113 research outputs found
Measurement of inclusive D+-(s) photoproduction at HERA
No full textThe first measurement of inclusive D-s(+/-) photoproduction at HERA has been performed with the ZEUS detector for photon- proton centre-of-mass energies; 130 lt W lt 280 GeV The measured cross section for 3 lt p(perpendicular to)(Ds) lt 12 GeV and \eta(Ds)\ lt 1.5 is sigma(ep→DsX) = 3.79 +/- 0.59(stat.)(- 0.46)(+0.26)(syst.) +/- 0.94(br.) nb, where the last error arises from the uncertainty in the D-s(+/-) decay branching ratio. The measurements are compared with inclusive D*(+/-) photoproduction cross sections in the same kinematic region and with QCD calculations. The D-s(+/-) cross sections lie above a fixed-order next-to-leading order calculation and agree better with a tree-level O(alpha alpha(s)(3)) calculation that was tuned to describe the ZEUS D* (+/-) cross sections. The ratio of D-s(+/-) to D*(+/-) cross sections is 0.41 +/- 0.07(stat.)(- 0.05)(+0.03)(syst.) +/- 0.10 (br.). From this ratio, the strangeness-suppression factor in charm photoproduction, within the LUND string fragmentation model, has been calculated to be gamma(s)= 0.27 +/- 0.05 +/- 0.07(br.). The cross-section ratio and gamma(s) are in good agreement with those obtained in charm production in e(+)e(-) annihilation
W production and the search for events with an isolated high-energy lepton and missing transverse momentum at HERA
No full textA search for the leptonic decays of W bosons produced in the reaction e/sup +/p to e/sup +/W/sup +or-/X at a centre-of-mass energy of 300 GeV has been performed with the ZEUS detector at HERA using an integrated luminosity of 47.7 pb/sup -1/. Three events consistent with W to e nu decay are found, giving a cross section estimate of 0.9/sub -0.7//sup +1.0/+or-0.2 pb, in good agreement with the standard model prediction. The corresponding 95% C.L. upper limit on the cross section is 3.3 pb. A search for the decay W to mu nu has a smaller selection efficiency and yields no candidate events. Limits on the cross section for W production with large hadronic transverse momentum have been obtained. A search for high-transverse-momentum isolated tracks in events with large missing transverse momentum yields results in good agreement with standard model expectations, in contrast to a recent report by the H1 collaboration of the observation of an excess of such events
Measurement of the spin density matrix elements in exclusive electroproduction of rho0 mesons at HERA
No full textExclusive electroproduction of rho(o) mesons has been measured using the ZEUS detector at HERA in two Q(2) ranges, 0.25 lt Q(2) lt 0.85 GeV2 and 3 lt Q(2) lt 30 GeV2. The low-Q(2) data span the range 20 lt W lt 90 GeV; the high-Q(2) data cover the 40 lt W lt 120 GeV interval. Both samples extend up to four-momentum transfers of \t\ = 0.6 GeV2. The distribution in the azimuthal angle between the positron scattering plane and the rho(o) production plane shows a small but significant violation of s- channel helicity conservation, corresponding to the production of longitudinally polarised (i.e, helicity zero) rho(o) mesons from transverse photons. Measurements of the 15 combinations of spin-density matrix elements which completely define the angular distributions are presented and discussed
Measurement of dijet production in neutral current deep inelastic scattering at high Q(2) and determination of alpha(s)
No full textDijet production has been studied in neutral current deep inelastic e(+)p scattering for 470 lt Q(2) lt 20000 GeV2 with the ZEUS detector at HERA using an integrated luminosity of 38.4 pb(-1). Dijet differential cross sections are presented in a kinematic region where both theoretical and experimental uncertainties are small. Next-to-leading-order (NLO) QCD calculations describe the measured differential cross sections well. A QCD analysis of the measured dijet fraction as a function of Q(2) allows both a precise determination of alpha (s)(M-z) and a test of the energy-scale dependence of the strong coupling constant. A detailed analysis provides an improved estimate of the uncertainties of the NLO QCD cross sections arising from the parton distribution functions of the proton. The value of cu,(Mz), as determined from the QCD fit, is alpha (s)(M-z) = 0.1166 +/- 0.0019(stat.)(- 0.0033)(+0.0024)(exp.)(-0.0044)(+0.0057)(th.)
Cultural influences on consumer interactions in the context of electronic commerce
No full textThis thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Researchers and academics from diverse disciplines have highlighted the role of 'trust' for establishing and strengthening existing relationships between individuals and organisations in the commercial and the social context. Trust in the cultural context specifically, is credited with being the social 'glue' for sustaining bonds between members of cultural groups. The 'trust' phenomenon has become a 'hallmark' of success for organizations as they become more involved with Information Technology (IT). A precondition for trust to manifest is the natural presence of risk or uncertainties in a potential decision. Since the fears and risks associated with online transactions in the context of ecommerce are high, gaining a customer's trust becomes a must. Some studies have found the ingrained cultural values, which form an essential part of the cultural heritage of a person, to be influential in evoking an individual's trust. Various sources in the marketing and consumer behaviour literature have highlighted the role that religious subcultures play in the purchase decisions of their members. The customs, values, and norms set by a religious group are highly esteemed by its members. The objective of this thesis is to investigate if religious Web sites are more likely to instil trust in online fellow-members than their generic counterparts. From a HCI point of view, we can say that our research will investigate an "abstract" interface of e-commerce systems: the 'theological' interface of a commercial Web site. Consequently, we can also ascertain if religious consumers basing their purchasing decisions on 'religious' trust alone overlook more important issues such as the privacy and security problems associated with financial transactions performed over the Internet. Our empirical findings have discovered that conservative Muslims, who are not very familiar with the Internet, trust a Muslim Web site more than a Christian Web site and a generic Web site. In contrast, conservative Muslims with higher Internet experience were found to be more cautious. They based their 'trust' on more appropriate criteria such as the extent of privacy and security safeguards adopted by a Web site. A qualitative analysis of the post-experimental interviews that we conducted purports that Web-based trust develops with a company's good reputation, previous personal purchasing experiences, and through word-of-mouth recommendations from friends and family or peers. In light of our findings, we argue that the time experience gained in using the Internet plays a major role on how consumers perceive culturally or religiously oriented Web sites. We believe that less experienced Internet users are unaware of the security vulnerabilities inherent in the Internet environment. Therefore, we assume that they are context-blind: they do not differentiate between traditional and the digital marketing environments. Consequently, they would trust purchasing from an electronic store (Web site) in the same manner they would trust purchasing from a 'brick-and mortar' store. In contrast, experienced Internet users deem reputable Web sites adopting good security and privacy safeguards for online transactions to be trustworthier than Web sites designed with a 'religious' interface. We conclude that in the context of e-commerce, one cannot expect to establish a trustworthy commercial relationship based on religious trust alone. From the findings of this study, it has become apparent that the trait of strict religious affiliation seems to disappear in the context of e-commerce. The threats and risks inherent in online transactions seem to restructure the religious community by merging it into a traditional global community of e-consumers. When contemplating a purchase from a Web site, traditional e-consumers pay more attention to the company's reputation and the extent of data security measures adopted by a Web site rather than basing their purchase decisions on the religious affiliations and cultural values taught by parents and ancestors. Thus, Web sites aiming to sell products behind a 'religious' interface could become disappointed. Having said that, we reiterate that the time experience in using the Internet seems to play an influential role in how users' perceive cultural or religious Web sites.Funding was obtained from the Lybian Interest Section
Measurement of the diffractive cross section in deep inelastic scattering using ZEUS 1994 data
No full textThe DIS diffractive cross section, d sigma(gamma*p-->XN)(diff)/dM(X), has been measured in the mass range M(X) XN)(diff) (M(X), W, Q(2))/dM(X) proportional to W(adiff) with a(diff) = 0.507 +/- 0.034(stat)(-0.046)(+0.155) (syst) corresponding to a t-averaged pomeron trajectory of (P) = 1.127 +/- 0.009(stat)(-0.012)(+0.039) (syst) which is larger than (P) observed in hadron-hadron scattering The W dependence of the diffractive cross section is found to be the same as that of the total cross section for scattering of virtual photons on protons. The data are consistent with the assumption that the diffractive structure function F(2)(D(3)) factorizes according to x(P)F(2)(D(3))(x(p), beta, Q(2)) = (x(0)/x(P))(n)F(2)(D(2)) (beta, Q(2)). They are also consistent with QCD based models which incorporate factorization breaking. The rise of x(P)F(2)(D(3)) with decreasing x(P) and the weak dependence of F(2)(D(2)) On Q(2) suggest a substantial contribution from partonic interactions
Measurement of deeply virtual Compton scattering at HERA
No full textThe cross-section for deeply virtual Compton scattering in the reaction ep → egammap has been measured with the ZEUS detector at HERA using integrated luminosities of 95.0 pb(-1) of e(+) p and 16.7 pb(-1) of e(-) p collisions. Differential cross-sections are presented as a function of the exchanged- photon virtuality, Q(2), and the centre-of-mass energy, W, of the gamma*p system in the region 5 lt Q(2) lt 100 GeV2 and 40 lt W lt 140 GeV. The measured cross-sections rise steeply with increasing W. The measurements are compared to QCD-based calculations. (C) 2003 Elsevier B.V. All rights reserve
Search for strange quark matter produced in relativistic heavy ion collisions
No full textWe present the final results from Experiment 864 of a search for charged and neutral strange quark matter produced in interactions of 11.5 GeV/c per nucleon Au beams with Pt or Pb targets. Searches were made for strange quark matter with A greater than or equal to 5. Approximately 3 X 10(10) 10% most central collisions were sampled and no strangelet states with A less than or equal to 100 were observed. We find 90% confidence level upper limits of approximately 10(-8) per central collision for both charged and neutral strangelets. These limits are for strangelets with proper lifetimes greater than 50 ns. Also limits for H-0-d and pineut production are given. The above limits are compared with the predictions of various models. The yields of light nuclei from coalescence are measured and a penalty factor for the addition of one nucleon to the coalescing nucleus is determined. This is useful in gauging the significance of our upper limits and also in planning future searches for strange quark matter
Elastic and proton dissociative rho0 photoproduction at HERA
No full textElastic and proton-dissociative ρ0 photoproduction (γp → p0p, γp → ρ0N, respectively, with p0 → π+π-) has been studied in ep interactions at HERA for photon-proton centre-of-mass energies in the range 50 < W < 100 GeV and for |t| < 0.5 GeV2, where t is the square of the four-momentum transfer at the proton vertex; the results on the proton-dissociative reaction are presented for masses of the dissociated proton system in the range M2N < 0.1W2. For the elastic process, the π+π- invariant mass spectrum has been investigated as a function of t. As in fixed target experiments, the ρ0 resonance shape is asymmetric; this asymmetry decreases with increasing |t|, as expected in models in which the asymmetry is ascribed to the interference of resonant and non-resonant π+π- production. The cross section has been studied as a function of W; a fit to the resonant part with the form Wa gives a = 0.16 ± 0.06 (stat.) +0.11-0.15 (syst.). The resonant part of the γp → π+π-p cross section is 11.2 ± 0.1 (stat.) +1.1-1.2 (syst.) μb at 〈W〉 = 71.7 GeV. The t dependence of the cross section can be described by a function of the type Aρ exp (-bρ|t| + cρt2) with bρ = 10.9 ± 0.3 (stat.) +1.0-0.5 (syst.) GeV-2 and cρ = 2.7 ± 0.9 (stat.) +1.9-1.7 (syst.) GeV-4. The t dependence has also been studied as a function of W and a value of the slope of the pomeron trajectory α IP′ = 0.23 ± 0.15 (stat.) +0.10-0.07 (syst.) GeV-2 has been deduced. The ρ0 spin density matrix elements r0400 r041-1 and ℜe[r0410] have been measured and found to be consistent with expectations based on s-channel helicity conservation. For proton-dissociative π+π- photoproduction in the ρ0 mass range, the distributions of the two-pion invariant mass, W and the polar and azimuthal angles of the pions in the helicity frame are the same within errors as those for the elastic process. The t distribution has been fitted to an exponential function with a slope parameter 5.8 ± 0.3 (stat.) ± 0.5 (syst.) GeV-2. The ratio of the elastic to proton-dissociative ρ0 photoproduction cross section is 2.0 ± 0.2 (stat.) ± 0.7 (syst.)
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