1 / 26

OUTLINE

First study of sensitivity of CMS detector to neutrinoless decay t  m+m-m- Santinelli Roberto - INFN Perugia CERN ,1 February 2002. OUTLINE. The chanel t 3m Tau lepton production at LHC Study of the signal Study of background Observability of the signal and exclusion limits.

javan
Download Presentation

OUTLINE

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. First study of sensitivity of CMS detector to neutrinoless decayt  m+m-m-Santinelli Roberto -INFN PerugiaCERN ,1 February 2002

  2. OUTLINE • The chanel t3m • Tau lepton production at LHC • Study of the signal • Study of background • Observability of the signal and exclusion limits

  3. The chanel t3m • It’s not foreseen in the Standard Model • Beyond the SM , the SUSY with R-parity broken, it can give us some values of BR accessible in the modern experiment. • Actual experimental limit :BR=1.9E-6 (Cleo II) (I will use this number in my analysis to renormalize the expected number of signal-events per year) • Very singular signature of this signal.

  4. Tau lepton production at LHC PYTHIA 6.152 +CTEQ4L+PDG decay’s tables stot (pp->t+X)=120mb s(ppW t+n)=19nb; (at order O(as²)) s(ppZ t+t)3nb (see Nucl.Pysics B345 331-368)

  5. Simulation Fast Simulation:I applied by “hand” a smearing of principal kinematics quantities • s(pt)/ pt =1-1.5% • s(q)=0.001rad • s(f)=0.001rad • s(Ldec)=100mm In the past I also used CMS121 +ORCA_4_5_4… ….but at this time I have not yet implemented the newest cuts of my analysis in to my class for the last orca’s version, so today you will see only some distribution to check the validity of my assumptions

  6. Signal:selection criteria • Trigger • LvL_1(2 muons L1:1 mu con Pt >8 and the other onePt>5GeV) • Identification • 3 muons • Pt> 3GeV in the barrel region (|eta|<0.8) • Total charge = ±1, • Topology • Secondary vertex • Missing transverse energy greater than 20GeV • No charged tracks inside a cone DR=0.4 around the tau with transverse momentum >0.7GeV • Cut of tau’s Pt distribution (not applied) • Mass • Reconstructed mass of three muons =(1.777 ±20)GeV

  7. Background:only one comment This is the most challenging aspect of the whole analysis . We have seen the signature of the signal is very clear.This means that to have enough statistic you should study “a priori” the possible events which,better than other, could mimic the signal, and force your generator to produce them. In doing that you should also be sure that you are not excluding other source of background. If for examples you do not follow this way and try to have 5000 three muons as I will use in my analysis (preselected) directly from cc inclusive events , you should make 5*10E+11 attempts = 300 Years CPU -1GHz time!

  8. Background: Principal sources of muons at LHC (see CMS NOTE 1997/096) • Heavy quarks mesons (D & B ) • Higgs • Primary interactions • Gauge bosonsand Drell Yan (Z,W) • From t • Mistag and punchtrough (non prompts muons) • Cosmic rays

  9. . We have two possibilities to generate three muons from cc (bb) events …otherwise

  10. Events with all three muons coming from a single B(D)meson To generate them we require the presence of cascades of decays in which there must be some resonance decaying in a rare way : f,w,r,h,h’ The total BR estimated after a very long investigation of all possibilities using the decay’s tables of PYTHIA are BR(bb3mu)=9x10^-6 BR(cc3mu)=8x10^-6. In my analysis I used as bkg the events generated as: Ds m+ nm +fm-m+. Bs m +nm+DsK(o p or)+fm-m+.

  11. Generated samples:resuming **For preselected I mean 3 muons with Pt>3GeV and |eta|<0.8

  12. Isolation criterion W->t->3m D->t->3m Main Bkg

  13. Missing energy calculated as sum of jets energy (PYCELL way) Jacobian peak Missing energy W->tn->3m Z->tt->3m+other Main bkg

  14. Rejection cut no.1 The biggest difference between two muon’s vertex position. (This will eliminate bb events type).

  15. The biggest difference between two decay’s length Taglio del massimo della differenza delle lunghezze di decadimento per segnale e fondi Cc events Bb events Signal

  16. Rejection cut no.2 Smallest difference between two muons reconstructed mass with Phi mass should be less than 20MeV Mf=1.020GeV

  17. Massa due mu in fast sim

  18. Massa due mu in orca

  19. Rejection cut no.3 Reconstructed mass of three muons in the range of tau mass ±20 MeV

  20. Massa ricostruita s= 18MeV (Fast Simulation)

  21. Massa ricostruita In orca s= 18MeV (ORCA_4_5_4)

  22. **These numbers are MC numbers The numbers of my analysis**

  23. After one year low luminosity Hypotesys 1:BR(t3m)=1.9E-6 Hypotesys2:only events with phi’s decay rare

  24. Plot 2

  25. Observability& sensitivity • After 1 year of low luminosity of LHC we have 17±1 and 0.6 ±0.4 background events • Using the Feldman-Cousins tables to calculate the sigma (at the 95%) we can resume for own signal that: • BR>4.3E-07 with an I.L.=10 fb-¹ • BR>1.7E-07 “ “ “ =30 fb-¹ • BR>7.6E-08 “ “ “ =100fb-¹ We can exclude at 95% a BR smaller than 4.5E-08 with a integrated luminosity of 300fb-¹

  26. Conclusions • First study of the observability of t3m at CMS • A fast simulation based study shows us the possibility to exlude a signal at 95%C.L. with a BR=4.3E-07 after 1 year of low luminosity @LHC • The spatial resolution for the secondary vertex and momentum resolution to reconstruct the mass of the tau are of the utmost importance. • Passing in ORCA is the next fundamental step… ….to be continued

More Related