π 0 production in Cu+Au at PHENIX Sarah Campbell for the PHENIX Collaboration Sept 23, 2014 Hot Quarks Sarah Campbell -- Hot Quarks 20141

Outline Why pions? – Measuring pions at PHENIX Path length dependence and energy loss measurements in Au+Au Why Cu+Au? – Centrality dependence – Reaction plane dependence Conclusions Sarah Campbell -- Hot Quarks 20142

Why study neutral pions? Identified particle with good signal-to-background, lots of statistics Low p T  medium effects – Experience flow, hadronization/recombination and soft medium effects High p T  good proxy for a jet – Leading particles of a jet are a good measure of the jet energy – Can probe the path length dependence of energy loss of the hard parton in the medium, qhat – Compare to reconstructed jet to learn about fragmentation Sarah Campbell -- Hot Quarks 20143

Measuring pi0s at PHENIX Sarah Campbell -- Hot Quarks 20144

5 where R AA in > R AA out R AA in - R AA out decreases as N Part increases, decreases PRC 87, (2013)

Sarah Campbell -- Hot Quarks PRC 87, (2013)

10-20% 20-30% 30-40% 40-50% 50-60% 60-70% R AA path length dependence Sarah Campbell -- Hot Quarks PRC (2007)

Models of energy loss a)AMY: radiative & coll. energy loss, high T b)HT: higher twist corrections to DIS, radiative processes c)ASW: radiative processes, λ >> r D d)ASW-AdS/CFT: ASW-like hard processes, strongly coupled soft processes  L 3 dependence L 2 dependence Sarah Campbell -- Hot Quarks PRC 87, (2013)

The limitations of R AA Sarah Campbell -- Hot Quarks PHENIX Au+Au 200 GeV ALICE Pb+Pb 2.76 TeV Energy loss is not the same BUT RHIC and LHC p T spectra have different shapes, powers PRC 87, (2013)

Fractional momentum loss, S loss Sarah Campbell -- Hot Quarks PHENIX Au+Au 200 GeV ALICE Pb+Pb 2.76 TeV S loss  How much does the parton’s momentum change in the medium? Energy loss is not the same BUT RHIC and LHC p T spectra have different shapes, powers PRC 87, (2013)

Why Cu+Au? Asymmetric collisions at RHIC – Higher energy densities – New collision geometries Cu embedded in the Au nucleus Asymmetric overlap region – Odd flow harmonics not from fluctuations Asymmetric pressure gradients Asymmetric density profiles Asymmetric path lengths Sarah Campbell -- Hot Quarks Glauber model CuAu b=4fm Participant density (log-z scale)

Charged Pions in Cu+Au Sarah Campbell -- Hot Quarks pT < 2.5 GeV/c

π ± R AA in Cu+Au Sarah Campbell -- Hot Quarks

π ± R AA in Cu+Au Cu+Au charged pion R AB agrees with Au+Au R AB at similar N Part or N Coll Does this hold at higher p T ? Sarah Campbell -- Hot Quarks

Uncorrected pion yields in Cu+Au centrality bins Able to reach p T ~ GeV/c Fine centrality bins Efficiency corrections not yet determined Sarah Campbell -- Hot Quarks MB 0-5% 5-10% 10-15% 15-20%

Cu embedded in the Au-nucleus Sarah Campbell -- Hot Quarks In events where the Cu is embedded in the Au nucleus, there should be very few hits in the North ZDC Cu Au

Data Glauber+NBD Glauber -Coalescence 1 Glauber -Coalescence 2 Glauber-No coalescence Data Cu embedded in the Au-nucleus ~70% of events in the 0-1% centrality bin have no hits in the Cu-going ZDC Sarah Campbell -- Hot Quarks Lines at 1% bin centers Lines at 1% bin centers N Coll

Glauber -Coalescence 1 Glauber -Coalescence 2 Glauber-No coalescence Data ~70% of events in the 0-1% centrality bin have no hits in the Cu-going ZDC Data Glauber+NBD Cu embedded in the Au-nucleus Sarah Campbell -- Hot Quarks Lines at 1% bin centers 0-1% Cu+Au Uncorrected yields

π ± v 2 in Cu+Au π ±, p v 2 follow n q -scaling Sarah Campbell -- Hot Quarks

h ± v 2 and v 3 in Cu+Au v 2  clear centrality dependence v 3  no significant centrality dependence Sarah Campbell -- Hot Quarks Similar to Au+Au behavior

Comparing h ± v 2, v 3 to other systems Sarah Campbell -- Hot Quarks System size dependence Au+Au > Cu+Au > Cu+Cu System size dependence is small

Comparing h ± v 2, v 3 to other systems Sarah Campbell -- Hot Quarks System size dependence Au+Au > Cu+Au > Cu+Cu System size dependence is small arXiv:

π ± and h ± v 2 at p T < 3 GeV/c Sarah Campbell -- Hot Quarks

π 0 azimuthal distributions w.r.t. ψ 2 p T reach out to ~6 GeV in Cu+Au Sarah Campbell -- Hot Quarks BBC SN ψ % Cu+Au

Odd Harmonics of π ± in Cu+Au Using SMD South ψ 1 plane can measure odd harmonics v 3 small v 1 > 0  More particles emitted from Au-side Sarah Campbell -- Hot Quarks

BBC ψ 2 South BBC ψ 2 North BBC ψ 1 North BBC ψ 1 South BBC ψ 2 and ψ 1 planes Correlations at: – ψ 1 = ψ 2 – ψ 1 = ψ 2 - π – ψ 1 = ψ 2 + π BBC S BBC N Au Cu

Define BBC ψ 21 Sarah Campbell -- Hot Quarks Create ψ 21 to resolve Cu+Au vs Au+Cu left right- asymmetry in ψ 2 plane – BBC ψ 2 with BBC ψ 1 South pointing in the Au direction – Benefit from good BBC ψ 2 resolution In progress Psi2 S Psi1 S Psi21

Conclusions In Au+Au: – At RHIC, π 0 energy loss has an L 3 (or higher) dependence In Cu+Au: – Higher energy densities – π ±, h ± v 3 small and v 1 > 0 at central rapidity more particles emitted from the Au-side – π 0 will extend out to higher p T ~10 GeV/c in R AA, ~6 GeV/c in v 2 Future of π 0 analysis – Working on calibrating simulations – Finalizing v 2, extracting odd harmonics Sarah Campbell -- Hot Quarks

Back up Sarah Campbell -- Hot Quarks

10-20% 20-30% 30-40% 40-50% 50-60% 60-70% S loss path length dependence Sarah Campbell -- Hot Quarks PRC (2007)

Sarah Campbell -- Hot Quarks

In plane 0-15% Mid-plane 30-45% Out-plane 75-90% Sarah Campbell -- Hot Quarks

Mass in p T slices Sarah Campbell -- Hot Quarks GeV/c GeV/c GeV/c No residual background Reduced combinatorial background

Sarah Campbell -- Hot Quarks

bb Sarah Campbell -- Hot Quarks

NEW: BBC Psi1, Psi2 N, S correlations

Simulation Calibration to data E scale and resolution Sarah Campbell -- Hot Quarks

Sarah Campbell -- Hot Quarks