1. 29,30 July 2010 India CMS Meeting,BARC Mumbai 1 Update on Z’-> τ τ->τ jet+ τ jet analysis Nitish Dhingra(P.U.,India) Kajari Mazumdar(TIFR,India) Jasbir Singh(P.U.,India)

2. 29,30 July 2010 India CMS Meeting,BARC Mumbai 2  Introduction.  Work done.  List of cuts.  Low statistics problem.  Scale factor determination.  Calculation of expected no. of events surviving at some luminosity using the idea of factorization.  No. of events at 100pb -1 for signal and background.  Conclusions & future plans. Outline

3. 29,30 July 2010 India CMS Meeting,BARC Mumbai 3 Introduction  New heavy gauge bosons( Z’, W’ etc.) occur quite frequently in the extensions of Standard Model like Superstring, Grand unified theories(GUTs), Extra dimensions etc.  LHC offers a very good opportunity to search for Z’ bosons at TeV mass scale even with reasonably low luminosity in electron and muon final states and simultaneously final state involving τ-pair will be searched for.  But tau final states are complicated --> more difficult. The reach from tau-pair will be slightly worse for same luminosity but its still a highly desirable result.  The signal extraction over the QCD background seems possible because the τ’s from the Z’ are expected to be highly boosted due to high Z’ mass and the QCD cross section decreases with the increase in the Pt.

4. 29,30 July 2010 India CMS Meeting,BARC Mumbai 4 Work done  Using CMSSW_3_1_6 at the moment. The signal samples(M Z’ = 500 GeV/c 2 ) are private production lying at FNAL :  /zprimeTauTau500_7TeV_STARTUP31X_V4_GEN-SIM-RAW/eluiggi- zprime500TauTauReco-1eb7407c99912735250bc247a04c22ce/USER  Binned QCD dijet background MC samples are taken from official Summer09 production :  /QCDDiJet_Pt20to30/Summer09-MC_31X_V3_7TeV-v1/GEN-SIM-RECO  /QCDDiJet_Pt30to50/Summer09-MC_31X_V3_7TeV-v1/GEN-SIM-RECO Up to  /QCDDiJet_Pt3000to3500/Summer09-MC_31X_V3_7TeV-v1/GEN-SIM-RECO  Presently I am studying the MC data and trying to devise a selection criteria that can reduce the QCD dijet background to an acceptable level. There is nice improvement over the previous results !!  The selection criteria is shown in the next slide.  Presenting work regularly in the CMS High Pt Tau Group’s weekly meetings.

5. Skim criteria for QCD: 1) Reconstructed PFTau with leading π or ɣ Pt > 5.0 GeV/c 2) At least one tau pair with DR(τ 1,τ 2 ) > 0.7 At analyzer level: 1) | η τ1 | & | η τ2 | < 2.1 2) τ crack cut (τ’s in the cracks are not considered). 3) Pt τ1 & Pt τ2 > 15.0 GeV/c 4) Electron veto [ H3X3/P lead > 0.03, H3X3/P lead is the ratio of energy deposited in the HCAL 3X3 cluster in R < 0.184 around ECAL impact point of leading track and the Lead track momentum, tau lead track minimum hits = 10] 5) Muon veto 6) Lead track Pt of τ 1 & τ 2 > 5.0 GeV/c 7) Tau isolation : isolation cone size = 0.5, (i) sum Pt max. of tracks =1.0 GeV/c (ii) sum Pt max. of gammas =1.0 GeV/c, Pt threshold for tracks = 1.0 GeV/c, Pt threshold for gammas = 1.5 GeV/c. 8) 1 prong requirement. 9) Opposite sign requirement i.e. q( τ 1 )*q( τ 2 ) < 0 10) -1.0 < Cos Δ φ (τ 1, τ 2 ) < -0.95 11) M(τ 1, τ 2 ) > 200 GeV/c 2 29,30 July 2010 India CMS Meeting,BARC Mumbai 5 List of cuts

6.  The problem that arises while dealing with QCD MC samples is of low statistics(very few events survived after all the cuts).  This problem can be tackled by using the idea of factorization.  For factorization some cuts/requirements have to be chosen that are uncorrelated or least correlated to the each other as well as with other cuts after them in the normal sequence of cuts.  For this purpose tau Isolation, opposite sign requirement & 1 prong requirement are chosen as “Factorization Variables” as they seem to be the suitable candidates satisfying above requirements.  The idea is to loosen the factorization variables so as to gain more statistics & then apply a “Scale Factor” corresponding to each of the factorization variable set “Tight” to the final calculations of the estimates at certain luminosity. 29,30 July 2010 India CMS Meeting,BARC Mumbai 6 Low statistics problem

7. 29,30 July 2010 India CMS Meeting,BARC Mumbai 7 Events Analyzed = N i Apply all cuts with all fact. variables set “loose” Events passing above cuts = N f loose Events Analyzed = N i Apply all cuts with particular fact. variable set “tight” Events passing above cuts = N f tight Scale Factor = N f tight /N i loose N(L) = σ*L*Scale Factor*N f loose /N i There is one scale factor per factorization variable Scale factor determination

8. 29,30 July 2010 India CMS Meeting,BARC Mumbai 8 Tau signal cone size = 0.07, Isolation cone size  0.5, Pt threshold for tracks = 1.0 GeV/c, Pt threshold for gammas = 1.5 GeV/c (a) Tight tracker isolation  sum Pt max. of all the tracks = 1.0 GeV/c (b) Loose tracker isolation  sum Pt max. of all the tracks = 5.0 GeV/c (c) Tight ECAL isolation  sum Pt max. of gammas = 1.0 GeV/c (d) Loose ECAL isolation  sum Pt max. of gammas = 5.0 GeV/c (e) Tight 1 Prong requirement  requires both τ’s to undergo 1 Prong decay. (f) Loose 1 Prong requirement  No 1 Prong requirement on both τ’s. (g) Tight OS requirement  opposite sign requirement on two τ’s. (h) Loose OS requirement  No opposite sign requirement on two τ’s. (i) All loose cuts  All factorization variables set loose + other cuts. Nomenclature for factorization

9. 29,30 July 2010 India CMS Meeting,BARC Mumbai 9 Pt hat binAll loose cuts Tight tracker isolation Tight ECAL isolation Tight 1 Prong requirement Tight OS requirement 20 to 30937602143 30 to 506713836767339 50 to 802781012513137 80 to 12027441221128571387 120 to 170348161467175 170 to 230291151023144 230 to 300385211484183 300 to 380450381476225 380 to 470413301163225 470 to 600146939276 600 to 8001691045186 800 to 1000477291293260 1000 to 1400426351206214 1400 to 18001391031168 1800 to 220030226722146 2200 to 26001481736070 2600 to 30001571139079 3000 to 35001561738377 Events survived at different selection levels

10. 29,30 July 2010 India CMS Meeting,BARC Mumbai 10  Scale factor corresponding to a particular factorization variable say tau tracker isolation in this case, is defined as the ratio of no. of events passing all cuts for the sample with tau tracker isolation set tight divided by the no. of events passing all cuts for the sample where all factorization variables are set loose.  N(L) is calculated as : N(L) = cross section*B.R.*Luminosity*ε filter *ε skim *ε cum_loose * Scale Factor(i)  The uncertainty in N(L) is calculated as: ΔN = W*ε total_cum_loose *ε filter *sqrt[ (Δε cum_loose /ε cum_loose ) 2 + (ΔS.F.(i)/S.F.(i)) 2 ], where, W = cross section*B.R.*Luminosity* Scale Factor(i), ε filter = 1, ε skim = No. of events left after skimming/Total no. of events before skimming, ε cum_loose = No. of events left after all cuts with all fact. variables set loose/No. of events after the skimming, ε total_cum_loose = No. of events passing all cuts with all factorization variables set loose/No. of events in the sample. Calculation of N@L & ΔN@L

11. 29,30 July 2010 India CMS Meeting,BARC Mumbai 11 Pt hat bin [GeV/c]Before mass cutAfter mass cut m ττ > 200 GeV/c 20 to 306599.13+- 2920.90 30 to 506560.19 +- 1348.9339.11 +- 21.06 50 to 80682.74 +- 290.967.37 +- 5.27 80 to 12072.95 +- 11.2911.91 +- 1.91 120 to 17013.88 +- 6.356.50 +- 2.99 170 to 2301.07 +- 0.680.80 +- 0.51 230 to 3000.30 +- 0.170.25 +- 0.14 Total65.95 +- 22.00 N@100 pb -1 Z’(500) (Signal)6.87 +- 0.265.28 +- 0.23  Only lower Pt hat bins up to Pt hat 230 to 300 GeV/c are found to contribute significantly. Details are given in the back up slides.

12. 29,30 July 2010 India CMS Meeting,BARC Mumbai 12 Visible mass  Some more efforts needed to nail down the QCD background !!

13. 29,30 July 2010 India CMS Meeting,BARC Mumbai 13 Conclusions & Future plans  The results are quite improved over the previous ones!!  Next step is to discover some new cuts/requirements to reduce the QCD background more to get better signal over background ratio. Possible candidates are: Pt asymmetry, Isolation cone size, Pt threshold of tracks & gammas, Leading track Pt cut, impact parameter.  To study the other possible backgrounds once the QCD background is hammered down to an appreciable S/B ratio.  To optimize the cuts for betterment of S/B ratio.  To analyze the LHC collision data.

14. 29,30 July 2010 India CMS Meeting,BARC Mumbai 14 Back Up

15. 29,30 July 2010 India CMS Meeting,BARC Mumbai 15 Scale factor for Tight tracker isolation Scale Factor=0.07527 +- 0.02736 Scale Factor=0.05663 +- 0.008923 Scale Factor=0.03597 +- 0.01117 Scale Factor=0.04446 +- 0.003935 Scale Factor=0.04598 +- 0.01123 Scale Factor=0.05155 +- 0.01296 Scale Factor=0.05455 +- 0.01157 Scale Factor=0.08444 +- 0.01311 Scale Factor=0.07264 +- 0.01277 Scale Factor=0.06164 +- 0.0199 Scale Factor=0.05917 +- 0.01815 Scale Factor=0.0608 +- 0.01094 Scale Factor=0.08216 +- 0.0133 Scale Factor=0.07194 +- 0.02192 Scale Factor=0.08609 +- 0.01614 Scale Factor=0.1149 +- 0.02621 Scale Factor=0.07006 +- 0.02037 Scale Factor=0.109 +- 0.02495 Scale factor for tight ECAL isolation Scale Factor=0.6452 +- 0.04961 Scale Factor=0.5469 +- 0.01922 Scale Factor=0.4496 +- 0.02984 Scale Factor=0.4111 +- 0.009393 Scale Factor=0.4195 +- 0.02645 Scale Factor=0.3505 +- 0.02797 Scale Factor=0.3844 +- 0.02479 Scale Factor=0.3267 +- 0.02211 Scale Factor=0.2809 +- 0.02211 Scale Factor=0.2671 +- 0.03662 Scale Factor=0.2663 +- 0.034 Scale Factor=0.2704 +- 0.02034 Scale Factor=0.2817 +- 0.02179 Scale Factor=0.223 +- 0.03531 Scale Factor=0.2384 +- 0.02452 Scale Factor=0.2432 +- 0.03527 Scale Factor=0.2484 +- 0.03448 Scale Factor=0.2436 +- 0.03437 Scale factor for Tight 1 Prong requirement Scale Factor=0.2258 +- 0.04336 Scale Factor=0.09985 +- 0.01157 Scale Factor=0.04676 +- 0.01266 Scale Factor=0.02077 +- 0.002723 Scale Factor=0.02011 +- 0.007526 Scale Factor=0.01031 +- 0.005921 Scale Factor=0.01039 +- 0.005168 Scale Factor=0.01333 +- 0.005407 Scale Factor=0.007264 +- 0.004179 Scale Factor=0.0137 +- 0.00962 Scale Factor=0.005917 +- 0.0059 Scale Factor=0.006289 +- 0.00362 Scale Factor=0.01408 +- 0.005709 Scale Factor=0.007194 +- 0.007168 Scale Factor=0.006623 +- 0.004667 Scale Factor=0 +- 0 Scale Factor=0.01923 +- 0.011 Pt hat bin 20 to 30 GeV/c Pt hat bin 3000 to 3500 GeV/c

16. 29,30 July 2010 India CMS Meeting,BARC Mumbai 16 Pt hat bin 20 to 30 GeV/c Pt hat bin 3000 to 3500 GeV/c Scale factor for Tight opposite sign requirement Scale Factor=0.4624 +- 0.0517 Scale Factor=0.5052 +- 0.0193 Scale Factor=0.4928 +- 0.02998 Scale Factor=0.5055 +- 0.009544 Scale Factor=0.5029 +- 0.0268 Scale Factor=0.4948 +- 0.02931 Scale Factor=0.4753 +- 0.02545 Scale Factor=0.5 +- 0.02357 Scale Factor=0.5448 +- 0.0245 Scale Factor=0.5205 +- 0.04135 Scale Factor=0.5089 +- 0.03846 Scale Factor=0.5451 +- 0.0228 Scale Factor=0.5023 +- 0.02422 Scale Factor=0.4892 +- 0.0424 Scale Factor=0.4834 +- 0.02876 Scale Factor=0.473 +- 0.04104 Scale Factor=0.5032 +- 0.0399 Scale Factor=0.4936 +- 0.04003 N@100ipb for QCD Pt hat 300to380 = 0.126091 +- 0.0560588 N@100ipb for QCD Pt hat 380to470 = 0.0151465 +- 0.00924629 N@100ipb for QCD Pt hat 470to600 = 0.00590631 +- 0.00468418 N@100ipb for QCD Pt hat 600to800 = 0.000547898 +- 0.000563139 N@100ipb for QCD Pt hat 800to1000 = 8.25997e-05 +- 5.04538e-05 N@100ipb for QCD Pt hat 1000to1400 = 4.48505e-05 +- 2.0122e-05 N@100ipb for QCD Pt hat 1400to1800 = 4.14146e-07 +- 4.39461e-07 N@100ipb for QCD Pt hat 1800to2200 = 1.89291e-08 +- 1.40319e-08 N@100ipb for QCD Pt hat 2200to2600 = 0 N@100ipb for QCD Pt hat 2600to3000 = 0 N@100ipb for QCD Pt hat 3000to3500 = 1.05541e-14 +- 6.77639e-15 N@100ipb