J Van Eldik’s research while affiliated with CERN and other places

A study of \it{\Lambda}_{\it{b}}^\rm{0} and \it{\Xi}_{\it{b}}^\rm{0} decays to $\it{\Lambda} h^{+} h^{\prime -}$ $(h^{(\prime)}=\pi, K)$ is performed using pp collision data collected by the LHCb experiment during LHC Runs 1$-$2, corresponding to an integrated luminosity of $9~\rm{fb}^{-1}$. The branching fractions for these decays are measured using the \it{\Lambda}_{\it{b}}^\rm{0}\to\it{\Lambda}_{\it{c}}^+(\to\it{\Lambda}\pi^+)\pi^- decay as control channel. The decays \it{\Lambda}_{\it{b}}^\rm{0}\to\it{\Lambda}\pi^+\pi^- and \it{\Xi}_{\it{b}}^\rm{0}\to\it{\Lambda}K^-\pi^+ are observed for the first time. For decay modes with sufficient signal yields, CP asymmetries are measured in the full and localized regions of the final-state phase space. Evidence is found for CP violation in the \it{\Lambda}_{\it{b}}^\rm{0}\to\it{\Lambda}K^+K^- decay, interpreted as originating primarily from an asymmetric \it{\Lambda}_{\it{b}}^\rm{0} \to \it{N}^{*+} \it{K}^- decay amplitude. The measured CP asymmetries for the other decays are compatible with zero.

CERN has been running a production OpenStack cloud since July 2013 to support physics computing and infrastructure services for the site. In the past year, CERN Cloud Infrastructure has seen a constant increase in nodes, virtual machines, users and projects. This paper will present what has been done in order to make the CERN cloud infrastructure scale out.

The hadronic part of the Electron Structure Function (ESF) has been measured for the first time, using e+e- data collected by the DELPHI experiment at LEP, at centre-of-mass energies sqrt(s) = 91.2-209.5 GeV. The data analysis is simpler than that of the measurement of the photon structure function. The ESF data are compared to predictions of phenomenological models based on the photon structure function. It is shown that the quasi-real photon virtuality contribution is significant. The presented data can serve as a cross-check of the photon structure function analyses and help in refining existing parametrizations.

The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have searched for pair-produced charged Higgs bosons in the framework of Two Higgs Doublet Models (2HDMs). The data of the four experiments have been statistically combined. The results are interpreted within the 2HDM for Type I and Type II benchmark scenarios. No statistically significant excess has been observed when compared to the Standard Model background prediction, and the combined LEP data exclude large regions of the model parameter space. Charged Higgs bosons with mass below 80 GeV/c 2 (Type II scenario) or 72.5 GeV/c 2 (Type I scenario , for pseudo-scalar masses above 12 GeV/c 2) are excluded at the 95 % confidence level.

The CERN Data Centre is reviewing strategies for optimizing the use of the existing infrastructure and expanding to a new data centre by studying how other large sites are being operated. Over the past six months, CERN has been investigating modern and widely-used tools and procedures used for virtualisation, clouds and fabric management in order to reduce operational effort, increase agility and support unattended remote data centres. This paper gives the details on the project's motivations, current status and areas for future investigation.

The nature of b-quark jet hadronisation has been investigated using data taken at the Z peak by the DELPHI detector at LEP. Two complementary methods are used to reconstruct the energy of weakly decaying b-hadrons, $E_{\mathrm{B}}^{\mathrm{weak}}$. The average value of $x^{\mathrm{weak}}_{\mathrm{B}} = E_{\mathrm{B}}^{\mathrm{weak}}/E_{\mathrm{beam}}$ is measured to be 0.699±0.011. The resulting $x^{\mathrm{weak}}_{\mathrm{B}}$ distribution is then analysed in the framework of two choices for the perturbative contribution (parton shower and Next to Leading Log QCD calculation) in order to extract measurements of the non-perturbative contribution to be used in studies of b-hadron production in other experimental environments than LEP. In the parton shower framework, data favour the Lund model ansatz and corresponding values of its parameters have been determined within PYTHIA 6.156 from DELPHI data: a= 1.84^{+0.23}_{-0.21}\quad\mbox{and}\quad b=0.642^{+0.073}_{-0.063}~\mathrm{GeV}^{-2}

Single top quark production via four-fermion contact interactions associated to flavour-changing neutral currents was searched for in data taken by the DELPHI detector at LEP2. The data were accumulated at centre-of-mass energies ranging from 189 to 209 GeV, with an integrated luminosity of 598.1pb−1. No evidence for a signal was found. Limits on the energy scale Λ, were set for scalar-, vector- and tensor-like coupling scenarios.

Semileptonic decays B→ D*-ℓ+νX were selected from a sample of 3.1 million hadronic Z decays collected by the DELPHI detector at LEP. A topological search for semileptonic B decays to resonant and non-resonant D*-π+ states was performed and the ratio of the branching fractions: Br(B → D*-ℓ+νX)/Br(B → D*-+νX) + Br(B0 → + D*-ℓ+ν) = 0.19 ± 0.10(stat) ± 0.06(syst) was determined. Taking into account this contribution, the differential decay width of B0 → D*-ℓ+ν was measured as a function of the momentum transfer from the B to the D*- in two separate analyses, using exclusive and inclusive methods of D*- reconstruction. The distributions were fitted over the full momentum transfer range to extract the product of {pipe}Vcb{pipe} times the normalization of the decay form factor F(q2max): F(q2max){pipe}Vcb{pipe} = (35.4 ± 1.9(stat) ± 2.4(syst)) · 10-3. The value of {pipe}Vcb{pipe} was computed using theoretical calculations of F(q2max), giving: {pipe}Vcb{pipe} = (38.9 ± 2.0(stat) ± 2.6(syst) ± 1.7(theory)) · 10-3. The total branching fraction Br(B0 → D*-ℓ+ν) was determined to be: Br(130, D*-ℓ+v) = (5.52 ± 0.17(stat) ± 0.68(syst))%.

An analysis of the direct soft photon production rate as a function of the parent jet characteristics is presented, based on hadronic events collected by the DELPHI experiment at LEP1. The dependences of the photon rates on the jet kinematic characteristics (momentum, mass, etc.) and on the jet charged, neutral and total hadron multiplicities are reported. Up to a scale factor of about four, which characterizes the overall value of the soft photon excess, a similarity of the observed soft photon behavior to that of the inner hadronic bremsstrahlung predictions is found for the momentum, mass, and jet charged multiplicity dependences. However for the dependence of the soft photon rate on the jet neutral and total hadron multiplicities a prominent difference is found for the observed soft photon signal as compared to the expected bremsstrahlung from final state hadrons. The observed linear increase of the soft photon production rate with the jet total hadron multiplicity and its strong dependence on the jet neutral multiplicity suggest that the rate is proportional to the number of quark pairs produced in the fragmentation process, with the neutral pairs being more effectively radiating than the charged ones.

The data taken by Delphi at centre-of-mass energies between 189and 209GeV are used to place limits on the CP-conserving trilinear gauge boson couplings DgZ1\Delta g^{Z}_{1}, λ γ and Δκ γ associated to W + W − and single W production at Lep2. Using data from the jj ℓ ν, jjjj, jjX and ℓ X final states, where j, ℓ and X represent a jet, a lepton and missing four-momentum, respectively, the following limits are set on the couplings when one parameter is allowed to vary and the others are set to their Standard Model values of zero: {l}\Delta g^Z_1=-0.025^{+0.033}_{-0.030},\\\noalign{\vskip6pt}\lambda_\gamma =0.002^{+0.035}_{-0.035}\qquad\mbox{and}\\\noalign{\vskip6pt}\Delta\kappa_\gamma =0.024^{+0.077}_{-0.081}.\begin{array}{l}\Delta g^Z_1=-0.025^{+0.033}_{-0.030},\\\noalign{\vskip6pt}\lambda_\gamma =0.002^{+0.035}_{-0.035}\qquad\mbox{and}\\\noalign{\vskip6pt}\Delta\kappa_\gamma =0.024^{+0.077}_{-0.081}.\end{array} Results are also presented when two or three parameters are allowed to vary. All observations are consistent with the predictions of the Standard Model and supersede the previous results on these gauge coupling parameters published by Delphi.