394
A. Ariga et al.
to and 350 μm along the beam direction. The total fiducial decay region for bottom
particles including emulsions and silicon planes was 12 cm long.
The emulsion analysis procedure first located the primary vertex. Six thousand
five hundred forty-two events were selected within the fiducial volume of the
emulsion and for all but 9 the primary vertex was found thanks to the excellent
performance of the electronic detectors. The majority of the events were discarded
by requiring a stringent angular agreement (2 mrad for tracks with a slope within
40 mrad) between the reconstructed spectrometer track and any track at the primary
vertex. Three hundred and fifty-nine events in which the muon did not come from
the primary vertex were retained for the secondary vertex search. Nine events met
the selection criteria for bottom [53]. The b lifetime was also measured.
At the end of the 1980s, the production of charmed particles from quark-gluon
plasma was expected to differ from that due to proton-nucleus interactions [54]. In
particular, a large enhancement of the charmed quark pair creation was expected.
From the experimental point of view, the major difficulty for charm detection in
such nucleus-nucleus interactions came from the very short-path decay in a region
close to the primary interaction where the particle density was extremely high. Two
studies were carried out at CERN on this subject with emulsions, one within the
NA34/2 emulsion-HELIOS programme [55] and the other one within the EMU09
Collaboration [56]. In NA34 [55], the production of charmed particles was detected
in 200 GeV/nucleon 16 O-emulsion interactions and its cross-section was measured.
Stacks of FUJI gel were exposed vertically to the 16 O beam. Each stack consisted
of 8 double-coated plates with a surface of 25 × 15 cm 2 and a thickness of 700 μm
(70 μm polystyrene base coated on both sides with a 315 μm thick emulsion layer).
In order to study charmed particle production in central interactions of 200 GeV
per nucleon 32 S nuclei, the EMU09 Collaboration designed an emulsion-counter
hybrid experiment at CERN [56]. The hybrid design was meant to reduce the
background from secondary interactions in the emulsion, which would have spoiled
the signal with heavier projectiles, differently from the case of 16 O. A thin and pure
target was made of 100 μm thick Ag and Pb plates. Two emulsion plates, in the form
of tapes, were placed downstream of the target and used as a tracking device, able
to detect short-path decay vertices and producing very little secondary activity. The
emulsion tape used in this experiment was derived from an Acetate base 200 μm
thick and FUJI gel poured on both sides of the base, to obtain 70 μm thick layers.
The emulsion analysis speed at that time did not allow to integrate a sufficiently
large statistics for such rare events.
Nuclear emulsions have also played an important role in the study of multiquark
systems and the quark confinement aspects of QCD. The hybrid emulsion experiment E176 [57] was carried out at KEK by using a 1.66 GeV/c K − beam to study
double-strangeness nuclei produced via − hyperon capture at rest. Indeed, the
K − p → K + − interaction produces a − , which at rest may be captured via
the process − p → . In the hypothesis that the H -dibaryon (ssuudd) exist,
the double hypernucleus can decay by emitting a H -dibaryon, in turn decaying
into − p within less than 1 mm from the − stopping point. Unlike old-fashioned
emulsion experiments where only emulsion stacks were exposed to K − beams [58],
A. Ariga et al.
to and 350 μm along the beam direction. The total fiducial decay region for bottom
particles including emulsions and silicon planes was 12 cm long.
The emulsion analysis procedure first located the primary vertex. Six thousand
five hundred forty-two events were selected within the fiducial volume of the
emulsion and for all but 9 the primary vertex was found thanks to the excellent
performance of the electronic detectors. The majority of the events were discarded
by requiring a stringent angular agreement (2 mrad for tracks with a slope within
40 mrad) between the reconstructed spectrometer track and any track at the primary
vertex. Three hundred and fifty-nine events in which the muon did not come from
the primary vertex were retained for the secondary vertex search. Nine events met
the selection criteria for bottom [53]. The b lifetime was also measured.
At the end of the 1980s, the production of charmed particles from quark-gluon
plasma was expected to differ from that due to proton-nucleus interactions [54]. In
particular, a large enhancement of the charmed quark pair creation was expected.
From the experimental point of view, the major difficulty for charm detection in
such nucleus-nucleus interactions came from the very short-path decay in a region
close to the primary interaction where the particle density was extremely high. Two
studies were carried out at CERN on this subject with emulsions, one within the
NA34/2 emulsion-HELIOS programme [55] and the other one within the EMU09
Collaboration [56]. In NA34 [55], the production of charmed particles was detected
in 200 GeV/nucleon 16 O-emulsion interactions and its cross-section was measured.
Stacks of FUJI gel were exposed vertically to the 16 O beam. Each stack consisted
of 8 double-coated plates with a surface of 25 × 15 cm 2 and a thickness of 700 μm
(70 μm polystyrene base coated on both sides with a 315 μm thick emulsion layer).
In order to study charmed particle production in central interactions of 200 GeV
per nucleon 32 S nuclei, the EMU09 Collaboration designed an emulsion-counter
hybrid experiment at CERN [56]. The hybrid design was meant to reduce the
background from secondary interactions in the emulsion, which would have spoiled
the signal with heavier projectiles, differently from the case of 16 O. A thin and pure
target was made of 100 μm thick Ag and Pb plates. Two emulsion plates, in the form
of tapes, were placed downstream of the target and used as a tracking device, able
to detect short-path decay vertices and producing very little secondary activity. The
emulsion tape used in this experiment was derived from an Acetate base 200 μm
thick and FUJI gel poured on both sides of the base, to obtain 70 μm thick layers.
The emulsion analysis speed at that time did not allow to integrate a sufficiently
large statistics for such rare events.
Nuclear emulsions have also played an important role in the study of multiquark
systems and the quark confinement aspects of QCD. The hybrid emulsion experiment E176 [57] was carried out at KEK by using a 1.66 GeV/c K − beam to study
double-strangeness nuclei produced via − hyperon capture at rest. Indeed, the
K − p → K + − interaction produces a − , which at rest may be captured via
the process − p → . In the hypothesis that the H -dibaryon (ssuudd) exist,
the double hypernucleus can decay by emitting a H -dibaryon, in turn decaying
into − p within less than 1 mm from the − stopping point. Unlike old-fashioned
emulsion experiments where only emulsion stacks were exposed to K − beams [58],