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D0 Analysis in cucu200GeV using Micro Vertex Code

D0 Analysis in cucu200GeV using Micro Vertex Code. Analysis Meeting @ BNL J.Bouchet, J.Joseph. Cuts Used in MuKpi macro. pure D0 : 950 MuDst files (400 possible D 0s per file) - |Zvertex| < 20 cm - NTpcHits > 15 - | η| in SSD acceptance, ie |η| <1.2 - pT > 0.1 GeV/c

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D0 Analysis in cucu200GeV using Micro Vertex Code

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  1. D0 Analysis in cucu200GeV using Micro Vertex Code Analysis Meeting @ BNL J.Bouchet, J.Joseph

  2. Cuts Used in MuKpi macro • pure D0 : 950 MuDst files (400 possible D0s per file) - |Zvertex| < 20 cm - NTpcHits > 15 - |η| in SSD acceptance, ie |η| <1.2 - pT > 0.1 GeV/c - decay length < 700μm - defaults cuts in the macro(applied to positive and negative tracks) • D0Mix: 1D0 embedded in Cu+Cu event, 290 files with 400 events. - same cuts as above • Real Data: Cu+Cu@200GeV MinBias (P07ic) : - ran over 20,000 files - dEdx cuts + same cuts as in pureD0 • The macro associates positive and negative tracks to reconstruct • the invariant mass

  3. Pure D0 Sample Resolution 0.589% No Cuts Resolution:0.589% • The Reconstruction Microvertex Code[MuKpi.C ] reconstructs D0 parameters pretty well in pure D0 sample. • Cuts on TpcHits(>20) and SiHits (SvtHits>0&SsdHits>0 )for pos and neg daughter tracks removes almost every bad associations in pure sample.

  4. D0Mix(No Cuts) Real Fake Real Fake Seems to be working with a cut on the Number of Tracks. S/B = 1.255 A Gaussian is fitted to the signal and a zero degree polynomial to the background. Pad 3: Signal/Background = 1.255

  5. Looking at some attempted cuts in MuKpi.C with pure D0 and D0Mix sample DCA of the Tracks Pure D0 D0 Mix • We see a small correlation for mass =1.86 and the low multiplicity • In order to remove fake association we can do a cut on • dca = |DCApos – DCAneg|< 0.1

  6. D0 Mass with cut on Dca S/B = 2.591 With the help of silicon detectors we can have more precision in DCAs and hence a more fine tuned cut in the analysis. The cut on Dca improves the Signal/Background ratio to 2.591

  7. Dca, Angle(made by Kaon in the CM frame) and Ntracks cuts analysis in D0Mix(For Ntracks<50) Angle made by K- in the CM Frame Pure D0 D0 Mix A cut (|angle|< 0.8 ) can possibly remove some background .

  8. D0Mass(with a cut on the opening angle of Kaon) S/B = 2.336 With a cut on the opening angle of Kaon, Signal/Background = 2.336 But removing the cut on NTracks leads to disappearance of the D0signal!

  9. D0Mix: Combining cuts on Ntracks, Dca, opening angle of Kaon, momenta of daughter tracks etc. Here we tried two sets of cuts to see how well it reconstructs the D0Mass from the mix sample • NoTracks<50 • |Kaon opening angle| < 0.8 • |pPos|>0.6, |pNeg|>0.6 • ChargePosTrack >0, ChargeNegTrack <0 • |dcaXY_pos – dcaXY_neg| < 0.1 • |dcaZ_pos – dcaZ_neg| < 0.1 • SsdHits(pos&neg) > 0 • SvtHits( pos&neg) > 0 • TpcHits(pos&neg) >20 • NoTracks<50

  10. D0 Mix: Mass plot and background • Mass plot with all the cuts mentioned in the previous slide • Background The shape of the Background (for each association, rotation of the pion track through π) differs from the actual mass distribution and hence the subtraction can lead to over-estimation of D0. Signal/Background=17.991

  11. Recalculation of Background • Try another value than π: same results • try random rotation in 2π for both daughters : same results • We tried to rotate the track around the primary vertex by rotating the pion track before doing the association. Rotation after association of tracks Rotation before association True fake In the following slides we look at three cuts: No of Tpc Hits, No of Si Hits and No of Tracks

  12. Fixed Rotation All associations Background

  13. Real DatadEdx of Real Data Red = Pi+ Blue = K-

  14. Real Data Mass plots True Fake

  15. Conclusion • Analysis of D0 reconstruction based on micro vertex code (using SSD and SVT hits) • We looked at Pure, D0Mix and Real Data • Applied different cuts in Pure and D0Mix to enhance the signal. • Evaluated the signal over background , tried different background calculation. • Investigation of background calculation(Like sign & Mix Events) • We plan to apply the same cuts but tuned for the real data (looked at real data, but no signal so far) • We can utilize the SiliconHits to have more tight cuts on DCA

  16. BackUp slides

  17. Mass Resolution with Si and TpcHits (pure D0) TPC > 30(*) σD0M =0.01054 eff =81.5% no cut σD0M =0.01087 Si > 1(*) σD0M =0.01068 eff=44.5% TPC>30 &&Si > 1(*) σD0M =0.01030 eff=35.2%

  18. Daughter momenta(D0Mix)

  19. Daughter Characteristics

  20. Random Rotation(D0Mix)

  21. SigmaDca(D0Mix) SigmaXY_pos – SigmaXY_neg D0Mix Pure D0

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