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First results from the L3+C experiment at CERN
Nuclear Physics B (Proc. Suppl.) 95 (2001) 237-240
First Results from the L3+C
www.elsevie.r.nUlocate/npe
Experiment at CERN
P. Ladron
a small 5 billion
1. Introduction The L3 detector
[l] at CERN’s
LEP accelerator
is located near Geneva ( 6.02’ E, 46.25’ N ) at an altitude of 450 m. L3 is underneath 30 m of molasse (15 GeV muon cutoff). High precision muon drift chambers are installed in a 1000 m3 B-field of 0.5 T. L3 has been operating very succesfully since 1989 to study e+e- interactions. The muon spectrometer has been converted in a powerful detector of atmospheric muons,without impact on the normal L3 activity. It was done by means of an additional equipment of a “to” detector composed by scintillators, and of an independent trigger and DAQ electronics, in 1998. It has been fully operational during 1999. From start 2000, a small air shower array was added on surface, in correlation
with the underground
detector,
and it is
operating since April 2000 (fig. 1). The growing evidences for the neutrino
oscil-
lation and solar neutrino deficit [2] make,among other, the study of the related muon flux, its energy spectrum and ratio between both charged components more and more interesting. Wide energy ranges, good filtering of the secondaries, precise momentum
measurement
Figure 1. Artist’s view of LS+C,showing the air shower array on surface and the L3 volume vertical cut. Shafts and other accesses are not represented.
The conjuntion with the air shower array put at reach studies of primary energy and primary composition and very forward production.
and huge statistics
can be achieved in the underground muon spectrometer of L3. A steady, continously monitored detector, active during a good part of the year, provides as well the conditions to study short time dependent phenomena as muon bursts, or to determine fine effects, such as sideral asymmetries.
2.
The L3+C
Experiment
The muon spectrometer,magnet
and scintilla-
tors are shown in fig. 2 as part of the L3 detector. Fig. 3 shows a simplified cross section. The muon spectrometer consists in 80 drift Pchambers
0920-5632/01/$ - see front matter0 2001 Elsevier Science B.V. All rights reserved. PII SO920-5632(01)01088-X
to measure
positions
in the bending
238
I? Ladrdn de GuevaralNuclear
Physics B (Proc. Suppl.)
Schematic view of the L3 detecFigure 2. tor.Outside the yoke the additional L3+C scintillators can be seen.
plane of the magnet and 96 drift Z-chambers to measure the coordinate along the magnetic field. The P chambers are arranged in 2 groups of 8 ‘octants’ each, in three layers, with the typical symmetry of a collider detector and the Z chambers are arranged in 2+2 layers sandwitching the inner and outer P chambers layers. Chamber alignments are continously monitored and are known to 20 pm. Single wire resolution is 200 pm. The detector is enclosed in a 12 m diameter magnet (coil and yoke) The arrival time of the muons is needed to determine the drift time in the chambers. It is provided by the t0 detector,consisting on 202 m2 of scintillators installed outside the magnetic yoke on face of three upper octants. The resultant acceptance on zenit angle is = 50’ and the geometrical acceptance is = 200 m2 sr. The air shower detector is installed on the flat roof belonging to a building located at the surface, above L3. It is composed of 50 scintillators of size 0.5 m2,distributed over an area of 30 x 54 m2. Fig. 4 shows an event recorded in the air shower array with an energy of about 1700 TeV. This air shower can measure the energy and di-
95 (2001) 237-240
Figure 3. Cross section of the L3 muon spectrometer. The outer octagons correspond to coil and yoke of the magnet. Scintillators are installed on the top.
rection of atmospheric showers. The energy resolution of the air shower array is 30 % for events with the core inside the array. An accuracy of l2O on the zenith angle is expected. The L3 muon spectrometer together with the surface array constitues the L3+C experiment.[3] The status of the L3+C detector is continously monitored (Run conditions, voltages and discriminator thresholds in muon chambers, t0 detector conditions, magnet status, temperature and atmospheric pressure at surface,etc.), to provide online survey and information to the DataBases. 3. Performance
and Data Acquisition
The molasse layer provides a shield against the electromagnetic and hadronic components of the air shower. It also imposes a muon threshold of 15 GeV/c and limits the angular resolution to 0.2 degrees above 100 GeV/c. A double measurement (one on the top half and one in the bottom half of the detector) enables the determination of the resolution, which at 100 GeV/c has been found to be 7.4 %. The full system performance has been determined at 45.6 GeV/c during the L3 calibrations
P Lad&
de Guevara/Nuclear
Physics B (Proc. Suppl.)
l
4. First Results Data from September to November of 1999 were used to determine a first muon momentum spectrum from 50 to 500 GeV/c. The total livetime used was slightly more than 30 days. Strict quality cuts have been applied, among others, the need for a good measurement in both upper and lower octant separate track segments and a good match between both to build the final track. The zenith angle has been restricted to a range of 0’ to 10’ to measure the vertical flux. The measured flux weighted by p3 can be seen (fig. 5) together
W+C preliminary 1
Figure 4. Air shower event in the LS+C scintillator array.
at the peak of the 2 resonance, using the e+e- + Z + p+p- reaction, where the back to back muons have the same topology as a cosmic muon going through the vertex. After requiring one of the muons to cross the scintillator region and the best quality for both tracks, a resolution of 5.1 % in E(beam)/E(mu) has been achieved in the 1999 calibrations. The dedicated data taking with the muon spectrometer started in 1999. From May to November a total 5 billion events were recorded, with a livetime of x 124 days. From April to November, 2000 a total of 6.8 billion events have been gathered with a livetime of M 188 days. The air shower array has been fully operational since April 2000 and by 13th November a total of M 33 million air shower events have been recorded. About 28% of these showers are accompanied by muon(s) in the spectrometer.
239
95 (2001) 237-240
Figure 5. The differential and vertical flux of atmospheric muons weighted with p3 ils a function of momentum p at 450 m above sea level.
with the results of other experiments [4] [5] [6] [7] [8] [9]. The systematic error of 9 % dominates the total error plotted. In the future we hope to reduce the total error to 2.5 %. and to extend the momentum range from 20 to 2000 GeV/c. The charge ratio was calculated from the same event sample. The preliminary result can be seen (fig. 6) along with the results of other published measurements [6] [7] [8] [9] . With the small sample used for the analysis up to now the statistical error is dominant at high momenta. 5. Conclusions. A new type of cosmic ray detector, L3+C combines air shower data with precise muon momentum measurements. First preliminary results on the muon spectrum and charge ratio in the range from 50 to 500 GeV/c have been presented. A substantial reduction in the statistical and systematic errors is expected in the future. REFERENCES 1. 2.
Adeva B. et al,NIM,A289 (1990) 35. Chiaki Yanagisawa, “Solar and atmospheric neutrinos: Results from Superkamiokande
240
P Lad&
de Guevara/Nuclear Physics B (Proc. Suppl.) 95 (2001) 237-240
Figure 6. The muon charge ratio as a function of momentum.
3. 4. 5. 6. 7. 8. 9.
and K2k”, “Solar and atmospheric neutrino oscillations” C. Gonzalez-Garcia, (invited papers to this Conference) http://13www.cern.ch/l3_cosmics/ O.C. Ahkofer et al.,Lett. Nuovo Cim,l2 (1975) 107. B. Baschiera et al.,11 Nuovo Cim. 2C (1979) 473. B.C. Pastin. J. Phys G.: Nucl. Phys. 10 (1984) 1629. M.P. De Pascale et al.,J. Geophys. Res.98 (1993) 3501. J. Kremer et al., Phys. Rev. Lett. 83, 4241 (1999) Hebbeker T. and Timmermans C., A compilation of High Energy Atmospheric Muon data at Sea Level, (to be published).
First Results from the L3+C
www.elsevie.r.nUlocate/npe
Experiment at CERN
P. Ladron
a small 5 billion
1. Introduction The L3 detector
[l] at CERN’s
LEP accelerator
is located near Geneva ( 6.02’ E, 46.25’ N ) at an altitude of 450 m. L3 is underneath 30 m of molasse (15 GeV muon cutoff). High precision muon drift chambers are installed in a 1000 m3 B-field of 0.5 T. L3 has been operating very succesfully since 1989 to study e+e- interactions. The muon spectrometer has been converted in a powerful detector of atmospheric muons,without impact on the normal L3 activity. It was done by means of an additional equipment of a “to” detector composed by scintillators, and of an independent trigger and DAQ electronics, in 1998. It has been fully operational during 1999. From start 2000, a small air shower array was added on surface, in correlation
with the underground
detector,
and it is
operating since April 2000 (fig. 1). The growing evidences for the neutrino
oscil-
lation and solar neutrino deficit [2] make,among other, the study of the related muon flux, its energy spectrum and ratio between both charged components more and more interesting. Wide energy ranges, good filtering of the secondaries, precise momentum
measurement
Figure 1. Artist’s view of LS+C,showing the air shower array on surface and the L3 volume vertical cut. Shafts and other accesses are not represented.
The conjuntion with the air shower array put at reach studies of primary energy and primary composition and very forward production.
and huge statistics
can be achieved in the underground muon spectrometer of L3. A steady, continously monitored detector, active during a good part of the year, provides as well the conditions to study short time dependent phenomena as muon bursts, or to determine fine effects, such as sideral asymmetries.
2.
The L3+C
Experiment
The muon spectrometer,magnet
and scintilla-
tors are shown in fig. 2 as part of the L3 detector. Fig. 3 shows a simplified cross section. The muon spectrometer consists in 80 drift Pchambers
0920-5632/01/$ - see front matter0 2001 Elsevier Science B.V. All rights reserved. PII SO920-5632(01)01088-X
to measure
positions
in the bending
238
I? Ladrdn de GuevaralNuclear
Physics B (Proc. Suppl.)
Schematic view of the L3 detecFigure 2. tor.Outside the yoke the additional L3+C scintillators can be seen.
plane of the magnet and 96 drift Z-chambers to measure the coordinate along the magnetic field. The P chambers are arranged in 2 groups of 8 ‘octants’ each, in three layers, with the typical symmetry of a collider detector and the Z chambers are arranged in 2+2 layers sandwitching the inner and outer P chambers layers. Chamber alignments are continously monitored and are known to 20 pm. Single wire resolution is 200 pm. The detector is enclosed in a 12 m diameter magnet (coil and yoke) The arrival time of the muons is needed to determine the drift time in the chambers. It is provided by the t0 detector,consisting on 202 m2 of scintillators installed outside the magnetic yoke on face of three upper octants. The resultant acceptance on zenit angle is = 50’ and the geometrical acceptance is = 200 m2 sr. The air shower detector is installed on the flat roof belonging to a building located at the surface, above L3. It is composed of 50 scintillators of size 0.5 m2,distributed over an area of 30 x 54 m2. Fig. 4 shows an event recorded in the air shower array with an energy of about 1700 TeV. This air shower can measure the energy and di-
95 (2001) 237-240
Figure 3. Cross section of the L3 muon spectrometer. The outer octagons correspond to coil and yoke of the magnet. Scintillators are installed on the top.
rection of atmospheric showers. The energy resolution of the air shower array is 30 % for events with the core inside the array. An accuracy of l2O on the zenith angle is expected. The L3 muon spectrometer together with the surface array constitues the L3+C experiment.[3] The status of the L3+C detector is continously monitored (Run conditions, voltages and discriminator thresholds in muon chambers, t0 detector conditions, magnet status, temperature and atmospheric pressure at surface,etc.), to provide online survey and information to the DataBases. 3. Performance
and Data Acquisition
The molasse layer provides a shield against the electromagnetic and hadronic components of the air shower. It also imposes a muon threshold of 15 GeV/c and limits the angular resolution to 0.2 degrees above 100 GeV/c. A double measurement (one on the top half and one in the bottom half of the detector) enables the determination of the resolution, which at 100 GeV/c has been found to be 7.4 %. The full system performance has been determined at 45.6 GeV/c during the L3 calibrations
P Lad&
de Guevara/Nuclear
Physics B (Proc. Suppl.)
l
4. First Results Data from September to November of 1999 were used to determine a first muon momentum spectrum from 50 to 500 GeV/c. The total livetime used was slightly more than 30 days. Strict quality cuts have been applied, among others, the need for a good measurement in both upper and lower octant separate track segments and a good match between both to build the final track. The zenith angle has been restricted to a range of 0’ to 10’ to measure the vertical flux. The measured flux weighted by p3 can be seen (fig. 5) together
W+C preliminary 1
Figure 4. Air shower event in the LS+C scintillator array.
at the peak of the 2 resonance, using the e+e- + Z + p+p- reaction, where the back to back muons have the same topology as a cosmic muon going through the vertex. After requiring one of the muons to cross the scintillator region and the best quality for both tracks, a resolution of 5.1 % in E(beam)/E(mu) has been achieved in the 1999 calibrations. The dedicated data taking with the muon spectrometer started in 1999. From May to November a total 5 billion events were recorded, with a livetime of x 124 days. From April to November, 2000 a total of 6.8 billion events have been gathered with a livetime of M 188 days. The air shower array has been fully operational since April 2000 and by 13th November a total of M 33 million air shower events have been recorded. About 28% of these showers are accompanied by muon(s) in the spectrometer.
239
95 (2001) 237-240
Figure 5. The differential and vertical flux of atmospheric muons weighted with p3 ils a function of momentum p at 450 m above sea level.
with the results of other experiments [4] [5] [6] [7] [8] [9]. The systematic error of 9 % dominates the total error plotted. In the future we hope to reduce the total error to 2.5 %. and to extend the momentum range from 20 to 2000 GeV/c. The charge ratio was calculated from the same event sample. The preliminary result can be seen (fig. 6) along with the results of other published measurements [6] [7] [8] [9] . With the small sample used for the analysis up to now the statistical error is dominant at high momenta. 5. Conclusions. A new type of cosmic ray detector, L3+C combines air shower data with precise muon momentum measurements. First preliminary results on the muon spectrum and charge ratio in the range from 50 to 500 GeV/c have been presented. A substantial reduction in the statistical and systematic errors is expected in the future. REFERENCES 1. 2.
Adeva B. et al,NIM,A289 (1990) 35. Chiaki Yanagisawa, “Solar and atmospheric neutrinos: Results from Superkamiokande
240
P Lad&
de Guevara/Nuclear Physics B (Proc. Suppl.) 95 (2001) 237-240
Figure 6. The muon charge ratio as a function of momentum.
3. 4. 5. 6. 7. 8. 9.
and K2k”, “Solar and atmospheric neutrino oscillations” C. Gonzalez-Garcia, (invited papers to this Conference) http://13www.cern.ch/l3_cosmics/ O.C. Ahkofer et al.,Lett. Nuovo Cim,l2 (1975) 107. B. Baschiera et al.,11 Nuovo Cim. 2C (1979) 473. B.C. Pastin. J. Phys G.: Nucl. Phys. 10 (1984) 1629. M.P. De Pascale et al.,J. Geophys. Res.98 (1993) 3501. J. Kremer et al., Phys. Rev. Lett. 83, 4241 (1999) Hebbeker T. and Timmermans C., A compilation of High Energy Atmospheric Muon data at Sea Level, (to be published).