arXiv subjects

H. P. Morsch

Publications and source records attributed to H. P. Morsch.

At least 19 recordsLinked to original sources

arXiv2025

Three-Nucleon Dynamics in the dp breakup collisions at 190 MeV/nucleon using the WASA detector at COSY-Jülich

The differential cross section for the $^{1}$H$(d,pp)n$ breakup reaction at deuteron beam energy of 380 MeV has been determined with high precision for 189 angular configurations of outgoing protons in the region of forward laboratory angles. The cross section data were compared to theoretical predictions based on the state-of-the-art nucleon-nucleon potentials, combined with a three-nucleon force, the Coulomb interaction or carried out in a relativistic approach. In the region of the lowest differential cross section, the discrepancy between the data and the theoretical predictions is observed, also in the case of relativistic calculations.

nucl-ex↗

arXiv2020

Search for eta mesic 3He with the WASA-at-COSY facility in the pd-> 3He 2gamma and pd-> 3He 6gamma reactions

We report on the experimental search for the bound state of an $η$ meson and $^{3}\hspace{-0.03cm}\mbox{He}$ nucleus performed using the WASA-at-COSY detector setup. In order to search for the $η$-mesic nucleus decay, the $pd\rightarrow$ $^{3}\hspace{-0.03cm}\mbox{He} 2γ$ and $pd\rightarrow$ $^{3}\hspace{-0.03cm}\mbox{He} 6γ$ channels have been analysed. These reactions manifest the direct decay of $η$ meson bound in $^{3}\hspace{-0.03cm}\mbox{He}$ nucleus. This non-mesonic decay channel has been considered for the first time. When taking into account only statistical errors, the obtained excitation functions reveal a slight indication for a possible bound state signal corresponding to an $^3$He-$η$ nucleus width $Γ$ above 20 MeV and binding energy $B_s$ between 0 and 15 MeV. However, the determined cross sections are consistent with zero in the range of the systematic uncertainty. Therefore, as final result we estimate only the upper limit for the cross section of the $η$-mesic $^{3}\hspace{-0.03cm}\mbox{He}$ nucleus formation followed by the $η$ meson decay which varies between $2$ nb and $15$ nb depending on possible bound state parameters.

nucl-ex↗

arXiv2013

On the structure of the new particle at 126 GeV (Higgs- or not Higgs-boson?)

A new particle - discovered recently with the Atlas and CMS detectors at LHC - has been interpreted as the long sought Higgs-boson. A corresponding scalar field is needed to make the weak interaction gauge invariant and to understand the quark masses in the Standard Model. However, the Standard Model is an effective theory with quark masses, which can be understood only in a fundamental theory. Such a theory has been constructed, based on a generalised second order extension of QED, in which the quarks can be understood as effective fermions with masses given by binding energies in a boson-exchange potential. In the present approach the Higgs-mechanism is not needed. In this framework a good understanding of particles in the "top" regime is obtained. Two J^π=1^- q-qbar states are predicted, identified with Z(91.2 GeV) and the t-tbar state at about 350 GeV. Further, two 0^+ q-qbar states are obtained, one with a mass consistent with that of the new particle, the other with a mass of about 41 GeV. A detection of the second scalar state will serve as a crucial test of the present model.

physics.gen-ph↗

arXiv2013

Solution of the relativistic bound state problem for hadrons

A second order extension of the QED Lagrangian (including boson-boson coupling) has been used to describe q\bar q hadrons. Assuming massless elementary fermions (quantons) this results in a finite theory without open parameters, which may be regarded as a fundamental description of the strong interaction. Two potentials are deduced, a boson-exchange potential and one, which can be identified with the known confinement potential in hadrons. This formalism has been applied the mesonic systems omega(782), Phi(1020), J/psi(3097) and Upsilon(9460), for which a good description is obtained. The most important results are: 1. The confinement of hadrons is not due to colour, but is a general property of relativistic bound states. 2. Massive quarks in the Standard Model (QCD) are understood as effective fermions with a mass given by the binding energy in the boson-exchange potential.

physics.gen-ph↗

arXiv2012

ABC Resonance Structure in the Double-Pionic Fusion to 4He

Exclusive and kinematically complete high-statistics measurements of the double pionic fusion reaction $dd \to ^4$He$π^0π^0$ have been performed in the energy range 0.8 - 1.4 GeV covering thus the region of the ABC effect, which denotes a pronounced low-mass enhancement in the $ππ$-invariant mass spectrum. The experiments were carried out with the WASA detector setup at COSY. Similar to the observation in the basic $pn \to d π^0π^0$ reaction, the data reveal a correlation between the ABC effect and a resonance-like energy dependence in the total cross section. The maximum occurs at m=2.37 GeV + 2$m_N$, i.e. at the same position as in the basic reaction. The observed resonance width $Γ\approx$ 160 MeV can be understood from broadening due to Fermi motion of the nucleons in initial and final nuclei together with collision damping. Differential cross sections are described equally well by the hypothesis of a $pn$ resonance formation during the reaction process.

nucl-ex↗

arXiv2012

The pK0Σ+ final state in proton-proton collisions

This paper reports results from a study of the reaction pp->pK0Σ+ at beam momenta of p_{beam} = 2950, 3059, and 3200 MeV/c (excess energies of ε= 126, 161, and 206 MeV). Total cross sections were determined for all energies; a set of differential cross sections (Dalitz plots; invariant mass spectra of all two-body subsystems; angular distributions of all final state particles; distributions in helicity and Jackson frames) are presented for ε= 161 MeV. The total cross sections are proportional to the volume of available three-body phase-space indicating that the transition matrix element does not change significantly in this range of excess energies. It is concluded from the differential data that the reaction proceeds dominantly via the N(1710)P_{11} and/or N(1720)P_{13} resonance(s); N(1650)S_{11} and Δ(1600)P_{33} could also contribute.

nucl-ex↗

arXiv2011

On the uniqueness of the Standard Model of particle physics

The running strong coupling $α(Q)_s$ and the gluon propagator from QCD have been compared to similar quantities in the quanton model, a generalisation of QED with massless fermions (quantons) and scalar coupling of boson fields. In the latter model a series of bound states (which can be related to different flavours) have been obtained. Assuming a weighting of their momentum distributions with the average momentum $\tilde Q_i$ of each state, a running of the coupling $α(Q)$ is obtained, which is in quantitative agreement with $α_s(Q)$ from QCD. Also with a similar weighting the gluon propagator from lattice QCD simulations is well described. This indicates clearly that QCD and thus the Standard Model is not a unique description of fundamental interactions. Different from the Standard Model, the quanton model is simple and yields bound states with correct masses. This may indicate that this model yields a more realistic description of fundamental forces.

physics.gen-ph↗

arXiv2010

Production of Lambda and Sigma^0 hyperons in proton-proton collisions

This paper reports results on simultaneous measurements of the reaction channels pp -> pK+Λand pp -> pK+Σ^0 at excess energies of 204, 239, and 284 MeV (Λ) and 127, 162, and 207 MeV (Σ^0). Total and differential cross sections are given for both reactions. It is concluded from the measured total cross sections that the high energy limit of the cross section ratio is almost reached at an excess energy of only about 200 MeV. From the differential distributions observed in the overall CMS as well as in the Jackson and helicity frames, a significant contribution of interfering nucleon resonances to the Λproduction mechanism is concluded while resonant Σ^0-production seems to be of lesser importance and takes place only through specific partial waves of the entrance channel. The data also indicate that kaon exchange plays a minor role in the case of Λ- but an important role for Σ^0-production. Thus the peculiar energy dependence of the Λ-to-Σ^0 cross section ratio appears in a new light as its explanation requires more than mere differences between the pΛand the pΣ^0 final state interaction. The data provide a benchmark for theoretical models already available or yet to come.

nucl-ex↗

arXiv2010

Influence of N*-resonances on hyperon production in the channel pp->K+ Lambda p at 2.95, 3.20 and 3.30 GeV/c beam momentum

Hyperon production in the threshold region was studied in the reaction pp -> K+Lp using the time-of-flight spectrometer COSY-TOF. Exclusive data, covering the full phase-space, were taken at the three different beam momenta of p_beam=2.95, 3.20 and 3.30 GeV/c, corresponding to excess energies of epsilon=204, 285 and 316 MeV, respectively. Total cross-sections were deduced for the three beam momenta to be 23.9+/-0.8 +/-2.0 ub, 28.4+/-1.3 +/-2.2 ub and 35.0+/-1.3 +/-3.0 ub. Differential observables including Dalitz plots were obtained. The analysis of the Dalitz plots reveals a strong influence of the N(1650)-resonance at p_beam=2.95 GeV/c, whereas for the higher momenta an increasing relative contribution of the N(1710)- and/or of the N(1720)-resonance was observed. In addition, the pL-final-state interaction turned out to have a significant influence on the Dalitz plot distribution.

nucl-ex↗

arXiv2010

Systematic study of the pp -> pp omega reaction

A systematic study of the production of omega-mesons in proton-proton-collisions was carried out in a kinematically complete experiment at three excess energies(epsilon= 92, 128, 173MeV). Both protons were detected using the large-acceptance COSY-TOF spectrometer at an external beam line at the Cooler Synchrotron COSY at Forschungszentrum Jülich. The total cross section, angular distributions of both omega-mesons and protons were measured and presented in various reference frames such as the overall CMS, helicity and Jackson frame. In addition, the orientation of the omega-spin and invariant mass spectra were determined. We observe omega-production to take place dominantly in Ss and Sp final states at epsilon = 92, 128 MeV and, additionally, in Sd at epsilon= 173 MeV. No obvious indication of resonant omega-production via N^*-resonances was found, as proton angular distributions are almost isotropic and invariant mass spectra are compatible with phase space distributions. A dominant role of ^3P_1 and ^1S_0 initial partial waves for omega-production was concluded from the orientation of the decay plane of the omega-meson. Although the Jackson angle distributions in the omega-p-Jackson frame are anisotropic we argue that this is not an indication of a resonance but rather a kinematical effect reflecting the anisotropy of the omega angular distribution. The helicity angle distribution in the omega-p-helicity frame shows an anisotropy which probably reflects effects of the omega angular momenta in the final state; this observable may be, in addition to the orientation of the omega decay plane, the most sensitive one to judge the validity of theoretical descriptions of the production process.

nucl-ex↗

arXiv2009

Hadron mass generation and the strong interaction

Based on a Lagrangian with a coupling of two gluons to J^pi=0^+ (the quantum numbers of the vacuum) which decay to q-qbar pairs, a model is presented, in which hadrons couple directly to the absolute vacuum of fluctuating gluon fields. By self-consistency requirements the confinement potential as well as hadron densities and masses are obtained, which are in good agreement with experimental data on scalar and vector mesons. In comparison with potential models additional states are predicted, which can explain the large continuum of scalar states in the low mass spectrum and new states in the charm region. The present model is consistent with the concept, that the hadron masses can be understood by binding effects of the quarks.

hep-ph↗

arXiv2009

On the Production of $π^+π^+$ Pairs in pp Collisions at 0.8 GeV

Data accumulated recently for the exclusive measurement of the $pp\to ppπ^+π^-$ reaction at a beam energy of 0.793 GeV using the COSY-TOF spectrometer have been analyzed with respect to possible events from the $pp \to nnπ^+π^+$ reaction channel. The latter is expected to be the only $ππ$ production channel, which contains no major contributions from resonance excitation close to threshold and hence should be a good testing ground for chiral dynamics in the $ππ$ production process. No single event has been found, which meets all conditions for being a candidate for the $pp \to nn π^+π^+$ reaction. This gives an upper limit for the cross section of 0.16 $μ$b (90% C.L.), which is more than an order of magnitude smaller than the cross sections of the other two-pion production channels at the same incident energy.

nucl-ex↗

arXiv2009

Single-Pion Production in pp Collisions at 0.95 GeV/c (II)

The single-pion production reactions $pp\to dπ^+$, $pp\to npπ^+$ and $pp\to ppπ^0$ were measured at a beam momentum of 0.95 GeV/c ($T_p \approx$ 400 MeV) using the short version of the COSY-TOF spectrometer. The central calorimeter provided particle identification, energy determination and neutron detection in addition to time-of-flight and angle measurements from other detector parts. Thus all pion production channels were recorded with 1-4 overconstraints. Main emphasis is put on the presentation and discussion of the $npπ^+$ channel, since the results on the other channels have already been published previously. The total and differential cross sections obtained are compared to theoretical calculations. In contrast to the $ppπ^0$ channel we find in the $npπ^+$ channel a strong influence of the $Δ$ excitation already at this energy close to threshold. In particular we find a $(3 cos^2Θ+ 1)$ dependence in the pion angular distribution, typical for a pure s-channel $Δ$ excitation and identical to that observed in the $dπ^+$ channel. Since the latter is understood by a s-channel resonance in the $^1D_2$ $pn$ partial wave, we discuss an analogous scenario for the $pnπ^+$ channel.

nucl-ex↗

arXiv2008

Two-Pion Production in Proton-Proton Collisions with Polarized Beam

The two-pion production reaction $\vec{p}p\to ppπ^+π^-$ was measured with a polarized proton beam at $T_p \approx$ 750 and 800 MeV using the short version of the COSY-TOF spectrometer. The implementation of a delayed pulse technique for Quirl and central calorimeter provided positive $π^+$ identification in addition to the standard particle identification, energy determination as well as time-of-flight and angle measurements. Thus all four-momenta of the emerging particles could be determined with 1-4 overconstraints. Total and differential cross sections as well as angular distributions of the vector analyzing power have been obtained. They are compared to previous data and theoretical calculations. In contrast to predictions we find significant analyzing power values up to $A_y$ = 0.3.

nucl-ex↗

arXiv2007

Multi-gluon field approach of QCD

The decay of 2-gluon colour singlets in quarks: 2g --> q-qbar +2q-2qbar has been simulated with the Monte-Carlo method, taking into account an effective 1-gluon exchange interaction between the emitted quarks, which was folded with a 2-gluon density determined self-consistently. 2-gluon densities were found with different radii, which correspond to 0^{++} glueballs of the size of light q-qbar, s-sbar, c-cbar, b-bbar, and heavier q-qbar systems. Binding potentials between the two gluons have been deduced, which are consistent with the confinement potential from lattice results. However, self-consistency for the deduction of 2-gluon densities requires massless (or very light) quarks for all flavours. The masses are given by the binding energies of quarks and gluons, yielding excitation spectra of 0^{++} glueballs and Phi, J/Psi, and Upsilon states consistent with observation. The sum of q-q potentials yields a strong coupling alpha_s consistent with the available data up to large momenta. The nucleon is described by a gluonium state coupled to 3 valence quarks, yielding ground state and radial excitations consistent with experiment. Finally, we discuss the compressibility of the nucleon and relate it to that of nuclear matter.

hep-ph↗

arXiv2007

Phenomenological study of two-gluon densities

The decay of colour neutral 2-gluon systems in qqbar and 2q2qbar has been simulated with the Monte-Carlo method, taking into account an effective 1-gluon exchange interaction between the emitted quarks, which was folded with a 2-gluon density determined self-consistently. Finite 2-gluon densities were obtained with a mean square radius of about 0.5 fm^2. These give a significant contribution to the 2-gluon field correlators and the gluon propagator from lattice QCD. By solving a relativistic Schroedinger equation the binding potential of the 2-gluon density is computed. By the relation 2g->(qqbar)^n this corresponds to the confinement potential between quarks, which is in excellent agreement with the confinement potential from lattice QCD. The lowest bound state in this potential allows an interpretation of the 2-gluon mass as binding energy of the two gluons. The lowest glueball with Eo=0.68+-0.10 GeV is in the mass region of the scalar sigma(550), with a mass significantly lower then obtained in lattice QCD simulations. However, the first and second radial excitations agree with the lattice results.

hep-ph↗

arXiv2007

Single π^- production in np collisions for excess energies up to 90 MeV

The quasifree reaction $np\to pp\pim$ was studied in a kinematically complete experiment by bombarding a liquid hydrogen target with a deuteron beam of momentum 1.85 GeV/c and analyzing the data along the lines of the spectator model. In addition to the three charged ejectiles the spectator proton was also detected in the large-acceptance time-of-flight spectrometer COSY-TOF. It was identified by its momentum and flight direction thus yielding access to the Fermi motion of the bound neutron and to the effective neutron 4-momentum vector $\mathbb{P}_n$ which differed from event to event. A range of almost 90 MeV excess energy above threshold was covered. Energy dependent angular distributions, invariant mass spectra as well as fully covered Dalitz plots were deduced. Sizeable $pp$ FSI effects were found as were contributions of $p$ and $d$ partial waves. The behavior of the elementary cross section $σ_{01}$ close to threshold is discussed in view of new cross section data. In comparison with existing literature data the results provide a sensitive test of the spectator model.

nucl-ex↗

arXiv2007

Improved study of a possible Theta+ production in the pp -> p K0 sigma+ reaction with the COSY-TOF spectrometer

The pp -> p K0 Sigma+ reaction was investigated with the TOF spectrometer at COSY at 3.059 GeV/c incident beam momentum. The main objective was to clarify whether or not a narrow exotic S = +1 resnance, the Theta+ pentaquark, is populated at 1.53 GeV/c2 in the K0 p subsystem with a data sample of much higher statistical significance compared to the previously reported data in this channel. An analysis of these data does not confirm the existence of the Theta+ pentaquark. This is expressed as an upper limit for the cross section sigma (pp -> p K0 Sigma+) < 0.15 microbarn at the 95 percent confidence level.

hep-ex↗