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A. Ferrari 1 2nd KLOE Physics Workshop
of the of the KKLL K KSS regeneration cross section: regeneration cross section:
F. Ceradini, A. Ferrari, A. PasseriF. Ceradini, A. Ferrari, A. PasseriUniversita’ di Roma Tre & INFNUniversita’ di Roma Tre & INFN
2nd KLOE Physics Workshop2nd KLOE Physics WorkshopOtranto, June 10th 2002Otranto, June 10th 2002
Measurement Measurement
a status reporta status report
A. Ferrari 2 2nd KLOE Physics Workshop
eNoss = NKL BR (KS+- ) rec(r) Preg -r(rig)/L
Preg = reg nd
nd=NA i df /Ai
d regenerator thickness densityf fraction in volume of the material i
Preg
Be
He
C
2.5 10-4
0.56 10-5
3.5 10-4
all wires 3.5 10-6
(Al +W)
A. Ferrari 3 2nd KLOE Physics Workshop
The 1999 analysis has been redone on 2000 data sample (17 pb-1)
~ 4.7 pb-1 of Monte Carlo events have been used for comparison
A. Ferrari 4 2nd KLOE Physics Workshop
Monte Carlo simulationMonte Carlo simulationModel dependent description, based on the eikonal approximation:
f(k, ) = (2l + 1) fl(k) Pl(cos ) [ 1 -e i0(b)] ~ /(1- ik)
KLOE: s-wave small momenta
bf(k, ) = ik b db J0(kb sin ) [ 1 -e i0(b)]
0(b) depends on forward scattering amplitudes for n and pdistribution of nuclear matter
impact parameter
scattering length
freg = f() - f() 2
2dreg f() - f() 2d =
The angular distribution has been implemented in a simplified way:
g() = p1 + p2 exp (-2/2 p32) kaon momentum
atomic weightsp1, p2 , p3 depend on
g() is truncated at 90o
A. Ferrari 5 2nd KLOE Physics Workshop
KL - Helium KL - CarbonKL - Berillium
reg reg vs pvs p
p(MeV/c) p(MeV/c) p(MeV/c)
A. Ferrari 6 2nd KLOE Physics Workshop
KLOE 1999:KLOE 1999:
(reg)bp = 75.7 9.6 10.6 mb
(reg)dc = 51.9 6.2 5.3 mb
110Beinc
110 BeT
Lack of experimental data on KL cross sections on nuclei:Lack of experimental data on KL cross sections on nuclei:
110 Cinc
545
Theory (mb)
(CMD-2)(CMD-2)
545 (CMD-2)(CMD-2)
Experiment (mb)pK (MV/c)Material
A. Ferrari 7 2nd KLOE Physics Workshop
Event selectionEvent selection
• KL TAGGING
• cut on mKs and pKs : 4 from the peak value • use BPOS only as constraint to evaluate the –decay point event by event• cut on the – decay position: 3 around the decay vertex• select KL candidates by looking at vertices inside a cone around the estimated KL flight path
I. KL candidate selection
A. Ferrari 8 2nd KLOE Physics Workshop
The angular cut KL flight path
pS
p V
d
F(d) = a2 + (b/d)2
The angular cut is a function of the distance - secondary vertex:
F() = p1 + [ p2 exp (-/2 p32) + p4 exp (-/2 p5
2) ] For different intervals in d the angular distribution has been studied:
A. Ferrari 9 2nd KLOE Physics Workshop
p3 and p5 are fitted in each d-interval
A. Ferrari 10 2nd KLOE Physics Workshop
F(d) = a2 + (b/d)2
= 3 (39.4)2 + (1111/d)2 mrad
Angular cut:
Fit results: p3 cone: a = 17.3 0.1 mrad b = 498.9 4.5 mrad cm
p5 cone: a = 39.4 0.8 mrad b = 1111 23 mrad cm
KL decay length
A. Ferrari 11 2nd KLOE Physics Workshop
KL candidate sample
KL decay length
cm
N(KL candidates) = 1096068
sel =N(KL candidates)N(KL tag)
= 12.8%
Data/MC = 93.3%
MC (KL charged) = 40.8%
A. Ferrari 12 2nd KLOE Physics Workshop
KL invariant mass selection
KL invariant mass
MeV/c2
MeV/c2
minv in [493.7, 501.7] MeV/c
Data/MC = 86.5%After the selection: 16025 events
A. Ferrari 13 2nd KLOE Physics Workshop
p distribution
p = |pest| -|pmeas|
-6 <p < 12 MeV/c
Cut:
Data/MC = 74.2%After the selection: 6940 events
A. Ferrari 14 2nd KLOE Physics Workshop
r(cm)
(cm)
After p cut:All CP violation + regeneration candidates
A. Ferrari 15 2nd KLOE Physics Workshop
to separate the internal Be regenerator:secondary vertex in [60o,120o]
(cm)
A. Ferrari 16 2nd KLOE Physics Workshop
(angular distribution)
All CP violation + regeneration candidates
MC generator angular distrib. is truncated at 90 degrees!
A. Ferrari 17 2nd KLOE Physics Workshop
CP violation events:
cut at 75 mrad
r(cm)
Good agreement !
A. Ferrari 18 2nd KLOE Physics Workshop
Specialized Angular distributions
Pipe
DC wall
A. Ferrari 19 2nd KLOE Physics Workshop
Selection efficiencies vs rSelection efficiencies vs r
CP violatingCP violating
regeneratedregenerated
A. Ferrari 20 2nd KLOE Physics Workshop
Conclusions and outlookConclusions and outlook
The 2000 data sample analysis is going to be completed - the MC correction reg/CP will be evaluated with high statistics specialized sample - a memo will be written by the summer In the next future:
- analysis on 2001 data sample - reduce systematics due to the knowledge of the regenerator thickness: measure it