Electromagnetic radiation hardness of diamond detectors

The behavior of artificially grown CVD diamond films under intense electromagnetic radiation has been studied. The properties of irradiated diamond samples have been investigated using the method of thermally stimulated current and by studying their charge collection properties. Diamonds have been found to remain unaffected after doses of 6.8 MGy of 10 keV photons and 10 MGy of MeV-range photons. This observation makes diamond an attractive detector material for a calorimeter in the very forward region of the proposed TESLA detector. (orig.)Available from TIB Hannover: RA 2999(01-117) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

The charge collection properties of CVD diamond

The charge collection properties of CVD diamond have been investigated with ionising radiation. In this study two CVD diamond samples, prepared with electrical contacts have been used as solid state ionisation chambers. The diamonds have been studied with beta particles and 10 keV photons, providing a homogeneous ionisation density and with protons and alpha particles which are absorbed in a thin surface layer. For the latter case a strong decrease of the signal as function of time is observed, which is attributed to polarisation effects inside the diamond. Spatially resolved measurements with protons show a large variation of the charge collection efficiency, whereas for photons and minimum ionising particles the response is much more uniform and in the order of 18%. These results indicate that the applicability of CVD diamond as a position sensitive particle detector depends on the ionisation type and appears to be promising for homogeneous ionisation densities as provided by relativistic charged particles. (orig.)25 refs.Available from TIB Hannover: RA 2999(98-027) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Measurement of elastic J/#psi# photoproduction at HERA

The reaction #gamma# p #-># J/#psi#p has been studied in ep interactions using the ZEUS detector at HERA. The cross section for elastic J/#psi# photoproduction has been measured as a function of the photon-proton centre of mass energy W in the range 40 < W < 140 GeV at a median photon virtuality Q"2 of 5 x 10"-"5 GeV"2. The photoproduction cross section, #sigma#_#gamma#_p_#->#_J_/_#psi#_p, is observed to rise steeply with W. A fit to the data presented in this paper to determine the parameter #delta# in the form #sigma#_#gamma#_p_#->#_J_/_#psi#_p #propor to# W"#delta# yields the value #delta# = 0.92 #+-# 0.14 #+-# 0.10. The differential cross section d#sigma#/d vertical stroke t vertical stroke is presented over the range vertical stroke t vertical stroke < 1.0 GeV"2 where t is the square of the four-momentum exchanged at the proton vertex. d#sigma#/d vertical stroke t vertical stroke falls exponentially with a slope parameter of 4.6 #+-# 0.4"+"0"."4_-_0_._6 GeV"-"2. The measured decay angular distributions are consistent with s-channel helicity conservation. (orig.)Available from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Fragmentation functions at ZEUS

The scaled momentum spectra of final state charged hadrons produced in Deep Inelastic Scattering in the ranges 10 < Q(2) < 1280 GeV2 and 6 . 10(-4) < x(Bjorken) < 5 . 10(-2) have been measured in the current region of the Breit frame using the ZEUS detector. The evolution with Q(2) of the scaled momentum, x(p) = 2p(Breit)/Q, has been investigated and preliminary results are presented which show evidence for scaling violations and support for the universality of quark fragmentation

Jet shapes at HERA

The shape of jets produced in quasi-real photon-proton interactions and deep inelastic positron-proton scattering (DIS) at high Q(2) (Q(2) > 100 GeV2) has been measured with the ZEUS detector at HERA. Jets with transverse energies E-T(jet) > 14 GeV and pseudorapidities (eta(jet)) in the range -1 collisions, and are similar to those in e(+)e(-) interactions

D* and J/psi inelastic photoproduction at HERA

Cross sections of D* and J/Psi inelastic photoproduction were measured by the ZEUS detector at HERA collider. Comparisons of the data with calculations in NLO pQCD and SHA QCD approaches were made

Measurement of the proton structure function F-2 and the total gamma*p cross-section at low Q(2) and low x

The ZEUS-experiment at HERA has significantly enhanced the kinematic coverage for low Q(2) and low x inelastic e(+)p --> e(+) X scattering with an upgrade of the ZEUS-detector in 1995 which extends the acceptance for small positron scattering angles. The upgrade included the modification of the beam pipe with low mass exit windows and the installation of a small electromagnetic sampling calorimeter, the Beam Pipe Calorimeter (BPC), to explore the region in Q(2) of 0.11 less than or equal to Q(2) less than or equal to 0.65 GeV2. A shift of two rear uranium calorimeter (RCAL) modules and the small rear tracking detector (SRTD) closer to the beam together with a data sample taken with a shifted event vertex extended the Q(2) coverage of the main detector down to 0.6 GeV2. Both data sets have been used to measure the proton structure function F-2 and the total virtual photonproton gamma*p cross-section. Results are presented for 0.11 less than or equal to Q(2) less than or equal to 6.10 GeV2 and 2.10(-6) less than or equal to x less than or equal to 7.10(-4) along with a comparison to various models

Measurement of dijets in DIS and comparison to NLO calculations

We report a measurement of the dijet production cross section in neutral current deep inelastic scattering with the ZEUS detector at the HERA ep collider. Dijet events are identified with the cone algorithm and the results are compared to next-to-leading order perturbative QCD calculations. The systematic uncertainties of both the measurement and the calculation we discussed

Diffractive production of charm and jets at HERA

Measurements are presented of dijet cross sections in diffractive photoproduction and of D*(+/-) production in diffractive deep inelastic scattering at HERA. A combined QCD analysis of the diffractive dijet cross sections and diffractive structure function results leads to a picture in which the pomeron has a substantial gluon component with a hard momentum spectrum

High Q(2) events in ep collisions

Using the ZEUS detector at HERA, we have studied the reaction e(+) p --> e(+) X for Q(2) > 5000 GeV2 with a 20.1 pb(-1) data sample collected during the years 1994 to 1996. For Q(2) below 15000 GeV2, the data are in good agreement with Standard Model expectations. For Q(2) > 35000 GeV2, two events are observed while 0.145 +/- 0.013 events are expected. For x > 0.55 and y > 0.25, four events are observed where 0.91 +/- 0.08 events are expected. The observed excess above Standard Model expectations is particularly interesting because it occurs in a previously unexplored kinematic region