Hadronic interactions of high energy cosmic-ray observed by emulsion chambers

The OPERA neutrino oscillation experiment has been designed to prove the appearance of ντ in a nearly pure νμ beam (CNGS) produced at CERN and detected in the underground Hall C of the Gran Sasso Laboratory, 730 km away from the source. In OPERA, τ leptons resulting from the interaction of ντ are produced in target units called bricks made of nuclear emulsion films interleaved with lead plates. The OPERA target contains 150000 of such bricks, for a total mass of 1.25 kton, arranged into walls interleaved with plastic scintillator strips. The detector is split into two identical supermodules, each supermodule containing a target section followed by a magnetic spectrometer for momentum and charge measurement of penetrating particles. Real time information from the scintillators and the spectrometers provide the identification of the bricks where the neutrino interactions occurred. The candidate bricks are extracted from the walls and, after X-ray marking and an exposure to cosmic rays for alignment, their emulsion films are developed and sent to the emulsion scanning laboratories to perform the accurate scan of the event. In this paper, we review the design and construction of the detector and of its related infrastructures, and report on some technical performances of the various components. The construction of the detector started in 2003 and it was completed in Summer 2008. The experiment is presently in the data taking phase. The whole sequence of operations has proven to be successful, from triggering to brick selection, development, scanning and event analysis.

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The OPERA experiment in the CERN to Gran Sasso neutrino beam

Multiple production of hadrons at cosmic ray energies (experimental results and theoretical concepts)

Recent results of emulsion chamber experiments on the observation of unusual events and new phenomena in cosmic ray particle interactions in the energy range beyond 10 PeV are presented in this review. Particular attention is given to the following items: 1. 1. Centauro-type events with violation of charge (isotopic) symmetry in hadron production; 2. 2. fan-shaped events which argue in favour of a new mechanism of coplanar emission of secondaries; 3. 3. events with halos produced by collimated bundles of high energy gammas and hadrons; 4. 4. penetrating hadrons with abnormal absorption in lead. The present paper contains main characteristics of the events and phenomena under review as well as discussion of their possible interpretation. It is conceivable that the observed events are the manifestation of New Physics beyond the Standard Model. Further progress in studying the new phenomena in cosmic ray experiments for the next few years, in view of LHC startup, is considered.

Results of emulsion chamber experiments with very high-energy cosmic rays which are difficult to explain in the framework of the standard model

We give a description of a nuclear event of new character observed in an emulsion chamber exposed on Mt. Chacaltaya. The interaction has its vertex within the chamber and contains 40 γ-rays, whose energies sum up to ∼42 TeV. The most remarkable feature of the event are: 1) Abnormally large transverse momenta. The average transverse momentum of the γ-rays is ∼0.5 GeV/c. 2) Abnormally high transverse-momentum density. That of the γ-rays is (70÷90) GeV/c per unit log tgϑ interval. 3) Multijetlike angular structure. At least three structures are observed. 4) Noncoplanarity. The γ-ray momentum distribution deviates appreciably from a coplanar one. If a fireball picture is adopted, the event can be interpreted as a production of a giant fireball, out of whose rest energy an energy of (60÷80) GeV is liberated in the form of γ-rays, and which decays into hadrons through smaller fireballs. The highest-energy γ-ray pair starts in an empty space within the chamber, suggesting that they come from a parent particle with a lifetime of the order of 10−13 s.

Michio Hazama

Papers

CHACALTAYA Emulsion Chamber Experiment