Axigluon production at ep colliders

We study the prospects for the production of axigluons, the massive color-octet gauge bosons present in all chiral-color models, in ep collisions. We find that HERA will likely be able to exclude the currently allowed “window” of light axigluon masses, 25 GeV < M_A < 125 GeV.     

Search for charginos,neutralinos and gravitinos in e+e− interactions at s=183 GeV

An update of the searches for charginos and neutralinos is presented, based on a data sample corresponding to the 53.9 pb⁻¹ recorded by the DELPHI detector in 1997, at a centre-of-mass energy of 183 GeV. No evidence for a signal was found. The lower mass limits are 4–5 GeV/c² higher than those obtained at a centre-of-mass energy of 172 GeV. The (μ,M₂) domain excluded by combining the neutralino and chargino searches implies a limit on the mass of the lightest neutralino which, for a heavy sneutrino, is constrained to be above 29.1 GeV/c² for tanβ≥ 1.     

Missing mass analysis of the A−2 at 6.0 GeV/c

The missing mass spectrum in the region of the A^?₂ has been measured in the reaction π^?p→X^?p at 6.0 GeV/c in the interval 0.27 <|t|<0.42 (GeV/c)², with an optical spark chamber system which simultaneously observed the decay X^?→ηπ^?. A signal of 230 events above background per five MeV interval is observed at the A₂ peak, with a signal-to-background ratio of greater than 1:1. A single D-wave Breit-Wigner distribution with a quadratic background gives a good fit to the data, yielding the parameters M₀=(1.324±0.003) GeV/c² and Γ₀=(0.104±0.009) GeV/c². The spectrum is incompatible with a dipole shape.     

Model-independent determination of the top Yukawa coupling from LHC and ILC

We show how a measurement of the process pp→tt̄H⁰+X at the Large Hadron Collider (LHC) and a measurement of the Higgs boson branching ratios BR(H⁰→bb̄) and BR(H⁰→W⁺W^-) at a future linear electron positron collider (ILC) can be combined to extract a value of the top quark Yukawa coupling in a model-independent way. We find that for masses with 120 GeV/c²<m_H<200 GeV/c² a measurement precision of 15% including systematic uncertainties can be achieved for integrated luminosities of 300 fb^-1 at the LHC and 500 fb^-1 at the ILC at a centre-of-mass energy of 350 GeV.     

Upper bounds on Higgs-Boson masses in the Weinberg-Salam model with three Higgs doublets

In the Weinberg-Salam model with three Higgs doublets, the positivity of masses and tree graph unitarity applied on Higgs scattering lead to the following upper bounds on Higgs masses: m_H1^±, m_H2^± < 883 GeV, m_H1⁰ < 500 GeV, m_H2⁰, m_H3⁰ < (958–1633) GeV, m_H4⁰, m_H5⁰ < (360–883) GeV.     

Study of the effective transverse momentum of partons in the proton using prompt photons in photoproduction at HERA

The photoproduction of prompt photons, together with an accompanying jet, has been measured with the ZEUS detector at HERA using an integrated luminosity of 38.6 pb⁻¹. A study of the effective transverse momentum, 〈k_T〉, of partons in the proton, as modelled within the framework of the PYTHIA Monte Carlo, gives a value of 〈k_T〉=1.69±0.18^+0.18_−0.20 GeV for the γp centre-of-mass energy range 134<W<251 GeV. This result is in agreement with the previously observed trend in hadron–hadron scattering for 〈k_T〉 to rise with interaction energy.     

Higgs boson searches at the Tevatron

This article reviews the Higgs searches at the Tevatron, as presented over the summer of 2012; both standard model (SM) and beyond the standard model (BSM) results are discussed as detailed (arXiv: 1207.0449; Phys. Rev. Lett., 2012, 109: 071804; Phys. Rev. D, 2012, 85: 032005). We discuss the combination of searches by the CDF and D0 Collaborations for the standard model Higgs boson in the mass range 100–200 GeV/c ² produced in the the gg → H, WH, ZH, t{ie27-1}H, and vector boson fusion production modes, and decaying in the H → b{ie27-2}, H → W ⁺ W ^?, H → ZZ, H → τ ⁺ τ ^?, and H → γγ modes. The data, collected at the Fermilab Tevatron collider in p{ie27-3} collisions at {ie27-4} TeV, correspond to integrated luminosities of up to 10 fb^?1. In the absence of signal, we expect to exclude the regions 100<m _H < 120 GeV/c ² and 139<m _H < 184 GeV/c ². We exclude, at the 95% C.L., two regions: 100<m _H < 103 GeV/c ², and 147<m _H < 180 GeV/c ². We observe a significant excess of events in the mass range between 115 and 140 GeV/c ². The local significance corresponds to 3.0 standard deviations at m _H = 120 GeV/c ²; the global significance (incorporating the look-elsewhere effect) for such an excess anywhere in the full mass range investigated is approximately 2.5 standard deviations. Furthermore, we separately combine searches for H → b{ie27-5}, H → W+W ^? and H → γγ. We find that the excess is concentrated in the H → b{ie27-6} channel, appearing in the searches over a broad range of m _H ; the maximum local significance of 3.3 standard deviations corresponds to a global significance of approximately 3.1 standard deviations. The observed signal strengths in all channels are consistent with the expectation for a standard model Higgs boson at m _H = 125 GeV/c ². The production of neutral Higgs bosons in association with b-quarks can be significantly enhanced in various beyond the standard model scenarios, including Supersymmetry. The recent combination of such searches from the two collaborations is discussed.     

Observation of πo mesons with large transverse momentum in high-energy proton-proton collisions

Invariant cross-sections are presented for the inclusive reaction p + p → π^o + anything, Measurements of large transverse momentum π^o's (2.5 GeV/c<p_⊥<9 GeV/c) were made near 90° at the CERN ISR at five centre-of-mass energies (√s = 23.5, 30.6, 44.8, 52.7 and 62.4 GeV. At large p_⊥, the invariant cross-sections are seem to vary with s and p_⊥, in good agreement with a fit of the form Ap_⊥^?nF(p_⊥/√s), with n≈8 and F(p_⊥/√s)≈exp(?26p_⊥/√s).     

On the mass and mixings of the ZE

The experimental data on the neutral current couplings are used to derive lower bounds on the mass of Z_E, the extra neutral gauge boson appearing in the minimal ‘beyond the standard model’ scenario favoured in superstring compactifications. This is based on the gauge group SU(3)_c×SU(2)_L×U(1)_Y×U(1)_E. Taking sin²θ_w=0.229, m_W=80.76 GeV and m_Z=91.59 GeV it is found that the mixing angle θ between Z and Z_E must satisfy −0.136<sin θ<−0.007 corresponding to m_ZE>152 GeV or, assuming E₆ unification m_ZE>155 GeV.     

Study of radiative leptonic events with hard photons and search for excited charged leptons at GeV

During the last 1995 data acquisition period at LEP, the DELPHI experiment collected an integrated luminosity of 5.9 pb⁻¹ at centre-of-mass energies of 130 GeV and 136 GeV. Radiative leptonic events (e, μ, τ) with high energy photons were studied and compared to Standard Model predictions. The data were used to search for charged excited leptons decaying through an electromagnetic transition. No significant signal was found. From the search for pair produced excited leptons, the limits m_e^* > 62.5 GeV/c², m_μ^* > 62.6 GeV/c² and m_τ^* > 62.2 GeV/c² at 95% confidence level were established. For single excited lepton production, upper limits on the ratio λ/m_l^* of the coupling of the excited charged lepton to its mass were derived.     

Remark on the status of non-conservation of parity in nuclear beta-decay

Equality of β-decay coupling constants C′_A/C_A = C′_V/C_V = 1, implying V - A interaction, is less verified than commonly assumed. Deducing limits 0.52 < C′_V/C_V < 1.93 and 0.82 < C′_A/C_A < 1.22 we discuss a possible V+A admixture with a mass ratio m(W^V?A)/m(W^V+A) < 0.56 for intermediate bosons W^V±A.     

Search for the standard model Higgs boson at the LEP2 collider near

During 1997 the ALEPH experiment at LEP gathered 57 pb⁻¹ of data at centre-of-mass energies near 183 GeV. These data are used to look for possible signals from the production of the Standard Model Higgs boson in the reaction e⁺e⁻→HZ. No evidence of a signal is found in the data; seven events are selected, in agreement with the expectation of 7.2 events from background processes. This observation results in an improved lower limit on the mass of the Higgs boson: m_H>87.9 GeV/c² at 95% confidence level.     

Limits to possible scalar-boson mass and coupling from e+e− collisions

Measurements of e⁺e^? → e⁺e^? at 2.8 GeV are reported and interpreted in terms of limits for the mass and coupling of a possible scalar boson of the type introduced in recent renormalizable models of weak interactions. In particular, in the Georgi-Glashow scheme of leptons we find that the scalar boson mass must be larger than 10 GeV for an m_W = 10 GeV (m_W mass of the W-boson) and of 6.5 GeV for m_W = 15 GeV. Alternatively its coupling is extremely weak.     

ϒ production at large transverse momentum as a probe of axigluons

Large-p_T production of J/Ψ and ϒ particles is suggested as a sensitive probe of axigluons of mass less than 40 GeV at the CERN collider and 80 GeV at the Tevatron. It is shown that existing CERN collider data on large-p_T ϒ production exclude axigluon masses less than around 20 GeV. At the projected SSC, ϒ and vector toponium production at large p_T through axigluon exchange by far outweighs the QCD contribution over a vast range of axigluon and toponium masses.     

Evidence for a change of slope in large-t elastic proton-proton scattering at s=53 GeV

New experimental results are presented on proton-proton elastic scattering in the range of momentum transfer 4 GeV² < ?t < 10 GeV² at the centre-of-mass energy of √s = 53 GeV. The data have been obtained using the Split-Field Magnet detector at the CERN Intersecting Storage Rings. We observe another change of slope of the differential cross section near ?t=6.5 GeV².     

Measurement of K production in the reaction Kp → Kp

The K^∗− spectrum in the reaction K⁻+p → K^∗−+p has been measured at beam momenta 10.9, 13.4 and 15.9 GeV/c using the missing mass technique. Production of the L(1770), and a Q-K^∗(1420) enhancement are observed. Differential cross sections in the range of momentum transfer 0.12 < | t_pp | < 0.40 (GeV/c)² are given. The L meson is observed with a width Γ = 100 ± 26 MeV. The mass spectrum between the L and 2.5 GeV does not show significant structure.     

Dijet production in diffractive deep inelastic scattering at HERA

The production of dijets in diffractive deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 61 pb^-1. The dijet cross section has been measured for virtualities of the exchanged virtual photon, 5 < Q² < 100 GeV², and γ^*p centre-of-mass energies, 100 < W < 250 GeV. The jets, identified using the inclusive k_T algorithm in the γ^*p frame, were required to have a transverse energy E^* _T,jet > 4 GeV and the jet with the highest transverse energy was required to have E^* _T,jet > 5 GeV. All jets were required to be in the pseudorapidity range -3.5<η^* _jet<0. The differential cross sections are compared to leading-order predictions and next-to-leading-order QCD calculations based on recent diffractive parton densities extracted from inclusive diffractive deep inelastic scattering data.     

Large-angle inclusive production of charged pions at the CERN ISR with transverse moment a less than 1.0 GeV/c

The inclusive production of π^± in proton-proton collisons has been measured for the transverse momentum range 0.15 to 1.0 GeV/c over an angular range of 29° to 89° in the centre-of-mass system and for centre-of-mass energies √_s = 30.6 and 52.8 GeV. For each energy the invariant cross-section foe fixed transverse momentum was found to increase by about 15% as the centre-of-mass rapidity decreases from 1 to 0, i.e. the “central plateau” has not yet been reached.     

Are CKM andW,Z phenomenology consistent withA=p=1 and δ≃π/3?

The expectation of the geometrical catamorphic representation of the quark-lepton families is that the parameters of the CKM matrix, in the Wolfenstein substitution, have the valuesA=p=1 and δ?π/3. No conflict is found with the geometrical expectation which, furthermore, requires 107<m _t<165 GeV/c², consistent withW, Z phenomenology.     

The transverse-energy distributions of 32S-nucleus collisions at 200 GeV per nucleon

Transverse-energy distributions have been measured for the collisions of the ³²S nucleus with Al, Ag, W, Pt, Pb, and U target nuclei, at an incident energy of 200 GeV per nucleon. The shapes of these distribution reflect the geometry of the collisions, including the deformation effects. For central collisions, the transverse-energy production in the region −0.1<η_lab<2.9 increases approximately as A^0.5, where A is the atomic mass number of the target. This increase is accompanied by a relative depletion in the forward region η_lab > 2.9. These results are compared with those obtained under similar conditions with incident ¹⁶O nuclei. A comparison is also made with the predictions of a Monte Carlo generator based on the dual parton model. Finally, we give estimates of the energy density reached and its dependence on the atomic mass number of the projectile.