Search

Abstract:: An exotic meson, the π1(1400) with J PC = 1- +, has been seen to decay into a p-wave ηπ system. If this decay conserves flavor SU(3), then it can be shown that this exotic meson must be a four-quark state ( q¯q + q¯q) belonging to a flavor ¯10 representation of SU(3). In contrast, the π1(1600) with a substantial decay mode into π is likely to be a member of a flavor octet.

We report results of a high resolution search for the tensor glueball candidate ξ(2230) in a p̄pformation experiment. π0π0and ηηdecay 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 ξare presented.

We have measured the branching ratios for 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 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 andπ+π−η′ in comparison toS-state annihilation. $$\begin{gathered} BR(S - wave \to \pi ^ + \pi ^ - \eta ) = (13.7 \pm 1.46) \cdot 10^{ - 3} \hfill \\ BR(P - wave \to \pi ^ + \pi ^ - \eta ) = (3.35 \pm 0.84) \cdot 10^{ - 3} \hfill \\ BR(S - wave \to \pi ^ + \pi ^ - \eta ') = (3.46 \pm 0.67) \cdot 10^{ - 3} \hfill \\ BR(P - wave \to \pi ^ + \pi ^ - \eta ') = (0.61 \pm 0.33) \cdot 10^{ - 3} . \hfill \\ \end{gathered} $$

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 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 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 for the ζ (1480) in the reaction (1480), ζ (1480) →π+π−π+π− to clarify whether the ζ (1480) is identical to the 4π-mode of thef2 (1520). No evidence for this decay mode was found. A prominent resonance in innihilation into five pions is the ω meson. We find two quasi-two-body intermediate states: and (1235). The mass and width of theb1 (1235) are determined to be:(1) $$M_{bI} = 1225 \pm 5\user2{MeV, }\Gamma _{b1} = 113 \pm 12MeV.$$

Abstract: Antiproton-proton annihilation at rest into $$\bar pp$$ 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 $$(qq\overline {qq} or N\bar N)$$ state.

Abstract: Annihilation of antiprotonic hydrogen atoms into $$\bar pp$$ atom; in the second sample only those events are selected for which a low-energy X-ray is observed in coincidence with the final state. The latter data sample contains a large fraction of events in which a radiative transition to the 2P level of the $$\bar pp$$ atom was followed by annihilation. The former data contain comparable fractions of annihilation fromS andP states. By subtraction of theP wave contribution annihilation fromS states can be studied. The spin-parity analysis of the $$\bar pp$$ annihilation fromS waves proceeds dominantly via production of $$\bar pp$$ atom. Strong interference with a background amplitude or an amplitude for rhov(1600) production is needed to obtain a satisfactory description of the data. The production off 2 mesons is weak.

We report measurements of branching ratios for production of a series of two meson final states in p annihilations at rest in liquid hydrogen. We find: $$\begin{gathered} BR(\bar pp \to \pi ^ + \pi ^ - ) = (3.07 \pm 0.13) \cdot 10^{ - 3} \hfill \\ BR(\bar pp \to K^ + K^ - ) = (0.99 \pm 0.05) \cdot 10^{ - 3} \hfill \\ BR(\bar pp \to \pi ^0 \pi ^0 ) = (6.93 \pm 0.43) \cdot 10^{ - 4} \hfill \\ BR(\bar pp \to \pi ^0 \eta ) = (2.12 \pm 0.12) \cdot 10^{ - 4} \hfill \\ BR(\bar pp \to \pi ^0 \omega ) = (5.73 \pm 0.47) \cdot 10^{ - 3} \hfill \\ BR(\bar pp \to \pi ^0 \eta ') = (1.23 \pm 0.13) \cdot 10^{ - 4} \hfill \\ BR(\bar pp \to \eta \eta ) = (1.64 \pm 0.10) \cdot 10^{ - 4} \hfill \\ BR(\bar pp \to \eta \omega ) = (1.51 \pm 0.12) \cdot 10^{ - 2} \hfill \\ BR(\bar pp \to \eta \eta ') = (2.16 \pm 0.25) \cdot 10^{ - 4} \hfill \\ BR(\bar pp \to \omega \omega ) = (3.32 \pm 0.34) \cdot 10^{ - 2} \hfill \\ BR(\bar pp \to \omega \eta ') = (0.78 \pm 0.08) \cdot 10^{ - 2} \hfill \\ \end{gathered}$$ These are the first measurements of the channels ??' and ??' and in almost all the other channels are more precise than previous results. We also obtain, in a more precise fashion, the following ratios of branching ratios:K+K-/p+p-=0.323±0.013, p0?'/p0?=0.548±0.056, ??'/??=0.31±0.15, ??'/??=0.515±0.040, p0?/p0p0=0.303±0.010, ??/p0p0=0.232±0.011 and p0?/??=0.377±0.12. The measurements are made for different ? and ?' decays, and we thus obtain G??3p0/G????=0.841±0.034, and .

Data ontaken 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)πwithL=0. It may be interpreted as theD2partner ofπ2(1670). A strong signal is also observed just above threshold inf2(1270)ηwithL=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)πandf2(1270)ηwithL=1. There is no evidence for resonances with decays toa0(980)π, σηorf0(980)η.

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?p0)=(7.03±0.72)×10-6, BR(¯pd??n)=(3.19+0.48)×10-6, BR(¯pd??n)=(22.8+4.1)×10-6, BR(¯pd??'n)14×10-6 (at 95% confidence level). Assuming charge independence, our result for¯ pd?p0n is compatible with measurements of the only other observed Pontecorvo reaction ¯pd ? p-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 nucleon). This agreement suggests that there may be appreciable rates for Pontecorvo reactions producing final state mesons with masses above 1 GeV.

Recent experiments at LEAR have found surprisingly large branching ratios for reactions$\bar{\mbox{N}}$ N $\rightarrow\ \phi\pi$ from S-wave initial states while no$\phi\pi$ production is observed from P states of the $\bar{p} p$ system. Also, no $\phi\pi$ is seen in radiative J/$\psi$ decays even though the rate for$\omega\pi$ is substantial. We calculate the$\phi\pi$ production rates for these three cases via $K K^*$ intermediate states and$K \bar K$ rescattering using the dispersion relation technique; we find that the large$\phi\pi$ rate in $p \bar{p}$ annihilations from S states can be reproduced with a reasonable cut-off for the dispersion integral; for J/$\psi$ decays the calculated $\phi\pi$ rate is compatible with the observed upper limit. We would, however, expect $\phi\pi$ to be seen from$\bar{p} p$ P-states, in contrast to experimental findings. Yet the branching ratio for$\bar p p \rar K^* \bar K$ via isospin $I=1$ of $\bar p p,\;^1P_1$ state is not known; and therefore no definite conclusion can be drawn. We also compare the Dalitz plots we obtain for direct$\phi$ production and for $\phi$ production via rescattering. Clear differences between the two theoretical distributions are observed; yet very high precision data would be required to establish the origin - direct production or rescattering - of the $\phi$ mesons. This observation supports the use of the isobar model in data analyses.

Recent experiments at LEAR have found surprisingly large branching ratios for reactions $$\bar NN \to \phi \pi $$ from S-wave initial states while noφπproduction is observed from P states of the $$\bar pp$$ system. Also, noφπis seen in radiative J/ψdecays even though the rate forωπis substantial. We calculate theφπproduction rates for these three cases viaKK* intermediate states and $$K\bar K$$ rescattering using the dispersion relation technique; we find that the largeφπrate in $$\bar pp$$ annihilations from S states can be reproduced with a reasonable cut-off for the dispersion integral; for J/ψdecays the calculatedφπrate is compatible with the observed upper limit. We would, however, expectφπto be seen from $$\bar pp$$ P-states, in contrast to experimental findings. Yet the branching ratio for $$\bar pp \to K*\bar K$$ via isospinI= 1 of $$\bar pp$$ ,1P1state is not known; and therefore no definite conclusion can be drawn. We also compare the Dalitz plots we obtain for directφproduction and forφproduction via rescattering. Clear differences between the two theoretical distributions are observed; yet very high precision data would be required to establish the origin — direct production or rescattering — of theφmesons. This observation supports the use of the isobar model in data analyses.

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.

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.

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 ofMp/Me=1836.1502(53) agrees with other more precise but indirect determinations of this quantity.

Abstract: Antiproton-proton annihilation at rest in a gaseous H2 target at NTP into the final state $$\bar K^0 $$ has been investigated. We observe theE(1420) resonance in the invariant mass spectrum (K 0)miss K ± $$\bar p$$ p rarrpgr+pgr– E 0,E 0rarrK 0 L K ±pgrmnplus 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) areJ pc=0–+ and not I++.

We use SU(3)- and charge conjugation-invariance to analyse the annihilation of abound state of definiteC-parity into two mesons. We introduce four sets of SU(3) invariant couplings and write down the transformations among them. They allow for a direct interpretation in terms of different physical assumptions. The couplings permit an easy incorporation of the quark line- (or OZI-) rule. The four sets of invariant couplings — even though mathematically equivalent — correspond to different pictures of the annihilation mechanism. One coupling scheme refers to a description ofannihilation in terms of baryon exchange. A second scheme specifies the octet decomposition of the s-channel intermediate states. The third scheme traces the flow of quarks from the initialsystem to the outgoing mesons. And finally, we use the octet coupling scheme. The latter has no obvious interpretation in form of a simple physical picture but is needed to relate the different coupling schemes by transformation matrices.

A new isoscalar ππ resonance AX(1565) has been observed at a mass of 1565±10 MeV/c2and a width of 170±20 MeV/c2. The resonance is produced in ppannihilation at rest into π+π−π0from P states of antiprotonic hydrogen atoms formed b y stopping antiprotons in hydrogen gas at normal temperature and pressure. Annihilation from P states is identified by coincident observations of the LX-ray series emitted in the cascade of ppatoms. The resonance is seen as striking peak in the π+π−invariant mass spectrum. The phase of the π+π−D wave shows a resonance-like behaviour. Hence we assign the quantum numbers IG(JPC) = 0+(2++) to the resonance.

The KαX-rays from pp̄ atoms formed in H2gas at normal temperature and pressure are unambiguously identified by coincidences with L X-rays populating the 2P level. Background due to inner bremsstrahlung is suppressed by selecting events annihilating into neutral final states only. The Kαline is observed with a significance of more than 25 standard deviations at an energy of 8.67 (15) keV. From fits to the Kαline we obtain a strong-interaction shift and width of the 1S level, averaged over the unresolved spin singlet and triplet contributions, of ΔE+ iΓ/2 = [−0.70(15) + i0.80(20)] keV.

It is shown that a previously described method for measuring the spin resonance of free electrons in a trap can also be used to measure their (g-2) anomaly. The electrons are trapped in an electrostatic quadrupole field with a superimposed homogeneous axial magnetic field, and are polarized by spin exchange. The spin and (g-2) resonance are monitored through the spin dependence of the excitation processe+Na (3S)→e+Na(3P). Calculations are made of the energy levels and transition probabilities of the trapped electrons.

Elektrons were stored for several minutes in a homogeneous magnetic field and an electrical quadrupol field V = (U0/R2) · (x2+ y2— 2z2). The solution of the SCHRÖDINOER equation can be reduced to the problem of three harmonic oscillators. The frequencies of these oscillators were measured experimentally and thus the cyclotron frequency of free electrons was determined.