1. 
 Aaron, F. D., et al.
(författare)

Measurement of charm and beauty jets in deep inelastic scattering at HERA
 2011

Ingår i: European Physical Journal C. Particles and Fields.  Springer.  14346044. ; 71:1

Tidskriftsartikel (refereegranskat)abstract
 Measurements of cross sections for events with charm and beauty jets in deep inelastic scattering at HERA are presented. Events with jets of transverse energy ET(jet) > 6 GeV and pseudorapidity  1.0 < eta(jet) < 1.5 in the laboratory frame are selected in the kinematic region of photon virtuality Q(2) > 6 GeV2 and inelasticity variable 0.07 < y < 0.625. Measurements are also made requiring a jet in the Breit frame with ET(*jet) > 6 GeV. 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 jets are determined using variables reconstructed using the H1 vertex detector with which the impact parameters of the tracks to the primary vertex and the position of secondary vertices are measured. The measurements are compared with QCD predictions and with previous measurements where heavy flavours are identified using muons.


2. 
 Aaron, F. D., et al.
(författare)

Measurement of isolated photon production in deepinelastic scattering at HERA
 2008

Ingår i: European Physical Journal C. Particles and Fields.  Springer.  14346044. ; 54:3, s. 371387

Tidskriftsartikel (refereegranskat)abstract
 The production of isolated photons in deepinelastic scattering ep > e gamma X is measured with the H1 detector at HERA. The measurement is performed in the kinematic range of negative fourmomentum transfer squared 4 < Q(2)< 150 GeV2 and a mass of the hadronic system WX > 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 < ET(gamma)< 10 GeV and pseudorapidity range 1.2 <eta(gamma)< 1.8 is measured as a function of ET(gamma), eta(gamma) and Q(2). Isolated photon cross sections are also measured for events with no jets or at least one hadronic jet. The measurements are compared with predictions from Monte Carlo generators modelling the photon radiation from the quark and the electron lines, as well as with calculations at leading and next to leading order in the strong coupling. The predictions significantly underestimate the measured cross sections.


3. 
 Aaron, F. D., et al.
(författare)

Measurement of the cross section for diffractive deepinelastic scattering with a leading proton at HERA
 2011

Ingår i: European Physical Journal C. Particles and Fields.  Springer.  14346044. ; 71:3

Tidskriftsartikel (refereegranskat)abstract
 The cross section for the diffractive deepinelastic scattering process ep > eXp is measured, with the leading final state proton detected in the H1 Forward Proton Spectrometer. The data sample covers the range x(P) < 0.1 in fractional proton longitudinal momentum loss, 0.1 < vertical bar t vertical bar < 0.7 GeV2 in squared fourmomentum transfer at the proton vertex and 4 < Q(2) < 700 GeV2 in photon virtuality. The cross section is measured fourfold differentially in t, x(P), Q2 and beta = x/x(P), where x is the Bjorken scaling variable. The t and x(P) dependences are interpreted in terms of an effective pomeron trajectory and a subleading exchange. The data are compared with perturbative QCD predictions at nexttoleading order based on diffractive parton distribution functions previously extracted from complementary measurements of inclusive diffractive deepinelastic scattering. The ratio of the diffractive to the inclusive ep cross section is studied as a function of Q(2), beta and x(P).


4. 
 Aaron, F. D., et al.
(författare)

Search for squarks in Rparity violating supersymmetry in ep collisions at HERA
 2011

Ingår i: European Physical Journal C. Particles and Fields.  Springer.  14346044. ; 71:3

Tidskriftsartikel (refereegranskat)abstract
 A search for squarks in Rparity violating supersymmetry is performed in e(+/)p collisions at HERA using the H1 detector. The full data sample taken at a centreofmass energy root s = 319 GeV is used for the analysis, corresponding to an integrated luminosity of 255 pb(1) of e(+)p and 183 pb(1) of e()p collision data. The resonant production of squarks via a Yukawa coupling. lambda' is considered, taking into account direct and indirect Rparity violating decay modes. Final states with jets and leptons are investigated. No evidence for squark production is found and mass dependent limits on lambda' are obtained in the framework of the Minimal Supersymmetric Standard Model and in the Minimal Supergravity Model. In the considered part of the parameter space, for a Yukawa coupling of electromagnetic strength lambda' = 0.3, squarks of all flavours are excluded up to masses of 275 GeV at 95% confidence level, with downtype squarks further excluded up to masses of 290 GeV.


5. 
 Aaron, F. D., et al.
(författare)

Three and fourjet production at low x at HERA
 2008

Ingår i: European Physical Journal C. Particles and Fields.  Springer.  14346044. ; 54:3, s. 389409

Tidskriftsartikel (refereegranskat)abstract
 Three and fourjet production is measured in deepinelastic 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 threejet 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 fourjet data in absolute normalisation and shape.


6. 
 Aaron, F. D., et al.
(författare)

Deeply virtual Compton scattering and its beam charge asymmetry in e(+/)p collisions at HERA
 2009

Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and HighEnergy Physics.  Elsevier.  03702693. ; 681:5, s. 391399

Tidskriftsartikel (refereegranskat)abstract
 A measurement of elastic deeply virtual Compton scattering gamma*p > gamma p using e(+) p and e() p collision data recorded with the HI detector at HERA is presented. The analysed data sample corresponds to an integrated luminosity of 306 pb(1), almost equally shared between both beam charges. The cross section is measured as a function of the virtuality Q(2) of the exchanged photon and the centreofmass energy W of the gamma*p system in the kinematic domain 6.5 < Q(2) < 80 GeV2, 30 < W < 140 GeV and t < 1 GeV2, where t denotes the squared momentum transfer at the proton vertex. The cross section is determined differentially in t for different Q(2) and W values and exponential tslope parameters are derived. Using e(+) p and e() p data samples, a beam charge asymmetry is extracted for the first time in the low Biorken x kinematic domain. The observed asymmetry is attributed to the interference between BetheHeitler and deeply virtual Compton scattering processes. Experimental results are discussed in the context of two different models, one based on generalised parton distributions and one based on the dipole approach. (C) 2009 Elsevier B.V. All rights reserved.


7. 
 Aaron, F. D., et al.
(författare)

Determination of the integrated luminosity at HERA using elastic QED Compton events
 2012

Ingår i: European Physical Journal C. Particles and Fields.  Springer.  14346044. ; 72:10

Tidskriftsartikel (refereegranskat)abstract
 A measurement of the integrated luminosity at the ep collider HERA is presented, exploiting the elastic QED Compton process ep > e gamma p. The electron and the photon are detected in the backward calorimeter of the H1 experiment. The integrated luminosity of the data recorded in 2003 to 2007 is determined with a precision of 2.3%. The measurement is found to be compatible with the corresponding result obtained using the BetheHeitler process.


8. 
 Aaron, F. D., et al.
(författare)

Diffractive dijet photoproduction in ep collisions at HERA
 2010

Ingår i: European Physical Journal C. Particles and Fields.  Springer.  14346044. ; 70:12, s. 1537

Tidskriftsartikel (refereegranskat)abstract
 Measurements are presented of single and doubledifferential dijet cross sections in diffractive photoproduction based on a data sample with an integrated luminosity of 47 pb(1). The events are of the type ep > eXY, where the hadronic system X contains at least two jets and is separated by a large rapidity gap from the system Y, which consists of a leading proton or lowmass proton excitation. The dijet cross sections are compared with QCD calculations at nexttoleading order and with a Monte Carlo model based on leading order matrix elements with parton showers. The measured cross sections are smaller than those obtained from the nexttoleading order calculations by a factor of about 0.6. This suppression factor has no significant dependence on the fraction x (gamma) of the photon fourmomentum entering the hard subprocess. Ratios of the diffractive to the inclusive dijet cross sections are measured for the first time and are compared with Monte Carlo models.


9. 
 Aaron, F. D., et al.
(författare)

Inclusive deep inelastic scattering at high Q(2) with longitudinally polarised lepton beams at HERA
 2012

Ingår i: Journal of High Energy Physics.  Springer.  10298479. ; :9

Tidskriftsartikel (refereegranskat)abstract
 Inclusive e(+/)p 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 centreofmass energy of root s = 319 GeV 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, Q(2), between 60 and 50 000GeV(2), 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)(gamma Z). A measurement of the neutral current parity violating structure function F2(gamma Z) 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 nexttoleading order QCD fit based on all published H1 inclusive cross section data which are used to extract the parton distribution functions of the proton.


10. 
 Aaron, F. D., et al.
(författare)

Inclusive measurement of diffractive deepinelastic scattering at HERA
 2012

Ingår i: European Physical Journal C. Particles and Fields.  Springer.  14346044. ; 72:7

Tidskriftsartikel (refereegranskat)abstract
 The diffractive process ep > eXY, where Y denotes a proton or its low mass excitation with MY < 1.6 GeV, is studied with the H1 experiment at HERA. The analysis is restricted to the phase space region of the photon virtuality 3 <= Q(2) <= 1600 GeV2, the square of the fourmomentum transfer at the proton vertex vertical bar t vertical bar < 1.0 GeV2 and the longitudinal momentum fraction of the incident proton carried by the colourless exchange x(P) < 0.05. Triple differential cross sections are measured as a function of x(P), Q(2) and beta = x/x(P) where x is the Bjorken scaling variable. These measurements are made after selecting diffractive events by demanding a large empty rapidity interval separating the final state hadronic systems X and Y. High statistics measurements covering the data taking periods 19992000 and 20042007 are combined with previously published results in order to provide a single set of diffractive cross sections from the H1 experiment using the large rapidity gap selection method. The combined data represent a factor between three and thirty increase in statistics with respect to the previously published results. The measurements are compared with predictions from NLO QCD calculations based on diffractive parton densities and from a dipole model. The proton vertex factorisation hypothesis is tested.

