[show abstract][hide abstract] ABSTRACT: Deep-inelastic e^\pm p scattering at high squared momentum transfer Q^2 up to 30000 GeV^2 is used to search for eq contact interactions associated to scales far beyond the HERA centre of mass energy. The neutral current cross section measurements d sigma / d Q^2, corresponding to integrated luminosities of 16.4 pb^-1 of e^- p data and 100.8 pb^-1 of e^+ p data, are well described by the Standard Model and are analysed to set constraints on new phenomena. For conventional contact interactions lower limits are set on compositeness scales Lambda ranging between 1.6 - 5.5 TeV. Couplings and masses of leptoquarks and squarks in R-parity violating supersymmetry are constrained to M / lambda > 0.3 - 1.4 TeV. A search for low scale quantum gravity effects in models with large extra dimensions provides limits on the effective Planck scale of M_S > 0.8 TeV. A form factor analysis yields a bound on the radius of light quarks of R_q < 1.0 x 10^-18 m.
Physics Letters B 09/2013; 568:35-47. · 4.57 Impact Factor
[show abstract][hide abstract] ABSTRACT: Inclusive e\pmp single and double differential cross sections for neutral and
charged current deep inelastic scattering processes are measured with the H1
detector at HERA. The data were taken at a centre-of-mass energy of \surds =
319GeV with a total integrated luminosity of 333.7 pb-1 shared between two
lepton beam charges and two longitudinal lepton polarisation modes. The
differential cross sections are measured in the range of negative fourmomentum
transfer squared, Q2, between 60 and 50 000GeV2, and Bjorken x between 0.0008
and 0.65. The measurements are combined with earlier published unpolarised H1
data to improve statistical precision and used to determine the structure
function xF_3^gammaZ. A measurement of the neutral current parity violating
structure function F_2^gammaZ is presented for the first time. The polarisation
dependence of the charged current total cross section is also measured. The new
measurements are well described by a next-to-leading order QCD fit based on all
published H1 inclusive cross section data which are used to extract the parton
distribution functions of the proton.
Journal of High Energy Physics 06/2012; 1209:061. · 5.62 Impact Factor
[show abstract][hide abstract] ABSTRACT: Inclusive charm and beauty cross sections are measured in e-p and e+p neutral current collisions at HERA in the kinematic region of photon virtuality 5<Q^2<2000 GeV^2 and Bjorken scaling variable 0.0002<x<0.05. The data were collected with the H1 detector in the years 2006 and 2007 corresponding to an integrated luminosity of 189 pb^-1. The numbers of charm and beauty events are determined using variables reconstructed by the H1 vertex detector including the impact parameter of tracks to the primary vertex and the position of the secondary vertex. The measurements are combined with previous data and compared to QCD predictions.
European Physical Journal C 01/2010; 65:89-109. · 5.25 Impact Factor
[show abstract][hide abstract] ABSTRACT: The production of jets is studied in deep-inelastic e+p scattering at low negative four momentum transfer squared 5<Q^2<100 GeV^2 and at inelasticity 0.2<y<0.7 using data recorded by the H1 detector at HERA in the years 1999 and 2000, corresponding to an integrated luminosity of 43.5 pb^-1. Inclusive jet, 2-jet and 3-jet cross sections as well as the ratio of 3-jet to 2-jet cross sections are measured as a function of Q^2 and jet transverse momentum. The 2-jet cross section is also measured as a function of the proton momentum fraction xi. The measurements are well described by perturbative quantum chromodynamics at next-to-leading order corrected for hadronisation effects and are subsequently used to extract the strong coupling alpha_s.
European Physical Journal C 01/2010; 67:1-24. · 5.25 Impact Factor
[show abstract][hide abstract] ABSTRACT: A search for excited quarks is performed using the full e±p data sample collected by the H1 experiment at HERA, corresponding to a total integrated luminosity of 475 pb−1. The electroweak decays of excited quarks q∗→qγ, q∗→qZ and q∗→qW with subsequent hadronic or leptonic decays of the W and Z bosons are considered. No evidence for first generation excited quark production is found. Mass dependent exclusion limits on q∗ production cross sections and on the ratio f/Λ of the coupling to the compositeness scale are derived within gauge mediated models. These limits extend the excluded region compared to previous excited quark searches.
[show abstract][hide abstract] 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
* ± meson in the event. The fragmentation parameters extracted for the two phase space regions are found to be different.
European Physical Journal C 01/2009; 59:589-606. · 5.25 Impact Factor
[show abstract][hide abstract] ABSTRACT: A first measurement is presented of the charge asymmetry in the hadronic final state from the hard interaction in deep-inelastic ep neutral current scattering at HERA. The measurement is performed in the range of negative squared four momentum transfer 100Q28000 GeV2. The difference between the event normalised distributions of the scaled momentum, xp, for positively and negatively charged particles, measured in the current region of the Breit frame, is studied together with its evolution as a function of Q. The results are compared to Monte Carlo models at the hadron and parton levels.
[show abstract][hide abstract] 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, 12 GeV2≤Q
2≤150 GeV2, and Bjorken x, 2×10−4≤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
=27.6 GeV and E
=920 GeV, respectively. The data are combined with previously published data, taken at E
=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.
European Physical Journal C 01/2009; 64:561-587. · 5.25 Impact Factor
[show abstract][hide abstract] 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 GeV^2 and the inelasticity 0.1 < y < 0.6. The K_s and Lambda production cross sections and their ratios are determined. K_s production is compared to the production of charged particles in the same region of phase space. The Lambda - anti-Lambda asymmetry is also measured and found to be consistent with zero. Predictions of leading order Monte Carlo programs are compared to the data.
European Physical Journal C 01/2009; 61:185-205. · 5.25 Impact Factor
[show abstract][hide abstract] ABSTRACT: The ATLAS detector as installed in its experimental cavern at point 1 at CERN is described in this paper. A brief overview of the expected performance of the detector when the Large Hadron Collider begins operation is also presented.
Journal of Instrumentation 01/2008; 3:S08003. · 1.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: The ATLAS (A Toroidal LHC ApparatuS) Inner Detector provides charged particle tracking in the centre of the ATLAS experiment at the Large Hadron Collider (LHC). The Inner Detector consists of three subdetectors: the Pixel Detector, the Semiconductor Tracker (SCT), and the Transition Radiation Tracker (TRT). This paper summarizes the tests that were carried out at the final stage of SCT+TRT integration prior to their installation in ATLAS. The combined operation and performance of the SCT and TRT barrel and endcap detectors was investigated through a series of noise tests, and by recording the tracks of cosmic rays. This was a crucial test of hardware and software of the combined tracker detector systems. The results of noise and cross-talk tests on the SCT and TRT in their final assembled configuration, using final readout and supply hardware and software, are reported. The reconstruction and analysis of the recorded cosmic tracks allowed testing of the offline analysis chain and verification of basic tracker performance parameters, such as efficiency and spatial resolution, in combined operation before installation.
[show abstract][hide abstract] ABSTRACT: The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have searched for the neutral Higgs bosons which are predicted by the Minimal Supersymmetric standard model (MSSM). The data of the four collaborations are statistically combined and examined for their consistency with the background hypothesis and with a possible Higgs boson signal. The combined LEP data show no significant excess of events which would indicate the production of Higgs bosons. The search results are used to set upper bounds on the cross-sections of various Higgs-like event topologies. The results are interpreted within the MSSM in a number of "benchmark" models, including CP-conserving and CP-violating scenarios. These interpretations lead in all cases to large exclusions in the MSSM parameter space. Absolute limits are set on the parameter tan beta and, in some scenarios, on the masses of neutral Higgs bosons.
[show abstract][hide abstract] ABSTRACT: The Transition Radiation Tracker (TRT) sits at the outermost part of the ATLAS Inner Detector, encasing the Pixel Detector and the Semi-Conductor Tracker (SCT). The TRT combines charged particle track reconstruction with electron identification capability. This is achieved by layers of xenon-filled straw tubes with periodic radiator foils or fibers providing TR photon emission. The design and choice of materials have been optimized to cope with the harsh operating conditions at the LHC, which are expected to lead to an accumulated radiation dose of 10 Mrad and a neutron fluence of up to 2middot10<sup>14</sup> n/cm<sup>2 </sup> after ten years of operation. The TRT comprises a barrel containing 52 000 axial straws and two end-cap parts with 320 000 radial straws. The total of 420 000 electronic channels (two channels per barrel straw) allows continuous tracking with many projective measurements (more than 30 straw hits per track). The assembly of the barrel modules in the US has recently been completed, while the end-cap wheel construction in Russia has reached the 50% mark. After testing at the production sites and shipment to CERN, all modules and wheels undergo a series of quality and conformity measurements. These acceptance tests survey dimensions, wire tension, gas-tightness, high-voltage stability and gas-gain uniformity along each individual straw. This paper gives details on the acceptance criteria and measurement methods. An overview of the most important results obtained to-date is also given
IEEE Transactions on Nuclear Science 01/2006; · 1.22 Impact Factor
[show abstract][hide abstract] ABSTRACT: The transition radiation tracker (TRT) is one of three particle tracking detectors now under construction for the ATLAS experiment, whose goal is to exploit the highly exciting new physics potential at CERN's next accelerator, the so called Large Hadron Collider (LHC). The TRT consists of 370000 straw proportional tubes of 4 mm diameter with a 30 micron thick anode wire, which will be operated with a Xe/CO<sub>2 </sub>/O<sub>2</sub> gas mixture at a high voltage of approximately 1.5 kV. While the construction of the TRT is now well under way, a number of interesting and challenging questions need to be solved with regard to wire aging phenomena, which are induced by pollution originating from very small amounts of silicon-based vacuum materials in some components of the gas system. Finally a guideline to avoid aging in wire chamber detectors in high luminosity experiments is given
IEEE Transactions on Nuclear Science (IEEE T NUCL SCI); 11/2005