1. October 28, 2003V.Kekelidze 1 Experiment NA48/2 A Precision Measurement of Charged Kaon Decay Parameters (CERN/SPSC 2000-003) Status Report (SPSC-2003-033) CERN, Chicago, Dubna, Ferrara, Firenze, Mainz, Northwestern, Perugia, Pisa, Saclay, Torino, Vienna Cambridge, Edinburgh, Siegen Collaboration:

2. October 28, 2003V.Kekelidze 2 NA48 Collaboration (Pisa, September, 2003)

3. October 28, 2003V.Kekelidze 3 Report content Goals New beam line Set-Up upgrade Beam detector KABES Trigger Data taking in 2003 Asymmetry express analysis: - observable definition - major systematics estimation Ke4 & Rare decay examples Semileptonics Conclusions & beam request

4. October 28, 2003V.Kekelidze 4  Direct CP violation in K ±   ±  +  -, K ±   ±  0  0  (A g )  10 – 4 (limited by statistics) Goals g + - g - A g = ———— g + + g - Requirements to experiment: high statistics (> 2  10 9 decays) stability in time set –up symmetry

5. October 28, 2003V.Kekelidze 5  K e4 to measure  -  scattering length  ( ) < 1  10  2 required statistics > 10 6 (430k )  Rare decays to test  PT & search for A CP K      , K      0  DE K     e + e , K      +  , K  e2 K   l  l + l  K      0 , K      0 l + l , … etc.  Semileptonic decay Br’s: K  e3, K   3 to improve precision of |V us | & check CKM unitarity Goals Goals (continuation)

6. October 28, 2003V.Kekelidze 6 Simultaneous K + and K - beam line (schematic vertical section) not to scale axes are steered to coincide within 1 mm

7. October 28, 2003V.Kekelidze 7  - =4.0, mm  + =4.1, mm 0 =1.23  0.01, mm = -0.08  0.01, mm K-K- K-K- K+K+ Beam spots on the DCH1 -50 0 +50 x, mm +50 y, mm -50 0 +50 x, mm -50 achromat: K + Down (H D ) K+K+ K+K+ K+K+ K-K- -50 0 +50 x, mm -50 0 +50 x, mm achromat: K + Up (H U )

8. October 28, 2003V.Kekelidze 8 New K12 beam line built for NA48/2 first achromat second achromat

9. October 28, 2003V.Kekelidze 9 Set-up Upgrade Beam detector KABES (TPC micromegas) 3 double stations + read-out: put in operation DCH3: fully instrumented DCH1- 4 read-out electronics: re-mapped to be Right –Left ( Saleve – Jura ) symmetric L2 trigger: new processors & interface to neutral part Decay vacuum tank: extended (+24 m) magnetic field remeasured Beam profile monitor: new pixel detector

10. October 28, 2003V.Kekelidze 10 Upgraded NA48 Set-Up (schematic top view) not to scale

11. October 28, 2003V.Kekelidze 11 KABES-1/2 entrance window K + time resolution 67 ps K - time resolution 63 ps T/2 ns, Station2 – Station3 Beam rate ~20 MHz P 0 /P(K) - P 0 /P(S) Momentum resolution 1.1% P(S), GeV/c 50 60 70 P(K), GeV/c -0.2 0 +0.2 50 60 70 Beam rate ~20 MHz K +, K - X,Y space resolution ~100  m -10 0 10 T/2 ns, Station2 – Station3 moved out by ~20 cm

12. October 28, 2003V.Kekelidze 12 Three stage logic for (satisfies K e4 ): pre-trigger: 2 tracks in Hod & no surrounding anti L2 processor (mass-box) 2 vertices (~ 94%) or 1 vertex (~ 98%) or “fake track” (excluding  ±  0 mode ) (~99.5%) L3 software flags (to simplify splits) Trigger logic Logic for K ±   ±  0  0 : pre-trigger: clusters in LKr Cal (Nx > 2 or Ny > 2) L2 “fake track” L3 flags + various triggers for: rare decays, semileptonics, efficiency study, random events,...

13. October 28, 2003V.Kekelidze 13 Stability of trigger efficiencies day-sample u 1% level trigger inefficiency 00 for K +   +  +  - ( ) & K -   -  -  + ( )

14. October 28, 2003V.Kekelidze 14 MNP33 current alternation each day (B U / B D ) swapping of achromat magnetic fields (H U / H D ) during each MD on Wednesday (due to long tuning procedure) data taking cycle two weeks - a supersample Running conditions to compensate variation in time of beam and set-up: more frequent alternation desirable (even on the expense of statistics) as learned from 2003:

15. October 28, 2003V.Kekelidze 15 Beam availability & supersamples SS-1 August 6- 20

16. October 28, 2003V.Kekelidze 16 Statistics for asymmetry Statistics of supersamples in raw K ±   ±  +  - without acceptance cuts (not to scale to the Proposal) H D B U H D B D H U B U H U B D 154 166 38 358 150 58 76 284 127 162 50 339 130 142 60 332 1 2 3 total total 561 528 224 1313 ~ 450 mln K ±   ±  +  - events of SS-1 reprocessed for the express analysis in 10 6 ~ 50 millions of K ±   ±  0  0

17. October 28, 2003V.Kekelidze 17 Reconstructed K ±   ±  +  - P K, GeV/c 40 50 60 70 80 K-K- 0 P  GeV/c K+K+ 0 M(3  ) + GeV/c 2 K+K+ K-K- M(3  ) - GeV/c 2 ~120 mln ~220 mln SS-1 : 1 - 12 day-samples 1 - 6 samples 1 - 3 - H D 4 - 6 - H U

18. October 28, 2003V.Kekelidze 18 Dalitz for accepted u = (2M K /m 2 )  (M K /3 - E *  )  M(u,v)  2  1 + g  u + h  u 2 + k  v 2 v = (2M K /m 2 )  E * 2  Square of matrix element u v run 15323

19. October 28, 2003V.Kekelidze 19 N + (u) a + (u) (1 + g +  u) N - (u) a - (u) (1 + g -  u) A g = ————— if a + (u) = a - (u) - acceptance cancel R(u) = N + (u) / N - (u) ~ 1 +  g  u  g = (g + - g - )  2g  A g R(0) = 1 - normalization g  – 0.2 - 1.170 < u < 1.267 Definitions for asymmetry u = (2M K /m 2 )  (M K /3 - ) u = (m 2 2  -M 2 K /3) / m 2 - 1 g + - g - g + + g - slope

20. October 28, 2003V.Kekelidze 20 u- spectra & their Ratios N+(u)N+(u)N - (u) R(u)R(u) (not normalized) statistics of SS-1 (each plot - one momentum bin) beam pipe cut

21. October 28, 2003V.Kekelidze 21 Observable: A S & A J - slopes of R(u) BU N+(u)BU N+(u) if a S (u) & a J (u) are stable in time t ~ 1 day A S = A J   g A = 0.5 (A S + A J )   g if R a (u) = a S (u) / a J (u) is stable in time BU N-(u)BU N-(u) BD N+(u)BD N+(u) BD N-(u)BD N-(u) aS(u)aS(u) -acceptance aS(u)aS(u) ASAS aJ(u)aJ(u) aJ(u)aJ(u) A J

22. October 28, 2003V.Kekelidze 22 BU N+(u)BU N+(u) BU N-(u)BU N-(u) BD N+(u)BD N+(u) BD N-(u)BD N-(u) Systematic checks A+A+ t = 1 day A-A- AUAU ADAD R a (u) = a S (u) / a J (u): S a - slope A U   g + S a ; A D   g - S a if S a is stable in time A +  + S a ; A -  - S a ; (A + + A - )/ 2  0 -S a +S a -S a (A U + A D )/ 2   g

23. October 28, 2003V.Kekelidze 23 Selection criteria radial cuts around the beam centres (in DCH1,4) to symmetrize acceptances day-by-day definition of the beam COG’s in each momentum bin to reduce acceptance variations in time Conservative cuts: R  (DCH1) > 11.5 cm R  (DCH4) > 13.5 cm leave 60% of raw statistics ( beam stability dependent )

24. October 28, 2003V.Kekelidze 24 Spectrometer alignment M K – M PDG, KeV/c 2 ~ 35 KeV/c 2 ~4  m / day  x DCH4 day-sample B U K + & B D K - ( to Jura ) B D K + & B U K - ( to Saleve) surprising effect time variation term was compensated (after fine tuning of B)

25. October 28, 2003V.Kekelidze 25 Acceptance cancellation check = (A + + A - )/ 2 = (1.2  2.3)  10 -4

26. October 28, 2003V.Kekelidze 26 Beam geometry effects A ± for different achromat polarities HDHD HUHU > 0 < 0

27. October 28, 2003V.Kekelidze 27 Time stability of acceptances in momentum bins

28. October 28, 2003V.Kekelidze 28 A stability with momentum

29. October 28, 2003V.Kekelidze 29 Time stability of acceptances HDHD HDHD HUHU HUHU different achromats

30. October 28, 2003V.Kekelidze 30 Time stability of A HDHD HUHU

31. October 28, 2003V.Kekelidze 31 Systematics summary Major systematics related to - acceptance asymmetry - time variation effects are under control Other possible systematics: - residual (+ Earth) magnetic fields - trigger efficiencies - DCH’s efficiencies - accidentals - ….. are found to be less significant

32. October 28, 2003V.Kekelidze 32 First look on K ±   +  - e ± 15807 events in SS-1  BR = (3.87 ± 0.20)  10 -5 ( PDG: (4.08 ± 0.09)  10 -5 ) 7  10 5 expected K ±   +  - e ± in 2003 Background ~1% of K e4 from K ±   +  -  ± ~1% of K e4 from K ±   ±  0 D M(3  ) GeV/c 2 P K, GeV/c K mass

33. October 28, 2003V.Kekelidze 33 Rare decay K  Rare decay K     e + e - 0.40 0.44 0.48 0.52 0.56 0.60 500 400 300 200 100 0 1400 events in 1 month of data taking ~ 3500 events expected in 2003 run M    e + e -  GeV/c 2 Events / 2 MeV/c 2

34. October 28, 2003V.Kekelidze 34 Semileptonics study In addition, all major modes: leptonic & semi.. K  e2, K  e3, K   2, K   3 hadronic K  2 , K  3  are accumulated with min. bias trigger  strong constraint for Br’s 0 (missing mass) 2, (GeV/c 2 ) 2 0 70 example of K   e  selected from ~1700 burts

35. October 28, 2003V.Kekelidze 35 Conclusion NA48/2 experiment has been prepared: beam line, detector and trigger are put in operation & tuned the major systematics are under control & do not exceed statistical precision to reach the proposal goals quoted statistics are needed can profit from more Beam Request for 2004 as much proton time as possible (400 GeV protons ~1·10 12 ppp on T10) as few beam interruptions as necessary