Topical discussion: Di-Hadron Correlations and ZYAM in HI

These pages are intended to discuss/collect material concerning the ZYAM approach ("Zero Yield At Minimum" + subtraction of elliptic flow modulated background) in di-hadron correlations  to extract "jet-like" correlations in heavy-ion collisions at RHIC in order to measure/quantify "jet-quenching" effects.

(The following pages/outline are under development!)
Following an outline/template (additional sub pages should be added according to topics; to be discussed)

What is it what we wanna discuss? Definition of ZYAM:

ZYAM (Zero Yield At Minimum) is an approach/assumption to subtract the background in heavy-ion collisions in di-hadron correlations (azimuthal correlation of associated particles in a given pT,Assoc window wrt to a trigger particle in a given pT,Trig window) to measure jet-like correlations.
The main assumptions in this approach are:
a) there is a region in the dN/dDeltaPhi correlation where there is no correlated signal yield B(DeltaPhi) (based on jet-like correlations in p+p) (ZYAM)
b) the background can be decomposed/decoupled from the signal and can be described by a flow modulation according to <v2,Trig>*<v2,Assoc> (ignoring v2 fluctuations). The elliptic flow values are in the usual approach taken from "separate" measurements (v2{EP},v2{2},v2{4} ...).
⇒ dN/dDeltaPhi = Signal(DeltaPhi)+Bkg(DeltaPhi)
with Bkg(DeltaPhi) = B(DeltaPhi)*(1+2 <v2,Trig>*<v2,Assoc>*cos(2*DeltaPhi)


The main (broader) goal of this topical discussion effort is to evaluate/quantify the validity/systematics of the ZYAM method used in di-hadron correlations (as discussed/defined above). The intended strategy is to evaluate/quantify the assumptions of ZYAM in a controlled approach via "standardized" analytical and simulation references. Further aspects should involve further measurements to test ZYAM and the connection to jet physics, as well as possible future measurements. 


  • Analytical/published di-hadron correlation data:
    - Effect of variation of the background level B(DeltaPhi) on signal shape and yields
    - Effect of v2 on signal shape and yields
  • MC analysis (what exactly and how to be discussed, but needed for additional measurements)
  • Further analysis: Di-Hadron correlations with trigger particle associated to a fully reconstructed jet (and more ...)
  • Future measurements: Can we turn off elliptic flow by using asymmetric ion collisions: Pb-Ca ?



  • Materials/studies should be posted on these pages to have a central archive and allow access to everyone interested
  • A mailing-list would be preferable and will be posted here asap.
  • A svn/cvs repository for simulations/analysis code would be preferable (still to be discussed)
  • (Phone) Meetings will be held when enough/new material is available