Summary on CP Violation with Kaons

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Summary on CP Violation with Kaons Patrizia Cenci

Interaction and Neutrinos Delphi, June 7th 2005 On

Chicago, Dubna, Edinburgh, Ferrara, Firenze,

1 Summary on CP Violation with Kaons Patrizia Cenci INFN Sezione di Perugia XX Workshop on Weak Interaction and Neutrinos Delphi, June 7th 2005 On behalf of the NA48 Collaboration Cambridge, CERN, Chicago, Dubna, Edinburgh, Ferrara, Firenze, Mainz, Northwestern, Perugia, Pisa, Saclay, Siegen, Torino, Vienna

2 Overview Introduction CP Violation with Kaons Experiments: KLOE, KTeV, NA48 Results: Direct CP Violation with neutral Kaons Charge Asymmetry in K 0 e3 K S 3π 0 Direct CP Violation in K ± 3π decays K S,L π 0 l + l - Prospects and conclusions

3 Introduction Why Kaons crucial for the present definition of Standard Model search for explicit violation of SM: key element to understand flavour structure of physics beyond SM Motivation for Kaons experiments Test of fundamental symmetries CP Violation: charge asymmetry, T violating observables CPT test: tigher contraints from Bell-Steinberger rule, K S /K L semileptonic decays Sharpen theoretical tools Study low energy hadron dynamics: χpt tests and parameter determination, form factors Probe flavour structure of Standard Model and search for explicit violation (e.g. Lepton Flavour Violation) Rare decays suppressed (FCNC: 2nd order weak interactions) or not allowed by SM Sensitivity to physics BSM

4 CP Violation with Kaons CP Violation: a window to physics beyond SM Brief History of CP Violation 1964: CP violation in K 0 (Cronin, Christenson, Fitch, Turlay) : Direct CP violation in K 0 (NA31, NA48, KTeV) 2001: CP violation in B 0 decay with oscillation (Babar, Belle) 2004: Direct CP violation in B 0 (Belle, Babar) CP Violation in Kaon decays can occur either in K 0 -K 0 mixing or in the decay amplitudes Only Direct CP Violation occurs in K ± decays (no mixing) Complementary observables to measure Direct CP Violation in Kaons: ε /ε, rare decays, A g

Experiments with Kaons CERN NA48 1997-2001 K L,K S NA48/1 2000,2002 K S NA48/2 2003-2004 K ±

5 Experiments with Kaons CERN NA K L,K S NA48/1 2000,2002 K S NA48/ K ± Active Experiments Fermilab KTeV: 1997,1999 K L,K S Frascati - DaФne KLOE > 2000 K S,K L,K ±

FNAL - KTeV Experiment Parallel K beams: 2 proton lines (~ 10 12 ppp) K from K S L on Regenerator (scintillator plates), K S identification via x-y position switches beam line once per cycle π + π -

6 FNAL - KTeV Experiment Parallel K beams: 2 proton lines (~ ppp) K from K S L on Regenerator (scintillator plates), K S identification via x-y position switches beam line once per cycle π + π - : Magnetic Spectrometer σ(p)/p 0.17% p[gev/c]% π 0 π 0 : CsI calorimeter σ(e)/e 2.0%/ E 0.45% σ + π - M (π 0 π 0 ) ~ σ M (π+π-)) ~ 1.5 MeV Photon veto and muon veto Experimental Program KTeV: 1997,1999 K L,K S

044% x p [GeV/c[ GeV/c] π 0 π 0 :LKr Calorimeter E/E = 3.2%/ E 9%/E 0.

7 CERN - NA48 Experiment Simultaneous K beams: split same proton beam (~10 12 ppp) convergent K L -K S beams K S from protons on near target K S identification via proton tagging π + π - : Magnetic Spectrometer p/p = 1.0% 0.044% x p [GeV/c[ GeV/c] π 0 π 0 :LKr Calorimeter E/E = 3.2%/ E 9%/E 0.42% [GeV[ GeV] σ M (π 0 π 0 ) ~ σ M (π+π-)) ~ 2.5 MeV Photon and muon veto Beam pipe Experimental Program NA K L,K S NA48/1 2000,2002 K S NA48/ K ±

LNF DaФne: the Ф Factory Ф Factory: e + e - collider@ s =1019.4 MeV = M Ф Ф Decays: BR(Ф K L K S )=34.3%; BR(Ф K + K - )=49.

1/pb New KLOE run in progress L peak = 1.

8 LNF DaФne: the Ф Factory Ф Factory: e + e - collider@ s = MeV = M Ф Ф Decays: BR(Ф K L K S )=34.3%; BR(Ф K + K - )=49.31% tagged K decays from Ф KK pure K beams clean investigation of K decays and precision measurements KLOE data taking: /pb New KLOE run in progress L peak = cm -2 s -1 May 2005 Goal: collect 2 fb -1 by end 2005 May Integrated 2005Luminosity φ decays φ decays (Recent results from KLOE: S. Dell Agnello LNF SC Open Meeting, may 05 and M. Martini Krare Workshop@LNF, may 05)

9 LNF: the KLOE detector EM Calorimeter: Lead and scintillating fibres Drift Chamber: Stereo geometry

10 The recent past

Direct CP Violation: experimental results on ε /ε Direct CPV established in K 0 ππ by NA48 and KTeV more results expected (KTeV, KLOE) no third generation experiments Result (roughly) compatible with

11 Direct CP Violation: experimental results on ε /ε Direct CPV established in K 0 ππ by NA48 and KTeV more results expected (KTeV, KLOE) no third generation experiments Result (roughly) compatible with SM Exclude alternative to CKM mechanism (superweak models and approximate-cp) Despite huge efforts, ε /ε not yet computed reliably due to large hadronic uncertainties Improvement of the calculation expected with lattice New physics may contribute as a correction to SM predictions (16.7 ± 2.6) 10-4 Final Result ( ) Half Statistics ( ( ) Re(ε /ε)

12 K 0 Charge e3 Asymmetry Charge Asymmetry in K 0 e3 is due to K 0 -K 0 mixing (Indirect CPV) Limits on CPT and S= Q Il CPT is conserved and S= Q: + + Γ( K L e π ν ) Γ( K L e π ν ) δ L ( e) = 2 Re(ε) Γ + + ( K e π ν ) + Γ ( K e π ν ) L Results in NA48 (~2x10 8 K e3 ) and KTeV (~3x10 8 K e3 ) L KTeV (2002): δ L (e) = (3.322 ± stat ± syst ) x 10-3 NA48 (2003): δ L (e)=(3.309 ± stat ± syst ) x 10-3 δ χ 2 /n.d.f=0.90 (n.d.f.=9) P π (GeV/c) PDG2004: δ L (e) = (3.27 ± 0.12) x 10-3

13 The present

14 Semileptonic K S decays KLOE: first measurement (2002), update in progress Method: K S tagged by opposite K L (Ф KK) Identify πe pairsusingtof Event counting by fitting the [E(πe)-P] distribution (test for ν) Independent measurement of the two charge modes Selected ~10 4 signal events per charge in the data (0.5 fb -1 ) New preliminary result: Data MCsig + bkg BR(K S πeν) = (7.09 ± 0.07 stat ± 0.08 syst ) E miss P miss (MeV) CPT Test: new measurement of the charge asymmetry in K S : (δ L (e) = 3.32 ± 0.07) 10-3 ) δ S (e)= (-2 ± 9 ± 6) 10-3

15 CP Violation in K S π 0 π 0 π 0 K S 3π 0 is CP violating [ CP(K S ) = +1, CP(3π 0 ) =- 1] Allowed by SM, but never observed According to SM: 2 τ S BR ( K S 3π ) ε BR ( K L 3π ) = τ L Last limit from direct search: BR(K S 3π 0 ) < 1.4x10-5 (SND, 1999) Can be parametrized with the amplitude ratio η 000 η ( S π ) ( L π ) A K ( S π ) ( L π ) 3 BR K τ L 000 = = 0 0 A K 3 τ S BR K 3 η 000 = If CPT is conserved: Re(η 000 ): CPV in mixing Im(η 000 ): direct CPV The uncertainty on K S 3π 0 amplitude limits the precision on CPT test (Bell-Steinberger relation) * ( + i φ )( Reε ii mδ ) = A ( K f) A( K f) 1 tan SW S L CP CPT f

16 KLOE search for K S π 0 π 0 π 0 Direct search, new result Rarest decay studied by KLOE so far Data sample: 0.5 fb - 1 ( run) 37.8 x 10 6 (K L -crash tag + K S 2π 0 ) Require 6 prompt photons large background ~40K events Kinematic fit, 2π2 0, 3π 0 estimators (ζ( 2, ζ 3 ) After all analysis cuts (ε( 3π = 24.4%) 2 candidate events found expected background: 3.13 ± 0.82 ± 0.37 BR(K S 3π 0 ) 1.2 x CL Best limit Submitted to Phys. Lett. hep-ex/ Prospects with 2 fb -1 : if background ~ negligible level UL will improve by factor ~ 10 (down to few 10-8 )

17 NA48/1: K S π 0 π 0 π 0 and η000 Measurement in NA48 Sensitivity to η 000 from K S -K L interference superimposed on a huge flat K L π 0 π 0 π 0 component Aim: O(1%) error on Re(η 000 ) and Im(η 000 ) Method: measure K S -K L interference near the production target use 3π 0 events from near-target run for η000 normalize to K L 3π 0 from far-target run use MC to correct for residuals acceptance difference and Dalitz decays Time evolution of K L,S 3π 0 :

NA48/1 results on K S π 0 π 0 π 0 Data samples (run 2000): Near-target run: 4.

18 NA48/1 results on K S π 0 π 0 π 0 Data samples (run 2000): Near-target run: K L,S 3π 0 data K L 3π 0 MC Far-target (K L ) run: K L 3π 0 data K L 3π 0 MC Fit method: fit double ratio Final Results (PL B ) : Re(η 000 ) = ± stat. ±0.015 syst Im(η 000 ) = ± stat. ±0.017 syst η < % CL Br(K S 3π 0 ) < % CL If Re(η 000 ) = Re(ε) ) = (CPT): Im(η 000 ) CPT = ± stat. ±0.017 syst η CPT < % CL Br(K S 3π 0 ) CPT < % CL Ratio of near-target and far-target data corrected for acceptance (3 Energy intervals)

19 Direct CP Violation in K ± 3π π 1even K ± π 2even π 3odd K ± 3π matrix element M(u,v) 2 ~ 1 + gu + hu 2 + kv 2 BR(K ± π ± π + π )=5.57% BR(K ± π ± π 0 π 0 )=1.73% Dalitz variables u = v = s s 3 s 0 2 m π s m π s i = (PK p πi) 1 s0 = s 3 i i=3 is the odd pion 2 i=1,2,3 K π + π - π ± : g = K π 0 π 0 π ± : g = h, k << g K π + π - π ± K + -K - asymmetry in g A g g = g g g Direct CP violation if A g 0 NA48/2: search for Direct CPV by comparing the linear slopes g ± for K ±

20 A g Experimental and theoretical status Experimental results 10-2 Ford et al. (1970) HyperCP prelim. (2000) TNF prelim. (2002) - neutral mode charged NA48/2 proposal neutral SM estimates of A g vary within an order of magnitude (few 10-6 to 8x10-5 ). Models beyond SM predict substantial enhancements partially within the reach of NA48/2. (theoretical analyses are by far not exhaustive by now) Theory SM SUSY physics New CPV asymmetry in decay width is much smaller than in Dalitz-plot slopes A g (SM: ~ )

21 NA48/2 goal and method Primary NA48/2 goal: 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 mode and > 10 8 in neutral mode in charged 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

P K spectra, 60±3 GeV/c 54 60 66 NA48/2 experimental set-up magnet ~7 10 11 ppp 1cm K + K Front-end Achromat Split +/- Select momentum Recombine +/- K + K Second Achromat Cleaning Beam spectrometer

22 P K spectra, 60±3 GeV/c NA48/2 experimental set-up magnet ~ ppp 1cm K + K Front-end Achromat Split +/- Select momentum Recombine +/- K + K Second Achromat Cleaning Beam spectrometer Quadrupole quadruplet Focusing µ swapping focusing beams /- beams overlap within ~1mm all along 114m decay volume vacuum tank He tank + spectrometer beam pipe not to scale BM m z 10 cm

23 NA48/2 Data Taking Data taking finished 2003 run: ~ 50 days 2004 run: ~ 60 days Total statistics in 2 years: K ± π π + π ± : ~ 4x10 9 K ± π 0 π 0 π ± : ~ 2x10 8 ~ 200 TB of data recorded This presentation: first result based on 2003 K ± π ± π π + sample

24 K ± statistics 3π Data taking x10 9 K ± π ± π π + events Events σ M =1.7 MeV/c 2 V even pion in beam pipe π µν odd pion in beam pipe Invariant πππ mass Accepted statistics K + : 1.03 x10 9 events K : 0.58 x10 9 events U K + /K 1.8

25 A g measurement strategy - 1 Use only the slopes of ratios of normalized u-distribution Build u-distributions of K + and K - events: N + (u), N - (u) Make a ratio of these distributions: R(u) Fit a linear function to this ratio: normalised slope g + R( N ( u ) u ) = = R R( 1 + gu ) g A g = 2 g N ( u) + 1+ g u 1+ g u e.g. uncertainty δag < corresponds to δ g < Compensate unavoidable detector asymmetry inverting periodically the polarity of the relevant magnets: Every day: magnetic field B in the spectrometer (up/down: B+/B-) Every week: magnetic field A of the achromat (up/down: A+/A-)

26 A g measurement strategy - 2 Four ratios are used to cancel acceptances: R R R R US UJ DS DJ = = = = N( A+ B+ K+ ) N( A + B K ) N( A+ B K+ ) N( A+ B+ K ) N( A B+ K+ ) N( A B K ) N( A B K + ) N( A B+ K ) Achromat beam line: K + Up beam line: K + Down Supersample data taking strategy: Y B X B+ Jura (left) Saleve (right) beam line polarity (U/D) direction of kaon deviation in the spectrometer (S/J) achromat polarity (A) was reversed on weekly basis spectrometer magnet polarity (B) was reversed on daily basis Spectrometer field 1 Supersample ~ 2 weeks 2003 data: 4 Supersamples Z

27 A g measurement strategy - 3 Quadruple ratio is used for further cancellation: R = R US R UJ R DS R DJ ~ g u Cancellation of systematic biases: 1) Beam rate effects: global time-variable biases (K + and K - simultaneously recorded) 2) Beam geometry difference effects: beam line biases (K + beam up / K - beam up etc) 3) Detector asymmetries effects (K + and K - illuminating the same detector region) Acceptance is defined respecting azimuthal symmetry: 4) Effects of permanent stray fields (earth, vacuum tank magnetisation) cancels The result is sensitive only to time variation of asymmetries in experimental conditions (beam+detector) with a characteristic time smaller than the corresponding field-alternation period (e.g. the supersample time scale: beam-week, detector-day)

28 Beam systematics Time variations of beam geometry ¾ Acceptance largely defined by central beam hole edge (R~10 cm) ¾ Acceptance cut defined by a (larger) virtual pipe - centered on Y, cm averaged beam positions - as a function of charge, time and K momentum Sample beam profile at DCH1 Beam movements: ~ 2 mm 5mm 2 mm Beam widths: ~ 5 mm X, cm

29 Spectrometer systematics Time variations of spectrometer geometry ¾ DCH drifts by O(100µm) in a 3 month run: asymmetry in p measurement ¾ alignment is fine tuned by forcing the average value of the reconstructed invariant 3π masses to be equal for K+ and K- M Mπππ πππ Maximum equivalent horizontal shift: or or Momentum scale ¾ due to variations of the magnet current (10-3) ¾ sensitivity to a 10 3 error on field integral: M 100 kev ¾ mostly cancels due to simultaneous beams ¾ in addition, it is adjusted by forcing the average value of reconstructed invariant 3π masses to the PDG value of MK+

30 Trigger systematics Measure inefficiencies using control data from low bias triggers Assume rate-dependent trigger inefficiencies symmetric L1 trigger (2 hodoscope hits) stable and small inefficiency ( ): no correction L2 trigger (online vertex reconstruction): time-varying inefficienciy ( 0.2% to 1.8%) flat in u within measurement precision: u-dependent correction applied L2 inefficiency 3x10-3 cut cut

31 Fit linearity: 4 Supersamples SS0: g=(0.6±2.4)x10-4 χ 2 =39.7/38 SS2: g=( g=(-3.1±2.5)x10-4 χ 2 =29.5/38 SS1: g=(2.3±2.2)x102.2)x10-4 U χ 2 =38.1/38 SS3: g=( g=(-2.9±3.9)x10-4 U χ 2 =32.9/38 U U

32 Systematics summary and results Combined result in g x 10 4 units (3 independent analyses) SS0 SS1 Raw 0.0± ±2.0 Corrected for L2 eff 0.5± ±2.2 Conservative estimation of systematic uncertainties Acceptance and beam geometry Spectrometer alignment Analyzing magnet field π ± µν decay U calculation and fitting Effect on gx SS2-2.8± ±2.5 Pile-up 0.3 SS3 Total 2.0± ± ± ±1.3 Systematic errors of statistical nature Trigger efficiency: L2 0.8 χ 2 2.2/3 3.2/3 Trigger efficiency: L1 0.4 L2 trigger correction included Total systematic error 1.3

33 Stability of the result g =(-0.2±1.0 stat. ±0.9 stat.(trig.) ±0.9 syst. )x10-4 g =(-0.2 ± 1.7) x 10-4 g Quadruple ratio with K(+)/K(-) g K(right)/K(left) K(up)/K(down) E K (GeV) g 4 supersamples give consistent results control of detector asymmetry control of beam line asymmetry MC reproduces these apparatus asymmetries z vertex (cm)

34 Preliminary result on A g 10-2 A g A g = (0.5±2.4 stat. ±2.1 stat.(trig.) ±2.1 syst. )x10-4 A g = (0.5±3.8) x 10-4 Smith et al. (1975) ( N ) SM Ford et al. (1970) ( C ) HyperCP prelim. (2000) ( C ) TNF (2004) ( N ) C N SUSY NA48/2 New physics NA48/ data This is a preliminary result, with conservative estimate of the systematic errors The extrapolated statistical error is δa g = data: expected smaller systematic effects (more frequent polarity inversion, better beam steering)

2 10-4 Extrapolation to 2003 + 2004 data: δa g = 1.

35 Neutral mode asymmetry K ± π ± π 0 π 0 Statistics analyzed: 28 x 10 6 events (1 month of 2003) Statistical error with analyzed data: δa g = Extrapolation to data: δa g = Similar statistical precision as in charged mode Possibly larger systematics errors Dalitz-plot σ M =1.1 MeV/c 2 g fit for SS1 χ 2 =45.3/50 δ =4.8x10-4 M(3π), GeV/c 2 u

36 A glance to the future

Search for K S π 0 e + e Motivation: determination of the indirect CP violating amplitude of the decay K L π 0 e + e K L π 0 e + e BR(SM)=3-10x10-12, BR(γγe + e ) 6 10 7 3 contribution to this decay

37 Search for K S π 0 e + e Motivation: determination of the indirect CP violating amplitude of the decay K L π 0 e + e K L π 0 e + e BR(SM)=3-10x10-12, BR(γγe + e ) contribution to this decay (χpt): A 1 (CPC): not predicted, derived from K L π 0 γγ (K 2 π 0 γ*γ* π 0 e + e, NA48, KTeV) A 2 (CPV Ind ): not predicted, measured by K S π 0 e + e - (NA48/1) A 3 (CPV Dir ): predicted in terms of CKM phase (electroweak penguins and W boxes with top) A + A BR 10 = 15.3( a ) s 4 4 { 10 )} 2.8{ 10 } 6.8 ( a ) Im( λ + I m( λ) s t t Indirect CPV e + e - 2 KTeV limits (90%CL) BR(π 0 ee) < 2.8x10-10 BR(π 0 µµ) < 3.8x10-10

38 NA48/1: K 0 S π0 l + l Main motivation for the NA48/1 proposal K S π 0 ee K S π 0 µµ 7 events, bkg events, bkg First measurement BR(π 0 ee) = (stat) ± 0.8(syst) 10-9 a s = (stat) ± 0.07 (syst) PLB 576 (2003) First measurement BR(π 0 µµ) = (stat) ± 0.2(syst) 10-9 a s = (stat) ± 0.05 (syst) PLB 599 (2004)

39 B B K K 0 0 L SM prediction for K 0 L π0 l + l From K L measurement: small CPC contribution From K S measurement: indirect CPV contribution dominates Sensitivity of BR to CKM phase depends on the (unmeasurable( unmeasurable) relative sign of the two CPV terms L π e e Constructive + π µ µ = = B B K K L π e e 0 0 L + π µ µ Destructive = = ( ) Br(K πµ µ ) 10 L Isidori et al. EPJC36 (2004) ( ) Br( Κ π e e ) 10 L Theory: constructive interference favored * Sensitivity to new physics: enhanced electroweak penguins would enhance the BR J. Buras et al. hep-ph/ NP B697 (2004) B B NP K L π e e NP K π µ µ L = = * Two indeopendent analysis: G. Buchalla, G. D Ambrosio, G. Isidori, Nucl.Phys.B672,387 (2003) - S. Friot, D. Greynat, E. de Rafael, hep-ph/ , PL B 595

40 Prospects and conclusions Kaon was central in the definition of SM Quantitative tests of CKM mechanism and search for new physics beyond SM are possible with rare Kaon decay mesurements High level of precision is attainable Constraints to CKM variables and further test of CPV from FCNC processes ( golden decays ): K L π 0 e + e decays K π νν decays see M. Gorbahn and M. Diwan talks, this conference

Results on direct CP Violation in K ± 3π decays from the NA48/2 experiment at CERN

Crimea 2005 Giuseppina Anzivino 1 Results on direct CP Violation in K ± 3π decays from the NA48/2 experiment at CERN Giuseppina Anzivino University of Perugia and INFN On behalf of the NA48/2 collaboration: