Showing papers by "Roland Horisberger published in 2001"

Deep inelastic inclusive e p scattering at low x and a determination of alpha(s)

Abstract: A precise measurement of the inclusive deep-inelastic e^+p scattering cross section is reported in the kinematic range 1.5 = Q^2 =150 GeV^2 and 3*10^(-5) = x =0.2. The data were recorded with the H1 detector at HERA in 1996 and 1997, and correspond to an integrated luminosity of 20 pb^(-1).The double differential cross section, from which the proton structure function F_2(x,Q^2) and the longitudinal structure function F_L(x,Q^2) are extracted, is measured with typically 1% statistical and 3% systematic uncertainties. The measured partial derivative (dF_2(x,Q^2)/dln Q^2)_x is observed to rise continuously towards small x for fixed Q^2. The cross section data are combined with published H1 measurements at high Q^2 for a next-to-leading order DGLAP QCD analysis.The H1 data determine the gluon momentum distribution in the range 3*10^(-4) = x =0.1 to within an experimental accuracy of about 3% for Q^2 =20 GeV^2. A fit of the H1 measurements and the mu p data of the BCDMS collaboration allows the strong coupling constant alpha_s and the gluon distribution to be simultaneously determined. A value of alpha _s(M_Z^2)=0.1150+-0. 0017 (exp) +0.0009-0.0005 (model) is obtained in NLO, with an additional theoretical uncertainty of about +-0.005, mainly due to the uncertainty of the renormalisation scale.

Radiation hard silicon detectors—developments by the RD48 (ROSE) collaboration

Abstract: The RD48 (ROSE) collaboration has succeeded to develop radiation hard silicon detectors, capable to withstand the harsh hadron fluences in the tracking areas of LHC experiments. In order to reach this objective, a defect engineering technique was employed resulting in the development of Oxygen enriched FZ silicon (DOFZ), ensuring the necessary O-enrichment of about 2×1017 O/cm3 in the normal detector processing. Systematic investigations have been carried out on various standard and oxygenated silicon diodes with neutron, proton and pion irradiation up to a fluence of 5×1014 cm−2 (1 MeV neutron equivalent). Major focus is on the changes of the effective doping concentration (depletion voltage). Other aspects (reverse current, charge collection) are covered too and the appreciable benefits obtained with DOFZ silicon in radiation tolerance for charged hadrons are outlined. The results are reliably described by the “Hamburg model”: its application to LHC experimental conditions is shown, demonstrating the superiority of the defect engineered silicon. Microscopic aspects of damage effects are also discussed, including differences due to charged and neutral hadron irradiation.

Developments for radiation hard silicon detectors by defect engineering—results by the CERN RD48 (ROSE) Collaboration

Abstract: This report summarises the final results obtained by the RD48 collaboration. The emphasis is on the more practical aspects directly relevant for LHC applications. The report is based on the comprehensive survey given in the 1999 status report (RD48 3rd Status Report, CERN/LHCC 2000-009, December 1999), a recent conference report (Lindstrom et al. (RD48), and some latest experimental results. Additional data have been reported in the last ROSE workshop (5th ROSE workshop, CERN, CERN/LEB 2000-005). A compilation of all RD48 internal reports and a full publication list can be found on the RD48 homepage (http://cern.ch/RD48/). The success of the oxygen enrichment of FZ-silicon as a highly powerful defect engineering technique and its optimisation with various commercial manufacturers are reported. The focus is on the changes of the effective doping concentration (depletion voltage). The RD48 model for the dependence of radiation effects on fluence, temperature and operational time is verified; projections to operational scenarios for main LHC experiments demonstrate vital benefits. Progress in the microscopic understanding of damage effects as well as the application of defect kinetics models and device modelling for the prediction of the macroscopic behaviour has also been achieved but will not be covered in detail.

A pixel read-out chip for the PILATUS project

Abstract: For the protein crystallography beamlime of the Swiss Light Source (SLS), which will be operational in summer 2001, the PILATUS detector ( PI xe L A ppara TU s for the S LS) is currently being built. The goal of the PILATUS project is a hybrid pixel system with a size of 40×40 cm 2 having 2000×2000 pixels. The detector will be operated in single photon counting mode for 12 keV X-rays. The prototype pixel read-out chip has a noise of 75 e − with sensor, a low threshold dispersion and a maximum count rate of 1 MHz/pixel. Due to the expected radiation dose in operation at the beamline, the chip is designed in radiation hard DMILL technology.

Diffractive jet production in deep-inelastic e+p collisions at HERA

Abstract: A measurement is presented of dijet and 3-jet cross sections in low-\(|t|\) diffractive deep-inelastic scattering interactions of the type \(ep \rightarrow eXY\), where the system X is separated by a large rapidity gap from a low-mass baryonic system Y. Data taken with the H1 detector at HERA, corresponding to an integrated luminosity of 18.0 pb\(^{-1}\), are used to measure hadron level single and double differential cross sections for \(4 4 \rm GeV\). The energy flow not attributed to jets is also investigated. The measurements are consistent with a factorising diffractive exchange with trajectory intercept close to 1.2 and tightly constrain the dominating diffractive gluon distribution. Viewed in terms of the diffractive scattering of partonic fluctuations of the photon, the data require the dominance of \(q\overline{q}g\) over \(q\overline{q}\) states. Soft colour neutralisation models in their present form cannot simultaneously reproduce the shapes and the normalisations of the differential cross sections. Models based on 2-gluon exchange are able to reproduce the shapes of the cross sections at low \(x_\mathbb{P}\) values.

Photoproduction with a leading proton at HERA

Abstract: The total cross section for the photoproduction process with a leading proton in the final state has been measured at γp centre-of-mass energies W of 91, 181 and 231 GeV. The measured cross sections apply to the kinematic range with the transverse momentum of the scattered proton restricted to pT⩽0.2 GeV and 0.68⩽z⩽0.88, where z=Ep′/Ep is the scattered proton energy normalised to the beam energy. The cross section dσγp→Xp′(W,z)/dz is observed to be independent of W and z within the measurement errors and amounts to (8.05±0.06 ( stat )±0.89 ( syst )) μb on average. The data are well described by a Triple Regge model in which the process is mediated by a mixture of exchanges with an effective Regge trajectory of intercept α i (0)=0.33±0.04 ( stat )±0.04 ( syst ) . The total cross section for the interaction of the photon with this mixture (γαi→X) can be described by an effective trajectory of intercept α k (0)=0.99±0.01 ( stat )±0.05 ( syst ) . Predictions based on previous triple Regge analyses of pp→pX data assuming vertex factorisation are broadly consistent with the γp data. The measured cross sections are compared with deep inelastic scattering leading proton data in the same region of z and pT for photon virtuality Q 2 >2.5 GeV 2 . The ratio of the cross section for leading proton production to the total cross section is found to rise with Q2.

Searches at HERA for squarks in R-parity violating supersymmetry

Abstract: A search for squarks in R-parity violating supersymmetry is performed in e^+p collisions at HERA at a centre of mass energy of 300 GeV, using H1 data corresponding to an integrated luminosity of 37 pb^(-1). The direct production of single squarks of any generation in positron-quark fusion via a Yukawa coupling lambda' is considered, taking into account R-parity violating and conserving decays of the squarks. No significant deviation from the Standard Model expectation is found. The results are interpreted in terms of constraints within the Minimal Supersymmetric Standard Model (MSSM), the constrained MSSM and the minimal Supergravity model, and their sensitivity to the model parameters is studied in detail. For a Yukawa coupling of electromagnetic strength, squark masses below 260 GeV are excluded at 95% confidence level in a large part of the parameter space. For a 100 times smaller coupling strength masses up to 182 GeV are excluded.

A CVD-diamond based beam profile monitor for undulator radiation

Abstract: First results obtained with prototypes of a new type of beam profile monitor based on semi-transparent CVD-diamond are presented. The devices consists of a few micrometer thin membrane on a Si-substrate. Ti/Al-pixel are generated lithographically on the membrane while the signal wires are deposited on a dielectric in order to minimise signal pickup. Synchrotron radiation tests at 8 keV showed good signal homogeneity, spatial resolution and linearity for low resistivity diamond membranes. Considerable difficulties were encountered in the test of a detector grade diamond membrane. They are most likely related to enhanced surface conductivity and capacitive effects.

Design and test of pixel sensors for the CMS experiment

Abstract: The Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC) will have a silicon pixel detector as its innermost trackingdevice. The pixel system will be exposed to the harsh radiation environment of the LHC. Prototype sensors have been designed to meet the specifications of the CMS experiment. The sensors are n + –n devices to allow partial depletion operation after bulk type inversion. The isolation of the n + pixels is provided through a novel double open p-ring design that allows sensors testing before bump bonding and flip chipping. The prototype wafers contain a variety of p-stop designs and are fabricated by two vendors on different bulk substrates includingoxyg enated silicon. A study of the static measurement of the prototype sensors before irradiation is presented. # 2001 Elsevier Science B.V. All rights reserved.

Readout architectures for Pixel detectors

Abstract: The use of pixel detectors in high rate collider experiments requires the recording and readout of large amounts of data. The architectural choices for managing these large data flows are reviewed and illustrated on specific pixel projects.