Wedgebox analysis of four-lepton events from neutralino pair production at the LHC

A ‘wedgebox’ plot is a two-dimensional scatter-plot of two invariant mass quantities. Here pp→e⁺e^-μ⁺μ^-+≠E signature LHC events are analyzed by plotting the di-electron invariant mass versus the di-muon invariant mass. Data sets of such events are obtained across the MSSM input parameter space in realistic event-generator simulations, including cuts designed to remove SM backgrounds. Their study reveals several general features. Firstly, regions in the MSSM input parameter space where a sufficient number of events are expected so as to be able to construct a clear wedgebox plot are delineated. Secondly, the presence of box shapes on a wedgebox plot either indicates the presence of heavy Higgs bosons’ decays or restricts the location to a quite small region of low μ and M₂ values, ≲ 200 GeV, a region denoted as the ‘lower island’. In this region, wedgebox plots can be quite complicated and change in pattern rather quickly as one moves around in the (μ,M₂) plane. Thirdly, direct neutralino pair production from an intermediate Z^0* may only produce a wedge shape since only decays can contribute significantly. And fourthly, a double-wedge or wedge-protruding-from-a-box pattern on a wedgebox plot, which results from combining a variety of MSSM production processes, yields three distinct observed endpoints, almost always attributable to decays, which can be utilized to determine a great deal of information about the neutralino and slepton mass spectra and related MSSM input parameters. Wedge and double-wedge patterns are seen in wedgebox plots in another region of higher μ and M₂ values, denoted as the ‘upper island’. Here the pattern is simpler and more stable as one moves across the (μ,M₂) input parameter space.     

High energy radiation femtochemistry of water molecules: early electron-radical pairs processes

The damages triggered by ionizing radiation on chemical and biological targets depend on the survival probability of radicals produced in clusters of ionization-excitation events. In this paper, we report on femtolysis (FEMTOsecond radioLYSIS) of pure liquid water using an innovative laser produced high-energy, ultra-short electron bunches in the 2.5-15 MeV range and high energy radiation femtochemistry (HERF) measurements. The short-time monitoring of a primary reducing radical, hydrated electron e^-_aq^{-}_{aq}, has been performed in confined ionization spaces (nascent spurs). The calculated yield of hydrated electrons at early time, G(e^-_aq)_ETG({\rm e}^{-}_{aq})_{ET}, is estimated to be 6.5 ± 0.5 (number/100 eV) at t ~ 5 ps after the ultrafast energy deposition. This estimated value is high compare to (i) the available data of previous works that used scavenging techniques; (ii) the predictions of stochastic water radiolysis modelling for which the initial behaviour of hydrated electron is investigated in the framework of a classical diffusion regime of independent pairs. The HERF developments give new insights into the early ubiquitous radical escape probability in nascent aqueous spurs and emphasize the importance of short-lived solvent bridged electron-radical complexes [H₃O^+...{\rm H}_{3}{\rm O}^{+...}  e_aq^-{\rm e}_{aq}^{-} ..OH]_nH2O{\rm OH}]_{n{\rm H}_2{\rm O}} (non-independent pairs). A complete understanding of the G(e^-_aq)_ET{\rm e}^{-}_{aq})_{ET} value needs to account for quantum aspects of 1s-like trapped electron ground state and neoformed prototropic radicals that govern ultra-fast recombination processes within these non-independent pair configurations. Femtolysis data emphasize that within a time-dependent non-diffusion regime, spatio-temporal correlations between hydrated electron and nearest neighbours OH radical or hydrated proton (H₃O⁺{\rm H}_{3}{\rm O}^{+}) would assist ultrafast anisotropic 1D recombination within solvent bridged electron-radical complexes. The emerging HERF domain would provide guidance for understanding of ultrashort-lived sub-structure of tracks and stimulate future semi-quantum simulations on prethermal radical reactions.     

Vision of a fully laser-driven ${\sf n\gamma}{-}{\sf m\gamma}$ collider

The use is suggested of a laser-accelerated dense electron sheet with an energy of (E=[(g)\tilde] mc²E=\tilde{\gamma} mc^2) as a relativistic mirror to reflect coherently a second laser with photon energy ħω, generating by the Doppler boost high-energy γ photons with $ \hbar \omega ' = 4\tilde \gamma ^2 \hbar \omega $ \hbar \omega ' = 4\tilde \gamma ^2 \hbar \omega and short duration [A. Einstein, Annalen der Physik 17, 891 (1905); D. Habs et al., Appl. Phys. B 93, 349 (2008)]. Two of these counter-propagating γ beams are focused by the parabolically shaped electron sheets into the interaction region with small, close to diffraction-limited, spot size. Comparing the new nγ-mγ collider with former proposed γγ collider schemes we achieve the conversion of many photon-pairs in a small space-time volume to matter-antimatter particles, while in the other discussed setups only two isolated, much more high-energetic photons will be converted, reaching in the new approach much higher energy densities and temperatures. With a γ-field strength somewhat below the Schwinger limit we can reach this complete conversion of the γ bunch energy into e⁺e^- or quark-antiquark q[`(q)]q\bar{q}-plasmas. For a Bose-Einstein condensate (BEC) [A. Einstein, Physikalisch-mathematische Klasse (Berlin) 22, 261 (1924); A. Einstein, Physikalisch-mathematische Klasse (Berlin) 22, 3 (1925); A. Griffin, D.W. Snoke, S. Stringari, Bose-Einstein Condensation (Cambridge University Press, 1995)] final state or for the Cooper pair ground state at higher densities [A.J. Leggett, Quantum Liquids, Oxford Graduate Texts (Oxford University Press, 2006)] the strong induced transition into this coherent state is of special interest for single-cycle γ pulses. Due to annihilation these cold coherent states are very short-lived. For γ beams with photon energies of 1–10 keV the rather cold e<sup>+</sup>e<sup>-</sup>-plasma or e<sup>+</sup>e<sup>-</sup>-BEC expands to a cold dense aggregate of positronium (Ps) atoms, where the production of Ps molecules is discussed. For photon energies of 1–10 MeV we discuss the production of a cold induced π<sup>0</sup>-BEC followed by the formation of molecules. For the direct population of higher q[`(q)]q\bar{q} densities we can study condensates of color-neutral mesons with enhanced population. For a γγ collider with several-cycle laser pulses the following cycles heat up the fermion-antifermion f[`(f)]f\bar{f} system to a certain temperature. Thus we can reach high energy densities and temperatures of an e⁺e^-γ plasma, where the production of hadrons in general or the quark-gluon phase transition can be observed. Within the long-term goal of very high photon energies of about 1 GeV in the nγ-mγ-collider, even the electro-weak phase transition or SUSY phase transition could be reached.     

η, h￠ \eta{^\prime} → πl+l- in a chiral unitary approach

The decays η, → π⁺π^- l ⁺ l ^- (with l = e,μ are investigated within a chiral unitary approach which combines the chiral effective Lagrangian with a coupled-channels Bethe-Salpeter equation. Predictions for the decay widths and spectra are given.     

Updated estimate of the muon magnetic momentusing revised results from <Emphasis Type="Italic">e</Emphasis><Superscript> + </Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>-</Superscript>annihilation

A new evaluation of the hadronic vacuum polarization contribution to the muon magnetic moment is presented. We take into account the reanalysis of the low-energy e ⁺ e ^-annihilation cross section into hadrons by the CMD-2 Collaboration. The agreement between e ⁺ e ^-and spectral functions in the channel is found to be much improved. Nevertheless, significant discrepancies remain in the center-of-mass energy range between 0.85 and , so that we refrain from averaging the two data sets. The values found for the lowest-order hadronic vacuum polarization contributions are where the errors have been separated according to their sources: experimental, missing radiative corrections in e ⁺ e ^-data, and isospin breaking. The corresponding Standard Model predictions for the muon magnetic anomaly read where the errors account for the hadronic, light-by-light (LBL) scattering and electroweak contributions. The deviations from the measurement at BNL are found to be (1.9 ) and (0.7 ) for the e ⁺ e ^-- and -based estimates, respectively, where the second error is from the LBL contribution and the third one from the BNL measurement.Received: 7 September 2003, Published online: 30 October 2003     

Error cancellation in the semiclassical calculation of the scattering length

We investigate the effects of two approximations concerning long range dispersion forces that are made in the derivation of the semiclassical formula for the scattering length of a pair of neutral atoms. We demonstrate numerically, using a published model interaction potential for a pair of Cs atoms in the ³S_u⁺^3{\rm\Sigma}_{\rm u}^+ molecular state, that the subsequent long range errors tend to cancel and we show, from an approximate analytical relationship, that the first order errors do indeed largely cancel. We suggest a hybrid method that combines quantum mechanical and semiclassical calculations. We explore its use in finding the scattering lengths of ⁷Li atoms and ¹³³Cs atoms interacting via the X¹S⁺^1{\rm\Sigma}^+ and a³S⁺^3{\rm\Sigma}^+ molecular potentials and we use it to demonstrate that the semiclassical formula fails for cold collisions of H atoms in the X¹S_g⁺^1{\rm\Sigma}_{\rm g}^+ molecular state because of the long range errors rather than because of inadequacies in describing the motion over the potential well semiclassically.     

Study of W-boson polarisations and triple gauge boson couplings in the reaction e+e-→W+W- at LEP 2

A determination of the single W spin density matrix (SDM) elements in the reaction e⁺e^-→W⁺W^-→lνqq̄(l=e/μ) is reported at centre-of-mass energies between 189 and 209 GeV. The data sample used corresponds to an integrated luminosity of 520 pb^-1 taken by DELPHI between 1998 and 2000. The single W SDM elements, ρ_ττ’ ^W± (τ,τ’=± 1 or 0), are determined as a function of the W^- production angle with respect to the e^- beam direction and are obtained from measurements of the W decay products by the application of suitable projection operators, Λ_ττ’, which assume the V-A coupling of the W-boson to fermions. The measured SDM elements are used to obtain the fraction of longitudinally polarised Ws, with the result: at a mean energy of 198 GeV. The SDM elements are also used to determine the triple gauge couplings Δg₁ ^Z,Δκ_γ,λ_γ and g₄ ^Z, and . For the CP-violating couplings the results of single parameter fits are: The errors are a combination of statistical and systematic errors. All results are consistent with the Standard Model.     

Lowest- Q2 measurement of the γp → Δ reaction: Probing the pionic contribution

To determine nonspherical angular-momentum amplitudes in hadrons at long ranges (low Q²), data were taken for the p(ˉe, e'p)π⁰ reaction in the Δ region at Q ² = 0.060 (GeV/c)² utilizing the magnetic spectrometers of the A1 Collaboration at MAMI. The results for the dominant transition magnetic dipole amplitude and the quadrupole to dipole ratios at W = 1232 MeV are , Re( )%, and Re( )%. These disagree with predictions of constituent quark models but are in reasonable agreement with lattice calculations with nonlinear (chiral) pion mass extrapolations, with chiral effective field theory, and with dynamical models with pion cloud effects. These results confirm the dominance, and general Q² variation, of the pionic contribution at large distances.     

Lifetime vibrational interference during the NO 1s-1π* resonant excitation studied by the NO+(A 1Π → X 1Σ+) fluorescence

Dispersed fluorescence from fragments formed after the de-excitation of the 1s^-1π^* resonances of N^*O and NO^* has been measured in the spectral range of 118–142 nm. This range is dominated by lines of atomic nitrogen and oxygen fragments and by the bands in the NO⁺ ion which result from the participator Auger decay of the 1s^-1π^* resonances. Ab-initio calculations of the transition probabilities between vibrational levels during the reaction NO N^*O ⇒ NO were used to explain the observed intensity dependence for the fluorescence bands on the exciting-photon energy across the resonances and on both v^′ and v^′′ vibrational quantum numbers. The multiplet structure of the 1s^-1π^* resonance and lifetime vibrational interference explain the observed exciting-photon energy dependence of the fluorescence intensity. A strong spin-orbit coupling between singlet and triplet states of NO⁺ is proposed to reduce additional cascade population of the state via radiative transitions from the and states and to explain remaining differences between measured and calculated integral fluorescence intensities.     

QED radiative corrections to the decay π<Superscript>0</Superscript>→e<Superscript>+</Superscript>e<Superscript>-</Superscript>

We reconsider QED radiative corrections (RC) to the π⁰→e⁺e^- decay width. One kind of RC investigated earlier has a renormalization group origin and can be associated with the final state interaction of electron and positron. It determines the distribution of lepton pair invariant masses in the whole kinematic region. The other type of RC has a double-logarithmic character and is related to almost on-mass-shell behavior of the lepton form factors. The total effect of RC for π⁰→e⁺e^- decay is estimated to be 3.2%, and for η→e⁺e^- decay it is 4.3%. PACS  13.25.Cq; 12.38.Lg; 12.38.-t     

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.     

On the elliptic flow for nearly symmetric collisions and nuclear equation of state

We present the results of elliptic flow for the collision of nearly symmetric nuclei (₁₀Ne²⁰+ ₁₃Al²⁷_{10}{\rm Ne}^{20}+\,_{13}{\rm Al}^{27}, ₁₈Ar⁴⁰+ ₂₁Sc⁴⁵_{18}{\rm Ar}^{40}+\,_{21}{\rm Sc}^{45}, ₃₀Zn⁶⁴+ ₂₈Ni⁵⁸_{30}{\rm Zn}^{64}+\,_{28}{\rm Ni}^{58}, ₃₆Kr⁸⁶+ ₄₁Nb⁹³_{36}{\rm Kr}^{86}+\,_{41}{\rm Nb}^{93}) using the quantum molecular dynamics (QMD) model. General features of elliptic flow are investigated with the help of theoretical simulations. The simulations are performed at beam energies between 45 and 105 MeV /nucleon. A significant change can be seen from in-plane to out-of-plane elliptic flow of different fragments with incident energy. A comparison with experimental data is also made. Further, we show that elliptic flow for different fragments follows power-law dependence as given by the function C(A_tot)^tC{(A_{\rm tot})^\tau}.     

Semi-analytic approach to higher-order corrections in simple muonic bound systems: Vacuum polarization,self-energy and radiative-recoil

The current discrepancy of theory and experiment observed recently in muonic hydrogen necessitates a reinvestigation of all corrections to contribute to the Lamb shift in muonic hydrogen (μH), muonic deuterium (μD), the muonic \hbox{³He{}^3{\rm He}} 3 He ion (denoted here as μ ³He⁺), as well as in the muonic \hbox{⁴He{}^4{\rm He}} 4 He ion (μ ⁴He⁺). Here, we choose a semi-analytic approach and evaluate a number of higher-order corrections to vacuum polarization (VP) semi-analytically, while remaining integrals over the spectral density of VP are performed numerically. We obtain semi-analytic results for the second-order correction, and for the relativistic correction to VP. The self-energy correction to VP is calculated, including the perturbations of the Bethe logarithms by vacuum polarization. Subleading logarithmic terms in the radiative-recoil correction to the 2S–2P Lamb shift of order α(Zα)⁵ μ ³ln(Zα) / (m _μ m _N ) are also obtained. All calculations are nonperturbative in the mass ratio of orbiting particle and nucleus.     

Production of stop,sbottom, and stau at LEP2

We present a comprehensive study of pair production and decay of stops, sbottoms, and staus in e⁺e^? annihilation at LEP2. We give numerical predictions within the Minimal Supersymmetric Standard Model for cross sections and decay rates, and discuss the important signatures. In the case of stau production we also study the polarization of the τ in the decays ${\tilde \tau}_{1}\rightarrow \tau \ {\tilde \chi}_{1,2}^{0}$ .     

ω- πγtransition form factor in proton-proton collisions

Dalitz decays of ω and ρ mesons, and , produced in pp collisions are calculated within a covariant effective meson-nucleon theory. We argue that the ω transition form factor is experimentally accessible in a fairly model-independent way in the reaction pp → ppπ⁰ e ⁺ e ^- for invariant masses of the π⁰ e ⁺ e ^- subsystem near the ω pole. Numerical results are presented for the intermediate-energy kinematics of envisaged HADES experiments.     

Temperature dependence of the quenching of N<Subscript>2</Subscript> (C <Superscript>3</Superscript>Π<Subscript>u</Subscript>) by N<Subscript>2</Subscript> (X) and O<Subscript>2</Subscript> (X)

The temperature dependences of the quenching rate constants of the states N₂ (${\rm C} \ {^{3}{ \rm \Pi }_{u}}${\rm C} \ {^{3}{ \rm \Pi }_{u}} v^′=0,1) by N₂ (X) and of the state N₂ (${\rm C} \ {^{3}{ \rm \Pi }_{u}} \ v^{\prime}=0${\rm C} \ {^{3}{ \rm \Pi }_{u}} \ v^{\prime}=0) by O₂ (X) are studied. Time-resolved light emission from the gas was analyzed in the temperature range from 300 K to 210 K keeping the gas at constant density. In case of quenching by N₂ (X), the quenching rate constant for the vibrational level v^′= 0 increases by (13 ±3)% with gas cooling whereas the quenching rate constant for v^′= 1 decreases by (5.0 ±2.5)% in this temperature range. For quenching by O₂ (X), the quenching rate constant decreases by (3 ±2)% with gas cooling. The temperature variation of the N₂ (C ³Π_u v^′=0) emission intensity for pure nitrogen and dry air are calculated using the obtained quenching rate constants and is compared with the experimental data available in the literature.     

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.