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Natalia Molokanova Joint Institute for Nuclear Research

Rare kaon and hyperon decays in NA48 experiment. Natalia Molokanova Joint Institute for Nuclear Research on behalf of the NA48/2 Collaboration Cambridge, CERN, Chicago, Dubna, Edinburgh, Ferrara, Firenze, Mainz, Northwestern, Perugia, Pisa, Saclay, Siegen, Torino, Vienna

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Natalia Molokanova Joint Institute for Nuclear Research

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  1. Rare kaon and hyperon decays in NA48 experiment Natalia Molokanova Joint Institute for Nuclear Research on behalf of the NA48/2 CollaborationCambridge, CERN, Chicago, Dubna, Edinburgh, Ferrara, Firenze, Mainz, Northwestern, Perugia, Pisa, Saclay, Siegen, Torino, Vienna 13th Lomonosov Conference on Elementary Particle Physics Moscow, Russia, August 23-29, 2007

  2. Outline • K±  p±p0gdecay • formalism • experimental status • NA48/2 measurement • K±→p±e+e−g decay • NA48/2 measurement • Decay asymmetries of X0→L and X0→0 • NA48/1 measurement • X0→L0e+e-decay • NA48/1 measurement

  3. The NA48/2 beam line 114 m • Primary proton beam  p = 400 GeV/c (71011 ppp) • Simultaneous K+/K− beams  p = (60 ± 3) GeV/c • K+/K− beam flux  3.8 (2.6) × 107 ppp

  4. => PT KICK = 120 MeV Beam pipe The NA48 detector • Magnetic spectrometer (4 DCHs): Δp/p = 1.0% + 0.044%*p [GeV/c] +-±mass resolution about 1.7 Mev/c • Liquid Krypton EM calorimeter (LKr) High granularity, quasi-homogenious; ΔE/E = 3.2%/√E + 9%/E + 0.42%[GeV] sx ,sy ~ 1.5 mm 00± mass resolution about 1.4 Mev/c • Hodoscope fast trigger; precise time measurement (150ps). • Hadron calorimeter, muon veto counters, photon vetoes. LV1 trigger: hodoscope and DCH multiplicity LV2 trigger: on-line data processing

  5. K±  p±p0g

  6. K±  p±p0g. Decay formalism. IB DE DE IB IB INT DE P*K = 4-momentum of the K±P*p = 4-momentum of the p±P*g = 4-momentum of the g G± depends on 2 variables (T*pand W) that can be reduced to only one integrating over T*p IB, DEandINTcomponents can be separated kinematically using the Lorentz invariant variable W which is defined as follows:

  7. K±  p±p0g. Amplitudes. Inner Bremsstrahlung(IB) : (2.75±0.15)·10-4 PDG (2006)(55<T*p<90 MeV) Direct Emission (DE) : (4.4±0.7)·10-6 PDG(2006)(55<T*p<90 MeV) Interference (INT) : not yet measured Two types of contributions: Electric (J=l±1) dipole (E) Magnetic (J=l) dipole (M) Electric contributions are dominated by the Inner Bremsstrahlungterm DE shows up only at order O(p4) in CHPT: is generated by both E and M contributions INT term is sensitive to E only

  8. K±  p±p0g. Exp results for DE and INT. History of DE Branching ratio Interference estimations*: • All the measurements have been performed: • in the T*pregion55-90 MeV to avoid p±p0andp±p0p0 background • assuming INT = 0 BNL E787 KEK E470 *not quoted as measurements by authors

  9. What’s new in NA48/2 measurement • In flight Kaon decays • Both K+ and K− in the beam (possibility to check CP violation) • Very high statistics(220k π±π0γ candidates, 124k used in the fit ) • EnlargedT*πregion in the low energy part (0 <T*π< 80 MeV) • Negligiblebackground contribution < 1% of the DE component • Good W resolution mainly in the high statistic region • More bins in the fit to enhance sensitivity to INT • Order‰ γ mistagging probability for IB, DE and INT • Fit with free interference term

  10. K±  p±p0g. Enlarged T*pregion. T*p(IB) T*p(INT) T*p(DE) Standard region Standard region Standard region Use standard region 55<T*p<90 MeV as safe choice for BG rejection But…. region <55 MeV is the most interesting to measure DE and INT This measurement is performed in the region 0 < T*p< 80 MeV to improve statistics and sensitivity toDE

  11. K± p±p0p0 • K±p±p0g K±  p±p0g.The selected data sample. • Event selection • requirements on tracks • requirements on LKR clusters • effort into gs pairing • requirements on the event closure • All physical BG can be explained in terms ofp±p0p0events only • Very small contribution from accidentals is neglected • g mistagging probability (a self background) is order of ‰ Selected region 220Kevents

  12. K±  p±p0g. W shapes from MC. IB DE INT • 3 MC data samples for the 3 contributions to the decay

  13. K±  p±p0g. Data-MC comparison. W(Data)/W(IBMC) Data MC for Eg (W<0.5) IB dominatedregion Fitting region Egmin cut Radiatedgenergy (IBdominated) IB dominated part of the W spectrum • MC • −data • IB contribution is very well reproduced by MC

  14. K±  p±p0g. Fit results. • fit the W data spectrum using MC shapes with the weights to be extracted:Wdat=(1-a-b)WIB+aWDE+bWINT • systematic dominated by Trigger efficiency. • parameters are highly correlated correlation coefficient: ρ = -0.92 First evidence of non zero INT term! NA48/2 Preliminary Frac(DE)0<T*p<80MeV = (3.35 ± 0.35 ± 0.25)% Frac(INT)0<T*p<80MeV = (-2.67 ± 0.81 ± 0.73)% 2004 data set: x4 # events and lower systematic due to trigger

  15. K±  p±p0g. Comparison. • For comparison with previous experiments the fraction of DE has been also measured, with: • INT = 0 • 55<T*p<90 MeV Frac(DE)55<T*p<90 MeV = (0.85 ± 0.05 ± 0.02)% Consistent, although the analysis of fit’s residuals shows a badc2 Indication for a non-null INT term

  16. K±→p±e+e−g

  17. K±→p±e+e−g. BR measurement. Never observed before Naïve estimation of the BR: BR(K±→p±e+e−g)=BR(K±->p±gg)·2a~ 1.6·10-8 Theoretical expectation (Pt based, Gabbiani 99):BR(K±→p±e+e−g)=(0.9-1.6)·10-8 • Event sample: • 92 candidates events with • 1±1 accidental background • 5.1±1.7 physical background • Normalization channel: • K±->p±p0D: 14M events BR(K±→±e+e−g) = (1.27±0.14stat±0.05sys)·10−8 NA48/2 Preliminary

  18. Radiative Hyperon decays from NA48/1

  19. Radiative Hyperon decays from NA48/1 NA48/1 Beam line • same detector as NA48/2 • neutral beam: mainly Ks, X0,

  20. X0→Ldecay asymmetry (I) • Use the L→p-as analyser • dN/dcos  1 - LXcos • L= 0.642± 0.013 (PDG) • 43814X0→L  events selected • 0.8 % background

  21. X0→L decay asymmetry (II) NA48/2 Preliminary (X0→L )= -0.68 ± 0.02stat ± 0.06syst

  22. X0→0 decay asymmetry • Same method as for X0→, but one additional decay 0→ • 13068X0→0 events selected • ≈ 3% background (X0→0)= -0.68 ± 0.03stat ± 0.07syst NA48/2 Preliminary

  23. X0→L0e+e- Never observed before Naïve estimation of the BR: BR(X0→Le+e-)=BR(X0->Lg)·a~ 8.8·10-6 Theoretical expectation (QED based, Bernstein 65):BR(X0 →Le+e-) = (6.4-7.3)·10-6 • Event sample: • 412 candidates events with • 7±5 accidental background • 8±3 physical background • Normalization channel: • X->Lp0D: 30K events BR(XLee) =(7.7±0.5stat±0.4syst)·10−6 a(XLee) = −0.8 ± 0.2 NA48/2 Preliminary

  24. Conclusion • NA48/2 recent results in charged radiative Kaon decays • first evidence of non 0 INT term in K±→p±p0g • first measurement of K±→p±e+e-gBR • NA48/1 recent results in radiative hyperon decays • new measurement of X0→Lgand X0→0g decay asymmetries • first measurement of the X0→Le+e- BR and decay asymmetry

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