A measurement of the reaction e+e- →e+e-η′ and the radiative width Γη′→γγ at petra

The reaction e⁺e^- → e⁺e^-η' has been observed in the JADE experiment at PETRA, by detecting the final state π⁺π^-γ, resulting from the decay η' → γ?⁰. The cross section was measured at an average beam energy of 17.15 GeV to be σ(e⁺e^- → e⁺e^-η') = 2.2 ± 0.2 (stat.) ± 0.4(syst.) nb, yielding the radiative width Γ_η'γγ= 5.0 ± 0.5(stat.) ± 0.9 (syst.) keV.     

Measurements of the absolute branching fractions for D→K̄πe+νe, D→K̄*e+νe and determination of Γ(D+→K̄*0e+νe)/Γ(D+→K̄0e+νe)

Using the data of about 33 pb^-1 collected at and around 3.773 GeV with the BES-II detector at the BEPC collider, we have studied the exclusive semileptonic decays D⁺→K^-π⁺e⁺ν_e, D⁰→K̄⁰π^-e⁺ν_e, D⁺→K̄^*0e⁺ν_e and D⁰→K^*-e⁺ν_e. The absolute branching fractions for the decays are measured to be BF(D⁺→K^-π⁺e⁺ν_e)=(3.50±0.75±0.27)%, BF(D⁰→K̄⁰π^-e⁺ν_e)=(2.61±1.04±0.28)%, BF(D⁺→K̄^*0e⁺ν_e)=(5.06±1.21±0.40)% and BF(D⁰→K^*-e⁺ν_e)=(2.87±1.48±0.39)%. The ratio of the vector to pseudoscalar semileptonic decay rates Γ(D⁺→K̄^*0e⁺ν_e)/Γ(D⁺→K̄⁰e⁺ν_e) is determined to be 0.57±0.17±0.02.     

Determination of αS using jet rates at LEP with the OPAL detector

Hadronic events produced in e⁺e^- collisions by the LEP collider and recorded by the OPAL detector were used to form distributions based on the number of reconstructed jets. The data were collected between 1995 and 2000 and correspond to energies of 91 GeV, 130-136 GeV and 161-209 GeV. The jet rates were determined using four different jet-finding algorithms (Cone, JADE, Durham and Cambridge). The differential two-jet rate and the average jet rate with the Durham and Cambridge algorithms were used to measure in the LEP energy range by fitting an expression in which calculations were matched to a NLLA prediction and fitted to the data. Combining the measurements at different centre-of-mass energies, the value of () was determined to be α_S(M_Z) = 0.1177 ± 0.0006 (stat.) ± 0.0012 (expt.) ± 0.0010 (had.) ± 0.0032 (theo.).     

Search for D+→φl+ν and measurement of the branching fraction for D+→φπ+

Using a data sample of integrated luminosity of about 33 pb^-1 collected around 3.773 GeV with the BESII detector at the BEPC collider, the semileptonic decays D⁺→φe⁺ν_e, D⁺→φμ⁺ν_μ and the hadronic decay D⁺→φπ⁺ are studied. The upper limits of the branching fractions are set to be BF(D⁺→φe⁺ν_e)<2.01% and BF(D⁺→φμ⁺ν_μ)<2.04% at the 90% confidence level. The ratio of the branching fractions for D⁺→φπ⁺ relative to D⁺→K^-π⁺π⁺ is measured to be 0.057±0.011±0.003. In addition, the branching fraction for D⁺→φπ⁺ is obtained to be (5.2±1.0±0.4)×10^-3.     

The E687 cryptoexotic vector meson candidate

A new study of the dip observed at 1.9GeV by the Fermilab experiment E687 in diffractive photoproduction of 3π ⁺3π ^- is presented. The E687 and the BABAR data on the annihilation cross-section σ(e ⁺ e ^-→3π ⁺3π ^-), obtained with initial-state radiation, are fitted all together. The fit function is based on a simple mixing mechanism that explains the manifestation of a resonance as a dip. Possible interpretations in terms of hybrids and tetraquark states are considered.     

Partial wave analysis of πproduction in two-photon collisions at LEP

The reaction γγ → π⁺π^-π⁰ with quasi-real photons is studied with a total integrated luminosity of 663pb^-1, collected by the L3 detector at LEP at center-of-mass energies from 183 to 209GeV. The results of an energy-dependent partial wave analysis in the mass region 1.1≤M(π⁺π^-π⁰)≤2.2GeV are presented. The reaction is dominated by a₂(1320) formation. A strong signal consistent with the first radial excitation of the isovector tensor state, a₂(1700), is present and confirms the previous L3 observation. Its two-photon partial width is found to be Br(3π) = 0.37^+0.12_-0.08keV, the relative branching ratio of ρ(770)π to f₂(1270)π is 3.4±0.4. For all observed states the product of γγ partial width and 3π branching ratios is measured.     

Mixing and decays of ρ- and ω-mesons

Isospin-violating mixing of ρ- and ω-mesons is reconsidered in terms of propagators. Its influence on various pairs of (ρ,ω)-decays to the same final states is demonstrated. Some of them, (ρ,ω)↦π⁺π^- and (ρ,ω)↦πγ, have been earlier discussed in the literature, others (e.g., (ρ,ω)↦ηγ and (ρ,ω)↦e ⁺ e ^-) are new in this context. Changes in partial widths for all the decay pairs are shown to be correlated. The set of present experimental data, though yet inconclusive, provides some limits for the direct (ρω)-coupling and indirectly supports enhancement of ρ↦πγ in comparison with ρ^±↦π^±γ, though not so large as in some previous estimates. Received: 16 September 2002 / Accepted: 23 September 2002 / Published online: 4 February 2003 RID="a" ID="a"e-mail: azimov@pa1400.spb.edu Communicated by V.V. Anisovich     

Measurement of the e+e-→W+W- cross section and W decay branching fractions at LEP

From a total data sample of 701.1 pb^-1 recorded with e⁺e^- centre-of-mass energies of 161–209 GeV with the OPAL detector at LEP, 11693 W-pair candidate events are selected. These data are used to obtain measurements of the W-pair production cross sections at 10 different centre-of-mass energies. The ratio of the measured cross sections to the standard model expectation is found to be: , where the uncertainties are statistical, experimental systematics and theory systematics respectively. The data are used to determine the W boson branching fractions, which are found to be consistent with lepton universality of the charged current interaction. Assuming lepton universality, the branching ratio to hadrons is determined to be 67.41±0.37(stat.)±0.23(syst.)%, from which the CKM matrix element |V_cs| is determined to be 0.969±0.017(stat.)±0.012(syst.). The differential cross section as a function of the W^- production angle is measured for the qqeν and qqμν final states. The results described in this paper are consistent with the expectations from the standard model. This paper is dedicated to the memory of Ben Shen.     

Search for direct CP violating charge asymmetries in K±→π±π+π- and K±→π±π0π0 decays

A measurement of the direct CP violating charge asymmetries of the Dalitz plot linear slopes A_g=(g⁺-g^-)/(g⁺+g^-) in K^±→π^±π⁺π^- and K^±→π^±π⁰π⁰ decays by the NA48/2 experiment at CERN SPS is presented. A new technique of asymmetry measurement involving simultaneous K⁺ and K^- beams and a large data sample collected allowed a result of an unprecedented precision. The charge asymmetries were measured to be A^c _g=(-1.5±2.2)×10^-4 with 3.11×10⁹K^±→π^±π⁺π^- decays, and Aⁿ _g=(1.8±1.8)×10^-4 with 9.13×10⁷K^±→π^±π⁰π⁰ decays. The precision of the results is limited mainly by the size of the data sample.     

Precise measurement of Γ(KS→π+π-(γ))/Γ(KS→π0π0) with the KLOE detector at DAΦNE

Using a sample of over 400 million φ→K_SK_L decays produced during the years 2001 and 2002 at the DAΦNE e⁺e^- collider, the ratio R_S ^π=Γ(K_S→π⁺π^-(γ))/Γ(K_S→π⁰π⁰) has been measured with the KLOE detector. The result is R_S ^π=2.2555±0.0012_stat±0.0021_corr-stat±0.0050_syst, which is in good agreement with the previously published result based on the KLOE data sample from the year 2000. The average of the KLOE results is R_S ^π=2.2549±0.0054, reducing the total error by a factor of three, to 0.25%.     

Understanding the newly observed Y(4008) by Belle

Very recently a new enhancement around 4.05 GeV was observed by the Belle experiment. We discuss some possible assignments for this enhancement, i.e. the ψ(3S) and D^*D̄^* molecular states. In these two assignments, Y(4008) can decay into J/ψπ⁰π⁰ with a branching ratio comparable with that of Y(4008)→J/ψπ⁺π^-. Thus, one suggests high energy experimentalists to look for Y(4008) in J/ψπ⁰π⁰ channel. Furthermore one proposes further experiments to search for the missing channels DD̄, DD̄^*+h.c. and especially χ_cJπ⁺π^-π⁰ and η_cπ⁺π^-π⁰, which will be helpful to distinguish the ψ(3S) and D^*D̄^* molecular state assignments for this new enhancement. PACS 13.30.Eg 13.75.Lb     

Detection of the production and decays of neutral charmed mesons in proton-nucleus interactions at 70 GeV with the SVD-2 facility

The results of processing the data of the SERP-E-184 experiment that studied mechanisms of the production of charmed particles in proton-nucleus interactions at 70 GeV and their decays are reported. The data were obtained in irradiating the SVD-2 active target consisting of carbon, silicon, and lead plates with a proton beam of energy 70 GeV. A signal from the two-body decay of neutral charmed mesons D ⁰ and Ď ⁰ is separated. The signal-to-background ratio is (51 ± 17)/(38 ± 13). A detailed simulation of relevant processes on the basis of the FRITIOF and GEANT codes made it possible to find meson-detection efficiencies and to evaluate the charm-production cross section at this energy: σ(c ĉ) = 7.1 ± 2.4(stat.) ± 1.4(syst.) μb/nucleon.     

Search for and study of low-mass scalar mesons in reactions np → npπ+π? at neutron beam momentum Pn = (3.83 ± 0.12) GeV/c

The results of a search for and study of the scalar 0⁺ [0⁺⁺] σ₀ mesons in a π⁺π⁻ system produced in the reaction np → npπ⁺π⁻ at the quasi-monochromatic neutron beam momentum P _n = (3.83 ± 0.12) GeV/c are presented as derived from analyzing the data obtained during the exposure of a 1-meter hydrogen bubble chamber at the Laboratory of High Energy, Joint Institute for Nuclear Research (LHE JINR). It is found that there is a significant bump in the effective mass distribution at M_{p⁺ p^-} = (404 ±5)MeV/c²M_{\pi ^ + \pi ^ - } = (404 \pm 5)MeV/c^2 and Γ_res^exp = (14±5.4) MeV/c ², which is observed with more than four standard deviations from the background. The spin of this resonance is estimated to be most likely equal to zero. Its quantum numbers are found to be 0⁺ [0⁺⁺].     

A measurement of σtot(e+e− → hadrons) for cm energies between 12.0 and 36.7 GeV

The ration R = σ(e⁺e^? → hadrons)σ_μμ was measured between 12.0 and 36.7 GeV c.m. energy W with a precision of typically ± 5.2%. R is found to be constant with an average R = 4.01 ± 0.03 (stat) ± (syst.) for W ? 14 GeV. Quarks are found to be point-like, the mass parameter describing a possible quark form-factor being larger than 186 GeV. Fits including QCD corrections and a weak neutral-current contribution are presented.     

a 0 + (980)-resonance production in the reaction pp → dπ + η close to the K\bar K threshold

The reaction pp → dπ ⁺ η has been measured at a beam energy of T _p = 2.65 GeV (p _p = 3.46 GeV/c) using the ANKE spectrometer at COSY-Julich. The missing-mass distribution of the detected dπ ⁺ pairs exhibits a peak around the η mass on top of a strong background of multipion pp → dπ ⁺(nπ) events. The differential cross section d ⁴ σ/dΩ_d dΩ _π ⁺ dp _d dp _π ⁺ for the reaction pp → dπ ⁺ η has been determined model independently for two regions of phase space. Employing a dynamical model for the a ₀ ⁺ production allows one then to deduce a total cross section of σ(pp → da ₀ ⁺ → dπ ⁺ η) = 1.1 ± 0.3_stat ± 0.7_syst μb for the production of π ⁺ η via the scalar a ₀ ⁺ (980) resonance and σ(pp → dπ ⁺ η) = 3.5 ± 0.3_stat ± 1.0_syst μb for the nonresonant production. Using the same model as for the interpretation of recent results from ANKE for the reaction , the ratio of the total cross sections is , which is in agreement with branching ratios in the literature. The text was submitted by the authors in English.     

Measurement of photons via conversion pairs in $\sqrt{s_{NN}}$ =200 GeV Au+Au collisions with the PHENIX experiment at RHIC

Thermal photons can provide information on the temperature of the new state of matter created at RHIC. In the p_T region of 1–3 GeV/c thermal photons are expected to be the dominant direct photon source. Therefore, a possible excess compared to a pure decay photon signal due to a thermal photon contribution should be seen in the double ratio (γ/γ(π⁰))_Measured/(γ/γ(π⁰))_Simulated, if sufficient accuracy can be reached. We present a method to reconstruct direct photons by measuring e⁺e^--pairs from external photon conversions.     

Tests of the final-state radiation model at DAFNE near <Emphasis Type="Italic">π</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">π</Emphasis><Superscript>-</Superscript> threshold

Effects due to the non-pointlike behaviour of pions in the process e ⁺ e ^-→π ⁺ π ^- γ can arise for hard photons in the final state. By means of a Monte Carlo event generator, which also includes the contribution of the direct decay φ→π ⁺ π ^- γ, we estimate these effects in the framework of the resonance perturbation theory. We consider angular cuts used in the KLOE analysis of the pion form factor at threshold. A method to reveal the effects of the non-pointlike behaviour of pions in a model-independent way is proposed.     

Search for the f1(1285) → π+π-π0 decay with the VES detector

The isospin-violating decay f ₁(1285) → π⁺π^-π⁰ has been studied at the VES facility. This study is based on the statistics acquired in π^- Be interactions at 27, 36.6 and 41 GeV/c in the diffractive reaction π^- N → (f ₁π^-)N . The f ₁(1285) → π⁺π^-π⁰ decay is observed. The preliminary ratio of decay probabilities BR(f ₁(1285) → π⁺π^-π⁰) to BR(f ₁(1285) → ηπ⁺π^-)^. BR(η → γγ) is ∼ 2% . Original article based on material presented at HADRON 2007.     

Measurement of inclusive π 0 production in hadronic Z 0 decays

An analysis is presented of inclusiveπ ⁰ production inZ ⁰ decays measured with the DELPHI detector. At low energies,π ⁰ decays are reconstructed by using pairs of converted photons and combinations of converted photons and photons reconstructed in the barrel electromagnetic calorimeter (HPC). At high energies (up to ) the excellent granularity of the HPC is exploited to search for two-photon substructures in single showers. The inclusive differential cross section is measured as a function of energy forqq andbb events. The number ofπ ⁰’s per hadronicZ ⁰ event isN(π ⁰)/Z _had ⁰ =9.2±0.2(stat)±1.0(syst) and forbb events the number ofπ ⁰’s is N(π ⁰)/bb=10.1±0.4(stat)±1.1(syst). The ratio of the number ofπ ⁰’s inbb events to hadronicZ ⁰ events is less affected by the systematic errors and is found to be 1.09±0.05±0.01. The measuredπ ⁰ cross sections are compared with the predictions of different parton shower models. For hadronic events, the peak position in theξ _p=ln(1/x_p) distribution isξ* _p =3.90 _−0.14 ^+0.24 . The average number ofπ ⁰’s from the decay of primary B hadrons is found to be N(B→π ⁰ X)/B hadron=2.78±0.15(stat)±0.60(syst).     

Isoscalar-isovector interferences in πN↦Ne+e- reactions as a probe of baryon resonance dynamics

The isoscalar-isovector (ρ-ω) interferences in the exclusive reactions π^- p↦ne ⁺ e ^- and π⁺ n↦pe ⁺ e ^- near the ω threshold leads to a distinct difference of the dielectron invariant-mass distributions depending on beam energy. The strength of this effect is determined by the coupling of resonances to the nucleon vector-meson channels and other resonance properties. Therefore, a combined analysis of these reactions can be used as a tool for determining the baryon resonance dynamics. Received: 14 August 2001 / Accepted: 3 October 2001