Kaon regeneration cross section measurement in KLOEWorking report

12.04.2006

• 2001/2002 sample for data and MC• KLTAG : same selection as for KL BR measurements

reg = Preg n t

Preg= Nreg / NKL =

Thickness known at 5-10 % ! Need a dedicated study

For each regenerator:1

Nkltag exp(-r0

Nreg obs

tagrecsel

rec 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.)

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, distributions after the selection. use background shape from MC scan cuts up to very loose values : use MC to extrapolated to sel = 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 + p2 miss

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.

2 pion invariant mass after KL tag:

MC has a higher peak due to more regeneration events.

Control sidebands

reference cut

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

Drift chamber wall

Beam piperegion

Need a combinedr, fit to disentangle pipe fromberyllium layer

For the moment only d.c. studied in details

Reference cut2/ndf = 1.7

Nreg = 24700

Regeneration peakShaped with 2 gaussians

data

mc

Data/mc

Sidebands usedto correct MC shapeaccording to dataefficiency

Reference cut pulls

Scan of the cuts

TighterDelta p

Tighter Minv

Extrapolation points to

Nreg ∼ 28000

N reg

cut

Fit to the Minv distribution under way, depends very much on peak shape.

Preliminary fit gives Nreg ∼ 36000 still far from previous method

Regenerator thickness study: evaluate 0 mass in +-0 KL decays as a function of the vertex position

Bare agreement data-mc

A more refined study canbe performed