HERA-B is a fixed target spectrometer which uses
920
GeV
protons incident on various target materials. The experiment is aimed to study various aspects of beauty and charm physics. The detector is ...designed to operate at high interaction rates with an average of 4–5 interactions per event. The First-Level Trigger (FLT) is required to reduce the input rate by more than two orders of magnitude while keeping high efficiency for beauty and charm channels. The trigger performs online track reconstruction and takes decisions based on particle momenta or pair masses. A pipeline architecture is implemented on about 100 pipelined hardware processors to perform this job. The working principle and first results of the FLT performance based on the data acquired during the run in the year 2000 are described.
Measurements of the kinematic distributions of
J
/
ψ
mesons produced in
p
–C,
p
–Ti and
p
–W collisions at
in the Feynman-
x
region −0.34<
x
F
<0.14 and for transverse momentum up to
p
T
=5.4 GeV/c ...are presented. The
x
F
and
p
T
dependencies of the nuclear suppression parameter,
α
, are also given. The results are based on 2.4×10
5
J
/
ψ
mesons reconstructed in both the
e
+
e
−
and
μ
+
μ
−
decay channels. The data have been collected by the HERA-B experiment at the HERA proton ring of the DESY laboratory. The measurement explores the negative region of
x
F
for the first time. The average value of
α
in the measured
x
F
region is 0.981±0.015. The data suggest that the strong nuclear suppression of
J
/
ψ
production previously observed at high
x
F
turns into an enhancement at negative
x
F
.
A study of the angular distributions of leptons from decays of
J
/
ψ
’s produced in p-C and p-W collisions at
has been performed in the
J
/
ψ
Feynman-
x
region −0.34<
x
F
<0.14 and for
J
/
ψ
...transverse momenta up to 5.4 GeV/
c
. The data were collected by the HERA-B experiment at the HERA proton ring of the DESY laboratory. The results, based on a clean selection of 2.3×10
5
J
/
ψ
’s reconstructed in both the
e
+
e
−
and
μ
+
μ
−
decay channels, indicate that
J
/
ψ
’s are produced polarized. The magnitude of the effect is maximal at low
p
T
. For
p
T
>1 GeV/
c
a significant dependence on the reference frame is found: the polar anisotropy is more pronounced in the Collins-Soper frame and almost vanishes in the helicity frame, where, instead, a significant azimuthal anisotropy arises.
We have searched for Theta+(1540) and Xi(--)(1862) pentaquark candidates in proton-induced reactions on C, Ti, and W targets at midrapidity and square root of s = 41.6 GeV. In 2 x 10(8) inelastic ...events we find no evidence for narrow (sigma approximately 5 MeV) signals in the Theta+ --> pK0(S) and Xi(--) --> Xi- pi- channels; our 95% C.L. upper limits (UL) for the inclusive production cross section times branching fraction B dsigma/dy/(y approximately 0) are (4-16) mub/N for a Theta+ mass between 1521 and 1555 MeV, and 2.5 mub/N for the Xi(--). The UL of the yield ratio of Theta+/Lambda(1520) < (3-12)% is significantly lower than model predictions. Our UL of B Xi(--)/Xi(1530)0 < 4% is at variance with the results that have provided the first evidence for the Xi(--).
Ratios of the ψ′ over the J/ψ production cross sections in the dilepton channel for C, Ti and W targets have been measured in 920 GeV proton-nucleus interactions with the HERA-B detector at the HERA ...storage ring. The ψ′ and J/ψ states were reconstructed in both the μ+μ- and the e+e- decay modes. The measurements covered the kinematic range -0.35≤xF≤0.1 with transverse momentum pT≤4.5 GeV/c. The angular dependence of the ratio has been used to measure the difference of the ψ′ and J/ψ polarization. All results for the muon and electron decay channels are in good agreement: their ratio, averaged over all events, is Rψ′(μ)/Rψ′(e)=1.00±0.08±0.04. This result constitutes a new, direct experimental constraint on the double ratio of branching fractions, (B′(μ)B(e))/(B(μ)B′(e)), of ψ′ and J/ψ in the two channels. The ψ′ to J/ψ production ratio is almost constant in the covered xF range and shows a slow increase with pT.
Track finding at 10-MHz hadronic event rate Bruinsma, M.; Fleckenstein, H.; Gerndt, E.K.E. ...
IEEE transactions on nuclear science,
04/2002, Letnik:
49, Številka:
2
Journal Article
Recenzirano
Hera-B is a fixed target experiment using a halo target inside the HERA proton ring to generate B mesons in 920 GeV proton-nucleus interactions. The first-level trigger (FLT) of the experiment has to ...reduce the primary 10-MHz input rate by a factor 200 in less than 10 /spl mu/s to make it acceptable to the second level trigger (SLT). The trigger strategy is based on the tracking of charged particles and on the reconstruction of their kinematic parameters. The combination of track pairs can also be used for the final decision. A parallel and pipelined set of approximately 60 dedicated boards was designed and built to perform this job. In this paper, the working principle of the system and some results obtained by analyzing the data collected during the run in the year 2000 are described.
Inclusive doubly differential cross sections d2σpA/dxF dpT2 as a function of Feynman-x (xF) and transverse momentum (pT) for the production of KS0, Λ and \(\bar{\varLambda}\) in proton-nucleus ...interactions at 920 GeV are presented. The measurements were performed by HERA-B in the negative xF range (−0.12<xF<0.0) and for transverse momenta up to pT=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 V0 species. The atomic number dependence is parameterized as σpA=σpN⋅Aα where σpN 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.
Inclusive doubly differential cross sections d super(2) s sub(pA )/dx sub(F ) dp sub(T ) super(2) as a function of Feynman-x (x sub(F )) and transverse momentum (p sub(T )) for the production of K ...sub(S ) super(0) , and $\bar{\varLambda}$ in proton-nucleus interactions at 920 GeV are presented. The measurements were performed by HERA-B in the negative x sub(F )range (-0.12<x sub(F )<0.0) and for transverse momenta up to p sub(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 super(0) species. The atomic number dependence is parameterized as s sub(pA )=s sub(pN ); A super(a )where s sub(pN )is the proton-nucleon cross section. The measured values of a 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.
In this paper we describe the operation and performance of the HERA-B Outer Tracker, a 112
674 channel system of planar drift tube layers. The performance of the HERA-B Outer Tracker system ...fullfilled all requirements for stable and efficient operation in a hadronic environment, thus confirming the adequacy of the honeycomb drift tube technology and of the front-end readout system. The detector was stably operated with a gas gain of
3
×
10
4
in an
Ar
/
CF
4
/
CO
2
(65:35:5) gas mixture, yielding a good efficiency for triggering and track reconstruction, larger than 95% for tracks with momenta above
5
GeV
/
c
. The hit resolution of the drift cells was 300–
320
μ
m
and the relative momentum resolution can be described as:
σ
(
p
)
/
p
%
=
(
1.61
±
0.02
)
+
(
0.0051
±
0.0006
)
·
p
GeV
/
c
. At the end of the HERA-B running no aging effects in the Outer Tracker cells were observed.
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