1 / 24

Lepton Universality Tests in Kaon Decays at NA62

Lepton Universality Tests in Kaon Decays at NA62. Francesca Bucci, INFN Sezione di Firenze o n behalf of the NA62 Collaboration. The XIth International Conference on Heavy Quarks and Leptons June 11-15, 2012, Prague , Czech Republic. Introduction.

sun
Download Presentation

Lepton Universality Tests in Kaon Decays at NA62

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. LeptonUniversalityTests in KaonDecaysat NA62 Francesca Bucci, INFN Sezione di Firenze on behalf of the NA62 Collaboration The XIth International Conference on HeavyQuarks and Leptons June 11-15, 2012, Prague, Czech Republic

  2. Introduction • Precise measurements of FCNC processes in the B sector have severely restricted the parameters space of new-physics (NP) models • Experiments at the LHC have started a direct exploration of the physics in the TeV range • In this scenario, the study of LeptonFlavorUniversality (LFU) in kaondecaysisequallyinteresting and fullycomplementary to search for NP effects F. Bucci

  3. K+l+Sensitivity to New Physics • Leptonickaondecayswithin the SM are mediated by a chargedcurrentattreelevel • The natural size of the non-standard contributions depends on the particular BSM scenario • In Models with 2 HiggsDoublet (2HDM-II includingSUSY) sizablechargedHiggs (H) exchangecontributions obstructed by hadronicuncertainties (fK ) F. Bucci

  4. RK=G(K→en)/G(K→mn) in the SM • In the ratio RK =G(K→en/K→mn) hadronic uncertainties cancel • The SM prediction of RK has reached <0.1% precision • dRKis the correction due to the Inner Bremsstrahlung part of the radiative K →engprocess [V. Cirigliano and I. Rosell Phys. Rev. Lett. 99 (2007) 231801] helicitysuppressionfactor F. Bucci

  5. RadiativeK→engDecays • In K→eng (Ke2g), g can be produced via internalbremsstrahlung (IB) or direct-emission, the latterbeingdependent on the hadronicstructure (SD) • RKisdefined to be inclusive of the IB, ignoringhowever the SD contributions • To compare data with SM prediction the SD contribution must be carefullyestimated and subtracted. IB SD g g e± e± K± K± ne ne F. Bucci

  6. RK beyond the SM [A. Masiero, P.Paradisi, R. Petronzio Phys. Rev. D74 (2006) 0011701] • ChargedHiggsbosons (H) appearing in any model with twoHiggsdoublets (including SUSY case) can contributeattreelevel • Suchcontributiondoesnotaffect the ratio RK • LFV couplings, present at one loop level, can contribute to RKSM at the % level • Limited by recentBs+-measurement slepton mixing [Fonseca, Romão, Teixiera, arXiv:1250.1411]

  7. The NA62 Experiment The NA62 Collaboration: Birmingham, Bratislava, Bristol, CERN, Dubna, Fairfax, Ferrara, Florence, Frascati, Glasgow, Liverpool, Louvain, Mainz, Merced, Moscow, Naples, Perugia, Pisa, Prague, Protvino, Rome I, Rome II, San Luis Potosì, SLAC, Sofia, Turin NA62 (RK) 2007-2008: Ke2 ,Km2 data taking NA62 (K++ ) 2007-2013: design & construction 2014 ? : K++ data taking after the long CERN acceleratorsshutdown F. Bucci

  8. NA62 (RK) Detector Primary SPS protons (400 GeV/c)  1.81012 /SPS spill Unseparatedsecondary positive and/or negative hadronicbeam (p=74.01.4 GeV/c) Composition: K () = 5% (63 %) K decaying in vacuum tank  18% Heliumfilled tank Mainsubdetectors: Magnet LKrelectromagnetic calorimeter: sE/E = (3.2/√E  9.0/E  0.42)% (E in GeV) sx=sy= (4.2/ √E + 0.6)mm (E in GeV) Hodoscope: Fast trigger for charged particle and timing for the event(st 150ps) Magnetic spectrometer: sp/p = (0.48  0.009 p)% (p in GeV/c) beam F. Bucci

  9. NA62 (RK) Data Taking The data takingstrategyhasbeenoptimized to measure the twomain backgrounds in the Ke2 sample: • Beamhalomuons • K2decays with a muonmisidentifiedas an electron Data taking: •  4 months in 2007 •  2 weeks in 2008 (used for systematicsstudies) Data samples: • K+, K-samples • with different background conditions: with leadwall (Pb), withoutleadwall (noPb) (seenext)  K+ (noPb), K+(Pb),K-(noPb),K- (Pb) F. Bucci

  10. acceptance LKr trigger efficiency # background events # signal events measured PID efficiency LKrreadout efficiency MeasurementStrategy • Ke2, Km2collected simultaneously: • No dependence on K fluxmeasurement; • Cancellation of severalsystematiceffects in the ratio at first order • MC simulationsusedto a limitedextent: • Acceptancecorrection and the geometricalparts of the acceptances for mostbkgprocesses • PID, trigger, read out efficiencies and muonhalobkg are measureddirectly from data • Analysis performed in bins of the reconstructed lepton momentum downscalingfactor of Km2 F. Bucci

  11. Trigger Logic Minimum bias (high efficiency, butlowpurity) trigger configurationused • Ke2condition: Q1ELKr1Trk • K2condition: Q11Trk/D, downscalingfactor D=150 F. Bucci

  12. Ke2vs Km2Selection • Geometry • One reconstructed charged track • 13 < p < 65 [GeV/c] • Geometrical acceptance cut • Cut on K decay vertex position • Photon veto using LKr • Kinematics • Missing mass: Mmiss2(l)=(PK-Pl)2 • Sufficient Ke2/K2separation up to 30 GeV/c • Particle ID(ELKR/pspectr) • e: (0.9 to 0.95) < E/p < 1.1 • m: E/p < 0.85  suppression in e sample: 106 F. Bucci

  13. K2 Background in Ke2 Sample Muon‘catastrophic’ energyloss in or in front of the LKris the largestbkg source The probability of mis-identify a muonas an electron Pme310-6 (and momentum dependent) Measurement of Pmeon data • To avoid electron contamination from muondecay(10-4) a 9.2 X0 thickleadwallcovering 18% of the acceptancewasinstalledbetween the HOD planesfor 50% of the run time • K2 candidates : tracktraversing Pb, p>30GeV/c, E/p>0.95 (positroncontamination < 10-8) • Pmeis modified by the Pb wall due to: • ionizationlosses in Pb (low p) • bremsstrahlung in Pb (high p) m e F. Bucci

  14. MuonMisidentification The correctionfPb=Pme/PmePb evaluated with a dedicated Geant4-based simulation Correction for Pb:fPb=Pme/PmePb PmePb(Pb wallinstalled) vs momentum MC precision fPb/fPb= 2% MC precision Pme/Pme = 10% Result : B/(S+B) = (5.640.20)% F. Bucci

  15. Muon Halo Background in Ke2 Sample The muonsweepingsystemwasoptimized for the positive beam • Muonhalo background measured on the data • K+ (K- ) onlysample used to measuremuonhalo background in K- (K+ ) sample • Control samplesnormalized to the data in the Mmiss2regionpopulatedmainly by beamhaloevents (-0.3 < Mmiss2 < - 0.1 (GeV/c2)2) • Stronglydepends on decayvertex position and trackmomentum • Regionsdelimited by solid line are excluded • Probabilityto reconstruct a Ke2candidate due to a decay of an opposite signkaonhasbeentakeninto account Ke2+ (noPb) Ke2- (noPb) pe+ (GeV/c) pe- (GeV/c) z vertex (m) z vertex (m) Result : B/(S+B) = (2.110.09)% F. Bucci

  16. K±→e±ng Background in Ke2 Sample SD contribution of the K±→e±n gdecaysmust be carefullyestimated and subtracted • The SD+ (positive photonhelicity) componentpeaksathigh electron momentum in the K rest frame and isthereforekinematicallysimilar to the Ke2decay • SD-decays and the interferencebetween the IB and SD processes are negligible • The SD+ background contributionhasbeenestimated by using MC simulationbased on the measuredK±→e±ng (SD+) differentialdecayrate SD+ Ee (MeV) IB [J. Bijnens, G. Colangelo, G. Ecker, J. Gasser, arXiv:hep-ph/9411311] SD- [F. Ambrosino et al., Eur. Phys. J. C 65 (2010) 703] E (MeV) Result : B/(S+B) = (2.600.11)% F. Bucci

  17. Ke2 Sample Ke2candidates 145,958 K±e ±ncandidates B/(B+S) = (10.950.27)% e± ID efficiency = (99.28 0.05)% F. Bucci

  18. Ke2Background Ke2candidates and backgrounds in momentumbins K+ (noPb) F. Bucci

  19. K2 Sample and Background The onlysignificant background source in the Km2 sample is the beamhalo 42.817 106K±m ±ncandidates(collecting with downscaling factor D=150) B/(S+B) = (0.50 ± 0.01)% K+ (noPb) F. Bucci

  20. NA62 Result (full data set) Fit over 40 RKmeasurements (4 data samples 10 momentumbins) includingcorrelations: c2/ndf=47/39 RK=(2.488 ± 0.007stat ±0.007syst ) x 10-5=(2.488 ± 0.010) x10-5 F. Bucci

  21. Uncertainties on RK

  22. RK World Average July 2011 world average : RK= (2.488 ± 0.009) 10-5(RK/RK= 0.4%) For non-tiny values of D13 the sensitivity to H± in RK is strong b  sg PDG 2010 (KLOE result): RK= (2.493 ± 0.031) 10-5 (RK/RK= 1.3%) B→tn[HFAG 2010] Rm23 [Eur. Phys. J. C 69 (2010) 399 ] b→sg[HFAG 2010] F. Bucci

  23. Future Prospects NA62 (K++) data takingforeseen in 2014 after the long CERN acceleratorsshutdown • Hermetic veto (large-angle and small-angle veto counters) willstronglydecrease the Ke2 background. • Beamspectrometer (beamtracker plus Cherenkovbeamtagger) willallow time correlationbetweenkaons and decayproducts. Beamhalo background expected to be reduced to negligiblelevel. Requiredstatisticaluncertainty  0.05% 1 month of data takingsufficient for such RKmeasurement F. Bucci

  24. Conclusions • The analysis of the full data sample taken by NA62 is completed • The measuredvalueisRK=(2.488 ± 0.010) x10-5, reaching a record level of accuracy of  0.4% • The combinedexperimentalaccuracyhasimproved by an order of magnitudesince 2008, butisstill an order of magnitudebiggerthan the SM predictionprecision • Excellentprospects for future measurementsof RKwithin the NA62experimentalprogram F. Bucci

More Related