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D + with KFParticle

D + with KFParticle. J. Bouchet. outline. MuKPi, as written now, cannot handle decay vertex fit with 3 particles (have to write a new class) Switch to KFParticle since it’s easier (just add another track/particle). KFParticle particle[5];// vertex + track1 + track2 + track3 + mother … …

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D + with KFParticle

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  1. D+ with KFParticle J. Bouchet

  2. outline • MuKPi, as written now, cannot handle decay vertex fit with 3 particles (have to write a new class) • Switch to KFParticle since it’s easier (just add another track/particle) KFParticle particle[5];// vertex + track1 + track2 + track3 + mother … … const KFParticle pVertex = particle[0]; int NDaughters = 3; const KFParticle *vDaughters[3] = {&particle[1],&particle[2],&particle[3]}; KFParticle DP; DP.Construct(vDaughters,NDaughters,&pVertex,-1,0);  Define array of 5 KFparticles • Define the number of daughters • Define the Dplus particle and the Construct() method is doing all the job • It’s ok to use KFParticle since we have seen similar results with TCFIT for the D0 decay. • KFParticle also provides easily, via Get() methods, the properties of the reconstructed particle DTree.KFZ[cand] = DP.GetX(); DTree.KFMass[cand] = DP.GetMass(); DTree.KFDecayLength[cand] = DP.GetDecayLength(); DTree.KFErrDecayLength[cand] = DP.GetErrDecayLength();; • Get the X position of 2nd vertex • Get the mass, decay length ….

  3. test • Use starsim with : • 10k D+ • Vertex centred at 0.01 smeared with gausian of rms = 5 cm • Flat pT in [0,5] • Flat rapidity (from now on, I will use rapidity instead on pseudo-rapidity) • SL08f : Slow simulator + Y2007G geometry • In MuKpi, I use nsigmadEdx from Bichsel (see last slide for issue in simu of nsigmadEdx from bichsel/MuDst) to select Kaon and pions (cut at |n|<3

  4. Check (.fz file) • the quantities from the .fz files are as expected

  5. Pt of daughters • Output from MuKpi : cuts applied are not too restrictive as this point • The selection of these daughters tracks used : • Good PID • chargeK<0 and charge pion1, pion2 >0

  6. Invariant mass • We see the same as for the D0 : the reflection due to wrong signs is making the distribution broader • When selecting Kaon and pions candidates+ good signs, there is clearly the good peak

  7. Decay length

  8. Decay length (closer look) Mean is ~300µm

  9. Significance of decay length • Significance is defined by : • KFDecayLength/KFErrDecayLength

  10. Dalitz plot • We can also plot the mass of (Kπ1) vs mass of (Kπ2) • As I choose the non resonant decay D+Kππ, the dalitz plot is homogeneous (we should see preferred horizontal and vertical bands in case of resonant decay, like D+antiK*0π )

  11. Decay length check From PDG • By plotting the quantity (decayLength*mass) / momentum, we can estimate the proper life time ctau • Here the fit gives a slope of 1/ctau =26.9 cm  370 µm • It’s a bit overestimated but the order of magnitude is correct

  12. summary • MuKpi for 3 bodies (D+) is set up using KFParticle. • I have also done it with the ‘new’ D0Tree (see my post last week related to the changes of the code) • Single D+ gives reasonable results • Did not yet investigate other cuts. • Next : go to mix D+ in hijing or directly test on the real data ?

  13. ndEdx • The ndEdx distribution is • centred at 0 when taking • the bichsel estimation

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