1. Search for direct CP-violation in K ±   ±  +  – decays by NA48/2 Ivan Mikulec HEPHY Vienna, Austria On behalf of the NA48/2 collaboration: Cambridge, CERN, Chicago, Dubna, Edinburgh, Ferrara, Firenze, Mainz, Northwestern, Perugia, Pisa, Saclay, Siegen, Torino, Vienna XXXXth Rencontres de Moriond EWI&UT La Thuile March 5-12 2005

2. I. Mikulec: Search for direct CP-violation in K± by NA482 Overview  Direct CP violation in K ± →3  decays  NA48/2 experimental setup  Measurement principle  Systematic effects  Preliminary result in K ±   ±  +  – decay mode  Outlook for K ±  ±  0  0 analysis  Conclusions

3. I. Mikulec: Search for direct CP-violation in K± by NA483 Brief history of CP violation 1964 - CP violation in K 0 (Cronin, Christenson, Fitch, Turlay) 1993-99 - Direct CP violation in K 0 (NA31, NA48, KTeV) 2001 - CP violation in B 0 (Babar, Belle) 2004 - Direct CP violation in B 0 (Belle, Babar) CP violation and especially direct: A window to physics beyond SM Complementary observables in Kaons:  ’/  ↔A g ↔ rare decays  Look for direct CP violation in K ± ! (only direct CPV in K ± possible – no mixing)

4. I. Mikulec: Search for direct CP-violation in K± by NA484 K ± →3  matrix element: Direct CP-violation observable A g K + -K - asymmetry in g:  Direct CP violation Dalitz variables i=3 odd pion K  π + π - π ± : g = -0.2154 K  π 0 π 0 π ± : g = 0.652 |h|, |k| << |g|  2even  1even  3odd K±K± Kπ+π-π±Kπ+π-π± if

5. I. Mikulec: Search for direct CP-violation in K± by NA485 Experimental and theoretical status 10 -6 |A g | Experimental results 10 -5 10 -4 10 -3 10 -2 Ford et al. (1970) HyperCP prelim. (2000) TNF prelim. (2002) “neutral” mode NA48/2 proposal SM estimates of A g vary within an order of magnitude (few 10 -6 …8x10 -5 ). “charged” “neutral” Theory Asymmetry in decay widths A  expected to be smaller than in Dalitz-plot slopes A g (SM: ~10 -7 …10 -6 ). SM SUSY Newphysics Models beyond SM predict substantial enhancements partially within the reach of NA48/2. (theoretical analyses are by far not exhaustive by now)

6. I. Mikulec: Search for direct CP-violation in K± by NA486 Goals and method Primary NA48/2 goals: –Measure slope asymmetries in “charged” and “neutral” modes with precisions δA g <2.2x10 -4, and δA g 0 <3.5x10 -4, respectively. –Statistics required for this measurement: >2x10 9 in “charged” mode and >10 8 in “neutral” mode. NA48/2 method: –Two simultaneous K + and K – beams, superimposed in space, with narrow momentum spectra; –Detect asymmetry exclusively considering slopes of ratios of normalized U distributions; –Equalise K + and K – acceptances by frequently alternating polarities of relevant magnets.

7. I. Mikulec: Search for direct CP-violation in K± by NA487 Experimental setup P K spectra, 60  3 GeV/c 54 60 66 1cm 50100 10 cm 200250 m He tank + spectrometer Front-end achromat Momentum selection Quadrupole quadruplet Focusing  sweeping Second achromat Cleaning Beam spectrometer ~7  10 11 ppp K+K+ KK Beams coincide within ~1mm all along 114m decay volume focusing beams Analysing magnet vacuum tank not to scale K+K+ KK beam pipe

8. I. Mikulec: Search for direct CP-violation in K± by NA488 Data taking 2003 run: ~ 50 days 2004 run: ~ 60 days Total statistics in 2 years: K      +   : ~4x10 9 K    0  0   : ~2x10 8 ~ 200 TB of data recorded First result based on 2003 K ±   ±  +  – sample will be presented here

9. I. Mikulec: Search for direct CP-violation in K± by NA489 Accepted statistics U |V| even pion in beam pipe Data-taking 2003: 1.61x10 9 K ±   ±  +  – 1.61x10 9 K ±   ±  +  – events K + : 1.03 x10 9 events K  : 0.58 x10 9 events K + /K – ≈ 1.8  odd pion in beam pipe  M =1.7 MeV/c 2 Events Invariant  mass

10. I. Mikulec: Search for direct CP-violation in K± by NA4810 Principle of the experiment Build u-distributions of K + and K - : N + (u),N - (u) Make a ratio of these distributions: R(u) Fit a linear function to this ratio: normalised slope ≈  g e.g. uncertainty δAg<2.2∙10 -4 corresponds to δ  g<0.9∙10 -4 But, achromat and spectrometer magnet  unavoidable sources of apparatus asymmetry!

11. I. Mikulec: Search for direct CP-violation in K± by NA4811 Four ratios Z X Y Jura(left) Saleve(right) Achromats: K + Up Achromats: K + Down B+ BB ’s Indeces of R’s correspond to UD beamline polarity (U/D) SJ kaon deviation in spectrometer mag. field (S/J). Supersample data taking strategy: –achromat polarity (A) was reversed on weekly basis; –spectrometer magnet polarity (B) was reversed on daily basis. 1 Supersample ~ 2 weeks  2003 data 4 supersamples

12. I. Mikulec: Search for direct CP-violation in K± by NA4812 Quadruple ratio R = R US R UJ R DS R DJ ~ 1+4  g·u 3-fold cancellation of systematic biases: 1) Global time-variable biases (K +,K - simultaneously recorded) 2) Beam line biases (K + beam up / K - beam up etc.) 3) Detector asymmetries (K + toward Saleve / K - toward Saleve etc.) In addition, acceptance is defined respecting azimuthal symmetry 4) Effects of permanent stray fields (earth, vacuum tank magnetisation) cancel only The result is sensitive only to time variationasymmetries time variation of asymmetries in experimental conditions with a characteristic time smaller than corresponding field-alternation period (beam-week, detector-day)

13. I. Mikulec: Search for direct CP-violation in K± by NA4813 Monte Carlo simulation Still MC is used to study systematics. MC features: –Based on GEANT; –Full detector geometry and material description; –Local DCH inefficiencies simulated; –Variations of beam geometry and DCH alignment are followed; –Simulated statistics similar to experimental one. Example of data/MC agreement: mean beam positions @DCH1 K + data K  data K + MC K  MC K+K+ KK Due to acceptance cancellations, the analysis does not rely on Monte-Carlo to calculate acceptance

14. I. Mikulec: Search for direct CP-violation in K± by NA4814 Beam systematics Time variations of beam geometry Acceptance largely defined by central beam hole edge (~10 cm radius) Acceptance cut defined by (larger) “virtual pipe” centered on averaged beam positions as a function of charge, time and K momentum Y, cm Sample beam profile at DCH1 0 0.4 0.8-0.4 -0.8 0 0.4 0.8 -0.4 -0.8 X, cm Beam movements: ~ 2 mm Y, cm x,y-beam vs. K momentum Beam widths: ~ 5 mm 5mm 2mm

15. I. Mikulec: Search for direct CP-violation in K± by NA4815 Spectrometer systematics Time variations of spectrometer geometry - Alignment is fine tuned by forcing mean reconstructed invariant  masses to be equal for K + and K - Maximum equivalent horizontal shift: ~200  m @DCH1 or ~120  m @DCH2 or ~280  m @DCH4 E.g. sensitivity to DCH4 horizontal shift:  M/  x  1.5 keV/  m Momentum scale variation due to limited control of spectrometer magnet current (10 -3 ) cancels due to simultaneous beams In addition, it is adjusted by forcing mean reconstructed invariant  masses to PDG value of M K+  M 

16. I. Mikulec: Search for direct CP-violation in K± by NA4816 Trigger systematics Inefficiencies measured using control data from low bias triggers. Rate-dependent parts of trigger inefficiencies assumed to be symmetric. L2 inefficiency L2 trigger (online vertex reconstruction): time-varying inefficiency (local DCH inefficiencies) 1-  ≈ 0.2% to 1.8% flat in u within measurement precision u-dependent correction applied 3x10 -3 cut statistical uncertainty from control sample L1 trigger (2 hodoscope hits): stable and small inefficiency 1-  ≈ 0.7·10-3 (no correction) L2 correction  Δgx10 4 SS00.5±1.8 SS11.4±1.0 SS2-0.2±1.2 SS3-4.5±1.9  Possibility to use MC studied

17. I. Mikulec: Search for direct CP-violation in K± by NA4817 Other systematics No magnetic field correction Magnetic field corrected for Bias due to resolution in u calculation Sensitivity to fitting interval and method Effects connected to  →  decay Effects due to event pile-up  + /  - interactions in material Track charge misidentification Further systematic effects studied: Residual effects of stray magnetic fields (magnetised vacuum tank, earth field) minimised by explicit field map correction Field map in decay volume: Y projection Decay volume: Z coordinate

18. I. Mikulec: Search for direct CP-violation in K± by NA4818 Fit linearity – four supersamples  2 =39.7/38 SS0:  g=(0.6±2.4)x10 -4  2 =38.1/38 SS1:  g=(2.3±2.2)x10 -4  2 =29.5/38 SS2:  g=(-3.1±2.5)x10 -4  2 =32.9/38 SS3:  g=(-2.9±3.9)x10 -4 U U U U

19. I. Mikulec: Search for direct CP-violation in K± by NA4819 Time stability Quadruple ratio with K(right)/K(left) K(up)/K(down) K(+)/K(-) 4 supersamples give consistent results control of detector asymmetry control of beam line asymmetry By regrouping the components in quadruple ratio – check residual detector and beam line asymmetries (~few 10 -4 ) – they cancel safely in  g fits gg MC can reproduce these apparatus asymmetries

20. I. Mikulec: Search for direct CP-violation in K± by NA4820 Systematics summary and result Preliminary estimates of systematic uncertainties Effect on Δgx10 4 Acceptance and beam geometry0.5 Spectrometer alignment0.1 Analyzing magnet field0.1  ±  decay0.4 U calculation and fitting0.5 Pile-up0.3 Syst. errors of statistical nature Trigger efficiency: L20.8 Trigger efficiency: L10.4 Total systematic error1.3 RawCorrected for L2 eff SS00.0±1.50.5±2.4 SS10.9±2.02.2±2.2 SS2-2.8±2.2-3.0±2.5 SS32.0±3.4-2.6±3.9 Total-0.2±1.0-0.2±1.3 22 2.2/33.2/3 Combined preliminary result: in Δgx10 4 units (3 independent analyses) Including L2 trigger correction

21. I. Mikulec: Search for direct CP-violation in K± by NA4821 Preliminary result K ±  ±  +  - (2003 data) Δg =(-0.2±1.0 stat. ±0.9 stat.(trig.) ±0.9 syst. )x10 -4 Δg =(-0.2±1.7)x10 -4 A g = (0.5±2.4 stat. ±2.1 stat.(trig.) ±2.1 syst. )x10 -4 A g = (0.5±3.8)x10 -4 This is a preliminary result with conservative estimate of systematic uncertainties Extrapolated statistical uncertainty 2003+2004:  A g =1.6x10 -4 Expect smaller systematic effects in 2004 data (due to more frequent polarity alternation, better L2 performance). Converted to asymmetry:

22. I. Mikulec: Search for direct CP-violation in K± by NA4822 Comparison K ±  ±  +  - NA48/2 prelim.: 2003 data 10 -6 |A g | 10 -5 10 -4 10 -3 10 -2 SM SUSY Ford et al. (1970) HyperCP prelim. (2000) NA48/2 goal: 2003-04 data Newphysics This preliminary result is already an order of magnitude better than previous experiments

23. I. Mikulec: Search for direct CP-violation in K± by NA4823 K ±  ±  0  0 analysis ∙ u can be reconstructed with LKr calorimeter only ∙ Statistics analyzed: 28 × 10 6 events (1 month of 2003) ∙ Statistical error with analyzed data:  Ag(stat)= 2.2 × 10 −4 ∙ Extrapolation to 2003+2004 data:  Ag(stat)= 1.3 × 10 −4 ∙ Similar statistical precision as in “charged” mode ∙ Possibly larger systematic errors v -1.5 -0.5 0 0.5 1.0 u 0 -2 1 2 3 Dalitz-plot Statistical precision in A g 0 similar to “charged” mode: - Ratio of “neutral” to “charged” statistics: N 0 /N ± ~1/20 (√=1/4.5) - Ratio of slopes: |g 0 /g ± |  3 - More favourable Dalitz-plot distribution (gain factor f~1.5)

24. I. Mikulec: Search for direct CP-violation in K± by NA4824 Observation of  scattering effect in K→3  decays 1 bin = 0.00015 GeV 2 MC (no rescattering) Data K ±  ±  0  0 M(  0  0 ) GeV/c 2 4m π + 2 Charge exchange process  +    0  0 not negligible under 2m  threshold, destructive interference generates a cusp in the Dalitz plot, not seen earlier by lower precision experiments 30M events 4m π + 2 Great potential for a new accurate measurement of ππ scattering lengths from this data New preliminary result at Moriond QCD!

25. I. Mikulec: Search for direct CP-violation in K± by NA4825 Conclusions  Preliminary NA48/2 result (2003 data) on direct CP−violating charge asymmetry in K ±   ±  +  – decays is A g = (0.5 ± 2.4 stat. ± 2.1 stat.(trig.) ± 2.1 syst. )×10 -4  >10 times better precision than previous measurements  Further room to decrease systematic uncertainties  2004 data contain another 2×10 9 K ±   ±  +  – events, with higher quality  Neutral mode asymmetry: complementary, comparable sensitivity  Design goal is within reach in both decay modes  Other interesting results will follow (  scattering lengths, other CP asymmetries, rare decays)

26. I. Mikulec: Search for direct CP-violation in K± by NA4826 Spare slides

27. I. Mikulec: Search for direct CP-violation in K± by NA4827 Theoretical predictions of A g Standard Model L.Maiani, N.Paver ’95(2.3±0.6)x10 -6 A. Bel’kov ’95<4x10 -4 G.D’Ambrosio, G.Isidori ’98<10 -5 E.Shabalin ’01<3x10 -5 E.Gamiz, J.Prades, I.Scimemi ’03(-2.4±1.2)x10 -5 E.Shabalin ’05 (La Thuile’05) <8x10 -5 SUSY G.D’Ambrosio, G.Isidori, G.Martinelli ~10 -4 New physics E.Shabalin ’98 [Weinberg model of extended Higgs doublet] ~4x10 -4 I.Scimemi ’04>3x10 -5

28. I. Mikulec: Search for direct CP-violation in K± by NA4828 Experimental results so far ”Charged” mode K ±  3 π ± : ”Charged” mode K ±  3 π ± : Ford et al. (1970) at BNL: A g =(-7.0±5.3)∙10 -3 ; Statistics: 3.2M K ± ; HyperCP prelim. (2000) at FNAL: A g =(2.2±1.5±3.7)∙10 -3 ; Statistics: 41.8M K +, 12.4M K  ; Systematics due to knowledge of magnetic fields; Systematics due to knowledge of magnetic fields; Published as PhD thesis W.-S.Choong LBNL-47014 Berkeley 2000; Published as PhD thesis W.-S.Choong LBNL-47014 Berkeley 2000; ”Neutral” mode K ±  π ± π 0 π 0 : ”Neutral” mode K ±  π ± π 0 π 0 : Smith et al. (1975) at CERN-PS: A g 0 =(1.9±12.3)∙10 -3 ; Statistics: 28000 K ± ; TNF (2004) at IHEP Protvino: A g 0 =(0.2±1.9)∙10 -3 ; Statistics: 0.52M K ±.

29. I. Mikulec: Search for direct CP-violation in K± by NA4829 NA48 detector Main detector components: Magnetic spectrometer (4 DCHs): redundancy  high efficiency; Δp/p = 1.0% + 0.044%*p [GeV/c] Δp/p = 1.0% + 0.044%*p [GeV/c] Hodoscope fast trigger; precise time measurement (150ps). precise time measurement (150ps). Liquid Krypton EM calorimeter (LKr) High granularity, quasi-homogenious; ΔE/E = 3.2%/√E + 9%/E + 0.42% [GeV]. ΔE/E = 3.2%/√E + 9%/E + 0.42% [GeV]. Hadron calorimeter, muon veto counters, photon vetoes. Beam pipe

30. I. Mikulec: Search for direct CP-violation in K± by NA4830 KAon Beam Spectrometer (KABES) 3 MICROMEGA gas chamber stations measure beam particle charge (prob. mis-ID~10 -2 ); momentum (  p/p=0.7%); position in the 2nd achromat (  x,y  100  m). Not used yet for K ±  3  ± analysis Measurement of kaon momentum: Reconstruct K 3 π with a lost pion; Redundancy in K 3 π analysis; Resolve K e4 reconstruction ambiguity.

31. I. Mikulec: Search for direct CP-violation in K± by NA4831 Break down of K ±  ±  +  - statistics DatesSub- samples Achromat A+Achromat A– K+K+K+K+ KK–KK– K+K+K+K+ KK–KK– 022.06-25.0726229.6125.9201.0114.0 16.08-20.0812122.568.1135.175.4 220.08-3.0912147.281.8105.558.9 33.09-7.09440.622.654.530.4 Total54Total events selected1613.2 Statistics selected for A g measurement, events x10 6

32. I. Mikulec: Search for direct CP-violation in K± by NA4832 Cancellation of beam spectra Achromat reversal reverses K + and K – beam spectra Systematic differences of K + and K – acceptance due to beam spectra mostly cancel in R U *R D Supersample 1 Supersample 2 SS 3 Systematic check: Reweighting K + events so as to equalise momentum spectra leads to negligible effect  Δg=0.03x10 -4 K+K+K+K+ K–K–K–K–

33. I. Mikulec: Search for direct CP-violation in K± by NA4833 Fits to the “cusp” effect in K ±  ±  0  0 M(  0  0 ), GeV/c 2 Standard Dalitz-plot parametrization  2 = 133/139 for M(  0  0 )>80 MeV/c 2 One-loop exchange:  2 = 463/149 One and two loops:  2 = 159/147 Incl.  +   atoms:  2 = 144/146 M(  0  0 ), GeV/c 2 Cabibbo: PRL 93 (2004) 121801 Cabibbo, Isidori: hep-ph/0502130