Recent results on NN physics

Nuclear Physics AS08 (1990) 2G%-214~ North-Holland

209~

RECENT RESULTS ON NN PHYSICS

D.V. BUGG Queen Mary College, London El 4NS, UK

New np elastic data of Abegg et al. stabilise I= 0 phase shifts from 200 to 500 MeV. New data of Hutcheon et al. on KSS for pp + dn+ at 515 MeV agree well with the amplitude analysis of Bugg, Hasan and Shypit and correct a sign error in some published data of Cantale et al. A new analysis is reported of all current data of NN -LNNa from 420 to 800 MeV. A strong threshold cusp is observed in the NA S wave; it is not yet clear whether or not a bound state pole (quasi-deuteron)is required. In other partial waves, phases of amplitudes are negative or weakly positive and rule out dibaryon resonances.

1. NN ELASTIC PNASE SHIFTS There have recently been two precise measurements of np elastic scattering at 1 TRIDMF. Firstly, Abegg et al. have measured the ratio DT/RT at 160° at four 7 energies from 223 to 492 MeV with errors tO.01. Secondly, the same group- has measured

at 220, 325 and 425 MeV from 52 to 145' with errors of ANN* ANO and AoN %O.Ol to 0.02. These data stabilise significantly3 the I= 0 phase shifts from 200 to 500 MeV, although there are no large systematrc changes. In partrcular, 4 cl is much improved and smoother, and agrees well with the latest predrction of the Bonn potential.

f

2, PP +D?r

At TRIDMF, Kutcheon et al.5 have recently measured the spin transfer parameter KSS in pp + dn+ at 515 MeV.

0.15

Results, shown in Fig. 1, agree 0.10

reasonably well with the Latest amplitude analysis of Bugg, Hasan and Shypit6. Theydisagree in sign with results of Cantale J et al. The Geneva group now

Unceriojnties due to errorbarson iTl1and T21

0.05 a : 000 w -3 -0.05

agree that their &LS(x) and ezs(x) results at 447 and 515 MeV should be reversed in sign and their sLS(z) and ~~~(2) data should be reversed in sign at all energies, The amplitude

1

-0.15

0

I

30

I

I

t

,

60 90 120 150 oeuteronc-m.angle

1 181)

Fig. 1. KsS data of Hutcheon et al. and the prediction of Bugg,Hasanand Shyprt,

0375-9474 I90 / $3.500 Else&rScience Pubfishers B.V. (North-Holland)

21oc

D.V. Bugg I Recent results on NN physics

of Bugg, Hasan and Shypit used ratios

analysis

of data and is unaffected

by

these sign changes.

3. AMPLITUDE

ANALYSIS

An outstanding

OF NN -+ NNa: DATA AND INGREDIENTS

issue is whether

or not there exist broad dibaryon

(or bound states) in the range 5008 al. first proposed their existance AaT data. analysis ever,

in the Argand

Hidaka

et

on the basis of peaks and dips in AaL and

diagrams

that the opening

A resonance

to be coupled

strongly

to NA, and it 1s

of the NN + NA channel will produce

channel bearing

(via analyticity)

a strong resemblancetothe

at s= so should produce

NN -+ NN and NN -f NA, hence wave amplitude

are observed In NN elastic phase shift 13 for D2, F3 and 3~2 (and possibly 3F4). How-

are well known

cusps in the elastic loops.

resonances

Well defined half-loops

these states

certain

800 MeV of proton beam energy.

an amplitude

a rapid anti-clockwise

= (6

0

observed half-1 In both

- 6)

phase variation

in the partial

for NN + NA.

An amplitude

analysis

is in progress

using

the complete

set of world

data on

NN -+ NNn. of Wicklund et The main data sets are: (i) doldS1, ANo, AS0 and A 9 LPO at 800 MeV, al. at 569 and 806 MeV, (ii) do/da and AN0 of Hancock et al. plus AN0 and recoil proton NN' D9f' DLQ 12 and Riley et al. at 650, 733 and 800 polarisation AooNo of Hollas et al. 13 at 492, 576, MeV, (iv) ALL, ASL, ANL, ANo, ASo, AI0 and AOL of Shypit et al. 14 at 650 and 800 MeV of Bhatia et al. 643, 729 and 796 MeV, (v) ANN and ALL at (iii) Wolfenstein

parameters

D

650 and 800 MeV, and (vi) ANN, ASS, PtL, ASL, AN0 and AON at 510, 465 and 420 15 et al. ++ In this analysis, partial wave amplitudes are parametrrsed for pp + nA as

MeV of Waltham

fL,J where

= AI, J(s)

BL J(s) eioLtJcs)

BL J is the Born partial

exchange'and

(1)

,

wave amplitude

A and 4 are real parameters

Born amplitudes

++ for pp + nA

via single

fitted to the data at each energy.

The

take the form MA

BL,J a MA - M

(2)

- ir A (Mpn+) gL,J(B'e")' Pr+

is the mass of the pn+ pair and MA, rA are a Layson P+ The function parametrising the nN P33 phase shift accurately.

where M

standard

angular momentum

decompostion

form gL,J gives the

in terms of 8, the production

angle of

and Treiman-Yang angles of the A decay. the A++ and (El,+) the Gottfried-Jackson + The amplitudes for pp + pA are added coherently with isospin Clebsch-Gordan coefficient dependence

l/3 and with

identical

parameters

to

(1) and (2) but kinematrc

on M,,+ and 8', 8', $I', the angles describing

the nr+ pair.

211c

D.V. Bugg I Recent results on NN physics

The small nN partial in Born approximation S wave)

waves

in 3Pl + 3Sl, which

the elastic

NN phase

Sll, S31, Pl3, P31 and Pll are presently

(+= O), except

is a large amplitude; Later,

shift.

to 6NN, but this requires

has been investigated,

< 1890 MeV; below

events

this mass,

included

for the xN

here A is fitted and $ = 6NN,

it is the intention

that all $Iwill be set

a full partial wave decomposition,

The NN final state interaction role for M(np)

for NN + NS (where S stands

not yet Implemented.

but appears

are discarded

to play no In order to

avoid this complication. One might determined

think that the 16 helicity

amplitudes

using 31 spin configurations.

a spin change AS = 2 or 3 and are accurately (AL dominantly the alignment

Also, density matrix

0 or 1).

of the A via the dependence

for NN -+ NA could only be

However,

8 of the amplitudes

predicted

by OPE at low momenta

elements

for A decay determine

of observables

is that all partial waves are well determined 5 3 PO + 3Po and '02 + 3D2). very small ('So + Do, Results

are presented

in Table

but merely

phase

a parametrisation

The

which

are

1, setting 4(s) = 6 (s) + $(s). Note that 16 NN have pointed out) and Lee" (as Hoshizaki

shift

of the effect

Fig. 2 shows that 6F becomes

on 6, 9 and 9.

except for those

upshot

~5~ is not the NA elastic

involve

of the final state interaction.

the NA elastic

phase shift in the limit of weak

scattering. Ryskin whether

absolute

or whether

18

and Strakovsky phases

dibaryon

A __----

N have questioned

are well determined,

resonances

&F

&NN

might be

present

in -all (dominant) partial waves. The answer is that the OPE contributions to 'GL and 3H5 amplitudes

0

N

N

from 650 to 800

MeV are large and act as a powerful interferometer, with an accuracy

defining

absolute

of 6- 9O.

phases

Furthermore,

Fig. 2.

The motivation

behind

form chosen for equn.

at low energies, between

theinEerference 3 NN -f NA and the Pl + 3Sl NN + NS amplitude

the

(1).

is large.

There

is a

strong NN repulsion in the initial state of the latter partial wave and a mild 0 (~10 1 repulsion in the IIN final S state. It therefore appears an unlikely candidate

for a partial

reference

phase.

wave which will resonate,

Allowing

and can be used to fix a

for the initial and ITN phases,

the fits are consistent

with 6 = O", with an error of again 6 - 9“. This gives a second NS determination of absolute phases, consistent with the first.

independent

4. INTERPRETATION For NA P and D waves,

6, takes small positive

values

or is negative,

D.V. Bugg I Recent results on NN physics

212c

Table

1. Current Errors

scaling

factors A and phases

are statistical.

Angles

6F for NN + NA amplitudes.

are in degrees.

-----_ Energy 576

643

729

(1)

(1)

(1)

1.35kO.6 (1) ------~-

-5.25 2.2

-2.8~ 1.0

-4.5+ 0.6

-2.8* 0.4

1.3-+ 0.3

0.3+ 0.2

0.7* 0.1

0.682 0.06

3Pl 2; 5P2 :a2 "2 ! 5D I 5 2l P3 i

-1.85t 0.2

1.09+0.15

0.33+ 0.03

1.3+ 0.5

1.32 0.2

0.92 0.2

-4.5f 0.8

-4.5t 0.4

2.9+ 0.4

3.4+ 0.4

1.7 * 0.2

1.2+0.14

1.06 ? 0.12

1.18kO.08

1.05i: 0.16 0.78 f 0.16

0.70+0.08

-2.8

(1)

(1) (1)

(0.851)

(0.771)

(0.761)

(0.741)

(1)

(1)

(1)

(1)

(1)

(1)

3.1+ 0.3

0.14

1.05& 0.10

(0)

(0)

(0)

(16)

(0)

(0)

1.12kO.08

+0.3

(1)

I3.95+

5D 3O pO

796

-4.8f 1.4 3.1tO.6

SF

-1.54fO.14 1.62eO.08

0.78kO.02 (1)

2.2 * 0.2

0.92+0.06

1.4

0.82 f 0.04

(0)

(0)

232 9

(0)

43f8

46? 7

(0)

12i: 6

-4? 7

(0)

-9? 16

C-20)

-35+ 10

-73+5

(0)

C-10)

C-15)

-27f 5

-37c3

11* 11

-2f 6

6+5

56t9

43+ 7

36? 4

(0)

(0)

C-7) 18? 7

(0) (0) 92 14

ruling

out dibaryon

resonances.

phases

are positive;

however,

partial

+0.12

0.84+ 0.02

7f7

-4*4

24+4

11+2

/

(0)

(0)

;

-7* 7

-30"8

-6026

I

16+ 5

13f4

18+ 2

~

determined,

1

(MeV)

492

and is sensitive

waves are modified,

The one possible this partial

eg by leaving

not make too much of this partial For the NA S wave,

wave

(major systematic

is in

falling

I

3 PO, where

is very weak and poorly shifts when the small ?rN

out the small P waves).

wave until

BF takes values

exception

~-

its determination

One should

is more certain.

from 56' at 492 MeV to 11' at

796 MeV, as shown in Fig. 3. A similar result has been deduced by Ferreira, 19 The large values and Dosch from data on rrd elastic scattering.

de Andrade

of 6 near threshold call for some quantitative explanation. F It seems likely It is clear that the NA threshold plays a dominant role. that the open channel NA -+ NN will

lead to a dependence

l/vNA for the NA total

213~

D.V. Bugg I Recent results on NN physics

smeared

optical

theorem,

6F

(deg)

a step in Im fL J(NA -+ NA) at

this implies threshold.

the

Using

cross section.

Of course,

out by the width

of the A.

this step requires

analyticity,

50

this siep wrll be

i

By

1

1

25

a cusp

x

in Re f

+ NA) at threshold. L,.J(NA What needs to be done, but has not yet

been done,

is to see whether

channel K matrix

or whether nearby

state or virtual

between analysis

Fig. 3.

his formalism needs

800 (MeV)

The NA

S wave phase.

for a

state.

claims that a bound

Hoshizaki"

a few MeV of the NA threshold,

large coupling

600

Lab energy

length

there is a requirement

appears within introduces

scattering

(with complex k for the A)

bound

400

the coupled

for NN, rd and NA can be

fitted with a simple prescription

f

0 !-_

to NNn channels

and the assumptions

i.e. a quasi-deuteron;

state pole however,

he

other than NA, and the consistency built

into the current

amplitude

clarification.

REFERENCES 1) R. Abegg

et al. Phys. Rev. C38 (1988) 2173.

2) R. Abegg

et al. submitted

3) D.V. Bugg submitted 4) R. Machleidt, York,

to Phys. Rev. C

to Phys. Rev. C.

Adv. Nucl. Phys.

19 (eds. J.W. Negele

and E. Vogt, Plenum,

New

1988) p. 189.

5) D.A. Hutcheon

et al. TRILJMF preprint

1989.

6) D.V. Bugg, A. Hasan and R.L. Shypit, Nucl. Phys. A477 7) G. Cantale 8) H. Hidaka

et al. Helv.

Phys. Acta 60 (1987) 398.

et al. Phys. Lett.

70B (1977) 479.

9) A.B. Wicklund

et al. Phys. Rev. D35 (1987) 2670.

10) A.D. Hancock

et al. Phys. Rev. C27 (1983) 2742.

11) C. Hollas

(1988) 546.

et al. Phys. Rev. Lett.

55 (1985) 29 and prrvate

communication.

12) P.J. Riley et al. Phys. Lett. B197 (1987) 23, 13) R.L. Shypit et al. Phys. Rev. Lett. 60 (1988) 901. 14) T.S. Bhattia

et al. Phys. Rev. C28 (1983) 2071.

15) C.E. Waltham

et al. Nucl. Phys. A433

16) N. Hoshrzaki, 17) T.-S.H.

LJnrv. of Kyoto

Lee, ANL preprint

18) M.G. Ryskin 19) E. Ferreira,

preprrnt

(1988).

(1989)

and 1.1. Strakovsky, S.C.B.

(1985) 649.

de Andrade

Phys. Rev. Lett. and H.G. Dosch,

61 (1988) 2384.

Phys. Rev. C36 (1987)

1916.