| 1. |
- Aktas, A, et al.
(författare)
-
A direct search for stable magnetic monopoles produced in positron-proton collisions at HERA
- 2005
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 41, s. 133-141
-
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.
|
|
| 2. |
- Aktas, A, et al.
(författare)
-
A general search for new phenomena in ep scattering at HERA
- 2004
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 602:1-2, s. 14-30
-
Tidskriftsartikel (refereegranskat)abstract
- A model-independent search for deviations from the Standard Model prediction is performed in e(+) p and e(-) p collisions at HERA using H1 data corresponding to an integrated luminosity of 117 pb(-1). For the first time all event topologies involving isolated electrons, photons, muons, neutrinos and jets with high transverse momenta are investigated in a single analysis. Events are assigned to exclusive classes according to their final state. A statistical algorithm is developed to search for deviations from the Standard Model in the distributions of the scalar sum of transverse momenta or invariant mass of final state particles and to quantify their significance. A good agreement with the Standard Model prediction is observed in most of the event classes. The most significant deviation is found for a topology containing an isolated muon, missing transverse momentum and a jet, consistent with a previously reported observation.
|
|
| 3. |
- Aktas, A, et al.
(författare)
-
Search for light gravitinos in events with photons and missing transverse momentum at HERA
- 2005
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 616:1-2, s. 31-42
-
Tidskriftsartikel (refereegranskat)abstract
- A search for gravitinos produced in e(+/-)p collisions is performed using the H1 detector at HERA. The data were taken at a centre-of-mass energy of 319 GeV and correspond to an integrated luminosity of 64.3 pb(-1) for e(+)p collisions and 13.5 pb(-1) for e(-)p collisions. If R-parity is not conserved, the t-channel exchange of a selectron can produce a neutralino, which, in models where the gravitino is the lightest supersymmetric particle, subsequently decays into a photon and a light gravitino. The resulting event signature, which involves an isolated photon, a jet and missing transverse energy, is analysed for the first time at HERA. No deviation from the Standard Model is found. Exclusion limits on the cross section and on R-parity-violating Yukawa couplings are derived in a Gauge Mediated Supersymmetry Breaking scenario. The results are independent of the squark sector. Neutralinos and supersymmetric partners of the left-handed electron with masses up to 112 GeV and 164 GeV, respectively, can be ruled out at the 95% confidence level for R-parity-violating couplings lambda' equal to 1, in some parts of the parameter space of the considered model.
|
|
| 4. |
- Aktas, A, et al.
(författare)
-
Evidence for a narrow anti-charmed baryon state
- 2004
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 588:1-2, s. 17-28
-
Tidskriftsartikel (refereegranskat)abstract
- A narrow resonance in D*(-)p and D*(+)(p) over bar invariant mass combinations is observed in inelastic electron-proton collisions at centre-of-mass energies of 300 GeV and 320 GeV at HERA. The resonance has a mass of 3099 +/- 3(stat.) +/- 5(syst.) MeV and a measured Gaussian width of 12 +/- 3(stat.) MeV, compatible with the experimental resolution. The resonance is interpreted as an anti-charmed baryon with a minimal constituent quark composition of uudd (c) over bar, together with the charge conjugate. (C) 2004 Elsevier B.V. All rights reserved.
|
|
| 5. |
- Aktas, A, et al.
(författare)
-
Measurement of charm and beauty photoproduction at HERA using D*mu correlations
- 2005
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 621:1-2, s. 56-71
-
Tidskriftsartikel (refereegranskat)abstract
- A measurement of charm and beauty photoproduction at the electron proton collider HERA is presented based on the simultaneous detection of a D*(+/-) meson and a muon. The correlation between the D* meson and the muon serves to separate the charm and beauty contributions and the analysis provides comparable sensitivity to both. The total and differential experimental cross sections are compared to LO and NLO QCD calculations. The measured charm cross section is in good agreement with QCD predictions including higher order effects while the beauty cross section is higher.
|
|
| 6. |
- Aktas, A, et al.
(författare)
-
Search for bosonic stop decays in R-parity violating supersymmetry in e(+)p collisions at HERA
- 2004
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 599:3-4, s. 159-172
-
Tidskriftsartikel (refereegranskat)abstract
- A search for scalar top quarks in R-parity violating supersymmetry is performed in e(+)p collisions at HERA using the H1 detector. The data, taken at roots = 319 GeV and 301 GeV, correspond to an integrated luminosity of 106 pb(-1). The resonant production of scalar top quarks t in positron quark fusion via an R-parity violating Yukawa coupling lambda' is considered with the subsequent bosonic stop decay t --> BW. The R-parity violating decay of the sbottom quark b --> dv(e) and leptonic and hadronic W decays are considered. No evidence for stop production is found in the search for bosonic stop decays nor in a search for the direct R-parity violating decay t --> eq. Mass dependent limits on lambda' are obtained in the framework of the minimal supersymmetric Standard Model. Stop quarks with masses up to 275 GeV can be excluded at the 95% confidence level for a Yukawa coupling of electromagnetic strength. (C) 2004 Elsevier B.V. All rights reserved.
|
|
| 7. |
- Aktas, A, et al.
(författare)
-
Inclusive production of D+, D-0, D-s(+) and D*(+) mesons in deep inelastic scattering at HERA
- 2005
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 38:4, s. 447-459
-
Tidskriftsartikel (refereegranskat)abstract
- Inclusive production cross sections are measured in deep inelastic scattering at HERA for meson states composed of a charm quark and a light antiquark or the charge conjugate. The measurements cover the kinematic region of photon virtuality 2 < Q(2) < 100 GeV2, inelasticity 0.05 < y < 0.7, D meson transverse momenta p(t)( D) greater than or equal to 2.5 GeV and pseudorapidity |eta( D)| less than or equal to 1.5. The identification of the D-meson decays and the reduction of the combinatorial background profit from the reconstruction of displaced secondary vertices by means of the H1 silicon vertex detector. The production of charmed mesons containing the light quarks u, d and s is found to be compatible with a description in which the hard scattering is followed by a factorisable and universal hadronisation process.
|
|
| 8. |
- Aktas, A, et al.
(författare)
-
Measurement of anti-deuteron photoproduction and a search for heavy stable charged particles at HERA
- 2004
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 36:4, s. 413-423
-
Tidskriftsartikel (refereegranskat)abstract
- The cross section for anti-deuteron photoproduction is measured at HERA at a mean centre-of-mass energy of W-gammap=200 GeV in the range 0.2 < p(T)/M < 0.7 and y < 0.4, where M, p(T) and y are the mass, transverse momentum and rapidity of the anti-deuteron in the HERA laboratory frame, respectively. The numbers of anti-deuterons per event are found to be similar in photoproduction to those in central proton-proton collisions at the CERN ISR but much lower than those in central Au-Au collisions at RHIC. The coalescence parameter B-2, which characterizes the likelihood of anti-deuteron production, is measured in photoproduction to be 0.010+/-0.002+/-0.001, which is much higher than in Au-Au collisions at a similar nucleon-nucleon centre-of-mass energy. No significant production of particles heavier than deuterons is observed and upper limits are set on the photoproduction cross sections for such particles.
|
|
| 9. |
- Aktas, A, et al.
(författare)
-
Measurement of beauty production at HERA using events with muons and jets
- 2005
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 41:4, s. 453-467
-
Tidskriftsartikel (refereegranskat)abstract
- A measurement of the beauty production cross section in ep collisions at a centre-of-mass energy of 319 GeV is presented. The data were collected with the H1 detector at the HERA collider in the years 1999-2000. Events are selected by requiring the presence of jets and muons in the final state. Both the long lifetime and the large mass of b-flavoured hadrons are exploited to identify events containing beauty quarks. Differential cross sections are measured in photoproduction, with photon virtualities Q(2) < 1 GeV2, and in deep inelastic scattering, where 2 < Q(2) < 100 GeV2. The results are compared with perturbative QCD calculations to leading and next-to-leading order. The predictions are found to be somewhat lower than the data.
|
|
| 10. |
- Aktas, A, et al.
(författare)
-
Measurement of dijet cross sections in ep interactions with a leading neutron at HERA
- 2005
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 41:3, s. 273-286
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements are reported of the production of dijet events with a leading neutron in ep interactions at HERA. Differential cross sections for photoproduction and deep inelastic scattering are presented as a function of several kinematic variables. Leading order QCD simulation programs are compared with the measurements. Models in which the real or virtual photon interacts with a parton of an exchanged pion are able to describe the data. Next-to-leading order perturbative QCD calculations based on pion exchange are found to be in good agreement with the measured cross sections. The fraction of leading neutron dijet events with respect to all dijet events is also determined. The dijet events with a leading neutron have a lower fraction of resolved photon processes than do the inclusive dijet data.
|
|
