Structure functions and the emc effect -where are we now and where are we going to ?-

NuclearPhysicsA434 (1985) 3c-24c North-Holland.Amsterdam

STRUCTUREFUNCTIONSAND THE EXC EFFECT -WHERE ARE WR NOWAND WHEREARE WE GOING TO ?-

S.J.

Wimpenny

Department

of

Physics,

University

of

Liverpool*

INTRODUCTION This deep

review

inelastic

shall

concerned

concentrate

ment on the

directly

reader

is

with

of

to

to

of

advances

the nucleon

structure

function

reviews

of

Dydak’

study

of

functions.

and will

only

measurements

For a more complete

recent

in the

structure

the “EMC Effect”

concerning

subject.

the

experimental

study

conventional

this

refered

recent

and the

on the data

status

relate

1.

is

scattering

discussion

I

com-

where they of

these

the

and Rith’.

STRUCTUREFUNCTIONSAND DEEP INELASTIC SCATTERING One of

provided cribed

the most direct by deep

in terms

inelastic of

picture

electron,

sum of

quasi-elastic

via

by Bjorken3 - 15 years

For an incident process

* Present

the

exchange

of

is

address

lepton

supported

beam of

EP Division,

energy,

is

well

is

des-

quarks

which

neutral

gluons.

In this

described

by the

incoherent

This

scenario

originally

has formed

the

effort.

E, the basic

1

0375-9474/85/$03.30 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)

the nucleon

charged

by experiment4

CERN, Geneva.

of

can be extremely

fractionally

and theoretical

in Fig.

structure

electrically

scattering

experimental

illustrated

of

from the quarks.

and rapidly of

the

The data

consist

scatters

proposed

studying

which

muon and neutrino

basis

tering

of

scattering.

nucleons

are bound together

of

methods

Switzerland.

deep

inelastic

scat-

S.J. Wimpenny { Structure $utctions and the E&K effect

Scattered Lepton Incident

Lepton

y’p

Final State tladrons

Target Nucleon

Fig.

where

the

quark

Q

and probe

2

u

Y=

in

the

mass to

the

are

squared, lepton

Process

below:

energy

of

the

probe.

angle

scattering

in the

lepton-nucleon

of mass.

fraction

The cross-sections

of

single

the

nucleon

momentum carried

photon/boson

exchange

by the

approximation

struck

quark.

5 are

then

by: charged

(e or u) a

lepton

da dxdy= tbl

defined

centre

02

(af

kinematics

relates

B

x = 2l4v

given

Scattering

invariant

PV

1

Deep Inelastic

*RR Q

scattering:

[xyaPl(~.Qa)

neutrino/anti-neutrfno

(11

+ (l-y-‘$)F2(~,p2)]

scattering:

?!

da” dxdy= where

F1 and P2 are

way anologuous functions function vation

GlnE S

of

to

the

the

parity

+ (l-~-~~‘Xt

neutrino

weak

the

than

cross-section

interaction

and its

nucleon

GR and GM but

just

Q2.

because sign

(2)

+ y(l+xF3(x,Q2))

target

Form Factors

x and Qs rather

in the

in the

F2(x.Q2f

STRUCTURE FUNCTIONS of

electromangetic

two variables

F3 appears of

Ixy2Plfx,Q2)

A third of

changes

the as

defined

in

in general structure non conserv + ;.

a

S.J. Wimperzny / Structure functions and the EMC effect

F1 and F2 are

related

via

F2Cx.Q’) R(x,Qa)

functions

is

given

- ZxFl(x.Qs) (3)

2xFl(x.QL)

Fl,F2,F3

by the

of

Model

incoherent

Thus for

the

(Q.P.M.1

sum of

u-nucleon

F2(x)

= f ef

qf(x)

is

ef

the charge

interaction

is

defined

in terms

of

the

struct-

or R,F2,F3.

In the Quark Parton

nucleon.

expression:

(I+$)

=

Thus the unknown physics ure

the

5C

picture

scattering

of

the

nucleon,

from the

F2 (at

constituents

large

of

Q2)

the

scattering:

xqf(x)

(4)

where the momentum distribution

and

Also

is

the constituent 2xFl(x)

of

the

quarks

the

f

th

quark

in the nucleon

quark. 1 2 so that

spin

(high

or more generally,

=

of

- F2(x)

- 0

R(x)

th

have

and R(x)

f

function

for

quarks

4(p ‘+I4 s) ++-

and the neutrino

of

Q2)

(5)

mass M and transverse q

(low

momentum PT:

Q=)

and muon (electron)

(6) F2’s

are related

by: (7)

Experimentally the measured (a)

opN+ FFN

(b)

o

UN

VN

+o

the

charged

;N

GN

functions lepton

given +F

(c)

d

(d)

measurements

--d

structure and neutral

are

determined

cross-sections

from combinations listed

of

below:

R

UN 2

(8)

+ XF 3 of

UN

o at fixed

x,Qs

values

but using

different

beem energies,

E-rR (e)

0

GN -

(1-y)’

a

VN limit Y-+1

+ q.

the

antiquark

or

sea quark

distribution

function,

6c

S.J. Wimpenny

The results

in general

/Structure

agree

very

functions

well

and the absolute normalisations agree 2 In particular the QPl4 picture Qs-dependence

Chromodynsmic eozpilation X.

of

the

can

one

shape

seen

which

the

Q* region

clearly sea

quark

is

their

x and Qs-dependences

5-7X between

seen

to work very

different well

exper-

and only

be understood in terms of Quantum 1 corrections. As an example Fig. 2 shows

(QCO) radiative for

Here

the

is

in both

to within

merits. small

and the EMC effect

10 < Q2 < 30 GeV2 plotted

see

a

can

the

applicability

distribution

of

which

as

the

falls

5 function

QPbl iS

rapidly

factor

with

a data

of and also

x and dies

out

by x * 0.3-0.4.

CDHS

X 1.07

a CCFRR

X 0.90

o CDHS

X 1.07

n

1.4

1.2

D CCFRR x 0.90

1.0

ir” +cDHs “F7’ jy

x1.07

0.8 i

0

0.4

0.2

1.0

0.8

0.6

X

Pkg. p2s

2.

xF3,

3 for

the

2

Q2 region

10 4 Qp < 30 GeV’

THE EWC EFFECT - WHATIS IT!’ Until

atomic tion tions,

recently weight

was

A that

simply

i.e. Fr(xf

experimental

for

apart

i multiplied

and theoretical from

Fermi

by the

dogma said

motion

sum of

effects, its

the

constituent

that

for

nucleus nucleon

a nucleus structure structure

of funcfunc-

iron

= $6

f26F2P(x)

+ 30F2n(x)l

(91

SJ.

7c

Wimpenny 1 Structure functions and the EMC effect

”

where

F p and P2 are the free proton and nucleon structure functions respect2 However in 1982 the European Muon Collaboration (MC) observed that the uN function F2 of the structure measured on iron when compared to that

ively. ratio

measured

on deuterium

showed

deviated

a significant I

from

the

expected

ratio

of one by up to

15% and

x-dependence’.

I

I

I

I

I

I

1.4 -

1.4 8. EMC

,,3

......... Frankfurt

j~Fe+pD,data

C Strikman’

Berlad et aI.”

---

9~02C170GeV2

Fermi

motion

Y Q

++N 1.1 -

-

\+\

F2 IF.1

1.2 -

c-z v

1.2 -

I

I

5 =-u!?

1.1 -

Y a” LL

I.1

F2 lD,I

‘.

,’

.-_____-*

0.9 -

slope=

0.9 0.8

\

-4 -052f0.04?0~21

I

I 0.2

G.0

1

I 0.4

I

I 0.6

/ I

0.8

Fig. (a)

Ratio

F2(Fe)/F2(D2)

(b)

Fermi

motion

Q2 range effect

are

effect

as

the

of

not

x.

the

which

is

motion

as

nucleons

correction

Fermi

3(a) Only

for are

at work

and that

basis

an incoherent the

deuterium

(Fig. the

I

I

I

0.6

X

been

systematic implies also

3(b)).

EUC effect

Fermi

even

after

of

does

not

than

motion

indicating

the

shown

available but

uncertainties

that

much smaller

over are

superposition

for

models

averaged errors

of

nucleus is

corrections

different

statistical

The effect

inside

motion

various

and have the

NOT corrected

expectation

Fermi

for

away or the

behave

the

larger.

in Fig. of

7% everywhere.

points

phenomenon even

than

does

motion

The data

shown value

be explained

less

nucleus

Fermi

of

each

cannot

these the

are

for

1 01.

0.2

3

without

predictions

I

I

0

X

The results

-

b.

08 1

free

Fermi

as large

that

for follow

another

motion

Qa

nucleons.

account

do not that

at

the

for iron.

the 8

the

trend

nuclear

correction

is

8c

S.J. Wimpemy /Structure

3.

THE EUC EFFECT - WHEREARE WB ROW? The original

scepticism.

EMC announcement However,

-SLAC-MIT group aluminium used

for

background

an ideal

under

completely

different

cell

cross

different

some surprise effect

and reanalysed

data.

subtractions

way of

the

The data

and considerable

was confirmed some 10 year

which

by a Rochester

old

had originally

in the E49B and E87 experiments

checking

the ElK observations

conditions

and so were

subject

steel

and

been taken

and

at SLAC pro-

as they were

taken

to completely

systematic

uncertainties. When compared to the deuterium data from the a(Pe) b(D2) and cr(Al) a(D ) ratios revealed the same x-dependence 2 11 by the EBC.

same experiments

as had been

seen

The publication perimental is

was met with

afterwards

who had gone back

empty target

vided

the

shortly

jimctions and the EMC effect

of

now available.

by Chris

these

and theoretical

have

The theoretical

Llewellyn-Smith

experimental

data activity

in a later

stimulated

a considerable

and 18 months

later

amount of

progress on the RIYCeffect will be reviewed 12 talk. I will now proceed to review the

situation.

Coll.boration

Beem

T.Cg*tl

"2Pa

CSSN WA21

ex-

much more information

Conml*nt*

combined SESC and CDHS" d.t. -1

hf.

17

CBS" "AZ*

VBS ",V

H?.Nt,

-1

19

CESW WZS/"A59

WSS ".B

D2.Ne

-1

20 21

CDllS

v.?

H2.P9

PSF."ILAS 1S'SC

"

D2Jh

-1

22 23

NO.

9c

S.J. Wimpenny / Structure functions and the EMC effect

New, high targets

measurements

statistics,

have been made at both

collaborations statistics

3.1

THE X-DEPENDENCE

neutrino

charged

first

consider

the

experimental

large

data

presented

data

Fig.

data

which

data

experiments

lepton

this.

the

is

it

are

precise

iron

range

can be seen

but are

that

completely values

: deuterium

comes

summarised

the most

at somewhat lower ratio

functions from nuclear 13 by the BCDKi and E13915

information

which

is by far

overlap

on the

structure

4 shows the kinematic

from which

Q2 have extensive

electron

of

and low Q2 values

at CERN and SLAC. Additional

lower

As the

high

of

1.

let

us

in x and Q2 covered

and extensive

by

the BCDMS and EMC data

separated of

from a variety

in Table

Qs.

Each group

and so this

at

from the El39 have

makes a natural

BCDMS

point

-I

x 0.5 -

O* (GeV’)

Fig. x - Q= ranges of

comparison.

by the

The data

B in extracting given of

are

two muon experiments

as the

for

presented where

R at small

not A-dependent

values

of of

- a fact

in the

a constant

Fp from the measured ratios

that

Note still

lepton

form of value

of

cross-sections.

cross-sections Qs.

4

charged

due to that

these

remains

structure 0.0

function

has been

The electron

possible are

data

worries

equivalent

to be established

about provided (see

ratios

assumed for data

are

the value that later).

R is

S.J. Wimpenny /Structure

1oc

The results

are

respectively. shape

shown in Figs.

normalisation

at smaller

I +4-

S(e)

and (b)

As one can immediately

and absolute

apparent

I

vaIues

I

1

I

,

see

for

of

functions and the EMC effect

the

for

there

the muon and electron

is

region

excellent

x > 0.25

agreement

data, in both

but differences

are

x.

I

I

I

a.

1.4 .

1.3 -

EMC ‘0.98

oRc.cheet~r.SLAC.MIT

9 s O2 < 170 GeV’

I.3

0 BCDMS [preliminary] 1.2 -

.SLAC

Systematic

0.0

0.2

0.4

El39

1.2

40102d190G.V2

0.8

0.8

I.0

Errors:

n SLAC E61 ICui

- -

X

Fig.

First

(a)

F2(Fe)/F2(D2)

(b)

u(Fe)/o(D2)

let

us consider

and preliminary x dependent

the

BCDHS (prelim.

data

feature

of

were taken

uncertainties

but

copper

rather

systematic

in a little

more detail.

in agreement

The EnC

and have nearly

f 0.04tstat)

?: O.Pl(syst)

- 0.56

f O.OS(stat)

f O.O3(syst)

in the

in Fig.

iron,

identical

of with

new experiments

so that

come from E49B/E87,

Qs regions. as the A of

comparison.

1-2X except

the

targets

nearly

is

all

that

the

systematic

ratio.

5(b)

but for

most of

from both

different

results

errors

inconsistencies

SLAC experiments

- 0.52

out

data than

Q’ data

the BCDtdSand indeed

slightly

these

Qs from various

are entirely

simultaneously

The electron

included

)24

cancel

similar

high

5

Qs from BCDM and 8l4C

of

BMC’

A nice

at small

BCDMSdata

slopes

at large

for

the muon data.

the

II61 and El39 which

The E61 data the

are

two materials

The data

agree

region

x < 0.2

Beyond x’-

0.65

well

in fact

is

similar

within

I have

the quoted

where there

the nuclear

cover

from

are

also

differences

S. J. Wimpenny /Structure

begin

to be swamped by the

in this

effects

functions and the EMC effect

of

Fermi motion

which

are

IlC

rapidly

growing

region.

One could dependence

argue

that

related

insufficient

to

iently

Qa range

large

the

small

to nuclear

test

this

x differences

shadowing

hypothesis

at small

as Qs+O are the result of a Qs25 However the current data are

effects.

as no single

experiment

spans

a suffic-

x.

0.6

0.4

02

0.0

0. 6

X

Fig. UA59/WA25 v. The neutrino in the example ratio

is

*

region

the

x-

6 which

as a function

where

is

of

consistent

the data

results

and y-dependences

shown in Fig.

2 5 which

Fig.

and antineutrino

form of

x.

on a(Ne)/a(Dg)

listed of

1 have been presented

cross-section ratios. - 20 shows the WA59IWA25 Y and v 21

the

below

in Table

the

The solid

with

dip

6

v data

line

results

is

within

one in a similar

A typical data

on the

the EWC slope

fit

taken

from

errors

for

small

x

except

manner to the

low Qs data

from E61. Each of

the neutrino

below

one at small

again

for

data

is

However, they

increased

lepton

rising

This from -

in general

contribute

charged

x,

x > 0.4.

results

little data.

the

basic

show similar above

one for

shape

is

trends x - 0.2

not

changed

with + 0.4 if

1 GeV’ to - 8 GeVs by cutting results

information

are

inconclusive beyond

due to

the

ratio

and falling

the

average

seen

to be

below Q2 of

one

the

away the low Qs events. lack

of

statistics

what has been established

by the

and

20

12c

S.J. Wimpenny / Structure functions and the EMC effect

3.2.

THE A-DEPENDENCE A new feature

Weight

of

collaboration targets

whether of

the

for

results

in the with

below

seen

(Fig.

7(a))

of

a logarithmic a(n) o(D2)

and/or

the

of

in the

above

A at fixed

on the nuclear

ratio

with

for

0.3

< x 5 0.8.

If

x then

a clear

A-dependence

well

described

in terms

can be equally increasing

the

average

+ b(x)

nuclear

A:

density:

p(A))

I11111,

I

I

I

11111,

!

8.

*El39 __,~-t~i,__--___--__---~

0

‘1, $ t?

I

- X7 0.30

,I,,,,,,,,,,,,,,,,,

a5

s 72

b” 1 1.0 -. b” -

to

ratios

results

and the variation

= a(1

I

depends

try

q(&, o(D ), show similar x-depend2 consistent with one for 0.1 < x < 0.3

form of

I.0

I

and Au

and 2 < pa < 15 GeV’ to

a A-dependent

7

1.1.

the Atomic the El39

on the Be,C,Al,Ca,Fe.Ag

< I < 0.9

as a function

decrease

with

o(D2)

of

CAa(x)

=

or linearly

study Recently

one in the manner described

are plotted

is

is

the

material.

presented

falling

0.09

is ratios.

out measurements region

each material

and then

IIHC effect

cross-section

the 8MC effect

target

The results,

on the

the

have carried

establish

the

of

in the kinematic

density

ences

the data

or A-dependence

-0.5 -1.0

tit, +t

E

tt

7

-----_-_ t

;-I----,-,-%

t

D 5

-

-1.5

-

-2.0

-1

0.02

:

it+’

,ep;O.O036 0.9

, -

,

,(,,,

I/

,

,

,I

,,,,,

,

x =0.62

1.0 -(_--__------_---_---_

3 $ VBCDMS

-

0

bQ

-0.02

’ ”

1 1 ’ ’ 1 1 1 ’ 1 1 1 1

0 I-

-_~t_t?l(_--___________~

t+t+

-

+t

P

tl

i

q

-0.04 0.8

2

I

I

IO

20

NUCLEAR

,llllill

I_ 100

WEIGHT

-0.06 0

200

A

Fig. A-dependence (a)

E139,

BCDHS data

(b)

x-dependence

of

-

for fit

of

+tt b.

t

1

o(A)/o(D2)

x E 0.3 parameters

t

’ ’ ’ ’ ’ ’ ’ ’ 1 ’ ’ ’ ’ 1 ’ ’ ’ 1 1 0.2 0.4 0.6 0.8 1.0 x

and 0.62 o,

6 from B139

S.J. Wimpenny /Structure

where o, nuclear

b are

x-dependent

fit

parameters

(Fig.

7(b))

13c

and p(A)

is

In addition

matic

to

the

region

results

for

have also

0.25

with

the W139 data

in very

good

agreement

iron

in the previous

preliminary

results

average

7(a)

from which

the A-dependence

it

are

difference,

suggested

that

A = F2(Fe)-F2(D2)

increase

in the

arguments

based

ment in ths x (valence

sea quark on the

the low x enhancement seen

x-dependence

small

x (sea

quark)

region.

quark) 26

in the of

region

A (Fig.

ratio

they

which

a small

F2(Fe) F2(D2)

are

and the

a substantial

This

nucleons.

B(a))

and only

the

may be due to

iron

that

kinecom-

above.

of

in the EMC data

distribution

the

shown for

can be seen

described

LOW x - AN INCREASE IN THE SEA QUARK. s DISTRIBUTION? has been

section

from N2 in the

These

and 40 < Q2 < 190 GeVs. in Fig.

with

discussed

presented

< x < 0.65

parison

It

the

density.

BCDMS collaboration

3.3

functions and the EMC effect

follows

shows a large

depletion

from enhance-

in the larger

1.5 CDHS

d 0.05 1.0

0.5

0.5

0.0

1.0

X

0.0

Fig.

A-distribution

Neutrino

8

have used lished

the

sususarised

from X4C

experiments

the y-dependence this

of

to determine

comparisons. in Table

i off

access

cross of

The results

to

in the

2 and show no evidence

q(Fe)/q(HP)

the nucleon

section nuclear

1.0

in 4 (b)

have direct

the neutrino

0.5 X

Low x - an increase (a)

b.

(equation and nucleon

form of for

from CDHS

i distributions

via

8(a)).

Several

targets

and have pub-

x-intergrated

the predicted

sea

s ratios increase.

groups are This

S.J. Wimpenny /Structure

14c

is

further

the

supported

by the

CDHS collaboration In all

clude

cases

that

out by these

which

the

a large

direct is

ratio shown

experimental increase

functions and the EMC effect

of

in Fig.

errors

in the

the

are

quark

and hydrogen

however

6 in large

one

is

A nuclei

from

led

to con-

has

been

ruled

2

Ratio

Average

Qs

WA241g

js(Ne)dx ,ifR2jdx

= 0.95f0.16

- 1 GeV’

WA25, WA5g2’

Ja(Ne)dx jq(D2)dx

= 0.91+0.06 0.85+0.10

- 1 Gel? - 8 GeV” (Qsz4.5)

Ig(Ne)dx jq(H2)dx

= 1.10f0.11t0.07

- 7 GeV’

THE GLUON STRUCTURE FUNCTION. G(xk By evaluating the

.the

momentum

The remaining them

of

Energy-Momentum

the

1 F2”N(x)dx

i.e.

inside

by the

carried

is

Sum Rule’

carried

27

functions

by gluons

Qs-evolution

There

q(x).

procedure

determinations (u-CaCOs see

regions) distribution

are

resulting

of G(x)

which

is

is

fixed

however

is

by fitting

by assuming

to date

reasonable

softer

the

quarks

and confine

the

gluons

is

the

The results agreement The only that

QCD evolution

+ G(x)dx

at

CDHS (v-Fe

within

shown the

difference

of CDHS.

of

problems x. 29

in Fig.

large

VN and F

that

shape

with

this

The best

and CRARW 9 from which

uncertainties is

standard

= 1 and the

small data)

Chromo-

success.

and technical

are

slight

and the

great

the

described

of Quantum

of G(x) with

uncertainties

come from

than

to

f F2(x)

many experimental

50%

28

framework

to

only

of

violations

be predicted

systematic

measurements. slightly

the

that

quarks.

= 0.14

couple

Within

scaling

‘measured’

collaborations.

there

on the

is

in large

dataj3’ that

or

R, F2 and xF3 can

Experimentally G(x) -VN The normalisation q *

can be shown constituent

j F2nN(x)dx

GLUON STRUCTURE FUNCTION, G(x). (QCD) the

it

by its

The momentum distribution

nucleon.

structure

from

nucleon = 0.51.

50% is the

dynamics

can

iron

measurements.

Collaboration

of

8(b).

sea,

in 22

large,

Table

3.4

seas

the

one

(shaded CHARI4

S.J. Wimpenny / Structure functions and the EMC effect

GLUON 6

STRUCTURE G(x)

at

5

152

FUNCTION

0’.10GtV*

-wlc

cons

-Z&Z%

CHARM

4

Fig. Structure

Gluotj

Recently to

the

for

iron

been

to measure

J/q

production

compare model

the

results.

to unfold

assumed

G(x)

only

via

are model

many of

the uncertainties

is

seen

and the

results

indicating atically the

errors

are

is

the two targets the

QCD diagram

photon

out.

the

of

has

and then

‘Photon-Gluon

Fusion’

mechanism

shown in Fig.

10(a)

for

ratio

the two cross-sections

of are

the nucleon.

shown in Fig.

_ 10 GeV’.

No obvious

is

so that

and G(x)

The results

and a Qa value

x O.lZ(Stat)

of via

to try

adopted

Here the J/$I production

order

when combined

off

possible,

approach

The procedure

The

10(b)

for

x-dependence

give:

2 0.20

(Syst)

D2

that larger

it

but by taking cancel

= 1.44

an alternative

cross-sections

leading

dependent

at Q2 = 10 GeVs

deuterium.

the virtual

< x < 0.08

G(xjFe G(x)

the

on v.Q * of

0.02

for

from oY(yN+J/v).32

results

the x range

G(x)

From these

to proceed

oY depends

with

G(x)

have tried

EI(C collaboration31

G(x)

compare

9

Functon

the

gluon

than that large

distribution for

in iron

deuterium.

and by combining

the

in this

However, three

sets

region

as with of

is

system-

the previous

results

results

from CDHS, CHARR

f..f. Wi~penny /Struchrre functions and the EMC effect

f6c

and EMC one can only that

the gluon

present

conclude

distribution

some tentative

may be different

the experimental

any more definite

that

and theoretical

indications

for

different

uncertainties

have been nuclei.

are

too

seen

For the

large

to

give

answer.

EMC preliminary

II 0 I,

‘Itt

10 -

t

a. b.

01

4

1

0

I

I

I

0.08

0.04

X Fig. Comparison

3.5

of

Gluon Distribution

‘Photon-Gluon

(a)

L.O.

(b)

EllC Results

10

for

Fusion’

in Iron Graph for

and Deuterium J/y

Production

G(x)Fe/G(x)DZ

IS R A-DKPRNDENT? In this

the

last

structure

any nuclear It sider

is

convenient

data

shows little For this

Table ificant ence

to divide

Qa data

or R which

-

i.e.

is

I will

discuss

to

if

see

our current

the data

it

3 from which kinematic at large’Q2

into

Q2 2 20 GeV

for of

allow

more

convenient result.

must also

that

on v,Qs to

that R is

be small.

.

knowledge for

integrate

it

of

to have

to

these

zero.

First

to

let

us con-

11 shows the RXC

in this

over

in addition

close

Q’.

Fig.

or x within

A suaxnary of

one may conclude dependence

low and high

the measurements

dependence

averaged

is

or Qs-v

the data data

typical

or no visible

reason

a pa-x

section

R and attempt

dependence.

the high

proton

duce

experimental function

regime

the errors. all

in that 28.33

variables

results a lack

is

it

and progiven

in

of any sign-

Thus any nuclear

depend-

S.J. Wimpenrly /Structure

functions and the EMC effect

=22.5GeV2

1lc


OL -

100

60

10

140

v IGeVl

20

LO

80

160

Q’ [GeV']

Fig.

11

The Q2 and v-dependencesof R at large Q2

Table 3

I

Collaboration

Beam/Target

UP uFe

R

Comments

-0.010+0.037+0.102

0.03=22.5 GeVa

0.03f0.11

uFe

-0.06+0.06f0.11

CDHS35

vFe

(0.039f0.014+_0.025

CCFRR34

vFe

tx>-0.3 preliminary large x limit =3S GeVa preliminary

Turning now to lower Q2 measurementsone finds that small but non-zero values are found for R and that there are some indicationsof an x-dependence in the SLAC-HIT electron and CDHS and CHARM neutrino data. These are shown in Fig. 12 together with the muon data from the CHIO collaboration.

S.J. Wimpenny/Structure functions and the EMC effect

1%

CDHS VFe SLAC -MIT eD oCHl0 fiE”p o SLAChllTeP

l

_

l

Fig. 12 The x-dependenceof R at In

addition

differences

to

x-dependence

there

are

smell

indications

of

Qa

small

target-dependent

and it would be tempting to try to interpret these as evidence for

a possible nuclear dependence of R.

However one atustbe very careful here as,

Table 4

Collaboration

Beam/Target

Coaxaents

ep ed

0.22f0.10 0.24t0.10

O.l
=p ed

0.138+0.010+0.056 0.~~5~G.00~~0.060 +0.25 0.52 -0.25

O.l,4 GeV*

O.OE-rO.15

0.5
0.32+0.12

as

up vFe

C?iARU40

R

vCaCO3

x
GeV*

for CDHS

S.J. Wimpenny / Stmcture fu~&tions and fhe EMC effect

with

the exception

of

come from different the large

Q” results

other

comparable

argue

that

Clearly,

to extract

of

to

look

in Table

some of

nuclear

of for

the

the 4.

targets

within

discussed

earlier data.

kinematic

average

along

El39

0.9 _

b.

R values it

line,

group

of

statistics

and the

preliminary

I 11l‘Sl

[preliminary]

0.4 X

Fig. The effect

of

0.6

13

an A-dependence

(a)

A-dependence

(b)

Resulting

0.8

of

of

R

F2(Pe)/F2(DZ)

ratios

R

low Q2 data

This

this

lack

one can

a Q2-dependence.

one needs

experiment.

and

that

Due to

variations

0.2

clear

and recently 16

the data

As with

from these

is

may be due to this

a single

I I T”“,

-

data,

x-Q= regions.

From these effect

further

R from their

1.00_1

different

observed

to proceed

experiment values

and electron-deuteron

and cover

I have sunsnarised

in order

by the El39

electron-proton

experiments

at least

from a variety

possible

the

experiments

19c

is

provided

have attempted

results

is

it

are

not

2oc

S.J. Wimpenny / Structwe fzmctiotns urzd the EMC effect

presented

in the

These

shown in Fig.

of

are

a possible

this

is

value

if

you use

function

result

of

is

0.15

translate

retaining

+- 0.11

errors

which

dependence between

4.

is

small

the

different

nuclei.

that

there

size

of

with

an A-independent

the data

agreement that

is

a hint

the errors

in this

large

present and large

it

for

can explain

earlier.

the present answer.

some of

the

ratio

uncharged

on R may give

any definite

The

Qa measurements

essentially

discussed

data

Q* hut that

to give

then

region

is

R

in the

the high

would

structure

the F2.s.

no low x rise with

x > 0.3

into

where the measured

of

consistent for

an A-dependence

ratios

to determine

instead

the current

at small

too

13fbl

has been used

entirely

such

cross-section

in Fig.

in that

is

Further the

are

(stat)

interesting

A-dependence

mental

five

consistent

what effect

the El39

has been done

Thus one can conclude possible

of

can be seen

are also

ask the question

to

a rise

the EMC group.

thereby

it

each

However due to

and the data

This

somewhat

one now sees of

it

ratios.

difference

A.

for

0.2

One can nonetheless have

R values

from which

in R with

conclusive

around

averaged 13(a)

increase

not

of

form of

a hint

of

a

the experiIf

small

however

such

a

x differences

Q’ measurements.

CONCLUDINGSDHMARY Taking

account

functions

one is

established within

There

-

-

excellent

A dependence electron

of

do not

dependence

approximately terms

the experimental

At small

data

and that

in the

now available

the EHC effect

on structure

has now been

bound and pseudo-free

same way.

nucleons

In particular

agreement

of

is

is

between

observed

rapidly

the

effect

all

in this

experiments region

the data may

swamped by Fermi motion

on the

atomic

weight,

to Log A and can be parameterised or a dependence

x the

electron,

but can be made consistent

for

of

8.

There

is

linear

however

Q2 > 9 GeVa and the

well.

The dependence

either

no evidence

smaller

equally

in the nuclear

muon and neutrino by assuming

x - 0.65

A has been observed

in proportion

of

agree

the region

effects.

and the

values

results

for

and beyond

and muon data

or an A-dependence Q’-dependence

fact

behave

a Log A dependence

(x > 0.25)

that

as follows:

is

nuclear

both

of

to conclude

No Q2-dependence

x z 0.25. the

all

as an experimental

the nucleus

be summarised

-

of

forced

Q2 electron

data a strong

in

grows well

in

density.

disagree Qa-dependence

in the muon data and neutrino

for

any

data

are

21c

S.J. Wimpenny /Structure functions and the EMC effect inconsistent data the

so that

errors

-

are

large

Neutrino

nucleons are

it

is

do show indications

-

to

however

that

deuterium

Clearly

and/or

effects are

sea quark

could

still

in the

in large

sea at small

tolerate

the gluon

could

a small

distributions

be enhanced

the

present

no effect.

distribution

increase

for

and small

A

Errors

x.

increase.

in iron

and deuterium

by up to 45% over

that

in

EFPBCT - WHEREARE WB GOING TO? to understand

what

questions

related

of

is

about

a gluon/sea

going

on in the

a pa-dependence

distribution

small

and/or

change

x region

and

an R-dependence

more high

precision

needed. for

statistics

experiments These

with

in R but

x region.

outstanding

The outlook high

the

of

in iron

small

in order

the

data

glue

in the

resolve

of

A-dependence

consistent

any large

comparisons

the

THE EXC

5.

out

and the data

Preliminary

suggest

and are also

rule

The new El39

to draw any conclusions.

8 possible

measurements

tend

large

difficult

of

the

data which

future

with

are

is

good

a larger

in that

Qa lever

running/planned

I have attempted

to

within

arm will

the next become

year

at CERR, FERMILAB (Tevatront

summarise

or so new

available

from and SLAC.

below.

CERN:

(1)

BCDMSCollaboration - Final

results

within

(2)

on C, N2 and Fe at large

a period

of

about

Qa should

be available

one year.

EPICCollaboration - Low Q2 X0.5 < Q2 < 2 GeVaf. experiment time Sn

are being

in the

fall

of

low x (x < 0.3)

analysed this

now and first

year.

This

includes

data

from a ‘shadowing*

results data

are expected

some-

on H2, D2 C, Ca,

and P6.

- New data

covering

He, Sn are being the questions - A subset extend final

of these

states.

a large taken

about

Q2 range

at present

the Q2-dependence

the collaboration studies

(I. < Q2 < 190 GeV’) and should

to other

are

also

nuclei

of

help

to

on D2, C, Cu, resolve

some of

the effect.

considering and to

study

a new proposal R and hadronic

to

22c

S.J. Wimpenny /Structure

FERMILAB (Tevatron

functions and the EMC effect

- 1000 GeV):

E665 Collaboration - In the

spring

of

1986 the

muon beam will

take

be taken

several

using

first

place

data-taking

and it

nuclear

is

run with

currently

the new 650 GeV

intended

that

data

will

targets.

SLAC El39 Collaboration - A subset to

of

study

this

the

group

are

discussing

x.Qs-dependence

heavy muclei.

This

would

of

a proposal

R ror

for

a new experiment

D2 and a comparison

be run in late

1985 and/or

with

early

1986.

Aknowlednements I would

like

contributed

thank my colleagues

much to

following R.G.

to

people

Arnold,.

W.A. Parker,

the work discussed

for

useful

T. Sloan,

here.

discussions

Benvenuti.

A.C.

from the EHC collaboration

A.H.

Wany thanks

on the data

Cooper,

who

are also

and cosxaents

A.W. Edwards,

due to

on this

the script:

E. Gabathuler.

G. Smadja.

References

1.

F. Dydak,

Proc.

Energies, 2.

K. Pith,

of

Int.

Cornell, Proc.

Brighton,

of

Symp. on Lepton

and Photon

Interactions

at High

1983. Int.

Europhysics

Conf.

on High Energy

Physics,

1983.

3.

J.D.

Bjorken.

4.

W.K.H.

Phys.

5.

P.E. Close,

6.

J.

7.

PMC, J.J.

Aubert

8.

A. Bodek,

J.L.

Panofsky,

Rev.

Proc.

179.

14th

1547,

Int.

(1969).

Conf.

on High Energy

Physics,

Vienna,

1968.

Carr,

1400,

L.L.

et

al.,

Richie.

Univ.

Frankfurt,

10.

G. Berlad

11.

A. Bodek et 534,

to Quarks

and Partons.

Academic

Press,

1979.

cosxnunication. Phys. Phys.

Lett.

Rev.

m.

m,

403. 1970,

(1983).

(1981).

Phys.

Rev.

m.

(1981).

A. Bodek. 9.

An Introduction

private

et

(1983).

Rochester W.I.

al., al.,

preprint

Strikman,

Phys. Phys.

Rev. Rev.

UR853. COO-3065-365,

Phys. m,

Lett.

Rep.

1547, 50.

x.

215,

(1983).

(1981).

(1980). 1431.

(19837,

Phys.

Rev.

Letts.

II.

S.J. Wimpenny /Structure

12.

23~

functions and the EMC effect

C.H. Llewellyn-Smith,'NuclearEffects in Deep Inelastic Scattering', talk given at this conference.

13.

Bologna-CERN-Dubna-Hunchen-Saclay. A.C. Benvenuti et al., paper submitted to XXII Int. Conf. on High Energy PHysics, Leipzig. 1984.

14.

S. Stein et al., Phys. Rev. D7. 1362, (1973).

15.

R.G. Arnold et al., SLAC-PUB-3257.(1983).

16.

R.G. Arnold, private communication.

17.

H. Griissleret al., paper submitted to Int. Symp. on Lepton and Photon

18.

CERN-Dortmund-Heidelberg-Saclay, H. Abramowicz et al., 2. Phys. m.

Interactionsat High Energies, Cornell, 1983. Paper No. C-206. 283,

(1983). 19.

I4.A.Parker et al., Nucl. Phys. 8232. 1, (1983).

20.

A.M. Cooper et al., Phys. Lett. 1618. 133. (19841.

21.

A.E. Cooper, private cosununication.

22.

H. Abramowicz et al., CERN EP/84-57. (1984).

23.

A.E. Astratyan et al., ITEP 83-110, (1983).

24.

R. Voss. talk presented at XI Int. Conf. on Neutrino Physics and Astrophysics,Dortmund, 1984.

25.

A. Bodek

Proc. XIV Int. Symp. on EultiparticleDynamics, Lake

A.W. Edwards 1 Tahoe, June 1983, and references contained therein. 26.

R.L. Jaffe, Phys. Rev. Lett. 50, 228 (1983).

27.

P.C. Bosetti et al., Nucl. Phys. 8203. 362, (1982).

28.

S.J. Wimpenny, talk presented at Int. EurophysicsConf. on High Energy Physics, Brighton, (1983).

29.

H. Abramowicz et al., 2. Phys. C@.

289, (1982).

30.

F. Bergsma et al., Phys. Lett. 1238. 269. (1983).

31.

REC. J.J. Aubert et al., 'A Measurement of the Difference Between the Single Nucleon Cross-Sectionsfor J/w Euoproduction in Iron and Hydrogen/DeuteriumTargets'. in preparation.

32.

T. Weiler. Phys. Rev. Lett. 44. 304, (1980).

33.

EMC. J.J. Aubert et al., Phys. Lett 1218. 87, (19831.

34.

A. Bodek. Rapporteur talk presented at XI Int. Conf. on Nuetrino Physics and Astrophysics,Dortmund. (1984).

35.

Ii.Abramowicz et al., 2. Phys. u.

36.

E.D. Eestayer et al., SLAC-PUB-2933,(1982).

37.

A.

38.

B.A. Gordon et al., Phys. Rev m.

39.

H. Abramowicz et al., Phys. Lett. &_D7B,141, (1981).

40.

F. Bergsma et al., CERN-BP/84-08.(1984).

Bodek et al., Phys. Rev. m.

283, (1983).

1471. (1979). 2645, (1979).