209842386
Neutral-current four-fermion production in e+e− interactions at LEP
Abstract Neutral-current four-fermion production, e + e − → f f ¯ f ′ f ¯ ′ , is studied in 0.7 fb −1 of data collected with the L3 detector at LEP at centre-of-mass energies s = 183 – 209 GeV . Four final states are considered: q q ¯ ν ν ¯ , q q ¯ l + l − , l + l − l ′ + l ′ − and l + l − ν ν ¯ , where l denotes either an electron or a muon. Their cross sections are measured and found to agree with the Standard Model predictions. In addition, the e + e − → Z γ ∗ → f f ¯ f ′ f ¯ ′ process is studied and its total cross section at the average centre-of-mass energy 〈 s 〉 = 196.6 GeV is found to be 0.29 ± 0.05 ± 0.03 pb , where the first uncertainty is statistical and the second systematic, in agreement with the Standard Model prediction of 0.22 pb. Finally, the mass spectra of the q q ¯ l + l − final states are analysed to search for the possible production of a new neutral heavy particle, for which no evidence is found.
19719907
Trigger System of BESIII
The trigger system of Beijing Spectrometer III, part of the upgrade of Beijing Electron Positron Collider, has been designed and implemented, and is ready for installation. This paper describes briefly the system components, its characteristics, and some technical issues. The system consists mainly of four parts: MDC (drift chamber) tracking subsystem, EMC (electromagnetic calorimeter) subsystem, TOF (time of flight) subsystem and global trigger. Some highlights in designing of this system includes: trigger scheme optimization with software simulation; optical transmission between trigger and FEEs to realize isolation with FEEs to avoid ground loop current interference; designed with most latest FPGA (Xilinx Spartan 3, VirtexII Pro...) for simplicity, high reliability and easy maintenance and hence smaller system; FPGA in-system programming or firmware online downloadable via onboard, panel connector and/or VME bus for modification flexibility during commissioning. Different from the usual fix delay data transmission from FEE to trigger, the RocketIO has been used as SEDES.
203030065
Search for anomalous couplings in the Higgs sector at LEP
Anomalous couplings of the Higgs boson are searched for through the processes e+e-→Hγ, e+e -→e+e-H and e+e -→HZ. The mass range 70 GeV<mH<190 GeV is explored using 602 pb-1 of integrated luminosity collected with the L3 detector at LEP at centre-of-mass energies s=189-209 GeV. The Higgs decay channels H→ff, H→γγ, H→Zγ and H→WW(*) are considered and no evidence is found for anomalous Higgs production or decay. Limits on the anomalous couplings d, d B, Δg1 Z, Δκγ and ξ2 are derived as well as limits on the H→γγ and H→Zγ decay rates. © 2004 Published by Elsevier B.V.
208868428
f1(1285) formation in two-photon collisions at LEP
Abstract The ηπ + π − final state in two-photon collisions is studied with the L3 detector at LEP, at centre-of-mass energies from 183 to 209 GeV with an integrated luminosity of 664.6 pb −1 . The f 1 (1285) meson is observed and the Q 2 dependence of its production is compared to different form factor models. The γγ -coupling parameter Γ γγ is found to be 3.5±0.6(stat.)±0.5(sys.) keV. The branching fraction Γ (f 1 (1285)→a 0 π )/ Γ (f 1 (1285)→ ηππ ) is also measured.
188198310
Preliminary design of BES-III trigger system
126182293
Evidence of psi(3770) nonD anti-D decay to J / psi pi+ pi-
85538672
Study of kaon decay to two pions
The weak decay of the kaon to two pions is studied within the model of Nambu and Jona-Lasinio. Using the standard effectiveweak Hamiltonian, both the decay amplitude arising from an intermediate state σ meson and the direct decay amplitude are calculated. The effect of final state interactions is also included. When the matching scale is chosen such that the decay amplitude with isospin I ¼ 2 is close to its experimental value, our model including the σ meson contributes up to 80% of the total I ¼ 0 amplitude. This supports recent suggestions that the σ meson should play a vital role in explaining the ΔI ¼ 1=2 rule in this system.
8142176
Gluino NLSP, dark matter via gluino coannihilation, and LHC signatures
The possibility that the gluino is the next to the lightest supersymmetric particle (NLSP) is discussed and it is shown that this situation arises in nonuniversal supergravity models within a significant part of the parameter space compatible with all known experimental bounds. It is then shown that the gluino NLSP (GNLSP) models lead to a compressed sfermion spectrum with the sleptons often heavier than the squarks at least for the first two generations. The relic density here is governed by gluino coannihilation which is responsible for a relatively small mass splitting between the gluino and the neutralino masses. Thus the GNLSP class of models is very predictive first because the supersymmetry (SUSY) production cross sections at the CERN LHC are dominated by gluino production and second because the gluino production itself proceeds dominantly through a single channel which allows for a direct determination of the gluino mass and an indirect determination of the neutralino mass due to a linear relation between these two masses which is highly constrained by coannihilation. A detailed analysis of these models shows that the jet production and tagged b jets from the gluino production can be discriminated from the standard model background with appropriate cuts.more » It is found that the GNLSP models can be tested with just 10 fb{sup -1} of integrated luminosity and may therefore be checked with low luminosity runs in the first data at the LHC. Thus if a GNLSP model is realized, the LHC will turn into a gluino factory through a profuse production of gluinos with typically only a small fraction < or approx. 5% of total SUSY events arising from other production modes over the allowed GNLSP model parameter space.« less
16549584
The nucleon axial charge and lowest moment hxi with Nf = 2 dynamical twisted mass fermions
We present results on the nucleon axial charge and the lowest moment x of the quark distribution using two degenerate flavors of light dynamical twisted mass fermions. The calculation is performed for pion masses in the range of 500 MeV to 300 MeV on a lattice of spatial size of about 2.1 fm.
118422616
Hadron properties from lattice QCD simulations with exact chiral symmetry
118545965
Low-mass Higgs bosons in the NMSSM and their LHC implications
A bstractWe study the Higgs sector of the Next to Minimal Supersymmetric Standard Model (NMSSM) in light of the discovery of the SM-like Higgs boson at the LHC. We perform a broad scan over the NMSSM parameter space and identify the regions that are consistent with current Higgs search results at colliders. In contrast to the commonly studied “decoupling” scenario in the literature where the Minimal Supersymmetric Standard Model CP-odd Higgs boson mass is large mA ≫ mZ , we pay particular attention to the light Higgs states in the case when mA ≲ 2mZ . The Higgs bosons in the NMSSM, namely three CP-even states, two CP-odd states, and two charged Higgs states, could all be rather light, near or below the electroweak scale, although the singlet-like states can be heavier. The SM-like Higgs boson could be either the lightest CP-even scalar or the second lightest CP-even scalar, but is unlikely to be the heaviest scalar. These NMSSM parameter regions have unique properties and offer rich phenomenology. The decay branching fractions for the SM-like Higgs boson may be modified appreciably. The correlations of γγ/V V and $ {VV \left/ {{b\overline{b}}} \right.} $ can be substantially altered. The new Higgs bosons may be readily produced at the LHC and may decay to non-standard distinctive final states, most notably a pair of Higgs bosons when kinematically accessible. We evaluate the production and decay of the Higgs bosons and comment on further searches at the LHC to probe the Higgs sector of the NMSSM.