Physics results and perspectives of the Baikal neutrino project

B. Shoibonov (JINR, Dubna)for the Baikal collaboration

February 2009

1. Institute for Nuclear Research RAS, Moscow, Russia.2. Irkutsk State University, Irkutsk, Russia.3. Skobeltsyn Institute of Nuclear Physics MSU, Moscow, Russia.4. Joint Institute for Nuclear Research, Dubna, Russia.5. DESY-Zeuthen, Zeuthen, Germany.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

~50 authors

The underwater detection was suggested by M.Markov and K.Greisen in 1960. It is based on registration of cherenkov radiation of induced charged particles

Physics Background: atmospheric neutrinos A. Point sources “Find the sources on the sky” + high angular resolution

- needs strong enough single sources

B. Anomalies in atmospheric spectrum

+ high energy resolution

+ all weak point sources should add up

+ model predictions ~ experimental sensitivities

Astrophysical ’s: two detection methods

Skyplot with Hot spot(s) (galactic coordinates)Muons from (CC) N µ X

Electron / hadron cascades fromCC + NC e / / ()

log

[ E2

· Flu

x(E

) 3 96

AGN

atmospheric

log (E /GeV)

The Site

● 3.6 km to shore● 1.1 km depth ● Absorption Length: ~25 m● Scatt. Length (geom) ~ 30-60

m <cos θ> ~ 0.85-0.9

3600 m

1366

m

NT200+

Ice as a natural deployment platform

Thick ice stable for 6-8 weeks/year: – Maintenance & upgrades – Test & installation of new

equipment

Winches are used for deployment

4-string stage (1996)

One of the first neutrinoevents recorded with thefour-string version NT96

● 1990 - Proposal NT200● 1993 – NT36 (36 PMTs at 3 strings)

The First Underwater Neutrino Array ever built 3-dimensional Muon reconstruction Verify BG-suppression & check MC/Water/.. First underwater neutrino events

Baikal - Milestones

• 1998 – NT200 (192 PMTs at 8 strings) • Full Physics program started

• since 2005 - Activity towards Gigaton Volume Detector in Lake Baikal

• 2005 – NT200+ (NT200 + 3 long external strings)• 2008 – „New technology“ prototype string

Outline:

1. Physics Results (selected) : NT200 1998-2002- Search for point sources- Search for a diffuse flux of HE neutrinos- Search for fast magnetic monopoles- Search for neutrinos from WIMP annihilation- Search for GRB correlated neutrino flux- *(Acoustic neutrino detection activity)2. Gigaton Volume Detector in Lake Baikal- a) NT200+ (10 Mt Detector) - intermediate stage to GVD- b) “New technology” prototype string

- Conclusion

The NT-200 Telescope-8 strings: 72m height - 192 optical modules = 96 pairs (coincidence)- measure T, Charge - σT ~ 1 ns - dyn. range ~ 1000 p.e.

Effective area: 1 TeV ~2000 m² Eff. cascade volume: 0.2Mt (10TeV)

Quasar PM: =37cm

Height x = 70m x 40m, Vinst=105 m3

Search for point sources

- 372 events (1998-2002, 1008 live days)

- MC: 385 ev. Expected (20%BG). - Angular resolution is 2.2 degrees- Ethr ~ 15-20 GeV- No indication for Point Sources found.

AMANDA:2000-2003, Baikal: 1998-2002galactic coordinates

Galactic coordinates

Exposure map

Search for high energy neutrinosEvents with upward moving

light signals are selected

(„BG“)

e cascades

NT200

large effective volume

Allowed by excellent scatt scatt=30-50m Radius, m

New analysis based on reconstruction of cascade coordinates, direction and energy increases efficiency of selecting neutrino events.

Selecting HE Cascades

Cuts: tmin > -10 ns, Nhit > 18, χ2 < 3, LA < 20

6%,20lg%,70

EE

rr

No events observed ( 24% system. err.) n90% = 2.4 The 90% C.L. “all flavour” limit (1038 days) for a =2 spectrum Ф ~ E-2 (20 TeV < E < 20 PeV), and assuming e:: = 1 1 1 at Earth (1 2 0 at source)

E2 Ф < 2.9 ·10-7 GeV cm-2 s-1 sr-1 (Baikal 2008)

Final Cut: Esh > 130 TeV

Cascade energy distribution

Volume for cascades E ≥ 100 TeV: Veff~ 0.5-1

km³ dlg(E) ~ 0.1, dψmed < 4o

Muon threshold ~10-30 TeV

Eff. area for muons Seff ~ 0.2-0.3 km2

A future Gigaton (km3) Detector in Lake Baikal. Sparse instrumentation: ~2000 OMs12 clusters X 8 strings~400 m string height~20 OMs per stringInterstring distances ~100m

*(MC optimization is in progress)

NT200+ - intermediate stage to Gigaton Volume Detector (km3 scale) has been operating since

2005Main R&D goal: verify many new key elements and design principles of the future km3-scale telescopeMain Physics goal: energy spectrum of all flavor extraterrestrial HE-neutrinos (E > 100 TeV)

Total number of OMs – 228 / 11 stringsInstrumented volume – 5 MtDetection volume >10 Mt for En>10 PeV

High resolution of cascade vertex and energy neutrino energy

Light source

Ice camp view during winter expedition

Installation of a “new technology” string as an integral part of NT200+

(April 2008)

Investigation and in-situ tests of basic knots of future detector: optical modules, DAQ system, new cable communications.

Studies of basic DAQ/Triggering approach for the km3-scale detector.

Confrontation of classical TDC/ADC approach with FADC readout.

“New technology” prototype string for a km3 Baikal neutrino telescope

13” Hamamatsu R8055 12” Photonis XP 1807

Summary

1. For the planned km3-detector in lake Baikal, R&D-activities have been started.

2. The existing NT200+ allows to verify all key elements and design principles of km3-detector.

3. A full scale “new technology” string was installed in spring 2008 as an integral part of NT200+ for investigation and in-situ tests of basic knots of future detector: optical modules, DAQ system, new cable communications.