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Investigation of K-π+ Invariant Mass using Additional Kinematic Cuts

This study analyzes the K-π+ invariant mass in a recent production dataset, focusing on the effectiveness of tight nSigma(dEdx) cuts versus geometrical cuts. Results show promising removal of background with gRefMult and pT cuts, while also discussing potential fake mass reconstruction sources. Future analysis will include a larger dataset.

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Investigation of K-π+ Invariant Mass using Additional Kinematic Cuts

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  1. Inv. Mass for the recent production

  2. details • Not all the production (only for day124 to day153 ; I merged those files before we finished the full prod. this week) • So it represents ~ 22M events • Idea : previous look by tightening nSigma(dEdx) cuts did not improve a lot, so I don’t use them (|nSigma|<2 by default) and I tried to use geometrical cuts (as TCFiT is a geometrical method) • I rerun over all the files produced with additionnal cuts

  3. Additionnal cuts • |cos*|<.6 • cos ( pointing) > .90 • gRefMult > 800 • pT>1 • Probability(TCFIT) >.75 • 0.02 < slength(TCFIT)<.07 • siliconHits ==4 for both daughters • It seems that gRefMult and pT are efficient to remove the background • For the pT cut, it takes advantage of tracks less curved and also we gain in pointing resolution

  4. Inv. Mass K-π+ • The single bin remains above the background line even by varying the cuts so I’m not sure it’s only a fluctuation (it’s also far above the background line)

  5. Inv. mass fit (i) • In that case, BRTW fit gives a significance of 3.56 • The mean is not 1.86 but slightly shifted (1.855)

  6. Inv. Mass fit (ii) • Here cos ( pointing) > .97 • Fit by BRTW gives significance = 4.13

  7. comments • With tighter cuts to decrease the background, a ‘signal’ can be seen • It’s a bit worrying that it’s only 1 bin but it remains above the background line even by varying cuts • Mixing and cutting the kinematical variables (pT, angle in lab and rest frame) could be a source of fake mass reconstruction • Will look at the full production (~ 55Mevents we produced)

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