| 1. |
- Schael, S, et al.
(författare)
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Precision electroweak measurements on the Z resonance
- 2006
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Ingår i: Physics Reports. - : Elsevier BV. - 0370-1573 .- 1873-6270. ; 427:5-6, s. 257-454
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Forskningsöversikt (refereegranskat)abstract
- We report on the final electroweak measurements performed with data taken at the Z resonance by the experiments operating at the electron-positron colliders SLC and LEP. The data consist of 17 million Z decays accumulated by the ALEPH, DELPHI, L3 and OPAL experiments at LEP, and 600 thousand Z decays by the SLID experiment using a polarised beam at SLC. The measurements include cross-sections, forward-backward asymmetries and polarised asymmetries. The mass and width of the Z boson, m(Z) and Gamma(Z), and its couplings to fermions, for example the p parameter and the effective electroweak mixing angle for leptons, are precisely measured: m(Z) = 91.1875 +/- 0.0021 GeV, Gamma(Z) = 2.4952 +/- 0.0023 GeV, rho(l) = 1.0050 +/- 0.0010, sin(2)theta(eff)(lept) = 0.23153 +/- 0.00016. The number of light neutrino species is determined to be 2.9840 +/- 0.0082, in agreement with the three observed generations of fundamental fermions. The results are compared to the predictions of the Standard Model (SM). At the Z-pole, electroweak radiative corrections beyond the running of the QED and QCD coupling constants are observed with a significance of five standard deviations, and in agreement with the Standard Model. Of the many Z-pole measurements, the forward-backward asymmetry in b-quark production shows the largest difference with respect to its SM expectation, at the level of 2.8 standard deviations. Through radiative corrections evaluated in the framework of the Standard Model, the Z-pole data are also used to predict the mass of the top quark, m(t) = 173(+10)(+13) GeV, and the mass of the W boson, m(W) = 80.363 +/- 0.032 GeV. These indirect constraints are compared to the direct measurements, providing a stringent test of the SM. Using in addition the direct measurements of m(t) and m(W), the mass of the as yet unobserved SM Higgs boson is predicted with a relative uncertainty of about 50% and found to be less than 285 GeV at 95% confidence level. (c) 2006 Elsevier B.V. All rights reserved.
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| 2. |
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| 3. |
- Acciari, V. A., et al.
(författare)
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Radio Imaging of the Very-High-Energy gamma-Ray Emission Region in the Central Engine of a Radio Galaxy
- 2009
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 325:5939, s. 444-448
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Tidskriftsartikel (refereegranskat)abstract
- The accretion of matter onto a massive black hole is believed to feed the relativistic plasma jets found in many active galactic nuclei (AGN). Although some AGN accelerate particles to energies exceeding 10(12) electron volts and are bright sources of very-high-energy (VHE) gamma-ray emission, it is not yet known where the VHE emission originates. Here we report on radio and VHE observations of the radio galaxy Messier 87, revealing a period of extremely strong VHE gamma-ray flares accompanied by a strong increase of the radio flux from its nucleus. These results imply that charged particles are accelerated to very high energies in the immediate vicinity of the black hole.
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| 4. |
- Aktas, A, et al.
(författare)
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A direct search for stable magnetic monopoles produced in positron-proton collisions at HERA
- 2005
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 41, s. 133-141
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Tidskriftsartikel (refereegranskat)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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| 5. |
- Aktas, A., et al.
(författare)
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Elastic J/psi production at HERA
- 2006
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 46:3, s. 585-603
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Tidskriftsartikel (refereegranskat)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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| 6. |
- Aktas, A., et al.
(författare)
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Forward jet production in deep inelastic scattering at HERA
- 2006
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 46:1, s. 27-42
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Tidskriftsartikel (refereegranskat)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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| 7. |
- Aktas, A., et al.
(författare)
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Measurement of event shape variables in deep-inelastic scattering at HERA
- 2006
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 46:2, s. 343-356
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Tidskriftsartikel (refereegranskat)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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| 8. |
- Aktas, A., et al.
(författare)
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Photoproduction of dijets with high transverse momenta at HERA
- 2006
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 639:1, s. 21-31
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Tidskriftsartikel (refereegranskat)abstract
- Differential dijet cross sections are measured in photoproduction in the region of photon virtualities Q(2) < 1 GeV2 with the H1 detector at the HERA ep collider using an integrated luminosity of 66.6 pb(-1). Jets are defined with the inclusive k perpendicular to algorithm and a minimum transverse momentum of the leading jet of 25 GeV is required. Dijet cross sections are measured indirect and resolved photon enhanced regions separately. Longitudinal proton momentum fractions up to 0.7 are reached. The data compare well with predictions from Monte Carlo event generators based on leading order QCD and parton showers and with next-to-leading order QCD calculations corrected for hadronisation effects.
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| 9. |
- Aktas, A., et al.
(författare)
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Search for doubly-charged Higgs boson production at HERA
- 2006
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 638:5-6, s. 432-440
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Tidskriftsartikel (refereegranskat)abstract
- A search for the single production of doubly-charged Higgs bosons H-+/-+/- in ep collisions is presented. The signal is searched for via the Higgs decays into a high mass pair of same charge leptons, one of them being an electron. The analysis uses up to 118 pb(-1) of ep data collected by the H1 experiment at HERA. No evidence for doubly-charged Higgs production is observed and mass dependent upper limits are derived on the Yukawa couplings h(el) of the Higgs boson to an electron-lepton pair. Assuming that the doubly-charged Higgs only decays into an electron and a muon via a coupling of electromagnetic strength h(e mu) = root 4 pi alpha(em) similar or equal to 0.3, a lower limit of 141 GeV on the H-+/-+/- mass is obtained at the 95% confidence level. For a doubly-charged Higgs decaying only into an electron and a tau and a coupling h(e tau) similar or equal to 0.3, masses below 112 GeV are ruled out.
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| 10. |
- Aaron, F. D., et al.
(författare)
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Multi-lepton production at high transverse momenta in ep collisions at HERA
- 2008
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 668:4, s. 268-276
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Tidskriftsartikel (refereegranskat)abstract
- Processes leading to a final state with at least two high transverse momentum leptons (electrons or muons) are studied using the full e(+/-) p data sample collected by the H1 experiment at HERA. The data correspond to an integrated luminosity of 463 pb(-1). Di-lepton and tri-lepton event classes are investigated. Cross sections of the production of e(+)e(-) and mu(+)mu(-) pairs are derived in a restricted phase space dominated by photon-photon collisions. In general, good agreement is found with Standard Model predictions. Events are observed with a total scalar sum of lepton transverse momenta above 100 GeV where the Standard Model expectation is low. In this region, combining di-lepton and tri-lepton classes, five events are observed in e(+) p collisions, compared to a Standard Model expectation of 0.96 +/- 0.12, while no such event is observed in e(-) p data for 0.64 +/- 0.09 expected. (C) 2008 Elsevier B.V. All rights reserved.
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| 11. |
- Aaron, F. D., et al.
(författare)
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Strangeness production at low Q(2) in deep-inelastic ep scattering at HERA
- 2009
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 61:2, s. 185-205
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Tidskriftsartikel (refereegranskat)abstract
- The production of neutral strange hadrons is investigated using deep-inelastic scattering events measured with the H1 detector at HERA. The measurements are made in the phase space defined by the negative four-momentum transfer squared of the photon 2 < Q(2) < 100 GeV2 and the inelasticity 0.1 < y < 0.6. The K-s(0) s and Lambda((Lambda) over bar) production cross sections and their ratios are determined. K-s(0) s production is compared to the production of charged particles in the same region of phase space. The Lambda-(Lambda) over bar asymmetry is also measured and found to be consistent with zero. Predictions of leading order Monte Carlo programs are compared to the data.
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| 12. |
- Aaron, F. D., et al.
(författare)
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Study of charm fragmentation into D (* +/-) mesons in deep-inelastic scattering at HERA
- 2009
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 59:3, s. 589-606
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Tidskriftsartikel (refereegranskat)abstract
- The process of charm quark fragmentation is studied using D (* +/-) meson production in deep-inelastic scattering as measured by the H1 detector at HERA. The parameters of fragmentation functions are extracted for QCD models based on leading order matrix elements and DGLAP or CCFM evolution of partons together with string fragmentation and particle decays. Additionally, they are determined for a next-to-leading order QCD calculation in the fixed flavour number scheme using the independent fragmentation of charm quarks to D (* +/-) mesons. Two different regions of phase space are investigated defined by the presence or absence of a jet containing the D (* +/-) meson in the event. The fragmentation parameters extracted for the two phase space regions are found to be different.
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| 13. |
- Aktas, A., et al.
(författare)
-
Diffractive deep-inelastic scattering with a leading proton at HERA
- 2006
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 48:3, s. 749-766
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Tidskriftsartikel (refereegranskat)abstract
- The cross section for the diffractive deep-inelastic scattering process ep -> eX(P) is measured, with the leading final state proton detected in the H1 Forward Proton Spectrometer. The data analysed cover the range x(P) < 0.1 in fractional proton longitudinal momentum loss, 0.08 < vertical bar t vertical bar < 0.5 GeV-2 in squared four-momentum transfer at the proton vertex, 2 < Q(2) < 50 GeV2 in photon virtuality and 0.004 < beta = x/x(P) < 1, where x is the Bjorken scaling variable. For x(P) less than or similar to 10(-2), the differential cross section has a dependence of approximately d sigma/dt proportional to e(6t), independently of x(P), beta and Q(2) within uncertainties. The cross section is also measured triple differentially in x(P), beta and Q(2). The x(P) dependence is interpreted in terms of an effective pomeron trajectory with intercept alpha(P) (0) = 1.114 +/- 0.018(stat.) +/- 0.012(syst.)(-0.020)(+0.040) (model) and a subleading exchange. The data are in good agreement with an H1 measurement for which the event selection is based on a large gap in the rapidity distribution of the final state hadrons, after accounting for proton dissociation contributions in the latter. Within uncertainties, the dependence of the cross section on x and Q(2) can thus be factorised from the dependences on all studied variables which characterise the proton vertex, for both the pomeron and the sub-leading exchange.
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| 14. |
- Aktas, A., et al.
(författare)
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Diffractive photoproduction of rho mesons with large momentum transfer at HERA
- 2006
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Ingår i: 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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Tidskriftsartikel (refereegranskat)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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| 15. |
- Aktas, A, et al.
(författare)
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First measurement of charged current cross sections at HERA with longitudinally polarised positrons
- 2006
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 634:2-3, s. 173-179
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Tidskriftsartikel (refereegranskat)abstract
- Data taken with positrons of different longitudinal polarisation states in collision with unpolarised protons at HERA are used to measure the total cross sections of the charged current process, e(+) p -> nu X, for negative four-momentum transfer squared Q(2) > 400 GeV2 and inelasticity gamma < 0.9. Together with the corresponding cross section obtained from the previously published unpolarised data, the polarisation dependence of the charged current cross section is measured for the first time at high Q(2) and found to be in agreement with the Standard Model prediction. (c) 2006 Elsevier B.V. All rights reserved.
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| 16. |
- Aktas, A., et al.
(författare)
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Inclusive D-*+/- meson cross sections and D-*+/--jet correlations in photoproduction at HERA
- 2007
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 50:2, s. 251-267
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Tidskriftsartikel (refereegranskat)abstract
- Differential photoproduction cross sections are measured for events containing D-*+/- mesons. The data were taken with the H1 detector at the ep collider HERA and correspond to an integrated luminosity of 51.1 pb(-1). The kinematic region covers small photon virtualities Q(2) < 0.01 GeV2 and photon-proton centre-of-mass energies of 171 < W gamma(Cep) < 256 GeV. The details of the heavy quark production process are further investigated in events with one or two jets in addition to the D-*+/- meson. Differential cross sections for D-* + jet production are determined and the correlations between the D-*+/- meson and the jet(s) are studied. The results are compared with perturbative QCD predictions applying collinear- or k(t)-factorisation.
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| 17. |
- Aktas, A., et al.
(författare)
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Measurement and QCD analysis of the diffractive deep-inelastic scattering cross section at HERA
- 2006
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 48:3, s. 715-748
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Forskningsöversikt (refereegranskat)abstract
- A detailed analysis is presented of the diffractive deep-inelastic scattering process ep -> eXY, where Y is a proton or a low mass proton excitation carrying a fraction 1 - x(IP) > 0.95 of the incident proton longitudinal momentum and the squared four-momentum transfer at the proton vertex satisfies |t| < 1 GeV2. Using data taken by the H1 experiment, the cross section is measured for photon virtualities in the range 3.5 <= Q(2) <= 1600 GeV2, triple differentially in x(IP), Q(2) and beta = x/x(P), where x is the Bjorken scaling variable. At low x(IP), the data are consistent with a factorisable x(IP) dependence, which can be described by the exchange of an effective pomeron trajectory with intercept alpha(IP)(0) = 1.118 +/- 0.008(exp.)(-0.010)(+0.029)(model). Diffractive parton distribution functions and their uncertainties are determined from a next-to-leading order DGLAP QCD analysis of the Q(2)and beta dependences of the cross section. The resulting gluon distribution carries an integrated fraction of around 70% of the exchanged momentum in the Q(2) range studied. Total and differential cross sections are also measured for the diffractive charged current process e(+) p -> (v) over bar eXY and are found to be well described by predictions based on the diffractive parton distributions. The ratio of the diffractive to the inclusive neutral current ep cross sections is studied. Over most of the kinematic range, this ratio shows no significant dependence on Q(2) at fixed x(P) and x or on x at fixed Q(2) and beta.
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| 18. |
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| 19. |
- Aktas, A., et al.
(författare)
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Search for a narrow baryonic resonance decaying to K(s)(0)p or K-s(0)(p)over-bar in deep inelastic scattering at HERA
- 2006
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 639:3-4, s. 202-209
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Tidskriftsartikel (refereegranskat)abstract
- A search for a narrow baryonic resonance decaying to K(s)(0)p or K-s(0)(p) over bar is carried out in deep inelastic ep scattering with the H1 detector at HERA. ss Such a resonance could be a strange pentaquark Theta(+), evidence for which has been reported by several experiments. The K(s)(0)p and K-s(0)(p) over bar invariant ss mass distributions presented here do not show any significant peak in the mass range from threshold up to 1.7 GeV. Mass dependent upper limits on sigma(ep -> e Theta X+) x BR(Theta(+) -> K(0)p) are obtained at the 95% confidence level.
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| 20. |
- Aktas, A., et al.
(författare)
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Tau lepton production in ep collisions at HERA
- 2006
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 48:3, s. 699-714
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Tidskriftsartikel (refereegranskat)abstract
- The production of tau leptons in ep collisions is investigated using data recorded by the H1 detector at HERA in the period 1994-2000. Tau leptons are identified by detecting their decay products, using leptonic and hadronic decay modes. The cross section for the production of tau lepton pairs is measured for the first time at HERA. Furthermore, a search for events with an energetic isolated tau lepton and with large missing transverse momentum is performed. The results are found to be in agreement with the Standard Model predictions.
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| 21. |
- Aaron, F. D., et al.
(författare)
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A search for excited neutrinos in e(-) p collisions at HERA
- 2008
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 663:5, s. 382-389
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Tidskriftsartikel (refereegranskat)abstract
- A search for first generation excited neutrinos is performed using the full e(-) p data sample collected by the HI experiment at HERA at a centre-of-mass energy of 319 GeV, corresponding to a total luminosity of 184 pb(-1). The electroweak decays of excited neutrinos nu* -> nu gamma, v* -> nu Z and nu* -> eW with subsequent hadronic or leptonic decays of the W and Z bosons are considered. No evidence for excited neutrino production is found. Mass dependent exclusion limits on nu* production cross sections and on the ratio of the coupling to the compositeness scale f/boolean AND are derived within gauge mediated models. A limit on f/boolean AND A, independent of the relative couplings to the SU(2) and U(1) gauge bosons, is also determined. These limits extend the excluded region to higher masses than has been possible in previous excited neutrino searches. (c) 2008 Elsevier B.V. All rights reserved.
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| 22. |
- Aaron, F. D., et al.
(författare)
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Inclusive photoproduction of rho(0), K*(0) and phi mesons at HERA H1 Collaboration
- 2009
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 673:2, s. 119-126
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Tidskriftsartikel (refereegranskat)abstract
- Inclusive non-diffractive photoproduction of rho(770)(0), K*(892)(0) and phi(1020) mesons is investigated with the H1 detector in ep collisions at HERA. The corresponding average gamma p centre-of-mass energy is 210 GeV. The mesons are measured in the transverse momentum range 0.5 < p(T) < 7 GeV and the rapidity range vertical bar y(lab)vertical bar < 1. Differential cross sections are presented as a function of transverse momentum and rapidity, and are compared to the predictions of hadroproduction models. (C) 2009 Elsevier B.V. All rights reserved.
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| 23. |
- Aaron, F. D., et al.
(författare)
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Measurement of diffractive scattering of photons with large momentum transfer at HERA
- 2009
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 672:3, s. 219-226
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Tidskriftsartikel (refereegranskat)abstract
- The first measurement of diffractive scattering of quasi-real photons with large momentum transfer gamma p -> gamma Y, where Y is the proton dissociative system, is made using the H1 detector at HERA. The measurement is performed for initial photon virtualities Q(2) < 0.01 GeV2. Single differential cross sections are Measured as a function of W, the incident photon-proton centre of mass energy, and t, the square of the four-momentum transferred at the proton vertex, in the range 175 < W < 247 GeV and 4 < |t| < 36 GeV2. The W dependence is well described by a model based on perturbative QCD using a leading logarithmic approximation of the BFKL evolution. The measured |t| dependence is harder than that predicted by the model and those observed in exclusive vector meson production. (C) 2009 Published by Elsevier B.V.
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| 24. |
- Aaron, F. D., et al.
(författare)
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Measurement of the proton structure function F-L(x, Q(2)) at low x
- 2008
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 665:4, s. 139-146
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Tidskriftsartikel (refereegranskat)abstract
- A first measurement is reported of the longitudinal proton structure function FL(X, Q(2)) at the ep collider HERA. It is based on inclusive deep inelastic e(+)p scattering cross section measurements with a positron beam energy of 27.5 GeV and proton beam energies of 920, 575 and 460 GeV. Employing the energy dependence of the cross section, FL is measured in a range of squared four-momentum transfers 12 <= Q2 <=, 90 GeV2 and low Bjorken x 0.00024 <= x <= 0.0036. The F-L values agree with higher order QCD calculations based on parton densities obtained using cross section data previously measured at HERA. (C) 2008 Elsevier B.V. All rights reserved.
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| 25. |
- Aaron, F. D., et al.
(författare)
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Search for excited electrons in ep collisions at HERA
- 2008
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 666:2, s. 131-139
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Tidskriftsartikel (refereegranskat)abstract
- A search for excited electrons is performed using the full e(+/-) p data sample collected by the HI experiment at HERA, corresponding to a total luminosity of 475 pb(-1). The electroweak decays of excited electrons e* -> e gamma, e* -> eZ and e* -> vW with subsequent hadronic or leptonic decays of the W and Z bosons are considered. No evidence for excited electron production is found. Mass dependent exclusion limits on e* production cross sections and on the ratio f/Lambda of the coupling to the compositeness scale are derived within gauge mediated models. These limits extend the excluded region compared to previous excited electron searches. The e* production via contact interactions is also addressed for the first time in ep collisions. (C) 2008 Elsevier B.V. All rights reserved.
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