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ARGUS results on antideuteron production
Nuclear Physics B (Proc. Suppl.) 16 (1990) 314-316 North-Holland
314
ARGUS RESULTS ON ANTIDEUTERON PRODUCTION A. Lindner$ Institut für Physik der Universität Dortmund, Federal Republic of Germany Using the ARGUS detector at the DORIS II storage ring we have studied the production of antideuterons in e+eannihilation at centre-of-mass energies around 10 GeV. From 21 events containing d candidates we determined fd the inclusive cross section 1/Qd - da/dp and the production rate in direct hadronic T(1S),T(2S) decays, which was measured to be (6.0 f 2.0 t 0.6) - 10-s d per event while in the continuum e+e- --+ qq only an upper limit of 1.7 - 10-5 d per event (90% CL) could be obtained . Comparisons with a simple model and other ARGUS measurements hint at the underlaymg production mechanism of antideuterons. In the region of 10 GeV centre-of-mass energy fragmentation processes can be studied in the gluon me-
continuum. In this analysis the search was restricted to
continuum reactions, where a primary quark antiquark
wall interactions. To find d we made use of the particle
analyzing meson and baryon production3-4. One exci-
momentum and energy loss measurements in the main
hancment of baryons in the gluonic decays of the T(1S)
deposited energy in the electromagnetic calorimeter . To
d, since in spite of an effective event selection, deute-
diated direct hadronic decays of T resonances and in
rons still suffer contamination from beam gas and beam
pair is produced .
This has been done extensively by
identification capabilities of the detector provided by the
ting result which was first observed in 1981 5 is the en-
drift chamber, the time-of-flight measurement, and the
and T(2S) resonances as compared to their production
ensure a good identification a momentum less than 1.7
the production rate in direct hadronic T(15),T(2S) de-
distributions of energy loss and time-of-flight measure-
in continuum events . While r (defined as the ratio of cays to the rate in continuum events) for mesons l,2 has been measured to be around 1.1, barynns3 have a value
GeV/c for d candidates was required . The expected
ments as well as the remaining background were deter-
mined from data . Further details of the analysis can be
of r in the range of 2 to 3.
found in reference8 .
terons in e+e- annihilation was published by ARGUS in
ning a d candidate, which consist of 12 events from
based on a much larger data sample and puts emphasis
events taken at the centre-of-mass energy of the T(4S).
The first and up to now only observation of antideu1985 6. Here I report on a more detailed study which is
on the differences between the production in direct ha-
After all cuts we are left with 21 events each contaidata on the T(1S), 7 events from the T(2S), and 2 No candidate was found in the continuum data . The
dronic decays of the T(1S) and T(2S) resonances and
two events recorded at the T(4S) energy are kinemati-
in the nearby qq continuum .
cally inconsistent with B meson decays and so they are
The data were collected with the ARGUE detector? at the e+e- storage ring DORIS II at different centre-of-
either background or originate from the continuum be-
mass energies between 9.4 and 10 .6 GeV. The analyzed event samples correspond to integrated luminosities of 31 .6 pb -1 on the T(1S), 38 .2 pb -1 on the T(2S),
104.5 pb -1 on the T(4S), and 47 .1 pb -1 in the nearby tRepresenting the ARGUS collaboration
0920-5632/90/$3.50 © Elsevier Science Publishers B.V . North-Holland
low the T(4S) resonance. The expected backgrounds are two events in total for the T(1S) and T(2S) data
and three d candidates for the combined multihadronic events from T(4S) decays and the continuum.
Assuming that the baryon number is balanced by protons and neutrons with equal probability we expect 8
A. Lindner/Antideuteron production 1/a do/ dp [ 10-5GeV-'c]
31 5
a Maxwell distribution f(p) = a .02 - exp(-E/b)
10.0
where E and p denote energy and momentum of the antideuteron, ,ß stands for its velocity and the free parameters a and b were fit to the data . The result with b = (195 f 80) MeV is shown as the solid line
5.0 / 0.0
~~
0.0
0.5
1 .0
in fig.l .
COW.. .
VR 1.5
From this we derive a production rate of
(6.0 f 2.0 f 0.6) -10 -5 antideuterons per direct hadro-
l~.
2.0
P [GeV/c]
nic T(1S),T(2S) decay where the first error is statistical
and the second systematic . Assuming the same momentum distribution for
d produced in continuum reactions
and not correcting for any background the two observed
antideuteron candidates give an upper limit at the 90%
Figure 1: T(1S) and T(2S) data (full points), fitted
confidence level of 1.7 -10-5 d per continuum event.
fied coalesence model (shaded histogramm).
distinctly enhanced in gluon mediated T decays compa-
Maxwell distribution (line) and prediction from a modi-
events with one well identified proton (momentum less
than 1 .2 Get//c) and 2 events with two protons. In our d sample 8 events contain one proton and 3 events two protons which is fully consistent with the expectation . Scaling the number of selected d events of the combined
T(4S) and continuum sample according to luminosity and the hadronic continuum cross section results in 0.5
events each for the T(1S) and T(2S) data . Therefore the observed events cannot be explained by pure continuum production of
d. The ratio of the number of d
events from T(1S) and T(2S) data agrees with the ratio of the corresponding number of direct hadronic decays of these resonances. So we have observed
d production
in the gluon mediated decays of the T(15) and T(2S)
resonances while no evidence for antideuterons origina-
ting from continuum events or T(4S) decays could be found .
In order to achieve better statistics and because of the good agreement between the two samples, the T(1S) and T(2S) data were combined to calculate the diffe-
rential cross section. After background subtraction and
efficiency correction, the momentum distribution of the antideuterons is shown in fig.l . To extrapolate we use
Therefore we conclude that antideuteron production is red to the continuum reaction e+e- -+ qq . Compared
to antiproton production', (0 .254 f 0.014) p/event, antideuterons are suppressed T(1S), T(2S) decays
by
in
a factor
direct
hadronic
4 . 10 3 and
with respect to the production of baryon pairs9, (2 .00 f 0.12) .10-3 (pp + pp)/event, by a factor of 30 .
No fragmentation model makes predictions for d pro-
duction . Assuming that antideuterons am produced directly in the fragmentation chain the d rates should be similar to other hadrons with approximately the same
mass and not differ by orders of magnitude. In direct ha-
dronic T(1S) decays the production rate of the S2 - , having a mass only 11% less than the d, was determined to be (1 .83 f 0.62 f 0.32) . 10 -3 i2 - / event. This number is very similar to two baryon production and therefore strengthens the assumption that the production of
hadrons in the fragmentation process is mainly a matter of their invariant mass. With respect to the 12 - antideuterons show again a suppression by a factor of 30 .
From these comparisions a direct production of antideuterons in the fragmentation process seems to be rather unlikely .
However, the d production can be related to our measurement of antiproton production in direct hadronic
T(1S) decays using a model which was first develo-
A. Lindner/Antideuteron production
31 6
ped to interp'ete deuteron production in high energy nucleus nucleus collisionsl 0.
Independently produced
V and n may coalesce into a d if their momenta are
close enough in momentum space. Therefore the anti-
deuteron cross section may be expressed as the product of the p and n cross sections if the difference of their momentum vectors lies inside a sphere with radius pp : d 3 Q(d) _ 47r 3 1 d3c , (p) p0-Y 3 Orhsd dap o (ohad da p _1
3 1 d a(n) had
dap
Here, p denotes the momentum per nucleon, y is a Lorentz factor y = [1 + ( p2 /mn)J t /2 with the nucleon mass m . In high energy hadron collisions pp was found to be around 130
eV/c . If we assume the same value
for e+e- data, an isotropic particle production in direct
hadronic 1fdecays, an equal antineutron and antiproton
production rate and use the measured inclusive p cross sectionl, the model predictions can be compared to the d measurement. This is done in fig.l where the shaded
histogram shows the model calculations . In spite of the rough assumptions, data and model agree within a factor of two. If the coalesence model holds then the enhancement r in direct hadronic decays relative to continuum events for d should be similar to the value found for baryon pairs, although the absolute production rates
differ by a factor of 30. ARGUE has measured a large enhancement r(pp + pp) = 4,45 f 0.51. If one divides
the observed d rates for the T data by this number the result is very compatible with our upper limit for d production in the continuum.
Summing up these comparisons, the antideuteron production may be explained by the coalescence of indepen-
dently produced P and n while it can hardly be described by direct production in the fragmentation chain.
This work was supported by the German Bundesminis-
terium für Forschung und Technologie under contract number 054D051P . References : 1. ARGUS Collaboration, H . Albrecht et al ., DESY 89-014 (1989) . 2. ARGUS Collaboration, H . Albrecht et al ., DESY 89-066 (1989) . 3. ARGUS Collaboration, H . Albrecht et al ., Z.Phys.C 39, 177 (1988). 4. ARGUS Collaboration, H . Albrecht et al ., Z.Phys .C 41, 557 (1989). 5. DASD 11 Collaboration, H. Albrecht et al ., Phys.Lett.102 , 291 (1981) . 6. ARGUS Collaboration, H . Albrecht et al ., Phys.Lett. 157B, 326 (1985) . 7. ARGUS Collaboration, H . Albrecht et al ., Nucl . Instr.Methods X1275, 1 (1989). 8. M. Paulini, Diplorna thesis, University Erlangen, Erlangen, FRG ARGUS Collaboration, H. Albrecht et al ., Publication in preparation . 9. ARGUS Collaboration, H. Albrecht et al ., Publication in preparation . 10. H .H . Gutbrod et al ., Phys .Rev .Lett. 37, 667 (1976) . H .Sato, K.Yazaki, Phys .Lett. 98B, 153 (1981) .
314
ARGUS RESULTS ON ANTIDEUTERON PRODUCTION A. Lindner$ Institut für Physik der Universität Dortmund, Federal Republic of Germany Using the ARGUS detector at the DORIS II storage ring we have studied the production of antideuterons in e+eannihilation at centre-of-mass energies around 10 GeV. From 21 events containing d candidates we determined fd the inclusive cross section 1/Qd - da/dp and the production rate in direct hadronic T(1S),T(2S) decays, which was measured to be (6.0 f 2.0 t 0.6) - 10-s d per event while in the continuum e+e- --+ qq only an upper limit of 1.7 - 10-5 d per event (90% CL) could be obtained . Comparisons with a simple model and other ARGUS measurements hint at the underlaymg production mechanism of antideuterons. In the region of 10 GeV centre-of-mass energy fragmentation processes can be studied in the gluon me-
continuum. In this analysis the search was restricted to
continuum reactions, where a primary quark antiquark
wall interactions. To find d we made use of the particle
analyzing meson and baryon production3-4. One exci-
momentum and energy loss measurements in the main
hancment of baryons in the gluonic decays of the T(1S)
deposited energy in the electromagnetic calorimeter . To
d, since in spite of an effective event selection, deute-
diated direct hadronic decays of T resonances and in
rons still suffer contamination from beam gas and beam
pair is produced .
This has been done extensively by
identification capabilities of the detector provided by the
ting result which was first observed in 1981 5 is the en-
drift chamber, the time-of-flight measurement, and the
and T(2S) resonances as compared to their production
ensure a good identification a momentum less than 1.7
the production rate in direct hadronic T(15),T(2S) de-
distributions of energy loss and time-of-flight measure-
in continuum events . While r (defined as the ratio of cays to the rate in continuum events) for mesons l,2 has been measured to be around 1.1, barynns3 have a value
GeV/c for d candidates was required . The expected
ments as well as the remaining background were deter-
mined from data . Further details of the analysis can be
of r in the range of 2 to 3.
found in reference8 .
terons in e+e- annihilation was published by ARGUS in
ning a d candidate, which consist of 12 events from
based on a much larger data sample and puts emphasis
events taken at the centre-of-mass energy of the T(4S).
The first and up to now only observation of antideu1985 6. Here I report on a more detailed study which is
on the differences between the production in direct ha-
After all cuts we are left with 21 events each contaidata on the T(1S), 7 events from the T(2S), and 2 No candidate was found in the continuum data . The
dronic decays of the T(1S) and T(2S) resonances and
two events recorded at the T(4S) energy are kinemati-
in the nearby qq continuum .
cally inconsistent with B meson decays and so they are
The data were collected with the ARGUE detector? at the e+e- storage ring DORIS II at different centre-of-
either background or originate from the continuum be-
mass energies between 9.4 and 10 .6 GeV. The analyzed event samples correspond to integrated luminosities of 31 .6 pb -1 on the T(1S), 38 .2 pb -1 on the T(2S),
104.5 pb -1 on the T(4S), and 47 .1 pb -1 in the nearby tRepresenting the ARGUS collaboration
0920-5632/90/$3.50 © Elsevier Science Publishers B.V . North-Holland
low the T(4S) resonance. The expected backgrounds are two events in total for the T(1S) and T(2S) data
and three d candidates for the combined multihadronic events from T(4S) decays and the continuum.
Assuming that the baryon number is balanced by protons and neutrons with equal probability we expect 8
A. Lindner/Antideuteron production 1/a do/ dp [ 10-5GeV-'c]
31 5
a Maxwell distribution f(p) = a .02 - exp(-E/b)
10.0
where E and p denote energy and momentum of the antideuteron, ,ß stands for its velocity and the free parameters a and b were fit to the data . The result with b = (195 f 80) MeV is shown as the solid line
5.0 / 0.0
~~
0.0
0.5
1 .0
in fig.l .
COW.. .
VR 1.5
From this we derive a production rate of
(6.0 f 2.0 f 0.6) -10 -5 antideuterons per direct hadro-
l~.
2.0
P [GeV/c]
nic T(1S),T(2S) decay where the first error is statistical
and the second systematic . Assuming the same momentum distribution for
d produced in continuum reactions
and not correcting for any background the two observed
antideuteron candidates give an upper limit at the 90%
Figure 1: T(1S) and T(2S) data (full points), fitted
confidence level of 1.7 -10-5 d per continuum event.
fied coalesence model (shaded histogramm).
distinctly enhanced in gluon mediated T decays compa-
Maxwell distribution (line) and prediction from a modi-
events with one well identified proton (momentum less
than 1 .2 Get//c) and 2 events with two protons. In our d sample 8 events contain one proton and 3 events two protons which is fully consistent with the expectation . Scaling the number of selected d events of the combined
T(4S) and continuum sample according to luminosity and the hadronic continuum cross section results in 0.5
events each for the T(1S) and T(2S) data . Therefore the observed events cannot be explained by pure continuum production of
d. The ratio of the number of d
events from T(1S) and T(2S) data agrees with the ratio of the corresponding number of direct hadronic decays of these resonances. So we have observed
d production
in the gluon mediated decays of the T(15) and T(2S)
resonances while no evidence for antideuterons origina-
ting from continuum events or T(4S) decays could be found .
In order to achieve better statistics and because of the good agreement between the two samples, the T(1S) and T(2S) data were combined to calculate the diffe-
rential cross section. After background subtraction and
efficiency correction, the momentum distribution of the antideuterons is shown in fig.l . To extrapolate we use
Therefore we conclude that antideuteron production is red to the continuum reaction e+e- -+ qq . Compared
to antiproton production', (0 .254 f 0.014) p/event, antideuterons are suppressed T(1S), T(2S) decays
by
in
a factor
direct
hadronic
4 . 10 3 and
with respect to the production of baryon pairs9, (2 .00 f 0.12) .10-3 (pp + pp)/event, by a factor of 30 .
No fragmentation model makes predictions for d pro-
duction . Assuming that antideuterons am produced directly in the fragmentation chain the d rates should be similar to other hadrons with approximately the same
mass and not differ by orders of magnitude. In direct ha-
dronic T(1S) decays the production rate of the S2 - , having a mass only 11% less than the d, was determined to be (1 .83 f 0.62 f 0.32) . 10 -3 i2 - / event. This number is very similar to two baryon production and therefore strengthens the assumption that the production of
hadrons in the fragmentation process is mainly a matter of their invariant mass. With respect to the 12 - antideuterons show again a suppression by a factor of 30 .
From these comparisions a direct production of antideuterons in the fragmentation process seems to be rather unlikely .
However, the d production can be related to our measurement of antiproton production in direct hadronic
T(1S) decays using a model which was first develo-
A. Lindner/Antideuteron production
31 6
ped to interp'ete deuteron production in high energy nucleus nucleus collisionsl 0.
Independently produced
V and n may coalesce into a d if their momenta are
close enough in momentum space. Therefore the anti-
deuteron cross section may be expressed as the product of the p and n cross sections if the difference of their momentum vectors lies inside a sphere with radius pp : d 3 Q(d) _ 47r 3 1 d3c , (p) p0-Y 3 Orhsd dap o (ohad da p _1
3 1 d a(n) had
dap
Here, p denotes the momentum per nucleon, y is a Lorentz factor y = [1 + ( p2 /mn)J t /2 with the nucleon mass m . In high energy hadron collisions pp was found to be around 130
eV/c . If we assume the same value
for e+e- data, an isotropic particle production in direct
hadronic 1fdecays, an equal antineutron and antiproton
production rate and use the measured inclusive p cross sectionl, the model predictions can be compared to the d measurement. This is done in fig.l where the shaded
histogram shows the model calculations . In spite of the rough assumptions, data and model agree within a factor of two. If the coalesence model holds then the enhancement r in direct hadronic decays relative to continuum events for d should be similar to the value found for baryon pairs, although the absolute production rates
differ by a factor of 30. ARGUE has measured a large enhancement r(pp + pp) = 4,45 f 0.51. If one divides
the observed d rates for the T data by this number the result is very compatible with our upper limit for d production in the continuum.
Summing up these comparisons, the antideuteron production may be explained by the coalescence of indepen-
dently produced P and n while it can hardly be described by direct production in the fragmentation chain.
This work was supported by the German Bundesminis-
terium für Forschung und Technologie under contract number 054D051P . References : 1. ARGUS Collaboration, H . Albrecht et al ., DESY 89-014 (1989) . 2. ARGUS Collaboration, H . Albrecht et al ., DESY 89-066 (1989) . 3. ARGUS Collaboration, H . Albrecht et al ., Z.Phys.C 39, 177 (1988). 4. ARGUS Collaboration, H . Albrecht et al ., Z.Phys .C 41, 557 (1989). 5. DASD 11 Collaboration, H. Albrecht et al ., Phys.Lett.102 , 291 (1981) . 6. ARGUS Collaboration, H . Albrecht et al ., Phys.Lett. 157B, 326 (1985) . 7. ARGUS Collaboration, H . Albrecht et al ., Nucl . Instr.Methods X1275, 1 (1989). 8. M. Paulini, Diplorna thesis, University Erlangen, Erlangen, FRG ARGUS Collaboration, H. Albrecht et al ., Publication in preparation . 9. ARGUS Collaboration, H. Albrecht et al ., Publication in preparation . 10. H .H . Gutbrod et al ., Phys .Rev .Lett. 37, 667 (1976) . H .Sato, K.Yazaki, Phys .Lett. 98B, 153 (1981) .