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SPIN EFFECTS IN FRAGMENTATION OF GEV POLARIZED DEUTERONS

L.S. Zolin

Joint Institute for Nuclear research

Dubna

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Outline

• Introduction• Study deuteron breakup and backward dp-elastic at

Saclay and Dubna facilities and problems at explanation of Nd(k), T20, ko - data at k > 0.25 GeV/c

• GeV polarized deuteron beams as tool to study a spin structure of short range NN-forces

• Study dAX in cumulative regime as means to investigate the deuteron core spin structure

• Analyzing powers Ayy(xc,Pt) and Ay(xc,Pt) in dAX • Comporision SSA in dAX and pAX • Conclusion

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E >1GeV - the region of accelerator physics where interests of particle physicists and NN-force physicists are overlapped:

The structure of the short-range NN-force cannot be understood without knowledge of nucleon substructure.

Information on SR NN-forces can be extracted :

in DIS experiments with light nuclei, available rNN-scale is limited by low cross sections of (e,l )N-reactions ;

a) in the reaction of nuclei fragmentation with use h-probes (NA,piA), very low rNN are available (~ 0.2 fm) but interpretation is difficult due to distortion carried in by strong interacting probe.

We will discuss here results obtained at fragmentation of polarized deuterons with energies from 1 to 3.65 GeV/nucleon.

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GeV polarized deuteron beams is effective tool to study the deuteron spin structure in the region of deuteron core

Single spin asymmetry (SSA) in the reaction with polarized deuterons can be studied without use of expensive polarized target with the large dilution factor.

At fragmentation of high momentum deuterons one can test what is k- limit (rNN) for use of the nucleon model of the deuteron with disregard of nucleon substructure.

As it was demonstrated by spin experiments at intermediate energiesthe spin effects are very sensitive to a structure of the short rangeNN-forces.

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A.P.Kobushkin, Proc. of the Int.Symp.“Dubna Deuteron-93”,p.71,Dubna,1993

GeV deuteron beams permit to extract information of deuteron structure at internal momentum up to k=1 GeV/c

In 1982-83 Dubna (dp-breakup) and SLAC (ed-scattering) data showed that the nucleon mom. distribution in the deuteron deviates from IA-predictions based on standard DWF at k higher 0.25 GeV/c. The some models were successful at explanation this discrepancy but they encountered a difficulty at description of spin effects in the same region of internal momentum k0.25 GeV/c.

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Deuteron breakup N(d,p)X and backward elastic scattering p(d,p)d are the reactions where a pole mechanism (ONE) should dominate and IA calculations seems to be well based.

However, Saclay and Dubha measurements of the tensor analyzing power T20 and the polarization transfer ko revealed significant deviations from IA at k 0.25 GeV/c.

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What is the reason of these discrepancies? Is DWF constructed with realistic NNP not correct at rNN 0.4 fm?Comparison of data with different probes at study the same subject can preserve from hasty conclusion. In JLAB d(e,de’) experiment t20 was measured up to Q equivalent of k=0.65 GeV/c.At use of em-probe a rather good agreement with IA-predictionswas observed.

Q

So dN-reactions give a chance to probe the deuteron at very high k (k of 1 Gev/c is reached) but a number of mechanisms affecting ona behavior of observables must be taken into account at data interpretation (FSI,3NF, rescatt.and so on)

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Xc/XF - 1< 0.1 at E= 9 CeV

Xc XF at E >> MN

Among hadrons probes a meson as mediator of NN-forces might bring a rich information on SR NN-forces. What sign can identify that the meson is produced at short rNN ?

One can use a meson production in dNhX reaction in the cumulative region, with mom. above available in NN-interaction. So the cumulative meson can be produced on strong correlated NN-pair only (in the d-core).

The invariant variable xc is used for the cumulative reactions. It is defined by 4-mom. conservation: xcPd+PN=Ph+Px, Pd is 4-mom. per nucleon. So xc is min. fragmenting mass (in Mn unit) to produce h. In dNhX xc ranges up to 2. It is a some analog of xF for a case of NA-interaction.

Pbeam = 4.5 GeV/c/nucl.

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More motivations for study the reaction dApX in the cumulative regime:

1) Identify the two alternative mechanisms of the cumulative regime

a) based on Fermi motion: p is produced by high momentum nucleon

NN->NNp, IA can be applied to calculate T20 and the prediction

can be compare with data;

b) based on fragmentation 6q-component in the deuteron with hadronization of struck quark into the meson;

no theoretical recipe to predict a behavior spin observables, but one can try to apply Collins or/and Sivers mechanisms to 6q fragmentation for data interpretation;

2) The large SSA were observed in pppX in beam fragmentation region at Pt> 0.5 GeV/c (FNAL data) and at xF > 0.5 (BNL data). One can wait a remarkable spin effects at d-fragmentation into high momentum pions with high Pt if similar mechanisms dominate at fragmentation of 3q- and 6q-system.

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E704, 200 GeV/c BNL , 22

GeV/c

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VBLHE experimental setup for study an inclusive meson production A(d,p)X

sr,W(p/p)=2.4x10 p/p=2.2%

Acceptance of the focusing spectrometer

Momentum range 1.5 to 6 GeV/c

Deuteron beam intensity Id = 2x10 d/spillPzz(+) = 0.640 +- 0.033 +- 0.026 (sys)Pzz(-) = -0.729 +- 0.024 +- 0.029 (sys)

TOF-bases: Ls1-s5 =28m Ls2-s5 = 21m

TOF-resolution =0.2 ns

TOF 1,2 - correlation

-5

9

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Tensor analyzing power Ayy in A(d,)X at Pd=9 GeV/c

The sign of Ayy at xc >1 is negative at all (contrary to DPM IA-prediction)

Magnitude of Ayy increases with rise of Ayy increases with rise of xc and reaches –0.4 at xc=1.5 (close to maximum of D-wave contrib. in DWF)

and k –dependences in A(d,)X is contrary to A(d,p)X

))(Ap21

)(Ap23

1)(()( yyzzyz0

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Transverse momentum dependence of Ayy in A(d,)X

Ayy rises in magnitude at increase of Pt from 0.4 to 0.8

Ayy(Pt)-rise is linear at of 135 and 180 mrad to find the limit of linear rise a study of higher Pt is desirable

Pt-threshold effect near 0.5 GeV/c is known for An(pppX) - Collins effect (PFF).Ayy(Pt)-effect is connected with D-state of 6q in the deuteron core. Sivers mechanism (PDF) can be applied to connect Ayy(Pt) with the orbital momentum (L=2) of 6q

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Ayy at fragmentation of 5 GeV/c tensor polarized deuterons

At low Pt (~0) Ayy shows weak xc-dependence varying from +0.1 to –0.1 when Pd ranges from 5 to 9 GeV/c

The large tensor effects (D-wave) become apparent at xc > 1with rise of Pt above ~0.4 GeV/c

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Vector analyzing power Ay in A(d,)X

Ay was measured with 9 GeV/c vectorpolarized d-beam at = 180 mrad

Ay changes monotonously from 0.1 to –0.1 at q increase from 1.5 to 4 GeV/c (0.4 < xc < 1.7, 0.25 < Pt < 0.7) crossingzero near 3 GeV/c where xc = 1

Sign of Ay is similar for both sign of due to isospin I=0 of the deuteron

The significant growth of Ay-magnitudemight be at Pt > 0.7 GeV/c as inp(p,)X at high energies

(+) , o (-) 180 mrad

(-) 135 mrad.

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Comparison Ay(dAX) and An(pppX)

• At high energies An(ppX) has opposite sign for (+) and(-) and show linear rise at Pt > 0.5 GeV/c (accordance with Collins effect)

• At moderate energies a behavior An(+) is the same but An(-) is small and Pt- indefinite

• If SSA mechanisms for 3q- and 6q-systems are the same than the similar tendencies have to be observed for Ay in dpX and ppX.

• One can note: Ay(+) tends to increase its magnitude at xc > 1; Ay(-) shows more flat form. “-”sign of AY(+) seems due to opposite spin directions for the deuteron and for nucleons in D-waveLower Ay comparing with AN could be expected: SU(6) approach leads to Ay(d)<<An(p) due to diff. quark content :p() [u()u()d()] 2u of 3q contribute to An[p(+)]d() [u()u()d()][u()d()d()] 1u of 6q contributes to Ay[d(+)]

ANL, pp11GeV/c

Dubna, dp4.5GeV/c/n

E704, pp200GeV/c

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ConclusionThe vector Ay and tensor Ayy analyzing powers were studied at 5 and 9 GeV/c d -fragmentation into cumulative pions. Those pions permit to probe the deuteron core structure up to rNN ~ 0.2 fm where two correlated nucleon can be studied as 6q-system

Ayy at Qp =180 mrad shows a linear rise at increase Pt from 0.4 to 0.8 GeV/c – the threshold effect similar to An(ppX).Ayy(Pt)-effect is connected with the orbital momentum of 6q (D-state in deuteron core) - Sivers mechanism can be applied (PDF).Ay in dpX is small due to isospin I=0 (u,d-symmetry of pn-pair).Ay(Pt) can be explane just as An(Pt) in the framework of Collins effect

Precision measurements at Pt > 0.7 GeV/c are desirable to find a limit of Ayy(Pt) linear rise and to clarify Pt-dependence of Ay at xc > 1.

Study polarized deuteron fragmentation into cumulative kaonsdpKX could bring info on strangeness role in spin structure of short range NN-forces.

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