15 research outputs found
Search for the Flavor-Changing Neutral Current Decay with the HERA-B Detector
We report on a search for the flavor-changing neutral current decay using events recorded with a dimuon trigger in
interactions of 920 GeV protons with nuclei by the HERA-B experiment. We find
no evidence for such decays and set a 90% confidence level upper limit on the
branching fraction .Comment: 17 pages, 4 figures (of which 1 double), paper to be submitted to
Physics Letters
Measurement of the J/Psi Production Cross Section in 920 GeV/c Fixed-Target Proton-Nucleus Interactions
The mid-rapidity (dsigma_(pN)/dy at y=0) and total sigma_(pN) production
cross sections of J/Psi mesons are measured in proton-nucleus interactions.
Data collected by the HERA-B experiment in interactions of 920 GeV/c protons
with carbon, titanium and tungsten targets are used for this analysis. The
J/Psi mesons are reconstructed by their decay into lepton pairs. The total
production cross section obtained is sigma_(pN)(J/Psi) = 663 +- 74 +- 46
nb/nucleon. In addition, our result is compared with previous measurements
Orientation of emissive dipoles in OLEDs: Quantitative in situ analysis
The orientation of the emissive dipole moments in organic light-emitting diodes (OLEDs) has a major impact on the optical outcoupling efficiency and, consequently, on the device performance as well as on possible optimization strategies. In this study we propose and demonstrate a general method to quantify the amounts of parallel and perpendicular emissive sites in OLEDs. The presented in situ-method is based on measurements of the far-field emission of an electrically operating device and corresponding optical reverse simulations. A well adapted OLED stack is utilized, where the contribution of perpendicularly oriented dipoles to the radiation pattern in air is optically enhanced. Additionally, for the reverse simulation we take advantage of the fact that perpendicular dipoles do contribute to transverse-magnetic polarized light emission only. We apply the method to a polymeric OLED and show that the radiation pattern is generated by 93.5% parallel and 6.5 % perpendicular dipoles. Assuming a Gaussian distribution of dipole orientations, the dipoles stagger around the preferred parallel direction with an 1/e-angle of +/- 22 degrees
Intrinsic OLED emitter properties and their effect on device performance
The optical properties of OLEDs can be tailored by optimization of the layer stack and by implementation of micro- and/or nano-optical structures. But the effect of changing the OLED configuration on the device performance crucially depends on the optical properties of the emissive layer. The aim of this contribution is twofold. First, we will propose and demonstrate a general and reliable method to determine the intrinsic optical emitter properties via simple optical characterization and corresponding reverse simulations. Second, the influence of the emitter properties on homogeneous OLEDs as well as on OLEDs with micro/nano-optical structures is discussed
Evidence for two-particle core polarization in the isomeric 29/2+ and 21/2? states of the \pi \left( {h_{{9 \mathord{\left/ {\vphantom {9 2}} \right. \kern-\nulldelimiterspace} 2}}^2 } \right)_{8^ + } i_{1 {3 \mathord{\left/ {\vphantom {3 2}} \right. \kern-\nulldelimiterspace} 2}} v\left( {j^{ - 2} } \right)_{0^ + } and \pi \left( {h_{{9 \mathord{\left/ {\vphantom {9 2}} \right. \kern-\nulldelimiterspace} 2}}^3 } \right)v\left( {j^{ - 2} } \right)_{0^ + } configurations in209At
Limits for the central production of Θ+ and Ξ−− pentaquarks in 920-GeV pA collisions
We have searched for Θ+(1540) and Ξ−−(1862) pentaquark candidates in proton-inducedreactions on C, Ti, and W targets at midrapidity and s√=41.6 GeV. In 2×108 inelastic eventswe find no evidence for narrow (σ≈5 MeV) signals in the Θ+→pK0S and Ξ−−→Ξ−π− channels; our 95% C.L. upper limits (UL) forthe inclusive production cross section times branching fraction B dσ/dy $y ≈0 are (4-16) μb/N for a Θ+ mass between 1521 and 1555 MeV,and 2.5μb/N for the Ξ−−. The UL of the yield ratio of Θ+/Λ(1520)<(3-12)% is significantly lower than model predictions.Our UL of B Ξ−−/Ξ(1530)0<4% is at variance with the results that have provided the first evidencefor the Ξ−−
Luminosity Determination at HERA-B.
A detailed description of an original method used to measure the luminosity
accumulated by the HERA-B experiment for a data sample taken during the
2002-2003 HERA running period is reported. We show that, with this method, a
total luminosity measurement can be achieved with a typical precision,
including overall systematic uncertainties, at a level of 5% or better. We also
report evidence for the detection of delta-rays generated in the target and
comment on the possible use of such delta rays to measure luminosity.Comment: 24 pages, 5 figure
Bottom Production Cross Section from Double Muonic Decays of b-Flavoured Hadrons in 920 GeV Proton-Nucleus Collisions
The b-bbar production cross section in 920 GeV proton-nucleus fixed target
collisions is measured by observing double muonic decays of b-flavored hadrons
in the kinematic region -0.3<\xF(\mu)<0.15.
A total number of b-bbar events is obtained with a likelihood fit
of the signal and background simulated events to the data.
The resulting cross section is \sigbb = 16.2 \pm 2.5_{stat} \pm 2.8_{sys}
\nbpn, or, when combined with a previous Hera-B measurement of similar
precision, \sigbb = 15.4 \pm 1.7_{stat} \pm 1.2_{sys}^{uncorr.} \pm
1.9_{sys}^{corr.} \nbpn, which is consistent with recent NLO calculations.Comment: 10 pages, 5 figure
Polarization of and in 920-GeV Fixed-Target Proton-Nucleus Collisions
A measurement of the polarization of Lambda and Anti-Lambda baryons produced
in pC and pW collisions at sqrt(s)=41.6 GeV has been performed with the HERA-B
spectrometer. The measurements cover the kinematic range of 0.6 GeV/c < p_T<1.2
GeV/c in transverse momentum and -0.15<x_F<0.01 in Feynman-x. The polarization
results from the two different targets agree within the statistical error. In
the combined data set, the largest deviation from zero, +0.054 +- 0.029, is
measured for x_F < -0.07. Zero polarization is expected at x_F=0 in the absence
of nuclear effects. The polarization results for the Lambda agree with a
parametrization of previous measurements which were performed at positive x_F
values, where the Lambda polarization is negative. Results of Anti-Lambda
polarization measurements are consistent with zero.Comment: 11 pages, 3 figure