First Hints of Jet Quenching at RHIC

At this conference first data from RHIC has been presented. Spectra of charged hadrons and identified neutral pions obtained in central collisions exhibit a depletion at large transverse momenta compared to expectations deduced from $pp$ and $\bar{p}p$ data and lower energy heavy ion data. While spectra measured in peripheral collisions exhibit the expected power-law shape, spectra from central collisions are closer to exponential. In addition, a significant azimuthal anisotropy of high momentum charged particle production has been found. All observations are in qualitative agreement with theoretical predictions that quark matter formed in heavy ion collisions quenches jet production.Comment: Proceedings of a summary talk given at the Quark Matter 2001 conferenc

Mitigation of the LHC Inverse Problem

The LHC inverse problem refers to the difficulties in determining the parameters of an underlying theory from data (to be) taken by the LHC experiments: if they find signals of new physics, and an underlying theory is assumed, could its parameters be determined uniquely, or do different parameter choices give indistinguishable experimental signatures? This inverse problem was studied before for a supersymmetric Standard Model with 15 free parameters. This earlier study found 283 indistinguishable pairs of parameter choices, called degenerate pairs, even if backgrounds are ignored. We can resolve all but 23 of those pairs by constructing a true \chi^2 distribution using mostly counting observables. The elimination of systematic errors would even allow separating the residual degeneracies. Taking the Standard Model background into account we still can resolve 237 of the 283 "degenerate" pairs. This indicates that (some of) our observables should also be useful for the purpose of determining the values of SUSY parameters.Comment: 32 pages, 13 figures, typo in (3.6) corrected, version to appear in Phys. Rev.

CP-violating Supersymmetric Higgs at the Tevatron and LHC

We analyze the prospect for observing the intermediate neutral Higgs boson ($h_2$) in its decay to two lighter Higgs bosons ($h_1$) at the presently operating hadron colliders in the framework of the CP violating MSSM using the PYTHIA event generator. We consider the lepton+ 4-jets+ \met channel from associate $W h_2$ production, with W h_2 \ra W h_1 h_1 \ra \ell \nu_\ell b \bar b b\bar b. We require two, three or four tagged $b$-jets. We explicitly consider all relevant Standard Model backgrounds, treating $c$-jets separately from light flavor and gluon jets and allowing for mistagging. We find that it is very hard to observe this signature at the Tevatron, even with 20 fb$^{-1}$ of data, in the LEP--allowed region of parameter space due to the small signal efficiency, even though the background is manageable. At the LHC, a priori huge SM backgrounds can be suppressed by applying judiciously chosen kinematical selections. After all cuts, we are left with a signal cross section of around 0.5 fb, and a signal to background ratio between 1.2 and 2.9. According to our analysis this Higgs signal should be viable at the LHC in the vicinity of present LEP exclusion once 20 to 50 fb$^{-1}$ of data have been accumulated at $\sqrt{s}=14$ TeV.Comment: 27 pages, 12 figure

Determining the Mass of Dark Matter Particles with Direct Detection Experiments

In this article I review two data analysis methods for determining the mass (and eventually the spin-independent cross section on nucleons) of Weakly Interacting Massive Particles with positive signals from direct Dark Matter detection experiments: a maximum likelihood analysis with only one experiment and a model-independent method requiring at least two experiments. Uncertainties and caveats of these methods will also be discussed.Comment: 24 pages, 10 figures, 1 reference added, typos fixed, published version, to appear in the NJP Focus Issue on "Dark Matter and Particle Physics

MRI and clinical resolution of a suspected intracranial toxoplasma granuloma with medical treatment in a domestic short hair cat

A two-year-old cat was presented with a left paradoxical vestibular syndrome. MRI of the brain revealed an extra-axial homogenously contrast enhancing mass in the region of the left caudal cerebellar peduncle. Toxoplasma serology was consistent with active infection and the lesion was suspected to be a toxoplasma granuloma. Following eight weeks of tapering oral prednisolone and 11 weeks of oral clindamycin treatment, repeat MRI revealed resolution of the lesion. Eighteen months after initial diagnosis, the cat remained neurologically normal. Differential diagnoses for a solitary, extra-axial, contrast enhancing mass lesion in the feline brain should include toxoplasma granuloma, which can undergo MRI and clinical resolution with medical treatment

Hour-glass magnetic spectrum in a stripe-less insulating transition metal oxide

An hour-glass shaped magnetic excitation spectrum appears to be an universal characteristic of the high-temperature superconducting cuprates. Fluctuating charge stripes or alternative band structure approaches are able to explain the origin of these spectra. Recently, an hour- glass spectrum has been observed in an insulating cobaltate, thus, favouring the charge stripe scenario. Here we show that neither charge stripes nor band structure effects are responsible for the hour-glass dispersion in a cobaltate within the checkerboard charge ordered regime of La2-xSrxCoO4. The search for charge stripe ordering reflections yields no evidence for charge stripes in La1.6Sr0.4CoO4 which is supported by our phonon studies. With the observation of an hour-glass-shaped excitation spectrum in this stripe-less insulating cobaltate, we provide experimental evidence that the hour-glass spectrum is neither necessarily connected to charge stripes nor to band structure effects, but instead, probably intimately coupled to frustration and arising chiral or non-collinear magnetic correlations

Weighing the universe with accelerators and detectors

Suppose the lightest superpartner (LSP) is observed at colliders, and WIMPs are detected in explicit experiments. We point out that one cannot immediately conclude that cold dark matter (CDM) of the universe has been observed, and we determine what measurements are necessary before such a conclusion is meaningful. We discuss the analogous situation for neutrinos and axions; in the axion case we have not found a way to conclude axions are the CDM even if axions are detected.Comment: 15 pages, 3 figures; minor changes included and typos fixe

Emittance measurements using Vernier Scans during Run 09 (pp at 250 GeV)

Emittance measurements using the vernier scan technique give reliable results for 250 GeV protons even though the transverse beam profiles have non-Gaussian tails. Those non-Gaussian tails were observed for the first time this run at the 250 GeV beam energy. The vernier scan measurements are in excellent agreement with the emittances derived from collision rates and show practically no fill to fill scatter if compared to the latter. The results are consistent with a {beta}* of 0.7 m and round beams. The IPM measurements show a discrepancy of up to 80% compared with the vernier scan data and a fill to fill scatter of up to 30%. If an uncertainty in the beta-function at the location of the IPM is the root cause, this uncertainty seems to be quite large. In any case, such an uncertainty could not explain the fill to fill variations of up to 30% which indicate yet another underlying reason that could explain fill to fill variations (candidates could be beam intensity issues with the IPM, beam position at the IPM, varying background etc.)

Open charm contribution to dilepton spectra produced in nuclear collisions at SPS energies

Measurements of open charm hadro-production from CERN and Fermilab experiments are reviewed, with particular emphasis on the absolute cross sections and on their A and sqrt(s) dependences. Differential pt and xf cross sections calculated with the Pythia event generator are found to be in reasonable agreement with recent data. The calculations are scaled to nucleus-nucleus collisions and the expected lepton pair yield is deduced. The charm contribution to the low mass dilepton continuum observed by the CERES experiment is found to be negligible. In particular, it is shown that the observed low mass dilepton excess in S-Au collisions cannot be explained by charm enhancement.Comment: 19 pages, 12 eps figures included. To be published in Z.Phys.

Inference on the tail process with application to financial time series modelling

To draw inference on serial extremal dependence within heavy-tailed Markov chains, Drees, Segers and Warcho{\l} [Extremes (2015) 18, 369--402] proposed nonparametric estimators of the spectral tail process. The methodology can be extended to the more general setting of a stationary, regularly varying time series. The large-sample distribution of the estimators is derived via empirical process theory for cluster functionals. The finite-sample performance of these estimators is evaluated via Monte Carlo simulations. Moreover, two different bootstrap schemes are employed which yield confidence intervals for the pre-asymptotic spectral tail process: the stationary bootstrap and the multiplier block bootstrap. The estimators are applied to stock price data to study the persistence of positive and negative shocks.Comment: 22 page