D0 Analysis in cucu200GeV using Micro Vertex Code

Analysis Meeting @ BNLJ.Bouchet, J.Joseph

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Cuts Used in MuKpi macropure 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: 1 D0 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

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The macro associates positive and negative tracks to reconstruct the invariant mass

Pure D0 Sample

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No CutsResolution: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)

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RealFake

Seems to be working with a cut on the Number of Tracks.

RealFake

A Gaussian is fitted to the signal and a zero degree polynomial to the background.

Pad 3: Signal/Background = 1.255

S/B = 1.255

Looking at some attempted cuts in MuKpi.C with pure D0 and D0Mix sample

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We see a small correlation for mass =1.86 and the low multiplicityIn 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

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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

S/B = 2.591

Dca, Angle(made by Kaon in the CM frame) and Ntracks cuts analysis in D0Mix(For Ntracks<50)

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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)

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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!

S/B = 2.336

D0 Mix: Mass plot and background

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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 BackgroundTry another value than π: same resultstry random rotation in 2π for both daughters :

same resultsWe tried to rotate the track around the primary

vertex by rotating the pion track before doing the association.

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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 tracks Rotation before association

Truefake

Fixed Rotation

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All associationsBackground

Real DatadEdx of Real Data

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Red = PiRed = Pi++Blue = K-Blue = K-

Real Data Mass plots

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TrueFake

ConclusionAnalysis of D0 reconstruction based on micro

vertex code (using SSD and SVT hits)We looked at Pure, D0Mix and Real DataApplied 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

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BackUp slides

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Mass Resolution with Si and TpcHits (pure D0)

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no cutσD0

M

=0.01087

TPC > 30(*)σD0

M =0.01054eff =81.5%

Si > 1(*)σD0

M

=0.01068eff=44.5%

TPC>30 &&Si > 1(*)σD0

M =0.01030eff=35.2%

Daughter momenta(D0Mix)

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Daughter Characteristics

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Random Rotation(D0Mix)

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SigmaDca(D0Mix)

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SigmaXY_pos – SigmaXY_neg

D0MixPure D0

D0 Analysis in cucu200GeV using Micro Vertex Code

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