The bb¯ production cross section in 920 GeV proton-nucleus fixed target collisions is measured by observing double muonic decays of b-flavoured hadrons in the kinematic region −0.3<xF(μ)<0.15. A ...total number of 83±12bb¯ events is obtained with a likelihood fit of the signal and background simulated events to the data. The resulting cross section is σbb¯=17.5±2.6stat±3.3sys nb/nucleon, or, when combined with a previous HERA-B measurement of similar precision, σbb¯=15.8±1.7stat±1.3sysuncorr±2.0syscorr nb/nucleon, which is consistent with recent NLO calculations.
Using the ARGUS detector at the
e
+
e
− storage ring DORIS II, we have measured the semileptonic branching ratios of the
D
0 meson to be
Br(
D
0 →
e
+
ν
e
X) = (6.9 ± 0.3 ± 0.5) % and
Br(
D
0 →
μ
+
ν
...μ
X) = (6.0 ± 0.7 ± 1.2) %, and the semileptonic branching ratio of the charmed hadron mixture from
e
+
e
− annihilation around 10 GeV to be
Br(
c →
e
+
ν
e
X) = (9.6 ± 0.4 ± 1.1) %.
The cross section ratio RJ/ψ=Br(ϒ→l+l−)⋅dσ(ϒ)/dy|y=0/σ(J/ψ) has been measured with the HERA-B spectrometer in fixed-target proton–nucleus collisions at 920 GeV proton beam energy corresponding to a ...proton–nucleon c.m.s. energy of s=41.6 GeV. The combined results for the decay channels ϒ→e+e− and ϒ→μ+μ− yield a ratio RJ/ψ=(9.0±2.1)×10−6. The corresponding ϒ production cross section per nucleon at mid-rapidity (y=0) has been determined to be Br(ϒ→l+l−)⋅dσ(ϒ)/dy|y=0=4.5±1.1 pb/nucleon.
Using data collected by the HERA-B experiment, we have measured the fraction of J/ψ's produced via radiative χc decays in interactions of 920 GeV protons with carbon and titanium targets. We obtained ...Rχc=0.32±0.06stat±0.04sys for the fraction of J/ψ from χc decays averaged over proton–carbon and proton–titanium collisions. This result is in agreement with previous measurements and is compared with theoretical predictions.
V0 production in p+A collisions at GeV Agari, M.; Amorim, A.; Aplin, S. J. ...
The European physical journal. C, Particles and fields,
2009/5, Letnik:
61, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Inclusive doubly differential cross sections
d
2
σ
pA
/
dx
F
dp
T
2
as a function of Feynman-x (
x
F
) and transverse momentum (
p
T
) for the production of
K
S
0
,
Λ
and
in proton-nucleus ...interactions at 920 GeV are presented. The measurements were performed by HERA-B in the negative
x
F
range (−0.12<
x
F
<0.0) and for transverse momenta up to
p
T
=1.6 GeV/
c
. Results for three target materials: carbon, titanium and tungsten are given. The ratios of production cross sections are presented and discussed. The Cronin effect is clearly observed for all three
V
0
species. The atomic number dependence is parameterized as
σ
pA
=
σ
pN
⋅
A
α
where
σ
pN
is the proton-nucleon cross section. The measured values of
α
are all near one. The results are compared with EPOS 1.67 and PYTHIA 6.3. EPOS reproduces the data to within ≈20% except at very low transverse momentum.
Luminosity determination at HERA-B Albrecht, H.; Aleksandrov, A.; Amaral, V. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2007, Letnik:
582, Številka:
2
Journal Article
Recenzirano
Odprti dostop
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
δ
-rays generated in the target and comment on the possible use of such delta rays to measure luminosity.
FrascatiPhys.Ser.41:265-274,2006 Today the B-factories BaBar and Belle have accumulated largest samples of
tau-tau events and are competing to be called tau-factories. Among the problems
to be tested ...and measurements to be done by BaBar and Belle are check of CP and
CPT invariance in tau decays, measurement of strange and non-strange spectral
functions, extraction of mass of strange quark and |V_us|, searches for lepton
flavor violation processes. In this paper, the latest results in tau physics by
these two experiments and measurements to be done within next few years are
reviewed.
A measurement of the polarization of Λ and Λ¯ baryons produced in pC and pW collisions at s=41.6 GeV has been performed with the HERA-B spectrometer. The measurements cover the kinematic range of ...0.6 GeV/c<p⊥<1.2 GeV/c in transverse momentum and −0.15<xF<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 xF≲−0.07. Zero polarization is expected at xF=0 in the absence of nuclear effects. The polarization results for the Λ agree with a parametrization of previous measurements which were performed at positive xF values, where the Λ polarization is negative. Results of Λ¯ polarization measurements are consistent with zero.
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