Measurement of the diffractive structure function in deep inelastic scattering at HERA

This paper presents an analysis of the inclusive properties of diffractive deep inelastic scattering events produced in $ep$ interactions at HERA. The events are characterised by a rapidity gap between the outgoing proton system and the remaining hadronic system. Inclusive distributions are presented and compared with Monte Carlo models for diffractive processes. The data are consistent with models where the pomeron structure function has a hard and a soft contribution. The diffractive structure function is measured as a function of \xpom, the momentum fraction lost by the proton, of $\beta$, the momentum fraction of the struck quark with respect to \xpom, and of $Q^2$. The \xpom dependence is consistent with the form \xpoma where $a~=~1.30~\pm~0.08~(stat)~^{+~0.08}_{-~0.14}~(sys)$ in all bins of $\beta$ and $Q^2$. In the measured $Q^2$ range, the diffractive structure function approximately scales with $Q^2$ at fixed $\beta$. In an Ingelman-Schlein type model, where commonly used pomeron flux factor normalisations are assumed, it is found that the quarks within the pomeron do not saturate the momentum sum rule.Comment: 36 pages, latex, 11 figures appended as uuencoded fil

Observation of hard scattering in photoproduction events with a large rapidity gap at HERA

Events with a large rapidity gap and total transverse energy greater than 5 GeV have been observed in quasi-real photoproduction at HERA with the ZEUS detector. The distribution of these events as a function of the $\gamma p$ centre of mass energy is consistent with diffractive scattering. For total transverse energies above 12 GeV, the hadronic final states show predominantly a two-jet structure with each jet having a transverse energy greater than 4 GeV. For the two-jet events, little energy flow is found outside the jets. This observation is consistent with the hard scattering of a quasi-real photon with a colourless object in the proton.Comment: 19 pages, latex, 4 figures appended as uuencoded fil

Measurement of Charged and Neutral Current e-p Deep Inelastic Scattering Cross Sections at High Q2

Deep inelastic e-p scattering has been studied in both the charged current (CC) and neutral current (NC) reactions at momentum transfers squared Q(2) above 400 GeV2 using the ZEUS detector at the HERA ep collider. The CC and NC total cross sections, the NC to CC cross section ratio, and the differential cross sections d sigma/dQ(2) are presented. From the Q(2) dependence of the CC cross section, the mass term in the CC propagator is determined to be M(W) = 76 +/- 16 +/- 13 GeV

Kalibration des elektromagnetischen Teils des ZEUS-Kalorimeters mit Elektronen

SIGLEAvailable from TIB Hannover: RN 4852(91-25) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Charm-Produktion in ep-Kollisionen mit dem ZEUS-Detektor bei HERA

The production of charmed mesons in ep collisions has been studied with the 1993 data from the ZEUS detector at HERA. Charm quarks are produced by the photoproduction process of photon-gluon fusion. Analysing a data sample corresponding to an integrated luminosity of 486 nb"-"1 D*(2010)"#+-# mesons have been found in two decay channels, D*"+#->#D"0#pi#"+#->#(K"-#pi#"+)#pi#"+ (+c.c.) and D*"+#->#D"0#pi#"+#->#((K_S"0#->##pi#"+#pi#"-)#pi#"+#pi#"-)#pi#"+. Clear signals in the mass difference #DELTA#M=M(D*)-M(D"0) as well as in the M(D"0) distribution are found. The ep cross section for D*"#+-# production with Q"2<4 GeV"2 and 115<W<275 GeV has been determined to be (32#+-#7_-_9"+"4) nb in the kinematic region #left brace#p_T(D*)#>=#1.7 GeV, vertical stroke #eta#(D*) vertical stroke <1.5#right brace#. Extrapolating outside this region, assuming a mass of the charm quark of 1.5 GeV, the ep charm cross section is estimated to be #sigma#(ep#->#c anti cX)=(0.45#+-#0.11_-_0_._2_1"+"0"."3"5#mu#b) at #sq root#(s)=296 GeV and 115<W<275 GeV. The average #gamma#p charm cross section #sigma#(#gamma#p#->#c anti cX) is found to be (6.3#+-#2.2_-_2_._9"6"."1) #mu#b in the range 115<W<205 GeV and (16.9#+-#5.2_-_8_._4"+"1"3"."1) #mu#b in the range 205<W<275 GeV. (orig.)SIGLEAvailable from TIB Hannover: RN 8452(95-06) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman