ultra-rare kaon decay For a precision test of the standard model Kristin Schimert

1. K+ → π+ ν`ν ultra-rare kaon decay For a precision test of the standard model Kristin Schimert University of california, berkeley Physics 129 7 December 2010

2. Overview Motivation Goals Theoretical background: see Francisco’s presentation Experimental strategy Detectors K+ → π+ ν`ν Kristin Schimert

3. Why study rare kaondecays? Explicit violations of the Standard Model (SM) SM parameters CP Violation Strong interactions at low energy Most common kaon decays: Kristin Schimert

4. The NA62 experiment 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

5. Motivation for using K+ → π+ ν`ν • 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

6. 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 Kristin Schimert

7. 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+ tracks Kristin Schimert

8. CERN SPS NA62 Kristin Schimert

9. Detector overview Tracking devices for both K+ and π+ Calorimeters to veto photons, positrons, and muons Particle 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

10. Kinematic rejection rejects more than 90% of K+ decays! Kristin Schimert

11. Detector overview Kristin Schimert http://na62.web.cern.ch/na62/Documents/MaterialPresentationSchemas.html

12. Detector layout Kristin Schimert

13. Large-angle photon veto γγ Kristin Schimert

14. Large-angle veto Kristin Schimert

15. References 1. Proposal to measure the rare decay K+ → π+ ν`νat the CERN SPS http://na62.web.cern.ch/na62/Documents/Proposal%20spsc-2005-013.pdf 2. Technical Design Document http://na62.web.cern.ch/NA62/Documents/TD_Full_doc_v10.pdf 3. The accelerator complex http://public.web.cern.ch/public/en/research/AccelComplex-en.html 4. Rare kaon decays http://pdg.lbl.gov/2009/reviews/rpp2009-rev-rare-kaon-decays.pdf 5. Super proton synchroton marks its 25th birthday http://cerncourier.com/cws/article/cern/28470 Kristin Schimert