PHENIX dileptons Thomas K Hemmick Stony Brook University
PHENIX dileptons Thomas K. Hemmick Stony Brook University
s. QGP Properties The matter is so opaque that even a 20 Ge. V p 0 is stopped. Heavy quarks are stopped All these interesting measurements Dilepton measurements probe the represent information recorded at the integral ofofthe evolution. endpoint thesystem evolution. PHENIX preliminary The matter modifies the shape of jets The matter alters J/y, dissolve+regen, stopped? Even heavy quarks flow
An Iconic Plot • In-Medium r Spectral Function • NA 60: SPS In+In • Is the spectral function the whole story? • Other components appear in RHIC collisions!
A quite difficult measurement Same analysis on data sample with additional conversion material Combinatorial background increased by 2. 5 Good agreement within statistical error Au+Au ssignal/signal = s. BG/BG * BG/signal 0. 25% ar. Xiv: 0706. 3034 p+p From the agreement converter/nonconverter and the decreased S/B ratio scale error < 0. 1% (well within the conservative 0. 25% error we assigned) large!!! ar. Xiv: 0802. 0050
The Reference: pp Mesonic Spectra • Start from the π0 , assumption: π0 = (π+ + π-)/2 • parameterize PHENIX pion data: ar. Xiv: 0802. 0050 PHENIX Preliminary Other mesons well measured in electronic and hadronic channel Other mesons are fit with: m. T scaling of π0 parameterization p. T→√(p. T 2+mmeson 2 -mπ2) fit the normalization constant All mesons m. T scale!!!
p+p Cocktail Comparison • Data absolutely normalized • Excellent agreement datacocktail • Extract charm and bottom cross section submitted to Phys. Lett. B ar. Xiv: 0802. 0050 Charm: integration after cocktail subtraction – scc=544 ± 39 (stat) ± 142 (sys) ± 200 (model) mb Simultaneous fit of charm and bottom: – scc=518 ± 47 (stat) ± 135 (sys) ± 190 (model) mb – sbb= 3. 9 ± 2. 4 (stat) +3/-2 (sys) mb
Charm and bottom cross sections CHARM Dilepton measurement in agreement with single electron, single muon, and with FONLL (upper end) BOTTOM Dilepton measurement in agreement with measurement from e-h correlation and with FONLL (upper end) First measurements of bottom cross section at RHIC energies!!!
Au+Au Cocktail Comparison • Data absolutely normalized • Cocktail filtered in PHENIX acceptance • Charm from submitted to Phys. Rev. Lett ar. Xiv: 0706. 3034 – PYTHIA – Single electron non photonic spectrum w/o angular correlations scc= Ncoll x 567± 57± 193 mb Low-Mass Continuum: enhancement 150 <mee<750 Me. V: 3. 4± 0. 2(stat. ) ± 1. 3(syst. )± 0. 7(model) Intermediate-Mass Continuum: Single-e p. T suppression & non-zero v 2: charm thermalized? PYTHIA single-e p. T spectra softer than p+p but coincide with Au+Au Angular correlations unknown Room for thermal contribution?
pp – Au. Au comparison p+p NORMALIZED TO mee<100 Me. V pp and Au. Au normalized to p 0 region p+p: follows the cocktail Au+Au: large Enhancement in 0. 15 -0. 75 Agreement in intermediate mass and J/ just for ‘coincidence’ (J/ happens to scale as p 0 due to scaling with Ncoll + suppression) submitted to Phys. Lett. B ar. Xiv: 0802. 0050 submitted to Phys. Rev. Lett ar. Xiv: 0706. 3034
Centrality Dependency LOW MASS p 0 region: • Agreement with cocktail Low Mass: • yield increases faster than proportional to Npart enhancement from binary annihilation (ππ or qq) ? Intermediate Mass: • yield increase proportional to Ncoll charm follows binary scaling submitted to Phys. Rev. Lett ar. Xiv: 0706. 3034
R. Rapp + H. van. Hees K. Dusling + I. Zahed E. Bratkovskaja + W. Cassing Theory comparison • Freeze-out Cocktail + “random” charm + r spectral function Low mass • M>0. 4 Ge. V/c 2: some calculations OK • M<0. 4 Ge. V/c 2: not reproduced Intermediate mass • Random charm + thermal partonic may work PARTONIC HADRONIC p-p annihilation q q q e+ e Gluon Compton g q-q annihilation g* q
p. T dependency Au+Au p+p All p. T 0. 7<p. T<1. 5 Ge. V/c p+p: follows the cocktail Au+Au: enhancement concentrated at low p. T 0<p. T<0. 7 Ge. V/c 1. 5<p. T<8 Ge. V/c ar. Xiv: 0706. 3034 ar. Xiv: 0802. 0050
p. T dependency II p+p Au+Au p+p: follows the cocktail for all the mass bins Au+Au: significantly deviate at low p. T
Understanding the p. T dependency • • Comparison with cocktail Single exponential fit: – – • 2 -components fits – – • Low-p. T: 0<m. T<1 Ge. V High-p. T: 1<m. T<2 Ge. V 2 exponentials m. T-scaling of p 0 + exponential Low p. T: – – inverse slope of ~ 120 Me. V accounts for most of the yield
Yields and Slopes SLOPES YIELDS Low-p. T yield 2 expo fit m. T-scaling +expo fit Total yield (DATA) • Intermediate p. T: inverse slope increase with mass, consistent with radial flow. • Low p. T: • inverse slope of only ~ 120 Me. V!!! • accounts for most of the yield!!! • Cold and Bright
Theory Comparison II Calculations from R. Rapp & H. van. Hees K. Dusling & I. Zahed E. Bratovskaja & W. Cassing (in 4 p) The cold component is not yet explained
High p. T Excess ar. Xiv: 0706. 3034 ar. Xiv: 0802. 0050 Au+Au p+p 0<p. T<8. 0 Ge. V/c 0. 7<p. T<1. 5 Ge. V/c 0<p. T<0. 7 Ge. V/c 1. 5<p. T<8 Ge. V/c Au+Au • Large enhancement at low p. T • Enhancement is also observed in p above 1 Ge. V/c in the low-mass below 300 Me. V
Dileptons at low mass and high p. T p+p Au+Au (MB) 1 < p. T < 2 Ge. V 2 < p. T < 3 Ge. V 3 < p. T < 4 Ge. V 4 < p. T < 5 Ge. V 1. Decompose mass spectrum into Dalitz and direct components in each p. T slice. 2. Determine the fraction of direct virtual photons in each slice. 3. Take this same fraction of REAL photons as a measurement of direct real photons. • Virtual Photons have a mass. • The distribution of a virtual photon’s mass depends explicitly upon the parent mass. • Thus, we can disentangle “Dalitz” virtual photons from direct virtual photons.
Fraction of direct photons Au+Au (MB) p+p μ = 0. 5 p. T μ = 1. 0 p. T μ = 2. 0 p. T • Fraction of direct photons • Compared to direct photons from p. QCD p+p – Consistent with NLO p. QCD – favors small μ Au+Au – Clear excess above p. QCD NLO p. QCD calculation is provided by Werner Vogelsang
Direct via * for p+p, Au+Au exp + TAA scaled pp Fit to pp NLO p. QCD (W. Vogelsang) • New p+p result with * method agrees with NLO p. QCD predictions, and with the measurement by the calorimeter • For Au+Au there is a significant low p. T excess above p+p expectations • The excess above TAA scaled p+p spectrum is characterized by the exponential fit explained in the previous slides. The inverse slope and the yield of the exponential is determined.
Theory comparison • Hydrodynamical models are compared with the data D. d’Enterria &D. Peressounko T=590 Me. V, t 0=0. 15 fm/c S. Rasanen et al. T=580 Me. V, t 0=0. 17 fm/c D. K. Srivastava T=450 -600 Me. V, t 0=0. 2 fm/c S. Turbide et al. T=370 Me. V, t 0=0. 33 fm/c J. Alam et al. T=300 Me. V, t 0=0. 5 fm/c Theory compilation by D. d’Enterria and D. Peressounko EPJC 46, 451 (2006) • Hydrodynamical models are in qualitative agreement with the data
Summary-I • First measurements of dielectron continuum at RHIC Au+Au p+p Low mass • Enhancement above the cocktail expectations: 3. 4± 0. 2(stat. ) ± 1. 3(syst. )± 0. 7(model) • Centrality dependency: increase faster than Npart • p. T dependency: enhancement concentrated at low p. T Intermediate mass • Extract charm and bottom • Agreement with PYTHIA: – sc = 544 ± 39 (stat) ± 142 (sys) ± 200 coincidence? Low mass • Excellent agreement with cocktail (model) mb – sb= 3. 9 ± 2. 4 (stat) +3/-2 (sys) mb • First measurements of direct photons for p. T~1 Ge. V at RHIC p+p • Excellent agreement with NLO p. QCD Au+Au • above NLO p. QCD thermal radiation?
RHIC Summary-II 1. Intermediate p. T shows similar shape to pp and mesonic cocktail. 2. Enhancement is from COLD component -- May also be observed at SPS. -- Flow at these masses should exclude this. -- The real mystery. 3. Higher p. T shows excess direct photon signal, perhaps direct thermal radiation from the early plasma -- Consistent with models of direct thermal emission from Ti=300 -600 Me. V SPS
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