High-statistics study of f0(1500) decay into π0π0

1995

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

1995

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…

φ production in annihilation at rest

1991

Abstract We report on measurements of the branching ratios for φ production in p p annihilation at rest in H 2 gas. Branching ratios for φπ 0 , φη, φϱ 0 , φω and φπ + π − are determined for two data sets with different contributions of annihilations from S and P states of the p p system. The branching ratios are compared to corresponding annihilation modes where the φ is replaced by an ω meson. We conclude that φ production is in most reactions enhanced with respect to the expectation based on the OZI rule. In annihilations from the spin triplet ground state of antiprotonic hydrogen into φπ the OZI rule is violated dramatically.

Study of annihilation at rest into ωηπ0

1994

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)%.

Antiproton-proton annihilation at rest in H2 gas into π+ π− π0

1990

Antiproton-proton annihilation at rest into π+ π− π0 has been studied by stopping antiprotons from LEAR in a H2 gas target at normal temperature and pressure. The reaction is observed in coincidence withL X-rays which are emitted in the cascade of\(\bar pp\) atoms. The X-rays populate one of the angular momentumL=1 states of a\(\bar pp\) atom which then annihilates. A spinparity analysis of the π+ π− π0 Dalitz plot gives contributions from the threeP states from which annihilation into three pions is allowed. The most striking features of the Dalitz plot are production of charged and neutral ϱ(770) and off2(1270) mesons. Production of ϱ(770) mesons proceeds via the isoscalar part of the1P1 …

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

1992

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)°.

A direct determination of the proton-electron mass ratio

1978

The cyclotron resonance of protons and electrons in a magnetic field of 5.7 Tesla produced by a superconducting solenoid has been measured. Protons and electrons were alternately confined in an electrostatic quadrupole trap. The quotient of the cyclotron frequencies provides a first direct determination of the proton-electron mass ratio. The result ofM p /M e =1836.1502(53) agrees with other more precise but indirect determinations of this quantity.

The ASTERIX spectrometer at LEAR

1989

The ASTERIX spectrometer has been used to study the formation and the ground state of the pp atom and exclusive final states of pp annihilation at rest in a H2 gas target at NTP, using antiprotons from the Low Energy Antiproton Ring (LEAR) at CERN. The article describes the mechanical construction of the apparatus, the trigger logic, the chamber readout, and the data acquisition system. The detector calibration and the offline processing of the 55 million reconstructed events are illustrated. An overview is given about the new physics results obtained by the experiment.

Test of chiral perturbation theory in η decays

1994

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…

Review of Particle Physics

2020

The Review summarizes much of particle physics and cosmology. Using data from previous editions, plus 2,143 new measurements from 709 papers, we list, evaluate, and average measured properties of gauge bosons and the recently discovered Higgs boson, leptons, quarks, mesons, and baryons. We summarize searches for hypothetical particles such as supersymmetric particles, heavy bosons, axions, dark photons, etc. Particle properties and search limits are listed in Summary Tables. We give numerous tables, figures, formulae, and reviews of topics such as Higgs Boson Physics, Supersymmetry, Grand Unified Theories, Neutrino Mixing, Dark Energy, Dark Matter, Cosmology, Particle Detectors, Colliders, …

Proton-antiproton annihilation at rest into two mesons and the quark line rule

1988

Proton-antiproton annihilation at rest into two mesons is analysed in a model describing annihilation by quark lines. The model allows to fit existing data with two parameters. The parameters describe the amplitudes for diagrams with and without rearrangement of quark lines.

Strangeness production inp�p annihilation at rest and the quark ? diquark structure of nucleons

1988

The importance of approximate isospin selection rules observed inN¯ N annihilation at rest into two strange mesons is emphasized. The selection rules are traced back to a symmetry between amplitudes describing annihilation by the flux of quarks. Presumably the symmetry reflects the symmetry of ¯qq annihilation vertices. The relation of the symmetry to a quark — diquark substructure of the nucleon is discussed.

New results on the Roper resonance and the P_{11} partial wave

2008

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

1992

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.

Observability of the sign of wave functions

1976

A change of the phase factor of -1 in the wave function of a molecular quantum system leads to observable consequences in transition probabilities between molecular quantum states in accordance with quantum-mechanical calculations.

Muon knight shift measurements in the alkali and alkaline earth metal series

1979

Antiproton-proton annihilation in-flight

1994

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

1992

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

1998

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

1994

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

2001

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.

$$N\bar N$$ annihilation at rest into five pions

1993

\(N\bar N\) annihilation at rest into five pions was studied in the ASTERIX spectrometer by stopping antiprotrons from LEAR in a H2 or D2 gas target. In\(\bar pp\) annihilations in H2 leading to the π+π−π+π−π0 final state, the invariant mass spectra of two, three, and four pions show no evidence for any new narrow states. In\(\bar pn \to \pi ^ + \pi ^ - \pi ^ + \pi ^ - \pi ^ - \) the difference of the four pion mass spectra recoiling against a π− and those recoiling against a π+ shows a resonance-like structure (“ζ (1480)”), confirming a previous analysis with a smaller event sample. The ζ (1480) mass is shown to depend strongly on the momentum of the spectator proton. In H2, we searched fo…

Evidence for two isospin zeroJ PC=2−+ mesons at 1645 and 1875 MeV

1996

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

1993

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.

Muon-substituted compounds in liquid bromine and water-determination of the relevant diamagnetic shieldings

1979

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

1995

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

1994

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.

Do p annihilations at rest choose the Eightfold way?

1993

Dynamical selection rules observed in pp annihilation at rest are linked to relations between SU(3) invariant amplitudes. The ϱπ puzzle, the KK suppression in P wave, and the unexplained production rates of πa2 (1320) are shown to be manifestions of one SU(3) amplitude ratio. The dynamical selection rules observed in the production of strange mesons lead to symmetries in SU(3) amplitudes. We conjecture that these symmetries reflect the underlying quark-gluon dynamic. It is shown that the contribution of annihilation diagrams to important annihilation channels like ϱ0π0 or ηω is small or vanishes. Hence rearrangement must play an important role. The use of SU(3) relations in the context of N…

A high resolution search for the tensor glueball candidate ξ(2230)

2001

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.

Comment on the Feasibility of Antiproton Polarization in LEAR by Means of the Transverse Stern-Gerlach Effect

1984

The study of polarization effects in nucleon-nucleon scattering experiments has increased considerably our understanding of the Nuclear forces. Correspondingly it can be expected that the study of polarization phenomena in antiproton-nucleon scattering will also help us to resolve — at least partly — the complicated spin structure of the antiproton-nucleon amplitudes.

Cascade of exotic helium atoms

1987

Abstract The cascade of muonic helium and its pressure dependence has been calculated over the whole pressure range from 1×10 −2 to 1×10 3 atm. The calculation does not use any free parameter. The results show good agreement with experimental data.

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

1995

The atomic cascade of kaonic and pionic hydrogen

1990

Abstract The X-ray intensities of kaonic and pionic hydrogen atoms are calculated as functions of the hydrogen density and are compared to experimental data. Data on kaonic hydrogen are statistically not very significant, the comparison with the cascade results allows to test their intrinsic consistency. X-ray intensities from pionic hydrogen agree reasonably with the results of the cascade model.

High-mass ϱ-meson states from p̄d-annihilation at rest into π−π0π0pspectator

1997

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

1997

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.

Dynamical selection rules in p annihilation at rest

1993

Abstract The branching ratios for p p annihilation at rest into two mesons show the existence of dynamical selection rules. The ratios for some annihilation modes are small even though much larger rates should be expected on the basis of statistical models. Dynamical selection rules are observed in annihilations in which strange mesons are produced, and in annihilations into two isovector mesons. The selection rules seem - to first order - not to depend on the spins or orbital angular momenta of the p p atom or of the two mesons produced. This observation suggests an underlying symmetry. It is argued that this symmetry is SU(3).

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

1994

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

1992

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

2012

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

1993

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

1994

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.

Antiproton-proton annihilation at rest intoπ + π − η ′ andπ + π − η from atomicS andP states

1990

We have measured the branching ratios for\(\bar pp\) annihilation at rest intoπ+π−η andπ+π−η′ in hydrogen gas in two data samples that have different fractions ofS-wave andP-wave initial states. The branching ratios are derived from a comparison with the topological branching ratio for\(\bar pp\) annihilations into four charged pions of (49±4)% and the branching ratio intoπ+π−π+π−π0 of (18.7±1.6)%. We find a significant reduction of the branching ratios fromP-states for\(\bar pp \to \pi ^ + \pi ^ - \eta \) andπ+π−η′ in comparison toS-state annihilation. $$\begin{gathered} BR(S - wave \to \pi ^ + \pi ^ - \eta ) = (13.7 \pm 1.46) \cdot 10^{ - 3} \hfill \\ BR(P - wave \to \pi ^ + \pi ^ - \eta …

Annihilation at rest of antiprotons and protons into neutral particles

2003

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…

Observation and analysis ofE mesons in $$\bar p$$ p annihilation at rest in H2 gas

1989

Antiproton-proton annihilation at rest in a gaseous H2 target at NTP into the final state π+ π−K± π∓ (K0) with an undetectedK0 or\(\bar K^0 \) has been investigated. We observe theE(1420) resonance in the invariant mass spectrum (K0)missK± π∓ with massME=1413±8 MeV/c2 and widthГE=62 ± 16MeV/c2 and find evidence for the production of thef1(1285). The absolute branching ratio of\(\bar p\)p → π+ π−E0,E0 →K0LK±π∓ at (61±6)%P wave annihilation is (3.0±0.9)·10−4 of all annihilations. The observed suppression of theE production fromP wave with respect to theS wave together with some simple selection rules suggest that the quantum numbers of theE(1420) areJpc=0−+ and not I++.

The ρ-mass, width and line shape in annihilation at rest into π+π−π0

1999

The rho mass, width and line shape in p(over)-bar-p annihilation at rest into pi(+)pi(-)pi(0)

Experimental determination of the ortho-positronium lifetime in vacuum

1987

Moderated positrons from a22Na source form positronium atoms at the surface of a channel plate multiplier in a weak magnetic field. They decay inside a finite volume and the decay quanta are registered by ten plastic scintillation detectors and counted in a fast data acquisition system with zero deadtime. After corrections for the escape of atoms from the observation volume and for prompt annihilation back-ground we obtain a lifetime of (142.22±0.14) ns. This is in fair agreement with the theoretical value of 142.07 ns but larger than previous experimental determinations. A possible correction from annihilation at the walls of the decay chamber would further increase the lifetime.

Search for a new light gauge boson in decays of π0 and η

1994

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

1995

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 …