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Measurement ofBR(K → eν)/BR(K → μν)

Phil Rubin

for the NA62 (CERN) Collaboration

Ultra-rare Kaon Decays

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Leptonic Decays

● Test theoretical tools● Search for new physics

━ Rates━ Lepton Universality

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Lepton Universality

[a few %]

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New Physicseg., MSSM

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Experimental Status

PDG '08 (based on '70s measurements)

KLOE '09~14K Ke2 events

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NA62(Phase I: Using the NA48 Detector)

● ~150 K Ke2 events

● < 10% background

● δRK/RK < 0.5%

Goal:

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Data Taking and Analysis

● 4-month run in 2007; 2-week (systematics) run in 2008

● Simultaneous Ke2 – Kμ2 collection

●

● RK calculated in 10 momentum bins (account for background-momentum dependencies)

● Primary systematic: NB(Ke2)

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Event Selection

● Kinematics

━ Good for pℓ < 25 GeV/c

● E/p

━ e: 0.9 < E/p < 1.1

━ μ: E/p < 0.85

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40% of the Data, Preliminary

~51 K Ke2 events, ~8% background

x5 x25 x5

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Preliminary Result

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RK Conclusion

● Measurement agrees with Standard Model prediction to 1.5σ

● Total NA62 data set will yield 0.4%-0.5% measurement.

0 100 200 300 400 500 600 700 800 900 1000

02

04

06

08

01

00

Charged Higgs Mass [GeV/c2]

tan

β

tan β vs mH

(95% Exclusion Limits)

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● Strongly suppressed

● Calculable with uncertainty O(10%)

● Very sensitive to new physics

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NA62● 10% measurement of

━ 1013 kaon decays (2 yrs); 10% bkgd uncertainty

● Decay-in-flight from high momentum beam● High resolution and hermiticity

━ 92% of Γ constrained kinematically━

━ Timing to match Kπ━ Veto photons and muons

● Particle identification

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NA62 Detector Layout

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Source Events/yrSignal 55Background 7.5-9.4

Channel Fraction (%)4.3-7.5

2.2≤3

≤1.5~2

~0.7

Schedule and Sensitivity

● First data in second half of 2012