POLARIZATION EFFECTS IN CHARGE-EXCHANGE REACTION AT 40 GeV/c

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POLARIZATION EFFECTS IN

CHARGE-EXCHANGE REACTION AT 40 GeV/c

N. Tyurin, V. Apokin, I. Avvakumov, N. Belikov, A. Derevshchikov, Yu.

Matulenko, A. Meshchanin, A. Morozov, A. Mysnik, S. Nurushev, et al.

To cite this version:

N. Tyurin, V. Apokin, I. Avvakumov, N. Belikov, A. Derevshchikov, et al.. POLARIZATION EF-

FECTS IN CHARGE-EXCHANGE REACTION AT 40 GeV/c. Journal de Physique Colloques, 1985,

46 (C2), pp.C2-175-C2-181. �10.1051/jphyscol:1985216�. �jpa-00224527�

JOURNAL DE PHYSIQUE

Colloque C2, supplément au n°2, Tome k(>, février 1985 page C2-175

POLARIZATION EFFECTS IN CHARGE-EXCHANGE REACTION AT 40 GeV/c

presented by : N.E. Tyurin

V.D. Apokin, I.A. Awakumov, N.I. Belikov, A.A. Derevshchikov,

Yu.A. Matulenko, A.P. Meshchanin, A.A. Morozov, A.I. Mysnik, S.B. Nurushev, A.F. Prudkogliad, V.L. Rykov, V.V. Siksin, L.F. Soloviev, V.L. Solovianov, A.N. Vasiliev, N^S. Borisov+, Yu.M. Kazarinov+, B.A. Khachaturov*, M.Yu. Liburg+, V.N. Matafonov4", A.B. Neganov*, B.S. Neganov"1", Yu.A. Usov4", Yu.sh. Bagaturia"1"1", L.N. Glonti+ + and G.G. Macharashvili++

Institute for High Energy Physios, Serpukhov, V.S.S.R.

+Joint Institute for Nuolear Research, Dubna, V.S.S.R.

++Institute for High Energy Physios, Tbilisi, V.S.S.R.

Résume - Nous présentons des résultats obtenus dans l'étude des réaction Ttp — n ? n , uTp —»T\n, nTp — » T|'(958)n,

rCp ——f(1270)n a 40 Ge?/o. Nous avons observé quelques nouveaux phénomènes dans le comportement de ces réactions.

Abstract - The results on measuring the asymmetries in the reactions rtrp -*- -nfn, TCp —•- r\xx, Ttrp — — Ti'(958)n, TCP — — f(1270)n at 40 GeV/o are presented. Some new pheno-

mena have been discovered in the asymmetry behaviour in these reactions.

INTRODUCTION

The results on measuring polarization in the reactions

o u p — » - T C n

^ 2 7 (1) and Ttp^-^Tin

U-2y (2) at 40 GeV/o for the 4-momentum transfer range 0<|t|<2(CeV/c)

2

for re-

action (1) and 0<|tl<1.5(GeV/c)

2

for reaction (2) are presented.

The experiment was carried out at the 70 GeV Serpukhov accelerator in the 40 GeV/c negative beam. The preliminary results for reactions (1) and (2) were published earlier /1-5/.

Polarization in reactions (1) and (2) was studied below 11 GeY/c by some other groups in the 70's /6-10/. The experimental results des- cribed in this paper are based on the big statistics (2.2 mln Ttf-me- sons and 500 thousands of r|-mesons) that has made possible to take a look at the structure in the polarization behaviour for both reac- tions. Two new phenomena have been discovered: a local minimum in the crossover region for reaction (1) and nonzero polarization (~-20%) for reaction (2) at It|~1(GeV/c)

2

. The results are being compared with the calculations of different theoretical models. Also the re- sults on measuring polarization in the reaction

rrp^C958)n

(3)

and asymmetry in the reaction

•nTp— f (1270)n

uy

at 40 GeV/c for 4-momentum transfer range 0<|t|<0,8 (GeV/c) for the reaction (3) and 0<ltl<1.2 (GeV/c)

2

for the reaction (4) are presented.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1985216

C2-176 JOURNAL DE PHYSIQUE

-

The

experimental

layout is shown in Fig.1, The principal u n i t s are:

beam appaxatua; polarized proton target of a froaen type (PPT), veto- counter syet em (VS) t o seleot neutral trigger, gamma-spectrometer (OS-260).

Fig 1 - Schematic view of the experimental s e t up PROZA, S1-83, 61-83 a r e s c i n t i l l a t i o n

and

threshold Eerenkov counters;

HI

,H2 are beam hodoacopee;

A

i a halo oounter;CMl,CMP a r e cornpeneating magnets;

VS is a veto ayate&; PPT is a polarised proton target;

X

1s t h e

mag-

net of the polariaed target;

A,,,AOB

,AI-4 a r e antiooincidence coun- t e r a ; GS i a a

gamma

ageotroneter~ H3 Is a hodoscope f o r adjusting the apectrometer i n the beam,

A

frozen polarieed proton target with a horizontal cryostat /11/ was u8ed in the experiment.

A

propane-diol sample (C3HB

0,)

was put i n t o the bubble

20

rum i n diameter and 200

nrm

long. The mean polarization value of the target was W . The veto-counter system surrounding t h e polariaed target w a s ueed

f o r

eelection of the events with a ^neutral f i n a l s t a t e . The veto-counter system suppressed the background events associated with

7- ya

other than those of i n t e r e s t o r ehargea parti- cles. n hodos~ope E r e n ~ o v speetromter cotmisting of 260 t o t a l ab- sorption counters with the radiator8 of lead glaea 38x38~450 mS was used t o detect photons from mesons decay, The amplitude analysia /12/

has been uaed t o get signals from the countera. The instrumentation haa been described i n more d e t a i l elsewhere /13,14).

OFF-LIWIS TREATMENT FOR

n-p-d'n AND

<p

- - ~ n

REACTIONS

About 107 events on the polarised target and 2.10 6 events on the background one were recorded a f t e r aeven runs fn 1980-1 982.

l

03mag- netio tapes have been written +(800 bpl density). Data proceasing was carried out in two stages. F i r s t , t h e energy and ooordinstea of pro- tons were reconstruoted and the data

sumnrary

tape8 were produced /15- -16/. Then the appropriate kinematio cuts on energy, mass, Cos

G*

(Q*

- ^is the polar decay angle in the c.m.

8.

of y-pair), angle bet- seen

two gamma$

were applied

/3,4/. A t

the second s t a t e two-gamma events were analysed, For them the distribu+iona over the t o t a l ener-

gy

and y-quanta p a i r massea were

reconstructed

a f t e r 1C-f it (Figs,

2a,

2b). Energy resolution of the ape<rtrometer was 9%

(FWIBf)

and

its

m a a resolution was 11% f o r xO's and 5% f o r ?-mesons. A s a result we

had

. ~ 2 . 2 * 1 0 ~ no-mesons and -5 -10 q -mesons f o r the polarized tar e t of

both signs

(22%

and 5% from the t r i g g e r level, reapectivelyy. The 4-momentum t r a n s f e r squared snd azimuthal angle of no - ^{and q-me-}

sons were determined f o r each aelected event and two-dimensional dia-

tributions were accumulated both f o r positive and negative polariza-

t i o n s of the t a r g e t and f o r t h e background carbon t a r g e t a s well, The polarization value f o r t h e reactions

(1

1

and (2)

was calculated using the formulas described elsewhere

/3,16/.

Fig.2 - a ) The measured energy speotnun f o r

2

y-events. The arrows indicate the i n t e r v a l ~ h o s e n f o r no- and q -masons, 32 g E h47 GeV.

The energy resolution of the spectrometer i a 9%. b) The mass spectrum of 2 y-events a f t e r applying 1C-fit, The points q d i c a t e the i n t e r v a l chosen gor mO- mad ?-mesons, 1 0 0 s m ~ 1 7 0 ( ~ e V / c ) and 4 9 0 ~ m s 6 1 0

(MeV/o) . The mass resolution

bm/m

11% f o r

TLO

and 5% f o r q-meaons.

BACKGROUND

FOR REACTIONS it-p

- ^{non AND m-p -7%}

For different i n t e r v a l s over t we present in Pig.3 t h e energy spec- t r a f o r two-gamma events on hydrogen, which were seleoted according t o the c r i t e r i a men$ioned above, except the seleotion by energy (the difference in r e l a t i v e u n i t s between t h e n o ~ l i z a d e f f e c t s on propa- ne-diol and carbon targets), The e l a s t i c peak is aeen t o be very pro- nounced, it kinematically shifts towards lower energies with the powth of -t. The eontribution from i n e l a s t i c events (BKG) under the e l a a t i c peak i n the energy range marked with arrows increases with the growth of t.

Fig.3 - The energy spectra of 2 y-events on hydrogen selected f o r mass of

no-

and q a t different values of t h e 4-momentum t r a n s f e r squared t. a , b l a r e f o r no, c,d) are f o r q .

The main source of t h e background f o r the reactionhi (1

) and (2)

i a

charge exchange on carbon nuclei. This background may be excluded i f

measuremente on the carbon t a r e t a r e used. The background prooessea

f o r e l a s t i c

reactions ( 1 )

and

f 2 )

a r e i n e l a s t i c onea 13-5/ when out

of four photons two a r e missed by the veto-system o r occur below the

detection energy threshold. One of the o r i t e r i a usea t o estimate the

correctneaa of the obtained physics r e a u l t a i s t h e measurement of

c2-178 JOURNAL.

DE

PHYSIQUE

d i f f e r e n t i a l cross sections i n our experiment. The d i f f e r e n t i a l cross section on hydrogen i s i n agreement with the r e s u l t s from papers

122, 23/*

DISCUSSIONS OF no RESULTS

The values obtained f o r polarization a r e presented

in

Fig.4, The er- r o r s a r e a t a t i s t i c a l . The r e l a t i v e systematic e r r o r brought about by uncertainties i n our measurements of the t a r g e t polarization and revelation of t h e "Dilution factorn i s l e s s than 10%. The setup llup and down asymmetry and f a l s e " l e f t - r i g h t w asymmetry due t o time d r i f t of the apparatus, are comparable with zero within the limita of s t a t i s t i c a l e r r o r s f o r a l l t r a n s f e r s ,

The following q u a l i t a t i v e features may be singled out i n the beha- viour of polarization:

1.

Polari%ation P(%) i n the range Ocltl<O.4 (G~v/c)' i s poaitive2 and reaches 4-6%. For instance, in t h e range O.l-4t1-=0.2 (GeV/c) polarization i s equal t o (3.6 2 0.8)%, i e , more than f o u r standard deviations from zero level. However, a t l t

1 ~ 0 . 2 4

( G ~ v / c ) ~ there was a f i r s t evidence f o r t h e minimum

lin

polarization behaviour.

Polarization

in

t h i s region is compatible with zero within the e r r o r limita. I f three experimental points a r e f i t t e d by a conatant

(

see Fig. 4b

)

t h e minimum

w i l l

be seen i n the region mentioned above with t h e aonfidence l e v e l of 9%.

It i s l n t e r e e t i n g t o note

that

near values

of

t h e momenbn t r a n s f e r s one oan observe an equality of d i f f e r e n t i a l craas sections f o r n f p e l a s t i o m a t t e r i n g (vcross-overn e f f e c t /27,28/

).

It may turn out t h a t both phenomena have the same origin.

2. In the d i p region of the d i f f e r e n t i a l crosa section f o r r e a c t i - on (1) polarization changes i t s s beooming negative and a t It l -

D.

5 ( G e ~ / c ) ~ it reaches

(-18

*

^{8% PL.}

3. In thk region 0 . 7 5 ~ 1 t 1 4 . 3 (Ge$/o)'

polarisation

i a positive again and equal t o

(18 i

51%.

4. Tn the gegion l . 3<1t 1 ~ 2 . 0 ( G e ~ / c ) ~ polarisation tends t o change its sim,

^{P P}

(-14 + 10)%.

The comparison of the experimental r e s u l t s with the theoretioal cal- culations has been made in paper /3/ and i t has been found t h a t there is no model t o describe a l l the q u a l i t a t i v e features mentioned above. Two papers

/26,29/

were released a f t e r our preliminary r e s u l t s had been publiahed,

In paper

/26/

t h e polarization e f f e c t a

in

the aharge-exchange reao- t i o n IT-p -non a r e treated in the model of t h e correlated reggeons,

It

is shown t h a t the presence of t h e l o c a l minimum

in

the region

l t 1 ~ 0 . 2 4 (G~v/c)' in t h e t-dependence of t h e polarisation parame- t e r P(t) f o r reaotion

( 1 )

does not contradict the avaf l a b l e data on the e l a s t i c process nf p

-,TC'~.

Unfortunately

In

t h i s paper there i s no description of the polarization behaviour a t lt1>0.4 (GeV/c) .

In paper /29/ i n a Regge-type model with nonlinear t r a j e c t o r i e s the data on d i f f e r e n t i a l cross sections, t o t a l cross section diffe- rence

A V

and polarization of the reaotion (1) a r e analysed. The s o l i d l i n e i n Fig, 48 i a the r e m l t of t h i s paper.

DISCUSS

IONS OF f p

- ⁷ n RESULTS

The values obtained f o r p o l a r i s a t i o n in the reactfon $p - q n a r e presented i n Fig. 5,

0.05<1t1<0.45 ( ~ e ~ / c ) ~ t h e polarisation is small and

)%.

The polarisation remains n e g a t h e up t o -t

^t.

is equal t o -(-l0 + ^3)$ i n the region 0,45<ltl<

(-37 + TO)$ i n the-region 0.8dIt 141.5 (GeV/o)'.

Fig.4 a ) Polarization f o r the reaction m-p -non a t 40 GeV/c. The aolid line indicates the result of paper

/ 2 9 / .

b) Polarization for the reaction

C p

- ^{e n at 40 GeV/c}

^{i n}

the crosa-over region.

Fig.5 - ^{a )} Polarieation for the reaction rc-p - ^{T n at 40 GeV/c,}

The aolid l i n e

i s

for the predlo- t i o n of paper

/26/.

b)

Polarization for the reaction X-p -<(958)n at 40 GeV/c.

c) Asymmetry f o r the

reaction TL-p

- ^f

^'(1

²⁷⁰⁾ⁿ

^at

40 GeV/c.

C2-180 JOURNAL DE PHYSIQUE

The average value of polarirmation in t h e wide region 0 . 6 4 t 141.5 ( G ~ v / c ) ~ is

-20

+ 5% i e , f o u r standard deviations from zero.

We would l i k e t o point out t h a t nonsero p o l a r i s a t i o n in t h e r e a c t i o n X - p - ~ n h a s been discovered f o r t h e first time a t t h e momenta p 3 5 GeV/c. The r e s u l t s of o t h e r groups (see paper

/4/)

a r e compa- t i b l e with zero within s t a t i s t i a a l errors.

Our

r e s u l t s a r e in a disagreement with t h e t h e o r e t i o a l oalculationa /24,25/. There i s a q u a l i t a t i v e agreement between our experimental r e s u l t s

and

c a l c u l a t i o n of t h e model with t h e c o r r e l a t e d reggeons

/26/ but, unfortunately, t h e r e are no prediction8 f o r l t 1>0, 8 ( ~ e ~ / c ) ? DISCUSSIOXS OF 1X-p-7[~ (958)n AND

T G - P - ~

'(1 270)n RESULTS

The r e e u l t a of p o l a r i z a t i o n in t h e r e a o t i o n n-p-y1(958)n

at

40 GeV/c a r e presented in Fig.5b).

'-27

We

have obtained 104 ttcleanw events of r e a c t i o n (3) a f t e r a p r o p r i a t e kinematic cuts. Nobody measured p o l a r i s a t i o n i n r e a c t i o n (37 i n t h e past. The t o t a l c r o s s seotion i a only 55 nb/30/ at 40 GeV/a, The po- l a r i z a t i o n i s negative at small 1 t l , but t h e s t a t i s t i c s is poor.

The mean value is -23 + 7% i n t h e region Ocltl<0.3 ( G ~ ~ T / c ) ~ , There i s an f n d i c a t i o n that p o l a r i e a t i o n ohangee its s i g n a t I t l ~ O . 3

(G~v/G)'.

In t h e region 0.34 t 1<0,8 ( G e ~ / c ) ~ it i a equal t o 19 + 1%.

The r e a u l t s of t h e l e f t - r i g h t asymmetry

in

r e a c t i o n ~~,p-P~(1270)n a r e presented

fn

F i g . 5 ~ ) . The nonzero asymmetry h a s been discovered f o r t h e f i r s t time i n r e a c t i o n

n'p-

fon. It 18 equal t o -25 + 4%

in t h e region

0 4

t 1 ~ 0 . 6 ( G ~ v / o ) ~ , ^U, more t h a n 6 standard deviations from zero. Unfortunately, t h e r e a r e no t h e o r e t i a a l p r e d i c t i o n s f o r t h e p o l a r i z a t i o n ( o r asymmetry) behaviour

in

r e a c t i o n s (3) and (4).

ACE;NOVn;EDGEMENTS

In

conclusion we would l i k e t o thank Professors Y.P.Dzhelepov, Yu.D.

Prokoshkin, L.

D.

Soloviev,

and

N.E.

T y u r i n

f o r h e l p f u l discussions

and

support of t h i s work,

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