Search for relativistic magnetic monopoles with the Baikal

Search for relativistic magnetic monopoles with the Baikal Neutrino Telescope E. Osipova -MSU (Moscow) for the Baikal Collaboration (Workshop, Uppsala, 2006)

The Baikal Collaboration 1. Institute for Nuclear Research, Moscow, Russia. 2. Irkutsk State University, Irkutsk, Russia. 3. Skobeltsyn Institute of Nuclear Physics MSU, Moscow, Russia. 4. DESY-Zeuthen, Germany. 5. Joint Institute for Nuclear Research, Dubna, Russia. 6. Nizhny Novgorod State Technical University, Nizhny Novgorod, 7. Russia. 8. 7. St. Petersburg State Marine University, St. Petersburg, Russia. 9. 8. Kurchatov Institute, Moscow, Russia.

Outline: Introduction Detector and Site Search strategy for fast magnetic monopole Atmospheric muon simulation and suppress background events Results Outlook

Introduction P. Dirac, 1931 g g * e = n /2 hc, n=0, ± 1, ± 2. . If there is a monopole somewhere in the Universe, even one of such object placed anywhere would be enough to explain the quantization of electric charges B gmin = 68. 5 e One would be surprised if nature had made no use of it P. A. M. Dirac’s string

Monopole mass and acceleration in magnetic fields of Universe In 1974 ‘t Hooft, Polyakov independently discovered monopole solution of the SO(3) Georgi-Glashow model Mmon ~ M V / = 1/137 In wide classes of models Monopole mass may be in the range 107 – 1014 Ge. V Monopole could be accelerated up to energy 1012 – 1015 Ge. V Monopoles with such masses may be relativistic S. Wick, T. Kephart, T. Weiler, P. Bierman Astropart. Phys. 18(2003) 663

Can monopole cross the Earth? lg( E loss, Ge. V) 16 15 Monopole Energy losses, crossing the Earth on diameter 14 13 Emon = 1015 Gev 12 E mon/M < 108 11 10 M> 107 Ge. V 0 2 4 6 8 lg (Emon / M) 1014 Ge. V > Mmon > 107 Ge. V

Cherenkov Light from Relativistic Magnetic Monopole d Nph/dl (M) = n 2 (g/e)2 d Nph/dl (muon) 8300 d Nph/dl (muon) Light flux from monopole Light flux from 10 Pe. V muon photons /cm ( n =1. 33) β

Baikal Neutrino Telescope NT-200 192 Optical modules on 8 strings OM’s are grouped in pairs –Channel Trigger >3 Chan within 500 ns OM could detect fast monopole up to 100 m Expected number of hits Nhit for fast Monopole vs distance from NT 200 center

Water characteristics OM response on fast monopole vs R, m p. e. Absoption Labs =22 -24 m (480 nm) Scattering Strongly anisotropic <cos(α)> 0. 85 -0. 9 Lscat =30 -70 m Lscat=30 m Lscat=15 m p. e with delay <τ P E from fast monopole with delay <τ for Lsc=15 m, Lsc=30 m OM faced to Cherenkov light (left) and in opposit side( right) τ, ns Lscat 15 m R, m 30 m Seff increases by 20% τ, ns

Atmospheric muon simulation The main background for fast monopole signatures are muon bundles, high energy muons and shower from muons Primary particles Air shower, muons Composition and spectral index for elements B. Wiebel-Smooth, P. Bierman, Landolt-Bornststain Cosmic Rays, 6, 1999, pp 37 -90 CORSIKA code J. Capdevielle et. al. Kf. K report (1992) QGSJET 1 model N. N Kalmykov et. al. Nucl. Phys. B 52 (1997) Pass at depth MUM E. Bugaev et. al. Phys. Rev. D 64 NT 200 response to all muon energy loss processes Baikal code I. Belolaptikov will be published

Аtmospheric muons as standard calibration signal Time distribution t = t 52 -t 53) MC EXP Amplitude distribution MC EXP t, ns Ph. el.

Search strategy and data analysis NT-200 1000 days of live time (April 1998 -February 2002) Selection events with high multiplicity Nhit>30 To reduce the background from atmospheric muons we search for monopole from the lower hemisphere To suppress atmospheric muons a cut on time_z correlation has been applied ti , zi - time & z-coordinates of fired channels, T, Z –their mean values per event σt , σz - root mean square

Background suppression CUT 1 : cor. TZ >0 & Nhit >30 leaves 0. 015% of events and reduces effective area for monopole (β=1) ~ 2 times Additional cuts after reconstruction: Cut 2 - Nhit>35& cor. TZ >0 & rec. Cut 3 - Nhit>Cut 2& χ2<3 Cut 4 -Nhit>Cut 3&θ>100 o cor. TZ for atmospheric muon (black-EXP, red-MC) and for fast monopole from the lower hemisphere (blue) Next cuts are different for different NT 200 configurations Cut 5 – Cut 4&Rrec>10 -25 m ( Rrec -distance from NT 200 center) Cut 6 - Cut 5& cor. TZ >0. 25 -0. 65 No events from experimental sample pass CUTS 1 -6

The main sources of background CUT 1 CUT 3 CUT 4 CUT 5 The events with a large number of muons in bandle are supressed after reconstruction with χ2<3 lg(Esh, Te. V) Number of muons in bundle MC events Simulated atmospheric muons satisfying CUT 1 vs cascade energy (upper) and vs number of muons in bundle (lower) Lg(Esh, Te. V

Comparison of experimental and MC data with respect to parameters which used for background rejection for events satisfying CUT 1 Distance from NT 200 center Reconstructed θ MC EXP Expected from monopole R, m θ, grad Simulation describes EXP data quite well even for very rare events. Number of fired channels

Passing rates versus Cut-level Passing rates MC EXP Seff for monopole (β=1) CUT level Effective area for fast monopole (β=1) decrease 2 times from CUT 1 –CUT 6

Upper limit on the flux of fast monopole From the non-observation of candidate events in NT 200 an upper limit on the flux of fast monopole is obtained Acceptance & Upper flux limit Aeff T β=1 β=0. 9 β=0. 8 cm 2 sec sr NT 200 4. 84 1016 3. 48 1016 1. 231016 NT 36+NT 96 0. 37 1016 0. 25 1016 0. 1 1016 Upper Limit 0. 46 10 -16 0. 65 10 -16 1. 8 10 -16 90% C. L. (cm 2 sec sr)-1 90% C. L. upper limit on the flux of fast monopole (1000 livedays NT 200)

Outlook NT 200+ put into operation in 2005. The main advantage of NT 200+ is the possibility to select cascades. It allows to reject background using more soft cuts. We expect increasing effective area for fast monopole at 1. 5 times comparing NT 200+ = NT 200 + 3 external string ( 36 OMs) - Height = 210 m - = 200 m - Volume ~ 4 Mton

A future Gigaton Volume Detector (Baikal-GVD) Sparse instrumentation: 90 – 100 strings 300 – 350 m lengths with 12 - 16 OM per string = 1300 - 1700 OMs (NT 200 = 192 OMs) distance between strings 100 m Expected sensitivity for fast monopole (1 year GVD) Fmon < 5 · 10 -18 cm-2 s-1 sr-1 Top view of the planned Baikal-GVD detector. Also shown is basic cell: a “minimized” NT 200+ telescope

CONCLUSION 1. BAIKAL Experimenal Upper limit on the Fast ( v/c =1) Monopole Flux 2. (90% C. L) 3. Fmon < 0. 46 · 10 -16 cm-2 sec-1 sr-1 4. The limit on fast magnetic monopole flux obtained in this analysis is the best at the present time 5. 6. 2. NEW configuration NT 200+ Permits to reject background using more soft cuts. Expected 1. 5 times increase of effective area for fast monopole comparing NT 200 3. Gigaton Volume (km 3 -scale) Detector (Baikal-GVD) Expected sensitivity for fast monopole (1 year operation) Fmon < 5 · 10 -18 cm-2 s-1 sr-1

Water characteristics Absorption and Scattering cross-section vs λ Absoption Strongly anisotropic <cos(α)> 0. 85 -0. 9 Scattering Baikal Lscat=30 -70 m Labs =22 -24 m Lscat 15 m Seff increases by 20% p. e. OM responce vs R, m τ, ns p. e with delay <τ OM faced to Cherenkov light R, m 30 m OM faced opposit Cherenkov light τ, ns