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Kaon regeneration cross section measurement in KLOE Working report 12.04.2006

Kaon regeneration cross section measurement in KLOE Working report 12.04.2006. 2001/2002 sample for data and MC KLTAG : same selection as for K L BR measurements. s reg = P reg n t. Thickness known at 5-10 % ! Need a dedicated study. For each regenerator:. N reg obs. 1.

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Kaon regeneration cross section measurement in KLOE Working report 12.04.2006

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  1. Kaon regeneration cross section measurement in KLOE Working report 12.04.2006

  2. 2001/2002 sample for data and MC • KLTAG : same selection as for KL BR measurements sreg = Preg n t Thickness known at 5-10 % ! Need a dedicated study For each regenerator: Nregobs 1 Preg= Nreg / NKL = etag erecesel Nkltag exp(-r0/l) erec for regeneration is being evaluated in each regenerator region using Ke3 events selected in data in the same way as the KL BR Measurement (i.e. electron id via t.o.f.)

  3. Extraction of the incoherent regeneration signal Two techniques: • select a regeneration-enriched sample by cutting on: • 2-pion invariant mass • total momentum of the 2 tracks (should be the KL momentum ) • count the regeneration events by fitting the r, r distributions after the selection. • use background shape from MC • scan cuts up to very loose values : use MC to extrapolated to esel = 1 • count the regeneration events by fitting the 2 pion invariant mass distrib for events • whose reconstructed vertex falls near a specific regenerator. • Reject KL 2 pion decays by cutting on E2 miss + p2miss • use background shapes from MC • Need MC correction for regenerated Minv distribution tails Note: MC does not reproduce neither the size neither the angular distribution of the regeneration, i.e. MC shapes for regenerated events cannot be safely used.

  4. 2 pion invariant mass after KL tag: MC has a higher peak due to more regeneration events. Control sidebands reference cut

  5. For incoherent regeneration the 2 tracks total momentum ∼ KL momentum (a small fraction of momentum is taken by the nucleus)

  6. Drift chamber wall

  7. Beam pipe region Need a combined r, r fit to disentangle pipe from beryllium layer For the moment only d.c. studied in details

  8. Regeneration peak Shaped with 2 gaussians Reference cut c2/ndf = 1.7 Nreg = 24700

  9. Sidebands used to correct MC shape according to data efficiency mc data Data/mc

  10. Reference cut pulls

  11. N reg Scan of the cuts Tighter Delta p Extrapolation points to Nreg∼ 28000 Tighter Minv cut

  12. Fit to the Minv distribution under way, depends very much on peak shape. Preliminary fit gives Nreg ∼ 36000 still far from previous method

  13. Regenerator thickness study: evaluate p0 mass in p+p-p0 KL decays as a function of the vertex position Bare agreement data-mc A more refined study can be performed

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