arXiv subjects

K. Desch

Publications and source records attributed to K. Desch.

54 records · Page 3Linked to original sources

arXiv2006

Readout of GEM Detectors Using the Medipix2 CMOS Pixel Chip

We have operated a Medipix2 CMOS readout chip, with amplifying, shaping and charge discriminating front-end electronics integrated on the pixel-level, as a highly segmented direct charge collecting anode in a three-stage gas electron multiplier (Triple-GEM) to detect the ionization from $^{55}$Fe X-rays and electrons from $^{106}$Ru. The device allows to perform moderate energy spectroscopy measurements (20 % FWHM at 5.9 keV $X$-rays) using only digital readout and two discriminator thresholds. Being a truly 2D-detector, it allows to observe individual clusters of minimum ionizing charged particles in $Ar/CO_2$ (70:30) and $He/CO_2$ (70:30) mixtures and to achieve excellent spatial resolution for position reconstruction of primary clusters down to $\sim 50 μm$, based on the binary centroid determination method.

physics.ins-det↗

arXiv2006

Towards the European strategy for particle physics: the Briefing Book

This document was prepared as part of the briefing material for the Workshop of the CERN Council Strategy Group, held in DESY Zeuthen from 2nd to 6th May 2006. It gives an overview of the physics issues and of the technological challenges that will shape the future of the field, and incorporates material presented and discussed during the Symposium on the European Strategy for Particle Physics, held in Orsay from 30th January to 2nd February 2006, reflecting the various opinions of the European community as recorded in written submissions to the Strategy Group and in the discussions at the Symposium.

hep-ph↗

arXiv2006

The Challenge of Determining SUSY Parameters in Focus-Point-Inspired Cases

We discuss the potential of combined LHC and ILC experiments for SUSY searches in a difficult region of the parameter space, in which all sfermion masses are above the TeV scale. Precision analyses of cross sections of light chargino production and forward--backward asymmetries of decay leptons and hadrons at the ILC, together with mass information on \tildeχ^0_2 and squarks from the LHC, allow us to fit rather precisely the underlying fundamental gaugino/higgsino MSSM parameters and to constrain the masses of the heavy virtual sparticles. For such analyses the complete spin correlations between the production and decay processes have to be taken into account. We also took into account expected experimental uncertainties.

hep-ph↗

arXiv2006

Les Houches "Physics at TeV Colliders 2005'' Beyond the Standard Model working group: summary report

The work contained herein constitutes a report of the "Beyond the Standard Model'' working group for the Workshop "Physics at TeV Colliders", Les Houches, France, 2-20 May, 2005. We present reviews of current topics as well as original research carried out for the workshop. Supersymmetric and non-supersymmetric models are studied, as well as computational tools designed in order to facilitate their phenomenology.

hep-ph↗

arXiv2005

Supersymmetry Parameter Analysis: SPA Convention and Project

High-precision analyses of supersymmetry parameters aim at reconstructing the fundamental supersymmetric theory and its breaking mechanism. A well defined theoretical framework is needed when higher-order corrections are included. We propose such a scheme, Supersymmetry Parameter Analysis SPA, based on a consistent set of conventions and input parameters. A repository for computer programs is provided which connect parameters in different schemes and relate the Lagrangian parameters to physical observables at LHC and high energy e+e- linear collider experiments, i.e., masses, mixings, decay widths and production cross sections for supersymmetric particles. In addition, programs for calculating high-precision low energy observables, the density of cold dark matter (CDM) in the universe as well as the cross sections for CDM search experiments are included. The SPA scheme still requires extended efforts on both the theoretical and experimental side before data can be evaluated in the future at the level of the desired precision. We take here an initial step of testing the SPA scheme by applying the techniques involved to a specific supersymmetry reference point.

hep-ph↗

arXiv2005

SUSY Parameter Measurements with Fittino

This article presents the results of a realistic global fit of the Lagrangian parameters of the Minimal Supersymmetric Standard Model with no assumptions on the SUSY breaking mechanism using the fit program Fittino. The fit is performed using the precision of future mass measurements of superpartners at the LHC and mass and polarized topological cross-section measurements at the ILC. Higher order radiative corrections are accounted for wherever possible to date. Results are obtained for a modified SPS1a MSSM benchmark scenario (general MSSM without assumptions on the breaking mechanism) and for a specific mSUGRA scenario. Exploiting a simulated annealing algorithm, a stable result is obtained without any {\it a priori} assumptions on the fit parameters. Most of the Lagrangian parameters can be extracted at the percent level or better if theoretical uncertainties are neglected. Neither LHC nor ILC measurements alone will be sufficient to obtain a stable result.

hep-ph↗

arXiv2005

The role of polarized positrons and electrons in revealing fundamental interactions at the Linear Collider

The proposed International Linear Collider (ILC) is well-suited for discovering physics beyond the Standard Model and for precisely unraveling the structure of the underlying physics. The physics return can be maximized by the use of polarized beams. This report shows the paramount role of polarized beams and summarizes the benefits obtained from polarizing the positron beam, as well as the electron beam. The physics case for this option is illustrated explicitly by analyzing reference reactions in different physics scenarios. The results show that positron polarization, combined with the clean experimental environment provided by the linear collider, allows to improve strongly the potential of searches for new particles and the identification of their dynamics, which opens the road to resolve shortcomings of the Standard Model. The report also presents an overview of possible designs for polarizing both beams at the ILC, as well as for measuring their polarization.

hep-ph↗

arXiv2004

Physics Interplay of the LHC and the ILC

Physics at the Large Hadron Collider (LHC) and the International e+e- Linear Collider (ILC) will be complementary in many respects, as has been demonstrated at previous generations of hadron and lepton colliders. This report addresses the possible interplay between the LHC and ILC in testing the Standard Model and in discovering and determining the origin of new physics. Mutual benefits for the physics programme at both machines can occur both at the level of a combined interpretation of Hadron Collider and Linear Collider data and at the level of combined analyses of the data, where results obtained at one machine can directly influence the way analyses are carried out at the other machine. Topics under study comprise the physics of weak and strong electroweak symmetry breaking, supersymmetric models, new gauge theories, models with extra dimensions, and electroweak and QCD precision physics. The status of the work that has been carried out within the LHC / LC Study Group so far is summarised in this report. Possible topics for future studies are outlined.

hep-ph↗

arXiv2004

Study of Higgs Boson Pair Production at Linear Collider

We study the potential of the TESLA linear collider operated at a center-of-mass energy of 500 to 1000 GeV for the measurement of the neutral Higgs boson properties within the framework of the MSSM. The process of associated Higgs boson production with subsequent decays of Higgs bosons into b-quark and tau-lepton pairs is considered. An integrated luminosity of 500 fb^{-1} is assumed at each energy. The Higgs boson masses and production cross sections are measured by reconstructing the bbbb and bbττfinal states. The precision of these measurements is evaluated in dependence of the Higgs boson masses. Under the assumed experimental conditions a statistical accuracy ranging from 0.1 to 1.0 GeV is achievable on the Higgs boson mass. The topological cross section σ(e+e- -> HA -> bbbb) can be determined with the relative precision of 1.5 - 6.6 % and cross sections σ(e+e- -> HA -> bb ττ) and σ(e+e- -> HA -> ττbb) with precision of 4 - 30 %. Constraints on the Higgs boson widths can be set exploiting bbττchannel. The 5σdiscovery limit corresponds to the Higgs mass of around 385 GeV for the degenerate Higgs boson masses in the HA -> bbbb channel at \sqrts = 800 GeV with integrated luminosity of 500 fb^{-1}. The potential of the Higgs mass determination for the benchmark point SPS 1a for the process e+e- -> HA -> bbbb at \sqrt{s} = 1 TeV and luminosity 1000 fb^{-1} is investigated.

hep-ph↗

arXiv2004

Susy searches in combined LHC/LC analyses

We present a case study for the synergy of combined LHC and LC analyses in Susy searches in which simultaneous running of both machines is very important. In this study only light non-coloured Susy particles are accessible at a Linear Collider with an initial energy of $\sqrt{s}=500$ GeV. Nevertheless the precise analysis at the LC leads to an accurate Susy parameter determination and prediction of heavy Susy particles. Providing these LC results as input for the LHC analyses could be crucial for the identification of signals resulting in a direct measurement of the heavy neutralinos. The interplay of the LHC and LC will thus provide an important consistency test of the underlying model.

hep-ph↗

arXiv2004

LHC/LC Interplay in the MSSM Higgs Sector

The interplay of prospective experimental information from both the Large Hadron Collider (LHC) and the Linear Collider (LC) in the investigation of the MSSM Higgs sector is analyzed in the SPS~1a and SPS 1b benchmark scenarios. Combining LHC information on the heavy Higgs states of the MSSM with precise measurements of the mass and branching ratios of the lightest CP-even Higgs boson at the LC provides a sensitive consistency test of the MSSM. This allows to set bounds on the trilinear coupling A_t. In a scenario where LHC and LC only detect one light Higgs boson, the prospects for an indirect determination of M_A are investigated. In particular, the impact of the experimental errors of the other SUSY parameters is analyzed in detail. We find that a precision of about 20% (30%) can be achieved for M_A = 600 (800) GeV.

hep-ph↗

arXiv2004

Les Houches "Physics at TeV Colliders 2003" Beyond the Standard Model Working Group: Summary Report

The work contained herein constitutes a report of the ``Beyond the Standard Model'' working group for the Workshop "Physics at TeV Colliders", Les Houches, France, 26 May--6 June, 2003. The research presented is original, and was performed specifically for the workshop. Tools for calculations in the minimal supersymmetric standard model are presented, including a comparison of the dark matter relic density predicted by public codes. Reconstruction of supersymmetric particle masses at the LHC and a future linear collider facility is examined. Less orthodox supersymmetric signals such as non-pointing photons and R-parity violating signals are studied. Features of extra dimensional models are examined next, including measurement strategies for radions and Higgs', as well as the virtual effects of Kaluza Klein modes of gluons. An LHC search strategy for a heavy top found in many little Higgs model is presented and finally, there is an update on LHC $Z'$ studies.

hep-ph↗

arXiv2004

Probing the CP nature of the Higgs boson at linear colliders with tau spin correlations; the case of mixed scalar--pseudoscalar couplings

The prospects for the measurement of the pseudoscalar admixture in the h-tau-tau coupling to a Standard Model Higgs boson of 120 GeV mass are discussed in a quantitative manner e+ e- collisions of 350 GeV centre-of-mass energy. Specific angular distributions in the h --> tau tau; tau --> rho nu decay chain can be used to probe mixing angles of scalar--pseudoscalar h-tau-tau couplings. In the discussion of the feasibility of the method, assumptions on the properties of a future detector for an e+ e- linear collider such as TESLA are used. The Standard Model Higgsstrahlung production process is taken as an example. For the expected performance of a typical Linear Collider set-up, the sensitivity of a measurement of the scalar--pseudoscalar mixing angle turned out to be 6 degree. It will be straightforward to apply our results to estimate the sensitivity of a measurement, in cases another scenario of the Higgs boson sector (Standard Model or not) is chosen by nature. The experimental error of the method is expected to be limited by the statistics.

hep-ph↗

arXiv2003

Higgs Boson Precision Studies at a Linear Collider

This report summarizes the progress in the study of Higgs physics at a future linear electron positron collider at center-of-mass energies up to about 1000 GeV and high luminosity. After the publication of the TESLA Technical Design Report, an extended ECFA/DESY study on linear collider physics and detectors was performed. The paper summarizes the status of the studies with main emphasis on recent results obtained in the course of the workshop.

hep-ph↗

arXiv2003

SUSY Parameter Determination in Combined Analyses at LHC/LC

We demonstrate how the interplay of a future e^+e^- LC at its first stage with sqrt{s} sim 500 GeV and of the LHC could lead to a precise determination of the fundamental SUSY parameters in the gaugino/higgsino sector without assuming a specific supersymmetry breaking scheme. We demonstrate this for the benchmark scenario SPS1a, taking into account realistic errors for the masses and cross sections measured at the LC with polarised beams, including errors coming from polarisation measurements, and mass measurements at the LHC. The results clearly demonstrate the complementarity of the LHC and LC, and the benefit from the joint analyses of their data.

hep-ph↗

arXiv2003

Measuring the Higgs boson parity at a Linear Collider using the tau impact parameter and tau --> rho nu decay

We demonstrate that a measurement of the impact parameter in one-prong tau decay can be useful for the determination of the Higgs boson parity in the H/A --> tau tau; tau --> rho nu decay chain. We have estimated that for a detection set-up such as TESLA, use of the information from the tau impact parameter can improve the significance of the measurement of the parity of the Standard Model 120 GeV Higgs boson to 4.5 sigma, and in general by factor of about 1.5 with respect to the method where this information is not used. We also show that the variation in the assumption on the precision of the measurement of the impact parameter and/or pi's momenta does not affect the sensitivity of the method. This is because the method remains limited by the type of twofold ambiguity in reconstructing the tau momentum.

hep-ph↗

arXiv2002

The Precision of Higgs Boson Measurements and Their Implications

The prospects for a precise exploration of the properties of a single or many observed Higgs bosons at future accelerators are summarized, with particular emphasis on the abilities of a Linear Collider (LC). Some implications of these measurements for discerning new physics beyond the Standard Model (SM) are also discussed.