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Kaon Experiments at CERN: Recent Results and Prospects

Kaon Experiments at CERN: Recent Results and Prospects. Francesca Bucci, INFN Sezione di Firenze Korea Institute for Advanced Study (KIAS), October 29, 2013. Introduction. Kaon decays have played a key role in the shaping of the Standard Model (SM) Parity violation

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Kaon Experiments at CERN: Recent Results and Prospects

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  1. KaonExperimentsat CERN: RecentResults and Prospects Francesca Bucci, INFN Sezione di Firenze Korea Institute for Advanced Study (KIAS), October 29, 2013

  2. Introduction Kaondecayshaveplayed a keyrole in the shaping of the Standard Model (SM) • Parityviolation • GIM mechanism • CP violation Kaondecays continue to have an important impact on flavordynamics • ChPTTests • Constrainingphysicsbeyond the SM F. Bucci

  3. NA48/n and NA62 Fixed target experimentsat the CERN Super Proton Synchrotron (SPS) F. Bucci

  4. NA48/n History NA48 Main goal: Search for direct CPV Measurementof ’/ Beams: KL+KS 1997 1998 1999 2000 2001 2002 2003 2004 2005 : 2013 : : NA48/1 Main goal: Rare KSdecays, hyperondecays, CPV tests Beams: KS NA48/2 Main goal: Search for direct CPV Chargeasymmetrymeasurement Beams: K+ + K- NA62 Main goal: Measurementof the K+ + decays Beams: K+ F. Bucci

  5. Outline Recentresults: NA48/2 and NA62 (RKphase) • ChPTTests • LeptonFlavorUniversality Prospects: NA62 • K++ • Other rare and forbiddendecaysstudies F. Bucci

  6. NA48/2 Beam(s) • SPS protonsat 400 GeV/c • Simultaneous, unseparated, focusedpositive and negative hadronicbeams • Kaonmomentum: 603 GeV/c (NA48/2), 741 GeV/c (NA62-RK) F. Bucci

  7. NA48/2 Detector •  100 m long decayregion in vacuum • Similaracceptance for K+ and K-decays Magnetic spectrometer: sp/p = (1.0  0.044 p)% (p in GeV/c) NA48/2 sp/p = (0.48  0.009 p)% (p in GeV/c) NA62-RK Momentum kick: 120 MeV/c NA48/2 265 MeV/c NA62-RK Hodoscope: st 150ps beam 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) F. Bucci

  8. Outline Recentresults: NA48/2 and NA62 (RKphase) • ChPTTests • LeptonFlavorUniversality Prospects: NA62 • K++ • Other rare and forbiddendecaysstudies F. Bucci

  9. ChiralPerturbationTheory The ChiralPerturbationTheory (ChPT) is the effectivefieldtheory of quantum chromodynamics (QCD) atlowenergies • In the ChPT the eightlightesthadrons (,0,K,K0,K0,) are the Goldstonebosons (GB) due to the spontaneous breakdown of the chiralsymmetry • The chiralLagrangian can be organized in terms of the increasingnumber of GB fieldsderivatives or, equivalently, in terms of the increasingpowers of theirmomentum (chiralpowers) • In the chiralexpansion, the intrinsichadronicuncertainties are parametrized by lowenergyconstants (LECs) whosevalue must be determined by phenomenology. F. Bucci

  10. NA48/2 and NA62-RKChPTTests ChPTis the idealframework to describekaondecays Radiative kaondecays: • K   0  EPJC 68 (2010) 75-87 • K    e+ e- PLB 659 (2008) 493-499 • K  e   (SD) • K   Non radiative kaondecays: • K  0 e , K  0  • K  + - e  EPJC 54 (2008) 411-423 , EPJC 70 (2010) 635-657, PLB 715 (2012) 105-115 • K  0 0e  • K    0 0EPJ C64 (2009) 589 • K    + -PLB 6495-6 (2007) 349-358 • K   e+e-, K   + -PLB 677 (2009) 246-254, PLB 697 (2011) 107-115 • K   0 e+ e- F. Bucci

  11. KDecayTheory In the ChPTframework the differential rate is: D’Ambrosio, Portolés, PLB 386 (1996) 403-412 • The leadingcontributionisatO(p4) • Rate and spectrum in z=m2/m2Kat O(p4) depend on a single unknownparameter N and L are fundamentalChPTparameters QCD loops and counterterms weakchirallagrangian F. Bucci

  12. KDecayTheory The dominantamplitude A isresponsible for a cuspat m = m2 Ecker, Pich, De Rafael, NPB 303 (1988) 665-702 Predictionsat O(p4) and O(p6) differ: may be testedexperimentally! D’Ambrosio, Portolés, PLB 386 (1996) 403-412 Gerard, Smith, Trine, NPB 730 (2005) 1 F. Bucci

  13. K Fit Data support the ChPTprediction of a cuspat the di-pionthreshold NA48/2 NA62-RK O(p6) O(p6) Fit the z distributions to extract the value of the ĉ parameter in the framework of the ChPT O(p4) and ChPT O(p6) F. Bucci

  14. K FitResults d/dz vs z BR(K) vs ĉ ChPT O(p4) vs O(p6) modelscannot be discriminatedwithin the currentexp. sensitivity Compute the BR in the full kinematicrangeassuming the ChPT O(p6) BR6 (K) = (1.010.06)10-6 PRELIMINARY F. Bucci

  15.  Scattering and K Decays • The S-wave scatteringlengthsaI in the isospin I=0 and I=2 states are preciselypredicted by ChPT • The DIRAC collaborationat CERN produced+- atoms to measureitslifetime and obtained The  scatteringlengthscan also be determined by precise measurements of the kaondecays with pions in the final state NPB 603 (2001) 125, PRL 86 (2001) 5008 F. Bucci

  16. Cusp Effect in K00 Decays Change of slope observed in the m2p0p0 distribution at the region near m2p0p0= (2mp+)2 zoom (2mp+)2 (2mp+)2 m2p0p0 (GeV/c2)2 m2p0p0 (GeV/c2)2 was interpreted as due to the strong pprescattering in the final state K+- Cabibbo PRL 93,2004 [a0,a2values in units of 1/m+] F. Bucci

  17. PhaseShift in K+-e(Ke4) Decays Verycleanhadronicenvironmentsincethere are onlytwopions in the final state • The shift () between the phasesof the S-wave, I=0 and P-wave, I=1 formfactorsismeasuredas a function of the +- invariant mass [EPJC 70 (2010) 635-657]. • Royequationsallow to connetmeasuredphaseshifts to  scatteringlengths[PLB 36 (1971) 353]. best ChPTprediction 68% CL contours [a0,a2values in units of 1/m+] F. Bucci

  18.  Scattering: Theory and Experiments Combine boththe cusp[EPJ C64 (2009) 589] and Ke4results[EPJC 70 (2010) 635-657] from NA48/2 [a0,a2values in units of 1/m+] Impressive agreement with ChPT F. Bucci

  19. Outline Recentresults: NA48/2 and NA62 (RKphase) • ChPTTests • LeptonFlavorUniversality Prospects: NA62 • K++ • Other rare and forbiddendecaysstudies F. Bucci

  20. 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

  21. 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

  22. RK beyond the SM • 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 • Recentmeasurements of BR(B s+-) and BR(Bu) significantlylower the SUSY contribution to RK • Sensitive to SM extensions with 4th generation, sterile  A.Masiero, P.Paradisi, R.PetronzioPhys. Rev. D74 (2006) 0011701, J. Girrbach and U. Nierste, arXiv:1202.4906 slepton mixing Fonseca, Romão, Teixiera, arXiv:1250.1411 Lackers, Menzel, JHEP 1007 (2012) 006 F. Bucci

  23. MeasurementStrategy • Ke2, Km2collected simultaneously • MC simulationsusedto a limitedextent • PID, trigger, read out efficiencies and muonhalobkg are measureddirectly from data • Analysis performed in bins of the reconstructed lepton momentum acceptance LKr trigger efficiency # background events downscalingfactor of Km2 # signal events measured PID efficiency LKrreadout efficiency F. Bucci

  24. RK FinalResult Fit over 40 RKmeasurements (4 data samples 10 momentumbins) includingcorrelations: c2/ndf=47/39 RK=(2.488 ± 0.010) x10-5 , RK/RK = 0.4% PLB 719 (2013) 326 F. Bucci

  25. RK World Average 2013 world average : RK= (2.488 ± 0.009) 10-5(RK/RK= 0.36%) Experimental accuracy still one order of magnitude away from the SM prediction Motivation for improved precision measurement 2013 average PDG 2010 (KLOE result): RK= (2.493 ± 0.031) 10-5 (RK/RK= 1.3%) Consistency with older measurements and with the Standard Model F. Bucci

  26. Outline Recentresults: NA48/2 and NA62 (RKphase) • ChPTTests • LeptonFlavorUniversality Prospects: NA62 • K++ • Other rare and forbiddendecaysstudies F. Bucci

  27. K in the SM FlavourChangingNeutralCurrent (FCNC) processforbiddenattreelevel in the SM • HighestCKM suppression  very sensitive to New Physics • High theoretical cleanness : • Dominated by short distancedynamics • In case of K+→p+nnsmall effects of long distance contributions due to charm • Hadronic matrix element extracted by K+→p0e+n • SM predictions • BR(KL0)=(2.43  0.39  0.06)10-11 • BR(K++)=(7.81  0.75  0.29)10-11 • BR proportional to |V*tsVtd|theoreticallycleanVtd dependance Pure theoreticalerrormostlyLD contribution Parametricerrordominated by Vcb , 

  28. K++ PreviousMeausrements E949/E787 experiment (BNL): 7 candidatesobserved in the twoallowedkinematicsregions • Lowenergyseparated K+beam • K decaysatrest • Hermeticcoverage Experimentaluncertainty > 50% NA62 aimsatmeasuring the BR with an accuracy of 10% F. Bucci

  29. K beyondthe SM Several SM extensionspredictsizabledeviations for the BR (hep-ph/0906.5454, hep-ph/0812.3803,hep-ph/0604074) NA62 expectedprecision E949/787 experimentaluncertainty RSc: Randall-Sundrum, LHT: LittlestHiggs with T-parity, SM4: SM with 4th generation F. Bucci

  30. The NA62 Beam and Detector Unseparated positive hadronbeam (K+ 6%) 10 MHz LAV 800 MHz 50 MHz SAV Target CHANTI Vacuum <10-5 mbar GTK KTAG-CEDAR LKr protons RICH hadronbeam 75 GeV/c STRAW Tracker CHOD MUV F. Bucci Signal signature: • Incoming high momentum (75 GeV/c) K+ • Outgoinglow momentum (<35 GeV/c) p+ in time with the incoming K+ F. Bucci

  31. ExperimentalTechnique • High K momentum • Low momentumto allowenough missing  energy(p0  40 GeV/c) to be detected by hermetic veto detectors (LAV,IRC,SAC,LKr) • Particleidentificationto separate  and  (RICH, MUV) • Kinematicalrejectionwith lightweightspectrometers (GTK, STRAW) • Beamparticleidentificationand inelasticeventsuppression (KTAG, CHANTI) • Fast timing F. Bucci

  32. Backgrounds 92% of kaondecaysseparated from signal by kinematiccuts • (m2miss ) < 10-3 GeV2/c4 • (pK)/pK 0.2%, (p)/p  1 % • keep multiple scatteringaslowaspossible • t=100 ps on + , t=150 ps on K+ K++0splits the signalregion in 2 F. Bucci

  33. Backgrounds 8% of kaondecaysnotseparated from signal by kinematiccuts •  identificationinefficiency < 10-5 •  veto inefficiency  10-5 • - separationat 10-3level F. Bucci

  34. ExpectedSensitivity Simple cut and countestimation with no optimization Background to be evaluated on data to reach the 10% accuracy F. Bucci

  35. Tracking Detectors: GTK Composed of 3 hybridsilicon pixel stationsmountedaroundfourachromatmagnets Inside the vacuumand subjetto a high and non-uniformbeamrate (750 GHz in total) 1 sensor, 10 bump-bonded chips • Provide precise • momentum ((p)/p0.2%), • time (t 175 psat 300V bias) • and angularmeasurements (()  16 rad) GTK1 Pixel 23 GTK2 Pixel 23 30 mm   245 ps   2  175 ps 60 mm F. Bucci

  36. Tracking Detectors: STRAWS Consists of 4 chambersintercepted in the middle by a dipolemagnet Minimize multiple scattering: ultra-light material, integrationin the vacuumtank • Measurement of • coordinates ( < 130 m), • and momentum ((p)/p0.3%) • of chargedparticlesoriginating from • the decay Eachchamberequipped with 1800 strawtubes, positioned in 4 views (u-v,x-y) F. Bucci

  37. PID Detectors: KTAG-CEDAR DifferentialCherenkovcounterfilled with H2 for positive K (50 MHz) identification Withoutkaontaggingvacuumshould be betterthan 610-8mbar Upgradedform of the CEDAR built for the SPS secondarybeam New PMTs and electronics, modifiedmechanics /optics Excellent time resolutionrequired (t =100 ps) F. Bucci

  38. PID Detectors: RICH Ring ImagingCherenkov detector composed of a cylindrical vessel (17 m long) filled with Ne slightlyaboveatmospheric pressure Project validated by strong R&D 17 m long radiator, 1 mirror, 400 PMTs Time Resolution (ps) Momentum (GeV) mMisIDProbability • Requirements: • / separation in 15< p <35 GeV/c with  mis-id probability <10-2 • Measure crossing time with t =100 ps • Level 0 trigger for chargedtracks Momentum (GeV) F. Bucci

  39. Photon Veto System To suppress the dominantdecay K++0 (BR 21%): • 0rejectioninefficiencyat 10-8level (  detectioninefficiencyat 10-4) • Hermetic  coverage up to 50 mrad • 3 different detectors to cover 3 differentangularregions • Large Angle Vetoes (LAV): 8.5 – 50 mrad • The NA48 Liquid krypton calorimeter (LKr): 1 – 8.5 mrad • Small Angle Vetoes:  1 mrad F. Bucci

  40. Large Angle Veto (LAV) 12 stationsformed by 4 to 5 overlappingrings of OPAL leadglasses The first eleven are part of the vacuumdecay tube, the last oneislocatedoutside the vacuum tank Inefficiency < 10-4 for 100 MeV < E < 35 GeV F. Bucci

  41. Muon Veto 3 muon veto (MUV) stations(partially re-use of the NA48 hadroncalorimeter) • MUV1+MUV2 • 24 (MUV1) and 22 (MUV2) iron/scintillatorlayers • reach a factor 106 in muonrejection (combined with the RICH) MUV 3 • MUV3 • After 80 cm iron, scintillatortiles with directphotondetection • Fast muon trigger (L0), 1 ns resolution (10 MHz muon rate) IRON MUV 2 MUV 1 F. Bucci

  42. Detector Status Detectors installed: KTAG, LAV(8/12), LKr, SAC Under construction/installation: CHANTI, STRAWS, RICH, IRC, MUV Installation completed by October 2014 F. Bucci

  43. Outline Recentresults: NA48/2 and NA62 (RKphase) • ChPTTests • LeptonFlavorUniversality Prospects: NA62 • K++ • Other rare and forbiddendecaysstudies F. Bucci

  44. LFV/LNV modes High fluxes and PID/veto capabilities of NA62 are wellsuited to look for LeptonFlavor/ LeptonNumberViolation mode bothin kaon and piondecays Expecteddecays in Fiducial Volume in 2 years of data taking: 1.21013 K+ decays, 2.5 1012 0 decays NA62 single-eventsensitivities:  10-12 for K+ decays,  10-11 for 0 decays

  45. Others F. Bucci

  46. Conclusions • More than 60 yearsaftertheirdiscovery, kaonsprovide a unique playground for testingourideas on fundamentalphysics • NA48 and NA62 collaborations are analyzing data taken in pastyears and producingvery precise results for leptonic, non-leptonic and semileptonickaondecays • The new generation NA62 apparatuswill start its data taking in fall 2014. Itsunprecedentedstatistics and itspowerful detector featureswillallow to pushfurtherourknowledge of rare (and forbidden) kaondecays F. Bucci

  47. Thankyou for yourattention F. Bucci

  48. AdditionalSlides

  49. The ChPTweakchirallagrangian • The basicS=1 O(p4) chirallagrangian can be writtenas: • 37 poorlyknown Ni coefficients and Wioperators • Combination of thesecouplings are accessible by measuringkaondecays branching ratio and formfactors F. Bucci

  50. 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

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