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D + with KFParticle

This document explores the utilization of the KFParticle framework for analyzing D+ decays involving three particles. It highlights the limitations of current methods in handling decay vertex fits and the need for a new class. By integrating KFParticle, we simplify adding additional tracks and particles, allowing for accurate reconstruction of particle properties such as mass and decay length. The results, validated through simulations and analysis of selected tracks, reveal significant findings about decay lengths and invariant mass distributions. This work sets the stage for future research, including tests on the real data.

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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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