Recent CP violation measurements at CERN-NA48 experiment For the NA48 and NA48/2 collaborations: Cagliari, Cambridge, CERN, Chicago, Dubna, Edinburgh, Ferrara, Firenze, Mainz, Northwestern, Orsay, Perugia, Pisa, Saclay, Siegen, Torino, Vienna, Warsaw Cristina Biino INFN, Torino ICHEP 2008 Philadelphia, Jul.29-Aug.5, 2008

ICHEP08Cristina Biino 2 A brief history of NA K  e2 /K   2 run NA62 NA48 ( ) : Direct CP-Violation in neutral K Re(ε’/ε) = (14.7 ± 2.2)·10 -4 NA48/1 (2002) : Rare K S decays and hyperons NA48/2 ( ) : Direct CP-Violation in charged K NA62 ( ) and P326 (2008…): R (K e2 /K  2 ), and proposal K +   + KTeV (2008) 19.2 ± 2.1  10 -4

ICHEP08Cristina Biino 3 NA48 detector 1 m Decay products From K decays Magnetic spectrometer 4 high-resolution DCHs Scintillator hodoscope 150 ps time resolution - fast trigger LKr electromagnetic calorimeter Quasi-homogeneous, high granularity, excellent e/  discrimination Hadron calorimeter,  veto counters,  vetos  p /p = (1.0  p)% (p in GeV/c)  E /E = (3.2/√E  9.0/E  0.42)% (E in GeV/)

ICHEP08Cristina Biino 4 CP violation in K 0 decays: Measurement of |    | with K L →     decays

ICHEP08Cristina Biino 5 The CP violation parameter |    |    =  +  ’ = A(K L   +  – ) A(K S   +  – )    is a fundamental observable of CP violation Indirect CPVDirect CPV Experimental method:  Measure precisely the ratio R = BR(K L   +  – ) / BR(K L   e ).  Extract |    | computed as:    = using the best single K S and K L lifetimes measurements and normalisation BR(K L   e ) and BR(K S   +  – ) from KLOE, KTeV and NA48. BR(K L   +  – ) BR(K S   +  – ) KSKS KLKL K L ~ K 2 +  K 1 CP = +1 CP =  1 CP(  +  – ) = + 1 K S ~ K 1 +  K 2

ICHEP08Cristina Biino 6 |    |: event selection K L →      CP-violating process  need to suppress dominant background channels (K e3, K  3, K 3  ) by 4-5 orders of magnitude  small background achieved: 0.5%  data well described by MC  about 47k events selected  selection based on electron identification in the LKr calorimeter ( E/p ≈ 1)  about 5 x 10 6 K e3 events selected with 0.5% background K L   e Dedicated 2-day run with a pure, low intensity K L beam: ~80 x tracks events recorded.

ICHEP08Cristina Biino 7 Results on |    | Uncertainty sourceCorrectionUncertainty Particle ID+1.34%0.05% K 2  background–0.49%0.03% Muon ID+0.48%0.18% Trigger–1.29%0.11% Energy spectrum0.20% Radiative corrections 0.10% MC statistics0.10% Total+0.04%0.33% Experimental value: R = BR(K L   +  – ) / BR(K L   e ) = (4.835  stat.  syst. )  10 –3 BR(K L  +  – )=(1.941  0.019)  10 –3 Published in Phys. Lett. B645 (2007) 26 Radiative corrections: -  +  –  Inner Bremsstrahlung (IB) component included - direct emission (DE) component subtracted (CP conserving) Corrections and systematics on R CP violation parameter: = (2.223  0.012)  10 –3 BR(K L  +  – ) BR(K S  +  – ) |  +- | = KLKL KSKS

ICHEP08Cristina Biino |    |: comparison of results The NA48 result is in very good agreement with KTeV and KLOE experiments These new measurements contradict the PDG’ 04 value ! BR(K L  +  – ) / BR(K L  e ) [10 –3 ] |  +– | [10 –3 ]

ICHEP08Cristina Biino 9 Search for direct CP violation: Measurement of the A g and A g 0 asymmetries in K         and K      0  0 decays

ICHEP08Cristina Biino 10 CP Violation in K ±  3  decays |M(u,v)| 2  1 + gu + hu 2 + kv 2 + … Dalitz plot for K ±  3  Only direct CP violation is involved in charged kaon decays! Matrix element: Asymmetry parameter: K ±        : g =  K ±        : g =  If A g  0  Direct CP Violation  2even  1even  3odd K±K± SM predictions: |A g | : If A g ~  New Physics ! u = 2m K (m K /3-E 3 * )/m  2 v = 2m K (E 1 * -E 2 * )/m  2 |h|, |k| << |g| If CP invariance holds: g K + = g K -

ICHEP08Cristina Biino 11 The NA48/2 approach NA48/2 method: - Use of intense simultaneous K + and K - beams, superimposed in space, with narrow P K spectra - Equalization of averaged K + and K - acceptances by frequent alternations of magnet polarities (magnetic spectrometer, K  beam lines) - Measurement of asymmetry from slopes of normalized u-distribution ratios (no MC acceptance correction required! ) : R(u) = N + (u) / N - (u)  n ( 1+  g u) A g =  g / 2g Induced instrumental asymmetry can only be due to charge-asymmetric and u- dependent effects that vary with time (-70  53)  BNL AGS (1970) A g = ( 22  40)  HyperCP (2000)prelim. { (19  125)  CERN PS (1975) A g 0 = (2  19)  Protvino IHEP(2005) { NA48/2 main goal: Measure linear slope (g) asymmetries for K         and K         decays with accuracies  A g  2.2  and  A g 0  3.5  respectively.  significant improvement w.r.t. present measurements Statistics required >2  10 9 events in “charged” mode and >10 8 in “neutral” mode

Selection of K         events U |V| even pion in beam pipe 2.00x10 9 K + events 1.11x10 9 K – events K + /K – ≈ 1.8  odd pion in beam pipe Invariant  mass Based only on Hodoscope and Magnetic Spectrometer Negligible    background  m = 1.7 MeV/c 2 Events  3-tracks vertex in decay volume  Acceptance limited mostly by beam pipe through DCHs K±K±

ICHEP08Cristina Biino 13 Acceptance equalization for K+ and K- Fit of R(u) is sensitive to the time variation of asymmetries in experimental conditions with characteristic time smaller than corresponding field alternation periods (beam  week, detector  day (2003), 3 hours(2004 )  data taken in 9 SUPER-SAMPLES of ~2 weeks each Cancellation of systematic biases: - Detector L-R asymmetries ( K +  Salève / K -  Salève and K +  Jura / K -  Jura ) - Beam line biases ( K + beam Up / K - beam Up and K + beam Down / K - beam Down) - Global time-variable biases (K + and K - simultaneously recorded) Z XY Achromats: K + Up Achromats: K + Down B+ B-B-B-B- Detector Left-Right asymmetry cancellation in the four K + /K ­ ratios: Jura Jura(Left) Salève(Right) Quadruple ratio: R(u) = R US (u)·R UJ (u)·R DS (u)·R DJ (u) ~ n· (1 + 4 Δg u) ♦♦♦♦♦♦♦♦

ICHEP08Cristina Biino 14 K ± →  ±     : A g final result Δg = (0.6 ± 0.7 stat. ± 0.4 stat. (trig.) ± 0.5 syst. )  K + /K - Result compatible with SM predictions No evidence for New Physics Published in Eur. Phys. J. C 52, 875 (2007) ΔgΔg  9 super-samples give consistent results  Detector and beam line asymmetry effects at level, reproduced by MC A g = (-1.5 ± 2.1)  A factor ~ 20 better precision than previous experiments Systematic effects on Δg  Δg (10 -4 ) Spectrometer alignment± 0.1 Spectrometer magnetic field ± 0.3 Beam geometry and stray magnetic fields ± 0.2 Resolution and fitting± 0.2 Accidental activity (pile-up) ± 0.2 Total systematics± 0.5 L1 trigger efficiency± 0.3 L2 trigger efficiency -0.1 ± 0.3 Time stability of result:

ICHEP08Cristina Biino 15 Selection of K      0  0 events  Consider two  0 →   decays which define K ± decay vertex position - no geometrical information from the  ± track to avoid charge-asymmetric biases - kaon momentum and invariant 3  cuts  Computation of u variable from the  0  0 invariant mass only:  charge-symmetric procedure Based on Charged Spectrometer and LKr Electromagnetic Calorimeter  m = 0.9 MeV/c 2 |v| Odd pion in beam pipe    and wrong photon pairings M(  0 ) 2  E i E k (D ik ) 2 /(Z ik )  10 7 events K±K± u Events M(3  ) [GeV/c 2 ]

ICHEP08Cristina Biino 16 K ± →  ±  0  0 : A g 0 final result Statistical precision in A g 0 similar to K ± →  ±     mode despite 34 times less events: |g 0 / g ± | ~ 3. A g 0 = (1.8 ± 1.8) x Systematic effects on Δg  Δg (10 -4 ) Overlap of LKr showers± 0.5 L1 HOD trigger efficiency± 0.1 L1 LKr trigger efficiency± 0.1 L2 trigger efficiency± 0.3 Stray magnetic fields± 0.1 Accidental activity(pile-up)± 0.2 Total± 0.6 Final result consistent with SM predictions: Published in Eur. Phys. J. C 52, 875 (2007) Δg = (2.2 ± 2.1 stat. ± 0.6 syst. )  Time stability of result: K + /K - ΔgΔg  7 super-samples give consistent results  Detector and beam line asymmetry effects at level,reproduced by MC

ICHEP08Cristina Biino 17 |V us | Measurement from K ± l3

ICHEP08Cristina Biino 18 |V us | Measurement from K ± l3 K ± collected during a special low intensity minimum bias run Measurement of leptonic and semileptonic decays. Method of Measurement: Normalize Ke3 and K  3 to K2  very similar topologies and selection criteria Select one track and two photons, consistent with a  0, from a common decay vertex Distinction of Kl3 and K2  mainly through kinematics Particle identification for electrons (  ~ 98.6%), pions (  ~ 99.5%) and muons (  ~ 99.8%)

ICHEP08Cristina Biino 19 |V us | Measurement from K ± l3 Channel Acc x P-Id K + (K - ) Ke3: 56k (31k) Kμ3: 49k (28k) π ± π 0 462k (257k) Acceptance x Particle ID K + (K - ) 6.98 ± 0.01 % (6.94 ± 0.01)% 9.27 ± 0.01 % (9.25 ± 0.01)% ± 0.01 % (14.12 ± 0.01)% Background < 0.1% ~ 0.2% ~ 0.3%

ICHEP08Cristina Biino 20 |V us | Measurement from K ± l3 R Ke3/K2  =  stat  sys R K  3/K2  =  stat  sys Quadratic expansion for f + (t) ( ’ + = (163), ” + = (62)) and linear expansion for f 0 (t) ( 0 = (34) from PDG2006 Form factor variations within their errors and differences to pole model parametrization taken as systematic uncertainties Results: Sistematics: Ke3/K2  : Mainly Ke3, K2  acceptance, trigger efficiency K  3/K2  : Mainly K  3 form factors and Ke3, K2  acceptance Accuracy 0.4% Published in Eur. Phys. J. C 50, 329 (2007) & erratum Form factors : Using new KLOE measurement of BR(K 2  (  ) ) = (5)(8) BR(K ± e3 ) =  stat  sys BR(K ±  3 ) =  stat  sys

ICHEP08Cristina Biino 21 |V us | Measurement from K ± l3 K e3 : |V us | f + (0) = (43) exp (52) norm,  (61) ext = (9) K  3 : |V us | f + (0) = (46) exp (52) norm,  (66) ext = (10) Use  K  = (19) ns (average PDG2006 & Kloe 2008 ), Very good agreement between Ke3 and K  3 Test of lepton universality: Ratio(K  3 /K e3 ) =  stat  sys Most precise measurement so far and consistent with lepton universality (SM prediction = 0.661(3)) Combination of K e3 and K  3 (taking into account correlation) : | V us | f + (0) =  and finally using f + (0) =  ( RBC-UKQCD’07 ) : | V us | =  Determination of |Vus |:

ICHEP08Cristina Biino 22 Spare slides