First analysis of the fully simulated channel

1. First analysis of the fully simulated channel Marco Zanetti CMS Padova Muon Week – Bologna 10/4/2003

2. Past analyses (e.g. M.Dittmar) have demostrated that this could be a very fast channel (with l=m ,<5fb-1 ~ 1 month @ LL) for the discovery of the SM Higgs in the intemediate mass region 130< MH <2 MZ, filling the gap of • Because of the 2 n impossible to distinguish a peak in the invariant mass distribution => not easy counting channel: =>the precise knowledge of all possible backgrounds processes is fundamental; Marco Zanetti CMS Padova

3. Reference sample Marco Zanetti CMS Padova

4. WWnr is the main bkgr, with the same final states but reducible(next slides) • Not yet considered: • Single top ( ) Marco Zanetti CMS Padova

5. Signal vs WWnr 1: small |h| muons gz~10 • Higgs produced mainly via g-g fusion (in 130< MH <2MZ 80% of the times) • WWnr produced by • z-boost gz~1 WWnr evs more boosted along the beam More isotropic signal muons spatial distribution Marco Zanetti CMS Padova

6. Signal vs WWnr 1: barrel endcap 8000 evs Di-m system polar angle Could depend on PDF used, but no significant differences between GRV94 (old) and CTEQ5L (DC04) Marco Zanetti CMS Padova

7. Signal vs WWnr 2: nearby m+m- Signal: • Higgs scalar, W vectors => to have JTot=0 spin wave function must be: TL coupling not allowed • Case TT: each muon has the same SZ of the mother and must be produced with definite elicity => max prob to have m+m- emitted in the same direction • Case LL: not easy to demostrate that => again max prob to have m+m- emitted in the same direction WWnr: • Unpolarized initial state => TL coupling is allowed and @ MWW~160 half of the production rate • Case TL: no correlation in m+m- emission Marco Zanetti CMS Padova

8. Signal vs WWnr 2: m+m- opening angle 8000 evs • Big difference in shape • Indipendece from the PDF • Implications also for MEt Marco Zanetti CMS Padova

9. Production chain Pythia 6.158 (GRV94LO) Pile up CMSIM 125 ORCA 6_2_3 (digi and reco) Analysis based on L3 reconstruction Marco Zanetti CMS Padova

10. HLT Selection Algorithmic Efficiency (Single+Di-m standard sel. in |h| < 2.1) Analisys starting point: HLT Di-mstandard sel. Signal overwhelmed (4 ord. mag.) Marco Zanetti CMS Padova

11. Offline selections 1) Pt cut: Pt1,2 > 25,15; isolation @ 97% for both; opposite charge; • High eff. for the signal ~70% • Huge Rej. factor ( =Rbefore/Rafter) ~500for sample; only 28 events survive • most of the g* contribution suppressed • good Rej. (5) for thanks to isolation 2) Missing Et cut: MEt > 40 GeV; • Only 1 event survives (low pt ns) with a integral rate of the same order of signal events (1.3·10-4 Hz) • Big Rej. (~21) for Z/g* • WWnr more rejected (2.1) than signal (1.3) as foreseen (spin correlation) Marco Zanetti CMS Padova

12. Offline selections 3) Invariant Mass cut: Mmm < 70 GeV; To reject m+m- events from Z peak; I will select events with nearby muons: Mmm = {2|p1||p2|(1-cosq)}1/2 => No lower bound • Rej. = 22.5 for Z/g* sample; 3 events surving but with a integral rate greater than the signal (2.7·10-3 vs 1.3·1 0-4 Hz) • Big rejection also for WZ+ZZ • no more events Marco Zanetti CMS Padova

13. Offline selections VETO REGION h 4) Jet veto: rejected events with one jet with Et>20 in |h|<2.4 ; Specific for top events (tt & Wtb) • Huge Rej. (~85)for ; only 5 events survive giving a smaller rate contribution than the signal (2.5·10-5 vs 4.7·10-5 Hz) • Much less effective for sample (if applied) • no more Z/g* events • not so small rejection also for the signal (Rejec=2.7) Marco Zanetti CMS Padova

14. Offline selections 5) Di-m polar angle cut: => Di-m System in the barrel • Signal Rejec = 1.9 WWnr Reject = 2.4; • no more events 6) Nearby ms: Df < 0.8 && Dh < 1.5 Final plot Final numbers Marco Zanetti CMS Padova

15. Statistical Results Results for other masses: • MH=120: not viable; other H production processes like Vector Bosons Fusion can be used (CMS Note 2002/26: pp->jjH, H->WW->llnn) • MH=200: different kinematic (e.g. no so effective spin correlation) different selectionsshould be used Marco Zanetti CMS Padova

16. Systematics Statistics of the background samples used insufficient, anyway: • sample depleted at the very beginning of the offline selection • before beeing cut away, events give a integral rate contribution smaller than the signal and following cuts more effective to them than to signal ones. • Huge rejection for Z events by cuts 5 and 6 ( inizial state and muons back-to-back in transvers plane) • in the present Z/g* sample not included qg->q(Z/g*) and => foreseen good rejection also by Jet veto No effective contribution after offline selections foreseen for these background processes Marco Zanetti CMS Padova

17. DC04 Production • WWnr sample: 200K events, Pt>7,7 => statistical error after offline selection • WZ ZZ samples: 200K +200Kevents, Pt>7,7 => statistical error after offline selection 95 % CL upper limit of Rate contribution after offline sel.if no events survive (for tt forseen contribution O(10-6 Hz)) Marco Zanetti CMS Padova

18. Missing bkgr processes NLO process, x-sec 1 ord. smaller than WWnr; because of the gg inizial state should be taken into account. Not yet implemented in Pythia.Not yet inculded in any analysis (Stefano Marcellini) x-sec ~ 0.5 and known to give a comparable contribution. particularly dangerous, to be generated with CompHEP Marco Zanetti CMS Padova

19. Conclusions • Although with not sufficient bkgr statistics, it has been shown the present channal is very promising for a fast (<5fb-1 ) discovery of SM H in the intermediate mass region • waiting for DC04 high statistics samples to confirm these results Marco Zanetti CMS Padova