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)%.

The pseudoscalar mixing angle ΘPS from ν and ν′ production in annihiltion at rest

Abstract We have determined ratios of branching ratios for p p annihilations at rest into π0η and π0η′, into ηη and ηη′, and into ωη and ωη′. All reactins are observed in two different all-neutral final states. The ratios permit a determination of the pseudoscalar mixing angle. We find ΘPS = −(17.3±1.8)°.

New states as observed by the Crystal Barrel experiment

Abstract The Crystal Barrel Detector has been in operation since October 1989. Results on the analysis of the annihilation of protonium at rest into three pseudoscalars is presented. The π 0 π 0 π 0 final state confirms the existence of ƒ 2 (1520)→π 0 π 0 . In the ηη system of the π 0 ηη final state an isoscalar J PC = 0 ++ resonance with a mass of 1560 MeV/c 2 and a width of 245 MeV/c 2 is observed. The identification with ƒ 0 (1590) is doubtful since the ηη' decay is not observed with the corresponding strength. Our analysis yields an upper limit for the relative branching ratio BR(ƒ 0 (1560)→ηη') BR(ƒ 0 (1560)→ηη) .

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…

The Crystal Barrel spectrometer at LEAR

The crystal Barrel spectrometer used at LEAR, CERN to study the products of pd annihilations is described. A 1380 element array of Csl crystals measures photons from the decay of π0, η, η′ and ω mesons. A segmented drift chamber in a 1.5T magnetic field is used to identify and measure charged particles. A fast on-line trigger on charged and neutral multiplicities and on the invariant mass of secondary particles is available. The performance of the detector is discussed.

Feasibility study for the measurement of πN transition distribution amplitudes at P¯ANDA in p¯p→J/ψπ0

The exclusive charmonium production process in (P) over barp annihilation with an associated pi 0 meson (p) over barp -> J/psi pi(0) is studied in the framework of QCD collinear factorization. The feasibility of measuring this reaction through the J/psi -> e(+) e(-) decay channel with the AntiProton ANnihilation at DArmstadt ((P) over bar ANDA) experiment is investigated. Simulations on signal reconstruction efficiency as well as the background rejection from various sources including the (P) over barp -> pi(+)pi(-)pi(0) and (p) over barp -> J/psi pi(0)pi(0) reactions are performed with PANDAROOT, the simulation and analysis software framework of the (P) over bar ANDA experiment. It is show…

Antiproton-proton annihilation in-flight

This is an overview of the preliminary results of\(\bar pp\) annihilation at incident\(\bar p\) momenta of 600, 1200 and 1940 MeV/c(*). The data was taken at LEAR with the Crystal Barrel Detector (E. Akeret al.:Nucl. Instrum. Methods A,321, 108 (1992)). In the two pseudoscalar final states seven different channels are observable and their angular distributions are measured. They are compared to older data, if existent, and are found to be equal within the experimental errors. In the three-meson final states, an overview of the already examined final states is given. Striking signals in the Dalitz plots and invariant-mass projections for a set of final states are observed. In the final state…

Proton-antiproton annihilation into ηηπ-observation of a scalar resonance decaying into ηη

Abstract The results of a measurement of pp annihilation at rest into ηηπ 0 are presented. Assuming a resonance dominated model for the annihilation process an isoscalar J PC =0 ++ resonance decaying into ηη is observed with a mass of 1560±25 MeV/ c 2 and a width of 245±50 MeV/ c 2 .

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.

Antiproton annihilation at rest in liquid deuterium into π−π0π0pS

With the Crystal Barrel detector, the final state π−π0π0pS at rest in liquid deuterium was measured for the first time. A preliminary partial-wave analysis was performed, which required two interesting features: besides the ρ(770), a second pole was needed in the ππP-wave and a narrow resonance in the ππS-wave, slightly above 1500 MeV/c2. With the same parametrization a high-statistics π+π−π0 data set could also be well described.

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.

Study of doubly strange systems using stored antiprotons

Bound nuclear systems with two units of strangeness are still poorly known despite their importance for many strong interaction phenomena. Stored antiprotons beams in the GeV range represent an unparalleled factory for various hyperon-antihyperon pairs. Their outstanding large production probability in antiproton collisions will open the floodgates for a series of new studies of systems which contain two or even more units of strangeness at the PANDA experiment at FAIR. For the first time, high resolution gamma-spectroscopy of doubly strange Lambda Lambda-hypernuclei will be performed, thus complementing measurements of ground state decays of Lambda Lambda-hypernuclei at J-PARC or possible …

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…

New results from crystal barrel

Results are presented on meson spectroscopy, two-body final states and meson decay modes observed in\(\bar pp\) annhilation at rest by the Crystal Barrel experiment at LEAR.

High statistics study of ƒ0(1500)s decay into ηη

Abstract A partial wave analysis of the reaction p p →π o ηη has been performed, using a high quality, high statistics data set of 198,000 events. In addition to the ƒ 0 (1370), a second scalar resonance decaying into ηη, the ƒ 0 (1500), with mass m = (1505 ± 15) MeV and width Γ = (120 ± 30) MeV has to be introduced to describe the data.

High-statistics analysis of $$\bar pp \to \pi ^0 \pi ^0 \pi ^0 $$ at restat rest

Antiproton-proton annihilation at rest into 3π0 is analysed based on a data sample of about 500 000 high-quality 3π0 events. In this high-statistics Dalitz plot two structures in the region of π0π0 invariant masses of about 1500 MeV show up, a small band and a blob at higher masses. In a first attempt to describe the data two different models are used to parametrize the dynamical amplitudes leading to the same conclusion: the data require a 0+ + and also a 2+ + resonance in the 1500 MeV region.

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.

First observation of the production of nucleon resonances in antiproton annihilation in liquid deuterium

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.

Partial-wave analysis of ππη in $$\bar pp$$ annihilation at restannihilation at rest

A new isovector scalar πη resonance with a mass of 1450 MeV is observed in a high-statistics study of\(\bar pp\) annihilation at rest into π0π0η.

P- versus S-wave at rest in LH2

Abstract The annihilation p p →π 0 π 0 was measured for antiprotons stopped in liquid hydrogen (LH2). This reaction is only allowed from odd angular momentum states of the p p - atom . The resulting branching ratio BR ( p p →π 0 π 0 ) LH 2 =(6.93±0.22 stat ±0.37 syst )×10 −4 , combined with a previous measurement of the branching ratio BR ( p p →π + π − ) 2 P in gas from the 2P-state of p p suggests a fraction of P-wave annihilation in LH2 of (28.8±3.5)%, much larger than the values obtained from other annihilation channels. A method of reconciling the contradictory results is discussed.

Transparency ratio in γA→η′A′ and the in-medium η′ width

Abstract The photoproduction of η ′ -mesons off different nuclei has been measured with the CBELSA/TAPS detector system for incident photon energies between 1500–2200 MeV. The transparency ratio has been deduced and compared to theoretical calculations describing the propagation of η ′ -mesons in nuclei. The comparison indicates a width of the η ′ -meson of the order of Γ = 15 – 25 MeV at ρ = ρ 0 for an average momentum p η ′ = 1050 MeV / c , at which the η ′ -meson is produced in the nuclear rest frame. The inelastic η ′ N cross section is estimated to be 3–10 mb. Parameterizing the photoproduction cross section of η ′ -mesons by σ ( A ) = σ 0 A α , a value of α = 0.84 ± 0.03 has been dedu…

Antiproton-proton annihilation at rest into two mesons

Abstract Branching ratios for antiproton-proton annihilations at rest into two mesons are given. The data were obtained at LEAR by stopping antiprotons in a liquid hydrogen target. Both charged and neutral annihilation products were detected in the Crystal Barrel detector. Representative data are presented, and their bearing on the general picture of annihilation dynamics is discussed. In addition, preliminary branching ratios for two-body radiative annihilations are given.

Hidden and open $$\bar ss$$ production in $$\bar pp$$ annihilation at restannihilation at rest

New branching ratios for\(\bar pp\) annihilation at rest into final states with a\(K\bar K\) pair or φ-meson are being measured with the Crystal Barrel detector at LEAR. The yield of φγ, relative to ωγ, appears to violate the OZI rule as strongly as φπ relative to ωπ.

Final states with strangeness from Crystal Barrel and Asterix

Abstract We discuss φ production in p p annihilation at rest from the Asterix and Crystal Barrel experiments and compare the branching ratios to similar final states without strangeness. The ωπ 0 φπ 0 production ratio is unexpectedly low. In the search for new states, the φπ0 mass spectrum shows no evidence for a resonance in the 1450 MeV/c2 mass range but the K☆K0π0 Dalitz plot shows interesting structure.

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 …