The time-of-flight detector of the DIRAC experiment Adeva, B; Gallas, M.V; Gómez, F ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2002, Letnik:
491, Številka:
1-2
Journal Article
Recenzirano
The construction and performance of a large area time-of-flight detector for the DIRAC experiment at CERN is reported. With an average time resolution of 123ps per counter at rates up to 1MHz, it ...allows excellent separation of pπ− from π+π− pairs up to 4.6GeV/c momentum, as well as of Coulomb-correlated pion pairs from accidentals. The optimization of scintillator material, photomultiplier performance and readout electronics is described.
One of the most interesting channels to search for SUSY is the direct pair-production of the \(\tau\)-lepton superpartner, \(\widetilde{\tau}\). The \(\widetilde{\tau}\) is with high probability the ...lightest of the scalar leptons, so one of the first SUSY particles that can be observerd, and the signature of \(\widetilde{\tau}\) pair production signal events is one of the most difficult ones, yielding to the ``worst'' and so most global scenario for the searches. Analysis performed at LEP set the current model-independent \(\widetilde{\tau}\) limits, suffering from the low energy of this facility. Only under strong model assumptions, these limits are extended to higher masses by LHC studies. In this contribution we show the capability of the ILC, a future electron-positron collider with energy up to 1 TeV, for determining \(\widetilde{\tau}\) exclusion/discovery limits in a model-independent way, including an overview of the current state-of-the-art. The determination of the ``worst'' scenario for \(\widetilde{\tau}\) exclusion/discovery, taking into account the effect of the \(\widetilde{\tau}\) mixing on \(\widetilde{\tau}\) production cross-section and efficiency, is also presented. For selected benchmarks, the prospect for measuring masses and polarised cross-sections will be shown. The studies were done studying events passed through the full detector simulation and reconstruction procedures of the International Large Detector (ILD) concept at the ILC. The simulation included all SM backgrounds, as well as the machine induced ones.
The DIRAC experiment at CERN has achieved a sizeable production of
π
+
π
−
atoms and has significantly improved the precision on its lifetime determination. From a sample of 21 227 atomic pairs, a 4% ...measurement of the S-wave
ππ scattering length difference
|
a
0
−
a
2
|
=
(
0.2533
−
0.0078
+
0.0080
|
stat
|
syst
−
0.0073
+
0.0078
)
M
π
+
−
1
has been attained, providing an important test of Chiral Perturbation Theory.
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
.
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.
Pair-production of the superpartner of the $\tau$-lepton, the $\tilde{\tau}$,
is one of the most interesting channels to search for SUSY in: The
$\tilde{\tau}$ is likely to be the lightest scalar ...lepton, and the signature of
$\tilde{\tau}$ pair production is one of the experimentally most difficult
ones, thereby constituting the "worst" possible scenario for SUSY searches. The
current model-independent $\tilde{\tau}$ limits comes from analyses performed
at LEP but they suffer from the limited energy of this facility. Limits
obtained at the LHC do extend to higher masses, but they are only valid under
strong assumptions. The International Linear Collider, the ILC, is a future
electron-positron collider, to operate initially at an energy of 250 GeV, then
to be upgraded to 500 GeV, and possibly to 1 TeV at a later stage. ILC will be
a powerful facility for SUSY searches. The capability of the ILC for
determining exclusion/discovery limits for the $\tilde{\tau}$ in a
model-independent way is shown in this paper. A detailed study of the "worst"
scenario for $\tilde{\tau}$ exclusion/discovery, taking into account the effect
of the $\tilde{\tau}$ mixing on $\tilde{\tau}$ production cross-section and
detection efficiency, is presented. The study also includes an analysis of the
effect of the overlay particles in the $\tilde{\tau}$ searches. The conclusion
is that both the exclusion and discovery reaches for this "worst" case would
extend to only a few GeV below the kinematic limit at the ILC. Also scenarios
with the $\tilde{\tau}$ and the Lightest SUSY Particle (the LSP) quite close in
mass can be discovered or excluded at most $\tilde{\tau}$ masses. The studies
were done using detailed detector simulation of the ILD concept at the ILC. For
signal, the fast detector simulation SGV was used, while the full Geant4 based
DDSim was used for the standard model backgrounds.
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.
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.
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