1. 
 Aktas, A., et al.
(författare)

Diffractive deepinelastic scattering with a leading proton at HERA
 2006

Ingår i: European Physical Journal C. Particles and Fields.  Springer.  14346044. ; 48:3, s. 749766

Tidskriftsartikel (refereegranskat)abstract
 The cross section for the diffractive deepinelastic 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 GeV2 in squared fourmomentum 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 subleading exchange.


2. 
 Aktas, A., et al.
(författare)

Measurement and QCD analysis of the diffractive deepinelastic scattering cross section at HERA
 2006

Ingår i: European Physical Journal C. Particles and Fields.  Springer.  14346044. ; 48:3, s. 715748

Forskningsöversikt (refereegranskat)abstract
 A detailed analysis is presented of the diffractive deepinelastic 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 fourmomentum 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 nexttoleading 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.


3. 
 Aktas, A., et al.
(författare)

Elastic J/psi production at HERA
 2006

Ingår i: European Physical Journal C. Particles and Fields.  Springer.  14346044. ; 46:3, s. 585603

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 photonproton centre of mass energy Wgamma p is analysed in the range 40 <= Wgamma p <= 305 GeV in photoproduction and 40 <= Wgamma p <= 160 GeV in electroproduction. The Wgamma 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 fourmomentum transfer at the proton vertex, are measured in the range vertical bar t vertical bar < 1.2 GeV2 as functions of Wgamma p and Q(2). Effective Pomeron trajectories are determined for photoproduction and electroproduction. The J/psi production and decay angular distributions are consistent with schannel 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.


4. 
 Aktas, A., et al.
(författare)

Measurement of charm and beauty dijet cross sections in photoproduction at HERA using the H1 vertex detector
 2006

Ingår i: European Physical Journal C. Particles and Fields.  Springer.  14346044. ; 47:3, s. 597610

Tidskriftsartikel (refereegranskat)abstract
 A measurement of charm and beauty dijet photoproduction cross sections at the ep collider HERA is presented. Events are selected with two or more jets of transverse momentum Pt > 11(8) GeV in the central range of pseudorapidity 0.9 <eta (jet1(2))< 1.3. The fractions of events containing charm and beauty quarks are determined using a method based on the impact parameter, in the transverse plane, of tracks to the primary vertex, as measured by the HI central vertex detector. Differential dijet cross sections for charm and beauty, and their relative contributions to the flavour inclusive dijet photoproduction cross section, are measured as a function of the transverse momentum of the leading jet, the average pseudorapidity of the two jets and the observable chi(obs)(gamma). Taking into account the theoretical uncertainties, the charm cross sections are consistent with a QCD calculation in nexttoleading order, while the predicted cross sections for beauty production are somewhat lower than the measurement.


5. 
 Aktas, A., et al.
(författare)

Search for a narrow baryonic resonance decaying to K(s)(0)p or Ks(0)(p)overbar in deep inelastic scattering at HERA
 2006

Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and HighEnergy Physics.  Elsevier.  03702693. ; 639:34, s. 202209

Tidskriftsartikel (refereegranskat)abstract
 A search for a narrow baryonic resonance decaying to K(s)(0)p or Ks(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 Ks(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.


6. 
 Aktas, A., et al.
(författare)

Search for doublycharged Higgs boson production at HERA
 2006

Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and HighEnergy Physics.  Elsevier.  03702693. ; 638:56, s. 432440

Tidskriftsartikel (refereegranskat)abstract
 A search for the single production of doublycharged 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 doublycharged Higgs production is observed and mass dependent upper limits are derived on the Yukawa couplings h(el) of the Higgs boson to an electronlepton pair. Assuming that the doublycharged 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 doublycharged 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.


7. 
 Aktas, A., et al.
(författare)

Diffractive photoproduction of rho mesons with large momentum transfer at HERA
 2006

Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and HighEnergy Physics.  Elsevier.  03702693. ; 638:56, s. 422431

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 photonproton 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 schannel helicity conservation, with contributions from both single and double helicityflip being observed. The results are compared to the predictions of perturbative QCD models.


8. 
 Aktas, A., et al.
(författare)

Tau lepton production in ep collisions at HERA
 2006

Ingår i: European Physical Journal C. Particles and Fields.  Springer.  14346044. ; 48:3, s. 699714

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 19942000. 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.


9. 
 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.  14346044. ; 46:1, s. 2742

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 dijet 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 nexttoleading order QCD calculations and with the predictions of various QCDbased models.


10. 
 Aktas, A., et al.
(författare)

Measurement of event shape variables in deepinelastic scattering at HERA
 2006

Ingår i: European Physical Journal C. Particles and Fields.  Springer.  14346044. ; 46:2, s. 343356

Tidskriftsartikel (refereegranskat)abstract
 Deepinelastic 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 Cparameter. The fourmomentum 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 nonperturbative 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).

