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A. V. Sarantsev

Publications and source records attributed to A. V. Sarantsev.

At least 91 records · Page 5Linked to original sources
arXiv2010

Photoproduction of $η'$-mesons off the deuteron

Quasi-free photoproduction of $η'$ mesons off nucleons bound in the deuteron has been measured with the combined Crystal Barrel - TAPS detector. The experiment was done at a tagged photon beam of the ELSA electron accelerator in Bonn for incident photon energies from the production threshold up to 2.5 GeV. The $η'$-mesons have been detected in coincidence with recoil protons and recoil neutrons. The quasi-free proton data are in good agreement with the results for free protons, indicating that nuclear effects have no significant impact. The coincidence with recoil neutrons provides the first data for the $γn \rightarrow nη'$ reaction. In addition, also first estimates for coherent $η'$-production off the deuteron have been obtained. In agreement with model predictions, the total cross section for this channel is found to be very small, at most at the level of a few nb. The data are compared to model calculations taking into account contributions from nucleon resonances and $t$-channel exchanges.

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arXiv2010

A fresh look at eta2(1645), eta2(1870), eta2(2030) and f2(1910) in pbar-p -> eta + 3pizero

There is a large discrepancy between results of Crystal Barrel and WA102 for the branching ratio R = BR[eta2(1870)->a2(1320)pi]/ BR[eta2(1870)->f2(1270)eta]. An extensive re-analysis of the Crystal Barrel data redetermines branching ratios for decays of eta2(1870), eta2(1645), eta2(2030) and f2(1910). This re-analysis confirms a small value for R of 1.60+-0.39, inconsistent with the value 32.6+-12.6 of WA102. The likely origin of the discrepancy is that the WA102 data contain a strong f2(1910)->a2-pi signal as well as eta2(1870). There is strong evidence that the eta2(1870) has resonant phase variation. A peak in f2(1270)a0(980) confirms closely the parameters of the a2(2255) resonance observed previously. A peak in eta2(2030)-pi is interpreted naturally in terms of pi2(2245) with reduced errors for mass and width M=2285+-20(stat)+-25(syst) MeV, Gamma=250+-20(stat)+-25(syst) MeV.

hep-ex↗
arXiv2010

P-wave excited baryons from pion- and photo-induced hyperon production

We report evidence for $N(1710)P_{11}$, $N(1875)P_{11}$, $N(1900)P_{13}$, $Δ(1600)P_{33}$, $Δ(1910)P_{31}$, and $Δ(1920)P_{33}$, and find indications that $N(1900)P_{13}$ might have a companion state at 1970\,MeV. The controversial $Δ(1750)P_{31}$ is not seen. The evidence is derived from a study of data on pion- and photo-induced hyperon production, but other data are included as well. Most of the resonances reported here were found in the Karlsruhe-Helsinki (KH84) and the Carnegie-Mellon (CM) analyses but were challenged recently by the Data Analysis Center at GWU. Our analysis is constrained by the energy independent $πN$ scattering amplitudes from either KH84 or GWU. The two $πN$ amplitudes from KH84 or GWU, respectively, lead to slightly different $πN$ branching ratios of contributing resonances but the debated resonances are required in both series of fits.

hep-ph↗
arXiv2010

Measurement of the Beam Asymmetry $Σ$ in the Forward Direction for pi0 Photoproduction

Photoproduction of neutral pions has been studied with the CBELSA/TAPS detector for photon energies between 0.92 and 1.68~GeV at the electron accelerator ELSA. The beam asymmetry~$Σ$ has been extracted for $115^\circ < θ_{\rm c.m.} < 155^\circ$ of the $π^0$~meson and for $θ_{\rm c.m.} < 60^\circ$. The new beam asymmetry data improve the world database for photon energies above 1.5~GeV and, by covering the very forward region, extend previously published data for the same reaction by our collaboration. The angular dependence of $Σ$ shows overall good agreement with the SAID parameterization.

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arXiv2010

Quark-diquark Systematics of Baryons: Spectral Integral Equations for Systems Composed by Light Quarks

For baryons composed by the light quarks ($q=u,d$) we write spectral integral equation using the notion of two diquarks: (i) axial--vector state, $D^{1}_{1}$, with the spin $S_D=1$ and isospin $I_D=1$ and (ii) scalar one, $D^{0}_{0}$, with the spin $S_D=0$ and isospin $I_D=0$. We present spectral integral equations for the $qD^{0}_{0}$ and $qD^{1}_{1}$ states taking into account quark--diquark confinement interaction.

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arXiv2010

Photoproduction of pions and properties of baryon resonances from a Bonn-Gatchina partial wave analysis

Masses, widths and photocouplings of baryon resonances are determined in a coupled-channel partial wave analysis of a large variety of data. The Bonn-Gatchina partial wave formalism is extended to include a decomposition of t- and u-exchange amplitudes into individual partial waves. The multipole transition amplitudes for $γp\to pπ^0$ and $γp\to nπ^+$ are given and compared to results from other analyses.

hep-ph↗
arXiv2010

Quark--Diquark Systematics of Baryons and the SU(6)SYMMETRY for Light States

We continue our attempts to systematize baryons, which are composed of light quarks ($q=u,d$), as quark--diquark systems. The notion of two diquarks is used: (i) $D^{1}_{1}$, with the spin $S_D=1$ and isospin $I_D=1$ and (ii) $D^{0}_{0}$, with $S_D=0$ and $I_D=0$. Here we try to resolve the problem of the low-lying $Δ(\frac 52^-)$ states: in the last experiments the lightest state is observed at $\ga 2200$ MeV, not at $1900 - 2000$ MeV as it has been stated 20 years ago. We are looking for different systematization variants with the forbidden low-lying $Δ(\frac 52^-)$ states in the mass region $\la 2000$ MeV. We see that the inclusion of the SU(6) constraints on $qD^{1}_{1}$ states with angular momentum L=1 results in a shift of the lightest $Δ(\frac 52^-)$ isobar to $\sim 2300$ MeV. The scheme with the SU(6) constraints for low-lying $qD^{1}_{1}$ and $qD^{0}_{0}$ states (with $L=0,1$) is presented in detail here.

hep-ph↗
arXiv2010

Searching for the quark--diquark systematics of baryons composed by light quarks $q=u,d$

Supposing quark--diquark structure of baryons, we look for systematics of baryons composed of light quarks ($q=u,d$). We systematize baryons using the notion of two diquarks: (i) axial--vector state, $D^{1}_{1}$, with the spin $S_D=1$ and isospin $I_D=1$ and (ii) scalar one, $D^{0}_{0}$, with the spin $S_D=0$ and isospin $I_D=0$. We consider several schemes for the composed baryons: (1) with different diquark masses, $M_{D^0_0} \ne M_{D^1_1}$, (2) with $M_{D^0_0} = M_{D^1_1}$ and overlapping $qD^0_0$ and $qD^1_1$ states (resonances), (3) with/without SU(6) constraints for low-lying states (with quark--diquark orbital momenta L=0). In the high-mass region the model predicts several baryon resonances at $M\sim 2.0-2.9$ GeV. Moreover, the model gives us the double pole structure (i.e. two poles with the same Re$M$ but different Im$M$) in many amplitudes at masses $M\ga 2.0$ GeV. We see also that for description of low-lying baryons (with L=0), the SU(6) constraint is needed.

hep-ph↗
arXiv2009

The study of the negative pion production in neutron-proton collisions at beam momenta below 1.8 GeV/c

A detailed investigation of the reaction np -> ppπ^{-} has been carried out using the data obtained with the continuous neutron beam produced by charge exchange scattering of protons off a deuterium target. A partial wave event-by-event based maximum likelihood analysis was applied to determine contributions of different partial waves to the pion production process. The combined analysis of the np -> ppπ^{-} and pp -> ppπ^{0} data measured in the same energy region allows us to determine the contribution of isoscalar partial waves (I=0) in the momentum range from 1.1 up to 1.8 GeV/c. The decay of isoscalar partial waves into (^1S_0)_{pp}π$ channel provides a good tool for a determination of the pp S-wave scalar scattering length in the final state which was found to be a_{pp}=-7.5\pm 0.3 fm.

hep-ph↗
arXiv2009

The analysis of reactions $πN\to two mesons + N$ within reggeon exchanges. 1. Fit and results

The novel point of this analysis is a direct use of reggeon exchange technique for the description of the reactions $πN\to two mesons + N$ at large energies of the initial pion. This approach allows us to describe simultaneously distributions over $M$ (invariant mass of two mesons) and $t$ (momentum transfer squared to nucleons). Making use of this technique, the following resonances (as well as corresponding bare states), produced in the $πN\to π^0π^0 N$ reaction are studied: $f_0(980)$, $f_0(1300)$, $f_0(1200-1600)$, $f_0(1500)$, $f_0(1750)$, $f_2(1270)$, $f_2(1525)$, $f_2(1565)$, $f_2(2020)$, $f_4(2025)$. Adding data for the reactions $p\bar p({\rm at rest, from liquid H_2})\to π^0π^0π^0$, $π^0π^0η$, $π^0ηη$ and $p\bar p({\rm at rest, from gaseous H_2})\to π^0π^0π^0$, $π^0π^0η$, $π^0ηη$, we have performed simultaneous $K$-matrix fits of two-meson spectra in all these reactions. The results of combined fits to the above-listed isoscalar $f_J$-states and to isovector ones, $a_0(980)$, $a_0(1475)$, $a_2(1320)$, are presented.

hep-ph↗
arXiv2009

Two-pion decays of mesons and confinement singularities

We consider the two-pion decay of the $ρ$-meson, the $^3S_1q\bar q$-state of the constituent quarks -- the decay being determined by the transition $q\bar q\to ππ$ contains information about confinement interactions. One can specify in this decay two types of transitions: ({\bf i}) the bremsstrahlung radiation of a pion $q\to q+π$ (or $\bar q\to\bar q+π$) with the subsequent fusion $q\bar q\to π$, and ({\bf ii}) the direct transition $q\bar q\to ππ$. We demonstrate how in the amplitudes of the corresponding transitions the quark singularities have to disappear, {\it i.e.} what is the way the quark confinement at relatively short distances can be realized. We calculate and estimate the contributions of processes with bremsstrahlung radiation of the pion and of the direct transition $q\bar q\to ππ$. The estimates demonstrate that the processes involving the direct transition $q\bar q\to ππ$ are necessary, but they cannot be determined unambiguously by the decay $ρ(775)\to ππ$. We conclude that for the determination of the $q\bar q\to ππ$ transition more complete data on the resonance decays into the $ππ$ channels are required than those available at the moment.

hep-ph↗
arXiv2009

The rho -> gamma pi and omega -> gamma pi decays in quark-model approach and estimation of coupling for pion emission by quark

In the framework of the relativistic and gauge invariant spectral integral technique, we calculate radiative decays rho(770)-> gamma pi(140) and omega(780)-> gamma pi(140) supposing all mesons (pi, rho and omega) to be quark-antiquark states. The q anti-q wave functions found for mesons and photon lead to a reasonably good description of data ($Γ^{(exp)}_{ρ^{\pm} \toγπ^{\pm}}=68\pm 30$ keV, $Γ^{(exp)}_{ρ^{0}\toγπ^0}=77\pm 28$ keV, $Γ^{(exp)}_{ω\toγπ^0}=776\pm 45$ keV) that makes it possible to estimate the coupling for the bremsstrahlung emission of pion by quarks $g_π\equiv g_π(u\to d π)$. We have found two values for the pion bremsstrahlung coupling: $|g_π|=16.7 \pm 0.3 ^{+0.1}_{-2.3}$ (Solution I) and $|g_π|=3.0 \pm 0.3 ^{+0.1}_{-2.1}$ (Solution II). Within SU(6)-symmetry for nucleons, Solution I gives us for pi NN coupling the value $16.4 \le g_{πNN}^2/(4π) \le 23.2$ that is in qualitative agreement with the pi N scattering data, $g_{πNN}^2/(4π)\simeq 14$. For excited states, we have estimated the partial widths in Solution I as follows: $Γ(ρ_{2S}^\pm\to γπ)\simeq 10 - 130$ keV, $Γ(ρ_{2S}^0\to γπ)\simeq 10 -130$ keV, $Γ(ω_{2S}\to γπ)\simeq 60 - 1080$ keV. The large uncertainties emphasise the necessity to carry out measurements of the meson radiative processes in the region of large masses.

hep-ph↗
arXiv2008

Linearly polarised photon beams at ELSA and measurement of the beam asymmetry in pi^0-photoproduction off the proton

At the electron accelerator ELSA a linearly polarised tagged photon beam is produced by coherent bremsstrahlung off a diamond crystal. Orientation and energy range of the linear polarisation can be deliberately chosen by accurate positioning of the crystal with a goniometer. The degree of polarisation is determined by the form of the scattered electron spectrum. Good agreement between experiment and expectations on basis of the experimental conditions is obtained. Polarisation degrees of P = 40% are typically achieved at half of the primary electron energy. The determination of P is confirmed by measuring the beam asymmetry, Σ, in pi^0 photoproduction and a comparison of the results to independent measurements using laser backscattering.

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arXiv2008

Photoproduction of $η$ mesons off neutrons from a deuteron target

A formalism is developed for the partial wave analysis of data on meson photoproduction off deuterons and applied to photoproduction of $η$ and $π^0$ mesons. Different interpretations of a dip-bump structure of the $η$ photoproduction cross section in the 1670 MeV region are presented and discussed. Helicity amplitudes for two low-mass $S_{11}$ states are determined.

hep-ph↗
arXiv2008

Polarization degrees of freedom in near-threshold photoproduction of omega mesons in the pi^0 gamma decay channel

We study polarization variables in the photoproduction of omega-mesons with subsequent omega to gamma pi^0 decay. Single and double polarization observables are calculated as a function of different final-state angles. Reaction models include pomeron (natural parity) and pi^0 (unnatural parity) exchange in the t-channel. In addition, the contribution of s-channel resonances is considered. The sensitivity of the polarization observables to the reaction dynamics is discussed.

hep-ex↗
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.

nucl-ex↗
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$^2$.

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