We have built a novel apparatus for the investigation of materials for the storage of ultracold neutrons. Neutrons are filled into a storage volume, confined at the bottom by a magnetic field, at the ...top by gravity and at the sides by the slit-less sample surface under investigation. For different beryllium and diamond-like carbon samples, storage times up to 200
s were obtained at room temperature. The corresponding loss parameters
η
for ultracold neutrons varied between 4.2 and
6.8
×
10
-
4
per wall collision.
The Breit frame provides a natural frame to analyze lepton–proton scattering events. In this reference frame, the parton model hard interactions between a quark and an exchanged boson defines the ...coordinate system such that the struck quark is back-scattered along the virtual photon momentum direction. In Quantum Chromodynamics (QCD), higher order perturbative or non-perturbative effects can change this picture drastically. As Bjorken-
x
decreases below one half, a rather peculiar event signature is predicted with increasing probability, where no radiation is present in one of the two Breit-frame hemispheres and all emissions are to be found in the other hemisphere. At higher orders in
α
s
or in the presence of soft QCD effects, predictions of the rate of these events are far from trivial, and that motivates measurements with real data. We report on the first observation of the empty current hemisphere events in electron–proton collisions at the HERA collider using data recorded with the H1 detector at a center-of-mass energy of 319 GeV. The fraction of inclusive neutral-current DIS events with an empty hemisphere is found to be
0.0112
±
3.9
%
stat
±
4.5
%
syst
±
1.6
%
mod
in the selected kinematic region of
150
<
Q
2
<
1500
GeV
2
and inelasticity
0.14
<
y
<
0.7
. The data sample corresponds to an integrated luminosity of 351.1 pb
-
1
, sufficient to enable differential cross section measurements of these events. The results show an enhanced discriminating power at lower Bjorken-
x
among different Monte Carlo event generator predictions.
A triple GEM detector with two-dimensional readout Ziegler, M; Sievers, P; Straumann, U
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
2001, Letnik:
471, Številka:
1
Journal Article
Recenzirano
Odprti dostop
For the LHCb experiment a micropattern gas detector has been proposed as a possible technology for the inner tracking. A prototype triple GEM detector was built for this purpose. Here, the ...performance of this detector in a hadronic beam is presented.
Observation of D0-D0 oscillations Abellan Beteta, C; Adametz, A; Alves, Jr, A A ...
Physical review letters,
2013-Mar-08, Letnik:
110, Številka:
10
Journal Article
Recenzirano
Odprti dostop
We report a measurement of the time-dependent ratio of D(0) → K(+) π- to D(0) → K(-) π(+) decay rates in D(*+)-tagged events using 1.0 fb(-1) of integrated luminosity recorded by the LHCb experiment. ...We measure the mixing parameters x('2) = (-0.9 ± 1.3) × 10(-4), y' = (7.2 ± 2.4) × 10(-3), and the ratio of doubly-Cabibbo-suppressed to Cabibbo-favored decay rates R(D) = (3.52 ± 0.15) × 10^{-3}, where the uncertainties include statistical and systematic sources. The result excludes the no-mixing hypothesis with a probability corresponding to 9.1 standard deviations and represents the first observation of D0-D0 oscillations from a single measurement.
The charmless decays B± → K+ K- π± and B± → π+ π- π± are reconstructed in a data set of pp collisions with an integrated luminosity of 1.0 fb(-1) and center-of-mass energy of 7 TeV, collected by ...LHCb in 2011. The inclusive charge asymmetries of these modes are measured to be A(CP)(B± → K+ K- π±) = -0.141±0.040 (stat)±0.018 (syst)±0.007(J/ψ K±) and A(CP)(B± → π+ π- π±) = 0.117±0.021 (stat)±0.009 (syst)±0.007(J/ψ K±), where the third uncertainty is due to the CP asymmetry of the B± → J/ψK± reference mode. In addition to the inclusive CP asymmetries, larger asymmetries are observed in localized regions of phase space.
A measurement is presented of the inclusive neutral current
e
±
p
scattering cross section using data collected by the H1 experiment at HERA during the years 2003 to 2007 with proton beam energies
E
...p
of 920, 575, and 460 GeV. The kinematic range of the measurement covers low absolute four-momentum transfers squared, 1.5 GeV
2
<
Q
2
<120 GeV
2
, small values of Bjorken
x
, 2.9⋅10
−5
<
x
<0.01, and extends to high inelasticity up to
y
=0.85. The structure function
F
L
is measured by combining the new results with previously published H1 data at
E
p
=920 GeV and
E
p
=820 GeV. The new measurements are used to test several phenomenological and QCD models applicable in this low
Q
2
and low
x
kinematic domain.
A
bstract
Using three- and four-body decays of
D
mesons produced in semileptonic
b
-hadron decays, precision measurements of
D
meson mass differences are made together with a measurement of the
D
0
...mass. The measurements are based on a dataset corresponding to an integrated luminosity of 1
.
0 fb
−1
collected in
pp
collisions at 7 TeV. Using the decay
D
0
→
K
+
K
−
K
−
π
+
, the
D
0
mass is measured to be
The mass differences
are measured using the
D
0
→
K
+
K
−
π
+
π
−
and
modes.
The H1 Collaboration at HERA reports the first measurement of groomed event shape observables in deep inelastic electron-proton scattering (DIS) at
s
=
319
GeV, using data recorded between the years ...2003 and 2007 with an integrated luminosity of 351
pb
-
1
. Event shapes provide incisive probes of perturbative and non-perturbative QCD. Grooming techniques have been used for jet measurements in hadronic collisions; this paper presents the first application of grooming to DIS data. The analysis is carried out in the Breit frame, utilizing the novel Centauro jet clustering algorithm that is designed for DIS event topologies. Events are required to have squared momentum-transfer
Q
2
>
150
GeV
2
and inelasticity
0.2
<
y
<
0.7
. We report measurements of the production cross section of groomed event 1-jettiness and groomed invariant mass for several choices of grooming parameter. Monte Carlo model calculations and analytic calculations based on Soft Collinear Effective Theory are compared to the measurements.
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