80 research outputs found
Recherche d'un isobare d'isospin I=5/2 dans la reaction a 1,9 GeV/c et calcul des spectres de masses , entre 1,6 et 4 GeV/c, a l'aide du modele d'echange d'un pion
No full textMeasurements of Inclusive Production with Large at the -Collider
No full textWe report results of inclusive measurements of anti-Lambda, produced in the forward direction at the SPS with sqrt(s) = 630 GeV, using the UA8 small angle Roman Pot spectrometers. These measurements cover the range in Feynman-x_f and transverse momentum, 0.6 < x_f < 1.0 and 0.4 < p_t < 0.7 GeV, respectively. Within a systematic uncertainty of +-20% on the absolute cross section measurements, the results are indistinguishable from those made by some of us in two earlier experiments at the CERN Intersecting Storage Rings, with energies, sqrt(s) = 53 and 62 GeV. In the x_f-range, 0.6-0.9, the absolute cross sections are lower by a factor of 2 to 3 than the predictions of the Lund model as embodied in the PYTHIA 5.6 and JETSET 7.3 Monte Carlo programs, indicating inadequacies in knowledge of the baryon fragmentation function. For the largest x_f-range, 0.9-1.0, the measurements agree with the Monte Carlo predictions. We have measured the average anti-Lambda polarization for our events and find (6 +- 12%), consistent with previous measurements at the ISR in the present region of x_f - p_t.We report results of inclusive measurements of anti-Lambda, produced in the forward direction at the SPS with sqrt(s) = 630 GeV, using the UA8 small angle Roman Pot spectrometers. These measurements cover the range in Feynman-x_f and transverse momentum, 0.6 < x_f < 1.0 and 0.4 < p_t < 0.7 GeV, respectively. Within a systematic uncertainty of +-20% on the absolute cross section measurements, the results are indistinguishable from those made by some of us in two earlier experiments at the CERN Intersecting Storage Rings, with energies, sqrt(s) = 53 and 62 GeV. In the x_f-range, 0.6-0.9, the absolute cross sections are lower by a factor of 2 to 3 than the predictions of the Lund model as embodied in the PYTHIA 5.6 and JETSET 7.3 Monte Carlo programs, indicating inadequacies in knowledge of the baryon fragmentation function. For the largest x_f-range, 0.9-1.0, the measurements agree with the Monte Carlo predictions. We have measured the average anti-Lambda polarization for our events and find (6 +- 12%), consistent with previous measurements at the ISR in the present region of x_f - p_t.We report results of inclusive measurements of anti-Lambda, produced in the forward direction at the SPS with sqrt(s) = 630 GeV, using the UA8 small angle Roman Pot spectrometers. These measurements cover the range in Feynman-x_f and transverse momentum, 0.6 < x_f < 1.0 and 0.4 < p_t < 0.7 GeV, respectively. Within a systematic uncertainty of +-20% on the absolute cross section measurements, the results are indistinguishable from those made by some of us in two earlier experiments at the CERN Intersecting Storage Rings, with energies, sqrt(s) = 53 and 62 GeV. In the x_f-range, 0.6-0.9, the absolute cross sections are lower by a factor of 2 to 3 than the predictions of the Lund model as embodied in the PYTHIA 5.6 and JETSET 7.3 Monte Carlo programs, indicating inadequacies in knowledge of the baryon fragmentation function. For the largest x_f-range, 0.9-1.0, the measurements agree with the Monte Carlo predictions. We have measured the average anti-Lambda polarization for our events and find (6 +- 12%), consistent with previous measurements at the ISR in the present region of x_f - p_t.We report results of inclusive measurements of anti-Lambda, produced in the forward direction at the SPS with sqrt(s) = 630 GeV, using the UA8 small angle Roman Pot spectrometers. These measurements cover the range in Feynman-x_f and transverse momentum, 0.6 < x_f < 1.0 and 0.4 < p_t < 0.7 GeV, respectively. Within a systematic uncertainty of +-20% on the absolute cross section measurements, the results are indistinguishable from those made by some of us in two earlier experiments at the CERN Intersecting Storage Rings, with energies, sqrt(s) = 53 and 62 GeV. In the x_f-range, 0.6-0.9, the absolute cross sections are lower by a factor of 2 to 3 than the predictions of the Lund model as embodied in the PYTHIA 5.6 and JETSET 7.3 Monte Carlo programs, indicating inadequacies in knowledge of the baryon fragmentation function. For the largest x_f-range, 0.9-1.0, the measurements agree with the Monte Carlo predictions. We have measured the average anti-Lambda polarization for our events and find (6 +- 12%), consistent with previous measurements at the ISR in the present region of x_f - p_t.We report results of inclusive measurements of A, produced in the forward direction at the Sp p S with √ s = 630 GeV, using the UA8 small angle Roman Pot spectrometers. These measurements cover the range in Feynman- χ F and transverse momentum, 0.6 < χ F < 1.0 and 0.4 < p t < 0.7 GeV, respectively. Within a systematic uncertainty of ±20% on the absolute cross section measurements, the results are indistinguishable from those made by some of us in two earliar experiments at the CERN Intersecting Storage Rings, with energies, √ s = 53 and 62 GeV. In the χ F -range, 0.6−0.9, the absolute cross sections are lower by a factor of 2 to 3 than the predictions of the Lund model as embodied in the PYTHIA 5.6 and JETSET 7.3 Monte Carlo programs, indicating inadequacies in knowledge of the baryon fragmentation function. For the largest χ F -range, 0.9−1.0, the measurements agree with the Monte Carlo predictions. We have measured the average A polarization for our events and find (6±12%), consistent with previous measurements at the ISR in the present region of χ F − p t
Cathodoluminescence of Ga_(1-x)In_xAs_ySb_(1-y) epitaxial layers
No full textCorresponding author: [email protected].
This work was carried out in the frame of the European network HPRN-CT-2001-00199. Partial support of MEC (MAT2003-00455) is acknowledged. The samples were grown in the Fraunhofer Institute ISE in Freiburg. The collaboration of N. P. Barradas and M. ReisQuaternary Ga_(1-x)In_xAs_ySb_(1-y) layers lattice matched to a GaSb substrate are of interest for applications in the infrared range. In this work, the luminescence of Ga_(1-x)In_xAs_ySb_(1-y) layers grown on GaSb by metal organic vapor phase epitaxy (MOVPE) with different In and As contents, has been studied by cathodoluminescence (CL) in a scanning electron microscope (SEM). CL images show a cellular structure which indicates the presence of dislocations decorated by recombination centers. Band gap values of 0.735 eV and 0.717 eV were measured from the CL spectra of two samples with diferent In content. This result is analyzed in the frame of existing theoretical models relating band gap with In and As content, in quaternary lattice matched layers. The band gap values are in good agreement with results of atomistic pseudopotential calculations.MECEuropean networkDepto. de Física de MaterialesFac. de Ciencias FísicasTRUEpu
Cross-section measurements of hard diffraction at the SS- Collider
No full textThe UA8 experiment previously reported the observation of jets in diffractive events containing leading protons (``hard diffraction"), which was interpreted as evidence for the partonic structure of an exchanged Reggeon, believed to be the \pom . An analysis of the longitudinal momentum distribution of the 2-jet system in the \pom -proton rest frame showed that the \pom\ structure is ``hard'', like , with an additional ``super-hard'' component near . In the present Letter, we report the final UA8 hard-diffractive (jet) cross section results and their interpretation. After corrections, the fraction of single diffractive events with mass from 118 to 189~GeV that have two scattered partons, each with \etj > 8~GeV, is in the range 0.002 to 0.003 (depending on \xp ). We determine the product, , of the fraction by which the \pom 's momentum sum rule is violated and the normalization constant of the \pom -Flux-Factor of the proton. For a pure gluonic- or a pure -\pom , respectively: = () and () GeV.The UA8 experiment previously reported the observation of jets in diffractive events containing leading protons (``hard diffraction''), which was interpreted as evidence for the partonic structure of an exchanged Reggeon, believed to be the Pomeron . In the present Letter, we report the final UA8 hard-diffractive (jet) cross section results and their interpretation. After corrections, the fraction of single diffractive events with mass from 118 to 189 GeV that have two scattered partons, each with Et_jet > 8 GeV, is in the range 0.002 to 0.003 (depending on x_p). We determine the product, fK, of the fraction by which the Pomeron's momentum sum rule is violated and the normalization constant of the Pomeron-Flux-Factor of the proton. For a pure gluonic- or a pure qqbar-Pomeron , respectively: fK = 0.30 +- 0.05 +- 0.09) and (0.56 +- 0.09 +- 0.17) GeV^-2.The UA8 experiment previously reported the observation of jets in diffractive events containing leading protons (“hard diffraction”), which was interpreted as evidence for the partonic structure of an exchanged Reggeon, believed to be the P omeron . In the present Letter, we report the final UA8 hard-diffractive (jet) cross section results and their interpretation. After corrections, the fraction of single diffractive events with mass from 118 to 189 GeV that have two scattered partons, each with E T jet >8 GeV, is in the range 0.002 to 0.003 (depending on x p ). We determine the product, fK , of the fraction by which the P omeron 's momentum sum rule is violated and the normalization constant of the P omeron -Flux-Factor of the proton. For a pure gluonic- or a pure q q ̄ - P omeron , respectively: fK = (0.30±0.05±0.09) and (0.56±0.09±0.17) GeV −2
High precision measurement of the form factors of the semileptonic decays K± → π0l±ν (Kl3) in NA48/2
No full textThe data collected by NA48/2 in 2003-2004 allowed several precise measurements in the charged kaon decay sector. In this paper we present the results obtained using a sample of 2.5×106 K± → π0μ±ν (Kμ3) and 4.0×106 K × → π0l ±ν (Ke3) events, collected in 2004 using a minimal trigger configuration. This unbiassed sample of kaon decays allows a high precision measurement of the semileptonic form factors. © Copyright owned by the author(s)
Measurements of Single Diffraction at = 630 GeV: Evidence for a Non-Linear of the Pomeron
No full textWe report measurements of the inclusive differential cross section for the single-diffractive reactions: p + pbar --> p + X and p + pbar --> X + pbar at sqrt(s) = 630 GeV, in the momentum transfer range, t = 0.8--2.0 GeV^2 and final state Feynman-x > 0.90. Based on the assumption of factorization, several new features of the Pomeron Flux Factor are determined from simultaneous fits to our UA8 data and lower energy data from the CHLM collaboration at the CERN-Intersecting Storage Rings. Prominent among these is that the effective Pomeron Regge trajectory requires a term quadratic in t, with coefficient, a'' = 0.079 +- 0.012 GeV^-2. We also show that the data require a Pomeron-proton cross section that first decreases with increasing diffractive mass (corresponding to the PPR term in the triple-Regge expansion) and then increases at larger mass (the PPP term), similar to real particle total cross sections. We measure the product, (K x sigma0) = 0.72 +- 0.10 mb/GeV^2, where K is the normalization constant of the Pomeron Flux Factor in the proton and sigma0 is the scale constant in the Pomeron-proton total cross section. Finally, we report the occurance of ``beam jets'' in the Pomeron direction in the rest frame of the diffractive system.We report measurements of the inclusive differential cross section for the single-diffractive reactions p i + p − → p ƒ + X and p + p − i → X + p − ƒ at √s = 630 GeV , in the momentum transfer range 0.8 0.90. Based on the assumption of factorization, several new features of the pomeron flux factor are determined from simultaneous fits to our UA8 data and lower energy data from the CHLM collaboration at the CERN Intersecting Storage Rings.We report measurements of the inclusive differential cross section for the single-diffractive reactions: p + pbar --> p + X and p + pbar --> X + pbar at sqrt(s) = 630 GeV, in the momentum transfer range, 0.8 0.90. Based on the assumption of factorization, several new features of the Pomeron Flux Factor are determined from simultaneous fits to our UA8 data and lower energy data from the CHLM collaboration at the CERN-Intersecting Storage Rings. Prominent among these is that the effective Pomeron Regge trajectory requires a term quadratic in t, with coefficient, a'' = 0.079 +- 0.012 GeV^{-4}. We also show that the data require a Pomeron-proton cross section that first decreases with increasing diffractive mass (corresponding to the PPR term in the triple-Regge expansion) and then increases at larger mass (the PPP term), similar to real particle total cross sections. We measure the product, (K x sigma0) = 0.72 +- 0.10 mb/GeV^2, where K is the normalization constant of the Pomeron Flux Factor in the proton and sigma0 is the scale constant in the Pomeron-proton total cross section. Finally, we report the occurence of ``beam jets'' in the Pomeron direction in the rest frame of the diffractive system
A Study of Inclusive Double-Pomeron-Exchange in at = 630 GeV
No full textWe report measurements of the inclusive reaction, p pbar -> p X pbar, in events where either or both the beam-like final-state baryons were detected in Roman-pot spectrometers and the central system was detected in the UA2 calorimeter. A Double-Pomeron-Exchange (DPE) analysis of these data and single diffractive data from the same experiment demonstrates that, for central masses of a few GeV, the extracted Pomeron-Pomeron total cross section, sigma_PomeromPromeron, exhibits an enhancement which exceeds factorization expectations by an order-of-magnitude. This may be a signature for glueball production. The enhancement is shown to be independent of uncertainties connected with possible non-universality of the Pomeron flux factor. Based on our analysis, we present DPE cross section predictions, for unit (1 mb) Pomeron-Pomeron total cross section, at the Tevatron, LHC and the 920 GeV fixed-target experiment, HERA-B.We report measurements of the inclusive reaction, p pbar -> p X pbar, in events where either or both the beam-like final-state baryons were detected in Roman-pot spectrometers and the central system was detected in the UA2 calorimeter. A Double-Pomeron-Exchange (DPE) analysis of these data and single diffractive data from the same experiment demonstrates that, for central masses of a few GeV, the extracted Pomeron-Pomeron total cross section exhibits an enhancement which exceeds factorization expectations by an order-of-magnitude. This may be a signature for glueball production. The enhancement is shown to be independent of uncertainties connected with possible non-universality of the Pomeron flux factor. Based on our analysis, we present DPE cross section predictions, for unit (1 mb) Pomeron-Pomeron total cross section, at the Tevatron, LHC and the 920 GeV fixed-target experiment, HERA-B
Study of leptonic and semileptonic kaon decays at CERN
No full textDuring 2003 and 2004, the NA48/2 experiment has collected at the CERN SPS the world largest amount of charged kaon decays, with the main goal to search for direct CP violation in the decay of K± into three pions. From a dedicated data sample collected in 2004, the analysis of K ±e3 and K±μ3 decay data has allowed precise measurements of the form factors in various parametrizations. Later, in 2007-2008, using the same detector but a modified beam and trigger logic, the NA62 experiment has taken data to measure the ratio of K → ev and K → v leptonic decays and has obtained a sub-percent measurement of the ratio RK = Γ(Ke2)/Γ(K μ2). © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence
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