Neutrino properties and interactions

NeutrinoProperties and Interactions

773c

Nuclear Physics AS27 (1991) 773c-792c North-Holland, Amsterdam

NEUTRINO

PROPERTIES

AND INTERACTIONS

F. BOEHM*

and H. EJIRI**

*Department

of Physics,

California

**Department

of Physics,

Osaka

The presentations cused future,

beta

topics:

decays

including

on Neutrino

and double

beta

plans;

activation;

Toyonaka,

1) Neutrino

new detector

ergy and neutrino

of Technology,

University,

in this workshop

on the following

by tritium

Institute

Osaka

Properties

mass

decays;

3) Neutrino

4) Dark matter

Pasadena, 560

CA

JAPAN

and Interactions

and the weak

have fo-

interaction

2) Neutrino

oscillations,

scattering

and reactions

searches

91125

studied

present

and

at high en-

and new detectors

for neutrinos

and dark matter.

1.

NEUTRINO

1.1

Improved

MASS Limit

AND THE

on the Mass

Free Molecular

Tritium

In 1980 the ITEP in tritium

beta

WEAK

of the Electron

(Presented

group

INTERACTION

claimed

Antineutrino

by T. J. Bowles, evidence

from

the Beta

for a finite

neutrino

decay. ‘) A mass this large would be sufficient

mass

of about

experiment

have been raised,

the group still claims

17 and 40 eV, and other experiments systematic caused

uncertainties

by finite

in the source) tritium direction effects.

in this experiment

spectrometer Such excitations

from

that

of spectrometer

response.

However,

the molecule),

calculations

spaces.

Thus,

produce

a distortion

of the beta

in experiments

using

group has designed

Atomic

can be calculated

due to atomic valine,

with

paper*)

it:

we described

m(v,)

we have made one being

the spectrometer

< 27 eV a number

the replacement

with a 96-pad

sets of data.

a system

neutrino

confidence

of substa,ntial of the simple

Si microstrip

The first data set resulted

uncertainty

level

(CL).

single-element array.

in

basis

in the deduced this uncertainty, tritium

as the

excitations

mass of less than a few eV.

and reported

improvements

detector

and 64 electrons

in which the atomic

briefly

The

of the system

and truncated

to eliminate

our a,pparatus

for these mass.

can only be modeled

19 atoms

in the deduced at 95%

neutrino

using free molecular

are the only systems

of one of the in the opposite

measurements

In order

The largest

be corrected

finite

out using approximations

and built

tritium

mass between

decay

spectrum

excitations

with

numerous about the

loss and backscattering

must

in a spurious

solid sources.

with an uncertainty

In an earlier

several

effects

must be carried

and molecular

taken

and the spectrum results

(in particular

the Los Alamos

principal

mass

as well

of the beta spectrum

the beta

can be dealt with by careful

source.

announced,

energy

there is a large (of order 15 or more eV) intrinsic

mass

obtained

(including during

the final state

For solid sources

neutrino

resolution

final states

resolution

a finite

have to do with distortions

of the distortion

theoretically.

to observe

ruled out this claim.

of atomic

due to neutrino

An overestimate

effects

energy

and excitations

atoms.

have not completely

of

35 eV

to close the universe,

as being the first indication of new physics beyond the standard model. Thus, groups have initiated experiments to check this claim. While many concerns ITEP

Decay

LANL)

With

Since

the initial that

result

result

to the apparatus, proportional

0375-%74191/$03.50 0 1991 - Elsevier Science Publishers B.V. (North-Holland)

the

counter

the new system,

in a limit of 13.4 eV;3)

was in

we have

the subsequent

F. Boehm, H. Ejiri / Net&no

114c

measurements

yielded

also investigated spectrometer

resolution

tube exactly However,

results

a number

consistent

lines and long tails.

process,

In order to be certain at the Stanford

demonstrated

the observed

that

directly

83mKr

measured

admixed

the change source

with

Auger

number

Table

of *3mKr,

dominant

and found

to be negligible. the results

3Hz source

This

keV conversion

also occur,

intensity, (space

experiment conclusively

in the krypton. the

ion trapping, have

of

is due to

voltage

has been

as well as wide range

which

We have

lineshape

uncertainty

in acceptance

of the experiments

satellite

excitations,

This

of the accelerating

charge,

electron.

yielding

by studying

systematic

change

the

which fills the source

Laboratory.

as a function

effects

I summarizes

We have

to determine

out a photoexcitation

Radiation

remaining

spectrum.

systematic

a 17.820

is due to excitations

loss in the

lines in 83mKr of known

of other

In order

excitations

we carried

of the spectrometer

used to scan the beta

using several investigated

structure The

the uncertainties.

that these tails were from Kr atomic

Synchrotron

energy

3Hz gas.

in acceptance

tube

A large

the

source

atomic

in the spectrometer,

on a Kr gas target

within

very carefully.

and decays emitting

conversion

and not due to scattering

also

effects

we use a gaseous

the same way as tritium

in the internal

with this limit

of systema.tic

precisely,

properties and interactions

of the

checked

tritium

etc.)

scans.

have been

reported

results.

In

addition to these experiments, there are several others which are now coming into operation with expected sensitivities of better than 10 eV (assuming zero neutrino mass). At present, the ITEP claims are completely ruled out by the recently announced results from both the Ziirich and Los Alamos groups. It is also clear that the mass of the electron antineutrino is by itself insufficient to close the universe. Tritium

Table I:

Source

Group ITEP4

Valine

LANL

Free 3Hg Gas

Ziirich’

Monolayer

Tokyo7

1.2

Polymer

Double

Beta

Decays

The neutrino-less vation

SUSY,

reabsorbed

double

particle

with a finite

nucleon

mass m,.

and provides element

by means

beta

Decay

Results

Stat (eVz)

Syst (eVz)

Limit (eV)

17 < m

CL

< 40

95

-147

55

58

9.4

95

-158

150

103

15.4

95

-82

87

29

95

Subjects

decay,

?

(Presented

by H. Ejiri,

Ovp/3, which violates test for theories

In the case that in the same

nucleus,

The Ov/?/3Hamiltonian

the lepton

beyond

the neutrino

the neutrino

from

University)

number

the standard

emitted

consists

Osaka

conser-

model,

such

one nucleon

is

has to be a Majorana

of the mass term

(m,)

and

current terms (X) and (17). The two-neutrino double beta decay, 2vpp, the standard theory, proves the feasibility of the rare /?/_? decay measurethe

A@” with the calculated Double

beta

and direct

and so on.

by another

the right-handed which is within

matrix

and Related

law, is a very sensitive

as GUTS,

ments,

m* (e?)

Monolayer

L-M

Beta

2vp/? matrix

element

one gives the nuclear

A@“. parameters

Thus comparison of the observed needed for evaluating the Ov/3/?

MO”. decays

of Ge detectors

from the UCSB/LBL*)

of 76Ge with

&PO = 2.041

with good energy

group giving

resolution.

MeV The

have been most

extensively

restrictive

a lower limit on the Ov/3p half-life

studied

result

of Z’$..(O+

+

comes O-) >

775c

F. Boehm, H. Ejiti / Neutrino properties and interactions 1.2 +10z4 y (90%

CL).

Efforts

are underway

76Ge /?p decays

to study

by using

enriched

76Ge detectors. “Se TPC

/?p decays

with Q = 2.995 “Se

with 14g of enriched

of T;/&(o+

y obtained

iooMo /3p decays The

Osaka

group”)

source

used ELEGANTS

(PL)

and

NaI

each

100 g, which

preliminary

detector

are chemically

year measurement “MO

foils.

The

The

Mexico

half-life

INR group12)

For 136Xe p/? decays The

half-life

Q = 2.478

below

detector

“‘MO

and

0.5 ppb

Expected

> 0.54 . 10”~

plastic

of U and Th.

sensitivities

for OYPP and 2vpp,

as Tf,Y2 > 2.7.

array

The

for a one

respectively.

with “‘MO

and

and TF,K2> 4.0 . 102’y.

10i8y

scintillator

arrays

“MO foils,

array

of T:/“? =

a half-life

MeV,

the Milan

group

used a high pressure

so far is TfT2 > 2.5 - 1.5 . 10z2 (68 - 90% CL),

obtained group

used a large

with the large Q-value

of T:/“2 > 2.4.

volume

of large phase Upper

space

limits

o+ --f o+ovpp.

TPC,

while

the

INR

group

Xe The

used an

left-handed

heavy

Majorana

on the quark

neutrino

of the first

counter

deduced

values

experimentally

very high

the limits

energy

a severe reduction parameters

grains

below

with

because

the limits

working

to study

developed

is also being

group”)

on the mass of a

weak boson, decay

the limits

M2” deduced from

element

is quite

small.

The

small.

These

M2”

elements,

and

is also quite

of the /3p nuclear

groups

10m6, and

for the 76Ge

on the mass M, of the right-handed

The matrix

for evaluating

CL)

matrix

MO”. will study

longer

2vpp

half-life

in several

region,

nuclei,

and

corresponding

to

1 eV.

The Milan

resolution

is being

1.6 eV, 2.3 - 2.5. 1024y (90%

‘) for the 82Se 2vpp

of the Osaka

to use cryogenic

development.

cube

superheated

experiment

the currently

mass region

of 1.2.

limit can be used to deduce

for Ovpp in a one order of magnitude

New techniques now under

half-life

pp nuclei

for p/3 experiments

as 1.2 -

the lower limit

mass in SUSY.

from data

interaction

In the near future the neutrino

Note that

and the mass MWR of the right-handed

M2” for “‘MO

will search

from

and the mixing,

neutrino

nuclear

the INR group obtained

are good candidates

(X) and (7) are derived

respectively,

mass and the gaugino

indicate

MeV,

1021y, respectively.

factors.

8, The Ovp/3 half-life

heavy

the results

loaM0 and 15’Nd,

on (m,),

0.2 - 0.02 . 10e6,

of Q = 3.367

and TF,Y2> 2.3.

10igy

large Qop, such as “Se,

detector

(DC),

and five natural

chamber.

For “‘Nd,

provide

been studied. Spectrometer)

of T$

limit

used a 40-silicon-detector

by using a large plastic

with

limit

CalTech-Neuchatel-PSI ionization limits

with five “‘MO

are enriched

to a level

are obtained

102’y

. 1018y and a limit of Tf,Y2 > 4.4 . 10zoy.

3.3 ‘i:z MPC.

used

of 1023y and 10”~

group”)

limits

obtained

array

The half-life

. 10”~ (68% CL).

are in the ranges

LBL-MT-New

Sources

purified

1.2::::

of 1.26f0.04.

-ray NeuTrino

of large drift chambers

(NaI).

A

The half-life

MeV have recently

GAmma

by NaI detectors.

arrays

give T,,, 2” -

data

(ELEctron

EL V consists

group.g)

and momenta.

measurements.

of Q = 2.034

of an 11-silicon-detector

disks surrounded

(68% CL) is obtained.

The

by geochemical

with a large Q-value

IV and V. EL IV consists (“MO)

by the UC1 (Irvine)

two /3tracks

. 10zoy (68% CL) agrees with the half-lives

-+ o+) = 1.1’;:;

and 1.0 f 0.4.10zo

MeV have been studied

was used to identify

detectors

for high resolution

group has been developing pp decays

for “‘MO studied.

of Ge, MO, Te,

and “jGe

/3p decays.

/3/3measurements

bolometric etc.

detectors

are with

A low background

Use of superconducting

F. Boehm, H. Ejiri f Neutrino properties and interactions

116c

2.

NEUTRINO

2.1

Search

OSCILLATIONS

for Neutrino

Oscillations:

MOSCOSO, DPhPE, Several presented.

new

beams.

experimental E776i4)

The

(fip) operation calculations. excluded Am2

results

Assuming region

agreement

the same

for the

V~ -+

neutrino

Combining

result

(Presented

oscillations

with

mass

have

them and to present at BNL

found

and mixing

using

by L.

values

angle

nuclear

with

the results

a new limit

the V~ Carlo

(2 -

4)

. 10e3 for

mixing. power reactors

obtained

of Am2

during

by Monte

for the v and V, the

(57 m) from the first two reactors data

data

by sin’ 28 e

eV2 for the maximum

us to reach

recently projects.

estimated

parameter

is limited

been

the future

the Ye and Vr wide-

in the collected

the expected

comes from three

the recorded allows

events

ve oscillations

is at the same distance

this experiment

and Perspectives

at the AGS

of e-(e+)-like

is in good

A new experimental third.

on

was performed

number

> 1 eV2 and Am2 = 9 x lo-’

detector

Status

13) The aim of this paper is to summarize

Experiment band

Present

CEN-Saclay)

= 9

in Siberia.13)

The

and at 231 m from the

with

a previous

set-up,i’)

10e3 eV2 at sin’ 26’ > 0.8 for

Qe --) V, oscillations. The needed

situation

show evidence results”) days

with

regard

of some

v-flux

an energy

threshold

are now available.

The

Homestake

cannot

results

The most recent (3.43kt.y)

good agreement

fluxes,

The

of neutrino results

Combining excluded

neutrinos

neutrinos

of a deficit The

are: an updater3) experiment

compatibility

is poor

between

and yields

oscillations,

poor (9. 10e3).

New 450

at 7.5 MeV,

neutrinos,

but the

of the Kamiokande

(156kt.y) these

may

which

are in

two results

to a confidence which

This plays against

experiment

allow us to reach

presented

results

on neutrino

and from the analyses

limits

in Fig.

or running

level of 2

modify

the

under

. 10Y3.

v, and vB

any conclusion

on the

of Am2

< 2

+10e3 eV2

mixing.

obtained neutrinos,

from reactors the limits

and of the

1 are obtained.

experiments

on accelerators

= 6

Am2

oscillations

for atmospheric

KAON).

with a neutrino

flux of ‘B

activity. combining

of = 40% on the vcL (fib) flux compared

10W4 for Y, c) vc (LSND)

obtained

time,

a threshold

< 5. 10e3 eV* for v,, ++ v, at the maximum

all the available

limit

with

with a constant

on sin’ 28 of a few times The

sunspot

oscillations.

experiments

New planned

with

are

Cl experiment

ruled out by this experiment.

of neutrino

of the Frejus

region

correlated

and 590 days

on atmospheric

remains

and new results

at 9.3 MeV

the predictions.

for ve +-+ Y,, and Am2 accelerator

time

are compatible

the hypothesis

confused

on 1040 days of running

and final results ‘s) from the Frejus

the compatibility

evidence

with

be completely

of “stable”

even with

is quite

experiment

shows evidence

with

the assumption

data

results

which

to the expectations

But

neutrinos

The results 16) from the Homestake

variations

from the Kamiokande

with

data

to solar

in order to add new constraints.

. 10e4 eV2 may be reached

beam from FNAL. ig) Also the limit

by using a 1000 t Gd-loaded

of 10 - 15 km from a power reactor.2”)

liquid-scintillator

will contribute

to reach

and for Ye ++ v, (CHARM-II, Am*

by irradiating

the IMB

limits P803,

detector

= 10e4 eV2 for v, H v, would be

underground

detector

at a distance

F. Boehm, H. Ejiri f Neutrinoproperties and interactions

l?lC

102 10 d-

1

2 N 5

10-l 1o-2 1o-3 10-4 10-4

ve H

vk

\

vp -

VT

Vee

VT

I 10-S

10-S 10-l

1

10-3 10-2 10-l

I 1

10‘3 10-2 10-l

1

sin228 Limits of excluded regions obtained by combining the results of accelerators and reactor experiments and atmospheric neutrino studies. Fig. 1:

2.2

A Large Low-Energy Neutrino Detector for Neutrino Oscillations Watch* (Presented by F. Boehm, CalTech)

and Supernova

We describe the results of our studies of a large, low-background, liquid scintillation detector with a fiducial mass of 1,000 tons capable of measuring positrons and neutrons from the reaction Pep + e+n. Efficient neutron detection is achieved with Gd loading resulting in neutron capture gamma rays totaling 8 MeV in energy. In developing the scintillator a light attentuation length of 6.lm at 450nm was achieved. With this a Gd concentration of 0.05% provides an optimum capture time (correlation time) of 46~s. With a positron kinetic energy threshold of 1 MeV and a neutron capture gamma threshold of 3.5 MeV (above the energy of natural radioactivities) the overall efficiency should be 50%. The Gd loaded mineral oil and pseudocumene-based scintillator is contained in a cylindrical acrylic vessel and surrounded by a lm thick mineral oil buffer which contains the 1,000 nineinch photomultiplier tubes (photocathode coverage 12%). We can determine the position of an event to 25cm from timing. To reduce the radioactive background from surrounding rock, an additional lm water shield is foreseen. Cosmic ray neutrons and muons are suppressed to an acceptable trigger level by placing the detector 200m underground. The background rate, based on a measured residual Th and U contamination in our mineral oil of 10-l’, is estimated to be two correlated events per day. The main purpose of the detector will be the exploration of neutrino oscillations down to mass parameters Am’ of 10M4eV2 (maximum mixing) and limits for the mixing angles sin2 20 of about 10-l (large Am’). To this end the detector will be installed (200m underground) at a distance of about 13 km from a power reactor. Per 1,000 GW (electric) reactor power there will be about six neutrino events per day at an estimated background rate of two per day. * F. Boehm, E. Bonvin, S. Hatamian,

S. Ludtke, K. van Blade1 and P. Willems, CalTech.

778~

F. Boehm, H. Ejiri / Neutrino properties and interactions

100

.OWl

,001

.Ol

1

.l

In a second goal the detector will serve as a neutrino observatory for supernovae and other astrophysical events. It will detect (and distinguish) the primary u, and the secondary se down to E, = 2.8 MeV. As a first step, we plan to build a 20-ton prototype. The Gd loaded sensitive volume is contained in a cylindrical acrylic vessel, 3m high and 3m in diameter. A concentric steel cylinder (4m high, 4m diameter) filled with mineral oil and containing 72 photomultiplier The geometrical photocathode coverage tubes surrounds the translucent inner cylinder. of 10% will be enhanced by reflectors. A further concentric cylinder, O.lm wider, filled with an unloaded scintillator serves as a muon veto. With this 20”ton detector an early oscillation experiment at I km from a reactor should yield a sensitivity of Am2 = 10m3 eV2, 2.3

A Future Neutrino LANL) The Liquid

groups

from

Oscillation

Experiment

at LAMPF

Scintillator

Neutrino

Detector

the California

Institute

of Technology,

(LSND)

(Presented

experiment University

by W. C. Louis,

is a collaboration

of California

of

at Irvine,

University of California at Riverside, CEBAF, L OS Alamos, Louisiana State University, University of New Mexico, University of Pennsylvania, and Temple University. The main physics objective is to search for vp + v, and cfi + 17,oscillations with high sensitivity in two independent ways by using neutrinos from B+ decay in flight and # decay at rest, respectively. Shown in Fig. 2 are the limiting curves expected from the I-i, ---t3, and I/~ + u, measurements of this proposal. The two measurements, carried out at the same time, in the ame beam(s), and with the same detector will provide independent checks on the validit 1 of the final result on neutrino oscillations not available from previous measurements. After two years of data collection, a 90% CL limit on sin2 26 of approximately 3.10-* for all Am2 > 1 eVz can be achieved, and a limit on Am2 of approximately 1.7. 10m2 eV2 will be obtained for sin’ 28 = 1. Other physics to be obtained includes a search for the lepton number violating decay p+ + e+Qe, measurements of the charged current reactions u,C + e-N and v,C ---t P-N, a measurement of the inelastic neutral current reaction YC + PC* (15.11 MeV y), a search for the rare decays T’ + vv and TJ-+ WV, and a study of vp elastic scattering.

F. Boehm, H. Ejiri / Neutrino properties and interactions

V9c

The proposed detector, shown in Fig. 3, consists of a cylindrical tank of dilute mineraloil-based liquid scintillator such that about 20% of the total light output will be Cherenkov light and 80% scintillation light. The tank is approximately 6m in diameter by 9m long with an active mass of 200 tons and will reside inside the existing E645 veto shield, which is located 27m downstream of the proton beam stop and is at an angle of approximately 17” to the beam direction. The proposed kinetic energy entering the beam line is 780 MeV and the typical proton current is 800pA. There will be 884 ten-inch diameter, very lowtime jitter photomultiplier tubes mounted uniformly over the inside tank surface (28% coverage). These tubes are manufactured by Burle Corporation (C83061E photomultiplier tube) and have excellent timing resolution, 2.3ns FWHM for single photons and full-face illumination, and single photoelectron separation.

Liquid Scintillator Detector

Fig. 3: A schematic viewof the LSNct detector, consistingof a 6m diameter by 9m long ~lindrica~ tank of dilute l~u~sc~l~tor with884 ten-inchd~meterphotomult~p~iertubes coveringabout 28% of the surface area of the tank

3. 3.1

NEUTRINO

SCATTERING

AND NEUTRINO

Neutrino-Electron Scattering and sin26w della Bascilicata and INFN Roma)

REACTION

(Presented

by P. F. Loverre, Universita

The measurement of sin* Bw in different reactions and at different energy scales is a fundamental test of the standard model of the electroweak interactions. The study of vQ (Y$) scattering on electrons is particularly interesting because it involves only leptons. The main difficulties of this study come from the very small value of the cross-section (0/S N 1.5 x lo-*2 cm’/GeV) and from the high level of background. The isolated electron produced in ,+ - e scattering has in fact to be discriminated from the hadronic showers produced in deep inelastic neutrino interactions on nuclei which have a rate N 2,000 times higher (the ratio of cross-sections being proportional to mN/m,). The basic requirements

F. Boehm, H. Ejiri / Neutrino properties and interactions

780~

high intensity beam, massive detector, for the study of vlr - e scattering are therefore: and good discrimination of electromagnetic vs. hadronic showers. The determination of sin’ Bw can then be performed

with good sensitivity a(vwe

R=

u

4

using the relation

vse)

(VP + i&e)

(1 - 4 sin’ 8~7 + 16 sin* &v) The use of R greatly efficiency

of the selections

reduces the systematic

errors:

and only the relative

neutrino

In spite of the experimental past by two experiments, CHARM

collaboration

difficulties,

the BNL-E734

22) They

at the CERN-SPS.

of sin* Bw with good precision with the foliowing ‘l)

BNL-E734 CHARM”)

R is practically

insensitive

to the

fluxes are needed.

a few hundred

USA-Japan

’

events were collected

collaboration

at the AGSzl’

were able to perform

in the and the

a measurement

results:

257 events

sin’ Bw = 0.195 f 0.22

195 events

sin* 19w = 0.211 f 0.37

I

The CHARM-II collaboration currently taking data at the CERN-SPS has collected by now more than 3,000 events, thus increasing the world statistics by almost an order of magnitude.

A value of sin’ Bw extracted

from the data collected

already been published. 23) Here I will briefly discuss the preliminary a new analysis which also includes the data collected The CHARM-II above.

detector

It is a sampling

was specifically

calorimeter

in 1987 and 1988 has result obtained

from

in 1989.

designed to match the requirements

with a total mass of 796 tons.

The target

stated

consists of

420 glass plates of 3.7m x 3.7m surface area and 48cm(= 0.5 x Xs) thickness. The sensitive elements are planes of plastic streamer tubes, one following each glass plate, with digital readout on the wires in one projection and analog readout on strips in the orthogonal projection. The discrimination of electromagnetic against hadronic showers is essentially based on the different widths: about 8cm for the electromagnetic showers and 80cm for the hadronic ones. The detector also allows one to reconstruct with high precision the direction of the electromagnetic direction

shower.

of the electron

The angular resolution calibration

data)

This is relevant

from vpe scattering obtained

since the a&e

is kinematically

by CHARM-II

(improved

with regard

constrained:

to the beam

E,O,’

< 2m,.

last year by the study of new

is 16 mrad/JE.

The data are collected

in the wide-band

neutrino beam at the CERN-SPS

with mean

energies of the vcL (fip) of the order 20 GeV. The results presented here include the I989 run with an increase of statistics of about 1.6 with respect to the data already published.3) Figures 4 and 5 show the variable EC@, ’ for the events containing a pure electromagnetic shower in the final state. background

The prominent

is due to quasi-elastic scattering

of v, and V, present

in the v,, beam

single rr’. The background

peak at zero is due to up - e scattering. on nucleons of the small contamination

and to the coherent

processes are well-understood

and diffractive

and have different

(-

production

The 1%) of

distributions.

From a simultaneous fit to the E and E,@,’ distributions of the signal and background contributions one obtains the following numbers of signal events: 1481 (v& beam) and 1621 (cp beam).

To get from the number of events the cross section ratio one has to compute

the relative flux ratio F. F is determined by directly measuring the rate of three different processes with known cross section and by measuring the flux of muons accompanying the

781~

F. Boehm, H. Ejiri / Neutn’no properties and interactions

500 w”

250 /--‘F;

E 0

2.5

75

5

Fig.

‘0

E,#$MeV)

”

(

.

0

.

,

.

2.5

N - eN (

5

715

I

Fig. 5

4

neutrino beam. The four different methods allow one to reach an accuracy of 2.4% on F. Taking into account the contaminations of wrong-sign neutrinos and electron-neutrinos present in the beam and performing the acceptance corrections (only electrons with energy between 3 and 24 GeV were accepted) we finally get the preliminary result: sin’ Bw = 0.240 f 0.009 (stat) f 0.008 (syst)

.

The main source of systematic errors comes from the background subtraction: final refinement of the analysis will allow the reduction of this error to 0.005. The quoted value of sin’ 0~ corresponds to the Born approximation. By including the four radiative corrections and assuming rn~ = mt = 100 GeV, one gets sin2Bw = 0.239 f 0.009 (stat) f 0.008 (syst) (with the Sirlin definition sin’ 0~ = 1 - m&/mz*). This value can be compared with the measurements performed in other sectors covering an impressive range of Q* values: Q* = lo4 GeV*

sin* 6’~ = 0.231 f 0.001

mz LEP)

Q* = lOi GeV*

sin* 0~ = 0.235 f 0.007

v,, d.i.s. (CHARM + CDHS)

Q* = 10-l GeV*

sin* 0~ = 0.239 f 0.012

u,,e (CHARM-II)

Q* = 10e6 GeV*

sin* 0~ = 0.219 * 0.019

Atomic P.V.

To conclude, I shall remark that the CHARM-II collaboration will still collect data in 1990 and perhaps in 1991 hoping to reach an accuracy of 0.007 on its final determination of sin* 6~.

F. Boehm, H. Ejiri / Neutrino properties and interactions

182c

3.2

Trilepton tion,

3.2.1.

Production

presented

Inverse Inverse

Standard

Muon

muon

model

by Neutrinos

by L. Gerla.nd,

and Inverse

II, University

Muon

Decay

(CHARM-II

Collabora-

of Hamburg)

Decay

decay

vpe-

predicts

-+ l-v,

the Born

is a purely

term

leptonic

of the total

weak reaction,

cross

section

without

for which

the

uncertainty

to

be u = c+~,E,

ci,,

=

verse

2m,G$/7r muon

=

decay

quasielastic-like appropriate ground

x 10e4*

background

occur the

measured

is the

asymptotic

at small

p:.

cross-section

(Fig.

6).

can hence

Recently

eas to be (16.93

f

p:

The

is much wider and almost

Vc distribution

the v,, distribution

have

cm’/GeV in vp beams

reactions

normalization

from

periments

17.23

can only

(1-&J

the CCFR24) f

to subtract

and muons.26)

1~2~1

< 0.405

3.2.2.

(CHARM-II)

Trilepton

0.41 (syst))

one

scattering section

the

weak

the interference with

respect

the nucleus.“) diffractive

+ A, also called

interaction

to the pure

involving

to the coherent

(off the nucleons)

‘,

precisely

j

0

muonic leads

charged-current

and can be calculated

component

In agreement The measured

with cross

of left-handed

elec-

1~2~ 1 < 0.43 (CCFR)

and

level (CL).

of W and 2 amplitudes

In addition

ex-

x 10W4’ cm’/GeV

by Neutrinos

vp(Va) + A -+ vp(Va)p’p*

to probe

and fiy are equal

form one obtains

at 90% confidence

Production

The reaction allows

In the helicity-projection

the back-

and CHARM-I125f

respectively. and (18.16 f 0.73 (stat) f 1.15 (syst)) x 10p4* cm*/GeV, the Standard Model, no energy dependence of &as has been found. section can be used to derive a limit for a possible scalar coupling trons

trident

only.

to a 40% reduction

interaction.

The

cross

given the electromagnetic

process,

where

scattering

uniquely Like

in v,e

of the crosssections

for 11~

form factor

of

is off the nucleus,

a

contributes.

CHARM-II

0.1

production,

currents

0.2

,

0.3

0.4

3.5

o:(GaV’/c’)

Fig. 6:

pi

tip normalized

distribution

In-

of the

equal for v,, and VP. After

be used

0.85 (stat)

slope.

distribution

of quasielastic-like

to the uI* distribution

(dots).

events

for

incident

v,, (solid

line)

and

783~

F. Boehm, H. Ejiri / Neutrino properties and interactions

80

-

0

20

40

80 100 120 140 160 180

60

Number of additional

Fig.

neutrino

of experiments

conclusive”)

until

observationzg)

Trident

low invariant consists where data

events

showing

of common

dimuon

pions

alone

neutrino

decay

leading

(3.0 * 0.9 (stat)

have

recently

mass

the

dimuon

for

hits

events of opposite

Neutrino

charge.

and anti-

data are combined.

A number been

activity

Vertex

7:

attempted

when are

the

characterized

no recoil events

before

activity

from

interacting.

to a signal

of 55 f

this

by an

charm It

process,

collaboration

but

(Fig.

none

reported

opposite-charge

at the vertex

7).

its

muon The

had clear

pair

at

background

production and single-pion production can be subtracted using experimental

16 events. per nucleus

X 10W41 cm’

f 0.5 (syst))

to observe

CHARM-II

This

corresponds

averaged

to a cross

over the neutrino

section

and anti-

spectra.

The

result

per nucleus, However,

agrees

but

well with a theoretical

does not allow

calculation

yielding

one to draw a conclusion

this has been the first time that

(1.9 f 0.4)

about

the weak interaction

x 10m4r cm’

the W-Z

involving

interference.

muonic

currents

only has been observed. 3.3

Determination

of the r-Neutrino

by H. Kolanoski,

University

In the Standard which

couples

lepton

universality,

left-handed

Model

to lepton both

like the other

In the following, from the ARGUS The leptonic

first

the T lepton

pairs

r Decays

(Presented

turns

into its neutrino

to ~LV,,) or quark have V-A

pairs

structure

qiqs;

by emitting

a W boson

Q = u, d, s).

or equivalently,

Assuming

the r neutrino

is

we report is a new,

on two new results

at the e+e-

storage

high statistics

on the Lorentz

structure

of r decays

ring DORIS.

determination

of the Michel

parameters

in

r decays:

(correspondingly results

from Parity-Violating

neutrinos.

r-

spectra.

(ev,

W vertices

experiment

result

Helicity

of Dortmund)

The

for r+). standard

-+ e-fi,v,

The Michel V-A

couplings

and

r-

parameters yield

+

p-~,,r+

are derived

values

from the lepton

pe = pp = 0.75.

are:30) pe = 0.746 f 0.054 zt 0.028 p,, = 0.734 f 0.055 f 0.026

.

The

momentum new ARGUS

784~

F. Boehm, H. Ejiri / Neutrino properties and interactions

Aexp(Qz) T*and 0.2

-

T- combined -+ + L-L-+-

0.0

1

-

0.6

0.8

1.0

1.2

1.4

1.6

1.8

I

2.0

QZ[CeVt/c4] Fig. 8 These high statistics measurements are consistent with the Standard Model and particularly do not confirm indications of previous experiments that the p parameters for electrons and muons might be unequal. From the measured Michel parameters the r neutrino helicity can be derived to be left-handed if one assumes that the ‘T decays via W exchange and that the eve and PLY, vertices have the standard V-A structure. A more independent determination of the v, helicity can be made by using a hadronic final state as spin analyzer. In Ref. [31] it has been pointed out that in the decay I=- 3 UlU, 4 p07r-vr -+ 7r+7r-K-v, the interference between the two possible amplitudes to form a p” from ~fnyields a parity violating asymmetry. This asymmetry is proportional to

combinations

where gA and gv are the vector and axial vector coupling constants. Standard left-handed T neutrinos yield ^(Av= 1. Experimentally the asymmetry is observed in the orientation of the three-pion plane with respect to the r direction in the three-pion CM system. The orientation of the pion plane is uniquely defined, e.g., by the cross product of the slower and the faster of the two identical pions. Averaging over all three-pion invariant masses, Q2, the observed asymmetry is +&r-) = -0.062 f 0.030 and A(r+) = $0.060 f 0.019 for r- and r+ decays, respectively. The change of sign between particles and antiparticles is expected if CP symmetry is conserved. The Q2 dependence of the background-corrected asymmetry combined for r- (with a sign change) and r + is shown in Fig. 8. The average asymmetry is A(T+ + r-) = 0.063 f 0.0155 which, for the first time, establishes parity violation in r decays (at the 40 level). The fitted normalization of the theoretical curve in Fig. 8 yields y~v = 1.14 f 0.34 which is consistent with left-handed r-neutrinos (TAv = 1).

F. Boehm, H. Ejiri / Neutrino properties and interactions 3.4

Neutrino

Activation

e- + l*N(gs) The neutrino with

a 15-ton

rest.

induced

tracking

Electrons

exclusive

of Carbon:

(Presented

reaction

reaction

calorimeter

emitted

Measurement

of the Exclusive

by D. A. Krakauer, between

the “C

detector

exposed

by neutrino

to the nitrogen

ANL,

absorption

ground

state

LAMPF

Reaction

E225

and i2N ground

was identified

-+

was observed

from

triggered

ue + “C

Collaboration) states

to 10i5v,/cm2

on carbon

185C

muon-decay

the

at

detector.

by the subsequent

The 15.9 ms

s) P-decay back to carbon. A clean sample of 181f17 such decays was used to measure ‘*N the i”,C(,, e-) 12N(gs) flux-averaged cross section to be 1.04 f O.lO(stat) f 0.10 (syst) x 10e41 cm’. This result this novelty, reactions

is the first real-time

and the direct

at astrophysical

data relevant The

(supernovae)

to weak nuclear

nuclear

observation

demonstration

physics

understood,

as confirmed

with several

published

energies,

physics

of the

of neutrino

-t

calculations.

1 + A cos 0, yields A = -0.166

provides

unique

transition

of the differential

f 0.152 in reasonable

neutrino

experimental

is believed

of the measured

Measurement

Besides

exclusive

interactions.

i2N(gs)e-

by the good agreement

radioactivity.

of measuring

this result

and astrophysical

v, “C

induced

of the feasibility

to be well-

neutrino

cross

section

da/d0

cross section,

=

agreement

with theoretical

expectation

theoretically

and provide

an additional

of A x -l/3. Transitions

to excited

test of the calculational as 1.41 f O.l7(stat) is 0.74 f 0.12, 4.

are less certain

f O.l5(syst)

in excellent

DARK

MATTER

DARK

MATTER

4.1

states

techniques.

The inclusive ve absorption cross section x 10-41cm *. The ratio of (exclusive/inclusive)

agreement

SEARCHES

Experimental

Searches

with Donnelly’s AND NEW

for

Dark

prediction

DETECTORS

Matter

Particles

is measured reactions

of 0.72. FOR

NEUTRINOS

(Presented

by D.

0.

AND

Caldwell,

UCSB) The

particle

is something constraints

which

outside

and recent

experiments,

accelerator

wide classes There

results,

of formerly

more massive

probably

more

Standard

Model

than

than

particularly especially

popular

those

90% of the mass of the universe

of particle

physics.

searches

are needed.

using

particles,

are few

Ge and Si ionization

at SLC and LEP,

candidate

There

A combination

have eliminated

such

detectors,

as dark matter

as weak isodoublet

neutrinos

N 30 eV/c2.

is convincing

evidence

from many types of measurements

that

there

is 10 - 100

as much matter in the universe as can be observed by other than its gravitational efAll common forms of baryonic matter can be eliminated as being this dark component

fects. except (<

minimal

on what it may be, and hence broad-range

of non-accelerator

times

constitutes

the

for small,

10s6

failed

stars

(“Jupiters”)

or lo6 solar masses).

baryonic

density

0 M 0.007 incredibly

to the critical

is observed, fine tuning

ward 0 or 00 unless constant.

While

Inflation

density

indicating

some

of parameters

or black

successful

for closing baryonic

in the early

it has the only time-stable theory

provides

a reason

holes outside

nucleosynthesis

theory

the universe dark matter. universe,

value of unity,

the range

of detectability

limits

the ratio

to w = 0.02 - 0.11, However,

unless

R would have been assuming

for 0 = 1, and some

of

only

there

driven

is to-

a zero cosmological observations

support

such a large value. Non-baryonic in the minimal Sz = 1. The

candidates Standard

for dark matter

Model,

which

are massless

but which would need a mass of N 30eV/c2

to produce

ve is known to be too light,

include

light

neutrinos,

but the v,, and v, are viable

candidates,

although

F. Boelzm, H. Ejiri / Neutrino properties and interactions

786~

there

are possible

dwarf galaxies. The axion, mass of lo-l5

problems resulting

eV/c’

to photons

sensitivity,

improvements

More with

accessible

small mass range an initial The

recent

generation the range

5-8

for weak accelerator to look Earth

has

recoils

width

at SLC

matter,

since

those detectors

in

or WIMP’s,

or Dirac

the former

a suitable

particles has a very

annihilation

has eliminated would

have

4-10

GeV/c2

also ruled out the possible which

had not yet been

rate

eliminated

a fourth-

had

to be in

mass

range

by the Ge non-

next. made

with

from

the scattering

semiconductor

halo of dark matter.

l/5 - l/3)

of that

per kg of detector

with underground

ray bombardment

ionization

of dark

matter

The expected While

detectors

detectors

as the

recoil energy

is small

and the signal

very low backgrounds

searching

rate

in the

for p/3 decay in 76Ge,

showed new background

of the detector

used

particles

goes into ionization,

per day.

to go to very low energies

are due to cosmic

strength,

and LEP

resulting (-

particles,

couplings

its mass

been

the galactic

only a fraction

when they were above

by their

of N lo*

can have a very wide range of masses,

as dark results

MeV region had been obtained of which

would need a

lack a factor

massive

can provide

of the 2’

described

be N 1 count/keV

altering

in

equilibrium.

neutrinos

search

moves through

would

These

Dirac

for nuclear

10 keV),

asymmetry

neutrino

GeV/c*.

interacting

with spin-dependent

while the latter

were in thermal

determination

broadest

CP problem,

32) have looked for axions

For a given interaction

to be dark matter,

experiments

The

are weakly

particles

couplings.

isodoublet

dark matter

are planned.

Majorana

Majorana

to the strong

sufficient

field, and while so far these

particle-antiparticle

when the particles

(-

in a magnetic

spin-independent

since

solution

and providing

0 = 1. Two experiments

experimentally

can be either

formation

from a possible

to provide

conversion

which

with galaxy

problems,

and surrounding

most

materials

ground.

These experiments use mainly spin-zero nuclei and hence are particularly sensitive to Dirac particles which exhibit nuclear coherent scattering, giving cross sections usually proportional such coherent

to the square

of the number

of neutrons.

All of the results

given below assume

interactions.

Three pp experiments have searched for dark matter. The CalTech, Neuchatel, Paul Scherrer Institute group 33) has achieved low thresholds and hence excluded Dirac neutrinos with the standard weak interaction in the range 10 GeV/c* to 1 TeV/c*. The first group 34) to do this work utilized the Pacific Northwest data. Now with better backgrounds their corresponding The

University

of California

(Santa

Barbara

Laboratories limits

and Berkeley)

and South

are 12 GeV/c*

and Lawrence

Carolina

to 4 TeV/c2.

Berkeley

Labo-

ratory

group 35) has the largest data sample. Their recent exclusion plot is shown in Fig. 9, the boundaries of which exclude at the 95% confidence level the particle with a particular mass and scattering cross section on Ge, assuming that particle alone is responsible for the galactic dark matter density of 0.3GeV/c2 cm3 = 5 x 10wz5 g/cm3. The curve labeled “Dirac Y” is the weak interaction cross section, and it is seen that such particles are excluded between 10 GeV/c* and 3 TeV/c *. The top boundary of the exclusion determined by the slowing of particles in the 600 m.w.e of rock above the detectors. ever,

all dark matter

of observations, passive

particles

including

Pb shielding

with larger

and also nearer

The UCSB/UCB/LBL

group,

efficiency by neutron scattering search for Cosmions,40) particles solar neutrino

problem.

cross

section

are excluded36)

data from this experiment

Cosmions

the Earth’s

joined

3’) taken surface.

by a Saclay

group

without

plot is How-

by a combination the active

(who measured

NaI and

the ionization

from silicon38)), have used 3g) Si ionization detectors to which could be not only dark matter but also solve the would be captured

in the sun and fall toward

the core,

F. Boehm, H. Ejiri / Neutrino properties and interactions

18lC

-24? 5

-

-28-

3~7 LIMIT

s m is o -32f5 -36

I 2

0

, 4

1 6

, 8

I IO

LOG MASS, GeV/c’

Exclusion plot foT the mad8 and elastic cross section on Ge for g: dark matter particles. The weak interaction CTOCW section is indicated by

Fig.

“Dirac

u “.

___~_......‘-------I _..-

..--

loor

Si, 3.7 kg d

3~ exclusion limits: -.-

0.1 0

v,~* =260 km/s vrmt= 300 km/s

I

1

1

I

I

I

I

2

4

6

8

IO

12

14

MASS, GeV/c2 Fig.

Exclusion

10:

as functions Cosmiong

neutrino

plots for

of their mass

are expected problem.

two values

and elastic

of the velocity

CTO~~section

to lie within the dashed lines,

of dark matter

on si.

Coherently

particles scattering

if they are to solve the solar

where their circulation to larger radii would cool the core by the N 10% needed to reduce the sB neutrino flux by the observed factor of N 3. Coherently scattering Cosmions would have to have masses and cross sections on Si within the dashed lines of Fig. 10 to cool the core sufficiently and not evaporate too rapidly from the sun’s surface. They would have root-mean-square velocities between 260 and 470 km/s. If the lower limit is used, the experiment excludes such Cosmions except in two small regions shown in the figure.

F. Boehm, H. Ejiri / Neutrino propetiies and interactions

788C

all such

300 km/s

For urrns 2 boundary.

Cosmions

are excluded,

as shown

by the other

exclusion

With such a wide range of possible dark matter candidates eliminated the continuing search becomes much more difficult. Light neutrinos, axions, and the lightest supersymmetric 4.2

particle

are now likely

Cryogenic

candidates,

Calorimeters

and all are very challenging

(Presented

by F. Probst,

MPI,

Munich)

Massive cryogenic calorimeters have several advantages neutrino detection. A unique property is their sensitivity variety

of suitable

imental

demands,

sections

(e.g.

materials

to search

spin-dependent)

the neutrinoless mass

absorber e.g.

to other differing

phase

A calorimeter

transition

detector

A weak thermal

is composed

coupling

is the thermal The

developed

of an absorber

sensitivity specific the

to a heat bath

coupling

heat

of suitable

of a pure

materials

falls mass

The

crystal same

the superconducting

transition

to the specific

becomes

any

with

cross

emphasis

on

group.4’)

with very low heat capacity

and an

of the calorimeter

r = C/G,

where

heat

Si and Ge.

For example

with

the Milan0

Group 42) obtained

based

with

again

G (units

temperature,

W/K)

an energy

where

high T the 0~ is

for superconductors where

the electronic

small.

solid

state

on the resistance

a commercial

eVK_‘,

holds

(T < 0.1 Tc)

temperature

so that

At low temperatures

approximately

negligibly

temperature-dependent

work has been

rapidly absorbers.

cmole = 1.22 x 10**(T/6’~)~

expression

well below

Most

exper-

temperature rise AT. AT is related C of the calorimeter: AT = AE/C.

constant

even for large

dielectric

temperature.

In principle

used,

by the Miinich

the temperature

a time

contribution mometry.

to specific

material-dependent

to the bath.

heat

can be obtained

Debye

returns

To with

temperature

specific

with

in the kind of thermometer

thermometers

attached thermometer to measure the particle induced to the deposited energy AE by the total heat capacity to its equilibrium

the detector

particles

and The

the active detector technique in searches for I discuss several approaches to larger P/Y-candidates.

mostly

superconducting

matter

searches events.

or to extend

@P-decay

calorimeters,

for dark matter to non-ionizing

allows one to adjust

for dark

to find.

property change

Ge thermistor

resolution

of AE

can be used for ther-

of doped

semiconductors

glued to an 11 g Ge absorber = 25 keV at an operating

tem-

perature To - 25 mK. Coron et al. achieved AE = 16 keV in a 25 g sapphire target To - 100 mK.43) For a suitable resistive behavior at T < 100 mK a very high precision

at of

the doping is required. The limiting problem however is the small read-out power handling capability of doped thermistors. 42) This “hot electron effect” has been recently studied in neutron

transmutation

thermal

decoupling

power

rises

the

doped

Ge thermistors

of electrons

and phonons

electron

temperature,

at T -

20 mIi44)

at low temperatures.

as measured

and was explained A relatively

by the resistance

of the

as a

small bias thermistor,

above the phonon temperature which is the quantity of interest. This effect reduces the sensitivity of calorimetric detectors. Another approach very similar to doped semiconductors is the use of commercial RuOs thick film resistors heat capacities.45) Their reproducible.

However,

less than that obtained crystal surface provides

with a modified low temperature the sensitivity

manufacturing characteristics

parameter

procedure to reduce their large (10 mK to 100 mK) are very

A = d(log(R))/d(log(T))

with Ge and Si thermistors. Melting good thermal contact of thermometer

appears

of the RuO2 powder and absorber.

to be on the

Magnetic thermometry based on a SQUID measurement of spin flips of paramagnetic ions in a garnet crystal in an external magnetic field has the advantage of dissipationless temperature measurement. Biihler and Umlauf4”) have achieved AE N 60 keV in a 7 g sapphire absorber at a very high operating temperature of To = 400 mK. A drawback is

F. Boehm, H. Ejiri / Neutrino properties and interactions

the long spin lattice

relaxation

changes.

For Ts = 400 mK

operating

temperature,

rr,, which limits

time

the authors

which is required

for improving

very difficult by the 12/T dependence of r,.. In the Munich group we have developed a superconducting

phase

superconductor contact.

evaporated

The

transition,

transition

onto the surface

calorimeter

is operated

in the

resistance:

region

which

of the

is rendered

of thermometry

thermometer

of the

induces

reduction

sensitivity,

method

41) The

of the crystal

change

speed of temperature

A further

the detector

an alternative

thermometer.

where a small temperature

the observable

T? = 140 ms.

report

789c

is a small

ensures

of

a good thermal

superconducting

a large change

using strip

to normal

in the thermometer’s

,n AR=gAT

A steep transition

(large dR/dT,

for high sensitivity. an optimally Results

The

requiring

resistance

(size:

2 mmx

high quality

of the thermometer

matched preamplifier. have been obtained with

thermometer

.

obtained

The measured

operated

we attribute

with semiconducting

temperature no attempt

running

with

crystal

(AlsOs)

at 135 mK.41)

an order of magnitude.

20 g) shows the expected heat capacity obtained with the sapphire calorimeter.

than expected,

an abnormally

an especially

thermometer

and an iridium

In a test with a 5 MeV

by more than

contributing

was made to obtain

an iridium

the SQUID

has been obtained. The corresponding exceeds the resolution of AT N 1 PK

thermistors

in the sapphire

films) is essential

which makes

rise of AT = 4.5 PK was 16 times smaller

to impurities

In this first test, presently

is small,

a 280 g sapphire

1 mmx0.4pm)

01 source, a resolution of AE N 70 keV (FWHM) temperature resolution of AT N 50 nK (FWHM) typically

of the evaporated

large heat

pure crystal.

on a high-purity

and also reproduces

which

capacity.

An experiment

silicon

crystal

the temperature

(IM =

resolution

With a pure 280 g sapphire crystal the energy resolution should improve to AE N 5 keV. Some further improvement is to be expected from optimizing thermometer and read-out parameters. However, the major reduction of detection To from should

thresholds

will come from going to lower operating

135 mK to the operating reduce

the absorber’s

temperatures.

A reduction

of

temperature

heat

of To - 15 mK of a tungsten thermometer by almost three orders of magnitude.

capacity

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