DIRAC: A high resolution spectrometer for pionium detection Adeva, B.; Afanasyev, L.; Benayoun, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2003, Letnik:
515, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The DIRAC spectrometer has been commissioned at CERN with the aim of detecting π+π− atoms produced by a 24GeV/c high intensity proton beam in thin foil targets. A challenging apparatus is required to ...cope with the high interaction rates involved, the triggering of pion pairs with very low relative momentum and the measurement of the latter with resolution around 0.6MeV/c. The general characteristics of the apparatus are explained and each part is described in some detail. The main features of the trigger system, data-acquisition, monitoring and set-up performances are also given.
We report the study of light baryon production in two-prong annihilation reactions due to antiprotons stopping in gaseous deuterium and detected by the OBELIX spectrometer (LEAR, CERN). A clear ...signal of the
Δ(1232) production in binary reactions was found in both annihilation channels:
p
̄
d→π
−Δ
+(Δ
+→π
0p)
and
p
̄
d→π
0Δ
0(Δ
0→π
−p)
. The annihilation probabilities for these reactions turned out to be
Y=(1.01±0.08)×10
−5 and
Y=(1.12±0.20)×10
−5, respectively. In addition, the annihilation probability for the prototype Pontecorvo reaction
p
̄
d→π
−p
was measured with the best world statistics:
Y=(1.46±0.08)×10
−5.
The
p
̄
p
annihilation at rest into the
φη final state was measured for three different target densities: liquid hydrogen, gaseous hydrogen at NTP and at a low pressure of 5 mbar. The yield of this ...reaction in the liquid hydrogen target is smaller than in the low-pressure gas target. The branching ratios of the
φη channel were calculated on the basis of simultaneous analysis of the three data samples. The branching ratio for annihilation into
φη from the
3S
1
protonium state turns out to be about ten times smaller as compared to the one from the
1P
1
state.
New experimental results on
pd
annihilation at rest into pions plus a high momentum proton in the final state are discussed. The data sample was collected using the OBELIX spectrometer at the LEAR ...facility (CERN). The annihilation probabilities, or more precisely the yields (
Y) via channels
pd → 2π
−π
+π
0p
and
pd → 3π
−2π
+π
0p
with proton momenta
p > 400 MeV/
c have been measured for the first time:
Y = (93.2 ± 1.6) × 10
−4 and
Y = (52.2 ± 1.4) × 10
−4, respectively. The signal in the invariant mass distribution of the
pπ
+ system in the region of the well-known
Δ
++(1232)-isobar is clearly seen in reactions
pd → 2π
−π
+p
,
pd → 2π
−π
+π
0p
,
pd → 3π
−2π
+p
and
pd → 3π
−2π
+π
0p
. The upper limit on reaction
p (Δ
−Δ
++) → 2π
−π
+p
in the
p
d
annihilation at rest, which could be interpreted as a manifestation of the ΔΔ component of the deuteron, was found to be
Y ≤ 6.5 × 10
−5 with a 90% confidence level.
We report in this paper the results of the study of the ƒ
0(1500)/ƒ
2(1565) resonances in the in-flight annihilation reaction
n̄p → 2
π
+
π
−, taking into account a possible dependence on the
n̄ ...momentum.
PDF
