arXiv subjects

J. Zlomanczuk

Publications and source records attributed to J. Zlomanczuk.

At least 19 recordsLinked to original sources

arXiv2020

Search for the $η$ mesic $^3$He in the $pd\rightarrow d p π^{0}$ reaction with the WASA-at-COSY facility

The excitation function for the $pd\rightarrow$ $d p π^{0}$ reaction has been measured by WASA-at-COSY experiment with the aim of searching for $^{3}\hspace{-0.03cm}\mbox{He}$-$η$ mesic nuclei. The measurement in the vicinity of $η$ meson production was performed using a ramped proton beam. The data analysis and interpretation was carried out with the assumption that the $η$-mesic Helium decays via the formation of an intermediate N$^{*}$(1535) resonance. No direct signal of the $η$-mesic nucleus is observed in the excitation function. We determine a new improved upper limit for the total cross section for the bound state production and decay in the $pd\rightarrow$ $(^{3}\hspace{-0.03cm}\mbox{He}$-$η)_{bound} \rightarrow$ $d p π^{0}$ process. It varies between 13 nb to 24 nb for the bound state with width in the range $Γ\in (5,50)$ MeV.

nucl-ex↗

arXiv2019

Study of Three-Nucleon Dynamics in the dp breakup collisions using the WASA detector

Differential cross section for the 1H(d,pp)n breakup reaction at deuteron beam energy of 340 MeV has been measured with the use of WASA detector at COSY-Juelich. The set of proton-proton coincidences registered at Forward Detector has been analysed on dense grid of kinematic variables, giving in total around 5600 data points. The cross section data are compared to theoretical predictions based on the state-of-the-art nucleon-nucleon potentials, combined with three-nucleon force, Coulomb interaction or carried out in a relativistic regime.

nucl-ex↗

arXiv2017

Spin dependence of η meson production in proton-proton collisions close to threshold

Taking advantage of the high acceptance and axial symmetry of the WASA-at-COSY detector, and the high degree of the polarized proton beam of COSY, the reaction pp{\to} ppη has been measured close to threshold to explore the analyzing power Ay. The angular distribution of Ay is determined with the precision improved by more than one order of magnitude with respect to previous results allowing a first accurate comparison with theoretical predictions. The determined analyzing power is consistent with zero for an excess energy of Q = 15 MeV signaling s wave production with no evidence for higher partial waves. At Q = 72 MeV the data reveals strong interference of P s and P p partial waves and cancellation of (P p) and Ss*Sd contributions. These results rule out the presently available theoretical predictions for the production mechanism of the η meson.

nucl-ex↗

arXiv2016

Search for eta-mesic 4He in the dd->3He n pi0 and dd->3He p pi- reactions with the WASA-at-COSY facility

The search for 4He-eta bound states was performed with the WASA-at-COSY facility via the measurement of the excitation function for the dd->3He n pi0 and dd->3He p pi- processes. The beam momentum was varied continuously between 2.127 GeV/c and 2.422 GeV/c, corresponding to the excess energy for the dd->4He eta reaction ranging from Q=-70 MeV to Q=30 MeV. The luminosity was determined based on the dd->3He n reaction and quasi-free proton-proton scattering via dd->pp n_spectator n_spectator reactions. The excitation functions determined independently for the measured reactions do not reveal a structure which could be interpreted as a narrow mesic nucleus. Therefore, the upper limits of the total cross sections for the bound state production and decay in dd->(4He-eta)_bound->3He n pi0 and dd->(4He-eta)_bound->3He p pi- processes were determined taking into account the isospin relation between both the channels considered. The results of the analysis depend on the assumptions of the N* momentum distribution in the anticipated mesic-4He. Assuming as in the previous works, that this is identical with the distribution of nucleons bound with 20 MeV in 4He, we determined that (for the mesic bound state width in the range from 5 MeV to 50 MeV) the upper limits at 90% confidence level are about 3 nb and about 6 nb for npi0 and ppi- channels, respectively. However, based on the recent theoretical findings of the N*(1535) momentum distribution in the N*-3He nucleus bound by 3.6 MeV, we find that the WASA-at-COSY detector acceptance decreases and hence the corresponding upper limits are 5 nb and 10 nb for npi0 and ppi- channels respectively.

nucl-ex↗

arXiv2016

Search for an Isospin I =3 Dibaryon

Various theoretical calculations based on QCD or hadronic interactions predict that in addition to the recently observed dibaryon resonance $d^*(2380)$ with $I(J^P) = 0(3^+)$ there should also exist a dibaryon resonance with mirrored quantum numbers $I(J^P) = 3(0^+)$. We report here on a search for such a $NN$-decoupled state in data on the $pp \to ppπ^+π^+π^-π^-$ reaction. Since no clear-cut evidence has been found, we give upper limits for the production cross section of such a resonance in the mass range 2280 - 2500 MeV.

nucl-ex↗

arXiv2011

Exclusive Measurements of pp -> dpi+pi0: Double-Pionic Fusion without ABC Effect

Exclusive measurements of the reaction pp -> dpi+pi0 have been carried out at T_p = 1.1 GeV at the CELSIUS storage ring using the WASA detector. The isovector pi+pi0 channel exhibits no enhancement at low invariant pipi masses, i. e. no ABC effect. The differential distributions are in agreement with the conventional t-channel Delta-Delta excitation process, which also accounts for the observed energy dependence of the total cross section. This is an update of a previously published version -- see important note at the end of the article.

nucl-ex↗

arXiv2010

Exclusive Measurement of the $pp \to nnπ^+π^+$ Reaction at 1.1 GeV

First exclusive data for the $pp \to nnπ^+π^+$ reaction have been obtained at CELSIUS with the WASA detector setup at a beam energy of $T_p$ = 1.1 GeV. Total and differential cross sections disagree with theoretical calculations, which predict the $ΔΔ$ excitation to be the dominant process at this beam energy. Instead the data require the excitation of a higher-lying $Δ$ state, most likely the $Δ(1600)$, to be the leading process.

nucl-ex↗

arXiv2010

Delta Delta Excitation in Proton-Proton Induced pi0pi0 Production

Exclusive measurements of the $pp \to ppπ^0π^0$ reaction have been performed at CELSIUS/WASA at energies from threshold up to $T_p$ = 1.3 GeV. Total and differential cross sections have been obtained. Here we concentrate on energies $T_p \ge$ 1 GeV, where the $ΔΔ$ excitation becomes the leading process. No evidence is found for a significant ABC effect beyond that given by the conventional $t$-channel $ΔΔ$ excitation. This holds also for the double-pionic fusion to the quasibound $^2$He. The data are compared to model predictions, which are based on both pion and $ρ$ exchange. Total and differential cross sections are at variance with these predictions and call for a profound modification of the $ρ$-exchange. A phenomenological modification allowing only a small $ρ$ exchange contribution leads to a quantitative description of the data.

nucl-ex↗

arXiv2010

Production of eta and 3pi mesons in the pd->3HeX reaction at 1360 and 1450 MeV

The cross sections of the pd -> 3He eta, pd -> 3He pi0 pi0 pi0 and pd -> 3He pi+ pi- pi0 reactions have been measured at beam kinetic energies T_p= 1360 MeV and T_p= 1450 MeV using the CELSIUS/WASA detector setup. At both energies, the differential cross section dsigma/dOmega of the eta meson in the pd -> 3He eta reaction shows a strong forward-backward asymmetry in the CMS. The ratio between the pd -> 3He pi+ pi- pi0 and the pd -> 3He pi0 pi0 pi0 cross sections has been analysed in terms of isospin amplitudes. The reconstructed invariant mass distributions of the pi-pi, 3He-pi and 3He-2pi systems provide hints on the role of nucleon resonances in the 3pi production process.

nucl-ex↗

arXiv2009

Two-Pion Production in Proton-Proton Collisions -- Experimental Total Cross Sections and their Isospin Decomposition

The two-pion production in pp-collisions has been investigated at CELSIUS in exclusive measurements from threshold up to $T_p$ = 1.36 GeV. Total and differential cross sections have been obtained for the channels $pnπ^+π^0$, $ppπ^+π^-$, $ppπ^0π^0$ and also $nnπ^+π^+$. For intermediate incident energies $T_p >$ 1 GeV, i.e. in the region which is beyond the Roper excitation but at the onset of $ΔΔ$ excitation, the total $ppπ^0π^0$ cross section falls behind theoretical predictions by as much as an order of magnitude near 1.2 GeV, whereas the $nnπ^+π^+$ cross section is a factor of five larger than predicted. An isospin decompostion of the total cross sections exhibits a s-channel-like energy dependence in the region of the Roper excitation as well as a significant contribution of an isospin 3/2 resonance other than the $Δ(1232)$. As possible candidates the $Δ(1600)$ and the $Δ(1700)$ are discussed.

nucl-ex↗

arXiv2009

Exclusive measurement of two-pion production in the dd --> 4Hepipi reaction

The results from the first kinematically complete measurement of the dd --> 4Hepipi reaction are reported. The aim was to investigate a long standing puzzle regarding the origin of the peculiar pipi-invariant mass distributions appearing in double pion production in light ion collisions, the so-called ABC effect. The measurements were performed at the incident deuteron energies of 712 MeV and 1029 MeV, with the WASA detector assembly at CELSIUS in Uppsala, Sweden. We report the observation of a characteristic enhancement at low pipi-invariant mass at 712 MeV, the lowest energy yet. At the higher energy, in addition to confirming previous experimental observations, our results reveal a strong angular dependence of the pions in the overall centre of mass system. The results are qualitatively reproduced by a theoretical model, according to which the ABC effect is described as resulting from a kinematical enhancement in the production of the pion pairs from two parallel and independent NN--> dpi sub-processes.

nucl-ex↗

arXiv2009

Production of the omega meson in the pd --> 3He omega reaction at 1450 MeV and 1360 MeV

The production of $ω$ mesons in the $pd \to{}^3$He$ ω$ reaction has been studied at two energies near the kinematic threshold, $T_p=1450$ MeV and $T_p=1360$ MeV. The differential cross section was measured as a function of the $ω$ cm angle at both energies over the whole angular range. Whereas the results at 1360 MeV are consistent with isotropy, strong rises are observed near both the forward and backward directions at 1450 MeV. Calculations made using a two-step model with an intermediate pion fail to reproduce the shapes of the measured angular distributions and also underestimate the total cross sections.

nucl-ex↗

arXiv2009

Double-Pionic Fusion of Nuclear Systems and the ABCEffect -- Aproaching a Puzzle by Exclusive and Kinematically Complete Measurements

The ABC effect - a puzzling low-mass enhancement in the $ππ$ invariant mass spectrum - is well-known from inclusive measurements of two-pion production in nuclear fusion reactions. Here we report on first exclusive and kinematically complete measurements of the most basic double pionic fusion reaction $pn \to d π^0π^0$ at 1.03 and 1.35 GeV. The measurements, which have been carried out at CELSIUS-WASA, reveal the ABC effect to be a $(ππ)_{I=L=0}$ channel phenomenon associated with both a resonance-like energy dependence in the integral cross section and the formation of a $ΔΔ$ system in the intermediate state. A corresponding simple s-channel resonance ansatz provides a surprisingly good description of the data.

nucl-ex↗

arXiv2008

Polarisation of the omega meson in the pd-->3He+omega reaction at 1360 and 1450 MeV

The tensor polarisation of omega mesons produced in the pd-->3He+omega reaction has been studied at two energies near threshold. The 3He nuclei were detected in coincidence with the pi0pi+pi- or pi0gamma decay products of the omega. In contrast to the case of phi meson production, the omega mesons are found to be unpolarised. This brings into question the applicability of the Okubo-Zweig-Iizuka rule when comparing the production of vector mesons in low energy hadronic reactions.

nucl-ex↗

arXiv2006

Evidence for a 'Narrow' Roper Resonance - the Breathing Mode of the Nucleon

All the time since its discovery the N$^*$(1440) baryon state, commonly known as Roper resonance, has been a state with many question marks - despite of its 4-star ranking in the particle data book. One reason is that it does not produce any explicit resonance-like structures in the observables of $π$N or $γ$N reactions. Only in partial wave analyses of $π$N scattering data a clear resonance strcuture gets obvious in the $P_{11}$ partial wave. Very recent measurements of the J/$Ψ$ decay by the BES collaboration and of the $pp \to npπ^+$ reaction at 1.3 GeV by the CELSIUS-WASA collaboration show for the first time a clear resonance structure in the invariant $nπ^+$ mass spectrum for the Roper resonance at M $\approx$ 1360 MeV with a width of about 150 MeV. These values agree very favorably with the pole position results of recent $π$N phase shift analyses. In consequence of this very low-lying pole postion, which is roughly 100 MeV below the nominal value, the decay properties have to be reinvestigated. From our two-pion production data we see that the decay mainly proceeds via N$^* \to $N$σ$, i.e. a monopole transition as expected for the breathing mode of the nucleon.

nucl-ex↗

arXiv2006

Two-Pion Production in Nucleon-Nucleon Collisions and the ABC-Effect - Approaching a Puzzleby exclusive and Kinematically complete Measurements

The ABC effect - a puzzling low-mass enhancement in the $ππ$ invariant mass spectrum - is known from inclusive measurements of two-pion production in nuclear collisions, where it always showed up, if the participating nucleons fused to a bound nuclear system in the final state. The first exclusive measurements on the ABC effect have been carried out very recently at CELSIUS-WASA for the fusion reactions leading to d, $^3$He and $^4$He nuclei in the final state. The data analyzed so far for the fusion processes to d and $^3$He reveal this effect to be a $σ$ channel phenomenon associated with the formation of a strongly attractive $ΔΔ$ system. The data for the strictly isospin-selective double-pionic fusion to $^4$He, where we expect the largest effect, are currently still analyzed. All inclusive data on this system are well described by our model, too. This case also constitutes the heaviest nuclear system, where exclusive measurements of double-pionic fusion can be carried out with present-day instruments. Surprisingly, the $pp \to ppπ^0π^0$ reaction in the $ΔΔ$ region is observed to also show a ABC-like low-$ππ$ mass enhancement, a phenomenon, which deserves special attention.

nucl-ex↗

arXiv2006

Exclusive Measurements of $pd\to ^3He ππ$ : the $ABC$ Effect Revisited

Exclusive measurements of the reactions $pd\to$ $^3He π^+ π^-$ and $pd\to$ $^3He π^0π^0$ have been carried out at $T_p=0.895$ GeV at the CELSIUS storage ring using the WASA detector. The $π^+π^-$ channel evidences a pronounced enhancement at low invariant $ππ$ masses - as anticipated from previous inclusive measurements of the ABC effect. This enhancement is seen to be even much larger in the isoscalar $π^0π^0$ channel. The differential distributions prove this enhancement to be of scalar-isoscalar nature. $ΔΔ$ calculations give a good description of the data, if a boundstate condition is imposed for the intermediate $ΔΔ$ system.

nucl-ex↗

arXiv2006

Anisotropy in the pion angular distribution of the reaction pp -> pp pi0 at 400 MeV

The reaction pp -> pp pi0 was studied with the WASA detector at the CELSIUS storage ring. The center of mass angular distribution of the pi0 was obtained by detection of the gamma decay products together with the two outgoing protons, and found to be anisotropic with a negative second derivative slope, in agreement with the theoretical predictions from a microscopic calculation.

nucl-ex↗