E. Popova

Registration of atmospheric neutrinos with the BAIKAL Neutrino Telescope NT-96

We present first neutrino induced events observed with a deep underwater neutrino telescope. Data from 70 days effective life time of the BAIKAL prototype telescope NT-96 have been analyzed with two different methods. With the standard track reconstruction method, 9 clear upward muon candidates have been identified, in good agreement with 8.7 events expected from Monte Carlo calculations for atmospheric neutrinos. The second analysis is tailored to muons coming from close to the opposite zenith. It yields 4 events, compared to 3.5 from Monte Carlo expectations. From this we derive a 90 % upper flux limit of 1.1 * 10^-13 cm^-2 sec^-1 for muons in excess of those expected from atmospheric neutrinos with zenith angle > 150 degrees and energy > 10GeV.We present neutrino induced events observed with a deep underwater neutrino telescope. Data from 70 days effective life time of the BAIKAL prototype telescope NT-96 have been analyzed with two different methods. With the standard track reconstruction method, 9 clear upward muon candidates have been identified, in good agreement with expectation from Monte Carlo calculations for atmospheric neutrinos. The second analysis is tailored to muons coming from close to the opposite zenith. It yields 4 events, compared to 3.5 from Monte Carlo expectations. From this we derive a 90% upper flux limit of 1:1 10 13 cm 2 sec 1 for muons in excess of those expected from atmospheric neutrinos with zenith angle > 150 degrees and energy > 10 GeV.Abstract We present the first neutrino induced events observed with a deep underwater neutrino telescope. Data from 70 days effective life time of the BAIKAL prototype telescope NT-96 have been analyzed with two different methods. With the standard track reconstruction method, 9 clear upward muon candidates have been identified, in good agreement with 8.7 events expected from Monte Carlo calculations for atmospheric neutrinos. The second analysis is tailored to muons coming from close to the opposite zenith. It yields 4 events, compared to 3.5 from Monte Carlo expectations. From this we derive a 90% upper flux limit of 1.1 · 10−13 cm−2 sec−1 for muons in excess of those expected from atmospheric neutrinos with zenith angle > 150 degrees and energy > 10 GeV.

Observation Of Very High Energy Cosmic-ray Families In Emulsion Chambers At High Mountain Altitudes (i)

Characteristics of cosmic-ray hadronic interactions in the 1015 − 1017 eV range are studied by observing a total of 429 cosmic-ray families of visible energy greater than 100 TeV found in emulsion chamber experiments at high mountain altitudes, Chacaltaya (5200 m above sea level) and the Pamirs (4300 m above sea level). Extensive comparisons were made with simulated families based on models so far proposed, concentrating on the relation between the observed family flux and the behaviour of high-energy showers in the families, hadronic and electromagnetic components. It is concluded that there must be global change in characteristics of hadronic interactions at around 1016 eV deviating from thise known in the accelerator energy range, specially in the forwardmost angular region of the collision. A detailed study of a new shower phenomenon of small-pT particle emissions, pT being of the order of 10 MeV/c, is carried out and its relation to the origin of huge “halo” phenomena associated with extremely high energy families is discussed as one of the possibilities. General characteristics of such super-families are surveyed.

Search for high-energy neutrinos in the Baikal neutrino experiment

A new analysis of the data from the NT200 neutrino telescope based on the reconstruction of parameters for high-energy showers generated in neutrino interactions has yielded new upper limits on the diffuse neutrino fluxes predicted by a number of theoreticalmodels. The upper limit on the all-flavor neutrino flux with an energy spectrum E−2 is E2Φν < 2.9 × 10−7 GeV cm−2 s−1 sr−1.

An upper limit on the diffuse flux of high energy neutrinos obtained with the Baikal detector NT-96

Abstract We present the results of a search for high-energy neutrinos with the Baikal underwater Cherenkov detector NT-96. An upper limit on the diffuse flux of ν e + ν μ + ν μ of E 2 Φ ν (E) −5 cm −2 s −1 sr −1 GeV within neutrino energy range 10 4 –10 7 GeV is obtained, assuming an E −2 behavior of the neutrino spectrum.

The BAIKAL neutrino experiment—Physics results and perspectives

We review the status of the Lake Baikal Neutrino Experiment. The Neutrino Telescope NT200 has been operating since 1998 and has been upgraded to the 10 Mton detector NT200+ in 2005. We present selected astroparticle physics results from long-term operation of NT200. Also discussed are activities towards acoustic detection of UHE-energy neutrinos, and results of associated science activities. Preparation towards a km3-scale (Gigaton volume) detector in Lake Baikal is currently a central activity. As an important milestone, a km3-prototype string, based on completely new technology, has been installed and is operating together with NT200+ since April, 2008.

The BAIKAL neutrino project: status report

We review the present status of the Baikal Neutrino Project and present preliminary results of a search for upward going atmospheric neutrinos, WIMPs and magnetic monopoles obtained with the detector NT-2000 during 1998. Also the results of a search for very high energy neutrinos with partially completed detector in 1996 are presented.We review the present status of the Baikal Neutrino Project and present preliminary results of a search for upward going atmospheric neutrinos, WIMPs and magnetic monopoles obtained with the detector NT-2000 during 1998. Also the results of a search for very high energy neutrinos with partially completed detector in 1996 are presented.

Observation of attenuation behaviour of hadrons in extremely high energy cosmic ray interactions: New hadronic state?

Abstract Experimental results are presented on high energy cosmic-ray hadron interactions recorded in homogeneous-type thick lead chambers (total thickness being 60 cm and 110 cm) exposed at the Pamirs (atmospheric depth 595 g/ cm 2 ). High energy cosmic-ray hadron flux is measured. The attenuation mean free path of the arriving cosmic-ray hadrons of E h γ ≥ 6 TeV measured in the chamber is obtained as 252 ± 30 g/cm 2 of lead. However, for the high energy hadrons ( E ( γ ) ≥ 10 TeV) constituting cosmic-ray families of the highest energy range, ΣE ( γ ) ≥ 700 TeV, which have been accumulated so far in the series exposures at the Pamirs and analysed by MSU group, the attenuation mean free path of hadrons in lead has turned out to be as short as 170 −26 +47 g/cm 2 with 95% CL by the maximum likelihood method. The present experimental result of such a short attenuation length of hadrons in cosmic-ray families is essentially consistent with that obtained for high energy hadrons ( E ( γ ) ≥ 10 TeV) constituting the “Chiron-type” families of ΣE ( γ )>100 TeV in the Chacaltaya two-storeyed chamber experiments. The anomalous transition characteristics of high energy hadrons in lead is found and examples are presented. The physical significance of the experimental results on extremely high energy hadron interactions is discussed.

Search for Neutrinos from Gamma-Ray Bursts with the Baikal Neutrino Telescope NT200

We present the results of our search for neutrino events coinciding in time and direction with gamma-ray bursts (GRBs) with the Baikal underwater neutrino telescope NT200. No events confirming a neutrino accompaniment of GRBs have been detected. Model-independent limits (Greens function) on the neutrino flux from GRBs have been obtained. For the Waxman-Bahcall neutrino spectrum, the limit on the neutrino flux from a GRB has been found to be Eν2Φν ⩽ 1.1 × 10−6 GeV cm−2 s−1 sr−1.

An experimental string of the NT1000 Baikal neutrino telescope

A project of the NT1000 deep-water neutrino telescope with an effective volume of ∼1 km3 is currently being developed by the BAIKAL collaboration. The telescope will be located in Lake Baikal in close vicinity of the NT200+ detector, which is currently in operation. The telescope will be composed of 12 clusters with 8 similar strings of optical modules in each (each string has two sections of the NT1000 optical modules). The section of the NT1000 optical modules has been developed using higher-efficiency photomultiplier tubes and state-of-the-art electronics. The field tests of the experimental string consisting of two sections with six optical modules in each have been performed. The results of these investigations are used in the project of the NT1000 neutrino telescope and in the hydrological study of Lake Baikal.

THE BAIKAL NEUTRINO TELESCOPE — RESULTS AND PLANS

New results from the Baikal neutrino telescope NT200, based on the first 5 years of operation (1998–2003), are presented. We derive an all-flavor limit on the diffuse flux of astrophysical neutrinos between 20 TeV and 50 PeV, extract an enlarged sample of high energy muon neutrino events, and obtain limits on the flux of high energy atmospheric muons. In 2005, the upgraded telescope NT200+ will be commissioned: 3 additional distant strings with only 12 photo-multipliers each will rise the effective volume to 20 Mton at 10 PeV for this largest running neutrino telescope in the Northern hemisphere.