Non accelerator particle physics

Nuclear Physics B (Proc. Suppl .) 16 (1990) 136-149 North-Holland

136

NON ACCELERATOR PARTICLE PHYSICS

Hinrich MEYER Fachbereich Physik der Universität Wuppertal, D5600 Wuppertal 1, W-GERMANY

field of high energy physics that

This is followed by part 6 on atmospheric neutrinos . In part 7 a brief account on 2ß-decay is given and in part

related particle beams as provided by

candidates are discussed and finally the

1 . INTRODUCTION

Non accelerator particle physics is a

exploits the sources of energy and

S limits on supersymmetric dark matter

nature . It works on grand scales of

space, time and energy by considering

possible sources of high energy photons within our galaxy are considered .I will

universe, single events of huge energy

developments of non accelerator particle

explosions and the process of energy production in stars as well as

here wére discussed in contributions to

e .g .the matter content of the whole

release like the big bang, supernova

acceleration of protons and electrons up to energies that are still far beyond the capabilities of man-made ac,alerators . It is the photons and neutrinos that carry very important

information on cosmic events to us observers on earth and may even give new insides on the basic properties of those particles . Some of the more recent

developments in this field will be covered in this talk, in part 2 new

constraints on the total amount of baryonic matter from big bang nucleosynthesis, in part 3 the recent status on searches for baryon number

violation, part4 will cover the solar neutrino problem and in part 5 a brief

account of supernova searches is given . 0920-5632/90/$3 .50 © Elsevier Science Publishers B.V . North-Holland

conclude with an outlook on future

physics . Most of the subjects covered

the parallel sessions, which should be consulted for more details .

2 . BIG BANG NUCLEOSYNTHESIS

One of the most successful fields of

non accelerator particle physics concerns the formation of the primordial light nuclei, D, 3He, 4He and 7Li in the

environment of an expanding gas of

protons, neutrons, electrons, photons and neutrinosl . In addition other (very)

weakly interacting stable or unstable

particles may have been present in large numbers and may consist the ubiquitous

dark matter present on all scales in the universe today2.

New experimental information relevant

for this problem has become available

recently, namely a precise measurement of

H. Meyer/ Non accelerator particle physics the neutron lifetime, rather safe limit on the number of different light neutrinos

from studies of the ZO particle in e+e--

measurements of 4He and 7 Li leads to estimate for 11 10 of - 2 . This can be

137 an

annihilation and finally a better estimate of the amount of primordial 4He from the

converted into a value for the baryonic density normalized to the critical density of Qb = p/pcrit x 1/h2 = 0 .0077/h2 using

4He abundance as seen today . I would like

to use this new data to reassess the ratio of baryons to photons, 11 = which is nb/ny estimated to be in the range of 10-9 - 10-

2 .75 OK for the temperatur of the

primordial photon background . This is not to far from the density of the visible matter Q is = 0 .005 using h = 1, where h

10 . Two new measurements of the neutron

lifetime using very different techniques have been performed recently at the

reactor in Grenoble . The results for the neutron lifetime Tn are 877±10sec using a magnetic neutron storage ring3 and 887 .6

±3sec from storing ultra cold neutrons in a glass box coated with reflecting oi14. Since the amount of 4He produced in the early universe, Yp, depends on the

uncertainty At of the neutron lifetime like Yp =0 .24 ±(2 " 10-4 " ®t(sec)) the small error in the neutron lifetime is now no

longer of great concern and it's influence on the YP is about a factor of ten smaller than a change in the number of different neutrino flavors by 1 .

New measurements of the width of the ZO

essentially rule out 4 neutrino flavors

and are in very good agreement with just 3

different neutrino species, the well known electron-, muon- and tae-neutrinoss .

From the measurements of 7Li abundance

is the Rubble constant in units of 100

km/sec/Mpc . The exact value of h is still a matter of debate, with a tendency to lower values, h < 0 .65 . The uncertainty in

h is indeed one of the main problems for a reliable estimate of the possible amount

of invisible baryonic matter . Based on the arguments given above I consider it a

likely possibility that in fact no dark

baryonic matter is required at all if only the lower limit on 1110 from the upper limit on primordial deuterium is relaxed

by about a factor of 2 .

3 . BARYON NUMBER VIOLATION

More than 20 years ago A .D .Sakarov suggested a very general reason to expect instability of nucleonsS . Based on the

existence of P- and CP-violations together with the absence of significant amounts of antimatter in an uniformely expanding

universe he argued that nucleons should decay! Meanwhile much more specific and

in old stars and a careful reanalysis of

detailed arguments came up in the context

units of 10 -10 ) a value of 2 .2 from 7Li

specific prediction uses SU5 as the unification group, with the result for the

the amount of primordial 4He 6 one obtains as nominal values for 1110 (11 measured in (choosing the lower of two possible

values) and 1 . 6 from 4He 7 .

This would seem to be in mild conflict with the lower limit on 11 10 = 2 .6 from the upper limit on the D and 3He abundance levels . Putting more weight on the

of attempts to achieve grand unification of the fundamental interactions9 . The most

proton lifetime 10

'tp = 10 28±1 (MX/2 . 10 4) 4 years

8. Meyer/Non accelerator particle physics

133

The evolution of the gauge couplings with energy as the basis of this

prediction is now known with impressive precision1l, however a common unification

mass is apparently missed (see Fig .1), and

involving neutrinos in the final state up to few times 10 32 y for modes with only electrons

and photons to be detected

(Ref .12) . Although IMB and KAII continue

taking data, only small improvements on

those limits can be expected . A big step forward could only be achieved by

construction of a really huge detector,

even bigger-than Superkamiokande 13 but to be able to suppress the neutrino

background it has to have energy- and

spatial resolution much better than the now running detectors . I think this is

beyond the limits of present experimental techniques also in view of the size of such a detector which, incidentally,

matches that of the cathedral of Toledo Z Fig .l

log E [Ger]

Energy dependence of coupling

constants from the ZO ma s into the GUT region . The value for Mxmin is determined from the lower limit on p -+ e+ XO .

furthermore the lower limit on proton

decay has reached values incompatible with the SU5 prediction 12 for the dominant decay mode p -+e+ nO (see Fig . 1) . It is however still important to

continue experimental searches for evidence in other possible decay modes of nucleons . This has been done notably by

the three large experiments IMB, Kamiokande II and Fréjus (see Ref .12) . It

turns out that the experiments come close to the unavoidable background level due to the interactions of atmospheric neutrinos with the nuclei of the detector material .

The limits obtained then mainly depend on detection efficiencies for a given channel and range from few times 10 31 y for modes

however I should like to remind you that it took about 500 years to complete that wonderful building .

Baryon number violation may also manifest itself through the AB = 2 process of nn oscillations 14 . Two very different

experimental approaches have been used to search for nn transitions 15,16 . In the first method a very cold neutron beam generated in a reactor,

carefully shielded

against the earth magnetic field passes

through a target . Antineutrons created along the flight path would annihilate

with neutrons and protons in the target to produce a multipion final state that has to be separated against the cosmic ray

interactions in the target(see Ref .15) .

Secondly the underground experiments to

search for nucleon decay also yield very interesting limits on nn oscillations

(see

Ref .16) . The transition of a neutron to an antineutron would occur inside a nucleus (160 or 56 Fe) with subsequent nN-

annihilation . The only background is frera atmospheric neutrino interactions in the

H. Meyer/Non accelerator particle pl`ysics

underground detectors . No evidence for

anticorrelation of the v-rate as observed

of the experiments . The best limits obtained are Tn > 1-2 . 10 8sec from the

year cycle of the number of dark spot on the solar surface (see Ref .18) . The recent

annihilation events has been seen in any

nucleon decay experiments (Ref .16) and Tn > 10 7sec from the recent experiment at the reactor in Grenoble

(Ref .15) .

The relevance of these experimental

limits for the underlying baryon number violating mechanism is not easily

assessed, since the theoretical frame work still has to many unknows one simply has to wait for future theoretical developments .

4 . SOLAR NEUTRINOS

Very interesting developments have

taken place recently in the field of solar neutrino observations . The sun is supposed to be a prolific source of electron neutrinos from the various energy

producing nuclear reaction chains deep

inside the sun17 . Two experimental methods

to detect the neutrinos yield data up to

now, 1 .) the charged current reaction 37 C1 + ve -+e- + 37Ar used since about 20 years by R. Davis and his collaborators

1&and more recently the neutral current scattering channel ve + e- -* ve + e- by

the Kamiokande II collaboration 19 .

Kamiokande not only confirmed the 37 C1

result of a reduced :solar neutrino flux,

it also proved that the neutrinos are coming from the sun since the eve-rts are pointing with an accuracy of about 20°

back to the sun . The detection threshold

of - 7 MeV fcr Kamiokande is much higher than in the Clorine case, (0 .814 MeV), but

for !both experiments the rate is dominated

by 8B neutrinos .

Since about 10 years there is a

discussion going on of a possible

in the Homestake Mine with the famous 11

measurements of both experiments during

the minimum of solar spot number in 19851987 of about 0 .4 - 0 .5 SNU are again on the high side of all observations

confirming the earlier observation of an apparent anticorrelation . Very recently

the 37 C1 readings are declining while the solar spot numbers approach a new record high2 O,

in fact the last three

measurements of the 37 Ar rate have zero counts so far! 21 . The analysis of the

Kamiokande data is completed only up to

April 198922 , and is consistent with the

Davis result . Just imagine that Kamiokande would again confirm the very low rate of the Davis experiment . This incidentally implies that the signal would become

undetectable in KA II because of the high background from spallation nuclei .

However, one would be forced to take the

anticorrelation with the sun spot activity very seriously . What could possibly be the physics behind it?23 .

But let us first consider another time dependent activitiy of the sun, the very large flare events that are known to be

correlated with the acceleration of protons that would produce pions near the sun . Neutrinos from the 7C-p.-e decay chain would have energies on order of magnitude higher than standard solar neutrinos and may therefore give large 37Ar production in the Homestake mine experiment24 . This

would imply that in Kamiokande a time correlation of v-signals with solar flares should be observed . This possible effect has been searched for in the KA I period (July '83 - October '84) where 8 flares

H Meyer/Non accelerator particle physics have been considered and the KA II period (November '85 - July '88) with 7 large flares . No additional neutrino signal has been observed25 in the 50-100 MeV range, short by 2-3 orders of magnitude to explain the excess 37Ar values from the Homestake experiment near maximum solar

changes in the density of matter traversed on the way out of the sun34 . Large density variations at a critical depth inside the sun are needed suitably correlated with

the spot number cycle, however most likely too large to be feasible35 . In this enigmatic situation more solar

activity . Increasing flare activities

neutrinos detections with different

1990/91 should give even stronger limits

value . They are rather soon to come36 . Two 71Ga experiments, with good sensitivity to

around solar spot maximum expected in

on possible contributions to neutrino

signals in the solar neutrino detectors from this source .

A finite magnetic moment of the electron neutrino, of the order of 10 -11pB could be an explanation of the effect, if the magnetic fields inside the sun have sufficient strenght and the proper

correlation with the sun spot number 26 . The left handed electron neutrino would be turned into a right handed one that would not interact with 37 C1 . The magnetic moment required is rather high on theoretical grounds27

(but see also28, 29)

and is in possible conflict with the observation of neutrinos from the supernova SN1987A30, 31 .

However there is one more interesting

correlation to be expected if the solar magnetic field changes the flux of lefthanded neutrinos, see Ref . 26 and 32,33 . The spatial structure of the solar magnetic field gives a maximum effect for neutrinos from the center of the sun in

March and September and little effect in June and December . There is even a hint in the 37C1 data that this correlation exists (see Ref .26) and we will eagerly await the new results on the time dependence of the neutrino flux in the two years to come . Another possibility are neutrino oscillations under the influence of

experiment4l methods would be of great

the primary process in the energy production chain in the sun, pp -+ de + Ve will show us to what extent our basic

understanding of the energetics of the sun is correct37 . If a very low rate is

observed, say close to the expected

background level then almost certainly neutrinos oscillate38 .

Another new and very promising reaction 1271 + Ve -+ e- + 127xe was recently rediscovered providing the high counting

rate to trace the time variations of the solar-neutrino signal39 . A test exposure seems possible already next year in the Homestake mine

(Ref .21) . If time

variations are confirmed it is unavoidable to pursue a really big effort with this new reaction, since e .g . to obtain a higher rate with 71 Ga requires huge

amounts of Gallium beyond the present

capabilities of the commercial market .

Of great interest in this context is

the proposal to build a solar neutrino detector based on deuterium, very deep below ground in the Sudbury mine in

Canada4 O . It provides accurate spectral informtion through Ve + n -+ e- + p, flux information independent of the neutrino flavor by n + d -+ n + p (follow by n + p -> d + y (2 .2 MeV)) . Most important the experiment is located deep enough,

H. Meyer/Non accelerator particle physics such that the dominating background at Kamiokande, muon induced spallation of oxygen into 12N,

12 B,

8B,

16N,

become, negligible . Still the required reduction 8Li,

of sources of natural radioactivity in all

parts of the detector remains a formidable task . The detector could be ready 1994/95 . The Superkamiokande proposal

(Ref .13)

still awaits full approval . It would

however be a bad decision to place it in

the Kamioka mine which is simply not deep enough what concerns the problem of muon induced radioactive nuclei . This

spallation background also completely

covers the otherwise very interesting process p + 3He -~ 4He + e+ + Ve with the highest endpoint energy of all reactions in the sun (20 MeV) .

From solar neutrino experiments we

learn about an interesting fact of life in

nonaccelerator physics, the very long time scale involved compared to accelerator

based experiments,for example just

consider that several solar spot cycles need to covered! A lot of patience is

required indeed since such experiments may easily extend over a physicist's entire scientificly active period .

5 . NEUTRINOS FROM SUPERNOVAE

It has been verified experimentally

that a supernovae event leads to an

observable neutrino signal in underground detectors4l . Since the supernova SN1987A

occured in the large Magellanic Cloud (LMC) -50 kpc away it is obvious that the

IMB detector for example has only been active for 2 .1 years out of a period of

5 .6 years . This data could however be used to set a limit of < 1 .5 SN/y for the whole galaxy42 . A similar analysis from

Kamiokande is not yet available . It is therefore of 'great interest to

learn at this conference that a new detector capable of seeing SN neutrinos is coming into operation43 . The MACRO detector designed to search for magnetic monopols and located in the Gran Sasso laboratory has enough scintillation-

counters operating at low background level (at this moment

100 to and -1000 to upon

completion end of 1990), to successfully

search for SN signals . For a galactic SN also the LSD detector in the Mont Blanc tunne144 and the scintillation counter

setup in the Baksan laboratory45 have a fair chance of seeing a statistically

significant signal . Other cosmic events

violent enough to produce a detectable neutrino burst have been discussed

recently, although the expected rate for

our galaxy is rather low -- few . 10-4 /y46 . Again this example shows the need to keep

the underground neutrino detectors running safely and continuously . 6 . ATMOSPHERIC NEUTRINOS The source of atmospheric neutrinos is

pion, kaon and muon decay in the upper atmosphere . The pions are produced in interactions of primary nucleons and

same detectors monitor easily the whole Galaxy for another supernova . It is

nuclei with atmospheric nuclei, the muons are from pion decay . The neutrino energy spectra are very steep, dN/dE - E-a , with

new detectors in order to minimize the chance of missing the next sups-nova . The

the order of 1 GeV that we want to

therefore of utmost importance to keep the experiments running and in addition have

a - 3 .7, the yield of neutrinos to antineutrinos is about 1 .3 and the ratio of Vg / Ve - 2 . For the lower energies of

142

H. Meyer/Non accelerator particle physics

consider here, many calculations of the atmospheric v-flux have been performed,

10 4 km atmospheric neutrino observations allow searches for v-oscillations in the

but in all cases with some simplifying assumptions 47 . A complete calculation will

large mixing angles due to the low rate50 .

be very involved, it has to take into

account a rather detailed pion and kaon production model for nucleon - nucleus

(mostly p + 14 N) collisions, a transport

equation of the pions through the

atmosphere with pion and muon decay

including muon polarisation and the energy loss of muons in the atmosphere, and

finally geomagnetic effects (including the influence of solar spot number cycle)

the flux of primary cosmic rays . The

on

absolute yield of atmospheric neutrinos is

at this stage assumed to be systematically

uncertain by about t 20%, however in all

region Amt > 10 -4 eV2 but only at rather The region of smaller mixing angles, sin220 > 10 -3 , becomes accessible only

with very large detectors (-10 5 to) before the limit due to systematic uncertainties of the flux calculations is reached . The absolute rates of neutrino events as observed by a number of underground

experiments are in very good agreement with the calculations available51, 52 but due to the large uncertainty of the absolute flux no useful limits on Voscillations could be obtained53 .

Two of the large nucleon decay

computations it is found that the ratio of

detectors, Kamiokande II and Fréjus (and with of smaller size the NUSEX detctor)

(anti) neutrino flux is rather precisely

muon neutrino from electron neutrino

the electron (anti)neutrino flux to muon know (to better than 5%), only the

influence of muon polarisation needs to

taken care of, as it was done recently48 . Atmospheric neutrinos can be observed in well shielded detectors deep underground,

however the rate is very low, even in very big detectors since the rate

is only about one event/day/3000 to's . For electron neutrino detection, volume

detectors are required, to fully contain an event it -sakes a volume of - 3m3 . Due to the leading muon that has long range,

muon neutrino events are usully not completeley contained . On the other hand charged current muon neutrino interactions can also be detected as upward going muon events even if the vertex is far outside the detector, at a rate of about one event/day for 500 m2 detector area49 .

It was realized long ago that due the long flight path through the earth of

have sufficient quality to distinguish

induced events to perform a much more sensitive search for v e - Vg and V;, - vti oscillations .No reault on ve - Vti

oscillations can be obtained at this time, due to the small number of events

available for analysis . KamiokandeII has reported54 a low energy

(< 1 GeV) muon

neutrino event deficit, that was

interpreted as evidence for neutrino oscillations 55 , 56 . The Fréjus experiment does not find such an effect57 and the

data can be used to define exclusion regions in Amt vs sin220, that include the central values allowed by the KaII data . The new limits for Amt are better. by more than a factor 10 compared to previous

accelerator results, with only about 200

events available for analysis . This shows the great potential of underground experiments for v-oscillation searches

given sufficient size and quality . Crucial

H. Meyer/Non accelerator particle physics to achieve such a result is the ability to distinguish electrons and muons with high reliability and that can be done very

safely in the Fréjus detector since it was calibrated with electron and muons and

pions at accelerators 58 . Kamiokande on the other hand has to rely on M.C . simulation techniques . The Fréjus result is

supported, although with less statistics,

prediction of the expected level of

neutrino masses is not yet available6t . 8 . SIGNALS FROM DARK MATTER ANNIHILATION It seems rather certain, that our

universe is filled with matter not accounted for by detectable

electromagnetic radiation6l . It is

recognized through gravitational effects

by Nusex (see Ref .52) .The discrepency

only, very clearly in flat rotation

resolved with more data e .g .from the new

range of Hubble classifications and

between Kamiokande and Frejus can only be Soudan II nucleon decay experiment,

however one will have to wait a rather

long time until sufficient statistics has

been collected .

7 . DOUBLE ß-DECAY A majorana mass for electron

neutrinos could manifest itself in zero neutrino double (3 decay . There are many (35)

candidate isotops available for

experimental searches . Of particular interest for practical reasons are 76 Ge, 136Xe and 10OMo which indeed have been

exploited since quite some time . The

natural abundance of these isotops is

less than 10% and considerable gain in

sensitivity can be reached if material isotopically enriched could be made

available . This route is now being followed with new experiments with the

potential to increase the sensitivity by at least an order of magnitude over present experiments59 . The majorana mass range probed will reach down to 0,1 eV (7 6Ge) and 1-3 eV (136Ba, 10OMo) with the planned new experiments6O . The theoretical calculations of decay rates as the basis for the limits are more reliable now, however a clear cut

curves of galaxies throughout the whole secondly by the application of the

virial theorem to clusters of galaxies . About 10-100 times more matter is seen than accounted for by the emission of light . This is the famous dark matter

problem .As I have argued in §2 above the dark matter is most likely nonbaryonic63 . From the particle physics point of view the lightest supersymmetric particle

(LSP) has been proposed as a dark matter candidate64 . They can be produced in the

big bang without spoiling the successful predictions of nucleosynthesis . They would constitute the dark matter also in our galaxy and both the sun. and the earth could capture them into Keplerian orbits well inside their main bodies65 . Above well defined particle masses of -3 GeV for the sun and - 10 GeV for the earth evaporation and capture become balanced and the particles build up an equilibrium abundance" . Particles and antiparticles could annihilate into

ordinary quarks and leptons . The quarks hadronize to produce high energy neutrinos from their subsequent decay . Since inside the sun and the earth one

has a beam dump situation a neutrino signal would mainly come from charm- and bottom particle decay6l . The neutrinos

H. Meyer/Non accelerator particle physics

144

can be observed in detectors deep

underground while waiting for nucleon decay to occur . The expected neutrino rates are very low but so is the

background from atmospheric neutrinos

within the angular acceptance from the direction of the sun (earth) . None of

the big anderground detectors reports an excess in the neutrino flux from the sun68 and for the Fréjus detector also limits on the neutrino flux from the

direction of the center of the earth are

available69 . The limits on the neutrino flux separately for electron neutrinos and muon neutrinos are shown in Fig .2 .

It may be convenient to convert these

limits into limits on the abundance of galactic dark matter for several

species .of dark matter particles . This can be done on the basis of quantitative calculations of capture- and

annihilation rates for the heavy

neutrinos from supersymmetry of Majorana VM, Dirac-VD and s-neutrino Ve,Vp, typ, see Fig .3 .For Dirac typ neutrinos the

Fig .3

Upper limits on the local

density of supersymmetric dark matter from Fréjusdata . 1011

Fig-2

10°

101 102 *E~min [ tieV ]

Upper :limits on V-flux fom the

sun (a) and the earth (b) a .. 90% C .L . The dashed-dotted line is fox CC muon neutrino events, the dashed line for CC electron neutrino events and the solid line for all neutrinos .

limit at lower particle masses

(< 1OGeV)

covers the interesting region not

excluded by the direct scattering

experiments using Ge-detectors 70 . The pure

(unmixed) photino has been proposed

as a viable candidate for the LSP but no usful abundance limit could be

obtained7 l . It seems more appropriate however to consider the more general

H. Meyer/Non accelerator particle physics case of a mixed particle the neutralino72 at the expense of more parameters that are unknown . Limiting regions in this

parameter space on the basis of several sources of experimental limits have been discussed recently73 .

The dark matter particles could as

well annihilate in the galactic halo,

with photons, antiprotons and positrons as annihilation products to be

detected74 . An anomalous cosmic ray

positron signal observed in the energy range < 50 GeV75 , could well be

indicative of a signal, however the

measurements need to be extended to

higher energies to obtain sufficient

difficult to detect on earth because typical detection efficiencies are very

low (between 10 -12 at 1 GeV and 10 -5 at 10 Tev) .and also due to the high atmospheric background ; photons however are much easier to detect at or near earth than neutrinos .

High energy photons will in general be produced through synchrotron

radiation of high energy electrons, by backward compton scattering of low energy photons off high energy electrons and finally by high energy T& decay .Below about 100 GeV detectors have to be located above the atmosphere on

evidence for dark matter annihilation as

satellites . At larger energies > 1000 GeV primary photons generate large

9.

through air cerenkov light detection in

the source of the positrons76 .

HIGH ENERGY PHOTONS FROM GALACTIC

SOURCES

The energy spectrum primary of cosmic

rays as observed near earth extends up

airshowers detectable in counter arrays at mountain altitudes and alternatively clear moonless nights using open photomultipliers 8l .

In the low energy range from 50 MeV

to about 10 20 eV = 10 11 GeV following

to 5 GeV two satellite experiments,

3 .1) to the upper end of the spectrum .

facinating first look on the high energy gamma ray sky . Mostly galactic y-ray

roughly a power law with spectral index (-2 .75) at energies 5 3-1015 eV and (The particle composition of the cosmic

ray flbx has been determined with ballon

SASII82 and COSB 83 , have provided a

sources have been detected84 , with the possible exception of the quasar 3C273 .

and satellite experiments up to about

The strongest point sources are pulsars ;

dominate 77 . The basic acceleration

by the characteristic time structure of

1000 GeV/nucleon and protons seem to

Vela, Crab and PSR 1820-11, identified

mechanisms and their site inside or even

photon emission . The Crab nebula has

both large scale as well as point like

the air-cerenkov technique with very high significance 85 . Most of the observed

outside the Galaxy are still not known,

sources have been proposed78 . Observation of primary photons (and neutrinos) are

crucial to help solving this outstanding problem79 . The most likely source of X+ (and neutrinos will be gt) decay that are produced in collisions of protons with ambient matter 8O . The neutrinos are

also been detected at > 700 Gev using

photon sources however have no definite identification so far (see Ref .84)

mainly because the large positional error boxes contain to many astronomical objects as possible candidates .

H. Meyer/Non accelerator particle physics

146

The photon flux from the galaxy is generally dominated by so called diffuse

the process yy -> e+e- with target photons from the ubiquitous 3°K

emission 86 . It most likely originates from RO-production in pp collisions . The

background will effectively absorb the

molecular form constitutes the target protons, the proton beam is provided by

absorption process is bound to

interstellar hydrogen,both in atomic and

cosmic rays assumed to have the same intensity and spectral shape as we

detect it near earth . The column density of the proton gas along a given line of sight through our galaxy is rather well known on the basis of 21 cm line observations

(atomic hydrogen) and also

of H2 using CO (carbonmonooxid) as a

tracer . This simple model provides a quantitative description of the observed diffuse photon flux

(see Refs . 84, 86) . A

comparison of the energy dependence of

the photon flux from the inner and the

outer galaxy reveals a flatter energy spectrum, (by about 0 .4 - 0 .5 in the spectral index) for photons from the

outer part of the galaxy 87 and

specifically at moderate galactic

latitudes88 .The reason may be a flatter energy spectrum of the primary protons in the outer part of the Galaxy . It

would be very interesting to extent these measurements-to much higher

energies, to near the energy where the

spectral index of the primary cosmic ray energy spectrum changes, E = 3*10 15 eV and where significant leackage out of

the Galaxy is expected . This is being attempted in a number of air shower

arrays notably with the new ones that are still under construction .

Photons of energy < 10 14 eV can travel very large distances in the universe of the order of Gpc without significant

scattering or absorption . Above 10 14 eV

high energy photons with a shortest mean free path of -7kpc89 . Therefore this influences photon fluxes already within our own Galaxy and becomes very

important for photons from all other

galaxies (Andromeda the nearest spiral galaxy is already 670kpc,or about 10 absorption length away) .

There is indirect evidence for a high

energy photon flux from our Galaxy from

an airshower experiment at Baksan9O . The daily rate of vertical showers with

threshold at -10 TeV is found to be

modulated with an amplitude of - 1/1000 coincident with the location in the outer part of the Galaxy . A more

detailed comparison shows that it

follows exactly the shape of the photon

flux from the galactic disk as observed

in the COSB experiment extrapolated with

a spectral index of -2 .1 . Unfortunately there is no proof that the excess

showers are due to primary photons . Note

that the energy of the showers is well below the yy absorption edge . It would be very important to confirm this result using an array with sufficient muon

coverage to safely identify showers

originating from primary photons since

they will have less than 3% of the muon content of the proton

(nuclei)

induced

background showers9l that are more

abundant by at least a factor of 1000 .

If a 10 TeV galactic photon flux could be followed into the yy absorption edge at > 140 TeV, a powerful new distance

calibration for the galaxy would become

available!

H. Meyer/Non accelerator particle physics ACKNOWLEDGEMENTS

I would like to thank R . Barloutaud, H .J . Daum, G . Giacomelli and M Treichel fo .c very useful discussions . This work received support from the BMFT, FRG under contract number 55WT84P . DISCUSSION R.Barbieri

(University Pisa/Italy)

Q .1 : From annihilation in the earth/sun, do you extend the mass region excluded already by Ge-experiments?

B .M . : For Dirac neutrinos the un6Lerground experiments exclude also the mass range 3 .5 GeV < M < 12 GeV not covered by the Ge-experiments and therefore clos(, the cosmological interesting window there .

Q .2 : I am surprised to hear that you think that there are many explanations

of the supposed anticorrelation between the solar activity and the homestake

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