The measurement of upward going muons using the MACRO detector

Nuclear Physics B (Proc. Suppl.) 70 (1999) 367-370

ELSEVIER

The measurement T. Montarulia

“Universit&

PROCEEUINGS SUPPLEMENTS

of upward going muons using the MACRO

for the MACRO

detector

Collaboration(*)

di Bari and INFN,

Dipartimento

di Fisica,

Via Amendola

173, 70126 Bari, Italy

The upward-going muon flux (Ep > 1 GeV) has been measured with the underground detector MACRO at LNGS. The total number of measured events is compatible at the 8% c.1. with the expected one. Moreover, the zenith angular distribution of the measured flux does not match the expectation showing a deficit in the vertical direction where the apparatus performance is best known. Assuming an oscillation hyphotesis with parameters in the range recently suggested to solve the atmospheric neutrino problem, the agreement increases, but not significantly. The results of an indirect dark matter search for a signal of WIMPS from the core of the Sun and of the Earth are given. Neutrino astronomy with MACRO is giving interesting results regarding possible high energy neutrino emission from pointlike sources and coincidences of neutrino events with -y-ray bursts.

1. The upward-going The

time-of-flight

discriminate

the

muon flux

tecnique

has been used to

atmospheric

neutrino

induced

muons travelling upwards against the background of atmospheric muons travelling in the opposite direction.

The liquid scintillator

system

of about

600 tons is made

of counters with time resolution of N 500 ps and the intrinsic angular resolution of the streamer tube tracking system is better than 0.5”. Neutrinos in the full MACRO detector are seen in three different topologies: throughgoing upgoing p’s produced by neutrinos with medium energy of - 100 Gel/, partially contained events produced by neutrinos interacting in the lower part of the detector ((E,) - 3 GeV), and stopping p’s ((E,) - 5 GeV). We present the results of the upward throughgoing muon analysis in the period since March 1989 to November 1996. More than 2 yr of data have been collected with the full apparatus and summed to the previous statistics [l] for a total number of 364 events. The requirement that muons cross at least 200 g/cm2 of absorber in the detector

reduces

at the

1% level the back-

ground due to soft pions produced

at large angle

by undetected down-going p’s. After background subtraction, the ratio of measured over expected events is 0.74 f 0.04,tat f 0.06,,, f 0.13th,,, compatible with 1 at 8% c.1.. The expectation is evaluated with a full Monte Carlo using the Bartol 0920-5632/98/$19.00 0 1998ElsevierScienceB.V. Allrightsreserved. PII SO920-5632(98)00454-X

flux [2]. Other calculations have been used, also a new one based on Fluka interaction model [3], but they do not produce significant differences. The zenith angular distribution of the measured flux compared to the expected one represented with the theoretical error of f17% is shown in Fig. 1. Excluding the horizontal bin (case > -0.1) due to a possible contamination of large angle scattering down-going muons, a x2 minimization with the normalization parameter of the calculation (Y free gives probability < 1% for Q = 0.75. If the parameters suggested by Superkamiokande [4] for a V~ - v7 oscillation hypothesis are assumed, the agreement increases, but not significantly.

2. WIMPS

from the Sun and the Earth

WIMPS in the halo could become gravitationally trapped inside the core of celestial bodies such as the Sun and the Earth and they could produce a flux of high energy v’s. These could be detected as upward-going muons by a directional analysis discriminating the signal between the background due to atmospheric v’s. As can be seen in Fig. 1, there is a deficit of measured events compared to the atmospheric u background in the region about the vertical direction of MACRO, hence we set conservative flux limits for WIMPS from Earth assuming that we measure the expected events [5]. For an exposure of 1900 m’yr, we evaluate in a window of 30“ a p

368

T. Montaruli/Nuclear

Physics B (Proc. Suppl.) 70 (1999) 367-370

the kinematics of the neutrino interactions, while it weakly depends on other details of the models. Considering the multiple scattering of muons propagating in the rock to the detector and the angular resolution of the detector, windows containing 90% of the signal have been evaluated using neutrino fluxes calculated by Bottino et al. [6] and are shown in Fig. 2. For mX = 60, 100, 200, 12.8’, 500 and 1000 GeV they are respectively 10.4’, 7.5’, 6.3”,4.2”. Fig. 3 shows the upgoing-

LI!

1”““““““““““““““““““‘~

~wm 8

SUN

1200

-

IWO

m, = m, = -m%= m,= ..

I

1 IX00 Figure 1. Zenith distribution of upgoing muon flux (Ep > 1 GeV). Two curves are shown for the indicated V~ -v, oscillation parameters (maximal mixing).

flux limit (E, > 1 GeV) of 2.67 x lo-l4 c~-~.s-~. As the Sun is a moving source, the background is less important than for the search for the Earth, hence we consider 624 events including the lower energy events which only cross the two upper scintillator layers and a new data sample up to June 97. For an exposure of 710 m2yr, the muon flux limit inside 30” from the Sun direction is 7.30 x lo-l4 cm-2s-1. The most plausible WIMP is considered the neutralino x. Its mass in Minimal Supersymmetric Models depends on a gaugino-mass parameter (if a GUT relation is assumed), on the higgsino mass parameter /I and on the ratio of the Higgs vacuum expectation values tan/?. We have studied the shape of the signal expected from neutralino annihilation to evalutate flux limits as a function of mx, which are useful in constraining theoretical models. The angular spread between the parent neutrino and the detected muon is a function of the neutralino mass which governs

Figure

1000 GeV (4.2“) 500 GeV (6,3” 200 GeV (7.5’ ) 100 GeV (10,4”) 60 GeV (12.81

2. v - p angle for x - X in the Sun.

muon fluxes (Efi > 1 GeV) evaluated by Bottino et al. [6] using central values of allowed intervals for cosmological parameters and minimal supersymmetric parameters varying in allowed intervals. The flux limits are shown too. They are evaluated in search cones which collect the 90% of the signal and using a fit of the angular shape of the signal, of the data and of atmospheric v background. As suggested in [7], limits evaluated with this second method are - 15% better. 3. Neutrino

astronomy

High energy neutrinos could probe the deep sky due to their low cross-sections. It is expected that beam dumps which produce y-rays from A’ decay should even produce neutrinos from ?y* decays.

T. Montaruli/Nuclear

Table 1 Flux limits

for some sources 6 40.6’ 38.1’ 38.45” 22.0” -45.10 -21.3”

Source cyg x-3 MRK 421 MRK 501 Crab Nebula Vela Pulsar Kepler 1604

I

Physics B (Proc. Suppl.) 70 (1999) 367-370

at 90% c.1. (p-flux Events 0 0 0 1 0 2

limits

limits

v-flux

limits

Published p limits 4.1 Baksan [9] 3.3 IMB [lo] 2.6 Baksan 0.78 IMB

in 10-5cm-2s-’

).

v-flux limits 4.25 3.87 3.98 1.82 0.30 0.85

have been found around any observable direction (30 clusters with > 3 events are detected and 28 are expected) and the largest signal found is of 2 events from Kepler 1604 (0.54 are expected). The muon and neutrino flux limits for some sources are given in Table 1 and they improve some published limits. A search for correlation with yray bursts from BATSE catalogs and upgoing-p events has been performed giving negative result in search cones of 20” (suitable to BATSE resolution) and inside f200 s from upgoing-p detection. The flux limit per average burst is 1.2 x 10-gem-2 (90% c.1.).

t

0

in 10-14cm-2s-1,

p-flux 10.50 7.74 7.96 3.64 0.61 1.71

Backg. 0.05 0.07 0.06 0.28 0.86 0.54

369

50

100

150

zoo

250

300 m,

(*) The MACRO

Collaboration:

UW

3. Upgoing ~1 flux vs mx for Eih > 1 Gel/ from the Sun [6]. Dotted line: MACRO flux limit from the fit; solid line: MACRO flux limit (90% signal); dashed line: Baksan flux limit (90% signal) [8]. Figure

Possible high energy neutrino point-like sources are SN remnants, X-ray binary systems, AGN and other sources with significant y emission in the TeV range. etc. A directional analysis have been performed using 646 events (the 624 events used for the WIMP search summed to the upgoing p’s detected during a construction period) using a search half-cone of 3”, which contains 90% of the signal as evaluated by Monte Carlo for v spectral index of 2.1. No significant cluster of events

M. Ambrosio12, R. Antolini7, C. Aramo79P, G. Auriemmai4j” A. Baldini13 G. C. Barbarino12: B. C. Barish \ , G. Battistoni’j’, R. Bellotti’, C. Bemporad13, P. Bernardini”, H. Bilokon’, V. Bisi16, C. Bloise6, C. Bowers, S. Bussino14, F. Cafagnal, M. Calicchio’, D. Campanar2, M. Carboni’, M. Castellanol, S. Cecchini2J, F. CeilSId, V. Chiarella’, S. Coutu’l, G. Cunti14, L. De Benedictis’, G. De Cataldo’, H. Dekhissi2J, C. De Marzol, I. De Mitrig, M. De Vincenzi141f, A. Di Credico7, 0. Erriquez’, C. Favuzzil, C. Forti’, P. Fuscol, G. Giacomelli2, G. Giannini13)g, N. Giglietto’, M. Grassi13, L. Gray4>7, A. Grillo7, F. Guarino l2 P. Guarnaccia ‘, C. Gustavino7, A. Habig3,‘K. Hanson”, A. Hawthorne’, R. Heinz’, E. Iarocci 6$, E. Katsavounidis4, E. Kearns3, S. Kyriazopoulou4, E. Lamannai4,

370

T. Montaruli/NuclearPhysicsB (Proc. Suppl.) 70 (1999) 367-370

C. Lane’, D. S. Levin”, P. Lipari14, N. P. Longley41m, M. J. Longoll, F. Maaroufi2+, G. Mancarellal’, G. Mandrioli2, S. Manzoor2~n, A. Margiotta Neri2, A. Marini’, D. Martellolol, A. Marzari-Chiesa16, M. N. Mazziottal, C. Mazzotta”, D. G. Michae14, S. Mikheyev71’, L. Millers, P. Monacellig, T. Montarulil, M. Monteno”, S. Mufson8, J. Mussel’, D. Nico16131d, R. Nolty4, C. 0kada3, C. Orth3, G. Osteria”, 0. Palamara lo V . Patera6>h , L. Patrizii2, R. Pazzi13, C: W. Peck4, S. Petrerag, P. Pistilli141f, V. Popa211, V. Pugliese 14, A. Rainol, J. Reynoldson7, F. Ronga’, U. Rubizzo12, A. Sanzgiri15, C. Satrianoi4+, L. Satta6ph, E. Scapparone7, K. Scholberg3v4, A. Sciubba’l*, P. Serra-Lugaresi2, M. Severii4, M. Sioli2, M. Sitta”, P. Spinelli’, M. Spinetti’, M. Spurio2, R. Steinberg5, J. L. Stone3, L. R. Sulak3, A. Surdo”, G. Tarlerl, V. Togo2, C. W. Walter314 and R. Webb15 1. Dipartimento di Fisica dell’Universita di Bari and INFN, 70126 Bari, Italy 2. Dipartimento di Fisica dell’Universiti di Bologna and INFN, 40126 Bologna, Italy 3. Physics Department, Boston University, Boston, MA 02215, USA 4. California Institute of Technology, Pasadena, CA 91125, USA 5. Department of Physics, Drexel University, Philadelphia, PA 19104, USA 6. Laboratori Nazionali di Frascati dell’INFN, 00044 Ffascati (Roma), Italy 7. Laboratori Nazionali de1 Gran Sass0 dell’INFN, 67010 Assergi (L’Aquila), Italy 8. Depts. of Physics and of Astronomy, Indiana University, Bloomington, IN 47405, USA 9. Dipartimento di Fisica dell’Universit8 dell’Aquila and INFN, 67100 L’Aquila, Italy 10. Dipartimento di Fisica dell’Universita di Lecce and INFN, 73100 Lecce, Italy 11. Department of Physics, University of Michigan, Ann Arbor, MI 48109, USA 12. Dipartimento di Fisica dell’Universiti di Napoli and INFN, 80125 Napoli, Italy 13. Dipartimento di Fisica dell’Universitir di Pisa and INFN, 56010 Pisa, Italy 14. Dipartimento di Fisica dell’Universita di Roma “La Sapienza” and INFN, 00185 Roma, Italy 15. Physics Department, Texas A&M University, College Station, TX 77843, USA 16. Dipartimento di Fisica Sperimentale dell’Universitb di Torino and INFN, 10125 Torino, Italy a Also Universita della Basilicata, 85100 Potenza, Italy

b Also INFN Milano, 20133 Milano, Italy c Also Istituto TESRE/CNR, 40129 Bologna, Italy d Also Scuola Normale Superiore di Pisa, 56010 Pisa, Italy e Also Faculty of Sciences, University Mohamed I, B.P. 424 Oujda, Morocco f Also Dipartimento di Fisica, Universita di Roma Tre, Roma, Italy 9 Also Universitir di Trieste and INFN, 34100 Trieste, Italy h Also Dipartimento di Energetica, Universita di Roma, 00185 Roma, Italy d Also Institute for Nuclear Research, Russian Academy of Science, 117312 Moscow, Russia I Also Institute for Space Sciences, 76900 Bucharest, Romania m Swarthmore College, Swarthmore, PA 19081, USA n RPD, PINSTECH, P.O. Nilore, Islamabad, Pakistan p Also INFN Catania, 95129 Catania, Italy

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