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

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, Zeuthen, Germany. 5.Joint Institute for Nuclear Research, Dubna, Russia. 6.Nizhny Novgorod State Technical University, Nizhny Novgorod, Russia. 7. St.Petersburg State Marine University, St.Petersburg, Russia. 8. Kurchatov Institute, Moscow, Russia. The Baikal Collaboration

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

Introduction B Dirac’s string P.Dirac, 1931 g g * e = n /2 hc, n=0, ±1, ±2.. g min = 68.5 e One would be surprised if nature had made no use of it P.A.M.Dirac 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

In wide classes of models Monopole mass may be in the range 10 7 – GeV Monopole could be accelerated up to energy –10 15 GeV Monopoles with such masses may be relativistic 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 M mon ~ M V /   = 1/137 S.Wick, T.Kephart, T.Weiler, P.Bierman Astropart.Phys. 18(2003) 663

Can monopole cross the Earth? lg( E loss, GeV) lg (E mon / M) E mon = Gev E mon /M < 10 8 M> 10 7 GeV Monopole Energy losses, crossing the Earth on diameter GeV > M mon > 10 7 GeV

Cherenkov Light from Relativistic Magnetic Monopole d N ph /dl  = n 2 (g/e) 2 d Nph/dl  muon)  8300 d Nph/dl  muon) ( n =1.33) Light flux from monopole Light flux from 10 PeV muon  Light flux from 10 PeV muon β photons /cm

Baikal Neutrino Telescope NT Optical modules on 8 strings OM’s are grouped in pairs –Channel Trigger >3 Chan within 500ns OM could detect fast monopole up to 100m Expected number of hits N hit for fast Monopole vs distance from NT200 center

Water characteristics Absoption L abs =22-24 m (480nm) Scattering Strongly anisotropic L scat =30-70 m OM response on fast monopole vs R,m p.e. R,m L scat 15m30m S eff increases by 20% p.e with delay <τ τ, ns P E from fast monopole with delay <τ for Lsc=15m, Lsc=30m OM faced to Cherenkov light (left) and in opposit side( right) L scat =30m L scat =15m

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, pp37-90 CORSIKA code J.Capdevielle et. al. KfK report ( 1992 ) QGSJET1 model N.N Kalmykov et.al. Nucl.Phys. B52 (1997) Pass at depth MUM E.Bugaev et.al. Phys.Rev.D64 NT200 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  t, ns MC EXP Ph.el. Amplitude distribution

Search strategy and data analysis Selection events with high multiplicity N hit >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 NT days of live time (April 1998-February 2002) t i,z i - time & z-coordinates of fired channels, T,Z –their mean values per event σ t,σ z - root mean square

Background suppression cor TZ for atmospheric muon (black-EXP, red-MC) and for fast monopole from the lower hemisphere (blue) Additional cuts after reconstruction: Cut2- N hit >35& cor TZ >0 & rec. Cut3 - N hit >Cut2& χ 2 <3 Cut4 -N hit >Cut3&θ>100 o Next cuts are different for different NT200 configurations Cut5 – Cut4&R rec >10-25 m ( R rec -distance from NT200 center ) Cut6- Cut5& cor TZ > No events from experimental sample pass CUTS 1-6 CUT 1 : cor TZ >0 & N hit >30 leaves 0.015% of events and reduces effective area for monopole (β=1) ~ 2 times

The main sources of background lg(E sh,TeV) Number of muons in bundle Simulated atmospheric muons satisfying CUT1 vs cascade energy (upper) and vs number of muons in bundle (lower) CUT1 CUT3 CUT4 CUT5 MC events Number of muons in bundle Lg(E sh,TeV The events with a large number of muons in bandle are supressed after reconstruction with χ 2 <3

Comparison of experimental and MC data with respect to parameters which used for background rejection for events satisfying CUT1 Distance from NT200 center Reconstructed θ R, m θ, grad Number of fired channels Simulation describes EXP data quite well even for very rare events. MC EXP Expected from monopole

CUT level Passing rates MC EXP S eff for monopole (β=1) Effective area for fast monopole (β=1) decrease 2 times from CUT1 – CUT6 Passing rates versus Cut-level

Upper limit on the flux of fast monopole 90% C.L. upper limit on the flux of fast monopole (1000livedays NT200) A eff T cm 2 sec sr β=1β=0.9β=0.8 NT NT36+NT Upper Limit 90% C.L. (cm 2 sec sr) From the non-observation of candidate events in NT200 an upper limit on the flux of fast monopole is obtained Acceptance & Upper flux limit

NT200+ = NT external string ( 36 OMs ) - Height = 210m - = 200m -  = 200m - Volume ~ 4 Mton NT200+ put into operation in The main advantage of NT200+ 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 NT200 Outlook

A future Gigaton Volume Detector (Baikal-GVD) Sparse instrumentation: 90 – 100 strings 300 – 350 m lengths with OM per string = OMs (NT200 = 192 OMs) distance between strings  100 m Top view of the planned Baikal-GVD detector. Also shown is basic cell: a “minimized” NT200+ telescope Expected sensitivity for fast monopole (1 year GVD) F mon < 5 · cm -2 s -1 sr -1

CONCLUSION 1.BAIKAL Experimenal Upper limit on the Fast ( v/c =1) Monopole Flux (90% C.L) F mon < 0.46 · cm -2 sec -1 sr -1 The limit on fast magnetic monopole flux obtained in this analysis is the best at the present time 2. NEW configuration NT200+ Permits to reject background using more soft cuts. Expected 1.5 times increase of effective area for fast monopole comparing NT Gigaton Volume (km3-scale) Detector (Baikal-GVD) Expected sensitivity for fast monopole (1 year operation) F mon < 5 · cm -2 s -1 sr -1

Water characteristics Absorption and Scattering cross-section vs λ Strongly anisotropic L scat =30-70 m L abs =22-24 m Baikal Absoption Scattering OM responce vs R,m L scat 15m30m S eff increases by 20% R,m p.e. τ, ns p.e. p.e with delay <τ OM faced to Cherenkov light p.e with delay <τ OM faced opposit Cherenkov light