CERN-NPA/Int. 69-10 19.6.69

a b I .. Budagov, D .. C. Cundy, C. Franzinetti, W. B. :F'retter,

H.W.K. Hopkins, C. Manfredotti, G. Myatt, F. A. Nezrick,c

M. Nikolic>d T. IL Novey)e R. B. Palmer,£ J.B.H. P.attis(m,

D. IL Perkins, C. A. Ramm, B. Roe,g R. Stump,h

ii. Ve.nu;;,:;, H .• W. Wachsmuth, H. Yoshiki

CERl~, Geneva, Switzerland

Using a propane bubble charr.her the avE:~rage cross-section for

single pion production by neutrinos on free protons has been determined to

b (1 13 ..i.. 0 28) 10-38 2 f ·. ~ b l d 4 G V e • . ~ • x: cm or neutr:i..nos or energy etween an · e •

* The invariant mass distribution of the (rrp) system indicates that N (1236)

production is the dominant: process. Angular distributions of the pion in

the (np) rest frar.ie are also pre:sented. The results of the experiment are

compared with theoretical predictions.

_......__·--------~---~----·--· ' ' '

8visitor from Labora.to·ry for Nuclear Problems, Jcdnt !nsti t.ute for Nuclear Research> Dubna, U.S.S.R.

bVisitor from University of California: Berkeley, California, U.S.A.

c Now at lfational Accelerator Laboratory i Batavia, Illinois, U.S.A.

'\fow at Institute of Nuclear Science, Beograd-Vini!a, Yugoslavia.

E!yisitor from Argonne National Laboratory:. Argonne, Ulinois, U.S.A.

fvisitar from Brookhaven National Laboratory, Upton, New York, U.S.A.

iv'isitor from University of Michigan, A..lln Arbor, Mi.c.higan., U.S.A.

hvisitor from University of Kansas, l,awrence, .Kansasi U.S.A.

PS/7276

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1 The CERN' Heavy Liquid Bubble Cha:nber with a propane filling was

exposed at the CERN PS for 1.08x106 pulses> corresponding to 6;8x1017

f 20 6 C V/ h .t:: 'L- • d. . b 2 protons o momentum • e c on t e target or t11e improve neutrino earn.

The neutrino spect"t'um is shown in Fig. la. It is based·on measure-.

3 men ts of the muon flux in the neutrino filter, and is estimated to be accu-

rate within :±: 15%. This error includes an estimate of systematic effects.

The spectrum calcuL1ted by using the available pion and kaon production data

is consistent vi th that of Fig. la, although subject to greater uncertainties.

The film was scanned for all interactions in the propane, whether

due to incident neutral or charged particles. 'l'he scanning efficiency de-

termined from a rescan of 14% of the film was (90 ± 10)%. The error allows

for the possibility o.f a variation in the scanning efficiency as a function

of position in the chamber, for which some evidence was found. · The events

were measured on image-plane digitizers and the measurements passed through

the DRAT-GPJ.Nn4 chain of progrannes. This report is based on 85% of the total

data.

We have determined the total and differential cross-sections for

the process

-+ VµP - µ. iT p (1)

occurring on the free protons in the propane• A fiducial volume of 509 Htr.es

was chosen to ensur.e good measurability. .All events which were compatible

with this three-prong topology were retained.

Use was made of bubble density and. delta-ray information to decide,

where. possible, be.tween pion and proton. hypotheses for .fast positive tracks.

If a delta-ray indicated that one of the tracks was incoming, the event was

rejected. There were 121 accepted events. Among the 121 events were 17 in

PS/7276

- 3 -

which either the oi proton interacted after such a short distance that

its moi:nentum co1.:ild be measured with an uncertain In

order to minimize back , thes<: 17 evE:nts were removed from the

and corrected far statistically.

!''or e. vent tlH:~ t tal mom:2'nt:i.b1 of all t:r..s.cks resolved the

neutriilo direction ( ·~·;as calcu,lat(~d 41 I.11 re.action this ty will

equal neutrino energy and in be of the order of l GeV or mo:re.

In Ct)nt:ras t for an r.::vent caused an' pion. will in be

track will be assumed for this

c.alculat.ion. A cut was therefore made

events bv ~

For the

neutrino b(~arn di.rec tion,, were calculated·'

of the mesons and t:he kinetic energy of the

For events of

> 300 Nineteen

tudinal momentum

Les transverse to the

is t.'he su1n o.f

and P should differ from r zero only by measurement errorB, for events i.n Fet"1ni rnoti.on.

and scattering in e nucleus can

distribution of £~PX. and PT for the

clear concentration of events with

as candidates for reaction

events

and x

va.tw;;s of these

. ' . is snotv11 1.n . 2.

f < 120

240MeV/c. As o:f th.e measU"t:ement ex.·rors :indic.ated that . =~=

genuine e.vents would be ected by these cuts. Fi t\./.o events

There is a

and <

% 0£

all

selection criteria and are used for the cross-section deter111ination.

The events may contain the types of background:

1. neutron interactions which simulate neutrtno

PS/7276

2. Even.ts caused p:Loi. .. rn ·which are not removed

the various criteria.

3 . Events cont a unidentified tracks.

1+. Ev+::.nt of the

5 . .Events in carbon .

l.n J1eut:.ron.-in.dl1~::.·e.d e1.lt?:nts li·/it'h. tl1~~ sarne ogy as reacti.on (1) the

interact in charJleT.'. Since no such .:vent with an. interac negative pion

passed all the cuts~ ·we f:':':.st:L,1ate the neutron to be less than 1.5

events.

Among a ch.osen set of events which wou.ld hav€.~ been candi-

dates for reaction had direction of the incoming not been indicated

by a delta-ray, there was no event which passed selection criteria and 37

had II' < 300 lfaV/c. x cut on X removed events from our original sample.

On this basis we es a bad·i.gtound of less than 0 .5 events from this source.

Of the 52 selec.ted events, 23 contained one. tive track whic.h was

too energetic l GeV/c) to be ionization and which did not have~

a. delta-ray of sufficient: en(~rgy to di.st the and proton

hypotheses. The nature. of the .i.cle was tak(~n as to satisfy the

~ + topology (µ n p). A statistical is ed on those pions ide.n-

ti f ied by a del ta~·ray to an estimated back of less than 1 • .3 events

of the types (p. - + TT ) or pp) among 23 ambiguous events.

Twelve. eve.nts of (p. or - + n 2·yp) were observed. If

PS/7276

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the y-r:ays had not [".ieen converted, three of these events would have been in-

U" '" the~ calculated average y-ray conversion

probability of 0 .23~ we estim2te a of (4,3 ::±: 2, events among the:

52 ted events.

we have studied two types of

a. events of the previous

neutrino .s in

b. el as prOCtcSS vn """ii· µ p in propane.

a. a. s c of (µ, events observed in freon and normal-

izing t.o the propane <lal::a on the basis of those ~~vents with lt.iPxl > 120 NeV/c

or PT > 240 MeV I c 31 '<?e ob ta in :1 back

events from bound n:uclecms in th,;;

estimate of (3.2 ± 1.2)

used to define the hydrogen sample.

However it is that background wou1d be hi when the events occur

in carbon rather than. in si.nce2 the on and proton ha,ve a lower proba*

bility to troy mom.entum balance by intera,~tion in nucleus. Calcula-

tions based on nuclt~.a:r sizes m:td pion-·nucleon and proton-nucleon cross-sections

caused by freon. '111e background estimate thus. becomes (4 .8 ± 1.8) events.

b. With a of 81 (µ. events observed in the present

ment we have made a estimation using those events with 120 < !tiPxl <

220 Mli:V/c and PT < - . - + to rwrmalize between the (p. p) and (µ rr p) events.

In this region Ferm.! motion should the major cause of unbalance and this

should be the same ln the t-.,,10 i?!vent We thus obtain a background esti-

mate of (4.0 :±: 2 events from bound nucleons.

Since estimates a. and b. are. e we comldue them to obtain

an estimated carbon. of .6 ±: 1.5) events.

PS/7276

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The total background est.imate becomes (8.9 :±: 2.9) events, i.e.

(17 % 6)%.

In order t:o calculate the cross-section for process (1) on free pro.o

tons we make the following corrections to the 52 observed events: background

subtraction (- 17 ± 6)%, un.In.ea.surable events (+ 16 ± 4)%, scanning efficiency

(+ 11 ± 11)%, good events failing selection criteria (+ 5 ± 2)%. The energy

distribution of the 52 events and the resulting cross-sections a.re shown in

Figs. lb and le respectively. In calculating the cross-section the non-uni-

formity of the neutrino flux over the. chamber was tal:.e.n into account.

6 We compare our data with theoretical predictions by Adler 1 Al tm::·elli

et al./ and Salin~8 These authors have calc\.1lated thli! cross-section for pro-

cess (1) with the nucleon axial-vector form factor YA parametrized as FA =

(1 + 2 2 -2 q /MA ) , where q is the four-momentum trans fer between the leptons"

The values of MA used by the various authors are indicated in Fig. le. It

ma'y be seen that the data are in good agreement with the calculations of

Altarelli et aL 1 · a11d of Salin with a value of MA close to that suggeste.d by

studies5 ' 9 of the quasi-elastic process, vn -• µ.-p, while the calculation by

Adler with a similar MA gives a lower cross-section.

For a more quantitative comparison we have computed the observed cross-

section in the region 1 to 4 GeV where the neutrino flux can be determined with

greater accuracy and the predicted cross-sections are approximately constant •

. d ( - + -38 2 We fan , cr vp .-. µ. rr p) "" (1.13 ± 0 .28) x 10 cm , where the error quoted

is partly statistical and partly the result of the estimated errors in the

neutrino flux,, scanning efficiency, and corrections. 'l'he various predict.ions

for this cross-secti..on are:

-+ 0.42 x 10-38 2 2 (Adler) cr{\lp _, µ. n p) = cm 1 MA = 0.84 GeV/c

0.85 x 10-38 2 . I 2 (Altarelli et al) "" cm , MA = 0.84 GeV c

0.77 x 10-38 2 2 (Salin) = cm , MA = 0.88 GeV/c

PS/7276

~· 7 -

3 ar02 shown the dis in ;.:md in the square of the

invariant mass of the p ) for the !+6 selected events

with EVIS > l GeV. The: his

space di .. .stt~"ibu t ion~ :Ibc expected di.s tri.bu t ion

for <mtirely 23 excitat.i.on is atso shotvn. It is clear that reaction (

y i.11 tb.e. forrnatio11 of'

">. vious experirne~ts in freon.J

We na\tfJ; alsc.· ttrdie.d tb.e

the pre-

dist fbution of the in the (1rp)

rest f ran:e . 'to do th .fiducla1 volurr:e than

tem.s: those proposed t~dl and ., . tr .• 10 b2roan and weitman. The definitions of

these systems are in • 4b resp cc ti The di.st:ribution.s

in. Adler's ,5 f:o:c events with covered

by his a.re shown in Fig. Lia. The dlstri .. butions in the angles e I

cp 1 defined by Herr::ian a:cd Veltrnan 2 fen: thosz: events with 1 .. 3 ·< < 1.9 c

For t.lon Berrn~.tn artd \'teltn:an

calculate th<:tt as s ..... 0 the distribution of the pion should become

) a; l + 3 CO (2)

The observed. distributLc~n in cos9 1 is consistent with Hm.Jever the dis tribu-

tion in cp' shows a 2.9 stancfard deviation as.JY.i:me with respect to the v)

plane. Conservation oJf. would require t this distribution c.

6 Adler has suggested l:I';::tt interference between the and tht.:i non~resonant

background ·.r·.ise to an effect of th.is n.ature ..

that at the

the various tions the determination of MA from our

measured cross-section.. The calculations of Al et al. and of Salin suggest

PS/7276

2

- 8 -

M """l A.

'ii - wh(::reas that of Adler would indi.ca.te > 2 Ge.V/

dlst.ribution in. dietr:Lbution of the pion indicate

is dominant process, but that inter

wi.th the non-rescnant c.:in

and Li i:r assistanc in the ex-

posure, support of obr , and stafJ:s i~s

Scienti Staff of N.P.A. Division

PS/'1276

1. C~ A. R3:m:rn and L, tti - Proc. Int. Conf. on Instr., t page

127 (1960).

2. A. Asner and Ch. Iselin - CERN 65-17,

l i.

3. D. Bloess~ J.B,2L Pattison G, PL.1ss 1 IL Rusch, W. VE~nus, and H, W. Wachsmuth -

H. W. (to he publ

4. Soop - NucL Te:.:hn. Instr. I I~ 216 (

R. Bock - NucL (19

5. M. M. Block et: aL - Lett . .s~rs (19

9

G. Altarelli, ' 1817 (1965).

8. Ph. Salin - Nuovo Cimento

9. J. L~vtH~th - IIuovo C i.mcmto

10. S. l)errn<:m and M~ Veltman -, Nuovo Cirnento 993

pS/7276

- 10 ..

Figure Captions

la~ Neutrino flux ove:r cm radius detector.

lb.

2.

3.

distribution of events accepted as - + -•µrrp.

Cross-section for vp - µ- The errors own are purely statistical;

the systematic errors a.re _;..

for candidates, LlP X vs.

2 q and (rrp) distributions for

Definition of used

fen: events w:Ltb < 1.39 GeV/

events with > 1 GeV.

Adler and distributions in cost.p and &

4b. Definition of lJ.S ed Berm1:m and Vel trnan and distributions

in cos9 1 .and

sin2er./2 < 0.1.

PS/7276

for events with 1.3 <

!..... z 0 l-o ·4 0::: 10 -­Q_

10

(j) f­z

0

15 -

~10 -Li.J

LL. 0

2

r---·

______ _]

3 4

E. GeV

j I I I I I I I I I I I I I I I I I I I I

' I ' I I I

6 8 10

(b)

_____________ L ______________ J_ ___________ _L ______ .......•.. L ... ----1 ;-------~----------~-'-~---~--~ 0 I 2 3 4 6 8 10

E, GeV (c}

3

(\j

E 2 (.)

ct) I')

'o b

0.8

0.6~ ~ ~ (9 0.4

l

•

0.6 0.8

• • • • • • • •• • • • • •

•• • • •• • • • . .,.

• •

• > • • 1ev

• 2 M (7Tp)= 2.62

·1 > •• 2 ev • • M (7rp)=2.85

N*(l236)RESONANCE

I

1.5

1.0"!-. -!< ~ C9 ...........

Q.5No-

-"'---.....A--A..--1--~ 0 6 4 2

NUMBER OF EVENTS

A A A (Pu x ) x K

sird1

ADLER ANGLES

cos rf,

O'-----~-------'···-----'--·--·' -IBO -90 0 90 180

3 DEGf~EES

( 0)

BERMAN -VELTMAN ANGLES

-1.0 -· .. 5

r­r-

0 cos e'

05

f 11 t- r--tJ j J tL_J

____ J... _______ J_ ___ ..J_ ______ _

-180 -90 0 90 180 ¢>1 DEGHEES

( b)