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SPIN EFFECTS AT FRAGMENTATION OF GEV POLARIZED DEUTERONS INTO PIONS WITH LARGE TRANSVERSE MOMENTUM

SPIN EFFECTS AT FRAGMENTATION OF GEV POLARIZED DEUTERONS INTO PIONS WITH LARGE TRANSVERSE MOMENTUM. ] Prehistory and motivation: d h p g pX & SSA in p h p g p X. L.S. Zolin for the SPHERA collaboration ( Dubna – Nagoya - Sofia ).

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SPIN EFFECTS AT FRAGMENTATION OF GEV POLARIZED DEUTERONS INTO PIONS WITH LARGE TRANSVERSE MOMENTUM

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  1. SPIN EFFECTS AT FRAGMENTATION OF GEV POLARIZED DEUTERONS INTO PIONS WITH LARGE TRANSVERSE MOMENTUM ] Prehistory and motivation:dhpgpX& SSA in phpgpX L.S. Zolin for the SPHERA collaboration ( Dubna – Nagoya - Sofia) • Study dhAgpX in cumulative regime – tool to investigate . spin structure of 6q-configuration in the deuteron ] Analyzing powers Ayy(xc,Pt) & Ay(xc,Pt) • Future plan: higher Pt, lower errors, study dhAgKX

  2. Study the deuteron spin structure at short distances in d-breakup A(d,p) and in backward elastic H(d,p)d with GEV polarized d-beams • Several GeV pol. deuteron beams in Saclay and Dubna permitted to examine the predictions of IA-calculations with realistic NN-potentials for spinobservables in A(d,p)X and H(d,p)d at internal momenta up to k=1 GeV/c. Study of spin observables, T20 and ko, showed considerable deviations from IA-predictions at k> 0.25 GeV/c • A lot of different models were proposed to explain this phenomena. The some of them permit to improve description of the data. However those of them ignoring QE- mechanism cannot explainsatisfactory T20 and ko behavior in all examined k-region up to 1 GeV/c. 2 2 w – uw sqrt(2) T20= - - Tensor analyzing power 2 2 U + W 2 2 u – w –uw/sqrt(2) Ko= - Polarization transfer 2 2 u + w

  3. Hadron and EM probes at study of the deuteron spin structure * h-probe T20 • The hadron probing experiments revealed significant deviations of spin observables behavior from expected in accordance with standard potentialmodels (for instance, T20 does not change sign as was expected). • Hadron probes permit to probe the deuteron structure at very high internal momentum (k=1. GeV/c is reached), however a number ofmechanisms influencing on behavior of observables should be taken into consideration (DD -, NN -,N N –components in DWF, P-wave admixture, FSI, 3NF and so on) • EM-probe permitted to probe the deuteron spin structure in non-destroying regime up to Q=6.5 fm (keqv= 0.65GeV/c): JNAL –data for ed-elast. Rather good agreement with IA-predictions show that distortion-sources peculiar to hadron probe is not active in this regime. • It seems among strong interacting probes nucleon one is too rough to study the deuteron core region. One can hope a meson probe can permit to extract more detail information. 0 * * * k (GeV/c) 1 e-probe -1 JLAB d(e,de’) -1 -1 Q(fm )

  4. Cumulative hadron production is tool to study of nucleon clusters in nuclei (6q-component in the deuteron) To study in explicit form the spin effects due to meson- and quark-exchange mechanisms atdeuteron fragmentation the reaction withcumulative meson production dA->hcX can be used . Pbeam = 4.5 GeV/c/nucl. • Cumulative hadron hc is defined as a high momentum hadron produced outside the kinematical limit for free NN collisions. At deuteron fragmentation hccan be produced off correlated nucleon pair only (off the deuteron core) which can be analyzed as 6q-configuration. • To describe hc- spectra the cumulativevariablexccan be used defined by 4-mom. conservation at lower limit of Mx: xcPb + Pt = Phc+Px, Pb(Pt) –4-mom. per beam (target)nucleon.xc is min. fragmenting mass (in MN unit) to produce hc. For NN->hcX xc ranges to 1, for dp->hcX xc-range from 1 to 2 corresponds to the cumulative regime. • In dp->pX at pd = 9 GeV/c the pions with momentum pp = 3.3 to 6.1 GeV/c are produced in cumulative regime . Xc gXF at E >> MN Xc/XF - 1< 0.1 at E= 9 CeV

  5. Motivation for study the reaction dAgpX in the cumulative regime • Two alternative mechanisms can be considered to explain hc - production: 1) thefirst is based onFermi motion , 2) the secondis based on consideration of multi-quark configurations in nuclei (6-quarkcomponent in the deuteron). • The numerical calculations forT20 in A(d,p) were performed in IA-approach (Fermi motion) supposing the direct production mechanism DPM:NN->NNp . • At DPMT20 in both A(d,p) and A(d,p) should besimilar (with extremum around k =0.25 GeV/c) because it is defined by asymmetry of nucleon momentum distribution in D-state (obviously, DPM disregards MEC in the deuteron). • Test of validity of DPM-hypothesis was one of motivations to study spin effects inA(d,p)X with use of cumulative regime to probe the deuteron core spin structure – it will be shown the test brought a negative answer.

  6. E704, 200 GeV/c • The second motivating fact: the large single spin asymmetries (SSA) AN in p(h)+pgp+X in beam fragmentation region at Pt>0.5 GeV/c (FNAL) and xF >0.5 (BNL). Pt=0.5 is a typical threshold where quark degrees of freedom manifest themselves. Thus,one could wait a remarkable spin effects at deuteron fragmentation into high momentum mesons with high Pt and/or high xc (if the samemechanismsdominate at fragmentation of 3q- and 6q-system). A detail study of analyzing power Ay and Ayy at fragmentation of 5-10 GeV polarized deuterons was started atDubna 10 GeV accelerator. BNL , 22 GeV/c

  7. Experimental Setup Acceptance of the focusing spectrometer -5 sr, DW(Dp/p)=2.4x10 Dp/p=2.2% TOF 1,2 - correlation Momentum range 1.5 to 6 GeV/c 9 TOF-bases: Ls1-s5 = 28m, Ls2-s5 = 21m Deuteron beam intensity Id = 2x10 d/spill Pzz(+) = 0.640 +- 0.033 +- 0.026 (sys) TOF-resolution: s = 0.2 ns Pzz(-) = -0.729 +- 0.024 +- 0.029 (sys)

  8. Tensor analyzing power Ayy in A(d,p)X A(d,p)X • The sign of Ayy in cumulative region (xc>1) is negative at all angles of pion emission (contrary to IA-predictions (DPM ) andAyy-behavior in A(d,p)X ) • Magnitude of Ayy(Q) increases with rise of emission angle (contrary to A(d,p)). • Ayy reaches a value of –0.4 atxc=1.5 where D/S-ratio in DWF is close to its maximum. • Some large D-state effects were revealed at fragmentation of 9 GeV tensor polarized deuterons into cumulative pions.

  9. Transverse momentum dependence of Ayy in A(d,p)X • As the pion transverse momentum increases from Pt=0.4 to 0.8 GeV/c the tensor analyzing power Ayy rises from magnitude of near zero to –0.4. • Starting point of Ayy(Pt)-rise corresponds to Pt=0.4-0.5 GeV/c and xc=1 – the beginning of cumulative regime. • Ayy(Pt)-rise is linear at both angles of pion emission, 135 and 180 mrad. At further study of Ayy it is desirable to measure Ayy at higher Pt to put limit of linear rise. • Remind: the same Pt-threshold is reviled for AN(ppgpX) and explanation can be done on base of Collins effect (PFF). But here it appears for the tensor analyzing power Ayy, it is connected to D-state of 6q-system (L=2). • Origin of Ayy(Pt)-rise is another, it dueto6q orbital momentum most likely instead of Collins effect.

  10. Vector analyzing power Ay in A(d,p)X • Ay was measured with 9 GeV vector polarized deuterons beam at Qp=180 mrad. • Ay monotonously changes from 0.1 to –0.1 with increase of qp from1.5 to 4 GeV/c (0.4< xc <1.7) crossing zero near xc=1. • Sign-similarityfor p and p can be due to isospin I=0 of fragmenting system. • The significant growth of Ay might be observed, presumably, at Pt>0.7 GeV/c as it takes place in p( p,p)X at high energies – to bemeasured. + - i- pos. pions, 180 mrad. o - pos. pions, 180 mrad [ - neg. pions, 135 mrad.

  11. More about Ay • At high energies (E704, 200 GeV/c) AN in ppgpX has opposite sign for p and p and at Pt>0.5 a linear approximation can be applied AN=a+bPt. Signs of AN(+) and AN(-) are in accordance with prediction of Collins effect (PFF). • At more moderate energies AN(+) demonstrate the same behavior but AN(-) is small and its Pt-dependence is indefinite (ANL, 11.75 GeV/c). If one supposes that mechanisms of SSA at fragmentation of 3q- and 6q-systems are the same the similar tendencies has to be observed for Ay in dpgpX. • Comparing ANL(ppgpX) and Dubna(dpgpX)data one can note: 1) Ay(+) tends to increase its negative value (in D-state nucleon spins are opposite to deuteron spin) beyond the typical threshold Pt=0.5 GeV/c. 2) Ay(-) demonstrates more flat form. • Evidently, precision of dgp data has to be improved and Pt-interval should be increased up to 0.8-0.9 GeV/c at least. It has to be done in the next runs. Lower Ay comparing with AN could be expected: SU(6) approach leads to Ay(d)<AN(p) due to diff. quark content : p(h) [u(h)u(h)d(i)] g 2u of 3q contribute to An[pgp(+)] d(h) [u(h)u(h)d(i)][u(i)d(h)d(h)]gonly 1u of 6q contributes to p n Ay[dgp(+)]

  12. Ayy at fragmentation of 5 GeV/c tensor polarized deuterons • To clarify an energy dependence of spin effects in dpgpX the measurement of Ayy at Pd=5 GeV/c was performed. • In deuteron breakup dpgpX Ed-dependence is weak because Ayy is defined by nucleon momentum distribution in the deuteron (DWF). • In dpgpX Ed-dependence demonstrate a threshold behavior in Pt-scale: Ayy shows a steep rice at Pt>0.5 GeV/c – deconfinement threshold (QDF manifestation). One can conclude: to study effectively 6q-conf. spin structure one needspolarized deuterons with Ed>6-8 GeV (Nuclotron design upper limit is Ed=11 GeV). • About Ayy-sign: indpgpX ds( )>ds( ) Ayy>0 . in dpgpX ds( )<ds( ) Ayy<0 . -form of nucleon density distribution in D-state • Pos. explanation in the model of multiquark config. fragmentation: the cumul. meson is produced at hadronization of quark-spectator which has a high mom.(x>1) as result of mom. randomization in 6q. Preferable direction of randomization is along spin axis: in orbit. mom. plane a constituent movement is regulated by rotation. The result is Ayy(p)<0

  13. Conclusion • The vector Ay and tensor Ayy analyzing powers were studied at fragmentation of 5 and 9 GeV/c polarized deuterons into high momentum pions (qp up to 5.3 GeV/c) produced in cumulative regime (xc >1). Those pions permit to probe the deuteron core structure (strong correlated NN-pair can be analyzed as 6q-configuration). • At pion emission at non-zero angles the Ayy demonstrates a steep rise beyond Pt =0.5 GeV/c – the same threshold as for SSA in p(h)pgpX (beam fragm. region). • The sign of Ayy is negative both for p(+) and p(-). It can be explained by zero isospin of fragmenting pn(6q)-system and preferable randomization of constituent momentum in 6q (L=2) along spin axis. • Ay(dgpx) is small and has similar sign for p(+) and p(-) at Pt<0.6 GeV/c due to quark content of pn-system (I=0). At Pt>0.6 Ay(p+) shows tendency to rise – it should be checked in future measurements at Pt=0.7 to 0.9 GeV/c. • Measurements at this Pt -range is needed to put upper limit of Ayy(Pt) linear rise too. • These measurements were proposed to be done in the next runs with dhat Nuclotron. New field of investigation is study of the reaction d(h)gKX in cumulativeregime to extract info of strangeness contribution in spin of strong correlated NN-pair (6q-system). • To realize future program the next parameter of polarized deuteron beam extracted from Nuclotron are required: Ed up to 11 GeV, Id >10^9d/spill (Pion program), Id> 10^10d/spill (Kaon program). These numbers are within the limits of Nuclotron design parameters.

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