Soft Physics at Forward Rapidity I.G. Bearden Niels Bohr Institute Københavns Universitet 6. April 2008 WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute

WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute Outline Introduction BRAHMS experimental details K/p ratio Why is it interesting? How does it look vs. rapidity? vs. pbar/p? Stopping What is it? Why is it interesting? BRAHMS results +systematics Summary 6. April 2008 WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute

WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute early universe QCD phase diagram quark gluon plasma SIS AGS SPS RHIC T TC~170 MeV crab nebula neutron stars temperature hadron gas Nuclear Matter baryon chemical potential mB 940 MeV 6. April 2008 WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute

how can we probe the plasma? e, pressure builds up System expands & cools g, g* e+e-, m+m- Real and virtual photons emitted as thermal radiation. Hard scattered partons, Heavy q’s probe plasma p, K, p, n, f, L, D, X, W, d, Hadrons reflect (thermal) properties when inelastic collisions stop (chemical freeze-out). 6. April 2008 WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute

WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute The BRAHMS Experiment It’s Broad RAnge Hadron Magnetic Spectrometers! 90° 30° and 30° to 90° (MRS) Two small solid angle spectrometers (FS and MRS) 2.3° 30° that can rotate from 2.3° to 30° provide excellent PID over broad range in y-pT 6. April 2008 WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute

WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute The BRAHMS experiment FS: TPC, TOF, Cherenkov 2.5 - 30 deg.  = 1.5 - 4 MRS: TPC, TOF 30 - 90 deg. = 0 - 1.5 Global: || < 5 6. April 2008 WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute

WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute A BRAHMS Event T2 D2 FFS at 6 degrees T1 D1 collision point (vertex) beam beam TPM1 D5 TPM2 Reconstructed tracks MRS at 90 degrees 6. April 2008 WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute

Particle Identification TIME-OF-FLIGHT RICH: Cherenkov light focused on spherical mirror ; ring on image plane Ring radius vs momentum gives PID p / K separation 20 GeV/c Proton ID up to 35 GeV/c CHERENKOV (2 settings) 6. April 2008 WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute

WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute Particle Spectra After appropriate corrections, we combine all data sets to obtain final invariant yields over a broad range of rapidity and pT p K p 6. April 2008 WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute

Particle Spectra (200 GeV Au+Au) PRL 94, 162301(2005) Top 5% central collisions Pions: power law Kaons: exponential Protons: Gaussian 6. April 2008 WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute

WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute Outline Introduction BRAHMS experimental details K/p ratio Why is it interesting? How does it look vs. rapidity? vs. pbar/p? Stopping What is it? Why is it interesting? BRAHMS results +systematics Summary 6. April 2008 WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute

Why look at ’low’ pT K and pi? 6. April 2008 WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute

Pt spectra from 0-10% central Au+Au collisions Pion spectra fitted with a power law at mid-rapidity and mt exponentials at forward rapidities. The kaon spectra fitted with mt exponentials at all rapidities. Quark Matter, 4-10 February, Jaipur, India

Anti-particle/particle ratios vs. rapidity At y~0 pbar/p ~0.47 K⁻/K⁺ ~ 0.85 π⁻/π⁺ ~ 0.98 At y~3 pbar/p~0.02 !! K⁻/K⁺ ~ 0.6 π⁻/π⁺ ~ 1.1 Quark Matter, 4-10 February, Jaipur, India

K⁻/K⁺ vs baryo-chemical potential The blue curve is a statistical model calculation with a chemical freez-out temperature fixed at 170 MeV but allowing the baryo-chemical potential to vary. I.G.Bearden et al., BRAHMS Collaboration, Phys.Rev.Lett. 90 (2003) 102301 F.Becattini et al., Phys.Rev. C64 (2001) 024901 Quark Matter, 4-10 February, Jaipur, India

K⁻/K⁺ vs baryo-chemical potential pbar/p K⁻/K⁺ vs baryo-chemical potential The blue curve is a statistical model calculation with a chemical freez-out temperature fixed at 170 MeV but allowing the baryo-chemical potential to vary. I.G.Bearden et al., BRAHMS Collaboration, Phys.Rev.Lett. 90 (2003) 102301 F.Becattini et al., Phys.Rev. C64 (2001) 024901 Quark Matter, 4-10 February, Jaipur, India

Integrated dN/dy vs rapidity UrQMD references: S.A.Bass et al., Prog.Part.Nucl.Phys.41 (1998) 225-370 M.Bleicher, E.Zabrodin et al., J.Phys.G25 (1999) 1859-1896 AMPT references: B.Zhang et al., Phys.Rev.C61 (2000) 067901 Z.-w. Lin et al., Nucl.Phys.A698 (2002) 375-378 The dN/dy distributions were fitted with gaussian functions with fixed centroids at y=0. The different kaonic widths reflect their different production mechanisms. Quark Matter, 4-10 February, Jaipur, India

Quark Matter, 4-10 February, Jaipur, India K/π ratios vs. Rapidity UrQMD and AMPT models fail to fit the K⁺/π⁺ ratio behaviour at forward rapidity. The negative ratio is reasonably explained. Quark Matter, 4-10 February, Jaipur, India

Quark Matter, 4-10 February, Jaipur, India K/π vs pbar/p I.G.Bearden et al., BRAHMS Collaboration, Phys.Rev.Lett.94 (2005) 032301 I.Arsene et al., BRAHMS Collaboration, Nucl.Phys.A757 (2005) 1-27 Quark Matter, 4-10 February, Jaipur, India

WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute Outline Introduction BRAHMS experimental details K/p ratio Why is it interesting? How does it look vs. rapidity? vs. pbar/p? Stopping What is it? Why is it interesting? BRAHMS results +systematics Summary 6. April 2008 WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute

Stopping or Transparency ? Before collision After collision Stopping Transparency y dN/dy (p-pbar) yb δy y y 6. April 2008 WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute

Stopping: where are the baryons? 6. April 2008 WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute

What you can do with 100 times more data… 6. April 2008 WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute

Stopping: where are the baryons? 6. April 2008 WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute

Measure @ 62 A GeV: Protons and antiprotons 6. April 2008 WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute

How many ’net’ protons : BRAHMS preliminary 6. April 2008 WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute

Rapidity loss: 6th order polynomial Gaussians in pz: 2.03  0.16 2.00  0.10 6 order polynomial Total E=25.72.1TeV Rapidity loss: 22. Oktober 2004 Forward Physics Workshop, KU I.G.Bearden, Niels Bohr Institute

Systematics of stopping 6. April 2008 WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute

Projectile net-baryons: Subtract ”target” contribution (characterized by exp(-y)[p+p] exp(-y/2)[ZPhysC43(1989)241] 6. April 2008 WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute

’Net’ baryon vs. rapidity as a function of beam energy AGS √snn=5 GeV SPS √snn=17 GeV RHIC √snn=62 GeV RHIC √snn=200 GeV LHC √snn=5500 GeV 6. April 2008 WNND08, South Padre Island I.G.Bearden, Niels Bohr Institute