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E. Klempt

Publications and source records attributed to E. Klempt.

At least 91 records · Page 5Linked to original sources
arXiv2008

Quasi-free photoproduction of eta-mesons of the neutron

Quasi-free photoproduction of eta-mesons off nucleons bound in the deuteron has been measured with the CBELSA/TAPS detector for incident photon energies up to 2.5 GeV at the Bonn ELSA accelerator. The eta-mesons have been detected in coincidence with recoil protons and recoil neutrons, which allows a detailed comparison of the quasi-free n(gamma,eta)n and p(gamma,eta)p reactions. The excitation function for eta-production off the neutron shows a pronounced bump-like structure at W=1.68 GeV (E_g ~ 1 GeV), which is absent for the proton.

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arXiv2008

Methods and Models for Hadron Physics

A round table held during the Hadron07 Conference focusing on experimental observations of new hadronic states, on theoretical perspectives for their description, and on the role of hadronic spectroscopy in furthering our knowledge of the fundamental theory of strong interactions.

hep-ph↗
arXiv2008

Further study of $D^+_s$ decays into $π^- π^+ π^+$

A Dalitz plot analysis of the OZI rule violating decay $D^+_s$ into $π^- π^+ π^+$ is presented using different partial wave approaches. Scalar and vector waves are described by $K$-matrices; their production is parameterized in a $P$-vector approach. Alternatively, Breit-Wigner amplitudes and Flatté parametrization are used. Special emphasis is devoted to scalar mesons. The $f_0(980)$ resonance provides the most significant contribution. Adding $f_0(1500)$ to the scalar wave leads to an acceptable fit while introduction of $f_0(1370)$ and/or $f_0(1710)$ does not lead to significant improvements. A scan of the scalar wave optimizes for $M=1452\pm 22$ MeV/c$^2$. When $f_0(1710)$ is added, the mass uncertainty increases, and the fit yields $M=1470\pm 60$ MeV/c$^2$ which is fully compatible with the nominal $f_0(1500)$ mass. The scalar wave seems to exhibit a phase motion of 270$^{\circ}$ units in the mass range from 1200 to 1650 MeV/c$^2$.

hep-ph↗
arXiv2008

Modification of the $ω$-Meson Lifetime in Nuclear Matter

The photo production of $ω$ mesons on the nuclei C, Ca, Nb and Pb has been measured using the Crystal Barrel/TAPS detector at the ELSA tagged photon facility in Bonn. The dependence of the $ω$ meson cross section on the nuclear mass number has been compared with three different types of models, a Glauber analysis, a BUU analysis of the Giessen theory group and a calculation by the Valencia theory group. In all three cases, the inelastic $ω$ width is found to be $130-150 \rm{MeV/c^2}$ at normal nuclear matter density for an average 3-momentum of 1.1 GeV/c. In the restframe of the $ω$ meson, this inelastic $ω$ width corresponds to a reduction of the $ω$ lifetime by a factor $\approx 30$. For the first time, the momentum dependent $ω$N cross section has been extracted from the experiment and is in the range of 70 mb.

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arXiv2007

N* and Delta* decays into N pi0 pi0

Decays of baryon resonances in the second and the third resonance region into N pi0 pi0 are studied by photoproduction of two neutral pions off protons. Partial decay widths of N* and Delta* resonances decaying into Delta(1232) pi, N(ππ)_{S}, N(1440)P_{11} pi, and N(1520)D_{13} pi are determined in a partial wave analysis of this data, and data from other reactions. Several partial decay widths were not known before. Interesting decay patterns are observed which are not even qualitatively reproduced by quark model calculations. In the second resonance region, decays into Delta(1232) pi dominate clearly. The N(ππ)_{S}-wave provides a significant contribution to the cross section, especially in the third resonance region. The P_{13}(1720) properties found here are at clear variance to PDG values.

hep-ph↗
arXiv2007

Further evidence for N(1900)P_{13} from photoproduction of hyperons

We report further evidence for $N(1900)P_{13}$ from an analysis of a large variety of photo- and pion-induced reactions, in particular from the new CLAS measurements of double polarization observables for photoproduction of hyperons. The data are consistent with two classes of solutions both requiring contributions from $N(1900)P_{13}$ but giving different $N(1900)P_{13}$ pole positions. $(M-iΓ/2) = (1915\pm50)-i(90\pm25)$ MeV covers both solutions. The small elasticity of 10% or less explains why it was difficult to observe the state in $πN$ elastic scattering. $N(1900)P_{13}$ is a 2-star resonance which is predicted by symmetric three-quark models. In diquark-quark models, the existence of the state is not expected.

hep-ph↗
arXiv2007

Baryon-baryon and baryon-antibaryon interaction amplitudes in the spin--momentum operator expansion method

Partial wave scattering amplitudes in baryon-baryon and baryon-antibaryon collisions and amplitudes for the production and decay of baryon resonances are constructed in the framework of the spin-momentum operator expansion method. The approach is relativistically invariant and it allows us to perform combined analyses of different reactions imposing analyticity and unitarity directly. The role of final state interactions (triangle and box diagrams) is discussed.

hep-ph↗
arXiv2005

Photoproduction of Baryons Decaying into N pi and N eta

A combined analysis of photoproduction data on γp to πN, eta N was performed including the data on K Lambda and K Sigma. The data are interpreted in an isobar model with s--channel baryon resonances and pi, rho,(omega), K, and K^* exchange in the t--channel. Three baryon resonances have a substantial coupling to eta N, the well known N(1535)S_{11}, N(1720)P_{13}, and N(2070)D_{15}. The inclusion of data with open strangeness reveals the presence of further new resonances, N(1840)P_{11}, N(1875)D_{13} and N(2170)D_{13}.

hep-ex↗
arXiv2005

Decays of Baryon Resonances into K Lambda, K^+ Sigma^0 and K^0 Sigma^+

Cross sections, beam asymmetries, and recoil polarisations for the reactions gamma p to K^+ Lambda ; gamma to K^+ Sigma^0, and gamma p to K^0 Sigma^+ have been measured by the SAPHIR, CLAS, and LEPS collaborations with high statistics and good angular coverage for centre-of-mass energies between 1.6 and 2.3 GeV. The combined analysis of these data with data from pi and eta photoproduction reveals evidence for new baryon resonances in this energy region. A new P_{11} state with mass 1840 MeV and width 140 MeV was observed contributing to most of the fitted reactions. The data demand the presence of two D_{13} states at 1870 and 2170 MeV.

hep-ex↗
arXiv2005

Measurement of the reaction gamma p --> K0 Sigma+ at photon energies up to 2.6 GeV

The reaction gamma p --> K0 Sigma+ was measured in the photon energy range from threshold up to 2.6 GeV with the SAPHIR detector at the electron stretcher facility, ELSA, in Bonn. Results are presented on the reaction cross section and the polarization of the Sigma+ as a function of the kaon production angle in the centre-of-mass system, cos(Theta_K^{c.m.}), and the photon energy. The cross section is lower and varies less with photon energy and kaon production angle than that of gamma p --> K+ Sigma0. The Sigma+ is polarized predominantly at cos(Theta_K^{c.m.}) \approx 0. The data presented here are more precise than previous ones obtained with SAPHIR and extend the photon energy range to higher values. They are compared to isobar model calculations.

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arXiv2005

Partial wave decomposition of pion and photoproduction amplitudes

Partial wave amplitudes for production and decay of baryon resonances are constructed in the framework of the operator expansion method. The approach is fully relativistically invariant and allow us to perform combined analyses of different reactions imposing directly analyticity and unitarity constraints. All formulas are given explicitly in the form used by the Crystal Barrel collaboration in the (partly forthcoming) analyses of the electro-, photo- and pion induced meson production data.

hep-ph↗
arXiv2005

The antinucleon-nucleon interaction at low energy : annihilation dynamics

The general properties of antiproton-proton annihilation at rest are presented, with special focus on the two-meson final states. The data exhibit remarkable dynamical selection rules : some allowed annihilation modes are suppressed by one order of magnitude with respect to modes of comparable phase-space. Various phenomenological analyses are reviewed, based on microscopic quark dynamics or symmetry considerations. The role of initial- and final-state interaction is also examined.

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arXiv2003

Measurement of gamma p --> K+ Lambda and gamma p --> K+ Sigma0 at photon energies up to 2.6 GeV

The reactions gamma p --> K+ Lambda and gamma p --> K+ Sigma0 were measured in the energy range from threshold up to a photon energy of 2.6 GeV. The data were taken with the SAPHIR detector at the electron stretcher facility, ELSA. Results on cross sections and hyperon polarizations are presented as a function of kaon production angle and photon energy. The total cross section for Lambda production rises steeply with energy close to threshold, whereas the Sigma0 cross section rises slowly to a maximum at about E_gamma = 1.45 GeV. Cross sections together with their angular decompositions into Legendre polynomials suggest contributions from resonance production for both reactions. In general, the induced polarization of Lambda has negative values in the kaon forward direction and positive values in the backward direction. The magnitude varies with energy. The polarization of Sigma0 follows a similar angular and energy dependence as that of Lambda, but with opposite sign.

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arXiv2002

$ SU(3) $ Classification of $ p $-Wave $ ηπ$ and $ η'π$ Systems

An exotic meson, the $π_1(1400)$ with $J^{PC}=1^{-+}$, has been seen to decay into a p-wave $ηπ$ system. If this decay conserves flavor SU(3), then it can be shown that this exotic meson must be a four-quark state ($q\bar q+q\bar q$) belonging to a flavor ${\bf10}\oplus{\bf\bar{10}}$ representation of SU(3). In contrast, the $π_1(1600)$ with a substantial decay mode into $η'π$ is likely to be a member of a flavor octet.

hep-ph↗
arXiv2002

Baryon resonances and strong QCD

Light-baryon resonances (with u,d, and s quarks in the SU(3) classification) fall on Regge trajectories. When their squared masses are plotted against the intrinsic orbital angular momenta {\rm L}, $Δ^*$'s with even and odd parity can be described by the same Regge trajectory. For a given {\rm L}, nucleon resonances with spin {\rm S}=3/2 are approximately degenerate in mass with $Δ$ resonances. To which total angular momentum {\rm L} and {\rm S} couple has no significant impact on the baryon mass. Nucleons with spin 1/2 are shifted in mass; the shift is - in units of squared masses - proportional to the component in the wave function which is antisymmetric in spin and flavor. Based on these observations, a new baryon mass formula is proposed which reproduces nearly all known baryon masses. It is shown that the masses are compatible with a quark-diquark picture while the richness of the experimentally known states require three particles to participate in the dynamics. This conflict is resolved by proposing that quarks polarize the QCD condensates and are surrounded by a polarization cloud shielding the color. A new interpretation of constituent quarks as colored quark clusters emerges; their interaction is responsible for the mass spectrum. Fast flavor exchange between the colored quark clusters exhausts the dynamical richness of the three-particle dynamics. The colored-quark-cluster model provides a mechanism in which the linear confinement potential can be traced to the increase of the volume in which the condensates are polarized. The quark-spin magnetic moment induces currents in the polarized condensates which absorb the quark-spin angular momentum: the proton spin is not carried by quark spins. The model provides a new picture of hybrids and glueballs.

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arXiv2001

Glueballs, Hybrids and Q\bar Q Mesons

Lattice gauge calculations predict the existence of glueballs. In particular a scalar glueball is firmly expected at a mass of about 1730 MeV. This prediction has led to an intense study of scalar isoscalar interactions and to the discovery of new meson resonances. The number of scalar states observed seems to exceed the number of states which can be accommodated in the quark model even when two states, the a_0(980) and f_0(980), are interpreted as K Kbar bound states and are removed from the list. However, none of these states has a decay pattern which is consistent with that of a pure glueball. A reasonable interpretation of the number of states and of their decay pattern is found only when mixing of scalar q qbar states with the scalar glueball is taken into account. In this paper we scrutinize the evidence for these states and their production characteristics. The f_0(1370) - a cornerstone of all qbar q-glueball mixing scenarios - is shown to be likely of non-qbar q nature. The remaining scalar states then do fit into a nonet classification. If this interpretation should be correct there would be no room for resonant scalar gluon-gluon interactions, no room for the scalar glueball. We also discuss the status of mesons with exotic quantum numbers, of mesons which cannot possibly have qbar q structure, and argue that these are, most likely, four-quark states and not excitations of the gluon string providing the binding between quark and antiquark.

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