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Matter Effects at SPS energies

Matter Effects at SPS energies. What we can learn about stopping from the system size dependence of net baryon rapidity distributions. H. Str ö bele, Univ. Frankfurt for the NA49 collaboration. Outline. Motivation and perspectives The data:

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Matter Effects at SPS energies

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  1. Matter Effects at SPS energies What we can learn about stopping from the system size dependence of net baryon rapidity distributions. H. Ströbele, Univ. Frankfurt for the NA49 collaboration

  2. Outline • Motivation and perspectives • The data: • Centrality selected net proton (d, 3He) distributions from min bias Pb+Pb collisions at 40 and 158 GeV/nucleon (new NA49 data). • Net proton distributions from p+p=> p + X at 158 GeV/c as reference (new NA49 data). • Some AGS and RHIC data for comparison • Resume

  3. NA49 preliminary Central data p+p (new) Motivation (I) Stopping in A+A versus p+p • Mean rapidity shift of incident nucleons • inelasticity (K) a measure of energy loss • shape change of dn/dy of net nucleons K= Einel /(sqrt(s)/2 -mp) C. Blume 2008

  4. Motivation (II) Freeze-out points in the T- μBplane at different energies and for different system sizes (NA61 strategy, but here for centrality selected Pb+Pb collisions and only two energies). No centrality dependence of μB predicted by SHM, Becattini, Manninen, Gazdzicki. hep-ph/0511092 NA49 NA61 planned

  5. Perspective Hydrodynamics predicts focusing of the system trajectories close to the critical point, which may be observed by studying T and μB as function of system size (or centrality). Nonaka, Asakawa, nucl-th/0410078

  6. The (new NA49) data dn/dy of net protons in Pb+Pb at different centralities beam beam 40 GeV/nucleon 158 GeV/nucleon preliminary

  7. The (new NA49) data dn/dy of net protons, d, and 3He in central Pb+Pb at 158 and 40 GeV/nucleon preliminary preliminary Mapping of configuration space on rapidity?

  8. Comparison to AGS AGS data (Au+Au) NA49 data (40 GeV/nucleon Pb+Pb) (Back et al., PRL86(2001)1970) preliminary No midrapidity plateau at 40 GeV/nucleon?

  9. Comparison to transport models(normalized, 158 GeV/nucleon data) HSD UrQMD no model comparison yet available at 40 GeV/nucleon

  10. p+p collision data 12, 24 GeV/c, 158 GeV/c (new!), and RHIC data midrapidity ylab Blobel et al., NPB69,454 NA49, arXiv:hep-ex/0904.2708 Dalsgaard, QM09

  11. p+p collision data dn/dy dn/dxF backward forward hemisphere midrapidities 24 40 158 NA49, arXiv:hep-ex/0904.2708 Scaling for 1 < ylab < 2 and structure in dn/dx

  12. Comparison to transport models(158 GeV/c p+p data) Significant differences in the region, where the energy loss per unit of rapidity is highest. Homework for the model experts. NA49, arXiv:hep-ex/0904.2708

  13. p+p collision data neutrons (-antiprotons) dn/dy (computed)dn/dxF NA49, arXiv:hep-ex/0904.2708

  14. The (new NA49) Pb+Pb datanormalized to Nw and comparison to NN 40 GeV/nucleon 158 GeV/nucleon calc. Watch the right side, when I switch centrality

  15. The (new NA49) Pb+Pb datanormalized to Nw and comparison to NN 40 GeV/nucleon 158 GeV/nucleon Watch the right side, when I switch centrality

  16. The (new NA49) Pb+Pb datanormalized to Nw and comparison to NN 40 GeV/nucleon 158 GeV/nucleon Watch the right side, when I switch centrality

  17. The (new NA49) Pb+Pb datanormalized to Nw and comparison to NN 40 GeV/nucleon 158 GeV/nucleon Watch the right side, when I switch centrality

  18. The (new NA49) Pb+Pb datanormalized to Nw and comparison to NN 40 GeV/nucleon 158 GeV/nucleon Watch the right side, when I switch centrality

  19. The (new NA49) Pb+Pb datanormalized to Nw and comparison to NN Little or no change in shape with centrality in the acceptance. Only the integral varies, as does number of wounded nucleons.

  20. The (new NA49) Pb+Pb datanormalized to Nw and comparison to NN 40 GeV/nucleon 158 GeV/nucleon Watch the left side, when I switch centrality

  21. The (new NA49) Pb+Pb datanormalized to Nw and comparison to NN 40 GeV/nucleon 158 GeV/nucleon Watch the left side, when I switch centrality

  22. The (new NA49) Pb+Pb datanormalized to Nw and comparison to NN 40 GeV/nucleon 158 GeV/nucleon Watch the left side, when I switch centrality

  23. The (new NA49) Pb+Pb datanormalized to Nw and comparison to NN 40 GeV/nucleon 158 GeV/nucleon Watch the left side, when I switch centrality

  24. The (new NA49) Pb+Pb datanormalized to Nw and comparison to NN 40 GeV/nucleon 158 GeV/nucleon Watch the left side, when I switch centrality

  25. The (new NA49) Pb+Pb datanormalized to Nw and comparison to NN 40 GeV/nucleon Little or no change in shape with centrality above ylab~ 1.6 corresponding to xF > 0.4. Constant “peak” position?

  26. Characteristics of stopping (in A+A) • It is important to include neutrons when studying stopping in A+A and p+p collisions. • Is coalescence at the origin of light fragments? (40AGeV) • Hyperbolic scaling for |xF| < 0.4, thus a y-range around midrapidity which increases with beam energy. • Tentative interpretation: • Nucleons in this range have undergone a violent interaction (in N+N and in A+A collisions). • Only one violent interaction of each nucleon in A+A collisions! • Secondary collisions change the shape of dn/dx distributions only in the range |xF| > 0.4

  27. Thank You

  28. Backup slides • There are three regions relevant for stopping: • diffractive regime for xF> xFdif (Ebeam) • standard energy loss xFstandard < xF < xFdif • central scaling |xF|< 0.4 (60% energy loss caused by violent interactions).

  29. p+p collision data on hyperons (Lambdas) dn/dy Ycm

  30. The (new NA49) data Extrapolation into unmeasured region by means of chargeand baryon number conservation preliminary

  31. The (new NA49) data preliminary preliminary Normalised to 1 at midrapidity and scaled

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