L 0 polarization in pp → p L 0 K + ( p + p - ) 5 at 27.5 GeV

1. L0 polarization in pp → pL0K+(p+p- )5 at 27.5 GeV Julián Félix Instituto de Física, Universidad de Guanajuato México

2. BNL 766 Collaboration J. Félix1, D.C. Christian 3, M.D. Church 4, M. Forbush 5 , E.E. Gottschalk 3, G. Gutiérrez 3, E.P. Hartouni 2, S.D. Holmes 3, F.R. Huson 5, D.A. Jensen 2, B.C. Knapp 4, M.N. Kreisler 2, J. Uribe 2, B.J. Stern 4, M.H.L.S. Wang 2, A. Wehmann 3 , L.R. Wrencke 4, J.T. White 5. 1 Universidad de Guanajuato, León, Gto. 2 University of Massachusetts, Amherst, MA 01003 USA 3 Fermilab, Batavia, IL 60510, USA 4 Columbia University, Nevis Lab. Irvington NY, 10533 USA 5 Department of Physics, Texas A&M University, College Station

3. INTRODUCTION • BNL 766 EXPERIMENT • DATA SELECTION • L0 POLARIZATION • RESULTS • CONCLUSIONS

4. 0 L P T Introduction 1.Elementary Concepts pp → pL0K+ C of M x 1.1 xF 1.2 PT P P xF z P y + K

5. xF L || 0 L max L || P x T P Transverse momentum T P P xF z P P P y + K

6. 1.3 n normal to the production plane P P X 0 0 L L 0 beam L n x P P X n 0 L beam P P P z y + K production plane

7. L0 K+ L0K+ 1.4Mxinvariant mass of {L0K+} system.

8. L0 X0 X- X+ S L0 B. Lundberg et al, PRD 40, 39 (1989) K. Heller et al, PRL 51, 7025 (1983) R. Rameika et al, PRD 33, 3172 (1986) P. M. Ho et al, PRL 65, 1713 (1990) A. Morelos et al, PRL 71, 2172 (1993) J. Felix et al, PRL 82, 5213 (1999); 88, 061801 (2002); 76, 22 (1996) 1.5 Hyperon polarization

9. T. De Grand et al, PRD 24, 2419 (1981) R. Barni et al, PLB 296 (1992) 251 G.L. Kane et al, PRL 41, 1689 (1978) M. Anselmino et al, PRD 63, (2001) 054029 C. Boros et al, PRD 62 (2000) 014021 W.G.D. Dharmaratna and G.R. Goldstein, PRD 53, 1073 (1996) 1.6 Models Semiclassical ideas Regge like QCD PQCD Fragmentation functions Gluon fusion

10. 2.Typical results of L0 polarization as function of xF and PT. (a) xF < 0 0.2 0 POLARIZATION P xF > 0 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 0 (b) -0.1 POLARIZATION P circles, this Experiment squares, reference 2 -0.2 -0.3 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 PT (GeV/c) PRL J. Felix 1996 Ref. 2 PRL, Heller 1978

11. In inclusive and exclusive p-nucleus reactions L0 polarization, in some kinematical regions is described very well by P(xF , PT) = +a xF PT a depends on target nature, it is independent of the beam energy. in pp → pL0K+(p+p- )N, N= 1, 2, 3, 4 at 27.5 GeV a = - 0.443 + 0.037 (GeV/c)-1 PRL J. Felix et al, (1999)

12. Typical results of L0 polarization as function of Mx{L0K+} J. Felix et al, PRL, (2002)

13. BNL 766 Experiment Was designed to study exclusive pp reactions up to 20 charged particles in the final state. E766 Spectrometer

14. collected ~ 320 million raw events ~ 3 million as exclusive events pp → pp (p+p- )N, N= 1, 2, 3, 4, 5 or pp → pL0K+(p+p- )N, N= 1, 2, 3, 4, 5

15. Data Selection Kinematical constraints 1. momentum 2. electric charge 3. strangeness 4. baryon number conservation

16. additionally to select pp → pL0K+(p+p- )5 1. Two vertices separated 2. L0 → pp- 3. Fourteen charged particles

17. L0 225 1973 events with small background 200 175 150 125 100 75 50 25 0 1.105 1.1075 1.11 1.1125 1.115 1.1175 1.12 1.1225 1.125 1.1275 1.13 L0 mass (GeV)

19. Events Mx (GeV)

21. typical reconstructed event pp → pL0K+(p+p- )5 p p- L0

22. L0 polarization y n p q dN N (1+ cos ) P q a 0 d W L0 x a = 0.642 + 0.013 Polarization p- z P

23. fitting to a straight line cos q distribution 2 dof = 0.68 1.61 < Mx < 1.70 cos q

24. m P = ab 2 ( ) + + DP =P Da Db Dm 2 ( ) 2 ( ) statistical only a m b

26. Results as function of xF

27. Results as function of PT J. Felix et al, PRL 2002 This experiment

28. Results as function of Mx J. Felix et al, PRL 2002

29. Conclusions - L0 polarization from pp → pL0K+(p+p- )5 at 27.5 GeV is akin to L0 polarization from pp → pL0K+ at 800 GeV. - L0 polarization depends on xF, PT and Mx {L0 K+}.