ULTRA-RARE KAON DECAY FOR A PRECISION TEST OF THE STANDARD MODEL

K R I S T I N S C H I M E R T

U N I V E R S I T Y O F C A L I F O R N I A , B E R K E L E Y

P H Y S I C S 1 2 9

7 D E C E M B E R 2 0 1 0

K+ → π+ ν`ν

Kristin Schimert

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Overview

1) Motivation

2) Goals

3) Theoretical background: see Francisco’s presentation

4) Experimental strategy

5) Detectors

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K+ → π+ ν`ν

Kristin Schimert

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Why study rare kaon decays?

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1) Explicit violations of the Standard Model (SM)

2) SM parameters

3) CP Violation

4) Strong interactions at low energy

Most common kaon decays:

Kristin Schimert

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The NA62 experiment

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NA62 Collaboration: Bern ITP, Birmingham, Bristol, CERN, Dubna, Ferrara, Fairfax, Florence, Frascati, Glasgow, IHEP, INR, Liverpool, Louvain, Mainz, Merced, Naples, Perugia, Pisa,Rome I, Rome II, San Luis Potosi, SLAC, Sofia, TRIUMF, Turin

Kristin Schimert

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Motivation for using K+ → π+ ν`ν

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• Excellent process to study flavor physics because of clean nature• Dominated by short-distance dynamics• Mainly one-loop diagrams with top-quark intermediate states

• High theoretical precision

• But most precise experimental result (at BNL) is

Gap between theoretical precision and experimental error: strong motivation for experimental precision

• Extract 10% precision measurement of CKM parameter |Vtd|• Deviation from theory indicates new physics

Kristin Schimert

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Experimental goals

Collect about 80 events with signal:background ratio of 10:1 in two years of data taking Requires 1013 K+ decays

with a branching ratio of 10-10

Construction criteria: kaon intensity, signal acceptance, background suppression

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Kristin Schimert

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Experimental strategy

400 GeV/c protons from CERN SPS hit a beryllium target, producing a secondary charged beam of 75 GeV/c (K+, π+, p+)

Signature of signal = a single π+ track reconstructed downstream of the decay volume and matched to a K+ track upstream

Need timing, spatial and angular info to match π+ and K+ tracks7 December 2010

Kristin Schimert

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CERN SPS

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NA62

Kristin Schimert

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Detector overview

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Tracking devices for both K+ and π+

Calorimeters to veto photons, positrons, and muonsParticle identification systems to identify incident kaons

and to distinguish π+ from μ+ and e+

Guiding principles for construction of NA62 detectors: “accurate kinematic reconstruction, precise particle timing, efficiency of the vetoes, and excellent particle identification”

Kristin Schimert

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Kinematic rejection

7 December 2010rejects more than 90% of K+ decays!

Kristin Schimert

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Detector overview

http://na62.web.cern.ch/na62/Documents/MaterialPresentationSchemas.html 7 December 2010

Kristin Schimert

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Detector layout

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Large-angle photon veto

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γγ

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Large-angle veto

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Kristin Schimert 15

References

1. Proposal to measure the rare decay K+ → π+ ν`ν at the CERN SPS http://na62.web.cern.ch/na62/Documents/Proposal%20spsc-2005-013.pdf

2. Technical Design Documenthttp://na62.web.cern.ch/NA62/Documents/TD_Full_doc_v10.pdf

3. The accelerator complexhttp://public.web.cern.ch/public/en/research/AccelComplex-en.html

4. Rare kaon decayshttp://pdg.lbl.gov/2009/reviews/rpp2009-rev-rare-kaon-decays.pdf

5. Super proton synchroton marks its 25th birthdayhttp://cerncourier.com/cws/article/cern/28470

7 December 2010