Update on the acceptance correction of 2+1 correlation

1. Update on the acceptance correction of 2+1 correlation Hua Pei July 28, 2008

2. A remind of the motivation • In the 2+1 correlation, we introduce the “conditional” particle, located on the away-side of trigger p0, to statistically enhance the back-to-back jets. • However, this “conditional particle” can come from underlying event, ie, from different source as of the near-side jet.

3. The 2+1 yield needs correction • We decide that if we do the exact ZYAM in 2+1 as we did in “normal” 2-particle correlation, the yield we get is: Here S/B is estimated by doing another 2-particle correlation, where we select the assoc pT range as the conditional pT range in previous plot. The ZYAM method will give us the flow background. Meanwhile, underlying yield is derived by another 2-particle correlation, which is actually the “2+1” removing “conditional” requirement, otherwise same trigger and assoc pT range.

4. The simulation steps • Back-to-back jets are from Pythia simulations. • Use EXODUS to generate flow background events (10% centrality) • Pythia trigger p0 mixed with EXODUS to get acceptance. • To generate “2+1” event, • each Pythia event containing a “good” p0 trigger is mixed with ntry=10 EXODUS events. • Then in each of these mixed events, we look for one away-side “conditional” charged particle, no matter if it’s from Pythia or EXODUS. • For each event that is found a “conditional” particle, this mixed event is filled as foreground “2+1” • the trigger p0 for this mixed event is then used to mix with another nmix=20 EXODUS events to generate “2+1” acceptance.

5. Note before I show plots • We have “exact” v2 from EXODUS • However, in current mixing framework, Pythia knows nothing about EXODUS. Thus, no v2 for trigger p0. • So our flow background in ZYAM is a straight line • And we use a Gaussian + flat line to fit the foreground. • Fitting range is initially [0.3, 1.4] • Then we shift the background (line) to touch the foreground in ZYAM. • For the acceptance, I simply made 2 pi/2 acceptance for p0 and charged. [-0.125*pi, 0.375*pi] + [0.625*pi, 1.125*pi]. • And the efficiency for this acceptance is defined as 0.5

6. Yields comparison Trigger p0 4<pT<10GeV Assoc charged 2<pT<3GeV Conditional charged 3<pT<10GeV Black points: real Pythia 2+1 yield Red points: 2+1 inclusive, before ZYAM Purple points: 2+1 underlying, before ZYAM

7. Yield of 2+1, inclusive conditonal Trigger p0 4<pT<10GeV Assoc charged 2<pT<3GeV Conditional charged 3<pT<10GeV

8. Yield of 2+1, underlying conditional (read as: no conditional requirement) Trigger p0 4<pT<10GeV Assoc charged 2<pT<3GeV Conditional charged 3<pT<10GeV

9. Yield of normal 2-particle, for S/B estimation Trigger p0 4<pT<10GeV Assoc charged 3<pT<5GeV (same as the conditional we used in previous slides) S/B: = ( 0.1311 – 0.0853 ) / 0.0853

10. Yield comparison after ZYAM and shifting Trigger p0 4<pT<10GeV Assoc charged 2<pT<3GeV Conditional charged 3<pT<10GeV Near-side yield: Black points: Pythia = 0.2556 +/- 0.0075 Blue points: Shifted correction = 0.2630 +/- 0.0170

11. If we change fitting range to [0.1, 1.4] Trigger p0 4<pT<10GeV Assoc charged 2<pT<3GeV Conditional charged 3<pT<10GeV Near-side yield: Black points: Pythia = 0.2556 +/- 0.0075 Blue points: Shifted correction = 0.2688 +/- 0.0180

12. If we change fitting range to [0.3, 1.1] Trigger p0 4<pT<10GeV Assoc charged 2<pT<3GeV Conditional charged 3<pT<10GeV Near-side yield: Black points: Pythia = 0.2556 +/- 0.0075 Blue points: Shifted correction = 0.2328 +/- 0.0170

13. Summary • Fitting range of foreground in ZYAM still affect our simulation result, as what we saw in real-data analysis • Do we need to simulate v2 of trigger p0 also? • The current mixing scheme let p0 see only charged particles from EXODUS. I think it’s OK as long as we need only acceptance from mixing • Anything else?