1. 
 Adloff, C, et al.
(författare)

Measurement of dijet cross sections in photoproduction at HERA
 2002

Ingår i: European Physical Journal C.  Springer.  14346044. ; 25:1, s. 1323

Tidskriftsartikel (refereegranskat)abstract
 Dijet cross sections as functions of several jet observables are measured in photoproduction using the HI detector at HERA. The data sample comprises e(+)p data with an integrated luminosity of 319 pb(1). Jets are selected using the inclusive k(perpendicular to) algorithm with a minimum transverse energy of 25 GeV for the leading jet. The phase space covers longitudinal proton momentum fraction x(p) and photon longitudinal momentum fraction x(gamma) in the ranges 0.05 < x(p) < 0.6 and 0.1 < x(gamma) < 1. The predict ions of nexttoleading order perturbative QCD, including recent photon and proton parton densities, are found to be compatible with the data in a wide kinematical range.


2. 
 Adloff, C, et al.
(författare)

A measurement of the t dependence of the helicity structure of diffractive rho meson electroproduction at HERA
 2002

Ingår i: Physics Letters B.  Elsevier.  03702693. ; 539:12, s. 2539

Tidskriftsartikel (refereegranskat)abstract
 The helicity structure of the diffractive electroproduction of rho mesons, e + p > e + rho + Y, is studied in a previously unexplored region of large fourmomentum transfer squared at the proton vertex, t: 0 < t' < 3 GeV2, where t' =  min. The data used are collected with the HI detector at HERA in the kinematic domain 2.5 < Q(2) < 60 GeV2, 40 < W < 120 GeV No t dependence of the r(00)(04) spin density matrix element is found. A significant t dependent helicity nonconservation from the virtual photon to the rho meson is observed for the spin density matrix element combinations r(00)(5) + 2r(11)(5) and r(00)(1) + 2r(11)(1). These t dependences are consistently described by a perturbative QCD model based on the exchange of two gluons.


3. 
 Adloff, C, et al.
(författare)

Energy flow and rapidity gaps between jets in photoproduction at HERA
 2002

Ingår i: European Physical Journal C.  Springer.  14346044. ; 24:4, s. 517527

Tidskriftsartikel (refereegranskat)abstract
 Dijet events in photonproton collisions in which there is a large pseudorapidity separation, Deltaeta > 2.5 between the two highest ET jets are studied with the H1 detector at HERA. The inclusive dijet cross sections are measured as functions of the longitudinal momentum fractions of the proton and photon which participate in the production of the jets, x(p)(jets) and x(gamma)(jets) respectively, Deltaeta, the pseudorapidity P separation between the two highest ET jets, and ET(gap), the total summed transverse energy between the jets. Rapidity gap events are defined as events in which ET(gap) is less than ET(cut), for ET(cut) varied between jets 0.5 and 2.0 GeV. The fraction of dijet events with a rapidity gap is measured differentially in Deltaeta, x(p)(jets) and x(gamma)(jets). An excess of events with rapidity gaps at low values of ET(cut) is observed above the expectation from standard photoproduction processes. This excess can be explained by the exchange of a strongly interacting colour singlet object between the jets.


4. 
 Adloff, C, et al.
(författare)

Inelastic leptoproduction of J/psi mesons at HERA
 2002

Ingår i: European Physical Journal C.  Springer.  14346044. ; 25:1, s. 4153

Tidskriftsartikel (refereegranskat)abstract
 The leptoproduction of J/psi mesons is studied in inelastic reactions for four momentorri transfers 2 < Q(2) < 100GeV(2). The data were taken with the H1 detector at the electron proton collider HERA and correspond to an integrated luminosity of 77 pb(1). Single differential and double differential cross sections are measured with increased precision compared with previous analyses. New leading order calculations within the nonrelativistic QCD factorisation approach including colour octet and colour singlet contributions are compared with the data and are found to give a reasonable description of most distributions. An exception is the shape of the distribution in the J/psi fractional energy. z, which deviates significantly from that of the data. Comparisons with photoproduction are made and the polarisation of the produced J/psi meson is analysed.


5. 
 Adloff, C, et al.
(författare)

Measurement of D*(+/) meson production and F2(c) in deepinelastic scattering at HERA
 2002

Ingår i: Physics Letters B.  Elsevier.  03702693. ; 528:34, s. 199214

Tidskriftsartikel (refereegranskat)abstract
 The inclusive production of D*+/(2010) mesons in deepinelastic scattering is studied with the HI detector at HERA. In the kinematic region 1 < Q(2) < 100 GeV2 and 0.05 < y < 0.7 an e(+) p cross section for inclusive D*+/ meson production of 8.50 +/ 0.42(stat.)(100)(+1.21)(syst.) nb is measured in the visible range p(tD*) > 1.5 GeV and eta(D*) < 1.5. Single and double differential inclusive D*+/ meson cross sections are compared to perturbative QCD calculations in two different evolution schemes, The charm contribution to the proton structure, Fc(2)(x, Q(2)), is determined by extrapolating the visible charm cross section to the full phase space. This contribution is found to rise from about 10% at Q(2) = 1.5 GeV2 to more than 25% at Q(2) = 60 GeV2 corresponding to x values ranging from 5 x 10(5) to 3 x 10(3). (C) 2002 Elsevier Science B.V. All rights reserved.


6. 
 Adloff, C, et al.
(författare)

Measurement of dijet electroproduction at small jet separation
 2002

Ingår i: European Physical Journal C.  Springer.  14346044. ; 24:1, s. 3341

Tidskriftsartikel (refereegranskat)abstract
 Deepinelastic scattering data in the range 150 < Q(2) < 35000 GeV2 are used to investigate the minimum jet separation necessary to allow accurate description of the rate of dijet production using nexttoleading order perturbative QCD calculations. The required jet separation is found to be small, allowing about 1/3 of DIS data to be classified as dijet, as opposed to approximately 1/10 with more typical jet analyses. A number of precision measurements made using this dijet sample are well described by the calculations. The data are also described by the combination of leading order matrix elements and parton showers, as implemented in the QCD based Monte Carlo model RAPGAP.


7. 
 Adloff, C, et al.
(författare)

Measurement of inclusive jet cross sections in photoproduction at HERA
 2003

Ingår i: European Physical Journal C.  EDP Sciences.  14346044. ; 29:4, s. 497513

Tidskriftsartikel (refereegranskat)abstract
 Inclusive jet cross sections are measured in photoproduction at HERA using the H1 detector. The data sample of e(+)p > e(+) + jet + X events in the kinematic range of photon virtualities Q(2) less than or equal to 1GeV(2) and photonproton centreofmass energies 95 less than or equal to Wgammap less than or equal to 285GeV represents an integrated luminosity of 24.1pb(1). Jets are defined using the inclusive k(perpendicular to) algorithm. Single and multidifferential cross sections are measured as functions of jet transverse energy ET(jet) and pseudorapidity eta(jet) in the domain 5 less than or equal to ET(jet) less than or equal to 75GeV and 1 less than or equal to eta(jet) less than or equal to 2.5. The cross sections are found to be in good agreement with nexttoleading order perturbative QCD calculations corrected for fragmentation and underlying event effects. The cross section differential in ET(jet), which varies by six orders of magnitude over the measured range, is compared with similar distributions from p (p) over bar colliders at equal and higher energies.


8. 
 Adloff, C, et al.
(författare)

Search for excited neutrinos at HERA
 2002

Ingår i: Physics Letters B.  Elsevier.  03702693. ; 525:12, s. 916

Tidskriftsartikel (refereegranskat)abstract
 We present a search for excited neutrinos using e() p data taken by the H1 experiment at HERA at a centerofmass energy of 318 GeV with an integrated luminosity of 15 pb(1). No evidence for excited neutrino production is found. Mass dependent exclusion limits are determined for the ratio of the coupling to the compositeness scale, f/Lambda, independently of the relative couplings to the SU(2) and U(1) gauge bosons. These limits extend the excluded region to higher masses than has been possible in previous searches at other colliders.


9. 
 Adloff, C, et al.
(författare)

Search for odderoninduced contributions to exclusive pi(0) photoproduction at HERA
 2002

Ingår i: Physics Letters B.  Elsevier Science.  03702693. ; 544:12, s. 3543

Tidskriftsartikel (refereegranskat)abstract
 A search for contributions to the reaction ep > epi(0)N* from photonodderon fusion in the photoproduction regime at HERA is reported, at an average photonproton centreofmass energy <W> = 215 GeV. The measurement proceeds via detection of the pi(0) decay photons, a leading neutron from the N* decay, and the scattered electron. No pi(0) signal is observed and an upper limit on the cross section for the photonodderon fusion process of sigma(gammap > pi(0)N*) < 49 nb at the 95% confidence level is derived, integrated over the experimentally accessible range of the squared fourmomentum transfer at the nucleon vertex 0.02 < < 0.3 GeV2. This excludes a recent prediction from a calculation based on a nonperturbative QCD model of a photonodderon fusion cross section above 200 nb. (C) 2002 Elsevier Science B.V. All rights reserved.


10. 
 Adloff, C, et al.
(författare)

Search for QCD instantoninduced processes in deepinelastic scattering at HERA
 2002

Ingår i: European Physical Journal C.  Springer Verlag.  14346044. ; 25:4, s. 495509

Tidskriftsartikel (refereegranskat)abstract
 Signals of QCD instantoninduced processes are searched for in deepinelastic scattering (DIS) at the electronproton collider HERA in a kinematic region defined by the Bjorkenscaling variables x > 10(3), 0.1 < y < 0.6 and photon virtualities 10 less than or similar to Q(2) < 100 GeV2. Several observables characterising hadronic final state properties of QCD instantoninduced events are exploited to identify a potentially instantonenriched domain. While an excess of events with instantonlike topology is observed it cannot be claimed significant given the uncertainty of the standard DIS background simulation. Upper limits on the crosssection for instantoninduced processes of between 60 pb and 1000 pb are set dependent on the kinematic domain considered. The data do not exclude the crosssection predicted by instanton perturbation theory for small instanton sizes. At large instanton sizes a naive extrapolation of instanton perturbation theory yields a crosssection in the range of sensitivity of this study. Such a crosssection is not observed, in agreement with nonperturbative lattice simulations of the QCD vacuum.

