Y. Kamiya

Energy-dependence of the positive excess of cosmic-ray μ-mesons

SummaryThe energy-dependence of the positive exeess of cosmic-rays has been measured in the energy range 5 to 200 GeV using a magnetic spectrometer which consists of a solid-iron-core electromagnet and a neon hodoscope. The results are not inconsistent with the theory of Hayman in which it is assured that there is an increase in the fluctuation of pion multiplicity with increasing primary energy.RiassuntoSi è misurata la dipendenza dall’energia dell’eccesso positivo dei raggi cosmici nel campo di energie fra 5 e 200 GeV, servendosi di uno spettrometro magnetico che consiste di un elettromagnete con nucleo di ferro pieno e di un odoscopio al neon. I lisultati non sono in disaccordo con la teoria di Hayman che afferma che la fluttuazione della molteplicità pionica cresce al crescere dell’energia primaria.

The trigger system of mutron, a cosmic ray magnetic spectrometer

Abstract A large magnetic spectrometer for cosmic-ray studies has been built at Cosmic Ray Laboratory, University of Tokyo, which consists of two 400 t solid iron magnets, multiwire proportional chambers (MWPC), wire spark chambers and a calorimeter. In this paper the trigger system will be described whose geometrical acceptance is about 1300 cm 2 sr including the magnets. The trigger system consists of twenty large area MWPCs. The trigger selection is made up of the momentum selection, which excludes low momentum muons, and the particle-number selection limiting the number of particles hitting the trigger detectors simultaneously. This combination for trigger reduces the background level and improves the ratio of muons to background. The trigger rate is about 1.0 per minute in the usual operation.

Cosmic-ray muon spectrum derived from the transferred energy spectrum of bursts observed by the mutron calorimeter

SummaryMeasurements of the energy transfer,E′, of bursts produced in a calorimeter are calibrated with the momenta of the incoming and outgoing muons measured by the Mutron magnet spectrometers. The relation between energy transferE′ and momentum difference Δpc was obtained in the energy range from 30 GeV to 1 TeV as follows:E′=(0.85±0.16) Δpc. Using this calibrated calorimeter, we observed distributions of the energy transfer of bursts produced in the calorimeter up to 6 TeV by the magnet spectrometer plus calorimeter triggers, as well as by the calorimeter trigger alone. From the observed burst spectrum, we have derived the muon energy spectrum at sea-level. The differential pion production spectrum combined with the data using composite triggers gives an exponentγ=2.58±0.19 in the muon energy region from 200 GeV to 6 TeV and 2.74±0.19 in the region from 1 TeV to 6 TeV. The muon energy spectrum thus obtained is compared with the direct measurement of the muon spectrum by the Mutron magnet spectrometers. It is thus established that measurements of the transferred energy spectrum of bursts are available for the derivation of the muon energy spectrum beyond the energy region measured by the magnet spectrometer.RiassuntoSi calibrano le misure del trasferimento d’energiaE′ di scrosci prodotti in un calorimetro con gl’impulsi dei muoni in entrata e in uscita misurati dagli spettrometri a magneti Mutron. Si ottiene la relazione tra il trasferimento di energiaE′ e la differenza d’impulsi Δpc nell’intervallo di energia da 30 GeV a 1 TeV come segue:E′=(0.85±0.16)Δpc. Usando questo calorimetro calibrato, sono state osservate le distribuzioni del trasferimento d’energia di scrosci prodotti nel calorimetro fino a 6 TeV sia mediante l’innesco dello spettrometro a magneti piú quello del calorimetro, che solamente con quello del calorimetro. Dallo spettro degli scrosci osservato, è stato derivato lo spettro d’energia dei muoni a livello del mare. Lo spettro differenziale di produzione di pioni combinato con i dati ottenuti usando inneschi composti dà un esponenteγ=2.58±0.19 nella regione d’energia muonica da 200 GeV a 6 TeV e 2.74±0.19 nella regione da 1 TeV a 6 TeV. Lo spettro d’energia muonica cosí ottenuto è confrontato con la misura diretta dello spettro muonico degli spettrometri a magneti Mutron. Si stabilisce cosí che le misure dello spettro d’energia trasferita degli scoppi permettono di derivare lo spettro d’energia muonica al di là della regione d’energia misurata dallo spettrometro a magneti.

Electromagnetic interactions of cosmic-ray muons up to 10 TeV (pair productions and bremsstrahlung)

SummaryElectromagnetic interactions (excluding nuclear interactions) of cosmic-ray muons were investigated by a combined arrangement of the Mutron magnet spectrometer and calorimeter. The interactions covered their transferred energies ranging from 1 GeV to several TeV produced by muons with energies up to 10 TeV. There is reasonable agreement between the experimental results and the theoretical predictions. For transferred energies less than 10 GeV, however, the observed number of events produced by muons around 1 TeV may be somewhat smaller than theoretically expected. The probability of accompaniment of a muon emerging from thick iron plates is also studied. The data are very useful for the measurement of the muon momentum by the magnet spectrometer. The ratio of the interaction probability for positive muons to that for negative muons is 0.94±0.02 for interactions with energy transfers over 1 GeV. However, by considering the measured accuracy of the value ±0.05 used for the charge ratio of incident muons, there is no evidence to support any suggestion that the interaction cross-sections of positive and negative muons for energy transfers above 1 GeV differ in the range from 100 GeV to 10 TeV.RiassuntoSono state studiate le interazioni elettromagnetiche (escludendo le interazioni nucleari) dei muoni dei raggi cosmici mediante una disposizione combinata dello spettrometro a magneti Mutron e del calorimetro. Le interazioni riguardano le energie trasferite che vanno da 1 GeV a qualche TeV prodotte da muoni con energie fino a 10 TeV. Si trova un discreto accordo tra i risultati sperimentali e le previsioni teoriche. Per energie trasferite minori di 10 GeV, comunque, il numero osservato di eventi prodotti da muoni a circa 1 TeV può essere un po’ piú piccolo di quanto previsto teoricamente. Si studia anche la probabilità di accompagnamento di un muone uscente da spesse piastre di ferro. I dati sono molto utili per misurare l’impulso del muone con lo spettrometro a magneti. Il rapporto tra la probabilità d’interazione per muoni positivi e quella per muoni negativi è di 0.94±0.02 per interazioni con trasferimenti di energia al di sopra di 1 GeV. Comunque, considerando l’accuratezza misurata del valore ±0.05 usato per il rapporto di carica dei muoni incidenti, non c’è nessuna prova che sostenga l’ipotesi che le sezioni d’urto d’interazione tra muoni positivi e negativi per trasferimento d’energia al di sopra di 1 GeV differiscano nell’intervallo da 100 GeV a 10 TeV.

A calorimeter to study cosmic ray muon interactions

Abstract A calorimeter with a volume of 3.6×4×2.4 m 3 has been built in the Institute for Cosmic Ray Research, University of Tokyo to study the interactions of cosmic ray muons of known momenta. The calorimeter is located between the two magnets of MUTRON, a magnet spectrometer built by the same laboratory to measure muon momenta up to a maximum of 17 TeV c −1 . In this article, the design of the calorimeter is described and the characteristics of the counters used are reported. The expected number of the interactions and the accuracy of energy determinations by the calorimeter are also discussed.

A point source of cosmic rays and its time variation

A point source of cosnfic rays was reported in 1955 at declination 0 deg sed right ascemsion 5 hr 30 min. Two G.-M. telescopes were used. Ower a period of several years the point source bus been observed four times with two telescopes st two different azimuths. The existence of a point source of cosmic rays bus heen confirmed and its variations observed. (A.C.)