Prospects for e+e- physics at Frascati between the φ and the ψ

We present a detailed study, done in the framework of the INFN 2006 Roadmap, of the prospects for e⁺e^- physics at the Frascati National Laboratories. The physics case for an e⁺e^- collider running at high luminosity at the φ resonance energy and also reaching a maximum center of mass energy of 2.5 GeV is discussed, together with the specific aspects of a very high luminosity τ-charm factory. Subjects connected to kaon decay physics are not discussed here, being part of another INFN Roadmap working group. The significance of the project and the impact on INFN are also discussed. All the documentation related to the activities of the working group can be found in http://www.roma1.infn.it/people/bini/roadmap.html.     

Fermion pair production in e+e- collisions at 189–209?GeV and constraints on physics beyond the standard model

Cross sections, angular distributions and forward-backward asymmetries are presented, of two-fermion events produced in e⁺e^- collisions at centre-of-mass energies from 189 to 209 GeV at LEP, measured with the ALEPH detector. Results for e⁺e^-, μ⁺μ^-, τ⁺τ^-, qq̄, bb̄ and cc̄ production are in agreement with the standard model predictions. Constraints are set on scenarios of new physics such as four-fermion contact interactions, leptoquarks, Z^′ bosons, TeV-scale quantum gravity and R-parity violating squarks and sneutrinos. Dedicated to the memory of John Strong who died on July 31, 2006     

Study of the η'→Ve~+e~- decay with hidden local symmetry model

Within the hidden local symmetry framework, the Dalitz decay η→Ve+e-is studied with the vector meson dominance model. It is found that the partial width Γ(η→ωe+e-)≈40 e V and branching ratio B(η→ωe+e-)≈2×10-4, and Γ(η→ρe+e-)≈10Γ(η→ωe+e-) and B(η→ρe+e-)≈10B(η→ωe+e-). The maximum position of the dilepton distribution is m e+e-≈1.33 Me V. These decays are measurable with the advent of high statistic ηexperiments.     

Optimizing Higgs factories by modifying the recoil mass

It is difficult to measure the WW-fusion Higgs production process(e~+e~-→νh)at a lepton collider with a center of mass energy of 240-250 Ge V due to its small rate and the large background from the Higgsstrahlung process with an invisible Z(e~+e~-→h Z,Z→ν).We construct a modified recoil mass variable,m~p_(recoil),defined using only the 3-momentum of the reconstructed Higgs particle,and show that it can separate the WW-fusion and Higgsstrahlung events better than the original recoil mass variable m_(recoil).Consequently,the m~p_(recoil)variable can be used to improve the overall precisions of the extracted Higgs couplings,in both the conventional framework and the effective-field-theory framework.We also explore the application of the m~p_(recoil)variable in the inclusive cross section measurements of the Higgsstrahlung process,while a quantitive analysis is left for future studies.     

Distinguishing indirect signatures of new physics at ILC with polarized beams: Z′ versus anomalous trilinear gauge couplings

We examine the sensitivity of the e ⁺ e ^? International Linear Collider (ILC) for probing the Z-Z′ mixing in W ^±-pair production process and its capability of distinguishing observable effects of the Z′ from analogous ones due to competitor models with anomalous trilinear gauge couplings (AGC) that can lead to the same or similar new physics experimental signatures.     

Study of triple-gauge-boson couplings ZZZ, ZZγ and Zγγ at LEP

Neutral triple-gauge-boson couplings ZZZ, ZZγ and Zγγ have been studied with the DELPHI detector using data at energies between 183 and 208 GeV. Limits are derived on these couplings from an analysis of the reactions e⁺e^-→Zγ, using data from the final states γff̄, with f=q or ν, from e⁺e^-→ZZ, using data from the four-fermion final states qq̄qq̄, qq̄μ⁺μ^-, qq̄e⁺e^-, qq̄νν̄, μ⁺μ^-νν̄ and e⁺e^-νν̄, and from e⁺e^-→Zγ^*, in which the final state γ is off mass-shell, using data from the four-fermion final states qq̄e⁺e^- and qq̄μ⁺μ^-. No evidence for the presence of such couplings is observed, in agreement with the predictions of the Standard Model.     

Measurement of the DAΦNE luminosity with the KLOE detector using large angle Bhabha scattering

We describe the method of measuring the integrated luminosity of the e⁺e^- collider DAΦNE, the Frascati φ-factory. The measurement is done with the KLOE detector selecting large angle Bhabha scattering events and normalizing them to the effective cross section. The e⁺e^-→e⁺e^-(γ) cross section is calculated using different event generators which account for the radiative initial and final state corrections, and the φ resonance contribution. The accuracy of the measurement is 0.6%, where 0.3% comes from systematic errors related to the event counting and 0.5% from theoretical evaluations of the cross section.     

Search for the radiative η′(958)+γ decay of the J/Ψ (3100) resonance produced in e+e− annihilation

The decay J/Ψ (3100)→ η(958) + γ has been searched for at tthe Adone e⁺e^+- storage ring. No candidate event has been found. This allows to set an upper limit of 1.0 keV (90% C.L.) for this decay partial width.     

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.     

Recent KLOE results on hadron physics

The KLOE experiment at the Frascati e ⁺ e ^- collider DAFNE has completed this year its data taking. An integrated luminosity of 2.7fb^-1 has been collected mostly at the φ-resonance peak. A wide experimental program is in progress. The detection of φ radiative decays allows to study the properties of the lowest-mass scalar and pseudoscalar mesons and to obtain information on their structure. The main results are reviewed together with the prospects for low-energy e ⁺ e ^- physics at Frascati.     

A hydrodynamic model for hadron production ine +−e − annihilation

We consider hadron production ine ⁺-e ^? annihilation within the framework of a hydrodynamic model. The two key assumptions in the moddel are (i) the initial shape of a Lorentz-contracted disc for the hadronic fireball, with the jet axis providing the necessary longitudinal direction and (ii) the criterion of a critical size of hadronic dimension for the expanding fireball to break up into finalstate particles. Experimental data on charged multiplicity, inclusive distributions, dispersions and particle spectra upto the highest centre-of-mass energy, presently accessible in colliding-beam machines, are explained satisfactorily with only three energy-independent parameters. The present analysis brings out the similarity in the mechanism for hadron production inp-p collision ande ⁺-e ^? annihilation and attributes the apparent differences to the presence of leading-particle effect in the former process.     

ρ-ω mixing in J/ø→VP decays

The study of ρ-ω mixing has mainly focused on vector meson decays with isospin I=1, namely the ρ(ω)→π⁺π^- process. In this paper, we present a study of ρ-ω mixing in ρ(ω)→π⁺π^-π⁰ (I=0) using a flavor parameterization model for the J/ø→ VP process. By fitting a theoretical framework to PDG data, we obtain the SU(3)-breaking effect parameters s_V=0.03±0.12, s_P=0.17±0.17 and the ρ-ω mixing polarization operator ∏_ρω=(0.006±0.011) GeV². New values are found for the branching ratios when the mixing effect is incorporated: Br(J/ψ→ ωπ⁰) = (3.64 ±0.37)×10^-4, Br(J/ψ→ ωη) = (1.48 ±0.17)×10^-3, Br(J/ψ→ ωη') = (1.55±0.56)×10^-4, these are different from the corresponding PDG2012 values by 19%, 15% and 15%, respectively.     

Virtual effects of split-SUSY in Higgs productions at linear colliders

In split supersymmetry, gauginos and higgsinos are the only supersymmetric particles possibly accessible at foreseeable colliders like the CERN Large Hadron Collider (LHC) and the International Linear Collider (ILC). In order to account for the cosmic dark matter measured by WMAP, these gauginos and higgsinos are stringently constrained and could be explored at the colliders through their direct productions and/or virtual effects in some processes. The clean environment and high luminosity of the ILC render the virtual effects at percent level meaningful in unraveling the new physics effects. In this work we assume split supersymmetry and calculate the virtual effects of the WMAP-allowed gauginos and higgsinos in the Higgs productions e⁺e^-→Zh and e⁺e^-→ν_eν̄_eh through WW fusion at the ILC. We find that the production cross section of e⁺e^-→Zh can be altered by a few percent in some part of the WMAP-allowed parameter space, while the correction to the WW fusion process e⁺e^-→ν_eν̄_eh is below 1%. Such virtual effects are correlated with the cross sections of chargino pair productions and can offer complementary information in probing split supersymmetry at the colliders. PACS 14.80.Ly; 95.35.+d     

A new jet algorithm based on the k-means clustering for the reconstruction of heavy states from jets

A jet algorithm based on the k-means clustering procedure is proposed which can be used for the invariant-mass reconstruction of heavy states decaying to hadronic jets. The proposed algorithm was tested by reconstructing e⁺e^-→tt̄→6 jets and e⁺e^-→W⁺W^-→4 jets processes at using a Monte Carlo simulation. It was shown that the algorithm has a reconstruction efficiency similar to traditional jet-finding algorithms, and leads to 25% and 40% improvement of the top-quark and W mass resolution, respectively, compared to the k_T (Durham) algorithm. In addition, it is expected that the peak positions measured with the new algorithm have smaller systematical uncertainty.     

Dilepton production in pp and CC collisions with HADES

e ⁺ e ^- production was studied using the High Acceptance DiElectron Spectrometer (HADES). In pp collisions at 2.2GeV kinetic beam energy, the exclusive η production and the Dalitz decay η→γe ⁺ e ^- have been reconstructed. The electromagnetic form factor of the latter decay was found to be in good agreement with the existing theoretical predictions. In addition, an inclusive e ⁺ e ^- invariant-mass spectrum from the ¹²C + ¹²C reaction at 2AGeV is presented and compared with a simplified thermal model.     

Space–time structure of new physics with polarized beams at the linear collider

We approach the issue of the discovery of new physics at high energies associated with the proposed International Linear Collider in the presence of longitudinal as well as transverse electron and positron beam polarization. We determine the beam polarization dependence and the angular distribution of a particle of arbitrary spin in a one-particle inclusive final state produced in e⁺e^- collisions through the interference of γ or Z amplitude with the amplitude from new interactions having arbitrary space–time structure. We thus extend the results of Dass and Ross, proposed at the time of the discovery of neutral currents, to beyond the standard model currents. We also extend the case of e⁺e^- annihilation in the s-channel to the production of bosons due to t- and u-channel processes. Our work provides an approach to model-independent determination of the space–time structure of beyond the standard model interactions. We briefly discuss applications of the framework to popular extensions of the standard model, and demonstrate that our framework is general enough to account for certain results in the minimal supersymmetric standard model.     

Dilepton and trilepton production by antineutrinos and neutrinos in neon

A sample of over 25,000 fully measured neutrino and antineutrino charged current interactions in BEBC includes 192 dilepton candidates. The prompt signal after subtraction of background is 41 ±7µ⁺ e ^-, 35±7µ⁺µ^- events from \(\bar v\) interactions, and 32±7µ^-µ⁺ events from ν interactions. There are 2 trileptons, µ^-µ^- e ⁺ and µ^-µ^-µ⁺. Results are compared with other experimental data and with the standard model. Limits to prompt like sign µ⁺ e ⁺, µ⁺µ⁺ and µ^-µ^- signals are given and compared with other experiments and with theoretical calculations.     

Fourier Transform Emission Spectroscopy of the FΣ-XΣ System of RuN

Emission spectra of RuN have been recorded at high resolution in the region 12 000-35 000 cm⁻¹ using a Fourier transform spectrometer. The molecules were excited in a ruthenium hollow cathode lamp in the presence of about 2.5 Torr of Ne and 5 m Torr of N₂. New bands with origins near 17 758.1, 18 866.4, 19 800.4 and 20 721.5 cm⁻¹ have been assigned as the 0-1, 0-0, 1-0, and 2-0 bands of a new ²Σ⁺-²Σ⁺ system with the lower state as the ground state. This transition has been labeled as F²Σ⁺-X²Σ⁺, with the F²Σ⁺ state arising from the 1σ²2σ²1π⁴1δ⁴4σ¹ configuration. A rotational analysis of these bands has been carried out and spectroscopic constants have been extracted. The principal equilibrium constants for the ground state of RuN are ΔG(1/2)″=1108.3235(22) cm⁻¹, B_e″=0.5545023(42) cm⁻¹, α_e″=0.0034468(57) cm⁻¹, r_e″=1.5714269(60) Å, while the equilibrium constants for the excited state are ω_e′=946.8471(40) cm⁻¹, ω_ex_e′=6.4229(14) cm⁻¹, B_e′=0.50085(21) cm⁻¹, α_e′=0.00375(10) cm⁻¹, r_e′=1.65345(34) Å. This transition is analogous to the E²Σ⁺-X²Σ⁺ system of RhC (W. J. Balfour et al., J. Mol. Spectrosc.198, 393 (1999)).