| 1. |
|
|
| 2. |
- Aad, G, et al.
(författare)
-
- 2015
-
swepub:Mat__t
|
|
| 3. |
|
|
| 4. |
|
|
| 5. |
|
|
| 6. |
- Schael, S, et al.
(författare)
-
Precision electroweak measurements on the Z resonance
- 2006
-
Ingår i: Physics Reports. - : Elsevier BV. - 0370-1573 .- 1873-6270. ; 427:5-6, s. 257-454
-
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.
|
|
| 7. |
- Schael, S., et al.
(författare)
-
Electroweak measurements in electron positron collisions at W-boson-pair energies at LEP
- 2013
-
Ingår i: Physics Reports. - : Elsevier BV. - 0370-1573 .- 1873-6270. ; 532:4, s. 119-244
-
Forskningsöversikt (refereegranskat)abstract
- Electroweak measurements performed with data taken at the electron positron collider LEP at CERN from 1995 to 2000 are reported. The combined data set considered in this report corresponds to a total luminosity of about 3 fb(-1) collected by the four LEP experiments ALEPH, DELPHI, 13 and OPAL, at centre-of-mass energies ranging from 130 GeV to 209 GeV. Combining the published results of the four LEP experiments, the measurements include total and differential cross-sections in photon-pair, fermion-pair and four-fermion production, the latter resulting from both double-resonant WW and ZZ production as well as singly resonant production. Total and differential cross-sections are measured precisely, providing a stringent test of the Standard Model at centre-of-mass energies never explored before in electron positron collisions. Final-state interaction effects in four-fermion production, such as those arising from colour reconnection and Bose Einstein correlations between the two W decay systems arising in WW production, are searched for and upper limits on the strength of possible effects are obtained. The data are used to determine fundamental properties of the W boson and the electroweak theory. Among others, the mass and width of the W boson, m(w) and Gamma(w), the branching fraction of W decays to hadrons, B(W -> had), and the trilinear gauge-boson self-couplings g(1)(Z), K-gamma and lambda(gamma), are determined to be: m(w) = 80.376 +/- 0.033 GeV Gamma(w) = 2.195 +/- 0.083 GeV B(W -> had) = 67.41 +/- 0.27% g(1)(Z) = 0.984(-0.020)(+0.018) K-gamma - 0.982 +/- 0.042 lambda(gamma) = 0.022 +/- 0.019. (C) 2013 Elsevier B.V. All rights reserved.
|
|
| 8. |
- Niemi, MEK, et al.
(författare)
-
- 2021
-
swepub:Mat__t
|
|
| 9. |
- Kanai, M, et al.
(författare)
-
- 2023
-
swepub:Mat__t
|
|
| 10. |
- Mishra, A, et al.
(författare)
-
Diminishing benefits of urban living for children and adolescents' growth and development
- 2023
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 1476-4687 .- 0028-0836. ; 615:7954, s. 874-883
-
Tidskriftsartikel (refereegranskat)abstract
- Optimal growth and development in childhood and adolescence is crucial for lifelong health and well-being1–6. Here we used data from 2,325 population-based studies, with measurements of height and weight from 71 million participants, to report the height and body-mass index (BMI) of children and adolescents aged 5–19 years on the basis of rural and urban place of residence in 200 countries and territories from 1990 to 2020. In 1990, children and adolescents residing in cities were taller than their rural counterparts in all but a few high-income countries. By 2020, the urban height advantage became smaller in most countries, and in many high-income western countries it reversed into a small urban-based disadvantage. The exception was for boys in most countries in sub-Saharan Africa and in some countries in Oceania, south Asia and the region of central Asia, Middle East and north Africa. In these countries, successive cohorts of boys from rural places either did not gain height or possibly became shorter, and hence fell further behind their urban peers. The difference between the age-standardized mean BMI of children in urban and rural areas was <1.1 kg m–2 in the vast majority of countries. Within this small range, BMI increased slightly more in cities than in rural areas, except in south Asia, sub-Saharan Africa and some countries in central and eastern Europe. Our results show that in much of the world, the growth and developmental advantages of living in cities have diminished in the twenty-first century, whereas in much of sub-Saharan Africa they have amplified.
|
|
| 11. |
|
|
| 12. |
- van Leeuwen, F., et al.
(författare)
-
Gaia Data Release 1 : Open cluster astrometry: Performance, limitations, and future prospects
- 2017
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 601
-
Tidskriftsartikel (refereegranskat)abstract
- Context. The first Gaia Data Release contains the Tycho-Gaia Astrometric Solution (TGAS). This is a subset of about 2 million stars for which, besides the position and photometry, the proper motion and parallax are calculated using Hipparcos and Tycho-2 positions in 1991.25 as prior information. Aims. We investigate the scientific potential and limitations of the TGAS component by means of the astrometric data for open clusters. Methods. Mean cluster parallax and proper motion values are derived taking into account the error correlations within the astrometric solutions for individual stars, an estimate of the internal velocity dispersion in the cluster, and, where relevant, the effects of the depth of the cluster along the line of sight. Internal consistency of the TGAS data is assessed. Results. Values given for standard uncertainties are still inaccurate and may lead to unrealistic unit-weight standard deviations of least squares solutions for cluster parameters. Reconstructed mean cluster parallax and proper motion values are generally in very good agreement with earlier Hipparcos-based determination, although the Gaia mean parallax for the Pleiades is a significant exception. We have no current explanation for that discrepancy. Most clusters are observed to extend to nearly 15 pc from the cluster centre, and it will be up to future Gaia releases to establish whether those potential cluster-member stars are still dynamically bound to the clusters. Conclusions. The Gaia DR1 provides the means to examine open clusters far beyond their more easily visible cores, and can provide membership assessments based on proper motions and parallaxes. A combined HR diagram shows the same features as observed before using the Hipparcos data, with clearly increased luminosities for older A and F dwarfs.
|
|
| 13. |
- Brown, A. G. A., et al.
(författare)
-
Gaia Data Release 1 Summary of the astrometric, photometric, and survey properties
- 2016
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 595
-
Tidskriftsartikel (refereegranskat)abstract
- Context. At about 1000 days after the launch of Gaia we present the first Gaia data release, Gaia DR1, consisting of astrometry and photometry for over 1 billion sources brighter than magnitude 20.7. Aims. A summary of Gaia DR1 is presented along with illustrations of the scientific quality of the data, followed by a discussion of the limitations due to the preliminary nature of this release. Methods. The raw data collected by Gaia during the first 14 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into an astrometric and photometric catalogue. Results. Gaia DR1 consists of three components: a primary astrometric data set which contains the positions, parallaxes, and mean proper motions for about 2 million of the brightest stars in common with the HIPPARCOS and Tycho-2 catalogues - a realisation of the Tycho-Gaia Astrometric Solution (TGAS) - and a secondary astrometric data set containing the positions for an additional 1.1 billion sources. The second component is the photometric data set, consisting of mean G-band magnitudes for all sources. The G-band light curves and the characteristics of similar to 3000 Cepheid and RR Lyrae stars, observed at high cadence around the south ecliptic pole, form the third component. For the primary astrometric data set the typical uncertainty is about 0.3 mas for the positions and parallaxes, and about 1 mas yr(-1) for the proper motions. A systematic component of similar to 0.3 mas should be added to the parallax uncertainties. For the subset of similar to 94 000 HIPPARCOS stars in the primary data set, the proper motions are much more precise at about 0.06 mas yr(-1). For the secondary astrometric data set, the typical uncertainty of the positions is similar to 10 mas. The median uncertainties on the mean G-band magnitudes range from the mmag level to similar to 0.03 mag over the magnitude range 5 to 20.7. Conclusions. Gaia DR1 is an important milestone ahead of the next Gaia data release, which will feature five-parameter astrometry for all sources. Extensive validation shows that Gaia DR1 represents a major advance in the mapping of the heavens and the availability of basic stellar data that underpin observational astrophysics. Nevertheless, the very preliminary nature of this first Gaia data release does lead to a number of important limitations to the data quality which should be carefully considered before drawing conclusions from the data.
|
|
| 14. |
- Prusti, T., et al.
(författare)
-
The Gaia mission
- 2016
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 595
-
Tidskriftsartikel (refereegranskat)abstract
- Gaia is a cornerstone mission in the science programme of the European Space Agency (ESA). The spacecraft construction was approved in 2006, following a study in which the original interferometric concept was changed to a direct-imaging approach. Both the spacecraft and the payload were built by European industry. The involvement of the scientific community focusses on data processing for which the international Gaia Data Processing and Analysis Consortium (DPAC) was selected in 2007. Gaia was launched on 19 December 2013 and arrived at its operating point, the second Lagrange point of the Sun-Earth-Moon system, a few weeks later. The commissioning of the spacecraft and payload was completed on 19 July 2014. The nominal five-year mission started with four weeks of special, ecliptic-pole scanning and subsequently transferred into full-sky scanning mode. We recall the scientific goals of Gaia and give a description of the as-built spacecraft that is currently (mid-2016) being operated to achieve these goals. We pay special attention to the payload module, the performance of which is closely related to the scientific performance of the mission. We provide a summary of the commissioning activities and findings, followed by a description of the routine operational mode. We summarise scientific performance estimates on the basis of in-orbit operations. Several intermediate Gaia data releases are planned and the data can be retrieved from the Gaia Archive, which is available through the Gaia home page.
|
|
| 15. |
- Aaron, F. D., et al.
(författare)
-
Multi-leptons with high transverse momentum at HERA
- 2009
-
Ingår i: Journal of High Energy Physics. - : Springer Science and Business Media LLC. - 1029-8479. ; :10
-
Tidskriftsartikel (refereegranskat)abstract
- Events with at least two high transverse momentum leptons (electrons or muons) are studied using the H1 and ZEUS detectors at HERA with an integrated luminosity of 0.94 fb(-1). The observed numbers of events are in general agreement with the Standard Model predictions. Seven di- and tri-lepton events are observed in e(+)p collision data with a scalar sum of the lepton transverse momenta above 100 GeV while 1.94 +/- 0.17 events are expected. Such events are not observed in e(-)p collisions for which 1.19 +/- 0.12 are predicted. Total visible and differential di-electron and di-muon photoproduction cross sections are extracted in a restricted phase space dominated by photon-photon collisions.
|
|
| 16. |
- Clementini, G., et al.
(författare)
-
Testing parallaxes with local Cepheids and RR Lyrae stars
- 2017
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 605
-
Tidskriftsartikel (refereegranskat)abstract
- Context. Parallaxes for 331 classical Cepheids, 31 Type II Cepheids, and 364 RR Lyrae stars in common between Gaia and the HIPPARCOS and Tycho-2 catalogues are published in Gaia Data Release 1 (DR1) as part of the Tycho-Gaia Astrometric Solution (TGAS). Aims. In order to test these first parallax measurements of the primary standard candles of the cosmological distance ladder, which involve astrometry collected by Gaia during the initial 14 months of science operation, we compared them with literature estimates and derived new period-luminosity (PL), period-Wesenheit (PW) relations for classical and Type II Cepheids and infrared PL, PL-metallicity (PLZ), and optical luminosity-metallicity (MV-[Fe/H]) relations for the RR Lyrae stars, with zero points based on TGAS.Methods. Classical Cepheids were carefully selected in order to discard known or suspected binary systems. The final sample comprises 102 fundamental mode pulsators with periods ranging from 1.68 to 51.66 days (of which 33 with sigma(omega)/omega < 0 : 5). The Type II Cepheids include a total of 26 W Virginis and BL Herculis stars spanning the period range from 1.16 to 30.00 days (of which only 7 with sigma(omega)/omega 0 : 5). The RR Lyrae stars include 200 sources with pulsation period ranging from 0.27 to 0.80 days (of which 112 with sigma(omega)/omega < 0 : 5). The new relations were computed using multi- band (V; I; J; K-s) photometry and spectroscopic metal abundances available in the literature, and by applying three alternative approaches: (i) linear least-squares fitting of the absolute magnitudes inferred from direct transformation of the TGAS parallaxes; (ii) adopting astrometry-based luminosities; and (iii) using a Bayesian fitting approach. The last two methods work in parallax space where parallaxes are used directly, thus maintaining symmetrical errors and allowing negative parallaxes to be used. The TGAS-based PL; PW; PLZ, and MV [Fe/H] relations are discussed by comparing the distance to the Large Magellanic Cloud provided by different types of pulsating stars and alternative fitting methods.Results. Good agreement is found from direct comparison of the parallaxes of RR Lyrae stars for which both TGAS and HST measurements are available. Similarly, very good agreement is found between the TGAS values and the parallaxes inferred from the absolute magnitudes of Cepheids and RR Lyrae stars analysed with the Baade-Wesselink method. TGAS values also compare favourably with the parallaxes inferred by theoretical model fitting of the multi-band light curves for two of the three classical Cepheids and one RR Lyrae star, which were analysed with this technique in our samples. The K-band PL relations show the significant improvement of the TGAS parallaxes for Cepheids and RR Lyrae stars with respect to the HIPPARCOS measurements. This is particularly true for the RR Lyrae stars for which improvement in quality and statistics is impressive.Conclusions. TGAS parallaxes bring a significant added value to the previous HIPPARCOS estimates. The relations presented in this paper represent the first Gaia-calibrated relations and form a work-in-progress milestone report in the wait for Gaia-only parallaxes of which a first solution will become available with Gaia Data Release 2 (DR2) in 2018.
|
|
| 17. |
|
|
| 18. |
-
- 2017
-
Ingår i: Physical Review D. - 2470-0010 .- 2470-0029. ; 96:2
-
Tidskriftsartikel (refereegranskat)
|
|
| 19. |
- Abadie, J., et al.
(författare)
-
Implementation and testing of the first prompt search for gravitational wave transients with electromagnetic counterparts
- 2012
-
Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 539
-
Tidskriftsartikel (refereegranskat)abstract
- Aims. A transient astrophysical event observed in both gravitational wave (GW) and electromagnetic (EM) channels would yield rich scientific rewards. A first program initiating EM follow-ups to possible transient GW events has been developed and exercised by the LIGO and Virgo community in association with several partners. In this paper, we describe and evaluate the methods used to promptly identify and localize GW event candidates and to request images of targeted sky locations. Methods. During two observing periods (Dec. 17, 2009 to Jan. 8, 2010 and Sep. 2 to Oct. 20, 2010), a low-latency analysis pipeline was used to identify GW event candidates and to reconstruct maps of possible sky locations. A catalog of nearby galaxies and Milky Way globular clusters was used to select the most promising sky positions to be imaged, and this directional information was delivered to EM observatories with time lags of about thirty minutes. A Monte Carlo simulation has been used to evaluate the low-latency GW pipeline's ability to reconstruct source positions correctly. Results. For signals near the detection threshold, our low-latency algorithms often localized simulated GW burst signals to tens of square degrees, while neutron star/neutron star inspirals and neutron star/black hole inspirals were localized to a few hundred square degrees. Localization precision improves for moderately stronger signals. The correct sky location of signals well above threshold and originating from nearby galaxies may be observed with similar to 50% or better probability with a few pointings of wide-field telescopes.
|
|
| 20. |
|
|
| 21. |
|
|
| 22. |
- Aaron, F. D., et al.
(författare)
-
A search for excited neutrinos in e(-) p collisions at HERA
- 2008
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 663:5, s. 382-389
-
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.
|
|
| 23. |
- Abreu, P., et al.
(författare)
-
Search for sleptons in e+e- collisions at √s = 183 to 189 GeV
- 2001
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 19:1, s. 29-42
-
Tidskriftsartikel (refereegranskat)abstract
- Data taken by the DELPHI experiment at centre-of-mass energies of 183 GeV and 189 GeV with a total integrated luminosity of 212 pb-1 have been used to search for the supersymmetric partners of the electrons, muons, and taus in the context of the Minimal Supersymmetric Standard Model (MSSM). The decay topologies searched for were the direct decay (ℓ̃ → ℓx̃), producing acoplanar lepton pairs plus missing energy, and the cascade decay (ℓ → ℓx̃0 2 → ℓγx̃0 1), producing acoplanar lepton and photon pairs plus missing energy. The observed number of events is in agreement with Standard Model predictions. The 95% CL excluded mass limits for selectrons, smuons and staus are mẽ ≤ 87 GeV/c2, mμ̃ ≤ 80 GeV/c2 and mτ̃ 75 GeV/c2, respectively, for values of μ=-200 GeV/c2 and tanβ=1.5.
|
|
| 24. |
- Abreu, P., et al.
(författare)
-
Study of dimuon production in photon-photon collisions and measurement of QED photon structure functions at LEP
- 2001
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 19:1, s. 15-28
-
Tidskriftsartikel (refereegranskat)abstract
- Muon pair production in the process e+e- → e+e- μ+μ- is studied using the data taken at LEP1 (√s ≃ mz) with the DELPHI detector during the years 1992-1995. The corresponding integrated luminosity is 138.5 pb-1. The QED predictions have been tested over the whole Q2 range accessible at LEP1 (from several GeV2/c4 to several hundred GeV2/c4) by comparing experimental distributions with distributions resulting from Monte Carlo simulations using various generators. Selected events are used to extract the leptonic photon structure function Fγ 2. Azimuthal correlations are used to obtain information on additional structure functions, Fγ A and Fγ B, which originate from interference terms of the scattering amplitudes. The measured ratios Fγ A/Fγ 2 and FγB/Fγ 2 are significantly different from zero and consistent with QED predictions.
|
|
| 25. |
|
|
| 26. |
|
|
| 27. |
- Abreu, P., et al.
(författare)
-
Measurement of the gluon fragmentation function and a comparison of the scaling violation in gluon and quark jets
- 2000
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 13:4, s. 573-589
-
Tidskriftsartikel (refereegranskat)abstract
- The fragmentation functions of quarks and gluons are measured in various three-jet topologies in Z decays from the full data set collected with the DELPHI detector at the Z resonance between 1992 and 995. The results at different values of transverse momentum-like scales are compared. A parameterization of the quark and gluon fragmentation functions at a fixed reference scale is given. The quark and gluon fragmentation functions show the predicted pattern of scaling violations. The scaling violation for quark jets as a function of a transverse momentum-like scale is in a good agreement with that observed in lower energy e+e- annihilation experiments. For gluon jets it appears to be significantly stronger. The scale dependences of the gluon and quark fragmentation functions agree with the prediction of the DGLAP evolution equations from which the colour factor ratio CA/CF is measured to be: CA/CF = 2.26 ± 0.09stat. ± 0.06sys. ± 0.12clus.,scale..
|
|
| 28. |
|
|
| 29. |
|
|
| 30. |
- Aaron, F. D., et al.
(författare)
-
Measurement of diffractive scattering of photons with large momentum transfer at HERA
- 2009
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 672:3, s. 219-226
-
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.
|
|
| 31. |
- Aaron, F. D., et al.
(författare)
-
Measurement of isolated photon production in deep-inelastic scattering at HERA
- 2008
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 54:3, s. 371-387
-
Tidskriftsartikel (refereegranskat)abstract
- The production of isolated photons in deep-inelastic scattering ep -> e gamma X is measured with the H1 detector at HERA. The measurement is performed in the kinematic range of negative four-momentum transfer squared 4 < Q(2)< 150 GeV2 and a mass of the hadronic system W-X > 50 GeV. The analysis is based on a total integrated luminosity of 227 pb(-1). The production cross section of isolated photons with a transverse energy in the range 3 < E-T(gamma)< 10 GeV and pseudorapidity range -1.2
|
|
| 32. |
- Aaron, F. D., et al.
(författare)
-
Measurement of the proton structure function F-L(x, Q(2)) at low x
- 2008
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 665:4, s. 139-146
-
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.
|
|
| 33. |
- Aaron, F. D., et al.
(författare)
-
Multi-lepton production at high transverse momenta in ep collisions at HERA
- 2008
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 668:4, s. 268-276
-
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.
|
|
| 34. |
- Aaron, F. D., et al.
(författare)
-
Search for excited electrons in ep collisions at HERA
- 2008
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 666:2, s. 131-139
-
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.
|
|
| 35. |
- Aaron, F. D., et al.
(författare)
-
Strangeness production at low Q(2) in deep-inelastic ep scattering at HERA
- 2009
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 61:2, s. 185-205
-
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.
|
|
| 36. |
- Aaron, F. D., et al.
(författare)
-
Study of charm fragmentation into D (* +/-) mesons in deep-inelastic scattering at HERA
- 2009
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 59:3, s. 589-606
-
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.
|
|
| 37. |
- Aaron, F. D., et al.
(författare)
-
Three- and four-jet production at low x at HERA
- 2008
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 54:3, s. 389-409
-
Tidskriftsartikel (refereegranskat)abstract
- Three- and four-jet production is measured in deep-inelastic ep scattering at low x and Q(2) with the H1 detector using an integrated luminosity of 44.2 pb(-1). Several phase space regions are selected for the three-jet analysis in order to study the underlying parton dynamics from global topologies to the more restrictive regions of forward jets close to the proton direction. The measurements of cross sections for events with at least three jets are compared to fixed order QCD predictions of O(alpha(2)(s)) and O(alpha(3)(s)) and with Monte Carlo simulation programs where higher order effects are approximated by parton showers. A good overall description is provided by the O(alpha(3)(s)) calculation. Too few events are predicted at the lowest x similar to 10(-4), especially for topologies with two forward jets. This hints to large contributions at low x from initial state radiation of gluons close to the proton direction and unordered in transverse momentum. The Monte Carlo program in which gluon radiation is generated by the colour dipole model gives a good description of both the three- and the four-jet data in absolute normalisation and shape.
|
|
| 38. |
- Aktas, A., et al.
(författare)
-
Inclusive D*(+/-) meson and associated dijet production in deep-inelastic scattering at HERA
- 2007
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 51:2, s. 271-287
-
Tidskriftsartikel (refereegranskat)abstract
- Inclusive D*(+/-) production is measured in deep-inelastic ep scattering at HERA with the H1 detector. In addition, the production of dijets in events with a D*(+/-) meson is investigated. The analysis covers values of photon virtuality 2 <= Q(2) <= 100 GeV2 and of inelasticity 0.05 <= y <= 0.7. Differential cross sections are measured as a function of Q(2) and x and of various D*(+/-) meson and jet observables. Within the experimental and theoretical uncertainties all measured cross sections are found to be adequately described by next-to-leading order (NLO) QCD calculations, based on the photon - gluon fusion process and DGLAP evolution, without the need for an additional resolved component of the photon beyond what is included at NLO. A reasonable description of the data is also achieved by a prediction based on the CCFM evolution of partons involving the kT- unintegrated gluon distribution of the proton.
|
|
| 39. |
- Aktas, A., et al.
(författare)
-
Measurement of inclusive jet production in deep-inelastic scattering at high Q(2) and determination of the strong coupling
- 2007
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 653:2-4, s. 134-144
-
Tidskriftsartikel (refereegranskat)abstract
- Inclusive jet production is studied in neutral current deep-inelastic positron-proton scattering at large four momentum transfer squared Q(2) > 150 GeV2 with the H1 detector at HERA. Single and double differential inclusive jet cross sections are measured as a function of Q(2) and of the transverse energy E-T of the jets in the Breit frame. The measurements are found to be well described by calculations at next-to-leading order in perturbative QCD. The running of the strong coupling is demonstrated and the value of alpha(s)(M-Z) is determined. The ratio of the inclusive jet cross section to the inclusive neutral current cross section is also measured and used to extract a precise value for ces (M-Z) = 0.1193 +/- 0.0014(exp.)(-0.0030)(+0.0047) (th.) +/- 0.0016(pdf). (c) 2007 Elsevier BX All rights reserved.
|
|
| 40. |
- Aktas, A., et al.
(författare)
-
Tests of QCD factorisation in the diffractive production of dijets in deep-inelastic scattering and photoproduction at HERA
- 2007
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 51:3, s. 549-568
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements are presented of differential dijet cross sections in diffractive photoproduction (Q(2) < 0.01 GeV2) and deep-inelastic scattering processes (DIS, 4 < Q2 < 80 GeV2). The event topology is given by ep -> eXY, in which the system X, containing at least two jets, is separated from a leading low-mass baryonic system Y by a large rapidity gap. The dijet cross sections are compared with NLO QCD predictions based on diffractive parton densities previously obtained from a QCD analysis of inclusive diffractive DIS cross sections by H1. In DIS, the dijet data are well described, supporting the validity of QCD factorisation. The diffractive DIS dijet data are more sensitive to the diffractive gluon density at high fractional parton momentum than the measurements of inclusive diffractive DIS. In photoproduction, the predicted dijet cross section has to be multiplied by a factor of approximately 0.5 for both direct and resolved photon interactions to describe the measurements. The ratio of measured dijet cross section to NLO prediction in photoproduction is a factor 0.5 +/- 0.1 smaller than the same ratio in DIS. This suppression is the first clear observation of QCD hard scattering factorisation breaking at HERA. The measurements are also compared to the two soft colour neutralisation models SCI and GAL. The SCI model describes diffractive dijet production in DIS but not in photoproduction. The GAL model fails in both kinematic regions.
|
|
| 41. |
- Aktas, A., et al.
(författare)
-
Elastic J/psi production at HERA
- 2006
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 46:3, s. 585-603
-
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.
|
|
| 42. |
- Aktas, A., et al.
(författare)
-
Forward jet production in deep inelastic scattering at HERA
- 2006
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 46:1, s. 27-42
-
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.
|
|
| 43. |
- Aktas, A., et al.
(författare)
-
Measurement of event shape variables in deep-inelastic scattering at HERA
- 2006
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 46:2, s. 343-356
-
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).
|
|
| 44. |
- Aktas, A., et al.
(författare)
-
Photoproduction of dijets with high transverse momenta at HERA
- 2006
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 639:1, s. 21-31
-
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.
|
|
| 45. |
- Aaron, F. D., et al.
(författare)
-
A general search for new phenomena at HERA
- 2009
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 674:4-5, s. 257-268
-
Tidskriftsartikel (refereegranskat)abstract
- A model-independent search for deviations from the Standard Model prediction is performed using the full e(+/-) p data sample collected by the H1 experiment at HERA. All event topologies involving isolated electrons, photons, muons, neutrinos and jets with transverse momenta above 20 GeV are investigated in a single analysis. Events are assigned to exclusive classes according to their final state. A dedicated algorithm is used to search for deviations from the Standard Model in the distributions of the scalar sum of transverse momenta or the invariant mass of final state particles and to quantify their significance. Variables related to angular distributions and energy sharing between final state particles are also introduced to study the final state topologies. No significant deviation from the Standard Model expectation is observed in the phase space covered by this analysis. (C) 2009 Elsevier B.V. All rights reserved.
|
|
| 46. |
- Aaron, F. D., et al.
(författare)
-
A precision measurement of the inclusive ep scattering cross section at HERA
- 2009
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 64:4, s. 561-587
-
Tidskriftsartikel (refereegranskat)abstract
- A measurement of the inclusive deep inelastic neutral current e(+) p scattering cross section is reported in the region of four-momentum transfer squared, 12GeV(2) <= Q(2) <= 150 GeV2, and Bjorken x, 2 x 10(-4) <= x <= 0.1. The results are based on data collected by the H1 Collaboration at the ep collider HERA at positron and proton beam energies of E-e = 27.6 GeV and E-p = 920 GeV, respectively. The data are combined with previously published data, taken at E-p = 820 GeV. The accuracy of the combined measurement is typically in the range of 1.3-2%. A QCD analysis at next-to-leading order is performed to determine the parton distributions in the proton based on H1 data.
|
|
| 47. |
- Aaron, F. D., et al.
(författare)
-
Events with isolated leptons and missing transverse momentum and measurement of W production at HERA
- 2009
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 64:2, s. 251-271
-
Tidskriftsartikel (refereegranskat)abstract
- Events with high energy isolated electrons, muons or tau leptons and missing transverse momentum are studied using the full e(+/-)p data sample collected by the H1 experiment at HERA, corresponding to an integrated luminosity of 474 pb(-1). Within the Standard Model, events with isolated leptons and missing transverse momentum mainly originate from the production of single W bosons. The total single W boson production cross section is measured as 1.14 +/- 0.25 (stat.) +/- 0.14 (sys.) pb, in agreement with the Standard Model expectation. The data are also used to establish limits on the WW gamma gauge couplings and for a measurement of the W boson polarisation.
|
|
| 48. |
- Aaron, F. D., et al.
(författare)
-
Inclusive photoproduction of rho(0), K*(0) and phi mesons at HERA H1 Collaboration
- 2009
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 673:2, s. 119-126
-
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.
|
|
| 49. |
- Aaron, F. D., et al.
(författare)
-
Jet production in ep collisions at high Q(2) and determination of alpha(s)
- 2010
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 65:3-4, s. 363-383
-
Tidskriftsartikel (refereegranskat)abstract
- The production of jets is studied in deep-inelastic e(+/-) p scattering at large negative four momentum transfer squared 150 < Q(2) < 15000 GeV2 using HERA data taken in 1999-2007, corresponding to an integrated luminosity of 395 pb(-1). Inclusive jet, 2-jet and 3-jet cross sections, normalised to the neutral current deep-inelastic scattering cross sections, are measured as functions of Q(2), jet transverse momentum and proton momentum fraction. The measurements are well described by perturbative QCD calculations at next-to-leading order corrected for hadronisation effects. The strong coupling as determined from these measurements
|
|
| 50. |
- Aaron, F. D., et al.
(författare)
-
Measurement of the inclusive ep scattering cross section at low Q (2) and x at HERA
- 2009
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 63:4, s. 625-678
-
Tidskriftsartikel (refereegranskat)abstract
- A measurement of the inclusive ep scattering cross section is presented in the region of low momentum transfers, 0.2 GeV2 a parts per thousand currency signQ (2)a parts per thousand currency sign12 GeV2, and low Bjorken x, 5a <...10(-6)a parts per thousand currency signxa parts per thousand currency sign0.02. The result is based on two data sets collected in dedicated runs by the H1 Collaboration at HERA at beam energies of 27.6 GeV and 920 GeV for positrons and protons, respectively. A combination with data previously published by H1 leads to a cross section measurement of a few percent accuracy. A kinematic reconstruction method exploiting radiative ep events extends the measurement to lower Q (2) and larger x. The data are compared with theoretical models which apply to the transition region from photoproduction to deep inelastic scattering.
|
|
