Kaon experiments at CERN: recent results & prospects Evgueni Goudzovski (University of Birmingham) Outline: 1) K decay experiments at CERN: NA48/2, NA62-R K , NA62 2) NA62 status and data quality 3) Recent results from Birmingham-led analyses 4) Conclusions Particle physics seminar University of Birmingham 2 November 2016 0
Energy & precision frontiers Discovery of a Higgs boson : success of the Standard Model (SM) No roadmap and “guaranteed discoveries” any longer: a data -driven era Limitations of the SM: “New physics” extensions: SM matter 5% of total mass-energy undiscovered particles Searches for New physics: two complementary approaches Precision (intensity) frontier Energy frontier (LHC) Low-energy observables: Direct production of new particles tests of precise SM predictions in high-energy collisions. for rare or forbidden processes. A collective effort A unique effort 1 E. Goudzovski / Birmingham, 2 November 2016
The precision frontier: kaon physics The kaon: One of the lightest unstable particles (discovered in 1947); the “ minimal flavour laboratory ”. High production rates: high statistical precision. An example of rare K decay measurement: BR(K L e + e ) = (9 5)×10 12 . (BNL E871) Essential in establishing the foundations of particle physics (quark mixing, CPV). Current focus: searches for new physics Example: with rare and forbidden decays. Tree-level process: X g X g X For and , 2 E. Goudzovski / Birmingham, 2 November 2016
Kaon physics facilities BNL CERN IHEP Protvino E865, E777, E787, E949 NA48, NA62 , LHCb ISTRA+, OKA, KLOD FNAL LNF KEK/J-PARC KTeV KLOE, KLOE-2 E391a, KOTO , TREK A variety of experimental techniques: K decay-in-flight (e.g. at CERN), stopped K + , factory 3 E. Goudzovski / Birmingham, 2 November 2016
Kaon experiments at CERN 4 E. Goudzovski / Birmingham, 2 November 2016
Kaon programme at CERN Earlier: NA31 1997: ’/ : K L +K S 1998: K L +K S Jura mountains France 1999: K L +K S K S HI NA48 NA48/NA62: discovery 2000: K L only K S HI centre of the LHC Switzerland SPS of direct CPV 2001: K L +K S K S HI LHC NA48/1 2002: K S /hyperons 2003: K + /K − NA48/2 2004: K + /K − N Geneva airport 2007: K e2 /K 2 tests NA62 R K phase 2008: K e2 /K 2 tests 2014: pilot run NA62 Kaon decay in flight experiments. 2015 : data taking NA62: currently ~200 participants, ~30 institutions 5 E. Goudzovski / Birmingham, 2 November 2016
K decay experiments at CERN Experiment NA48/2 NA62 (R K phase) NA62 (K ) (K ) (K + ) 2003 2004 2007 2008 2015 2018 Data taking period Beam momentum, GeV/c 60 74 75 RMS momentum bite, GeV/c 2.2 1.4 0.8 Spectrometer thickness, X 0 2.8% 2.8% 1.8% Spectrometer P T kick, MeV/c 120 265 270 M(K + ) resolution, MeV/c 2 1.7 1.2 0.8 K decays in fiducial volume 2×10 11 2×10 10 1.2×10 13 Main trigger multi-track; Min.bias + K + … K 0 0 e The NA48 detector The NA62 experiment New detector Main goal: collect 100 SM K + + decays, BR SM =(9.11 0.72)×10 11 . Buras et al., JHEP 1511 (2015) 033 +1.15 Current K + + experimental status: BR = (1.73 ) 10 10 from 1.05 7 candidates with expected background of 2.6 observed by BNL-E949. 6 PRL101 (2008) 191802 E. Goudzovski / Birmingham, 2 November 2016
NA48/2 and NA62-R K experiments 2003 – 2007: charged kaon beams, the NA48 detector Narrow momentum band K beams: P K = 60 (74) GeV/c , P K /P K ~ 1% (rms). Maximum K decay rate ~100 kHz ; NA48/2: six months in 2003 04; NA62-R K : four months in 2007. Principal subdetectors: Magnetic spectrometer (4 DCHs) 4 views/DCH: redundancy efficiency; p/p = 0.48% ⨁ 0.009%p [GeV/c] (in 2007) Scintillator hodoscope (HOD) Fast trigger, time measurement ( 150ps ). Liquid Krypton EM calorimeter (LKr) Vacuum High granularity, quasi-homogeneous; beam pipe E /E = 3.2%/E 1/2 ⨁ 9%/E ⨁ 0.42% [GeV]; x = y =4.2mm/E 1/2 ⨁ 0.6mm ( 1.5mm@10GeV ). 7 E. Goudzovski / Birmingham, 2 November 2016 Beam
The NA62 experiment Un-separated hadron (p/ + /K + ) beam. Total length: ~270m 400GeV SPS protons (10 12 /spill); K + : 75GeV/c ( ± 1%), divergence < 100 rad. SAV: 800MHz beam rate 45MHz K + rate Small Angle Photon Veto 5MHz K + decays in fiducial volume Vacuum tank GTK: beam NA62UK Hodoscope spectrometer KTAG Vacuum: p<10 – 5 mbar (Cherenkov kaon tagger) Anti- <80ps timing counters Beam <80ps timing pipe Decay region: L=65m Expected single event sensitivities: ~10 12 for K decays, ~10 11 for 0 decays. Kinematic rejection factors (limited by beam pileup and tails of MCS): 5×10 3 for K + + 0 , 1.5×10 4 for K + . Hermetic photon veto: ~10 8 suppression of 0 . Particle ID (RICH+LKr+MUV): ~10 7 muon suppression. 8 E. Goudzovski / Birmingham, 2 November 2016
Rare kaon decays: K SM: box and penguin diagrams SM branching ratios Ultra-rare decays with Buras et al., JHEP 1511 (2015) 033 the highest CKM suppression: BR SM 10 11 Mode A ~ (m t /m W ) 2 |V ts V td | ~ 5 * K + + ( ) 9.11 0.72 K L 0 3.00 0.31 Hadronic matrix element is related The uncertainties are largely to a measured quantity ( K + 0 e + ). parametric (CKM) SM precision surpasses any other FCNC process involving quarks. Theoretically clean, Measurement of |V td | complementary almost unexplored, to those from B B mixing or B 0 . sensitive to new physics. 9 E. Goudzovski / Birmingham, 2 November 2016
K : experiment vs theory CKM unitarity triangle with kaons BR(K L 0 ) vs BR(K + + ) Current experimental uncertainty (littlest Higgs D. Straub with T parity ) CKM 2010 NA62 aim: collect O(100) SM K + + decays with <20% background in 3 years of data taking using a novel decay-in-flight technique. Signature: high momentum K + ( 75GeV/c ) low momentum + ( 15 35 GeV/c ). max detected K + decays/proton ( p K /p 0 0.2 ); Advantages: efficient photon veto ( >40 GeV missing energy) Un-separated beam ( 6% kaons) high rates, additional background sources. 10 E. Goudzovski / Birmingham, 2 November 2016
NA62 physics programme NA62 Run 2 (2015 2018) : focused on the “golden mode” K + + . Trigger bandwidth for other physics is limited. Several measurements at nominal SES~10 12 : K + + A’ , 0 . A few measurements do not require extreme SES: K + ℓ + H , … In general, limited sensitivities to rare/forbidden decays ( SES~10 10 to ~10 11 , similar to NA48/2 and BNL-E865). A proof of principle for a broad rare/forbidden decay programme. NA62 Run 3 (2021 2024) : programme is under discussion. [Presented at “Physics Beyond C olliders” workshop, CERN, Sep 2016] Existing apparatus, different trigger logic: no capital investment . Rare/forbidden K + and 0 decays at SES~10 12 : K + physics: K + + ℓ + ℓ , K + + ℓ + ℓ , K + ℓ + , K + + , … 0 physics: 0 e + e , 0 e + e e + e , 0 3 , 0 4 , … Searches for LFV/LNV: K + ℓ + ℓ + , K + + e , 0 e , … Possibly K L rare decays ( SES~10 11 ), including K L 0 ℓ + ℓ [CPV]. Dump mode: hidden sector searches (long-lived HNL, DP , ALP). 11 E. Goudzovski / Birmingham, 2 November 2016
The lepton programme Neutrino oscillations discovery (1998) e + First non-SM phenomenon: 1) Lepton Flavour Violation; e 2) non-zero neutrino mass. Neutrino source Neutrino detector New physics scenarios involving LFV : # Neutrino is a Majorana fermion (identical to antineutrino) Heavy (possibly sterile) neutrino states Astrophysical consequences: Dark matter, nucleosynthesis, Supernova evolution, ... Birmingham-led programme (supported by ERC starting grant): search for forbidden states with lepton pair ( ee , , e ) 12 E. Goudzovski / Birmingham, 2 November 2016
NA62 status & data quality 13 E. Goudzovski / Birmingham, 2 November 2016
Data collection K + + + signal (2016) Rare decay: BR~10 7 Minimum bias ( ~1% intensity) and K test data collected in 2015 Most systems commissioned and meet the design requirements Beam time in 2016 : 3 May 14 November . running at ~35% of the nominal intensity now (limited by SPS capability) Long (~6 months) runs scheduled in 2017 and 2018 . Expect to reach a few SM K events sensitivity with 2016 data 14 E. Goudzovski / Birmingham, 2 November 2016
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