Baryon Stopping at 40 and 158 A GeV

June 2009 CPOD09 H. StröbeleGoethe-Universität Frankfurt

Baryon Stopping at 40 and 158 A GeV

Net proton spectra in pp, peripheral and central PbPb

collisions


outline

• energy loss and baryon transport• (normalized) rapidity and Feynman x• net protons, net baryons, baryochemical potential (Anti-

L/Anti-p)• rapidity loss: scaling in “fragmentation” and mid-rapidity

regions ??• sqrt(s) dependence of rapidity shape and ~ loss, • sqrt(s) dependence of chem.-temperature and <p_T>• centrality dependence of rapidity shape and ~ loss at 40

& 158 GeV/nucleon• centrality dependence of chem.-temperature(?) and

<p_T> at 40 & 158 GeV/nucleon• model comparison: HSD, UrQMD, core corona


energy loss and baryon transport

• In particle collisions part of the cm-energy of the incident particles is diverted into:– Thermal motion– Radial or transverse flow– Mass (particle production)

• The remaining energy stays in the longitudinal motion

• => plong ∙c = (√s – Ethermal – Eflow – ∑mi∙c2)/2


energy loss and baryon transport

• => plong ∙c = (√s – Ethermal + Eflow + ∑mi∙c2)/2

• Plong is commonly represented by– rapidity: y = ln((E+plong)/mT) (energy loss causes

rapidity shift (e.g. ΔEcm=0.5 ≈> Δy=0.7)).

• or– Feynman x: xF = plong/pbeam (energy loss is mapped

directly on xF (e.g. ΔE=0.5 ≈> xF= 1 – 0.5)).


• We will compare proton rapidity distributions from 40 and 158 A GeV PbPb collisions at different centralities to nucleon-nucleon (NN) data (as a base line).

• First get the base line, i.e. NN


energy loss and baryon transportexample: p+p =>p + X at 158 GeVnew from NA49 [arXiv:0904.2708v1 [hep-ex]

• rapidity XF distribution


energy loss and baryon transportexample: p+p =>p + X at 158 GeV

• Neutron complication

– dn/dx of net neutrons must be converted into dn/dy



• hyperon complication



• Base line for centrality dependend Pb+Pb collisions at 158 A GeV: – pp => p + X– pp => n + X– pp => Y+ X

• What about 40 A GeV (no data on elementary collisions )


energy loss and baryon transportexample: p+p =>p + X at 12 & 24 GeV (Blobel data)


energy loss and baryon transportexample: p+p =>p + X at 40 GeV/c


energy loss and baryon transportparametrization


energy loss and baryon transportrapidity shift in nuclear collisions


Results on Pb+Pb at SPS

158 A GeV



158 A GeV

net protons



158 A GeV

Normalized to

Nw



158 A GeV

net protons

peripheral

versus pp.

normalisation?



40 A GeV



40 A GeV

peripheral

versus

pp



40 A GeV

extrapolation

to y_beam??

Baryon Stopping at 40 and 158 A GeV

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