arXiv subjects

A. V. Anisovich

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

At least 73 records · Page 4Linked to original sources

arXiv2011

Partial wave analysiss of pbar-p -> piminus-piplus, pizero-pizero, eta-eta and eta-etaprime

A partial wave analysis is presented of Crystal Barrel data on pbar-p -> pizero-pizero, eta-eta and eta-etaprime from 600 to 1940 MeV/c, combined with earlier data on dσ/dΩand P for pbar-p->piminus-piplus. The following s-channel I=0 resonances are identified: (i) J^{PC} = 5^{--} with mass and width (M,Γ) at (2295+-30,235^{+65}_{-40}) MeV, (ii) J^{PC} = 4^{++} at (2020+-12, 170+-15) MeV and (2300+-25, 270+-50) MeV, (iii) 3D3 JPC = 3^{--} at (1960+-15, 150+-25) MeV and (2210+-4$, 360+-55) MeV, and a 3G3 state at (2300 ^{+50}_{-80}, 340+-150) MeV, (iv) JPC = 2^{++} at (1910+-30, 260+-40) MeV, (2020+-30, 275+-35) MeV, (2230+-30, 245+-45) MeV, and (2300+-35, 290+-50) MeV, (v) JPC = 1^{--} at (2005+-40, 275+-75) MeV, and (2165+-40, 160 ^{+140}_{-70}) MeV, and (vi) JPC = 0^{++} at (2005+-30, 305+-50) MeV, (2105+-15, 200+-25) MeV, and (2320+-30, 175+-45) MeV. In addition, there is a less well defined 6^{++} resonance at 2485+-40 MeV, with Gamma = 410+-90 MeV. For every JP, almost all these resonances lie on well defined linear trajectories of mass squared v. excitation number. The slope is 1.10+-0.03 Gev^2 per excitation. The f_0(2105) has strong coupling to eta-η, but much weaker coupling to pizero-pizero. Its flavour mixing angle between q-qbar and s-sbar is (59-71.6)deg, i.e. dominant decays to s-sbar. Such decays and its strong production in pbar-p interactions strongly suggest exotic character.

hep-ex↗

arXiv2011

I = 0 C = +1 mesons from 1920 to 2410 MeV

A combined fit is presented to data on pbar-p annihilation in flight to final states eta-pizero-pizero, pizero-pizero, eta-eta, eta-etaprime and piminus-piplus. The emphasis lies in improving an earlier study of eta-pizero-pizero by fitting data at nine pbar momenta simultaneously and with parameters consistent with the two-body channels. There is evidence for all of the I=0, C=+ q-qbar states expected in this mass range. New resonances are reported with masses and widths M,Gamma as follows: JPC = 4^{-+} (2328+-38, Gamma=240+-90) MeV, 1^{++} (1971+-15, 240+-45) MeV, 0^{-+} (2285+-20, 325+-30) MeV, and 0^{-+} (2010 ^{+35}_{-60}, 270+-60) MeV. Errors on the masses and widths of other resonances are also reduced substantially. All states lie close to parallel straight line trajectories of excitation number v. mass squared.

hep-ex↗

arXiv2011

Nucleon resonances in the fourth resonance region

Nucleon and $Δ$ resonances in the fourth resonance region are studied in a multichannel partial-wave analysis which includes nearly all available data on pion- and photo-induced reactions off protons. In the high-mass range, above 1850\,MeV, several alternative solutions yield a good description of the data. For these solutions, masses, widths, pole residues and photo-couplings are given. In particular, we find evidence for nucleon resonances with spin-parities $J^P=1/2^+...7/2^+$. For one set of solutions, there are four resonances forming naturally a spin-quartet of resonances with orbital angular momentum L=2 and spin S=3/2 coupling to $J=1/2,...,7/2$. Just below 1.9\,GeV we find a spin doublet of resonances with $J^P=1/2^-$ and $3/2^-$. Since a spin partner with $J^P=5/2^-$ is missing at this mass, the two resonances form a spin doublet which must have a symmetric orbital-angular-momentum wave function with L=1. For another set of solutions, the four positive-parity resonances are accompanied by mass-degenerate negative-parity partners -- as suggested by the conjecture of chiral symmetry restoration. The possibility of a $J^P=1/2^+, 3/2^+$ spin doublet at 1900\,MeV belonging to a 20-plet is discussed.

hep-ph↗

arXiv2011

Quasi-free photoproduction of eta-mesons off the deuteron

Precise data for quasi-free photoproduction of $η$ mesons off the deuteron have been measured at the Bonn ELSA accelerator with the combined Crystal Barrel/TAPS detector for incident photon energies up to 2.5 GeV. The $η$-mesons have been detected in coincidence with recoil protons and neutrons. Possible nuclear effects like Fermi motion and re-scattering can be studied via a comparison of the quasi-free reaction off the bound proton to $η$-production off the free proton. No significant effects beyond the folding of the free cross section with the momentum distribution of the bound protons have been found. These Fermi motion effects can be removed by an analysis using the invariant mass of the $η$-nucleon pairs reconstructed from the final state four-momenta of the particles. The total cross section for quasi-free $η$-photoproduction off the neutron reveals even without correction for Fermi motion a pronounced bump-like structure around 1 GeV of incident photon energy, which is not observed for the proton. This structure is even narrower in the invariant mass spectrum of the $η$-neutron pairs. Position and width of the peak in the invariant mass spectrum are $W\approx 1665$ MeV and FWHM $Γ\approx 25$ MeV. The data are compared to the results of different models.

nucl-ex↗

arXiv2011

Sigma-Meson and Confinement Singularity

We describe the meson-meson data for the ($IJ^{PC}=00^{++}$) wave at $280\leq\sqrt s\leq 1900$ MeV in two approaches: (i) the K-matrix approach and (ii) the dispersion relation D-matrix method. With a good description of low energy data (at $280\leq\sqrt s\leq 900$ MeV) as well as the data of two-meson transition amplitudes and antiproton-proton annihilation into three pseudoscalar meson states (at $450\leq\sqrt s\leq 1950$ MeV) we have found the positions of the resonance poles: (i) for the $σ$ meson pole: $M_σ= (390\pm 35)-i(235\pm 50)$ MeV; (ii) two poles for the $f_0(980)$, on the second sheet (under the $ππ$ cut): $M_{I} = (1011\pm 5)-i(35\pm 5)$ MeV, and on the third sheet (under the $ππ$ and $K\bar K$ cuts), $M_{II} = (1035\pm 50)-i(460\pm 50)$ MeV; for the $f_0(1370)$ meson, $M= (1285\pm 30)-i(160\pm 20)$ MeV; for the $f_0(1500)$ meson, $M = (1488\pm 4)-i(53\pm 5)$ MeV; for the $f_0(1790)$ meson, $M = (1775\pm 25)-i(140\pm 15)$ MeV and for the broad state $f_0(1200-1600)$ $M=(1540\pm 120)-i(550\pm 70)$ MeV. Our estimation of the scalar-isoscalar scattering length obtained under different parameterizations and assumptions about the quality of low energy $ππ$ scattering data is $a^0_0=(0.215\pm 0.040)μ^{-1}_π$. We also discuss the idea according to which the $σ$-meson could be a remnant of the confinement singularity, $1/s^2$, in a white channel.

hep-ph↗

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.

nucl-ex↗

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.

nucl-ex↗

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.

hep-ph↗

arXiv2010

Photoproduction of meson pairs: First measurement of the polarization observable I^s

The polarization observable I^s, a feature exclusive to the acoplanar kinematics of multi-meson final states produced via linearly polarized photons, has been measured for the first time. Results for the reaction g p -> p pi0 eta are presented for incoming photon energies between 970 MeV and 1650 MeV along with the beam asymmetry I^c. The comparably large asymmetries demonstrate a high sensitivity of I^s to the dynamics of the reaction. Fits using Bonn-Gatchina partial wave analysis demonstrate that the new polarization observables carry significant information on the contributing partial waves.

nucl-ex↗

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

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

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↗