm meson resonances inD→Pℓνdecays

Motivated by recent experimental results we reconsider semileptonic $D\ensuremath{\rightarrow}P\ensuremath{\ell}{\ensuremath{\nu}}_{\ensuremath{\ell}}$ decays within a model which combines heavy quark symmetry and properties of the chiral Lagrangian. We include excited charm meson states, some of them recently observed, in our Lagrangian and determine their impact on the charm meson semileptonic form factors. We find that the inclusion of excited charm meson states in the model leads to a rather good agreement with the experimental results on the ${q}^{2}$ shape of the ${F}_{+}({q}^{2})$ form factor. We also calculate branching ratios for all $D\ensuremath{\rightarrow}P\ensuremath{\ell}{\ensuremath{\nu}}_{\ensuremath{\ell}}$ decays.

Measurement of masses and widths of excited charm mesons [formula omitted] and evidence for broad states

Using data from the FOCUS experiment we analyze the D+π− and D0π+ invariant mass distributions. We measure the D2∗0 mass MD2∗0=(2464.5±1.1±1.9)MeV/c2 and width ΓD2∗0=(38.7±5.3±2.9)MeV/c2, and the D2∗+ mass MD2∗+=(2467.6±1.5±0.76)MeV/c2 and width ΓD2∗+=(34.1±6.5±4.2)MeV/c2. We find evidence for broad structures over background in both the neutral and charged final state. If each is interpreted as evidence for a single L=1, jq=1/2 excited charm meson resonance, the masses and widths are M1/20=(2407±21±35)MeV/c2, Γ1/20=(240±55±59)MeV/c2, and M1/2+=(2403±14±35)MeV/c2, Γ1/2+=(283±24±34)MeV/c2, respectively.

Two-pion decay widths of excited charm mesons

The widths for ππ decay of the L=1 charm mesons are calculated by describing the pion coupling to light constituents quarks by the lowest-order chiral interaction. The wavefunctions of the charm mesons are obtained as solutions to the covariant Blankenbecler–Sugar equation. These solutions correspond to an interaction Hamiltonian modeled as the sum of a linear scalar confining and a screened one-gluon exchange (OGE) interaction. This interaction induces a two-quark contribution to the amplitude for two-pion decay, which is found to interfere destructively with the single-quark amplitude. For the currently known L=1 D mesons, the total ππ-decay widths are found to be ∼1 MeV for the D 1(2420) and ∼3 MeV for the D ∗ 2(2460) if the axial coupling of the constituent quark is taken to be g A q =1 . The as yet undiscovered spin-singlet D 1 ∗ state is predicted to have a larger width of 7–10 MeV for ππ decay.

Measurement of the B semileptonic branching fraction into excited charm mesons

Measurement of the B semileptonic branching fraction into excited charm mesons

Production of orbitally excited charm mesons in c and b decays at LEP

A study of the production of L = 1 charmed mesons ( D ** states) has been performed using 4 million Z decays collected by the ALEPH detector at LEP. J P = 1 + states ( D 1 , D s l ) are observed in the decay channel D * π and D * K respectively, and the J P = 2 + states ( D * 2 ,D * 2 ) in the channels D* π , Dπ and DK respectively. Siince D ** states could originate from beauty hadron decay produced in Z 0 → bb or from charm fragmentation in Z 0 → cc events, rates are measured separately for b → D 1 , D * 2 , D s 1, D * 2 and c → D 1 , D * s2 , D s 1, D * s2 .

Universal Isgur-Wise form factors from QCD sum rules in HQET

We review the role of the universal Isgur-Wise functions parameterizing the B meson semileptonic matrix elements to excited charm states in the infinite heavy quark mass limit. We also discuss the determination of such form factors by QCD sum rules in the framework of the Heavy Quark Effective Theory.

Production of P-wave charm and charm-strange mesons in hadronic Z $^0$ decays

Results are presented on the production of excited charm and excited charm-strange mesons in hadronic Z(0) decays. The results are obtained from approximately 4.3 million hadronic Z(0) decays, collected on or near the Z(0) resonance using the OPAL detector at LEP. The D-1(0)(2420) and D*(0)(2)(2460) mesons are reconstructed in the D*(+)pi(-) final state and their separate production rates in charm fragmentation and in weak decays of b-hadrons are determined. Assuming that the decay widths of these mesons are saturated by the allowed D*pi and D pi final states, the charm hadronization fractions and the inclusive branching ratios of b-hadrons to these neutral P-wave charm mesons are determined to bef(c --> D-1(0)) = 0.021 +/- 0.007(stat) +/- 0.003(syst), f(c --> D*(0)(2)) = 0.052 +/- 0.022(stat)+/- 0.013(syst), f(b --> D-1(0)) = 0.050 +/- 0.014(stat) +/- 0.006(syst), f(b --> D*(0)(2)) = 0.047 +/- 0.024(stat) +/- 0.013(syst).We also present the first observation at LEP of the D-s1(+)(2536) meson which is reconstructed in both the D*K-+(s)0 and D*K-0(+) final states After correcting for the expected contribution from bb events, assuming that the D*K channels saturate the available final states, these results are used to derive the charm hadronization fraction f(c --> D-s1(+)):f(c --> D-s1(+)) = 0.016 +/- 0.004(stat) +/- 0.003(syst).

Production of orbitally excited charm mesons in semileptonic B decays

A sample of 3.6 million hadronic Z decays recorded between 1991 and 1995 with the ALEPH detector at LEP is used to investigate semileptonic decays of B mesons into final states involving orbitally excited charm mesons. Topological vertex criteria are used to search for decays involving narrow D$^{**}$ states as well as wide D$^{**}$ resonances and non-resonant D$^{(*)}\pi$ final states. The sum of the branching ratios for these processes is measured to be \begin{eqnarray*} \lefteqn{{\mathrm{Br}}({\overline {\mathrm{B}}} \to {\mathrm{D}}\pi\ell^-\overline\nu) +{\mathrm{Br}}({\overline {\mathrm{B}}} \to {\mathrm{D}}^*\pi\ell^-\overline\nu)}\\ & & = (2.26\pm 0.29(\mathrm{stat}) \pm 0.33(\mathrm{syst}))\%, \end{eqnarray*} which accounts for a significant fraction of the deficit between inclusive measurements and the sum of exclusive semileptonic B decay modes.

Semileptonic B decays into higher charmed resonances.

We apply HQET to semileptonic $B$ meson decays into a variety of excited charm states. Using three realistic meson models with fermionic light degrees of freedom, we examine the extent that the sum of exclusive single charmed states account for the inclusive semileptonic $B$ decay rate. The consistency of form factors with the Bjorken and Voloshin sum rules is also investigated.

Strong and electromagnetic decays of two newΛc*baryons

Two recently discovered excited charm baryons are studied within the framework of Heavy Hadron Chiral Perturbation Theory. We interpret these new baryons which lie $308 \MeV$ and $340 \MeV$ above the $\Lambda_c$ as $I=0$ members of a P-wave spin doublet. Differential and total decay rates for their double pion transitions down to the $\Lambda_c$ ground state are calculated. Estimates for their radiative decay rates are also discussed. We find that the experimentally determined characteristics of the $\Lambda_c^*$ baryons may be simply understood in the effective theory.

Reconstruction of the decay B− → D10(2414) π −

We present the results of a partial reconstruction of the decay channel B − → D j (∗)π − performed using the ARGUS detector operating at the e + e − storage-ring DORIS II. In the context of this paper, D j (∗)0 is an L = 1 excited charm meson decaying to D ∗+π − . The measured product of branching ratios is Br(B − → D 1 0(2414)π −) · Br Br(D 1 0 → D ∗+π −) = (0.17 ± 0.05 ± 0.04)% where the first error is statistical and statistical and the second systematic. No evidence for the decay B − → D 2 ∗0 (2459) π −) · Br(D 2 ∗0 → D ∗+π −) < 0.07% at the 90% confidence level.

Semileptonic decays ofB mesons into excited charm mesons: Leading order and 1/m c contributions

We use the heavy quark effective theory to investigate the form factors that describe the semileptonic decays of aB meson into excited daughter mesons. For an excited daughter meson with charm, a single form factor is needed at leading order, while five form factors and two dimensionful constants are needed to order 1/m c in the heavy quark expansion. For non-charmed final states, a total of four form factors are needed at leading order. For the processB→D*Xlν, four form factors are also needed at leading order.