Michael Doser

CERN | CERN · Physics Department (PH)

The branching ratios (Br) for the Pontecorvo reactions p̄ d →- nπ0, nη, nω, nη', and Δ0(1232)π0 are presented. The data were obtained at LEAR by stopping antiprotons in a liquid deuterium target. Outgoing mesons have been fully reconstructed. Assuming charge independence, Br(p̄ d → nπ0) was compared with measurements of the reaction p̄ d → pπ-. No...

Upper limits for the production of new light gauge bosons in pi(0), eta and eta' decays have been obtained with the Crystal Barrel detector. The kinematically well-constrained reactions <(p)over bar p> --> eta(0) eta(0) P have been studied, where P = eta(0), eta eta' decays through the emission of a single photon recoiling against a missing state X...

Crystal Barrel data on pp -> 5π0 at rest are presented. Mass spectra for 2π0 combinations, 3π0 and 4π0 and decay angular distributions all differ significantly from phase space. We present several ways of fitting the data. All agree on the definite presence of the f0(1500), observed in its 4π0 decay mode. It can decay into ππ(1300) and into σσ wher...

Data on [`(p)]p ® hp0 p0 p0\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=0J PC=2−+ resonances inηππ. The first, at 1645±14(stat.)±15(syst.) MeV with width 180 −21 +40 ±25 MeV, decays toα 2(1320)π withL=0. It may be interpreted as the q[`(q)]1q\bar q^1 D 2 partner ofπ 2(1670). A strong...

Upper limits for the production of new light gauge bosons in $\pi^0$,$\eta$ and$\eta^\prime$ decays have been obtained with the Crystal Barrel detector. The kinematically well-constrained reactions$\bar pp \rightarrow \pi^0\pi^0P$ have been studied, where $P\equiv\pi^0,\eta,\eta^\prime$ decays through the emission of a single photon recoiling again...

19> , R. McCrady m , J.P. Merlo a , C.A. Meyer m , L. Montanet f , A. Noble o5 , R. Ouared f , F. Ould-Saada o , K. Peters b , C.N. Pinder e , G. Pinter d , S. Ravndal b , C. Regenfus l , E. Schafer k6 , P. Schmidt g , M. Schutrumpf b , I. Scott i , R. Seibert g , S. Spanier o , H. Stock b , C. Straßburger c , U. Strohbusch g , M. Suffert n , U. Th...

Upper limits for the production of new light gauge bosons in ß 0 , j and j 0 decays have been obtained with the Crystal Barrel detector. The kinematically well-constrained reactions pp ! ß 0 ß 0 P have been studied, where P j ß 0 ; j; j 0 decays through the emission of a single photon recoiling against a missing state X. X can be a long-lived weakl...

We confirm the existence of the two IG(JPC) = 0+(0++) resonances f0(1370) and f0(1500) reported by us in earlier analyses. The analysis presented here couples the final states π0π0π0, π0π0η and π0ηη of p annihilation at rest. It is based on a 3 × 3 K-matrix. We find masses and widths of M = (1390±30) MeV, Γ = (380±80) MeV; and M = (1500±10) MeV, Γ...

A partial wave analysis of the reaction pp->pi0etaeta has been performed, using a high quality, high statistics data set of 198,000 events. In addition to the f0(1370), a second scalar resonance decaying into etaeta, the f0(1500), with mass m = (1505 +/- 15) MeV and width Gamma = (120 +/- 30) MeV has to be introduced to describe the data.

. Koch b , C. Kolo m , K. Konigsmann m7 , M. Kunze b , M. Lakata a , R. Landua f , J. Ludemann b , H. Matthaey b , R. McCrady l , M. Merkel k 8 , J.P. Merlo k , C.A. Meyer l , L. Montanet f , A. Noble o 9 , R. Ouared f , F. Ould--Saada o K. Peters b , C.N. Pinder e , S. Ravndal b 10 , C. Regenfus m , S. Resag c , E. Schafer k , P. Schmidt g , R. Se...

Crystal Barrel data on ¯ pp ! jß 0 ß 0 ß 0 at beam momenta of 1.94 and 1.2 GeV/c reveal evidence for two I = 0 J PC = 2 Gamma+ resonances in jßß. The first, at 1645 Sigma 14(stat:) Sigma 15(syst:) MeV with width 180 +40 Gamma21 Sigma 25 MeV, decays to a 2 (1320)ß with L = 0. It may be interpreted as the q¯q 1 D 2 partner of ß 2 (1670). A strong sig...

a , R. Landua f , F. Loser g , J. Ludemann b , H. Matthay b , M. Merkel k10 , J.P. Merlo k , C.A. Meyer m , L. Montanet f , A. Noble o , F. Ould-Saada o , K. Peters b , C.N. Pinder e , G. Pinter d , S. Ravndal b10 , C. Regenfus l , J. Salk b , E. Schafer k , P. Schmidt g , R. Seibert g , S. Spanier k , H. Stock b , C. Straßburger c , U. Strohbusch...

The annihilation pp → Φγ has been investigated with the Crystal Barrel detector at LEAR for antiprotons stopped in liquid hydrogen. The observed branching ratio BR(pp → Φγ = (1.7 ± 0.4) · 10-5 is almost two orders of magnitude higher than expected from the OZI-rule. As a by-product, the branching ratios BR(pp → KLKS) = (9.0 ± 0.6) · 10-4 and BR(pp...

The branching ratios Γ(η → 3π0) Γ(η → π+π-π0) = 1.44 ± 0.09 ± 0.10 and Γ(η → γγ) Γ(η → π+π-π0) = 1.78 ± 0.10 ± 0.13 have been determined using the Crystal Barrel detector at LEAR. The latter ratio yields a partial width of Γ(η → π+π-π0) = 0.26 ± 0.03 keV using the known value for Γ(η → γγ). The η → π+π-π0) Dalitz plot is compared to the predictions...

We report the observation of nucleon resonances in the reaction pd -> π0π0n for antiprotons stopping in liquid deuterium. The process pd -> Δ(1232)π0 is identified and its branching ratio determined to be (2.21 +/- 0.24).10-5.

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(pd0)=(7.030.72)10–6, BR(pdn)=(3.19+0.48)10–6, BR(pdn)=(22.8+4.1)10–6, BR(pdn)1410–6 (at 95% confidence level). Assuming charge independence, our result for pd0n is compa...

We report on the observation of an ηη′ threshold enhancement produced in p̄p annihilations at rest into π0ηη′, which we identify with the recently discovered f{hook}0(1500).

This is an overview of the preliminary results of [`(p)]p\bar pp annihilation at incident [`(p)]\bar p momenta of 600, 1200 and 1940 MeV/c(*). The data was taken at LEAR with the Crystal Barrel Detector (E. Aker et al.:Nucl. Instrum. Methods A,321, 108 (1992)). In the two pseudoscalar final states seven different channels are observable and their a...

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 u...

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.

Investigations of purely neutral final states in\(\bar pp\) annihilation are possible for the first time with the Crystal Barrel detector at LEAR. The high-mass resolution for π0-mesons allows the reconstruction of K S0-mesons in their neutral-pion decay. Moreover, non-interacting K L0-mesons can be well identified by the measurement of missing ene...

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.

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...

Investigations of purely neutral final states in ($) over bar pp annihilation are possible for the first time with the Crystal Barrel detector at LEAR. The high-mass resolution for pi(0)-mesons allows the reconstruction of K-S(0)-mesons in their neutral-pion decay. Moreover, non-interacting K-L(0)-mesons can be well identified by the measurement of...

New branching ratios for pp annihilation at rest into final states with a KK pair or phi-meson are being measured with the Crystal Barrel detector at LEAR. The yield of phi gamma, relative to omega gamma, appears to violate the OZI rule as strongly as phi pi relative to omega pi.

Antiproton-proton annihilation at rest into 3 pi(0) is analysed based on a data sample of about 500000 high-quality 3 pi(0) events. In this high-statistics Dalitz plot two structures in the region of pi(0) pi(0) 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 differen...

A new isovector scalar pi eta resonance with a mass of 1450 MeV is observed in a high-statistics study of ($) over bar pp annihilation at rest into pi(0) pi(0) eta.

With the Crystal Barrel detector, the final state pi(-)pi(0) pi(0)p(s) 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 rho(770), a second pole was needed in the pi pi P-wave and a narrow resonance in the pi pi S-wave, slightly above...

The rich variety of final states in ¯ pp annihilation at rest provides a promising environment for meson spectroscopy with particular emphasis on the search for exotic mesons like glue-balls, hybrids, and multi-quark states. Large statistics on pure neutral final states and on final states with charged and neutral particles have been accumulated wi...

We have searched for new light gauge bosons produced in π0 and η decays by studying the kinematically well-constrained reactions and , where one π0 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 ). No signal has been observed and branching ratio upp...

A new I(G) = 1- J(PC) = 0++ pieta resonance is observed in ppBAR annihilation at rest into pi0pi0eta. It has a mass M = (1450+/-40) MeV and a width GAMMA = (270+/-40) MeV.

The experimental information on the search for non $q \bar q$ mesons as glueballs, hybrids and multiquark states is reviewed. Candidate states which are particularly amenable to detailed study by accumulating large samples of $J/\psi$, $\eta_c$, $\chi$ decays at a $\tau$-charm factory are discussed.

From a simultaneous analysis of data on ppBAR --> pi0pi0pi0 and ppBAR --> etaetapi0 at rest, two I = 0, J(PC) = 0++ resonances are identified above 1 GeV. The first has mass M = 1365(-20/-55) MeV and width GAMMA = 268 +/- 70 MeV, close to the f0 (1400) of the Particle Data Group. The second has M = 1520 +/- 25 mev, GAMMA = 148(+20/-25) MeV.

We report an analysis of ppBAR annihilation at rest in to rho+rho-pi0 leading to the final state pi+pi-3pi0. A strong signal is observed for a scalar resonance with mass 1374 +/- 38 MeV/c2 and width 375 +/- 61 MeV/c2, decaying to rho+rho-. The resonance in rho+rho- represents 2.0 +/- 0.3% of all ppBAR annihilations at rest. It is also observed to d...

From a simultaneous analysis of data on pp ! ß 0 ß 0 ß 0 and pp ! jjß 0 at rest, two I = 0 J PC = 0 ++ resonances are identified above 1 GeV. The first has mass M = 1365 +20 Gamma55 MeV and width Gamma = 268 Sigma 70 MeV, close to the f 0 (1400) of the Particle Data Group. The second has M = 1520 Sigma 25 MeV, Gamma = 148 +20 Gamma25 MeV. 2 Text Me...

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→γ...

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

The annihilation of p ̄p at rest into KL0KS0π0 and KL0KS0η was investigated with the Crystal Barrel detector at LEAR. These final states with negative C-parity are dominated by φ and K0* resonances. The ratios of the branching ratios are B( p ̄p→φπ0) B( p ̄p→φη)=8.3±2.1 and B( p ̄p→K0 K ̄0*+ K ̄0K0*→KL0KS0π0) B( p ̄p→φπ0→KL0KS0π0)= 2.04±0.21.

N[`(N)]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 [`(p)]p\bar pp annihilations in H2 leading to the [`(p)]n ® p+ p- p+ p- p-\bar pn \to \pi ^ + \pi ^ - \pi ^ + \pi ^ - \pi ^ - the difference of the four pion mass spectra recoiling against a [`...

The annihilation channel , where ω decays to π0γ, was studied with antiprotons stopped in liquid hydrogen. This reaction is dominated by the production of b10(1235) with contributions from f2(1270) and the ππ S-wave. The branching ratio for of all annihilations. The branching ratios for b10(1235)π0 (b1 → ωπ0) and f2(1270)ω (f2 → π0π0) are (0.92 ± 0...

Radiative annihilation at rest into γγ, γπ0, γη, γω and γη′ has been measured with the Crystal Barrel detector at LEAR for antiprotons stopped in liquid hydrogen. The branching ratios are Bγπ0=(44±4)×10−6, Bγη=(9.3±1.4)×10−6 and Bγω=(68±18)×10−6, respectively. For Bγγ and Bγη′ we find new upper limits of 0.63×10−6 and 12×10−6 (95% CL), respectively...

We report measurements of branching ratios for production of a series of two meson final states in\(\bar p\) 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...

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 π0π0π0 final state confirms the existence of . In the ηη system of the π0ηη final state an isoscalar JPC = 0++ resonance with a mass of 1560 MeV/c2 and a width of 245 MeV/c...

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 annihi...

We discuss phi production in pp annihilation at rest from the Asterix and Crystal Barrel experiments and compare the branching ratios to similar final states without strangeness. The omegapi0/phipi0 production ratio is unexpectedly low. In the search for new states, the phipi0 mass spectrum shows no evidence for a resonance in the 1450 MeV/c2 mass...

.02> m , U. Meyer-Berkhout h , L. Montanet c , A. Noble m , K. Peters a , G. Pinter b , S. Ravndal a , A.H. Sanjari i , E. Schafer g , B. Schmid m , P. Schmidt d , S. Spanier g , C. Straßburger g , U. Strohbusch d , M. Suffert k , D. Urner m , C. Volcker h , D. Walther a , U. Wiedner d , N. Winter e , J. Zoll c , C. Zupancic h a Universitat Bochum,...

The results of a measurement of p̄p annihilation at rest into ηηπ0 are presented. Assuming a resonance dominated model for the annihilation process an isoscalar JPC=0++ resonance decaying into ηη is observed with a mass of 1560±25 MeV/c2 and a width of 245±50 MeV/c2.

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 pi0, eta, eta' and omega 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 an...

We have measured the cross section for γγ production with the TOPAZ detector in the energy region √s=50.0–61.4 GeV. The observed cross section for γγ production integrated over |cosθ| ⩽ 0.77 is 50.2±0.8±2.2 pb at 〈√s〉=57.6 GeV and the ratio of this value to the QED prediction is 1.01±0.02±0.04. The angular distribution is in good agreement with the...

The process e+e--->e+e-mu+mu- has been studied in single-tag and double-tag configurations using the TOPAZ detector at TRISTAN. The data correspond to the integrated luminosity of 45.3pb- at center-of-mass energies ranging from 52 to 61.4 GeV. The observed events in both configurations have shown a good agreement with QED predictions in order alpha...

An experimental study of b-quark jets using high-pT electrons was carried out at √s=58 GeV with the TOPAZ detector at the e+e− collider TRISTAN at KEK. The forward-backward charge asymmetry of the b-quark was obtained to be , consistent with the standard model prediction. Also, such jet properties of the b-quark as the average charged multiplicity...

The process e+e--->mu+mu-and e+e- have been studied in the energy range sqrt(s)=52-61.4 GeV, using the TOPAZ detector at TRISTAN. From an integrated luminosity of L = 74.0 pb-1, lowest-order cross sections and forward-backward asymmetries are measured to be =57.87 GeV. From the measured assymetry we derive axial vector couplings of acamu=0.96+/-0.0...

We have measured the cross section for gammagamma production with the TOPAZ detector in the energy region &surd;s=50.0-61.4 GeV. The observed cross section for gammagamma production integrated over |costheta| gammagammagamma was also studied and was found consistent with the QED prediction.

We report on a first measurement of the polarized-target asymmetry of the pion-proton bremsstrahlung cross section (Ï{sup +}{ital p}{r arrow}Ï⁻{ital p}γ). As in previous cross section measurements the pion energy (298 MeV) and the detector geometry for this experiment was chosen to optimize the sensitivity to the radiation from the magnetic dipo...

We have collected 122 multi-hadronic inclusive muon events with the TOPAZ detector at with . From this event sample we derived the differential cross section for B-hadron productions and determined B-hadron forward-backward asymmetry to be . A fit to the differential cross section, after correcting for the effect of mixing, yielded the axial-vector...

We report on measurements of the branching ratios for φ production in annihilation at rest in H2 gas. Branching ratios for φπ0, φη, φϱ0, φω and φπ+ π− are determined for two data sets with different contributions of annihilations from S and P states of the system. The branching ratios are compared to corresponding annihilation modes where the φ is...

The charge asymmetry of quark jets produced in e+e- annihilations at =57.9 GeV was measured with the TOPAZ detector at TRISTAN. The observed charge asymmetry is +0.091+/-0.014(stat.)+/-0.016(sys.). From the measured differential cross section, the axial vector coupling constant averaged over all quark flavors was determined to be 1.09-0.21+0.27. Th...

A vertex chamber has been designed and constructed for the TOPAZ detector at TRISTAN, KEK. The chamber is a jet-cell-type chamber aimed at a position resolution of 30-50 mum and a double-track separation of less than 1 mm. In this article the design and performance of the readout electronics for the TOPAZ vertex chamber are described. 10 ns signal...

We have searched for inclusive production of heavy stable particles with charge Q=2/3, 1 and 4/3in e+e- annihilation, using energy loss measurements by the TOPAZ TPC. In 23.6 pb-1 of data taken at the center of mass energy range &surd;s=52-61.4 GeV, no such particle was found and new upper limits for the production cross sections were obtained.

We have measured the branching ratios for {Mathematical expression} annihilation at rest into π+π-η and π+π-η′ in hydrogen gas in two data samples that have different fractions of S-wave and P-wave initial states. The branching ratios are derived from a comparison with the topological branching ratio for {Mathematical expression} annihilations into...

We searched for signatures of new stable particles in e+ e− annihilation using the TOPAZ detector at TRISTAN between √s = 52 and 60 GeV. The search made use of the particle identification by the Time Projection Chamber (TPC). We set new limits on the pair production of new stable charged particles with spins 0 and , and charges between and . The li...

First data are presented for the polarized-target asymmetry in the reaction {pi}{sup +}{ital p}{r arrow}{pi}{sup +}{ital p}{gamma} at an incident pion energy of 298 MeV. The geometry was chosen to maximize the sensitivity to the radiation of the magnetic dipole moment {mu}{sub {Delta}} of the {Delta}{sup ++}(1232 MeV). A fit of the asymmetry in the...

Annihilation of antiprotonic hydrogen atoms into [`(p)]p\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 [`(p)]p\bar pp atom was followed by...

We searched for pair production of charged Higgs bosons via e+e− annihilation, using data (23.3 pb−) collected by the TOPAZ detector in the energy range . We observed no evidence for charged Higgs pair production and extended the excluded region in the MH±BR (hadron) plane. The 95% CL lower mass limit is the most stringent for BR (hadron) = 0.6, g...

We have observed an isoscalar tensor meson at a mass of 1565 ± 10 MeV/c2 and a width of 170 ± 20 MeV/c2. The resonance is seen in annihilation at rest into π+π−π0 from P states of antiprotonic hydrogen atoms.

We have measured the total e+e− hadronic annihilation cross section at the center of mass energies between 50.0 GeV and 61.4 GeV with the TOPAZ detector at TRISTAN. The full electroweak radiative corrections (up to O(α3)) were applied to the data which were analysed together with the published data from PEP and PETRA. We then determined the standar...

We studied the e+e--->e+e-pi+pi- interaction with the untagged two-photon sample obtained by the TOPAZ detector at the TRISTAN e+e- collider. The sample was taken in the energy region sqrt(s)=55.0-60.8 GeV. One of the QED backgrounds, e+e--->e+e-, was clearly removed by the measurement of dE/dx by the TOPAZ-TPC. The pi+pi- invariant mass spectrum i...