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Charged Kaons at NA48

Charged Kaons at NA48. Current Status and Future Plans A. Maier CERN On behalf of the NA48 Collaboration. Overview. The NA48 Experiment The charged asymmetry measurement Status report –no result yet Analysis method described Progress so far Future Plans for NA48. Charged Asymmetry.

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Charged Kaons at NA48

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  1. Charged Kaons at NA48 Current Status and Future Plans A. Maier CERN On behalf of the NA48 Collaboration

  2. Overview • The NA48 Experiment • The charged asymmetry measurement • Status report –no result yet • Analysis method described • Progress so far • Future Plans for NA48 A. Maier CERN

  3. Charged Asymmetry A. Maier CERN

  4. Introduction • NA48/2 experiment • Data taking 2003-2004 • Simultaneous K+ and K- beams • The worlds largest multipurpose sample of charged kaon decays • Main goals: • Measurement of CP-violating charge asymmetry of K±π+π-π± and K±π0π0π± decays • Measurement of π-πscattering parameter a00 in Ke4decays [accuracy <0.01]; • Study of rare charged kaon decays: tests of Chiral Perturbation Theory A. Maier CERN

  5. The NA48 beam-line Simultaneous K+ and K- beams (vertical cross-section) 114m decay volume Beams coincide within <1mm A. Maier CERN

  6. The NA48 detector • Beam spectrometer (Kabes, 3 stations) • Resolution: σX = 50 μm [drift], σY = 80 μm [strips], σt = 0.7 ns, Δp/p<1% • Magnetic spectrometer (4 DCH) • Δp/p = 0.5% + 0.009%*p [GeV/c] • Liquid Krypton Calorimeter • ΔE/E = 3.2%/√E + 9%/E + 0.42% • Hadron Calorimeter, muon veto, veto counters A. Maier CERN

  7. NA48/2 data taking 2003 • Data taking 2003 ~50 days. • Data presented here: data of the last month (about 1/3 of the total 2003 sample) • Remaining data has different systematics • Run 2004 has started with 60 scheduled days of data taking A. Maier CERN

  8. K3 matrix element • Kinematical variables • Matrix element: Lorentz-invariants u = (s3-s0)/m2; v = (s2-s1)/m2; si = (PK-Pi)2, i=1,2,3; s0 = (s1+s2+s3)/3. |M(u,v)|2~ 1 + gu + hu2+ kv2 • Direct CP-violation Center of mass frame u = 2mK∙(mK/3-Eodd)/m2; v = 2mK∙(E1-E2)/m2. Ag = (g+-g-)/(g++g-)≠0 A. Maier CERN

  9. 720 m K+ events |V| even pion in beam pipe odd pion in beam pipe U K3π Dalitz plot A. Maier CERN

  10. Principle of measurement |M±(u,v)|2 ~ 1 + g±u + hu2+ kv2 • Project into u axis • Neglect quadratic slopes h and k • Remember |Ag|<<1 • Kπ+π-π±: g = -0.2154±0.0035 • Kπ0π0π±: g = 0.652±0.031 • |h|, |k| << |g| If acceptance is equal for K+ and K-, R(u) = N(1+g+u)/(1+g-u) ≈ ≈N(1+2g+Agu) Ag can be extracted from a linear fit to the ratio R(u) A. Maier CERN

  11. Acceptance cancellation • Symmetrization of acceptance: analyzing magnet polarity (B) is switched on daily basis; • Symmetrization of beam properties: achromat polarity (A) is switched on weekly basis. Data taking from August 6 to September 7, 2003 Achromat - B+ B- B+ B- B+ B- Super-sample 1 Week 1 12 day-samples B+ Achromat+ B+ B- B+ B- B- Week 2 Super-sample 2 B- B- Achromat - B+ B- B+ B+ Week 3 12 day-samples Achromat+ B+ B+ B- B+ B- B- Week 4 Super-sample 3 B- Achromat - B+ Week 5 4 day-samples Achromat+ B+ B- A. Maier CERN

  12. Acceptance cancellation (2) Top view of the setup Physical asymmetries (~Δg): • AS→ slope of ratio u(B+K+)/u(B-K-) • AJ→ slope of ratio u(B-K+)/u(B+K-) Apparatus-induced asymmetries: • A+→ slope of ratio u(B+K+)/u(B-K+) • A-→ slope of ratio u(B+K-)/u(B-K-) • ASJ = (AS+AJ)/2 physics asymmetry • A± = (A++A-)/2 = (AS-AJ)/2 • asymmetry induced by experimental setup • [ many of the effects observed in A± cancel in ASJ ] Saleve Z axis (beam direction) Jura X axis A. Maier CERN

  13. The role of time-instabilities • Measurement of AS, AJ, A+, and A- implies combining data from different day-samples • Therefore measurement is sensitive to time-instabilities of beams and setup. • The following instabilities were found significant and have been corrected for: • Time-dependence of spectrometer magnetic field; • Time-dependence of spectrometer alignment; • Time-dependence of beam geometry. A. Maier CERN

  14. Time-dependence of alignment MSaleve–MJura, keV/c2 Max. DCH4 shift of 70 m Spectrometer calibration • p = p0∙(1+β)∙(1+qbp0) p0 – measured momentum; p – corrected momentum; q – track charge; b – magnetic field sign. • Time-dependent corrections: • β– for magnetic field integral ~(m+ + m-)/2 •  – for spectrometer misalignment ~(m+ - m-)/2 Day-sample A. Maier CERN

  15. Sensitivity to beam geometry • Why is the measurement sensitive to beam geometry? • Acceptance is defined by beam pipe! • Time-dependent cuts following beams’ movement are introduced to symmetrize beam geometry. |V| Beam pipe “Virtual tube”: |ΣRπi-<RK>|>R0 at DCH1, DCH4 <RK> = f (kaon sign, time, momentum) A. Maier CERN U

  16. X, cm X, cm Beam movement in time DCH1 DCH4 Y, cm K+ K+ Y, cm B+ B- X, cm K- K- Y, cm Y, cm B+ B- X, cm A. Maier CERN

  17. DCH4 A+KJ, A-KS Y, cm 55 GeV/c 65 GeV/c 55 GeV/c X, cm A+KJ, A-KS Y, cm 55 GeV/c 65 GeV/c 65 GeV/c 55 GeV/c X, cm Momentum-dependence of beam position Split by analyzing magnet field A. Maier CERN

  18. Statistics in the “charged” mode Selected events per super-sample (in millions) K+ Events M3π, GeV/c2 Events K- A. Maier CERN M3π, GeV/c2

  19. Results on asymmetry • In the following slides asymmetries as functions of kaon momentum and time are presented: • Physics asymmetries ASJ are presented with offsets→ no result yet to be presented. • Apparatus-induced asymmetries – no offsets, indications of systematic effects. • Note that ASJ = 2g∙Ag≈ -0.43∙Ag Measured value Notation in theory papers A. Maier CERN

  20. Fixed achromat orientations Achromat UP Achromat DOWN Units of 10-4 OFFSET! OFFSET! Systematics cancellation A. Maier CERN

  21. Asymmetry vs. kaon momentum ΔASJ=1.17∙10-4 ΔAg=2.7∙10-4 2 = 6/11 Units of 10-4 54 66 OFFSET! OFFSET! ΔA±=(1.02±1.17)∙10-4 2 = 9/11 A. Maier CERN

  22. Time-stability of asymmetry Units of 10-4 OFFSET! 2=5.6/13 2=13.5/13 OFFSET! A. Maier CERN

  23. Future Plans A. Maier CERN

  24. Proposal (NA48/3) • NA48 detector upgrade to study K+→π+νν • Potential to measure |Vtd| to the 10% level • Availability of the experimental infrastructure (NA48/2) • Location of the experiment in ECN3 (high radiation area) • Beam line (high intensity slowly extracte protons from the SPS) • Available subdetectors (e.g. LKR calorimeter) • Goal: 50 events in a 2 years run A. Maier CERN

  25. decay in flight High energy Region I Region II Experimental features A. Maier CERN

  26. Vacuum Beam Layout A. Maier CERN

  27. Beam Layout • Beam features: • Unseparated positive Kaon beam Δp/p≤1% • p=75 GeV/c • Beam detectors • Cerenkov detector (CEDAR) • Kaon identification • Beam spectrometer (KABES) • Redundent measurement of beam momentum • Measurement of the kaon direction A. Maier CERN

  28. New high-intensity beam A. Maier CERN

  29. New high-insensity beam (2) A. Maier CERN

  30. Detector Layout • Double spectrometer • 6 drift chambers (4 chambers already existing) • 2 magnets (one already available in the current spectrometer) • Redundant measurement of momentum • Photon veto • Liquid krypton calorimeter • 2 small angle vetoes (CMS prototypes) • 8 rings of large angle vetoes (upgrade of the existing vetoes in NA48) • Hadron calorimeter • Muon veto A. Maier CERN

  31. Region I Region II Acceptance Acceptance 75 GeV/c 20 events per year @ BR= 10-10 PK = 75 GeV/c Pπ <40 GeV/c Acceptance (Region I) = 5% Acceptance A. Maier CERN

  32. Conclusions • Charged asymmetry measurement • K±π+π-π±: • >1.1∙109decays in one month of run 2003; • Major sources of systematics identified; No showstopper • Statistical error of Ag is 2.7∙10-4; • Uncertainty dominated by statistical error! • K±π0π0π±: • ~4∙107decays in one month of run 2003; • Expected statistical error of Ag is 5∙10-4. • Run 2004 started [60 days of data taking]. • Future program for NA48 in progress • Intention to move from qualitative to quantitative tests of the standard model • 40x flux of kaons without any additional upgrade of the SPS • An expression of interest has been submitted the CERN SPS Committee • A working group has been established A. Maier CERN

  33. Events accepted Region I Measured quantities Kinematical rejection A. Maier CERN

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