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A. V. Anisovich

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

At least 55 records · Page 3Linked to original sources
arXiv2012

Well-established nucleon resonances revisited by double-polarization measurements

The first measurement is reported of the double-polarization observable G in photoproduction of neutral pions off protons, covering the photon energy range from 620 to 1120 MeV and the full solid angle. G describes the correlation between the photon polarization plane and the scattering plane for protons polarized along the direction of the incoming photon. The observable is highly sensitive to contributions from baryon resonances. The new results are compared to the predictions from SAID, MAID, and BnGa partial wave analyses. In spite of the long-lasting efforts to understand γp -> pπ 0 as the simplest photoproduction reaction, surprisingly large differences between the new data and the latest predictions are observed which are traced to different contributions of the N (1535) with spin-parity J^P = 1/2^- and N (1520) with J^P = 3/2^- . In the third resonance region, where N (1680) with J^P = 5/2^+ production dominates, the new data are reasonably close to the predictions.

nucl-ex↗
arXiv2012

Light 2++ and 0++ mesons

The status of light I=0, J^{PC}=2^{++} and 0^{++} mesons is discussed, particularly the separation of n-nbar and s-sbar states. They fall into a simple scheme except for f_2(1810). A case is made that this has been confused with the f_0(1790). It should be possible to check this with existing or forthcoming data.

hep-ex↗
arXiv2011

Evidence for a spin-quartet of nucleon resonances at 2\,GeV

Results from a multi-channel partial wave analysis of elastic and inelastic $πN$ and $γN$ induced reactions are presented. The analysis evidences the existence of a spin-quartet of nucleon resonances with total angular momenta $J^P=1/2^+,..., 7/2^+$. All states fall into a $\pm130$\,MeV mass gap centered at 1.97\,GeV. The spin quartet is at variance with S-wave diquark configurations required in classical di-quark models.

hep-ex↗
arXiv2011

Evidence for a negative-parity spin-doublet of nucleon resonances at 1.88\,GeV

Evidence is reported for two nucleon resonances with spin-parity $J^P=1/2^-$ and $J^P=3/2^-$ at a mass just below 1.9\,GeV. The evidence is derived from a coupled-channel analysis of a large number of pion and photo-produced reactions. The two resonances are nearly degenerate in mass with two resonances of the same spin but positive parity. Such parity doublets are predicted in models claiming restoration of chiral symmetry in high-mass excitations of the nucleon. Further examples of spin parity doublets are found in addition. Alternatively, the spin doublet can be interpreted as member of the 56-plet expected in the third excitation band of the nucleon. Implications for the problem of the {\it missing resonances} are discussed.

nucl-ex↗
arXiv2011

Anomaly in the K^0_S Sigma^+ photoproduction cross section off the proton at the K* threshold

The $γ+ p \rightarrow K^0 + Σ^+$ photoproduction reaction is investigated in the energy region from threshold to $E_γ= 2250$\,MeV. The differential cross section exhibits increasing forward-peaking with energy, but only up to the $K^*$ threshold. Beyond, it suddenly returns to a flat distribution with the forward cross section dropping by a factor of four. In the total cross section a pronounced structure is observed between the $K^*Λ$ and $K^*Σ$ thresholds. It is speculated whether this signals the turnover of the reaction mechanism from t-channel exchange below the $K^*$ production threshold to an s-channel mechanism associated with the formation of a dynamically generated $K^*$-hyperon intermediate state.

nucl-ex↗
arXiv2011

Photoproduction of Neutral Pions off Protons

Photoproduction of neutral pions has been studied with the CBELSA/TAPS detector in the reaction $γp\to pπ^0$ for photon energies between 0.85 and 2.50 GeV. The $π^0$ mesons are observed in their dominant neutral decay mode: $π^0\toγγ$. For the first time, the differential cross sections cover the very forward region, $θ_{\rm c.m.}<60^\circ$. A partial-wave analysis of these data within the Bonn-Gatchina framework observes the high-mass resonances $G_{17}$(2190), $D_{13}$(2080), and $D_{15}$(2070).

nucl-ex↗
arXiv2011

Partial wave analysis of pbar-p annihilation channels in flight with I=1, C=+1

A combined analysis is reported of 3pizero, pizero-eta and pizero-etaprime data in the mass range 1960 to 2410 MeV. This analysis is made consistent also with eta-eta-pizero data, reported separately. The analysis requires s-channel resonances with a spectrum close to that published earlier for C = +1 states with I = 0; masses for I=1 states are lower on average by 20 MeV. Two alternative solutions are found, differing only for J^P = 2^+ and 4^+ states by small amounts in masses and widths. Both 3pizero and eta-pizero data prefer one of these two solutions. For this preferred solution, observed states have J^PC, masses and widths (M,Gamma) in MeV as follows: 4^-+: (2250+-15, 215+-25), 4^++: (2255+-40, 330 ^{+110}_{-50}) and (2005 ^{+25}_{-45}, 180+-30), 3^++: (2275+-35, 350 ^{+100}_{-50}) and (2031+-12, 150 \pm 18), 2^-+: (2245+-60, 320 ^{+100}_{-40}) and (2005+-15, 200+-40, 2^++: (2255+-20, 230+-15), (2175+-40, 310^{+90}_{-45}) and (2030+-20, 205+-30), and 1^++: (2270 ^{+55}_{-40}, 305 ^{+70}_{-35}). There are indications of further 2^-+, 2^++ and 1^++ contributions just below the available mass range, and also a 0^++ state at ~2025 MeV.

hep-ex↗
arXiv2011

A partial wave analysis of pbar-p -> eta-eta-pizero

A partial wave analysis of pbar-p -> eta-eta-pizero data from the Crystal Barrel experiment is made in terms of s-channel resonances. The decay channels a_0(980)-eta, f_0(1770)-pi and f_0(2105)-pi provide evidence for two I = 1 J^{PC} = 0^{-+} resonances. The first has mass M =2360 +- 25 MeV and width Gamma = 300^{+100}_{-50} MeV, and the second M =2070 \pm 35 MeV, Gamma = 310^{+100}_{-50} MeV. There is also evidence for a J^{PC} = 2^{-+} state with M = 2005 +- 15 MeV and Gamma = 200 +- 40 MeV, decaying strongly to a_0(980)-pi.

hep-ex↗
arXiv2011

Study of pbar-p -> eta-eta-pizero-pizero in flight

An analysis of data on pbar-p -> eta-eta-pizero-pizero is presented at pbar beam momenta 600 to 1940 MeV/c. There is evidence for an I = 1, J^PC = 2^-+ resonance in eta-eta-pizero with mass M = 1880 +- 20 MeV and width 255 +- 45 MeV, decaying strongly a2(1320)-eta; it is too strong to be explained as the high mass tail of π_2(1670) -> a2(1320)-eta. There is tentative evidence also for weak decays to f_0(1500)π. It makes a natural partner to the eta 2(1860).

hep-ex↗
arXiv2011

I=0, C=-1 mesons from 1940 to 2410 MeV

New Crystal Barrel data are reported for pbar-p -> omega-eta and pbar-p -> omega-pizero-pizero with omega decaying to piplus-piminus-pizero. The omega-eta data confirm angular distributions obtained earlier from data where omega -> pizero-gamma. The new omega-eta data provide accurate measurements of vector and tensor polarisations of the omega and lead to considerable improvements in masses and widths of s-channel resonances. A new J^PC = 3^+- I = 0 resonance is observed with mass M = 2025+-20 MeV and width Gamma = 145+-30 MeV. Polarisation is close to zero everywhere and tensor polarisations are large, as is the case also for pbar-p -> omega-pizero.

hep-ex↗
arXiv2011

Combined analysis of meson channels with I=1, C = -1 from 1940 to 2410 MeV

New Crystal Barrel data are reported for pbar-p -> omega-pizero and pbar-p -> omega eta-pizero with omega decaying to piplus-piminus-pizero. The shapes of angular distributions agree well with those for data where omega -> pizero-gamma; this is a valuable cross-check on systematic errors. The new data provide good measurements of vector and tensor polarisations P_y, T20, T21 and T22 of the omega. These lead to significant improvements in parameters of several resonances reported earlier. New values of masses and widths (in Mev) are: J^PC = 5^-- (2300+-45, 260+-75), J^PC = 3^-- (2260+-20, 160+-25), J^PC = 1^+- (2240+-35, 320+-85), and J^PC = 1^-- (2110+-35, 230+-50). A remarkable feature of the data is that vector polarisation P_y is close to zero everywhere. It follows that all interfering amplitudes have relative phases close to 0 or 180 deg. Tensor polarisations are large.

hep-ex↗
arXiv2011

A study of pbar-p -> eta-eta-eta for masses 1960 to 2410 MeV

Data on pbar-p -> 3eta for beam momenta 600--1940 MeV/c are presented. The strongest channel is f_0(1500)-eta from the initial pbar-p state 1S0. Together with eta-pizero-pizero data, the 3eta data determine the branching ratio BR[f_0(1500) -> eta-eta]/BR[f_0(1500) -> pizero-pizero] = 0.42+-0.09. They are consistent with a dominant contribution from an I=0, C=+1 J^{PC} = 0^{-+} resonance observed earlier in the eta-pizero-pizero data; from the combined eta-pizero-pizero and 3eta data, its mass is M = 2320 \pm 15 MeV and its width Gamma = 230+-35 MeV.

hep-ex↗
arXiv2011

Resonances formed by pbar-p and decaying into pizero-pizero-eta for masses 1960 to 2410 MeV

Data on pbar-b annihilation in flight into pizero-pizero-eta are presented for nine beam momenta 600 to 1940 MeV/c. The strongest four intermediate states are found to be f_2(1270)-eta, a_2(1320)-pi, sigma-eta and a_0(980)-pi. Partial wave analysis is performed mainly to look for resonances formed by pbar-p and decaying into pizero-pizero-eta through these intermediate states. There is evidence for the following s-channel I = 0 resonances : two 4^{++} resonances with mass and width (M,Gamma) at (2044, 208) MeV and (2320+-30, 220+-30) MeV; three 2^{++} resonances at (2020+-50, 200+-70) MeV, (2240+-40, 170+-50) MeV and (2370+-50, 320+-50) MeV; two 3^{++} resonances at (2000+-40, 250+-40) MeV and (2280+-30, 210+-30) MeV; a 1^{++} resonance at (2340+-40, 340+-40) MeV; and two 2^{-+} resonances at (2040+-40, 190+-40) MeV and (2300+-40, 270+-40) MeV.

hep-ex↗
arXiv2011

Search for Narrow Nucleon Resonance in $γp\to ηp$

Results of a partial wave analysis of new high-statistics data on $γp\to pη$ from MAMI are presented. A fit using known broad resonances and only standard background amplitudes can not describe the relatively narrow peaking structure in the cross section in the mass region of 1660-1750 MeV which follows a minimum. An improved description of the data can be reached by either assuming the existence of a narrow resonance at a mass of about 1700 MeV with small photo-coupling or by a threshold effect. In the latter case the observed structure is explained by a strong (resonant or non-resonant) $γp\toωp$ coupling in the $S_{11}$ partial wave. When the beam asymmetry data, published by part of the GRAAL collaboration, are included in the fit, the solution with a narrow $P_{11}$ state is slightly preferred. In that fit, mass and width of the hypothetical resonance are determined to $M\sim$1694 MeV and $Γ\sim 40$ MeV, respectively, and the photo-coupling to $\sqrt{{\rm Br}_{ηN}} A_{1/2}^p \sim 2.6\cdot 10^{-3}$ GeV$^{-1/2}$. High precision measurements of the target asymmetry and $F$-observable are mandatory to establish the possible existence of such a narrow state and to provide the necessary information to define which partial wave is responsible for the structure observed in the data.

hep-ph↗