Volume 76B, number 2 PHYSICS LETTERS 22 May 1978

CHARGED CURRENT NEUTRINO INTERACTIONS BELOW 30 GeV

A.E. ASRATYAN a, A.P. BUGORSKY b, V.Sh. EPSTEIN a, R.M. FAKHRUTDINOV b, V.A. GEMANOV a, V.N. GORYACHEV b, E.A. GRIGORIEV a, N.V. KALGANOV a, V.S. KAFTANOV a, V.G. KARTASHOVA b, V.D. KHOVANSKY a, L.A. KLIMENKO b, V.I. KOCHETKOV b, Yu.G. KORNELYUK a, M.A. KUBANTSEV a, A.V. KULIKOV b, V.I. KURBAKOV b, I.P. MAKSIMOV a, A.I. MUKHIN b, V.F. PERELYGIN b, V.G. PLATONOV b, B.F. POLYAKOV b, A.N. ROZANOV a, M.S. RYABININ a, M.M. SAVITSKY a, V.M. SEREZHIN a, V.V. SHAMANOV a, K.E. SHESTERMANOV b, V.G. SHEVCHENKO a, V.A. SMOTRYAEV a, Yu.G. STROGANOV b, Yu.M. SVIRIDOV b, I.S. TROSTIN a, A.A. VOLKOV b, A.S. VOVENKO b, V.A. YARBA b, A.A. ZAITSEV a, S.A. ZELDOVICH a, V.P. ZHIGUNOV b, Yu.A. ZUDIN b a Institute .for Theoretical and Experimental Physics, Moscow, USSR b b~stitute/or High Energy Physics, Serpukhov, USSR

Received 22 March 1978

Charged current data of a spark chamber neutrino experiment at the 70 GeV Serpukhov accelerator (10 200 events in the v beam and 3600 events in the F beam with energies up to 30 GeV) have been analyzed. Total neutrino and antineu- trino cross sections and v-distributions are obtained.

We have studied charged current neutrino and anti- neutrino interactions in the energy interval 3 - 3 0 GeV which lies between the well explored regions 2 - 1 2 GeV [1] and 3 0 - 2 0 0 GeV [2,3]. Data were taken in the wide-band neutrino and antineutrino beams of the Serpukhov 70 GeV accelerator with counter techniques and iron target [4]. Parabolic focusing lenses provided us with pure neutrino and antineutrino beams. The ad- mixture of F's in the neutrino exposure and that of u's in the antineutrino exposure was ~2 -3%. Intensities and profiles of the proton beam and muon fluxes in the shielding were continuously monitored.

Charged current candidates had a vertex location within a limited volume of the production part and at least one track with a visible range Rvi s ~> 48 cm of iron. That left us with ~ 10 200 neutrino and ~3600 antineutrino events.

For determination of the neutrino (antineutrino) energy spectra a special experiment was performed, in which pion and kaon production on the target identi- cal to that of the neutrino experiment was studied [5]. Using these data we have calculated the neutrino and

muofl spectra for our particular focusing system geom- etry. The agreement within 3% between the shapes of the calculated muon spectra and those measured in the shielding ensures that we correctly predict the shape of the neutrino spectrum as well. The absolute u and

fluxes (necessary for derivation of the total cross sections) were determined from the observed muon fluxes with 7% accuracy.

After correction due to scanning and geometry ef- ficiencies total neutrino and antineutrino cross sec- tions averaged over our energy interval were obtained. The results were recalculated for the isoscalar target assuming avn /o up = o-YP /a -~ n = 2 (~2% correction). Under the assumption of a linear rise of a v,~- = aV,~E

the slopes are (see fig. 1)

a v = (0.72 -+ 0.07) X 10 -38 cm2/GeV

( ( E ) = 11 GeV),

c~ ~- = (0.32 -+ 0.03) × 10 .38 cm2/GeV

((E v) = 7.5 CeV).

239

Volume 76B, number 2 PHYSICS LETTERS 22 May 1978

> '.3

u g~ I 0

~0

1.01

0.8

0.6

0.4

0.2

O o

_ l T

N E U T R I N O

ANTINEUTRINO

l i

B,O GGM V , ~ BEBC

& , ~ CITF

Q,O THIS EXPT.

-+--++

I i I i i i i i i

2 3 5 I0 20 30 SO 100 200

E,,g (GeV)

Fig. 1. Slopes of the total neutrino and antineutrino cross sections.

The ratio is R = ov-/o v = 0.44 + 0.03. The errors quoted include both statistical and syste-

matic uncertainties ,1. Within errors the slopes are the same as those explored in other experiments in neigh- bouring energy regions.

For further analysis we selected events with muons punching through at least 5 sections of magnetized iron (lB. dl = 3 T m). In addition a cut Pu/> 5 GeV/c was imposed. About 1800 neutrino and 640 antineu- trino events passed these criteria.

We analysed our data in terms of

q2. E. cos0) (1) o= 2Me; =-ag(1 -

As seen from eq. (1) o is a convenient variable for counter experiments where the muon is unambiguous- ly identified and its characteristics are well measured.

o-distributions corrected for efficiency are shown in fig. 2. The total number of events N = f(dN/do) do was estimated by extrapolation into the blind region o = 0.22 - 1. The contributions of this region were found to be (18 + 2)% and (4.5 -+ 0.4)% for neutrinos and antineutrinos, respectively. Monte-Carlo calcu- lations have convinced us that the efficiency is but weakly model-dependent: Ae(o)/e(o) £ 5% (this un-

¢I R is less affectedby systematic uncertainties than the ~'s.

mo ~ ~ N O ~ ;0

IO - 2 i i i i i 0 . 0 5 . 1 0 .15 . 2 0 . 2 5

V

Fig. 2. Corrected u-distributions. Solid curves are QPM pre-

dictions [61.

z.> ~ln~ 10-1

- I Z

240

Volume 76B, number 2 PHYSICS LETTERS 22 May 1978

u.l "X.

0.3C

0.25

0.2C

0.1!

r ~ r i

0 3 0

0.05 __

O[3 GAt~GAMELLE X 15' FNAL

Q I I I BEBC • TH IS EXPT.

N E U T R I N O

÷, ,

A N T I N E U T R I N O

I I I I I / I L I I

2 4 6 8 10 20 40 60 100

E G e V

Fig. 3. (q2)/E versus energy.

certainty was included in the errors). The agreement with QPM predictions [6] is reasonable except for the first points where q2 is too small anyway. Mean values derived from fig. 2 are:

(v) u 0.130 + 0.015 ( ( E ) v 12.4 GeV)

(v)v = 0.083 + 0.005 ( (E) v = 9.2 GeV) .

They fit in with the general trend of existing data [3] , i.e. a smooth decrease of (q2)/E with energy (see fig. 3).

A combined study of neutrino and antineutrino scattering may yield information on individual struc- ture functions. We concentrate on the quantity

= rr ( d o u da~- 1 A(v) ~ \ d q 2 ~ q 2 ]

1 v g

= f - - V

(2)

+ f 2 v/x - o2/x2 4

0

where v = q2/2ME. For an isoscalar target under the assumption of

charge symmetry the first integral is equal to zero so that only F 3 is left. Therefore 2x(v) is an efficient tool to explore valence partons.

Since our target is not purely isoscalar the first in- tegral is not zero. It can be estimated from the Adler sumrule [7] to be less than 0.1.

Assuming a linear rise of Oto t with energy we re- write the left-hand side of eq. (2) in the form

el o.

i

*,o "o v

1,5

1.0

o5}

0

• I T E P - I H E P E = 9 - 1 2 G e V

G G M E = 6 - 1 2 G e V

/X H P W F < E > = 1 5 G e V

0• ~ L J .215 • 5 . 1 0 . 1 5 . 2 0

v

Fig. 4. ,~ (v) = (rr/G 2) (daV/dq 2 - daV/dq2). Solid curve is QPM prediction [6].

241

Volume 76B, number 2 PHYSICS LETTERS 22 May 1978

d N v

2MG 2 dv ] J " (3)

The behaviour of A(o) as o goes to zero was pre- viously studied in refs. [ 1,8]. Results were obtained in the energy regions 2 - 12 GeV (Gargamelle) and 15 - 64 GeV (HPWF). While the GGM data converge towards QPM (or, more generally, Adler sum rule) pre- dictions, those of HPWF show the opposite tendency.

In fig. 4 we present data o f this experiment ,2 along with those of GGM and HPWF in the neighbour- ing energy regions. Our A(v) does not exhibit an anom- aly at v down to 0.01. Moreover, it agrees with QPM

bet ter than individual o-distributions do.

:~2 A (v) is given for our target S6Fe. One standard deviation of av (c~-) shifts all points in fig. 4 within statistical errors.

We are grateful to the accelerator staff and the scan- ning personnel of both laboratories for their efforts. Stimulating discussions with L.B. Okun, B.L. loffe and V.I. Zakharov are gratefully acknowledged.

References

[1] H. Deden et al., Nucl. Phys. B85 (1975) 269. [21 D. Perkins, Proc. 1975 Intern. Syrnp. on Lepton and pho-

ton interactions (Stanford, 1975) p. 571. [3] P.C. Bosetti et al., Phys. Lett. 70B (1977) 273;

B. Barish et al., Phys. Rev. Lett. 39 (1977) 1595. [4] A.E. Asratyan et al., Phys. Lett. 71B (1977) 439. [5] K. Akerlof et al., IHEP preprint 77-86 (1977). [61 R.P. Feynrnan and R.D. Field, Phys. Rev. D15 (1977)

2590. [7] S.L. Adler, Phys. Rev. 143 (1966) 1144. [8] D. Clirie, Invited Talk at the lrvine Conf. (1975).

242