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D. J. Miller

Publications and source records attributed to D. J. Miller.

89 records · Page 5Linked to original sources
arXiv2000

The triple Higgs self-coupling at future e+e- colliders: a signal-to-background study for the standard model

The experimental reconstruction of the Higgs self-energy potential is essential to a verification of the Higgs boson's role in spontaneous electroweak symmetry breaking. The first step towards this goal, the measurement of the triple Higgs self-coupling, can possibly be accomplished at the next generation of linear colliders. Here we present a background study of the most promising channel, double Higgs-strahlung off a Z boson, e+e- -> HHZ, with the subsequent decay H -> b bbar, and evaluate the feasibility of its measurement.

hep-ph↗
arXiv1999

Detecting Heavy Charged Higgs Bosons at the LHC with Four b-Quark Tags

We investigate the signature of a heavy charged Higgs boson of the Minimal Supersymmetric Standard Model in the lepton plus multi-jet channel at the Large Hadron Collider with four $b$-tags. The signal is the gluon-gluon fusion process $gg\to t\bar b H^-$, followed by the $H^-\to \bar t b$ decay, while the main background is from $gg\to t\bar t b\bar b$. We find that the two can be separated effectively by kinematic cuts and mass reconstruction, but the signal size is not very large in the end. Nonetheless, with a good $b$-tagging efficiency, $ε_b\sim50%$, this channel can provide a viable signature over a limited but interesting range of the parameter space.

hep-ph↗
arXiv1999

Can the trilinear Higgs self-coupling be measured at future linear colliders?

We assess the possibility of measuring the trilinear self-coupling of the Standard Model Higgs boson at future electron-positron linear colliders with centre-of-mass energies between 500 and 1500 GeV. We consider rather light Higgs scalars, with mass below the W+W- threshold, produced in the double Higgs-strahlung channel e+e- -> HHZ and decaying via the dominant mode H -> bbbar. Assuming ideal vertex tagging of the heavy-quark jets and mass reconstruction of the Z boson produced in association with the Higgs pair, we compare the yield of the above process to those of all irreducible electroweak and strong backgrounds proceeding through a bbbar bbbar Z intermediate state. Total cross sections and differential spectra of phenomenological relevance to the selection and analysis of the signal are given and discussed.

hep-ph↗
arXiv1999

Hadronic returns to the Z in electron-positron annihilation at high energy

The production of four hadronic jets in e+e- collisions above the Z pole is dominated by the QCD e+e- --> qqqq,qqgg processes and, for sufficiently high energy, the electroweak e+e- --> W+W- --> qqqq process. However there is another mechanism for producing four jets, e+e- --> Z gg --> qqgg, which can be regarded as a `hadronic return' to the Z pole. We investigate this new process in detail

hep-ph↗
arXiv1999

Direct Imaging of the First Order Spin Flop Transition in the Layered Manganite La1.4Sr1.6Mn2O7

Magnetic field induced transitions in the antiferromagnetic layered manganite La1.4Sr1.6Mn2O7 were studied using magnetization measurements and a high-resolution magneto-optical imaging technique. We report the first direct observation of the formation of ferromagnetic domains appearing at the first order spin-flop transition. The magnetization process proceeds through nucleation of polarized domains at crystal defect sites and not by domain wall motion. A small magnetic hysteresis is caused by the nucleation and annihilation of domains in the mixed state. These results establish a direct link betweeen the magnetic structure on the atomic scale as seen in neutron scattering and the macroscopic properties of the sample as seen in magnetization and conductivity measurements.

cond-mat↗
arXiv1999

Precision Studies at a Future Linear Collider

A future linear collider will complement the programme of the Large Hadron Collider, especially for precision physics. The RADCOR community has an important part to play in refining the predictions for rates and processes in Electroweak, Higgs, SUSY, top and QCD physics, for e^+ e^-, e^- e^-, $γγ$ and $γe$ collisions.

hep-ex↗
arXiv1998

The One-loop QCD Corrections for $γ^* to Q\bar Q q\bar q$

We calculate the one-loop QCD corrections for the decay of an off-shell vector boson with vector couplings into two pairs of quarks of equal or unequal flavours keeping all orders in the number of colours. These matrix elements are relevant for the calculation of the next-to-leading order ${\cal O}(α_s^3)$ corrections to four jet production in electron-positron annihilation, the production of a gauge boson accompanied by two jets in hadron-hadron collisions and three jet production in deep inelastic scattering. We use standard techniques for computing the interference of one-loop and tree level Feynman diagrams, but organise the results in terms of combinations of scalar loop integrals that are finite in the limit of vanishing Gram determinants and are therefore numerically stable.

hep-ph↗
arXiv1998

The One-loop QCD Corrections for gamma^* to q qbar gg

We compute the one-loop QCD amplitudes for the decay of an off-shell vector boson with vector couplings into a quark-antiquark pair accompanied by two gluons keeping, for the first time, all orders in the number of colours. Together with previous work this completes the calculation of the necessary one-loop amplitudes needed for the calculation of the next-to-leading order O(alpha_s^3) corrections to four jet production in electron-positron annihilation, the production of a gauge boson accompanied by two jets in hadron-hadron collisions and three jet production in deep inelastic scattering.

hep-ph↗
arXiv1998

Photon Structure and gamma-gamma Physics

The LEP experiments are making real progress in understanding the structure of the photon, though the results do not yet give such clear demonstrations of QCD in action as the proton structure has done. Other new results are reported, including QED related effects and $γγ\to Resonances$, from LEP and from CLEO II.

hep-ex↗
arXiv1998

The Multiplicity of Heavy Quark Pairs from Gluon Splitting in e+e- Annihilation

I will briefly review the progress which has been made in the investigation of secondary heavy quark production at LEP. I will show why a calculation of the secondary heavy quark multiplicity, keeping the dependence on an event shape variable, is essential for better exploitation of data, and I will present the results of such a calculation. This will be compared to Monte Carlo studies.

hep-ph↗
arXiv1998

Secondary Heavy Quark Pair Production in e+e- Annihilation

The multiplicity of heavy quarks from gluon splitting in e+e- annihilation has now been theoretically calculated and experimentally measured at LEP. However, the experimental measurement requires theoretical input for the shape of the multiplicity with respect to an event shape. In this paper we calculate the multiplicity of heavy quarks from gluon splitting in e+e- annihilation as a function of the heavy jet mass of the event, to next-to-leading logarithmic accuracy. We compare our result with Monte Carlo predictions.

hep-ph↗
arXiv1998

The Jet Multiplicity as a Function of Thrust

We calculate the average multiplicity of jets in e+e- annihilation as a function of both the jet resolution parameter, y_cut, and the thrust T. Our result resums to all orders the leading and next-to-leading logarithms in y_cut and 1-T, and is exact up to second order in alpha_s. This allows a comparison between the number of jets found using jet algorithms and the ability to distinguish different jet topologies via thrust.

hep-ph↗
arXiv1998

One-Loop Tensor Integrals in Dimensional Regularisation

We show how to evaluate tensor one-loop integrals in momentum space avoiding the usual plague of Gram determinants. We do this by constructing combinations of $n$- and $(n-1)$-point scalar integrals that are finite in the limit of vanishing Gram determinant. These non-trivial combinations of dilogarithms, logarithms and constants are systematically obtained by either differentiating with respect to the external parameters - essentially yielding scalar integrals with Feynman parameters in the numerator - or by developing the scalar integral in $D=6-2\e$ or higher dimensions. As an explicit example, we develop the tensor integrals and associated scalar integral combinations for processes where the internal particles are massless and where up to five (four massless and one massive) external particles are involved. For more general processes, we present the equations needed for deriving the relevant combinations of scalar integrals.

hep-ph↗
arXiv1997

Report of the Working Group on `W Mass and QCD' (Phenomenology Workshop on LEP2 Physics, Oxford, April 1997)

The W Mass and QCD Working Group discussed a wide variety of topics relating to present and future measurements of M(W) at LEP2, including QCD backgrounds to W+W- production. Particular attention was focused on experimental issues concerning the direct reconstruction and threshold mass measurements, and on theoretical and experimental issues concerning the four jet final state. This report summarises the main conclusions.

hep-ph↗
arXiv1997

The detective Modulation Transfer Function applied to scanned digital radiographic detectors

An extension of the traditional modulation transfer function (MTF), the detective MTF, is proposed for the evaluation of the resolution of X-ray imaging detectors with non-uniform efficiency on the scale of individual detector elements. The dMTF is shown to give a better representation than does the MTF of the improved resolution reported when the readout of the detectors is enhanced.

physics.ins-det↗
arXiv1997

An Experimenter's Highlights

This selection concentrates more on $γγ$ results, with some reference to the related HERA photoproduction data. Progress has been made on a wide range of topics, from $F_{2}^γ$ to the ``stickiness'' of glueball candidates, but many channels still need better statistics and/or a real photon target before they can match the comparable $ep$ studies.

hep-ex↗