A 2 nd proposal for a Low mass electron pair trigger

1. A 2nd proposal for a Low mass electron pair trigger Richard Seto University of CA, Riverside Light/Heavy PWG 6/14/2001

2. Assumptions • Assume we can take effectively 40 MB/sec • RCF writing speed 25 MB/sec @50% • Local speed 40 MB/sec @25% (local disk – 4 days?) • Request • 40% to MinBias  4x previous (useful for everyone) • 30% to electron arm trigger  1.5x previous • We request 10% for this trigger • 30% to muon trigger  1.5x previous • Tony did a calculation which shows the enrichment using a straight centrality trigger to get central events is not much better than taking min-bias So we assume also 25% duty factor=1.5M sec Min bias event=100kB • 40MB/sec/10kB/minbiasevent*40%=160 Minbias/sec • *1.5M secs=240M events R. Seto

3. General Scheme • New Assumptions • Min Bias data – Main data set • Level 2 triggers to enhance peripheral data set • Muon triggers used to enhance central events where trigger doesn’t work well • Bias? • Yields to phi in min bias sample (240M) • ~ (6240 omega to ee) 2900 phi to ee (exodus: 8900,1600) • Cent relative yield going to phi • 0-5% 18%=520 • 5-10 14%=405 • 10-20 25%=725 • 20-30 13%=380 • 30-40 10%=290 • 40-100 20%=580 R. Seto

4. What would we like? • We would like to make the following measurements • Branching ratio phi to ee/KK vs pt, centrality • Mt spectra vs centrality • Midrapidity Yield vs centrality • Fit peak in bins of pt and centrality • 3-5 Bins in mass, 3-5 bins in centrality, 7 bins in pt (mt) (250MeV) • Width of phi= 4.5 MeV, mass resolution?? 2-5 MeV bins? • First pass at line shape – vs pt, centrality (probably run 3) • Define R. Seto

5. Signal and background – 60M min bias • dM=5 MeV • Integrating the yield over all pT, we see the following yields per bin in various centrality classes. • Remember that PHENIX scales the widths of its centrality classes inversely to the multiplicity so for many classes the physical statistics is roughly the same. 100 Background pairs 30 Real Pairs From Tom, Ralf, Felix,Sergey R. Seto 0-5%5-15%15-30%30-60%60-80% 80-92%

6. What would we like? • With min bias in 0-5% bin • ~4*30=120 signal, 4x100=400 bkgd • S=120/sqrt(480)=5.8 … not bad • But we would like to bin in pt and centrality • Centrality bin 0-10%, pt bin 250 MeV (7bins) • So statistics is 2/7 or a 3.1 sigma effect • To get a 5 sigma effect we need (5/3.1)**2=2.6~3 increase in statistics • I.e. look for a rejection factor in a trigger R. Seto

7. Statistical Significance All RHIC 60M min bias 0-5%5-15%15-30%30-60%60-80% 80-92% R. Seto

8. In pt=100 MeV Bins All RHIC 60M min bias R. Seto

9. Rejection factors for the phi (Wei) • Still to try • PC3 cut using better emcal custering • emcal threshold of 380 MeV, • m> 0.7 GeV • Eff ~ 80% • centrality RF %BW prescale • 0-5% 1 x • 5-20% 1 x • 20-30% 1.3 x • 30-40% 2. (7%) 6 • 40-100% 35 (3%) 6 R. Seto

10. The Trigger • use 10% of the “designated” central arm trigger BW • Assume Min bias event size100 kB, central event 300 Kb, periph-80kB, 30-40%-120kB • 3% of BW goes to 40-100% rf ~35 • 7% of BW goes to 30-40% rf ~ 2 • Note – eff for phi is ~80% • To get enrichment factors • 40-100% • 40MB/sec*0.03(frac of Band width) /80kB/event*35(rf)/0.6(centrality)* = 870 events/sec • Enrichment factor of 870/160=5.4 (we wanted 3) • 30-40% • 40MB/sec*0.07(frac of Band width) /120kB/event*2(rf)/0.1(centrality)* = 470 events/sec • Enrichment factor 470/160=2.9 • 0-30% • We use the muon triggers here  R. Seto

11. Muon triggers as “min bias” • We may be able to use the muon triggers as a way to increase "min bias triggers". The argument goes as follows: • The muon triggers will have a strong dependence on centrality. • The rapidity difference between the muon arms and the central arm is large enough that stuff happening in one is largely independent of the other. • The muon triggers come largely from random pions decaying- again making the trigger dependent only on the centrality • A summary of deep-deep muon triggers(Jason) • % rf frac of events • 0-5 6 .40 • 5-15 14 .30 • 15-30 30 .22 • 30-60 300 .04 • 60-100 300 .04 • Total 50 • eff j/psi .70  Most of events come from 0-30% centrality! R. Seto

12. To get enrichment factor over MB X0.75 (since 30% of BW, not 40%) X “fraction of events” /centrality average event size is larger ~ e.g. for 0-5% 100/300 ~ .33 0-5% = 2 5-15% =1.1 15-30% = 0.7 Total enhancement factor (wanted 3) 0-5% 3 muon 5-15% 2.1 muon 15-30% 1.7 ? 30-40% 4 trigger 40-100% 6.4 trigger Npart vs centrality – what do we cover Most bins save 125-225 30 60 100% 40 0 15 Enrichment factors Marginal statistics Npart Centrality R. Seto

13. Conclusions/work • Homework • Can we use the muons triggers? • Mu-e events from charm ?? Study these • Trigger improvement using pc3? • Status • Level 2 Emcal/RICH electron trigger well underway – write up on web • Centrality trigger well underway • General write up of trigger on web p/draft/seto/trigger/triggerlvm.doc/pdf • Summary • Request • 40% Min Bias • 10% of Band width of central arm • Can do • Phi to ee/KK vs centrality, pt • Mt spectra vs centrality • Yield vs centrality • First look at line shape R. Seto