A precision test of lepton universality A precision test of lepton universality in K K + → l l + ν decays at CERN NA62 + → + ν in decays at CERN NA62 E vgueni Goudzovski (Univer sity of Bir mingham) email: eg@hep.ph.bham.ac .uk Outline: 1) Purely leptonic meson decays: why interesting? 2) Overview of kaon experiments at CERN 3) Analysis of NA62 dedicated K + → l + ν sample 4) Competitors, comparison to world data 5) The future: NA62 phase II 6) Summary Par tic le Physic s Se minar , Unive r sity of Bir mingham 1 12 May 2010
Leptonic meson decays: physics interest 2 E. Goudzovski / Birmingham, 12 May 2010 E. Goudzovski / Birmingham, 12 May 2010
Flavour physics in the LHC era Flavour physics in the LHC era Searches for physics beyond the Standard Model Rarity (High Intensity) Frontier Determine the flavour structure of NP via Energy Frontier (LHC) virtual effects in precision observables: Determine the energy scale of NP deviations from precise SM predictions in by direct production of NP particles rare or forbidden processes. LVF in A unique effort A collective effort μ and τ decays CP violation in B and K systems Neutron EDM Universality tests in B and K (g–2) μ Rare B and K decays Improved CKM fits Physics programme at the Rarity Frontier is complementary to direct searches for new physics at the Energy Frontier 3 E. Goudzovski / Birmingham, 12 May 2010 E. Goudzovski / Birmingham, 12 May 2010
→ l ν Leptonic meson decays: P P + l + Leptonic meson decays: + → + ν e+ µ + , Angular momentum conservation � suppressed SM contribution s + H + K (Higgs) Models with two Higgs doublets (2HDM-II including SUSY): u , ν ν sizeable charged Higgs (H ± ) exchange contributions e µ PRD48 (1993) 2342; Prog.Theor.Phys. 111 (2004) 295 =500GeV/ c 2 , tan β (numerical examples for M H = 40) R=Br(K →μν )/Br(K e3 ): π + → l ν : ΔΓ / Γ SM ≈ –2(m π /m H ) 2 m d /(m u +m d ) tan 2 β ≈ –2 × 10 –4 ( δ R/R) exp =1.0% K + → l ν : ΔΓ / Γ SM ≈ –2(m K /m H ) 2 tan 2 β ≈ –0.3% D + → l ν : ΔΓ / Γ SM ≈ –2(m D /m H ) 2 (m s /m c ) tan 2 β ≈ –0.4% s B + → l ν : ΔΓ / Γ SM ≈ –2(m B /m H ) 2 tan 2 β ≈ –30% BaBar, Belle: Br exp (B →τν )=(1.42 ± 0.43) × 10 –4 ΔΓ / Γ SM =1.07 ± 0.37 Br SM (B →τν )=(1.33 ± 0.23) × 10 –4 Standard Model: (JHEP 0811 (2008) 42) (SM uncertainties: δ f B /f B =10%, δ |V ub | 2 /|V ub | 2 =13%) Not hopeless, but obstructed by hadronic uncertainties 4 E. Goudzovski / Birmingham, 12 May 2010 E. Goudzovski / Birmingham, 12 May 2010
R =K /K in the SM R =K /K in the SM K e2 μ 2 2 K e2 μ Observable sensitive to lepton flavour violation and its SM expectation: (similarly, R π in the pion sector) Radiative correction (few %) due to K + → e + νγ (IB) process, by definition included into R K Helicity suppression: f~ 10 –5 s ν s e e+ µ + , s + + K + e ν e W + K • SM prediction: excellent sub-permille accuracy u , due to cancellation of hadronic uncertainties. ν ν e µ • Measurements of R K and R π have long been R K = (2.477 ± 0.001) × 10 –5 considered as tests of lepton universality. SM R π = (12.352 ± 0.001) × 10 –5 SM • Recently understood: helicity suppression of R K might enhance sensitivity to non-SM Phys. Lett. 99 (2007) 231801 effects to an experimentally accessible level. 5 E. Goudzovski / Birmingham, 12 May 2010 E. Goudzovski / Birmingham, 12 May 2010
R =K /K beyond the SM R =K /K beyond the SM K e2 μ 2 2 K e2 μ PRD 74 (2006) 011701, (including SUSY) JHEP 0811 (2008) 042 2HDM-I I : tree level e+ The charged Higgs H ± exchange contribution Δ 13 s + ��� ��� is flavour-independent ~ ��� ��� ��� ��� H ��� ��� ~ + l � Does not affect the ratio R K K B (Slepton) (Higgs) (Bino) ~ u ν 2HDM-I I : one-loop level ν (Sneutrino) τ Dominant contribution to Δ R K : H ± mediated LFV (rather than LFC) with emission of ν τ Analogous SUSY effect � R K enhancement can be experimentally accessible in pion decay is suppressed by a factor (M π /M K ) 4 ≈ 6 × 10 –3 (see also PRD76 (007) 095017) Large effects in B decays ~1% effect in large (but not extreme) due to (M B /M K ) 4 ~10 4 : tan β regime with a massive H ± B μν /B τν � ~50% enhancement; Example: B e ν /B τν � enhanced by ( Δ 13 =5 × 10 –4 , tan β =40, M H =500 GeV/c 2 ) ~one order of magnitude. lead to R K = R K SM (1+0.013). MSSM Out of reach: Br SM (B e ν ) ≈ 10 –11 6 E. Goudzovski / Birmingham, 12 May 2010 E. Goudzovski / Birmingham, 12 May 2010
R & R : experimental status R K & R : experimental status π K π Kaon experiments: R K world average (March 2009) � PDG’08 average (1970s measurements): R K =(2.45 ± 0.11) × 10 –5 ( δ R K /R K =4.5%) � Recent improvement: KLOE (Frascati). Data collected in 2001–2005, 13.8K K e2 candidates, 16% background. R K =(2.493 ± 0.031) × 10 –5 ( δ R K /R K =1.3%) (EPJ C64 (2009) 627) � NA62 current goal: dedicated data taking strategy, ~150K K e2 candidates, <10% background, δ R K /R K <0.5% : a stringent SM test. Pion experiments: � PDG’08 average (1980s, 90s measurements): R π =(12.30 ± 0.04) × 10 –5 ( δ R π /R π =0.3%) � Current projects: PEN@PSI (stopped π ) running (arXiv:0909.4358) PIENU@TRIUMF (in-flight) proposed (T. Numao, PANIC’08 proceedings, p.874) δ R π /R π ~0.05% foreseen (similar to SM precision) 7 E. Goudzovski / Birmingham, 12 May 2010 E. Goudzovski / Birmingham, 12 May 2010
Kaon experiments at CERN: NA48 and NA62 8 E. Goudzovski / Birmingham, 12 May 2010 E. Goudzovski / Birmingham, 12 May 2010
CERN NA48 and NA62 CERN NA48 and NA62 Earlier: NA31 1997: ε ’/ ε : K L + K S Jura mountains 1998: K L + K S France NA48 1999: K L + K S K S HI NA48/NA62: discovery centre of the LHC Switzerland of direct SPS 2000: K L only K S HI CPV LHC 2001: K L + K S K S HI NA48/1 2002: K S / hyperons 2003: K + / K – N NA48/2 Geneva airport 2004: K + / K – 2007: K ± / K ± tests NA62 μ 2 e2 (phase I) 2008: K ± / K ± tests μ 2 e2 NA62 phase I: Bern ITP, Birmingham, CERN, Dubna, Fairfax, 2007–2012: Ferrara, Florence, Frascati, IHEP Protvino, INR Moscow, Louvain, NA62 design & construction Mainz, Merced, Naples, Perugia, Pisa, Rome I, Rome II, Saclay, (phase II) 2013–2015: San Luis Potosí, SLAC, Sofia, TRIUMF, Turin K + →π + νν 9 data taking E. Goudzovski / Birmingham, 12 May 2010 E. Goudzovski / Birmingham, 12 May 2010
NA48/NA62 K ± beam line NA48/NA62 K ± beam line Kaon decays in flight: beamline+ setup are ~ 700 feet long 10 E. Goudzovski / Birmingham, 12 May 2010 E. Goudzovski / Birmingham, 12 May 2010
NA62 (phase I) K + beam line NA62 (phase I) K + beam line 2·10 12 protons Most data taken with Unseparated beam: π / K= 13 (400 GeV) per spill the K + beam only used 1.3M K + / SPS spill (lower halo background) Momentum selection (74.0 ± 1.6) GeV/ c magnet K + vacuum vacuum K + BM vacuum beam pipe vacuum beam pipe Be target z K − K − Second achromat • Cleaning • Beam spot: 7x7mm (rms). Beam spectrometer Front-end Quadrupole 18% of kaons decay in achromat was installed quadruplet the 114m long vacuum tank. in 2003-04 • Focusing • μ vacuum He tank sweeping 10 cm tank + spectrometer 1cm not to scale 11 50 100 200 250 m E. Goudzovski / Birmingham, 12 May 2010 E. Goudzovski / Birmingham, 12 May 2010
Data taking & detector: 2007/08 Data taking & detector: 2007/08 Data taking • Four months in 2007: ~400K SPS spills, ~400K SPS spills, ~300TB of raw data handled ~300TB of raw data handled • Two weeks in 2008: dedicated data sets allowing reduction dedicated data sets allowing reduction of the systematic uncertainties. of the systematic uncertainties. Principal subdetectors for R K : • Magnetic spectrometer (4 DCHs): 4 views/DCH: redundancy redundancy ⇒ ⇒ 4 views/DCH: efficiency; efficiency; Δ p/p = 0.47% + 0.020%*p [ Δ p/p = 0.47% + 0.020%*p [GeV/c GeV/c] ] • Hodoscope Vacuum beam pipe: fast trigger, precise t measurement (150ps). fast trigger, precise t measurement (150ps). non-decayed kaons • Liquid Krypton EM calorimeter (LKr) High granularity granularity, , quasi quasi- -homogeneous homogeneous; ; High σ σ /E = 3.2%/E /E = 3.2%/ E 1/2 + 9%/E + 0.42% [GeV + 9%/E + 0.42% [ GeV]; ]; 1/2 Decay volume E E He filled tank, σ = σ σ =0.42/E 1/2 + 0.6mm (1.5mm@10GeV). σ = =0.42/E 1/2 + 0.6mm (1.5mm@10GeV). is upstream x y x y atmospheric pressure 12 E. Goudzovski / Birmingham, 12 May 2010 E. Goudzovski / Birmingham, 12 May 2010
Electromagnetic LKr LKr calorimeter Electromagnetic calorimeter Depth: 27X 0 (127cm) Transversal segmentation: 13,248 cells (2 × 2cm 2 ), no longitudinal segmentation. Essential for the present analysis: (1) positron/muon identification (2) photon veto. 13 E. Goudzovski / Birmingham, 12 May 2010 E. Goudzovski / Birmingham, 12 May 2010
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