Neutrino spectroscopy with KARMEN

Progress in Particle and Nuclear Physics PERGAMON

Progress in Particle and Nuclear Physics 40 (1998) 183-192

Neutrino Spectroscopy with KARMEN R. MASCHUW

for the KARMEN A general introduction

to the KARMEN

gramme is presented.

collaboration’ neutrino

experiment

and its physics pro-

One of its major subjects is the experimental investiga-

tion of neutrino-nuclear

reactions mediated by both charged current (CC) and

neutral current (NC) weak interactions. ‘2C(~,,e-)‘2Ns.l,

Cross sections have been measured for 12C(v,v’)12C’ (1+1;15.1 MeV) (v = 12C(~e,e-)‘2N’, 13N and 56Fe ( v, , e- ) %o. Quantitative results from these

vp,ve,fiI1),lSC(ve,e-) experiments have been deduced for the NC isovector axialvector coupling strength, the NC davour universality and the nuclear axial charge distribution.

1

The KARMEN

Neutrino Experiment

The KarlsruheRntherford-Medium-Energy-Neutrinoexperiment

(KARMEN) denotes an experimental

programme of neutrino physics using neutrinos Y,,, ve and VP with energies up to 53 MeV to be detected in a large scintillation calorimeter. Major physics aims are the search for neutrino oscillations and the investigation of neutrino-nucleus interactions with implications on standard model and non standard model physics problems. The experiment is performed at the neutron spallation facility ISIS of the Rutherford Appleton Laboratory, England.

From a 50Hz Rapid Cycling Synchrotron an 800MeV,

200pA pulsed proton beam hits a Tantalum Heavy Water spallation target (TaDzO).

Apart from

neutrons, used for the condensed matter research programme at ISIS, also large numbers of pions are produced by the spallation process. target within about lo-”

It is the decay of these pions, after having been stopped in the

s, that provides the neutrinos for the KARMEN experiment. Negative pions

are captured and finally absorbed by nuclei. Stopped positive pions, however, undergo their characte ristic successive decay scheme A+ 3 Decay-At-Rest

/.i++ u,, followed by p+ *% e+ + v, + Y,, and produce the typical

neutrino spectrum (DAR) .1.e. monoenergetic u,, of 29.8MeV energy and, with equal

intensity, I+ and ti,, with energies up to 52.8 MeV (see Fig. la). A unique and the most important feature of the ISIS DAR-neutrino source, however, is its time structure which is closely related to that of the proton beam. Two pulses of protons of 100ns width, ‘B. Armbruster, G. Drexlin, V. Eberhard, K. Eitel, H. Gemmeke, T. Jannakos, M. Kleifges, J. Kleinfeller, C. Oehler, P. Plischke, J. Rapp, M. Steidl, J. Wolf, B. Zeitnitz: Forschungsrentwm hhrismhe and Universit6tKarlsmhe. B.A. Bodmann, E. Finckh, J. Hii51, P. Jiinger, W. Kretschmer: Universitiit Eriongen-Niimberg. C. Eichner, R. Maschuw, C. B.uf: Universitiit Bonn. I.M. Blair, J.A. Edgington, S. Seligmann: Queen Mary and Westfield College, London. N.E. Booth:

University

of Oxford.

0~46_64~0;98:$~9.00+0.00 PII: S0146-6410(98)00024-h

0

1998 Elsevier Science BV. All rights reserved.

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in Great

Britam

184

R. Moscl~uw/ Prog. Part. Nucl. PIqx

40 (1998)

183-192

separated in time by 300 ns, hit the TaDzO-target with a frequency of 50 Hz. Due to the short lifetime of?r+, r = 26 ns, one thus have two prompt bursts of monoenergetic V, within the first 500 ns. In a time window from 0.5 ps to 10 ps, where all vP have vanished already, one is left with V, and Y,, showing the characteristic exponential time slope of 2.2 ps from its producing $-decay time structure of the ISIS DAR-neutrino

(see Fig. 1b, bottom). This

source provides, as will be shown, a very stringent signature

for v-induced events as they have to fit the time distributions of the corresponding v-species. Detection of those neutrinos by exploiting their characteristic energy and time distributions requires a high mass, high resolution detector system, effectively shielded against fast neutrons from the spallation target and the hadronic component of cosmic radiation. KARMEN is an all active 56 ton liquid scintillation calorimeter (AE/E

= 12% /dm)

housed in a 7000 ton shielding blockhouse located

at a mean distance of 17 m from the neutrino source (for details see ref. [l]). The segmented central calorimeter (512 modules) is looked at by 2048 phototubes registrating energy deposit, time and po sition of each event.

It is surrounded by an active/passive sandwich anticounter system to identify

the rare neutrino events which create a signal only in the central detector. However, the veto system, by intelligent triggering, also allowed a detailed and thorough study of almost all, mostly p-induced background, i.e. stopped p-decay, p-induced electron bremsstrahlung, p-capture neutrons, p-induced spallation neutrons etc. With the precise knowledge of the morphology of the background it can either be suppressed effectively or taken care of in proper Maximum-Likelihood The signal of neutrino events in the KARMEN

analyses.

calorimeter is the detection of neutrino induced nu-

clear reactions where the mineral oil based scintillator with its Carbon and Hydrogen content serves as an active nuclear target. ‘*C ( V,

,

In the search for neutrino oscillations v,,+ V, and tip+ 4 the reactions

e- ) “N,,.. and ‘H ( V,-

,

e+ ) n respectively, are employed just to tag a neutrino of specific fla-

vour and appropriate energy and time as to see whether or not it might be an oscillated one (see ref. [2], (31 and (41 in this issue). In this paper it is the neutrino-nucleus interaction itself which is the topic of investigation where both, charged current (CC) and neutral current (NC) weak interaction processes are studied.

2 Neutrino-Nucleus Interactions: Physics Motivation Thephysics potential of KARMEN with respect to the investigation on neutrin*nucleus

interactions

can best be demonstrated referring to Fig. 2. It shows the CC and NC electroweak transitions between

.5?

5 r:

e

2 >

4r

*-i 5, y- : ,’

3

, #’ *’ ,’

2 ;: ,* 1

,’

4

,’

,’

IF

.I 0

.* 0

/’

~ 10

20

30

v-Energy[MeV]

,

I

y&J

V

,*’

:,I

[ ns]

Time

,’ vc

40

50

0

I

2

3

4

5

6

7

8

Tim IPI

Figure 1: Energy (a) and time (b) distributions of the ISIS DAR-neutrino

source.

R. Maschw 1 Prog. Parr. Nud. Phys. 40 ( 1998 1 183-19-7

185

Figure 2: The A = 12 isobaric analogue triplet

the ground state of “C and the isobaric analogue triplet states of the A = 12 system i.e. 12B, “C, “N. These transitions between nuclear states of well defined quantum numbers serve as a spin-isospin filter for the investigation of specific components of the weak hadronic current. In this particular case, with simultaneous spin- and isospinflip, AT = AS = 1, it is the isovector-axialvector

coupling that

dominates both, the CC and NC reactions. A quantitative measurement of the NC nuclear excitation 12C ( u, v’ ) 12C* ( l+ 1; 15.1 MeV ) , which has never been observed so far, would thus allow to determine this specific NC coupling constant [5] predicted to be one in the standard model (SM). Furthermore a comparison of this NC transition induced by the different species of neutrinos from ISIS, v,,, v, and g,,, would allow to prove the flavour universality of the v-Z0 coupling otherwise difficult to access. In the theoretical description of the above transitions, apart from the coupling strength, the extended structure of the nucleus has to be taken into account by weak nuclear formfactors. of “N and “B or from muon capture on Carbon, CL-+ 12C + l’B,...+

From p-decays

v,,, the dominant axialvector

formfactor Fa(q2) can be deduced only at zero or fixed momentum transfer respectively.

However,

studying the inverse P-decay reaction “C ( u, , e- ) “Ns.,. over the full range of energies of v, from ISIS with a detector of spectroscopic quality like KARMEN, gives access to the q2-dependence of this weak nuclear formfactor. The uncertainties in these formfactors are still a limiting factor in the precision of the calculations of weak semileptonic reactions. On the other hand many detectors for solar, atmospheric, galactic and terrestric neutrinos are based on nuclear signatures.

The measurement of cross sections of neutrino-nucleus

reactions is thus of

great importance to prove the validity of the underlying theoretical calculations. The same is true for the problem of neutrino induced nucleosynthesis in supernova explosions where the energy spectra of neutrinos with temperatures of about 5MeV for v, and about 10MeV for v,, respectively, cover the same energy range as the ISIS DAR-neutrino

source.

Quantitative experimental investigations of neutrino nuclear interactions at typical ‘nuclear physics’ energies of some ten MeV is thus a powerful tool to study basic weak interaction physics as well as other related physics phenomena.

R. A4aschuw/ Prog. Parr. Nucl. PIIJS. 40 (1998) 183-192

186

3

Experimental Results from KARMEN

KARMEN

at ISIS has taken data since 1990 with its last run in December 1995 when an upgrade

programme was started for an improved neutrino oscillation search (see ref. [3], [2]). Within that time an integrated proton intensity of 9122 C on target has been collected meaning an integrated neutrino flux of 6.43 x 1Or3v/cm* onto the KARMEN calorimeter. From these data results on various neutrine nucleus reactions have been deduced.

3.1

“C ( ve , e- ) 12Ng.s.

The CC reaction

The most stringent signature for a neutrino induced reaction at KARMEN is provided by the charged current exclusive inverse @decay trons with kinetic energies E,-

reaction “C (v, ,e- ) 12Nss.. With a Q-value of -17.3MeV

10 15 20 25 30 35

4

3.

8

10 12 14 16

d)

80 -1

g100 w .

; & 80

2

P

&

w

60

0 123456789

0

Electron Time (ps) 3:

6

Positron Energy (MeV)

Electron Energy (MeV)

Figure

elec-

< 35.5 MeV have to be detected in the time slot of v, i.e. 0.5~s to

Energy

and time spectra

of the prompt

“C (v, , e- ) 12Nss. followed by *2Ns..,.-+ “C + e+ + v,

cj

10

20

30

Positron Time (ms) and delayed

signal from

the reaction

R. Moschuw i Prog. Part. Nucl. Phy~. 40 I 199X1 16%192

5~s.

The exclusive

transition

to 12Ng+ is indicated

by also detecting

the positron

e+ from its decay

r2C + et + v, back to the ground state of “C with end point energy E,.,. = 16.3MeV

“Nsa.-+

lifetime t = 15.9ms. e--signal.

This delayed

Transitions

in the scintillation

e+-signal

to higher excited

detector

has to occur at the very same position

states

signal is actually appropriate

of 12N are all particle

because of the much lower light output

lifetime of 12Ns.*., r = 15.9 ms, corresponding

looked for over two beam periods once a prompt

energy and time cuts for this spatially

correlated

The corresponding

in Fig. 3. The time distribution

agreement

with the expected

energy spectrum reaction

(see Fig. 3a).

electron

The same agreement

a cross section averaged

from 12N-decay

elementary

particle

perimental

results

The result

therefore

(EPT)

p+--decay

predictions

LSND experiment calibration

was deduced

(CRPA)

have been adjusted

to be

electron

[7) or the to the ex-

scattering

on

an older one, the Los Alamos

(111. The reaction

reaction

free data

x 1O-42 cm2.

on “C and inelastic

p-capture

signal is

background

using either the one body density

also with those from two other experiments,

serve as a well understood

of the delayed

phase approximation

the formfactors

[6], [8], p rovided

from 12N and “B P-decay, (lo] and the recent

(see Fig. 3~). The measured

f 0.8 (syst.)]

random

The

signal is in complete

from the “C ( v, , e- ) “Ns.,.

of the DAR-v,-spectrum

with all theoretical

With

536 events

was only 14.5 events.

for the time and energy spectra

[5], [9], th e continuum

treatment

agrees

E225 experiment

agreement

(OBD)

signature,

of the prompt

energy distribution

(D (12C ( I+, e- ) *‘Nss. ) ) = [ 9.3 f 0.4 (stat.)

shell model approach

has been identified.

(see Fig. 3b, d). From these almost

over the energy distribution

This value is in excellent

candidate

‘off beam’ background

2.2 11sslope of I+ from its producing

also agrees with the expected

found with those expected

and will not be seen energy loss. With the

delayed coincidence

quality

of these data is reflected

unstable

of hadronic

and

prompt

as the

nicely to the beam pause of ISIS of 20 ms, the delayed

of this type have been detected.

“C.

187

“C ( ve ,e- ) 12Ns.,. might

for all future neutrino

experiments

operating

in this energy region.

3.2

and The Weak Axial Charge Radius of 12C

FA(q2)

The measured the excitation

energy spectrum function

response

function.

Q-value

of the reaction,

u(&),

of electrons the incident

dynamics

small e&t to determine deduced formfactor

by the axialvector

the Fermi function

from the weak magnetic the momentum

directly

formfactor,

and size is described

q2. At KARMEN

transfer

cross section is dominated

in the elementary

transfer

from the measured

assuming

is related to the measured

conserved

particle treatment

electron energy by the

FA(q’).

and I is an integral

cross section.

vector

current

p(q2) to the weak magnetic formfactor

is negligible.

The

where all information which are depend-

where q2 ranges from 0 5 lq21 5 0.4 rn$ the Referring

to [6] it is given as

with only weak q2-dependence

and tensor formfactor. of each individual

(EPT)

by weak nuclear formfactors

energies,

formfactor

of

(see Fig. la) and the detector

.E, = E, - 17.3 MeV, as the recoil energy to the 12N-nucleus

about nuclear structure, ent on the momentum

“C ( v, , e- ) 12Ng,. is a convolution

energy distribution

The energy of the incident neutrino

cross section u( EY) can be calculated

where F+ denotes

from the reaction neutrino

As KARMEN

CC reaction

However,

conservation

choosing

and a rather

has no angular

the formfactor

FA(q’)

resolution cannot

a dipole paramatrization

CVC, which relates

FM(q2), and also assuming

be

of the

the electromagnetic

scaling for FM(q’) and

R. Maschm,/

188

FA(q*)

(61, the dipole

distribution

parameter

Prog. Parr. Nucl. Piys. 40 (1998)

can be deduced

from the shape

183-192

of the measured

electron

energy

112). . _ With

FA(q*)_ F-do) the radius of the weak axial charge distribution

(1 - gB:

4*)*

of ‘*C has been determined

to be

RA = (3.S+::$fm. Within

the lo error this agrees with the electromagnetic

Only the shape of the electron FAN

or more precisely

the radius parameter

cross section of the reaction the axial formfactor

energy distribution

rms-radius

of l*C, R, = 2.478fm.

has been used to determine

RA of this formfactor.

the q*-dependence

From the measured

of

averaged

‘*C ( v, , e- ) r*Ns.,., however (see sec. 3.1) taking the above value of RA,

at zero momentum

transfer

can be deduced

to be

FA(0) = 0.73f0.11. From the average of the ft-values also in good agreement The energy spectroscopy transfer

dependence

hypothesis

3.3

of the reaction

‘*C ( v, , e- ) “NsS. with KARMEN

of the nuclear formfactor

for the vector and axialvector

The NC reaction

Neutral current neutrino been discovered

they are, except

and that the scaling

is a valid assumption.

have been suggested

of the non charge changing

reactions neutrino

are also quite important electron

below the /J- or r-mass

scattering,

as a most powerful tool to reveal

weak interaction

But it was only the KARMEN

the first NC inelastic nuclear scattering

[13], (141. NC nuclear v, at energies

formfactor

12C ( v , Y’ ) 12C* ( l+ 1) ; (v = v, + VP)

in the early seventies.

later that observed

showed that the momentum

has to be taken into account explicitly

induced nuclear reactions

the Lorentz and isospin structure

because

for the ,f?-decays of ‘*B and ‘*N one yields FA(O) = 0.711 which is

with the result from our experiment.

process

immediately

experiment

after it had

almost twenty years

‘*C ( v , v’ ) ‘*C* ( l+ 1; 15.1 MeV )

in the framework

the only processes

of neutrino

that are observable

oscillations for v,, or

respectively.

Time&n] Figure 4: Energy

(a) and time (b) spectrum of single prong events in the p-decay time window. The to the reaction ‘*C ( v, Y’) ‘*C*. The solid line in (b) represents a 2.2 p’s time

peak in (a) corresponds constant.

The signature for the NC process ‘*C ( Y , Y’ ) r*C* ( l+ 1; 15.1 MeV ) unfortunately has not the same stringent delayed coincidence structure as the CC reaction discussed before. The only signal is the de tection of 15.1 MeV monoenergetic gamma quanta from the decay of the excited state of l*C?. However, with an effective branching ratio of 94% for this decay back to the ground state 12CsS. a clear peak structure in the energy spectrum of single prong events within the appropiate v-time windows should show up at about 15 MeV visible energy. Taking the time slot for v, and VP, i.e. 0.5 ps 5 t 5 3.5 ps, the energy spectrum of single prong events in the central detector as shown in Fig. 4a is achieved. This spectrum, apart from a broad bumb of events with energies between 16MeV and 45MeV to be discussed below, indeed, shows the expected prominent peak between 11 MeV and 16MeV. This, unambiguousely, is asssociated with the NC inelastic scattering process ‘*C ( v , v’) ‘*C* ( l+ 1; 15.1 MeV)

induced by both, v, and V,,. A convincing

confirmation of this assignment is the time spectrum of all single prong events with energies between 11 MeV and 35 MeV taken over a time spread -20 ~LS5 t 5 +30 ps with respect to the ‘beam on target’ time to = 0 as shown in Fig. 4b. The excess events above a randomly distributed background show the typical 2.2~s exponential slope of v, and cfi from CL+-decay and are just the 695 events of Fig. 4a. A Maximum-Likelihood

(ML) fit to this spectrum taking into account also various inclusive CC reactions

discussed in sec. 3.5, assigned 473.2 f 32 NC events to the reaction ‘*C ( u, v’) ‘*C* ( l+ 1; 15.1 MeV ) . The cross section for this NC nuclear excitation induced by v, and v,, and averaged over the corresponding energy spectra was deduced to be (0 (l*C (u, v’) ‘*C* )) = [ 10.9 f 0.7 (stat.) f 0.8 (syst.)

] x 10e4* cm*; (v = v, + ti,)

As in the CC case (see sec. 3.1) there is excellent agreement with corresponding theoretical calculations using the EPT (61, [8], the CRPA [7] or the OBD SCheme [9]. This is not too surprising as the same nuclear structure applies for the isobaric analogue states ‘*Nss. and “C*(l+,l).

Experimentally, no

other experiment so far has measured this NC nuclear reaction.

3.4

Neutral Current Flavour universality

For a given u-energy the cross sections for the CC reaction ‘*C ( v, , e- ) l*Ns... and the NC reaction ‘*C ( v , v’ ) ‘*C* ( l+ 1; 15.1 MeV ) differ only by a Clebsch-Gordon isospin coefficient of l/2 because the nuclear structure of these transitions are the same as well as the relevant CC and NC isovector axialvector couplings.

As the NC excitation at KARMEN

is induced simultaneously by u, and V,,,

having almost the same energy distributions, the ratio of the measured cross sections of these reactions R = < a~~(u,+fi,,)>

/ < acc(u,)>

is expected to be one, provided there is identical coupling for fi,, and

u, to the intermediate vector boson Z”. The measurement of this ratio thus provides a flux independent determination of the p-e universality of the u-Z0 coupling. As the I+- and fi,,-energy spectra are not exactly the same (see Fig. la) and because there is a slight difference in the NC cross section for u or V the ratio is expected to be slightly bigger than one. The theoretical expectations vary between 1.1 and 1.2 whereas KARMEN has measured R = 1.17 f O.ll(stat.)

f O.O12(syst.).

Within the uncertainties this is a nice confirmation of the NC p-e universality at low energies, which is of great importance when bolometric techniques to detect astrophysical neutrinos via NC nuclear reactions are applied.

R. Mu.~cl~m~/ Prog. Purr. Nucl. PhFs. 40 (1998)

190

3.5

The Inclusive CC Reactions 12C( u, , e- ) 12N*, 13C( u, , e- ) 13N and 5sFe( V,

e- ) 56Co

,

In the single prong energy spectrum a variety of different

v,-induced

of Fig. 4a the broad bumb at energies above 16 MeV is made up by

CC reactions.

delayed ‘rN decay signal is missing, the events with the full exclusive content

the measured calculated electrons

spectrum

This provides

of -2.2

from the reaction

the largest contribution decays

model.

contribution

component

be observed

in the scintillation

(o (i3C ( ye, e- ) 13N ))

=

[ 0.5 f 0.37 (stat.)

(o (56Fe ( v, , e- ) 56Co ) )

=

[ 2.51 f 0.83 (stat.)

for the reactions the statistical

if compared

f

detector.

a residual

quite successful

to describe

0.5(syst.)]

x 10-42cmz

* 0.1 (syst.) ] x 10m4’ cm* f

0.42 (syst.) ] x 10e4’ cm*

predictions

interaction a variety

measured

cross sections

[15], [16], [17], [18]. Our result

states are constructed

It also is in agreement

with a

from generic continuum

lplh

derived from a meson exchange potential.

This scheme has been

of low energy v-scattering

as well as p-capture

cross sections

However, there is an open problem with the inclusive reaction

200 MeV energy recently

and by far

A careful Maximum-

for 13C are rather high the measured

to theoretical

[19] where the excited

states including

The remaining

from

yielded the following cross sections:

“C (v, ,e- ) ‘*N* agrees well with that from LSND [ll].

recent CRPA calculation

can be

13C ( u, , e- ) 13N and 56Fe ( u, , e- ) 56Co have never been measured

errors, particularily

are in the right order of magnitude for the reaction

O.s(stat.)

scattering

as bremsstrahlung

( v, , e- ) l*N* to excited states of r*N,

“C

(5.1 f

from v-e-

shielding.

13C ( Y+ , e- ) 13N.

to the high energy end of

was identified

“Fe ( v, , e- ) 56Co in the surrounding

=

Although

from the reaction contributing

taking into account all the above contributions

The cross sections

processes.

Another

is due to the inclusive CC reaction

(o(‘“C(v,,e-)‘*N’))

before.

a contribution

An additional

of which cannot

Likelihood analysis

from “C ( v, , e- ) 12Ns8., where the

MeV it is the only reaction

to which it can be fitted.

from the standard

the particle

The contribution

is easily calculated from the measured cross section deduced from There is a 1% natural abundance of 13C in the Carbon signature.

of the liquid scintillator.

Because of its low Q-value

3.6

183-192

i*C(v,,c(-)X

with v,, of about

at LSND [20].

The NC reaction 12C( v,, , v,,’ ) 12C* and the NC Isovector Axialvector Coupling Constant

In sec. 3.3 the NC reaction up to 52.8MeV monoenergetic

‘*C ( v, v’) ‘*C* ( l+ 1; 15.1 MeV)

have been discussed.

v, of 29.8 MeV from *+-decay

contamination

with fast neutrons

burst are dominated has been measured

from the spallation

later at the detector

by neutrinos. explicitly

followed by the capture

process.

Most fortunately

Furthermore

coincidence by Hydrogen

of a prompt

these neutrons,

This enables

spectra

single prong events as shown in Fig. 5a and 5b.

a reliable Maximum-Likelihood have been taken into account

analysis

in the

Cosmic ray background

reactions

from u, and fifi contamination

for events within the first 90 ns of each burst clearly shows the expected ‘*C ( ufi, u*‘) ‘*C?. Also shown is the background

process

placed

of the time and energy

spectrum

the reaction

having

of these fast neutrons n-p scattering

or some Gadolinium

optical segmentation. of all prompt

v,

there is still some

thus, the first 90ns of each particle

the shape of the time spectrum

neutron

using the

with those prompt

all heavy shielding,

than the neutrinos

making use of a delayed

of the thermalized

by v, and v,, with energies

has also been observed

[21]. H owever there is a problem

as within its short time window of 0 2 t v,, 5 5OOps, despite mass, arrive somewhat

induced

The same NC transition

and

as well. In Fig. 5b the energy

from fast neutrons

15 MeV peak from (light hatched)

as

6 6

Figure 5: Time (a) and energy (b) spectrum of single prong events in the v,, time window. Further explanation see text. well as from cosmic rays and v, and ti,, contamination (cross hatched) of the v,, bursts (dotted line in Fig. 5a). From these data the cross section for the NC reaction *‘C ( II* , u,,‘) ‘*C* at Ev,, = 29.8 MeV has been determined to be o(‘*C (v, ,v6’)12C*)

= 13.1 f 08(stat.)

f O.S(syst.)]

x 1O-42 cm2

Within the errors this is a further confirmation of theoretical calculations yielding 2.4

x

10T4’ cm2

(OBD) [9] and 2.8 x 10e4’ cm2 (CRPA) [7]. For the NC excitation “C (v,, ,v,,‘) r2C* at the fairly low energy of 29.8MeV

there is only a weak

dependence on the nuclear structure which referring to [5] can be deduced from the experimental results of 12N and “B @decay and p-12C capture. In the so called Long Wavelength Limit (LWL) the cross section, model independently, is given by

. (&&2 gLwL Y,Y’ = 1.08 x 10sscm2 with E, being the neutrino energy, w the excitation energy 15.1 MeV, MN the nucleon mass and p denoting the NC isovector axialvector coupling constant. [t17xy5u - &r5d]

It represents the strength of the amplitude

in the NC Lagrangian and is predicted to be one in the standard model. Taking our

measured cross section we derive ]p] = 1.08f0.18. Within its error it is in complete agreement with results from earlier high energy experiments and thus provides a nice confirmation of the validity of the standard model at even very low energies.

4

Concluding Remarks and Acknowledgement

This paper has only covered those objectives of the KARMEN

experiment were definitely positive

results on physical observables have been determined i.e. cross sections on various CC and NC neutrino induced nuclear reactions. These have been used to deduce some important features of weak interactions like weak formfactors, flavour universality and coupling strengths.

They also have important impact

in testing various schemes of theoretical calculations of semileptonic processes as well as on current

192

R. Maschuw/

and future

neutrino

spectroscopic

projects

investigation

Prog. Part. Nucl. Phys. 40 (1998)

using terrestrical

of neutrino

in ref. [3], (21 and [4]. Other non standard results of the KARMEN

experiment

the complete

data set.

KARMEN

the ISIS staff. enthusiasm

for the hospitality

model physics questions

by the Bundesministerium and the assistance

References [I] B. Zeitnitz,

and for the assistance

[2] G. Drexlin,

these proceedings

[3] B. Zeitnitz,

these proceedings

(1994) 351

[5] T.W. Donnelly, Phys. Lett. B 43 (1973) 93 et al., Phys. Lett. B 212 (1988) 139

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C 49 (1994) 1122 and Ref. 19

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Appleton

of the collaboration this paper.

in detail

influenced

by the

soon employing

fiir Bildung und Forschung

[4] K. Eitel, these proceedings

[6] M. Fukugita

is described

which are strongly

of the Rutherford

to prepare

Prog. Part. Nucl. Phys. Vol.32

The implications of this

oscillations

in [22] and will be updated

The author would like to thank all members

on this project

neutrinos.

on neutrino

have been described

This work was in part supported We are greatful

or astrophysical

nuclear reactions

183-192

(BMBF).

Laboratory

and

for their persistent