0000000000027843
AUTHOR
H. Matthäy
High-statistics study of f0(1500) decay into π0π0
Abstract A partial-wave analysis of the reaction p p →π 0 π 0 π 0 has been performed using a high-quality high-statistics data set of 712 000 events. In addition to the f0(975) and f0(1300), the scalar resonance with mass m = (1500 ± 15) MeV and width Γ = (120 ± 25) MeV is necessary to describe the data.
E decays to ηππ in annihilation at rest
Abstract We have observed the ηπ + π − and ηπ 0 π 0 decay modes of the E meson in p p annihilation at rest into π + π − π 0 π 0 η . The mass and width of the E meson are 1409 ± 3 and 86 ± 10 MeV. The production and decay branching ratio is B( p p → Eππ)B(E → ηππ) = (3.3 ± 1.0) × 10 −3 . With a spin-parity analysis we determine that J P = 0 − . The observation of the ηπ 0 π 0 decay mode establishes that E is isoscalar ( C = +1). We find that E decays to η ( ππ ) s (where ( ππ ) s is an S-wave dipion) and πa 0 (980)(→ πη ) with a relative branching ratio of (78 ± 16) %. Using the K K π production and decay branching ratio measured earlier we determine that B[E → K K π] B[E → ηππ] = 0.61 ± 0.1…
Study of annihilation at rest into ωηπ0
Abstract We have studied p p annihilations at rest in liquid hydrogen into the final state ωηπ 0 where ω decays to π 0 γ . This reaction is dominated by the production of α 0 (980) and contributions from a 2 (1320) and b 1 0 (1235). Upper limits for the production of an axial vector h ′ 1 (1380) meson and vector mesons ω(1390), ω(1600), and φ(1680) decaying to ωη are given. The branching ratio of p p annihilation into ωηπ 0 was determined to be (0.68±0.01±0.05)%.
Test of chiral perturbation theory in η decays
The decay of the η-meson into three pions plays an important role as a test of low-energy QCD calculations in the framework of chiral perturbation theory. Previous experiments show results that are inconclusive or even contradictory. The Crystal Barrel experiment at LEAR has determined the braching ratiosΓ(η→3π0)/Γ(η→π+π−π0)=1.47±0.09±0.15 andΓ(η→γγ)/Γ(η→π+π−π0)=1.88±0.10±0.17 using its unique features to detect charged particles as well as neutral particles. The value for the first ratio agrees nicely with the theoretical predictions and solves previous experimental uncertainties. The second value, which yields a partial width ofΓ(η→π+π−π0)=(0.24±0.03) keV, shows that the same next-to-lead…
New results on the Roper resonance and the P_{11} partial wave
Properties of the Roper resonance, the first scalar excitation of the nucleon, are determined. Pole positions and residues of the $P_{11}$ partial wave are studied in a combined analysis of pion- and photo-induced reactions. We find the Roper pole at $\{(1371\pm7)-i(92\pm10)\}$ MeV and an elasticity of $0.61\pm 0.03$. The largest decay coupling is found for the $N\sigma$ ($\sigma=(\pi\pi)$-$S$-wave). The analysis is based on new data on $\gamma p\to p\pi^0\pi^0$ for photons in the energy range from the two-pion threshold to 820 MeV from TAPS at Mainz and from 0.4 to 1.3 GeV from Crystal Barrel at Bonn and includes further data from other experiments. The partial wave analysis excludes the p…
Momentum dependence of the decay η→π+π−π0
Abstract The π 0 momentum dependence of the decay η → π + π − π 0 has been measured with the Crystal Barrel detector. The analysis is based on 3230 events. The results of this independent measurement are compared to new chiral perturbation theory calculations and previous measurements.
Branching ratios for p annihilation at rest into two-body final states
Abstract Measurements of two-body branching ratios for p p annihilations at rest in liquid and gaseous (12 ρ STP ) hydrogen are reported. Channels studied are p p →π 0 π 0 ,π 0 η , K 0 S K 0 L , K + K − . The branching ratio for the π 0 π 0 channel in liquid H 2 is measured to be ( 6.14±0.40)×10 −4 . The results are compared with those from other experiments. The fraction of P-state annihilation for a range of target densities from 0.002 ρ STP to liquid H 2 is determined. Values obtained include 0.11±0.02 in liquid H 2 and 0.48±0.04 in 12 ρ STP H 2 gas.
Evidence for two isospin zeroJ PC=2−+ mesons at 1645 and 1875 MeV
Data on\(\bar pp \to \eta \pi ^0 \pi ^0 \pi ^0 \) taken at beam momenta of 1.2 and 1.94 GeV/c reveal evidence for twoI=0JPC=2−+ resonances inηππ. The first, at 1645±14(stat.)±15(syst.) MeV with width 180−21+40±25 MeV, decays toα2(1320)π withL=0. It may be interpreted as the\(q\bar q^1 \)D2 partner ofπ2(1670). A strong signal is also observed just above threshold inf2(1270)η withL=0. It is 11–22 times stronger than is expected for the high mass tail of the 1645 MeV resonance. It can be fitted as a second 2−+ resonance at 1875±20±35 MeV with width 200±25±45 MeV. A third resonance havingJPC=2++ is observed at 2135±20±45 MeV withΛ=250±25±45 MeV, decaying to botha2(1320)π andf2(1270)η withL=1. T…
Antiproton-proton annihilation at rest into KKπ0π0
Abstract The annihilation channel p p →K + K − π 0 in liquid hydrogen at rest has been studied with the Crystal Barrel detector at LEAR. The measured branching ratio is: BR ( p p → K + K − π 0 )=(2.37±0.15)×10 −3 . A partial wave analysis shows that this reaction is dominated by the π (K K ) S , K K ∗ (892) and π φ (1020) intermediate states. Weak signals are observed for π a 2 (1320), π f 2 (1270), π f 2 ′(1525) and K(Kπ) S . A satisfactory description of the Dalitz plot requires the introduction of π (K K ) P intermediate states with at least one pole.
A high resolution search for the tensor glueball candidate ξ(2230)
Abstract We report results of a high resolution search for the tensor glueball candidate ξ(2230) in a p p formation experiment. π0π0 and ηη decay channels were measured in a scan of the mass region 2220 MeV to 2240 MeV. No evidence for the existence of ξ(2230) was found. 95% confidence upper limits for the possible existence of ξ are presented.
High-mass ϱ-meson states from p̄d-annihilation at rest into π−π0π0pspectator
Abstract A study of p -annihilation in liquid deuterium into π − π 0 π 0 and a spectator-proton is presented. A cut on the proton-momentum of ≤ 100 MeV/ c ensures that annihilation takes place on a quasi-free neutron. A partial wave analysis shows contributions from three vector mesons, with masses and widths of (763.7 ± 3.2; 152.8 ± 4.3), (1411 ± 14; 343 ± 20); (1780 −29 +37 ; 275 ± 45) MeV/ c 2 , respectively.
Measurement of the decay distribution of η′ → π+π−γ and evidence for the box anomaly
Abstract The distribution of m ( π + π − ) in the decay η ′ → π + π − γ has been measured with the Crystal Barrel detector. The results are based on a total of 7392 observed η′ decays. The box anomaly constant is extracted from this and its value is found to agree well with theoretical expectations. The pseudoscalar nonet parameters ( f 1 , f 8 and θ PS ) are determined. Finally, we find that there is a problem of consistency between QCD and the standard VDM assumption.
Annihilation at rest of antiprotons and protons into neutral particles
Abstract Annihilation of antiprotons and protons at rest into neutral particles has been studied with the Crystal Barrel detector at LEAR. Annihilation frequencies are determined for final states containing π 0 , η , η ′ and ω mesons using a liquid and a room temperature, 12 bar, gaseous hydrogen target. Including annihilation frequencies for production of neutral kaons from other experiments, the identified reactions for annihilation in liquid hydrogen add up to a branching fraction of (3.56±0.28)% per annihilation compared to the frequency of (3.50±0.30)% with which we observe the all-neutral decay modes inclusively. Since the exclusive final states are normalized to the Crystal Barrel me…
The ρ-mass, width and line shape in annihilation at rest into π+π−π0
The rho mass, width and line shape in p(over)-bar-p annihilation at rest into pi(+)pi(-)pi(0)
Search for a new light gauge boson in decays of π0 and η
Abstract We have searched for new light gauge bosons produced in π 0 and η decays by studying the kinematically well-constrained reactions p p→π 0 π 0 π 0 and p p→π 0 π 0 η , where one π 0 or the η decays through the emission of a single photon recoiling against a missing state X (where X is a long-lived weakly interacting particle or X →ν ν ). No signal has been observed and branching ratio upper limits of 6 × 10 −5 at 90% C.L. have been obtained for masses of the gauge boson lying between ∼65 MeV and 125 MeV ( π 0 decay), and 6 × 10 −5 at 90% C.L. for X masses between ∼200 MeV and 525 MeV (η decay). The π 0 -decay limit represents a factor of 4 to 8 improvement when compared to the existi…
First observations of Pontecorvo reactions with a recoiling neutron
We report the first observations of Pontecorvo reactions of the type ¯pd →Xn. We fully reconstruct the outgoing meson and, for antiprotons stopped in liquid deuterium, we measure: BR(¯pd→π0)=(7.03±0.72)×10−6, BR(¯pd→ηn)=(3.19+0.48)×10−6, BR(¯pd→ωn)=(22.8+4.1)×10−6, BR(¯pd→η′n)14×10−6 (at 95% confidence level). Assuming charge independence, our result for¯ pd→π0n is compatible with measurements of the only other observed Pontecorvo reaction ¯pd → π−p. The experimental ratios between the above branching ratios are in fair agreement with both the statistical model and dynamical two-step models (assumingN¯ N annihilation into two mesons, with subsequent absorption of one meson on the remaining …