1. |
- Aktas, A., et al.
(author)
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Forward jet production in deep inelastic scattering at HERA
- 2006
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In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 46:1, s. 27-42
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Journal article (peer-reviewed)abstract
- The production of forward jets has been measured in deep inelastic ep collisions at HERA. The results are presented in terms of single differential cross sections as a function of the Bjorken scaling variable (xB(j)) and as triple differential cross sections d3 sigma/dx(Bj)dQ(2)dp(t)(,jet)(2), where Q(2) is the four momentum transfer squared and p(t)(,iet)(2) is the squared transverse momentum of the forward jet. Also cross sections for events with a di-jet system in addition to the forward jet are measured as a function of the rapidity separation between the forward jet and the two additional jets. The measurements are compared with next-to-leading order QCD calculations and with the predictions of various QCD-based models.
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2. |
- Aktas, A, et al.
(author)
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A determination of electroweak parameters at HERA
- 2006
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In: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 632:1, s. 35-42
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Journal article (peer-reviewed)abstract
- Using the deep inelastic e(+) p and e(-) p charged and neutral current scattering cross sections previously published, a combined electroweak and QCD analysis is performed to determine electroweak parameters accounting for their correlation with parton distributions. The data used have been collected by the HI experiment in 1994-2000 and correspond to an integrated luminosity of 117.2 pb(-1). A measurement is obtained of the W propagator mass in charged current ep scattering. The weak mixing angle sin(2)theta w is determined in the on-mass-shell renormalisation scheme. A first measurement at HERA is made of the light quark weak couplings to the Z(0) boson and a possible contribution of right-handed isospin components to the weak couplings is investigated. (c) 2005 Elsevier B.V. All rights reserved.
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3. |
- Aktas, A, et al.
(author)
-
A direct search for stable magnetic monopoles produced in positron-proton collisions at HERA
- 2005
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In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 41, s. 133-141
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Journal article (peer-reviewed)abstract
- A direct search has been made for magnetic monopoles produced in e(+)p collisions at a centre of mass energy of 300 GeV at HERA. The beam pipe surrounding the interaction region in 1995-1997 was investigated using a SQUID magnetometer to look for stopped magnetic monopoles. During this time an integrated luminosity of 62 pb(-1) was delivered. No magnetic monopoles were observed and charge and mass dependent upper limits on the e(+)p production cross section are set.
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4. |
- Aktas, A., et al.
(author)
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Elastic J/psi production at HERA
- 2006
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In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 46:3, s. 585-603
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Journal article (peer-reviewed)abstract
- Cross sections for elastic production of J/psi mesons in photoproduction and electroproduction are measured in electron proton collisions at HERA using an integrated luminosity of 55 pb(-1). Results are presented for photon virtualities Q(2) up to 80 GeV2. The dependence on the photon-proton centre of mass energy W-gamma p is analysed in the range 40 <= W-gamma p <= 305 GeV in photoproduction and 40 <= W-gamma p <= 160 GeV in electroproduction. The W-gamma p dependences of the cross sections do not change significantly with Q(2) and can be described by models based on perturbative QCD. Within such models, the data show a high sensitivity to the gluon density of the proton in the domain of low Bjorken x and low Q(2). Differential cross sections d sigma/dt, where t is the squared four-momentum transfer at the proton vertex, are measured in the range vertical bar t vertical bar < 1.2 GeV2 as functions of W-gamma p and Q(2). Effective Pomeron trajectories are determined for photoproduction and electroproduction. The J/psi production and decay angular distributions are consistent with s-channel helicity conservation. The ratio of the cross sections for longitudinally and transversely polarised photons is measured as a function of Q(2) and is found to be described by perturbative QCD based models.
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5. |
- Aktas, A, et al.
(author)
-
Measurement of Fc(c)over-bar(2) and Fb(b)over-bar(2) at low Q(2) and x using the H1 vertex detector at HERA
- 2006
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In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 45:1, s. 23-33
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Journal article (peer-reviewed)abstract
- Measurements are presented of inclusive charm and beauty cross sections in e(+)p collisions at HERA for values of photon virtuality 12 <= Q(2) = 60 GeV2 and of the Bjorken scaling variable 0.0002 <= x <= 0.005. The fractions of events containing charm and beauty quarks are determined using a method based on the impact parameter, in the transverse plane, of tracks to the primary vertex, as measured by the H1 vertex detector. Values for the structure functions F-2(cc) and F-2(bb) are obtained. This is the first measurement of F-2(bb) in this kinematic range. The results are found to be compatible with the predictions of perturbative quantum chromodynamics and with previous measurements of F-2(cc).
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6. |
- Aktas, A., et al.
(author)
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Diffractive photoproduction of rho mesons with large momentum transfer at HERA
- 2006
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In: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 638:5-6, s. 422-431
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Journal article (peer-reviewed)abstract
- The diffractive photoproduction of rho mesons, ep -> e rho Y, with large momentum transfer squared at the proton vertex, vertical bar t vertical bar, is studied with the H1 detector at HERA using an integrated luminosity of 20.1 pb(-1). The photon-proton centre of mass energy spans the range 75 < W < 95 GeV, the photon virtuality is restricted to Q(2) < 0.01 GeV2 and the mass My of the proton remnant is below 5 GeV. The t dependence of the cross section is measured for the range 1.5 < vertical bar t vertical bar < 10.0 GeV2 and is well described by a power law, d sigma/d vertical bar t vertical bar proportional to vertical bar t vertical bar(-n). The spin density matrix elements, which provide information on the helicity structure of the interaction, are extracted using measurements of angular distributions of the rho decay products. The data indicate a violation of s-channel helicity conservation, with contributions from both single and double helicity-flip being observed. The results are compared to the predictions of perturbative QCD models.
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7. |
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8. |
- Aktas, A, et al.
(author)
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Measurement of charm and beauty photoproduction at HERA using D*mu correlations
- 2005
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In: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 621:1-2, s. 56-71
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Journal article (peer-reviewed)abstract
- A measurement of charm and beauty photoproduction at the electron proton collider HERA is presented based on the simultaneous detection of a D*(+/-) meson and a muon. The correlation between the D* meson and the muon serves to separate the charm and beauty contributions and the analysis provides comparable sensitivity to both. The total and differential experimental cross sections are compared to LO and NLO QCD calculations. The measured charm cross section is in good agreement with QCD predictions including higher order effects while the beauty cross section is higher.
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9. |
- Aktas, A, et al.
(author)
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Measurement of deeply virtual Compton scattering at HERA
- 2005
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In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 44:1, s. 1-11
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Journal article (peer-reviewed)abstract
- A measurement is presented of elastic deeply virtual Compton scattering gamma* p -> gamma p made using e(+) p collision data corresponding to a luminosity of 46.5 pb(-1), taken with the H1 detector at HERA. The cross section is measured as a function of the photon virtuality, Q(2), the invariant mass of the gamma* p system, W, and for the first time, differentially in the squared momentum transfer at the proton vertex, t, in the kinematic range 2 < Q(2) < 80 GeV2, 30 < W < 140 GeV and vertical bar t vertical bar < 1 GeV2. QCD based calculations at next-to-leading order using generalized parton distributions can describe the data, as can colour dipole model predictions.
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10. |
- Aktas, A., et al.
(author)
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Measurement of event shape variables in deep-inelastic scattering at HERA
- 2006
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In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 46:2, s. 343-356
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Journal article (peer-reviewed)abstract
- Deep-inelastic ep scattering data taken with the H1 detector at HERA and corresponding to an integrated luminosity of 106 pb(-1) are used to study the differential distributions of event shape variables. These include thrust, jet broadening, jet mass and the C-parameter. The four-momentum transfer Q is taken to be the relevant energy scale and ranges between 14 GeV and 200 GeV. The event shape distributions are compared with perturbative QCD predictions, which include resummed contributions and analytical power law corrections, the latter accounting for non-perturbative hadronisation effects. The data clearly exhibit the running of the strong coupling alpha(s)(Q) and are consistent with a universal power correction parameter alpha(0) for all event shape variables. A combined QCD fit using all event shape variables yields alpha(s)(m(Z)) = 0.1198 +/- 0.0013 (+0.0056)(-0.0043) and alpha(0) = 0.476 +/- 0.008 (+0.018)(-0.059).
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