1. 2 nd KLOE Physics Workshop A. Ferrari 1 of the K L  K S regeneration cross section: F. Ceradini, A. Ferrari, A. Passeri Universita’ di Roma Tre & INFN 2nd KLOE Physics Workshop Otranto, June 10th 2002 Measurement a status report

2. 2 nd KLOE Physics Workshop A. Ferrari 2 e N oss = N KL BR (K S  +  - )  rec (r) P reg -r(rig)/ L P reg =  reg  nd   nd  =N A  i  df  /A  i d regenerator thickness d d density f fraction in volume of the material i P reg Be He C 2.5 10 -4 0.56 10 -5 3.5 10 -4 all wires 3.5 10 -6 (Al +W)

3. 2 nd KLOE Physics Workshop A. Ferrari 3 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

4. 2 nd KLOE Physics Workshop A. Ferrari 4 Monte Carlo simulation Model dependent description, based on the eikonal approximation: f(k,  ) =  (2l + 1) f l (k) P l (cos  ) [ 1 -e i  0(b) ] ~  /(1- ik  ) KLOE: s-wave small momenta b  f(k,  ) = ik  b db J 0 (kb sin  ) [ 1 -e i  0(b) ]  0 (b) depends on forward scattering amplitudes for n and p distribution of nuclear matter impact parameter  scattering length   f reg = f(  ) - f(  ) 2 2 d  reg f(  ) - f(  ) 2 dd = The angular distribution has been implemented in a simplified way: g(  ) = p 1 + p 2 exp (-  2 /2 p 3 2 )  kaon momentum atomic weights p 1, p 2, p 3 depend on g(  ) is truncated at 90 o

5. 2 nd KLOE Physics Workshop A. Ferrari 5 K L - Helium K L - Carbon K L - Berillium  reg vs p p(MeV/c)

6. 2 nd KLOE Physics Workshop A. Ferrari 6 KLOE 1999: (  reg ) bp = 75.7  9.6  10.6 mb (  reg ) dc = 51.9  6.2  5.3 mb 110 Be  inc 110 Be TT Lack of experimental data on KL cross sections on nuclei: 110 C  inc 40.7 545 44.2 Theory (mb) (CMD-2) 40.7 (CMD-2) (CMD-2) 545 (CMD-2) 44.2 Experiment (mb) p K (MV/c) Material

7. 2 nd KLOE Physics Workshop A. Ferrari 7 Event selection K L TAGGING cut on m Ks and p Ks :  4  from the peak value use BPOS only as constraint to evaluate the f –decay point event by event cut on the f – decay position:  3  around the decay vertex select K L candidates by looking at vertices inside a cone around the estimated K L flight path I. K L candidate selection

8. 2 nd KLOE Physics Workshop A. Ferrari 8 The angular cut K L flight path pSpS pp VV d   F(d) =  a 2 + (b/d) 2 The angular cut is a function of the distance  - secondary vertex: F(  ) = p 1 +  [ p 2 exp (-  /2 p 3 2 ) + p 4 exp (-  /2 p 5 2 ) ] For different intervals in d the angular distribution  has been studied:

9. 2 nd KLOE Physics Workshop A. Ferrari 9   p 3 and p 5 are fitted in each d-interval 

10. 2 nd KLOE Physics Workshop A. Ferrari 10 F(d) =  a 2 + (b/d) 2  = 3  (39.4) 2 + (1111/d) 2 mrad Angular cut: Fit results: p 3 cone: a = 17.3  0.1 mrad b = 498.9  4.5 mrad cm p 5 cone: a = 39.4  0.8 mrad b = 1111  23 mrad cm K L decay length

11. 2 nd KLOE Physics Workshop A. Ferrari 11 K L candidate sample K L decay length cm N(K L candidates) = 1096068  sel = N(K L candidates) N(K L tag) = 12.8%  Data/MC = 93.3%  MC (KL  charged) = 40.8%

12. 2 nd KLOE Physics Workshop A. Ferrari 12 K L invariant mass selection K L invariant mass MeV/c 2 m inv in [493.7, 501.7] MeV/c  Data/MC = 86.5% After the selection: 16025 events

13. 2 nd KLOE Physics Workshop A. Ferrari 13 D p distribution D p = |p est | -|p meas | -6 < D p < 12 MeV/c Cut:  Data/MC = 74.2% After the selection: 6940 events

14. 2 nd KLOE Physics Workshop A. Ferrari 14 r(cm)  (cm) After D p cut: All CP violation + regeneration candidates

15. 2 nd KLOE Physics Workshop A. Ferrari 15 to separate the internal Be regenerator: secondary vertex in [60 o,120 o ]  (cm)

16. 2 nd KLOE Physics Workshop A. Ferrari 16 (angular distribution) All CP violation + regeneration candidates MC generator angular distrib. is truncated at 90 degrees!

17. 2 nd KLOE Physics Workshop A. Ferrari 17 CP violation events: cut at 75 mrad r(cm) Good agreement !

18. 2 nd KLOE Physics Workshop A. Ferrari 18 Specialized Angular distributions Pipe DC wall

19. 2 nd KLOE Physics Workshop A. Ferrari 19 Selection efficiencies vs r CP violating regenerated

20. 2 nd KLOE Physics Workshop A. Ferrari 20 Conclusions 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