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Summary on CP Violation with Kaons

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

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Summary on CP Violation with Kaons

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  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 K0e3 • KS → 3π0 • KS,L → π0 l+l- • Direct CP Violation in K±3π decays • 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, KS/KL 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 • Rare decays suppressed (FCNC: 2nd order weak interactions) or not allowed by SM (e.g. Lepton Flavour Violation) • 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 K0(Cronin, Christenson, Fitch, Turlay) • 1993-99:Direct CP violation in K0(NA31, NA48, KTeV) • 2001: CP violation in B0decay with oscillation(Babar, Belle) • 2004:Direct CP violation in B0(Belle, Babar) • CP Violation in Kaon decays can occur either in K0-K0 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,Ag , rare decays

  5. Experiments with Kaons CERN NA48 1997-2001 KL,KS NA48/1 2000,2002 KS NA48/2 2003-2004 K Active Experiments Fermilab KTeV: 1997,1999 KL,KS Frascati - DaФne KLOE > 2000 KS ,KL ,K

  6. FNAL - KTeV Experiment • Parallel K beams: • 2 proton lines (~ 1012 ppp) • KS fromKL on Regenerator (scintillator plates), • KS identification via x-y position • switches beam line once per cycle • +-:Magnetic Spectrometer (p)/p  0.17%  0.007 p[GeV/c]% • 00:CsI calorimeter (E)/E  2.0%/√E  0.45% M(00) ~ M(+-) ~ 1.5 MeV • Photon veto and muon veto M(00) ~ M(+-) ~ 1.5 MeV Experimental Program KTeV: 1997,1999 KL,KS

  7. CERN - NA48 Experiment • Simultaneous K beams (ε’/ε): • split same proton beam (~1012 ppp) • convergent KL-KS beams • KSfrom protons on near target • KS identification via proton tagging • +-:Magnetic Spectrometer Δp/p = 1.0% 0.044% x p [GeV/c] • 00:LKr Calorimeter • ΔE/E = 3.2%/√E  9%/E  0.42% [GeV] • Photon and muon veto Beam pipe Experimental Program NA48 1997-2001 KL,KS NA48/1 2000,2002 KS NA48/2 2003-2004 K M(00) ~ M(+-) ~ 2.5 MeV

  8. LNF DaФne: the Ф Factory May 2005 1/pb 2001 2004 2005 2002 Ф Factory:e+e- collider@s =1019.4 MeV= MФ • Ф Decays: BR(Ф→KLKS)=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: 2000-01-02-04-05 • New KLOE run in progress • Lpeak= 1.4 × 1032 cm-2s-1 • Goal: collect 2 fb-1 by end 2005 May 2005 Integrated Luminosity 920×106 f decays 550×106 f 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. Direct CP Violation: experimental results on ε’/ε • Direct CPV established in K0→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 (1997-2001) • Half Statistics ( (1996-1997) Re(/)

  11. K0e3 Charge Asymmetry • Charge Asymmetry in K0e3 is due toK0-K0 mixing (Indirect CPV) • Limits on CPT and ΔS=ΔQ • Il CPT is conserved and ΔS=ΔQ: • Results in NA48 (~2x108 Ke3) and KTeV(~3x108 Ke3)  2  Re(ε) KTeV:δL(e) = (3.322  0.058stat 0.047syst) x 10-3 NA48:δL(e)=(3.317  0.070stat 0.072syst) x 10-3 PDG2004: δL(e) = (3.27  0.12) x 10-3

  12. Semileptonic KS decays  Data — MCsig + bkg 0 -60 -40 -20 80 0 20 40 60 • Method: • KS tagged by opposite KL (Ф→KK) • Identify e pairs using TOF • Event counting by fitting the [E(e)-P] distribution (test for ν) • Independent measurement of the two charge modes • Selected ~104 signal events per charge in the 2001-02 data (0.5 fb-1) • KLOE: first measurement (2002), update in progress • New preliminary result: • CPT Test: new measurement of the charge asymmetry in KS :(δL(e) = 3.32  0.07)  10-3 ) Emiss– Pmiss(MeV) BR(KS  pen) = (7.09  0.07stat  0.08syst) 10-4 δS(e)= (-2  9  6)  10-3

  13. CP Violation in KSp0p0p0 CP CPT • KS 3p0is CP violating [ CP(KS)  +1, CP(3p0) =- 1] • Allowed by SM, but never observed • According to SM: • Last limit from direct search: BR(KS3p0) < 1.4x10-5(SND, 1999) • Can be parametrized with the amplitude ratio η000 • The uncertainty on KS  3p 0 amplitude limits the precision on CPT test (Bell-Steinberger relation) If CPT is conserved: Re(η000): CPV in mixing Im(η000): direct CPV | η000| = 

  14. KLOE search for KSp0p0p0 BR(KS) ≤ 1.2 x 10-7 @90% CL Best limit • Direct search, new result • Rarest decay studied by KLOE so far • Data sample: 0.5 fb-1 (2001-2002 run) • 37.8 x 106 (KL-crash tag + KS) • Require 6 prompt photons • large background ~40K events • Kinematic fit, 20,30 estimators (z2, z3) • After all analysis cuts (3 = 24.4%) • 2 candidate events found • expected background: 3.13 ± 0.82 ± 0.37 Submitted to Phys. Lett. hep-ex/0505012 Prospects with 2 fb-1: if background ~ negligible level UL will improve by factor~ 10 (down to few 10-8)

  15. NA48/1: KSp0p0p0and η000 • Measurement in NA48 • Sensitivity to η000 from KS-KL interference superimposed on a huge flat KL 000 component • Aim: O(1%) error on Re(η000) and Im(η000) • Method:measure KS-KL interference near the production target • use 3p0 events from near-target run for η000 • normalize to KL3p0 from far-target run • use MC to correct for residuals acceptance difference and Dalitz decays • Time evolution of KL,S 3p 0:

  16. NA48/1 results on KSp0p0p0 • Data samples (run 2000): • Near-target run: 4.9106KL,S 3p0 data 90106KL3p0 MC • Far-target (KL) run:109106KL3p0 data 90106KL3p0 MC • Fit method: fit double ratio Final Results (2004) : • Re(η000) = -0.002 ± 0.011stat. ± 0.015syst • Im(η000) = -0.003 ± 0.013stat. ± 0.017syst • |η| < 0.045 90% CL • Br(KS3p0) < 7.4  10-7 90% CL IfRe(η000) = Re(ε) = 1.66  10-3(CPT): • Im(η000)CPT = -0.000 ± 0.009stat. ± 0.017syst • |η|CPT < 0.045 90% CL • Br(KS3p0)CPT < 2.3  10-7 90% CL Ratio of near-target and far-target data corrected for acceptance (3 Energy intervals)

  17. KLOE search for KSp+p-p0 E621 (1996)4.8+2.2-1.6(stat) ± 1.1(syst)  10-7 CPLEAR (1997)2.5+1.2-1.0(stat)+0.5-0.6(syst)  10-7 PDG2004 (average)3.2 +1.2-1.0 10-7 χPT 2.4 ± 0.7  10-7 • Motivation: • Present status: • BR(CPC) ~ 3x10-7, BR(CPV) ~ 1.2x10-9 • Direct measurement of CPC part possible with ultimate 2fb-1 • Measurement tests of prediction (untested) of χPT • Data sample: 740 pb-1 • 373 pb-1 (2001/2 data) + 367 (2004 data) • Assuming BR=3x10-7: ~230 signal events produced • Prospect with 2 fb-1: • ~16events, of which~9background • ~60%statistical accuracyon BR(KS p+p-p0) • BR with accuracybelow 50% : competitive with other measurements, and the only direct search

  18. K± → 3 matrix element |M(u,v)|2 ~ 1 + gu + hu2+ kv2 Direct CP Violation in K±3 p1even BR(K±±+)=5.57% BR(K±±00)=1.73% p3odd K± p2even K π+π-π±: g = -0.2154 K π0π0π±: g = 0.652 |h|, |k| << |g| Dalitz variables K+-K- asymmetry ing • Direct CP violation if i=1,2,3 K π+π-π± i=3 is the odd pion NA48/2: search for Direct CPV by comparing the linear slopes g±forK±

  19. Experimental and theoretical status Experimental results Ford et al. (1970) SM estimates of Ag vary within an order of magnitude (few 10-6 to 8x10-5). 10-2 HyperCP prelim. (2000) |Ag| TNF prelim. (2002) -“neutral” mode 10-3 Models beyond SM predict substantial enhancements partially within the reach of NA48/2. (theoretical analyses are by far not exhaustive by now) NA48/2 proposal “neutral” 10-4 “charged” CPV asymmetry in decay width is much smaller than in Dalitz-plot slopes Ag (SM: ~10-7…10-6) 10-5 Theory 10-6 SM New physics SUSY

  20. NA48/2 goal and method • Primary NA48/2 goal: • Measure slope asymmetries in “charged” and “neutral” modes with precisions δAg < 2.2x10-4, and δAg0 < 3.5x10-4, respectively • Statistics required for this measurement: > 2x109 in “charged” mode and > 108in “neutral” mode • NA48/2 method: • Two simultaneous K+ and K– beams, superimposed in space, with narrow momentum spectra • Detect asymmetry exclusively considering slopesof ratios of normalized u distributions • Equalise K+ and K–acceptances by frequently alternating polarities of relevant magnets

  21. NA48/2 experimental set-up 54 60 66 PK spectra, 603GeV/c BM z 10 cm 200 250 m 1cm 50 100 magnet K+ K+ beam pipe focusing beams K ~71011 ppp K • Second Achromat • Cleaning • Beam spectrometer • Front-end Achromat • Split +/- • Select momentum • Recombine +/- +/- beams overlap within ~1mm all along 114m decay volume • Quadrupole quadruplet • Focusing • μ swapping vacuum tank He tank + spectrometer not to scale

  22. NA48/2 Data Taking Data taking finished 2003run: ~ 50 days 2004run: ~ 60 days Total statistics in 2 years: K +: ~ 4x109 K 00: ~ 2x108 ~ 200 TB of data recorded This presentation: first result based on 2003 K± + sample

  23. K±3 statistics Data taking 2003 1.61x109K±  +events M=1.7 MeV/c2 Events |V| even pion in beam pipe  Invariant mass odd pion in beam pipe Accepted statistics K+ : 1.03 x109 events K: 0.58 x109 events K+/K–≈ 1.8 U

  24. Ag measurement strategy - 1 • Use only the slopes of ratios of normalized u-distribution • Buildu-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 e.g. uncertainty δAg < 2.2∙10-4corresponds to δg < 0.9∙10-4 • 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-)

  25. Ag measurement strategy - 2 Four ratios are used to cancel acceptances: Spectrometer field Y X beam line: K+ Up B+ Jura (left) Achromat Z B Saleve (right) beam line: K+Down • beam line polarity (U/D) • direction of kaon deviation in the spectrometer (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

  26. Ag measurement strategy - 3 Quadruple ratio is used for further cancellation: R = RUS RUJ RDS RDJ~ 1 + 4 Dg  u • Cancellation of systematic biases: • Beam rate effects:global time-variable biases (K+ and K- simultaneously recorded) • Beam geometry difference effects: beam line biases (K+ beam up / K- beamup etc) • Detectorasymmetries effects(K+ and K- illuminating the same detector region) • Acceptance is defined respecting azimuthal symmetry: • Effects of permanent stray fields(earth, vacuum tank magnetisation) cancels The result is sensitive only to time variation of asymmetriesin 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)

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

  28. Spectrometer systematics • Time variations of spectrometer geometry • DCH drifts by O(100μm) in a 3 month run: asymmetry in p measurement • alignment is fine tuned by forcing the average value of the reconstructed invariant 3 masses to be equal for K+ and K- • Momentum scale • due to variations of the magnet current (10-3) • sensitivity to a 10−3 error on field integral: ΔM ≈ 100 keV • mostly cancels due tosimultaneous beams • in addition, it isadjustedby forcing the average value of reconstructed invariant 3 masses to the PDG value of MK+ DMppp Maximum equivalent horizontal shift: ~200m @DCH1 or ~120m @DCH2 or ~280m @DCH4

  29. 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 (≈ 0.7·10-3): 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

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

  31. Systematics summary and results Combined resultinΔg x 104 units (3 independent analyses) L2 trigger correction included

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

  33. Preliminary result on Ag Ag = (0.5±2.4stat.±2.1stat.(trig.)±2.1syst.)x10-4 Ag = (0.5±3.8) x 10-4NA48/2 - 2003 data Smith et al. (1975) (“N”) 10-2 Ford et al. (1970) (“C”) • This is a preliminary result, with conservative estimate of the systematic errors • The extrapolated statistical error 2003+04 is Ag=1.6×10-4 • 2004 data: expected smaller systematic effects (more frequent polarity inversion, better beam steering) |Ag| HyperCP prelim. (2000) (“C”) TNF (2004) (“N”) 10-3 NA48/2 N C 10-4 10-5 New physics SM SUSY 10-6

  34. Neutral mode asymmetryK±±00 • Statistics analyzed: 28 x 106 events (1 month of 2003) • Statistical error with analyzed data:Ag = 2.2 × 10-4 • Extrapolation to 2003 + 2004 data:Ag = 1.3 × 10-4 • Similar statistical precision as in “charged” mode • Possibly larger systematics errors

  35. Search for KS0e+e e+ Indirect CPV e- Motivation: determination of the indirect CP violating amplitude of the decay KL0e+e • BR(SM)=3-10x10-12, BR(e+e)≈610−7 • 3 contribution to this decay (χPT): • A1(CPC):not predicted, derived from KL0 (K20**0e+e, NA48, KTeV) • A2(CPVInd):not predicted, measured by KS →0e+e- (NA48/1) • A3(CPVDir):predicted in terms of CKM phase (electroweak penguins and W boxes with top) KL0e+e KTeV limits (90%CL) BR(p0ee) < 2.8x10-10 BR(p0mm) < 3.8x10-10

  36. NA48/1: K0S → p0l+l- Main motivation for the NA48/1 proposal KS→p0 ee KS→p0mm 6 events, bkg. 0.22+0.19-0.12 7 events, bkg. 0.15+0.10-0.04 First measurement BR(p0ee) = 5.8 +2.8-2.3(stat) ± 0.8(syst)  10-9 |as|=1.06+0.26-0.21 (stat) ± 0.07 (syst) PLB 576 (2003) First measurement BR(p0mm) = 2.9 +1.4-1.2(stat) ± 0.2(syst)  10-9 |as|=1.55+0.38-0.32 (stat) ± 0.05 (syst) PLB 599 (2004)

  37. SM prediction for K0L → p0l+l- Isidori et al. EPJC36 (2004) • From KL measurement: small CPC contribution • From KS measurement: indirect CPV contribution dominates • Sensitivity of BR to CKM phase depends on the (unmeasurable) relative sign of the two CPV terms • Theory:constructive interference favored * • Sensitivity to new physics: enhanced electroweak penguins would enhance the BR Constructive Destructive J. Buras et al. hep-ph/0402112 NP B697 (2004) * Two indeopendent analysis: G. Buchalla, G. D’Ambrosio, G. Isidori, Nucl.Phys.B672,387 (2003) - S. Friot, D. Greynat, E. de Rafael, hep-ph/0404136, PL B 595

  38. 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”): • KL0e+e decays • K  pnn decays

  39. SPARE

  40. The “golden” K pl l decays Motivation • FCNC processes, no tree level, proceed via loop diagrams • access to quark level physics with small theoretical uncertanties: • dominant short distance contributions • long distance only for charged lepton modes • matrix elements of quark operators related to Ke3 decays • CPV KL decays • Charged leptons final states: easier lepton identification but high levels of radiative background • Best change: K pnn decays: • no long distance contributions • clean theoretical predictions • no radiative background • KL decay dominated by direct CPV

  41. Why Kaon again? a g b Unitarity Triangle:Vud V*ub + Vcd V*cb + Vtd V*tb = 0 ρ and η precise measurements: important as precision test of the CMK formalism - used to describe CP and quark mixing -and search for new physics KL 0KOPIO@BNL KS  0e+e- KL 0e+e-KL  0 KL  e+e-  h (,) K+  + P326@CERN The study of K mesons allows quantitative tests of the SM independent and complementary to B physics r (0,0) (1,0) (1.4,0) KL → +-KL   KL  e+e-  KL  e+e- e+e- KL  e+e- +-

  42. Experimental prospects • K0Lp0nn • Large window of opportunity exists. • Upper limit is 4 order of magnitude from the SM prediction • Expect results from data collected by E391a (proposed SES~3 10-10) • Next experiment KOPIO@BNL • Future: JPARC and KLOD@IHEP • K0Lp0ee(mm) • Long distance contributions under better control • Measurement of KSmodes has allowed SM prediction • KS rates to be better measured (KLOE?) • Background limited (study time dep. Interference?) • 100-fold increase in kaon flux to be envisaged • K+p+nn • The situation is different: 3 clean events are published • Experiment in agreement with SM • Next round of exp. need to collect O(100) events to be useful: P326 at CERN • Move from stopped to in flight experiments

  43. 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). • Measurement of kaon momentum: • Reconstruct K3π with a lost pion; • Redundancy in K3πanalysis; • Resolve Ke4reconstruction ambiguity. Not used yet for K±3± analysis E. Goudzovski / CERN, 1 March 2005

  44. KL,S ee : why? CPV inner bremsstrahlung CPC direct emission CPV direct emission Charge radius For KL: interference gives indirect CP-violating asymmetry in the orientation of  and eedecay planes Easier access to polarization asymmetry in K  Large ( 14%) asymmetries predicted

  45. KL,S ee A = (13.3  1.7)% KTeV: KL [NA48:A = (14.2  3.6)%] 1.5K events BR = (3.63  0.18)  10-7 [NA48: BR = (3.08  0.2)  10-7] BR = (4.69  0.30)  10-5 NA48: KS,KL No asymmetry:A = (1.1  4.1)%

  46. KTeV: |η+- | measurement Direct CPV: AssumingΓ(KSπeν)=Γ(KLπeν), the result is: (hep-ex/0406002) 2.7σdiscrepancy with PDG average

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