Search Results (5 total)

We describe the status of our effort to realize a first neutrino factory and the progress made in understanding the problems associated with the collection and cooling of muons towards that end. We summarize the physics that can be done with neutrino factories as well as with intense cold beams of muons. The physics potential of muon colliders is reviewed, both as Higgs factories and compact high-energy lepton colliders. The status and time scale of our research and development effort is reviewed as well as the latest designs in cooling channels including the promise of ring coolers in achieving longitudinal and transverse cooling simultaneously. We detail the efforts being made to mount an international cooling experiment to demonstrate the ionization cooling of muons.

Next-to-leading-order QCD analyses of the ZEUS data on deep inelastic scattering together with fixed-target data have been performed, from which the gluon and quark densities of the proton and the value of the strong coupling constant α_s(M_Z) were extracted. The study includes a full treatment of the experimental systematic uncertainties including point-to-point correlations. The resulting uncertainties in the parton density functions are presented. A combined fit for α_s(M_Z) and the gluon and quark densities yields a value for α_s(M_Z) in agreement with the world average. The parton density functions derived from ZEUS data alone indicate the importance of HERA data in determining the sea quark and gluon distributions at low x. The limits of applicability of the theoretical formalism have been explored by comparing the fit predictions to ZEUS data at very low Q².

A search has been made for lepton-flavor-violating interactions of the type e⁺p→lX, where l denotes a μ or τ with high transverse momentum, at a center-of-mass energy sqrt[s] of 300 GeV with an integrated luminosity of 47.7 pb^-1 using the ZEUS detector at HERA. No evidence was found for lepton-flavor violation and constraints were derived on leptoquarks (LQs) that could mediate such interactions. For LQ masses below sqrt[s], limits are set on λ_eq1 sqrt[β_lq], where λ_eq1 is the coupling of the LQ to an electron and a first-generation quark q₁ and β_lq is the branching ratio of the LQ to l and a quark. For LQ masses exceeding sqrt[s], limits are set on the four-fermion contact-interaction term λ_eqα λ_lqβ/M_LQ² for leptoquarks that couple to an electron and a quark q_α and also to l and a quark q_β. Some of the limits are also applicable to lepton-flavor-violating processes mediated by squarks in R-parity-violating supersymmetric models. In some cases involving heavy quarks and especially for l=τ, the ZEUS limits are the most stringent published to date.

Characteristics of the hadronic final state of diffractive deep inelastic scattering events ep→eXp were studied in the kinematic range 4<M_X<35 GeV, 4<Q²<150 GeV², 70<W<250 GeV, and 0.0003<x_P<0.03 with the ZEUS detector at the DESY ep collider HERA using an integrated luminosity of 13.8 pb^-1. The events were tagged by identifying the diffractively scattered proton using the leading proton spectrometer. The properties of the hadronic final state X were studied in its center-of-mass frame using thrust, thrust angle, sphericity, energy flow, transverse energy flow, and “seagull” distributions. As the invariant mass of the system increases, the final state becomes more collimated, more aligned, and more asymmetric in the average transverse momentum with respect to the direction of the virtual photon. Comparisons of the properties of the hadronic final state with predictions from various Monte Carlo model generators suggest that the final state is dominated by qq̅ g states at the parton level.

A study of the ν̅ -jet mass spectrum in e⁺p→ν̅ X events at a center-of-mass energy 300 GeV has been performed with the ZEUS detector at the HERA collider at DESY using an integrated luminosity of 47.7 pb^-1. The mass spectrum is in good agreement with that expected from standard model processes over the ν̅ -jet mass range studied. No significant excess attributable to the decay of a narrow resonance is observed. By using both e⁺p→e⁺X and e⁺p→ν̅ X data, mass-dependent limits are set on the s-channel production of scalar and vector resonant states. Couplings to first-generation quarks are considered and limits are presented as a function of the e⁺q and ν̅ q branching ratios. These limits are used to constrain the production of leptoquarks and R-parity violating squarks.