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Observation of trimuon events produced in neutrino and antineutrino interactions
Volume 70B, number 3
PHYSICS LETTERS
OBSERVATION
10 October 1977
OF TRIMUON EVENTS PRODUCED IN NEUTRINO
AND ANTINEUTRINO
INTERACTIONS
M. HOLDER, J. KNOBLOCH, J. MAY, H.P. PAAR, P. PALAZZI, F. RANJARD, D. SCHLATTER, J. STEINBERGER, H. SUTER, H. WAHL and E.G.H. WILLIAMS CERN, Geneva, Switzerland F. EISELE, C. GEWENIGER, K. KLEINKNECHT, G. SPAHN and H-J. WILLUTZKI Institut ffir Physik ~ der Universita't, Dortmund, Germany W. DORTH, F. DYDAK, V. HEPP, K. TITTEL and J. WOTSCHACK Institut for Hochenergiephysik ~ der Universitfz't, Heidelberg, Germany A. BERTHELOT, P. BLOCH, B. DEVAUX, M. GRIMM, J. MAILLARD, B. PEYAUD, J. RANDER, A. SAVOY-NAVARRO and R. TURLAY D.Ph.P.E., CEN-Saclay, France F.L. NAVARRIA Istitu to di Fisica dell 'Universitd, Bologna, ltaly Received 9 August 1977 We report two trimuon events produced in u interactions. Of these, one is of the charge type - + % not previously reported. In an antineutrino exposure, one candidate of the charge type + - - has been observed. This type of event has also not been reported previously. The combined 7r--*~ and K ~/~ background for the three events are calculated to be ~ 0.7 events. The rate relative to charged current events corresponding to these three events is of the order of 4 x 10 -s.
Trimuon events have been reported from two previous experiments [1, 2]. Such events, produced by neutrinos or antineutrinos in a detector such as ours 1 , may originate in diverse processes: I) Background due to 7r and K decay. The chief contributors to this background are dimuon events in which one of the hadrons in the shower decays to a muon. 2) Normal charged current events for which a muon pair is associated with the hadron shower, perhaps due to the decay of a vector meson. 3) Events in which a charmed pair of particles are produced, and for which both decay with m u o n emission. * Supported by Bundesministerium fiir Forschung und Technologie. I For a description of the apparatus we refer the reader to Holder et al. [ 3 ].
4) Perhaps there exist processes in which as yet unknown particles are produced of either leptonic or hadronic character, and which decay such that at least two muons are emitted. The interest in trimuon events centres chiefly on the last possibility, but perhaps also processes (2) and (3) could eventually prove interesting. We have observed three such events, two in a neutrino exposure, and one in an antineutrino e x p o s u r e . In table 1 we list rates for single and m u l t i m u o n production. The v trimuon events, after computer reconstruction, are given in figs. 1 and 2. Some of the properties of the events are given in table 2. Owing to the large acceptance of the apparatus, the geometrical corrections to these numbers are small. However, in general, muons with less than 4.5 GeV are not detected (an exception is one of the muons in the antineutrino event), and this is a serious bias for multi393
Volume 70B, number 3
PHYSICS LETTERS
Table 1 Uncorrected rates for single and multimuon events
Ev > 1~ [4]
100 GeV
53 000 22 000
Ep > 100 GeV 15 000 3 400
U~ + u +- [4]
257
138
58
17
U~ + t~~ [5]
47
34
9
4
U-+u-+u +
1
1
1
0
U++U÷+U-
I
1
0
0
R3u/R2u
~ 4 X 10 - 5 ~ 8 X 10 . 5 ~ 7 X 10 - 3 1X 10 . 2
All neutrino energies
E v>lOOGeV All neutrino energies
E v>lOOGeV.
These are the combined rates for neutrinos and antineutrinos. 1
5
10
15
19
The dominant contribution to the background from ~-~/a and K - * ~ decay (Process 1) comes from the dimuon events. In estimating this background, it has to be kept in mind that the charmed and strange particles which are produced in these events produce normally also a kaon in their decay, and these kaons have a relatively larger chance of producing background muons than the otherwise dominant pions. We estimate the background for the four possible reactions, as follows for our total sample: u+ Fe-+/a- + ~ - + ~ + + ... 0.3 events u + Fe -+ ~ - + ~+ + ~+ + ... 0.3 events + Fe -+/J+ +/~- + ~ - + ... 0.05 events ~+ F e ~ + +/~+ + / a - + ... 0.05 events
m u o n events. The observed event numbers correspond to the following uncorrected relative rates (the ~ trim u o n event, because of the low energy of one of the muons, has been arbitrarily counted as one-half):
R3u/Rlu
10 October 1977
Total trimuon background due to pion and kaon decay: 0.7 +- 0.3 events. For a description of this calculation we refer to ref. [5]. We conclude that although any one of the observed events may quite well be due to this background, it is not likely that all of the observed events are due to this background. It may be important to add that, in
11
13
15
444.
TRIMUON EVENT (No 12697)
I+1111 I
17
2_L, X
""
I
/~"
/
/
/
/
='A
.i /B
FRONT view
FRONT view
l view
A: I~- 78 GeV B:lx° 8.6 GeV C:W 4 GeV
Ehoa= 30 GeV Etot =121 GeV
Fig. l. Display of the computer reconstruction of the - + - p trimuon. Left: The three drift-chamber views along the beam. Right: Projection into the plane perpendicular to the v. 394
X
I
"~
, .,4/
U view
Vview
'A
I
i view
]_LIlIo /11/11 11TTFlllllltt-ttl?
TRIMUON EVENT ( No 35 349)
"x,c
Y view
-! I~ lm
19
•
C B
A: p.* 23 GeV 8 : I i÷ 8GeV C :p.- 5.5 GeV
Eh~ =180 GeV Eio ~ =217 GeV
Vview
Fig. 2. Same as fig. 1, but for the - + + v event.
Volume 70B, number 3
PItYSICS LETTERS
10 October 1977
Table 2 Properties of trimuon events Eha d Eto t (GeV) 30
180
7
121
217
34
Charge
Px
Py
Pz
(GeV/c)
PTsh a) x b ) (GeV/c)
y b)
zxq5c)
0.47
0.35
1-2) 1-3) 2-3)
125 ° 2.2 156 ° 3.6 31 ° 0.3
4.2
1-2) 1-3) 2-3)
109 ° 2.1 161 ° 1.9 51 ° 1.5
3.2
1-2) 1-3) 2-3)
11 ° 0.3 132 ° 2.0 143 ° 2.0
2.8
1)2)3)+
3.5 0.05 -0.24
-3.5 0.3 0.61
78.4 4.1 8.6
0.38 0.47
1)2)+ 3) +
-0.7 -0.36 0.55
0.54 -1.1 -0.86
5.4 23.2 7.9
1.1 1.0
0.08
1)+ 2)3)--
0.7 0.56 -0.04
-0.55 -0.65 0.7
12.6 12.0 2.3
1.4 0.6
0.05
0.98
0.63
MI~~ (GeV)
M3t~ (GeV)
a) PTsh = transverse momentum with respect to the hadron shower direction [= (v -/21 ) × #ill v -/211, i = 2, 3]. b) X, Y = scaling variables. X = Q2/[2m(Ehad + E2 + E3)]. Y = (Ehad + E2 + E3)/Etot. c) Zxq~= azimuthal angular difference between ~1 and/ai, i = 2, 3 in the plane perpendicular to the incoming neutrino. particular, the event v ~ / ~ - / ~ + / l + does not seem to be due to this type o f background, since the small energy carried by the negative m u o n in this event is very atypical o f d i m u o n events. Processes (2) and (3) will result only in reactions o f the type v - + / l - / l - / l + and 9 ~/a+/l+/~ - . We have observed one event o f this type, and this m a y very well be due to one o f these processes, since we estimate that one might, very roughly, e x p e c t ~ 1 . 5 events f r o m process (2) for our sample 2, and ~ 0 . 7 for process (3) 3 . Also the observed k i n e m a t i c properties o f this event are in reasonable agreement w i t h those that one might e x p e c t for either o f these processes. The charge c o m b i n a t i o n s observed in the remaining two events are rather puzzling in the frame o f present ideas and, given the non-negligible background estimates, we prefer to wait for m o r e extensive data before speculating on the possible origin o f such events. The rates which correspond to the t r i m u o n events r e p o r t e d here are s o m e w h a t smaller than those corresponding to the previous publications. Barish et al. [1] report 2 events corresponding to 18 000 charged cur-
2 We take 10 -4 as the probability of a muon pair in the hadron shower and 0.25 as the probability for detecting both muons. 3 We take 0.8 X 10 -2 for the probability of charmed pair production (see M. Holder et al. [4] ) and a detection efficiency of 0.3 for each muon.
rent events and to 56 d i m u o n events. Benvenuti et al. [2] report that the 6 observed events correspond to a relative rate o f 5% with respect to d i m u o n events w i t h energy above 100 GeV. However, the numbers o f events are small, and the beams different, so that the differences m a y not be significant. We wish to acknowledge our great indebtedness and deep appreciation to our m a n y technical collaborators. In particular we wish to thank m o s t w a r m l y H. A t h e r t o n , S. Brehin, H.J. Bottner, A. Cyvoct, W. Horath, G. J u b a n , A. Lacourt, P. Lazeyras, G. Laverri~re, C. Leschevin, Y. Malbequi, H. Martin, W. Middelkoop, M. Morpurgo, J. Pelle, G. Petrucci, D. Pollmann, G. Pozzo, P. Schilly, M. S c h m i t t , G. Stefanini, G. Tarte and M. Vyso~ansk~,, as well as m e m b e r s o f the SPS staff for the o p e r a t i o n o f the accelerator.
References [1] B.C. Barish et al., Phys. Rev. Lett. 38 (1977) 577. [21 A. Benvenuti et al., Phys. Rev. Lett. 38 (1977) 1110. [3] M. Holder et al., A detector for high-energy neutrino interactions, to be published in Nuclear lnstrum. Methods. [41 M. Holder et al., Phys. Lett. 69B (1977) 377. [5l M. Holder et al., Phys. Lett. 70B (1977) 293.
395
PHYSICS LETTERS
OBSERVATION
10 October 1977
OF TRIMUON EVENTS PRODUCED IN NEUTRINO
AND ANTINEUTRINO
INTERACTIONS
M. HOLDER, J. KNOBLOCH, J. MAY, H.P. PAAR, P. PALAZZI, F. RANJARD, D. SCHLATTER, J. STEINBERGER, H. SUTER, H. WAHL and E.G.H. WILLIAMS CERN, Geneva, Switzerland F. EISELE, C. GEWENIGER, K. KLEINKNECHT, G. SPAHN and H-J. WILLUTZKI Institut ffir Physik ~ der Universita't, Dortmund, Germany W. DORTH, F. DYDAK, V. HEPP, K. TITTEL and J. WOTSCHACK Institut for Hochenergiephysik ~ der Universitfz't, Heidelberg, Germany A. BERTHELOT, P. BLOCH, B. DEVAUX, M. GRIMM, J. MAILLARD, B. PEYAUD, J. RANDER, A. SAVOY-NAVARRO and R. TURLAY D.Ph.P.E., CEN-Saclay, France F.L. NAVARRIA Istitu to di Fisica dell 'Universitd, Bologna, ltaly Received 9 August 1977 We report two trimuon events produced in u interactions. Of these, one is of the charge type - + % not previously reported. In an antineutrino exposure, one candidate of the charge type + - - has been observed. This type of event has also not been reported previously. The combined 7r--*~ and K ~/~ background for the three events are calculated to be ~ 0.7 events. The rate relative to charged current events corresponding to these three events is of the order of 4 x 10 -s.
Trimuon events have been reported from two previous experiments [1, 2]. Such events, produced by neutrinos or antineutrinos in a detector such as ours 1 , may originate in diverse processes: I) Background due to 7r and K decay. The chief contributors to this background are dimuon events in which one of the hadrons in the shower decays to a muon. 2) Normal charged current events for which a muon pair is associated with the hadron shower, perhaps due to the decay of a vector meson. 3) Events in which a charmed pair of particles are produced, and for which both decay with m u o n emission. * Supported by Bundesministerium fiir Forschung und Technologie. I For a description of the apparatus we refer the reader to Holder et al. [ 3 ].
4) Perhaps there exist processes in which as yet unknown particles are produced of either leptonic or hadronic character, and which decay such that at least two muons are emitted. The interest in trimuon events centres chiefly on the last possibility, but perhaps also processes (2) and (3) could eventually prove interesting. We have observed three such events, two in a neutrino exposure, and one in an antineutrino e x p o s u r e . In table 1 we list rates for single and m u l t i m u o n production. The v trimuon events, after computer reconstruction, are given in figs. 1 and 2. Some of the properties of the events are given in table 2. Owing to the large acceptance of the apparatus, the geometrical corrections to these numbers are small. However, in general, muons with less than 4.5 GeV are not detected (an exception is one of the muons in the antineutrino event), and this is a serious bias for multi393
Volume 70B, number 3
PHYSICS LETTERS
Table 1 Uncorrected rates for single and multimuon events
Ev > 1~ [4]
100 GeV
53 000 22 000
Ep > 100 GeV 15 000 3 400
U~ + u +- [4]
257
138
58
17
U~ + t~~ [5]
47
34
9
4
U-+u-+u +
1
1
1
0
U++U÷+U-
I
1
0
0
R3u/R2u
~ 4 X 10 - 5 ~ 8 X 10 . 5 ~ 7 X 10 - 3 1X 10 . 2
All neutrino energies
E v>lOOGeV All neutrino energies
E v>lOOGeV.
These are the combined rates for neutrinos and antineutrinos. 1
5
10
15
19
The dominant contribution to the background from ~-~/a and K - * ~ decay (Process 1) comes from the dimuon events. In estimating this background, it has to be kept in mind that the charmed and strange particles which are produced in these events produce normally also a kaon in their decay, and these kaons have a relatively larger chance of producing background muons than the otherwise dominant pions. We estimate the background for the four possible reactions, as follows for our total sample: u+ Fe-+/a- + ~ - + ~ + + ... 0.3 events u + Fe -+ ~ - + ~+ + ~+ + ... 0.3 events + Fe -+/J+ +/~- + ~ - + ... 0.05 events ~+ F e ~ + +/~+ + / a - + ... 0.05 events
m u o n events. The observed event numbers correspond to the following uncorrected relative rates (the ~ trim u o n event, because of the low energy of one of the muons, has been arbitrarily counted as one-half):
R3u/Rlu
10 October 1977
Total trimuon background due to pion and kaon decay: 0.7 +- 0.3 events. For a description of this calculation we refer to ref. [5]. We conclude that although any one of the observed events may quite well be due to this background, it is not likely that all of the observed events are due to this background. It may be important to add that, in
11
13
15
444.
TRIMUON EVENT (No 12697)
I+1111 I
17
2_L, X
""
I
/~"
/
/
/
/
='A
.i /B
FRONT view
FRONT view
l view
A: I~- 78 GeV B:lx° 8.6 GeV C:W 4 GeV
Ehoa= 30 GeV Etot =121 GeV
Fig. l. Display of the computer reconstruction of the - + - p trimuon. Left: The three drift-chamber views along the beam. Right: Projection into the plane perpendicular to the v. 394
X
I
"~
, .,4/
U view
Vview
'A
I
i view
]_LIlIo /11/11 11TTFlllllltt-ttl?
TRIMUON EVENT ( No 35 349)
"x,c
Y view
-! I~ lm
19
•
C B
A: p.* 23 GeV 8 : I i÷ 8GeV C :p.- 5.5 GeV
Eh~ =180 GeV Eio ~ =217 GeV
Vview
Fig. 2. Same as fig. 1, but for the - + + v event.
Volume 70B, number 3
PItYSICS LETTERS
10 October 1977
Table 2 Properties of trimuon events Eha d Eto t (GeV) 30
180
7
121
217
34
Charge
Px
Py
Pz
(GeV/c)
PTsh a) x b ) (GeV/c)
y b)
zxq5c)
0.47
0.35
1-2) 1-3) 2-3)
125 ° 2.2 156 ° 3.6 31 ° 0.3
4.2
1-2) 1-3) 2-3)
109 ° 2.1 161 ° 1.9 51 ° 1.5
3.2
1-2) 1-3) 2-3)
11 ° 0.3 132 ° 2.0 143 ° 2.0
2.8
1)2)3)+
3.5 0.05 -0.24
-3.5 0.3 0.61
78.4 4.1 8.6
0.38 0.47
1)2)+ 3) +
-0.7 -0.36 0.55
0.54 -1.1 -0.86
5.4 23.2 7.9
1.1 1.0
0.08
1)+ 2)3)--
0.7 0.56 -0.04
-0.55 -0.65 0.7
12.6 12.0 2.3
1.4 0.6
0.05
0.98
0.63
MI~~ (GeV)
M3t~ (GeV)
a) PTsh = transverse momentum with respect to the hadron shower direction [= (v -/21 ) × #ill v -/211, i = 2, 3]. b) X, Y = scaling variables. X = Q2/[2m(Ehad + E2 + E3)]. Y = (Ehad + E2 + E3)/Etot. c) Zxq~= azimuthal angular difference between ~1 and/ai, i = 2, 3 in the plane perpendicular to the incoming neutrino. particular, the event v ~ / ~ - / ~ + / l + does not seem to be due to this type o f background, since the small energy carried by the negative m u o n in this event is very atypical o f d i m u o n events. Processes (2) and (3) will result only in reactions o f the type v - + / l - / l - / l + and 9 ~/a+/l+/~ - . We have observed one event o f this type, and this m a y very well be due to one o f these processes, since we estimate that one might, very roughly, e x p e c t ~ 1 . 5 events f r o m process (2) for our sample 2, and ~ 0 . 7 for process (3) 3 . Also the observed k i n e m a t i c properties o f this event are in reasonable agreement w i t h those that one might e x p e c t for either o f these processes. The charge c o m b i n a t i o n s observed in the remaining two events are rather puzzling in the frame o f present ideas and, given the non-negligible background estimates, we prefer to wait for m o r e extensive data before speculating on the possible origin o f such events. The rates which correspond to the t r i m u o n events r e p o r t e d here are s o m e w h a t smaller than those corresponding to the previous publications. Barish et al. [1] report 2 events corresponding to 18 000 charged cur-
2 We take 10 -4 as the probability of a muon pair in the hadron shower and 0.25 as the probability for detecting both muons. 3 We take 0.8 X 10 -2 for the probability of charmed pair production (see M. Holder et al. [4] ) and a detection efficiency of 0.3 for each muon.
rent events and to 56 d i m u o n events. Benvenuti et al. [2] report that the 6 observed events correspond to a relative rate o f 5% with respect to d i m u o n events w i t h energy above 100 GeV. However, the numbers o f events are small, and the beams different, so that the differences m a y not be significant. We wish to acknowledge our great indebtedness and deep appreciation to our m a n y technical collaborators. In particular we wish to thank m o s t w a r m l y H. A t h e r t o n , S. Brehin, H.J. Bottner, A. Cyvoct, W. Horath, G. J u b a n , A. Lacourt, P. Lazeyras, G. Laverri~re, C. Leschevin, Y. Malbequi, H. Martin, W. Middelkoop, M. Morpurgo, J. Pelle, G. Petrucci, D. Pollmann, G. Pozzo, P. Schilly, M. S c h m i t t , G. Stefanini, G. Tarte and M. Vyso~ansk~,, as well as m e m b e r s o f the SPS staff for the o p e r a t i o n o f the accelerator.
References [1] B.C. Barish et al., Phys. Rev. Lett. 38 (1977) 577. [21 A. Benvenuti et al., Phys. Rev. Lett. 38 (1977) 1110. [3] M. Holder et al., A detector for high-energy neutrino interactions, to be published in Nuclear lnstrum. Methods. [41 M. Holder et al., Phys. Lett. 69B (1977) 377. [5l M. Holder et al., Phys. Lett. 70B (1977) 293.
395