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Single muons in the large volume detector
Nuclear Physics B (Proc. Suppl.) 35 (1994) 240-242 North-Holland
PROCEEDINGS SUPPLEMENTS
Single Muons in the Large Volume Detector The LVD Collaboration" Presented by G. Sartorelli, University of Bologna and INFN-Bologna, Italy. The first angular distribution data from 5547 hours of operation of the LVD detector are presented. A total of 452,630 single muons were reconstructed for this period. We present, for the first time from Gran Sasso Laboratory, data at near-horisontal zenith angles.
1. I n t r o d u c t i o n Near-horizontal underground muons could provide information on several particle physics and astrophysics questions [1-4]. The LVD tracking system is designed to examine this interesting reKlon with high precision. This paper provides the first look at the angular distributions in the Gran Sasso Laboratory for coaO below 0.3.
(LNGS) in Italy, at a depth of ,~3,600 meters of water equivalent. The LVD contains a streamer tube tracking system interleaved with a large volume of liquid scintillator and its support structure, which acts as a passive absorber. It is thus a high precision tracking calor/meter with the major part of its volume sensitive, and with the sensitive elements uniformly distributed throughout[5]. The LVD is further described in Section 2. This report is based on muon data acquired during one year of operation of the first tower. The single muon angular distributions are presented. It is noteworthy that we have data that extend to a nearly horizontal zenith ankle. This is the first time such data have been available from the Gran Sasso Laboratory. 2. D e t e c t o r D e s c r i p t i o n
Figure i. LVD tower 1 front view (looking west). The Large Volume Detector (LVD) experiment is located in the INFN Gran Sasso Laboratory "For the complete llst of the authors see p a p e r "Multiple
Muon Events Observed in the LVD Experiment" in these proceedings.
The completed LVD will contain 190 modules grouped into 5 identical aligned towers of 38 modules each. The characteristics of the first tower are summarized in Table I. A module consists of a steel carrier containing 8 liquid scintillation counters, each viewed from the top by 3 photomultiplier tubes. Each module also contains a double layer of 6.3 meters long limited streamer tubes mounted on an L-shaped structure. This structure is attached to the bottom and to one vertical side of the steel carrier. Each module contains about 9.6 tons of scintillator and about 9.5 tons of steel. As shown in Fig. I, the modules in a tower form 5 columns of 7 (side columns) or 8 (center columns) modules each. To provide maximum acceptance, tracking detectors on alternate levels
0920-5632/94/$07.00 © 1994 - Elsevier Science B.V. All rights reserved. SSDI 0920-5632(94)00462-5
LVD Collaboration~Single muons in the Large Volume Detector
Table 1 Characteristics of LVD (1 Tower). Characteristic Surface Area Acceptance for isotropic flux Length x Width x Height Scintillator Mass Iron Mass (scintillator containers and carrier) Tracking Channels Streamer Tubes Tracking Spatial Resolution Angular Resolution Energy Resolution
are wider and extend under the passageways. Details of the tracking data acquisition can be found in Refs. [6,7].
:! !~--~!
iL il
i~
~ ~I"~'~
241
Value 660 m 2
1768 m~'sr 7 m x 13 m x 12 m 368 tons 360 tons 17,408 2,928 __~ l c m < 4 mrad 15% at 10 MeV
3. E v e n t a n a l y s i s The LVD is a multipurpose detector, with hardware triggers designed for many physics topics.Coasequently, a software trigger must be iraposed for any specific study. The software trigger used for this study is described in detail in Ref. [6]. In essence, a muon must traverse at least 3 tracking planes and at least 1 scintillation counter in order to be included in this analysis. For the study discussed in this paper we have used runs occuring in the period from June 1992 to May 1993. After the cuts described in Ref. [6] 612,286 muon events of all multiplicities were selected in the d a t a sample in 5547 hours of llve time. For this study, we accepted only single muon events (584,951 events) where the reconstructed track contained at least three points (452,630 events). 4. R e s u l t s
0.2 ~ 0
-80 # t~,e,.Sg'*-
Figure 2. Lego plot of azimuth vs. cos 0 for single muon events. There are 11,589 events in the bin at cosO = 1 and ~b = -180.
Track reconstruction is performed in the frame of reference defined by the shape of the LVD detector, with the LVD x aTis pointing almost southwest and the y axis pointing southeast. The axis orientations are shown in Fig. 1. The relationskip between the geographical azimuth angle and the LVD azimuth angle is: (geographical) = 218.40 - ~ (LVD). Fig. 2 shows a lego plot of single muon intensity vs. u i m u t h ~b and cos0 in the LVD reference system. Most of the muons arrive at the LVD
242
LVD Collaboration~Single muons in the Large Volume Detector
through the plateau near c o s 8 : 0.9 and ~ = 40 °. A substantial number of muons also come through the valley between the two major sets of mountain peaks, near t~b I-- 180°. These muons arrive along the LVD's x ~i~. O O O
~2
Z W
4 5 2 6 ~ 0 . EVENTS a)
Fig.3 a) shows the single muon cos e distribution and Fig.3 b) is the azimuthal distribution in the LVD reference system. Because the acceptance is small only in regions of little data[6], the dips shown in the ~b distribution are primarily due to the absorption of muons by the nearby mountain ranges.
Q0
•
•
5. S u m m a r y
28
The LVD experiment has had one tower fully operational since June 1992. We have measured the angular distributions of the incident single muons that reach the first tower of the LVD detector. We have presented data near cos ~ : 0 . This is the first time such data have been available from the Gran Sasso Laboratory.
4
~-' 24
$
2o 16
12 REFERENCES 8
I. 4 o.
.._.--
13
L...';"I,,
,,
0.2
. °
i,,,,
2.
I , . . . i , . , ,
0.4
0.6
O.O
COS 0 0
o
3.
24
4.
0 oo
b)
e
5.
~o 20 Z t~
6. 16
e
0 e
Q
7. 12
0
I~,,.I.,..I
-160
....
--80
i ....
I ....
I ....
0
I ....
80
I ....
h
160
(deqcees)
Figure 3. Single muon angular distributions: (a) polar angle; (b) azimuthal angle.
E. Zas, F. Halzen and R. A. Vazquez, Astroparticie Physics 1 (1993) 297. T. K. Gaisser, Cosmic Rays and Particle Physics, (Cambridge University Press, Cambridge, 1990) pp. 77- 84. M. F. Crouch et al., Phys Rev. D 18, (1978) 2239. C. Castagnoli et al., Nuovo Cimento A 82, (1984) 78. G. Bali, et al., Nucl. Instrum. and Methods 11, (1989) 277. LVD Collaboration, "Single Muon Angular Distributions Observed in the LVD Particle Astrophysics Experiment", in preparation. W. Fulglone et al., IEEE Transactions on Nuclear Science 36, (1989) 1635.
PROCEEDINGS SUPPLEMENTS
Single Muons in the Large Volume Detector The LVD Collaboration" Presented by G. Sartorelli, University of Bologna and INFN-Bologna, Italy. The first angular distribution data from 5547 hours of operation of the LVD detector are presented. A total of 452,630 single muons were reconstructed for this period. We present, for the first time from Gran Sasso Laboratory, data at near-horisontal zenith angles.
1. I n t r o d u c t i o n Near-horizontal underground muons could provide information on several particle physics and astrophysics questions [1-4]. The LVD tracking system is designed to examine this interesting reKlon with high precision. This paper provides the first look at the angular distributions in the Gran Sasso Laboratory for coaO below 0.3.
(LNGS) in Italy, at a depth of ,~3,600 meters of water equivalent. The LVD contains a streamer tube tracking system interleaved with a large volume of liquid scintillator and its support structure, which acts as a passive absorber. It is thus a high precision tracking calor/meter with the major part of its volume sensitive, and with the sensitive elements uniformly distributed throughout[5]. The LVD is further described in Section 2. This report is based on muon data acquired during one year of operation of the first tower. The single muon angular distributions are presented. It is noteworthy that we have data that extend to a nearly horizontal zenith ankle. This is the first time such data have been available from the Gran Sasso Laboratory. 2. D e t e c t o r D e s c r i p t i o n
Figure i. LVD tower 1 front view (looking west). The Large Volume Detector (LVD) experiment is located in the INFN Gran Sasso Laboratory "For the complete llst of the authors see p a p e r "Multiple
Muon Events Observed in the LVD Experiment" in these proceedings.
The completed LVD will contain 190 modules grouped into 5 identical aligned towers of 38 modules each. The characteristics of the first tower are summarized in Table I. A module consists of a steel carrier containing 8 liquid scintillation counters, each viewed from the top by 3 photomultiplier tubes. Each module also contains a double layer of 6.3 meters long limited streamer tubes mounted on an L-shaped structure. This structure is attached to the bottom and to one vertical side of the steel carrier. Each module contains about 9.6 tons of scintillator and about 9.5 tons of steel. As shown in Fig. I, the modules in a tower form 5 columns of 7 (side columns) or 8 (center columns) modules each. To provide maximum acceptance, tracking detectors on alternate levels
0920-5632/94/$07.00 © 1994 - Elsevier Science B.V. All rights reserved. SSDI 0920-5632(94)00462-5
LVD Collaboration~Single muons in the Large Volume Detector
Table 1 Characteristics of LVD (1 Tower). Characteristic Surface Area Acceptance for isotropic flux Length x Width x Height Scintillator Mass Iron Mass (scintillator containers and carrier) Tracking Channels Streamer Tubes Tracking Spatial Resolution Angular Resolution Energy Resolution
are wider and extend under the passageways. Details of the tracking data acquisition can be found in Refs. [6,7].
:! !~--~!
iL il
i~
~ ~I"~'~
241
Value 660 m 2
1768 m~'sr 7 m x 13 m x 12 m 368 tons 360 tons 17,408 2,928 __~ l c m < 4 mrad 15% at 10 MeV
3. E v e n t a n a l y s i s The LVD is a multipurpose detector, with hardware triggers designed for many physics topics.Coasequently, a software trigger must be iraposed for any specific study. The software trigger used for this study is described in detail in Ref. [6]. In essence, a muon must traverse at least 3 tracking planes and at least 1 scintillation counter in order to be included in this analysis. For the study discussed in this paper we have used runs occuring in the period from June 1992 to May 1993. After the cuts described in Ref. [6] 612,286 muon events of all multiplicities were selected in the d a t a sample in 5547 hours of llve time. For this study, we accepted only single muon events (584,951 events) where the reconstructed track contained at least three points (452,630 events). 4. R e s u l t s
0.2 ~ 0
-80 # t~,e,.Sg'*-
Figure 2. Lego plot of azimuth vs. cos 0 for single muon events. There are 11,589 events in the bin at cosO = 1 and ~b = -180.
Track reconstruction is performed in the frame of reference defined by the shape of the LVD detector, with the LVD x aTis pointing almost southwest and the y axis pointing southeast. The axis orientations are shown in Fig. 1. The relationskip between the geographical azimuth angle and the LVD azimuth angle is: (geographical) = 218.40 - ~ (LVD). Fig. 2 shows a lego plot of single muon intensity vs. u i m u t h ~b and cos0 in the LVD reference system. Most of the muons arrive at the LVD
242
LVD Collaboration~Single muons in the Large Volume Detector
through the plateau near c o s 8 : 0.9 and ~ = 40 °. A substantial number of muons also come through the valley between the two major sets of mountain peaks, near t~b I-- 180°. These muons arrive along the LVD's x ~i~. O O O
~2
Z W
4 5 2 6 ~ 0 . EVENTS a)
Fig.3 a) shows the single muon cos e distribution and Fig.3 b) is the azimuthal distribution in the LVD reference system. Because the acceptance is small only in regions of little data[6], the dips shown in the ~b distribution are primarily due to the absorption of muons by the nearby mountain ranges.
Q0
•
•
5. S u m m a r y
28
The LVD experiment has had one tower fully operational since June 1992. We have measured the angular distributions of the incident single muons that reach the first tower of the LVD detector. We have presented data near cos ~ : 0 . This is the first time such data have been available from the Gran Sasso Laboratory.
4
~-' 24
$
2o 16
12 REFERENCES 8
I. 4 o.
.._.--
13
L...';"I,,
,,
0.2
. °
i,,,,
2.
I , . . . i , . , ,
0.4
0.6
O.O
COS 0 0
o
3.
24
4.
0 oo
b)
e
5.
~o 20 Z t~
6. 16
e
0 e
Q
7. 12
0
I~,,.I.,..I
-160
....
--80
i ....
I ....
I ....
0
I ....
80
I ....
h
160
(deqcees)
Figure 3. Single muon angular distributions: (a) polar angle; (b) azimuthal angle.
E. Zas, F. Halzen and R. A. Vazquez, Astroparticie Physics 1 (1993) 297. T. K. Gaisser, Cosmic Rays and Particle Physics, (Cambridge University Press, Cambridge, 1990) pp. 77- 84. M. F. Crouch et al., Phys Rev. D 18, (1978) 2239. C. Castagnoli et al., Nuovo Cimento A 82, (1984) 78. G. Bali, et al., Nucl. Instrum. and Methods 11, (1989) 277. LVD Collaboration, "Single Muon Angular Distributions Observed in the LVD Particle Astrophysics Experiment", in preparation. W. Fulglone et al., IEEE Transactions on Nuclear Science 36, (1989) 1635.