search for relativistic magnetic monopoles with the baikal neutrino telescope e. osipova -msu...
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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’sstring
P.Dirac, 1931 g
g * e = n /2 hc, n=0, ±1, ±2..
gmin = 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 theUniverse, even one of such object placedanywhere would be enough to explain thequantization of electric charges
In wide classes of models Monopole mass may be in the range 107 – 1014 GeVMonopole could be accelerated up to energy 1012 –1015 GeV
Monopoles with such masses may be relativistic
Monopole mass and acceleration in magnetic fields of Universe
In 1974 ‘t Hooft, Polyakov independently discovered monopolesolution of the SO(3) Georgi-Glashow model
Mmon ~ M V / = 1/137
S.Wick, T.Kephart, T.Weiler, P.BiermanAstropart.Phys. 18(2003) 663
Can monopole cross the Earth?
10
11
12
13
14
15
16 lg( E loss, GeV)
0 2 4 6 8 lg (Emon / M)
Emon = 1015 Gev E mon/M < 108
M> 107 GeV
Monopole Energy losses, crossing the Earth on diameter
1014 GeV > Mmon > 107 GeV
Cherenkov Light from Relativistic Magnetic Monopole
d Nph/dl= n2 (g/e)2 d Nph/dlmuon)
8300 d Nph/dlmuon)
( n =1.33)
Light flux from monopole
Light flux from 10 PeV muonLight flux from 10 PeV muon
β
phot
ons
/cm
Baikal Neutrino Telescope NT-200
192 Optical modules on 8 stringsOM’s are grouped in pairs –ChannelTrigger >3 Chan within 500nsOM could detect fast monopole up to 100m
Expected number of hits Nhit for fastMonopole vs distance from NT200 center
Water characteristics
AbsoptionLabs =22-24 m (480nm)ScatteringStrongly anisotropic <cos(α)> 0.85-0.9Lscat =30-70 m
OM response on fast monopole vs R,m
p.e.
R,m
Lscat 15m 30m
Seff increases by 20%
p.e
with
del
ay <
τ
p.e
with
del
ay <
τ
τ, ns τ, ns
P E from fast monopole with delay <τ for Lsc=15m, Lsc=30mOM faced to Cherenkov light (left) and in opposit side( right)
Lscat=30m
Lscat=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-BornststainCosmic 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 responseto all muon energy loss processes
Baikal code I.Belolaptikov will be published
Аtmospheric muons as standard calibration signal
Time distribution t = t52-t53)
MC
EXP
t, ns
MC
EXP
Ph.el.
Amplitude distribution
Search strategy and data analysis
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
NT-200 1000 days of live time (April 1998-February 2002)
01
zthit
ii
TZ Ncor
hitN
i
ZzTt
ti ,zi - time & z-coordinates of fired channels,T,Z –their mean values per event σt ,σz - root mean square
Background suppression
corTZ for atmospheric muon
(black-EXP, red-MC) and for fast monopole from the lower hemisphere (blue)
Additional cuts after reconstruction:Cut2- Nhit>35& corTZ >0 & rec. Cut3 - Nhit>Cut2& χ2<3Cut4 -Nhit>Cut3&θ>100o
Next cuts are different for different NT200 configurationsCut5 – Cut4&Rrec>10-25 m ( Rrec -distance from NT200 center)Cut6- Cut5& corTZ >0.25-0.65 No events from experimental sample pass CUTS 1-6
CUT 1 : corTZ >0 & Nhit >30 leaves 0.015% of events
and reduces effective area for monopole (β=1) ~ 2 times
The main sources of background
lg(Esh,TeV)
Number of muons in bundle
Simulated atmospheric muons satisfying CUT1 vs cascade energy (upper) and vs number of muons in bundle (lower)
CUT1CUT3CUT4CUT5
M
C
even
ts
Nu
mbe
r of
mu
ons
in b
und
le
Lg(Esh,TeV
The events with a large number ofmuons in bandle are supressed afterreconstruction with χ2<3
Comparison of experimental and MC data with respect toparameters 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.
MCEXPExpected from monopole
CUT level
Pas
sing
rat
es MCEXPSeff 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)
Aeff Tcm2sec sr
β=1 β=0.9 β=0.8
NT200 4.84 1016 3.48 1016 1.231016
NT36+NT96 0.37 1016 0.25 1016
0.1 1016
Upper Limit
90% C.L.
(cm2sec sr)-1
0.46 10-16 0.65 10-16 1.8 10-16
From the non-observation of candidateevents in NT200 an upper limit on theflux of fast monopole is obtained
Acceptance & Upper flux limit
NT200+=
NT200 +
3 external string
( 36 OMs)
- Height = 210m- Height = 210m- = 200m= 200m- Volume ~ 4 MtonVolume ~ 4 Mton
NT200+ put into operation in 2005. 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 12 - 16 OM per string = 1300 - 1700 OMs (NT200 = 192 OMs) distance between strings 100 m
Top view of the planned Baikal-GVD detector. Top view of the planned Baikal-GVD detector. Also shown is basic cell: a “minimized” NT200+ Also shown is basic cell: a “minimized” NT200+
telescopetelescope
Expected sensitivity for fast
monopole (1 year GVD)
Fmon < 5 · 10-18 cm-2 s-1 sr-1
CONCLUSIONCONCLUSION
1.1. BAIKAL Experimenal Upper limit on the Fast ( v/c =1) Monopole FluxBAIKAL Experimenal Upper limit on the Fast ( v/c =1) Monopole Flux (90% C.L)
Fmon < 0.46 ·10-16 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 NT200
3. Gigaton Volume (km3-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 Strongly anisotropic <cos(α)> 0.85-0.9
Lscat=30-70 mLabs =22-24 m Baikal
Baikal
Absoption Scattering
OM responce vs R,m
Lscat 15m 30m
Seff increases by 20%
R,m
p.e.
τ, nsτ, ns
p.e.
p.e
with
del
ay <
τ
OM faced to Cherenkov light
p.e
with
del
ay <
τ
OM faced opposit Cherenkov light
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