Analysis BNL J.Bouchet, J.Joseph 1

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 < 700 μm - defaults cuts in the macro(applied to positive and negative tracks) D0Mix : 1 D0 embedded in Cu+Cu event, 290 files with 400 events. - same cuts as above Real Data: MinBias (P07ic) : - ran over 20,000 files - dEdx cuts + same cuts as in pureD 0 2  The macro associates positive and negative tracks to reconstruct the invariant mass

Pure D0 Sample 3 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. Resolution 0.589%

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

Looking at some attempted cuts in MuKpi.C with pure D0 and D0Mix sample 5 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 DCA of the Tracks D0 Mix Pure D0

D0 Mass with cut on Dca 6 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 S/B = 2.591

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

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

D0Mix: Combining cuts on Ntracks, Dca, opening angle of Kaon, momenta of daughter tracks etc. 9 SsdHits(pos&neg) > 0 SvtHits( pos&neg) > 0 TpcHits(pos&neg) >20 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 Here we tried two sets of cuts to see how well it reconstructs the D0Mass from the mix sample

D0 Mix: Mass plot and background 10 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. Mass plot with all the cuts mentioned in the previous slide Background Signal/Background=17.991

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. 11 In the following slides we look at three cuts: No of Tpc Hits, No of Si Hits and No of Tracks Rotation after association of tracksRotation before association True fake

Fixed Rotation 12 All associations Background

Real Data dEdx of Real Data 13 Red = Pi + Blue = K-

Real Data Mass plots 14 True Fake

Conclusion Analysis of D 0 reconstruction based on micro vertex code (using SSD and SVT hits) We looked at Pure, D0 Mix and Real Data Applied different cuts in Pure and D0 Mix 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 15

BackUp slides 16

Mass Resolution with Si and TpcHits (pure D0) 17 no cut σ D0 M = TPC > 30(*) σ D0 M = eff =81.5% Si > 1(*) σ D0 M = eff=44.5% TPC>30 &&Si > 1(*) σ D0 M = eff=35.2%

Daughter momenta(D0Mix) 18

Daughter Characteristics 19

Random Rotation(D0Mix) 20

SigmaDca(D0Mix) 21 SigmaXY_pos – SigmaXY_neg D0Mix Pure D0