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1 Search for W R Bosons and Heavy Neutrinos of the Left-Right symmetric model in CMS and first data in CMS Mikhail Kirsanov (INR Moscow) ‏ QUARKS-2010,

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Presentation on theme: "1 Search for W R Bosons and Heavy Neutrinos of the Left-Right symmetric model in CMS and first data in CMS Mikhail Kirsanov (INR Moscow) ‏ QUARKS-2010,"— Presentation transcript:

1 1 Search for W R Bosons and Heavy Neutrinos of the Left-Right symmetric model in CMS and first data in CMS Mikhail Kirsanov (INR Moscow) ‏ QUARKS-2010, Kolomna, 09 June 2010

2 2 Analysis status.  CMS AN 2008/072  PAS EXO (14 TeV) – approved (Figures in this talk from this PAS) ‏  Previous studies at 14 TeV  Last studies at 7 TeV  CMS AN 2009/112 – being refereed

3 3 Introduction Heavy Neutrino:  Predicted by many models, frequently discussed: Left-Right Symmetric Model incorporates W R and Z’ and heavy right-handed (usually Majorana) neutrino states N l (l=e, μ, τ) that can be the partners of light neutrinos light neutrino masses are generated via See- Saw mechanism explains parity violation in weak interactions includes SM at ~ 1 TeV scale  in many SM extensions M(N l ) ~ TeV Previous studies: S.N. Gninenko, M.M. Kirsanov, N.V. Krasnikov, V.A. Matveev, CMS NOTE 2006/098 (2006) ‏ Enhance Motivation to search for these new particles at CMS! SuperK'98 result: neutrinos are massive But SM neutrino has no mass

4 4 Model parameters Masses:  M(W R ), M(Z’), M(N l ); l=e, μ, τ Reactions:  pp → Z’ → N l + N l + X  pp → W R → l + N l + X  N l → l + jet + jet Signature:  two high-Pt isolated leptons and two high-Pt jets Current direct limits (by Tevatron experiments):  M(W R ) > 0.8 TeV  M(N l ) > 0.3 TeV Our reference points M(W R ) = 1.5 TeV, M(N l ) = 600 GeV ; M(W R ) = 1.2 TeV, M(N l ) = 500 GeV (LRRP1, LRRP2)‏ Simulation and reconstruction in CMSSW_3_1_5 Misalignment and miscalibration as expected for int. luminosity of 0.1 fb -1 Dielectron and dimuon events are studied

5 5 Collision energies 14, 10, 7 TeV: cross section difference about factor 2 WR production cross sections at 14, 10, 7 TeV

6 6 Leptons momenta: hardest lepton and second one

7 7 Triggers and Datasets. The idea is to use single lepton triggers with as high threshold as possible  Electron channel: Signal efficiency >97%  Muon channel: Signal efficiency >97%. At 100 1/pb leptons are below 1 TeV: showers less important, so that triggers with isolation requirements can be used

8 8 Lepton selection  Default leptons ID except isolation  Pt cut 20 GeV  Isolation cone radius 0.3  Isolation variable Econe/Pt  Primary selection cut on isolation 0.2

9 9 Lepton selection (2)‏  Isolation cuts: electrons 0.09, muons 0.05  These cuts remove QCD background at 10 and 7 TeV  Electrons selection efficiency for our signal (LRRP1) 74% (isolation 94%) ‏  Muons selection efficiency 85% (isolation 95%) ‏

10 10 Jets  Cone 0.5, cut 40 GeV  Default reconstruction  Default energy corrections. E. g. Gamma – jet calibration to be used for real data. Calibration accuracy 5 – 10 % at 100 1/pb

11 11 Events selection: preliminary  At least 1 lepton and 1 jet (pT cut 20) ‏  At least 1 lepton with Pt > 42 GeV. Probably will be used for the lumi > 100 1/pb. If we increase further this cut, the Z control sample drops rapidly  After this we should have about 3000 Z events for the efficiency control sample and events for the QCD fake sample

12 12 Events selection: for signal (primary selection)‏  At least 2 leptons (of any flavour and sign) and 2 jets  At least 1 lepton with Pt > 42 GeV

13 13 Primary selection efficiency, MW=2000

14 14 Background reduction table, electrons

15 15 Backgrouns, CSA09, muons

16 16 Signal/background 100 1/pb, MW=1500 GeV, 14 TeV, electron channel

17 17 Signal/background 100 1/pb, MW=1500 GeV, MN=600, electrons, 14 TeV MW > 500MW > 1000

18 18 Fit  We use RooFit package for fitting  Unbinned likelihood fit  Model: (background) + (signal) ‏ P(MWc,MNc) = nsig*BW(MW,WW,MWc)* BW(r0,Wr,c) + nbg*exp(-k*MWc)*PBG(r) ‏ BW – Breit-Wigner function PBG – BG histogram shape MWc, MNc – inv. masses of WR and N candidates r = MNc/MWc, r0 = MN/MW We take the signal widths WW and Wr from the fit of the fully simulated signal

19 19 Fit(3)‏ Free parameters of the fit: nsig, nbg, k Quasi-free parameters of the fit: WW, Wr (assume for the moment 2% for WW, Wr fixed) ‏ This means that about BG in the MWc projection we only assume that it is a falling monotonous function of MWc

20 20 Pseudo-experiments (toy MC)‏  Based on parameter from fit we do toy MC  1000 pseudo-experiments

21 21 Significance Electrons 7.53Muons 5.5 LRRP2 (MWR=1200) ‏

22 22 BG control (2) Most important BG components:  tt events: electron – muon sample to control  Z+jets events: sample with relaxed Mll cut (80 GeV) to control: > 200 events with MW > 500 GeV. The shape can be different!  Events with fake leptons (W+jets, gamma+jets, QCD): Fake QCD sample and electron – muon sample with same sign to control

23 23 BG control procedure  tt distribution shape: we compare 1D projections of the electron – muon sample with MC (6 events at 100 1/pb: rather big errors) and can use directly these corrections  Z+jets distribution shape: we compare the sample with relaxed Mll cut (80 GeV) with MC. The shape can be different, so probably we cannot use directly the corrections.  Events with fake leptons (W+jets, gamma+jets, QCD): check electron – muon sample with same sign and compare the number with all signs. If the factor is much different from 5, we introduce weight and eventually try to tighten the lepton selection cuts

24 24 BG control procedure (2)‏

25 25 BG control procedure (3)‏

26 26 BG control procedure (4)‏  Events with fake leptons (W+jets, gamma+jets, QCD): Obtain fake QCD sample: lepton with a back- to-back jet and no no other loose lepton candidate in the event  Mostly events from QCD as shown by other PAG  From this we obtain the probability of a jet to produce a fake lepton p(ET) ‏  Take events with one lepton and jet(s), convert one jet into lepton  We obtain the shape of MWc distribution of BG with fake leptons

27 27 Efficiency from data  Needed to calculate sensitivity, limits etc., but also could change the shape of distributions  From the control Z sample  Tag and probe or simply use efficiency measured by POG  Efficiency in presence of jets, in particular isolation cuts efficiencies: additional checks

28 28 Summary  WR and Heavy neutrino N of the minimal Left-Right symmetric model can be discovered at 100 1/pb for the masses of WR up to 1500 GeV and masses of N from 200 to 700 GeV in the electron channel  More narrow discovery region in the muon channel (up to ~1300 GeV) ‏

29 29 Summary (2). Discovery and limits plot electron channel, 14 TeV

30 30 Towards the analysis of real data The work presented here is the proof of concept and the estimation of the sensitivity. For the real data a few things are to be checked, a few methods are to be worked on in more details. For the next thesis  Check that QCD BG is small, if it is not small check its shape. Use fake sample (see above): check that it works  More studies of BG shape. Calculations predict something like (1/MWc)**a or (1- MWc/sqrt(s))**a * (1/MWc)**b. Are they different for tt, Zjets etc? Use FastSim

31 31 Towards the analysis of real data (2)‏  Check that isolation cuts in data work as in MC. If not, work out ways of correcting the efficiencies  Various statistical checks and studies. What we see now is that the method of fit is more powerful than simple counting. But we must ensure that all possible real BG shapes are allowed by the fit. If we think that any funny BG shape is possible, even with bumps, then fit is useless

32 32 Towards the analysis of real data (3)‏  Started to look at the data /nb analysed. One Z candidate found (decay to electrons). It seems that nothing to do until we have a few tens of Z, just learn to read data

33 33 CMS and LHC operation  By the end of May /nb delivered by LHC, 17 1/nb recorded: efficiency ~ 90%  Two last weekends luminosity was doubled both times and reached 2*10 29  13 bunches now. Maximal possible number is 2808  Pictures below from D. Contardo, talk at IPRD10

34 34 CMS and LHC operation(2)

35 35 CMS and LHC operation(3)

36 36 CMS and LHC operation(4)

37 37 CMS and LHC operation(5)

38 38 CMS and LHC operation

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