1. ULTRA-RARE KAON DECAY FOR A PRECISION TEST OF THE STANDARD MODEL KRISTIN SCHIMERT UNIVERSITY OF CALIFORNIA, BERKELEY PHYSICS 129 7 DECEMBER 2010 K + → π + ν  ν

2. Overview 2 1) Motivation 2) Goals 3) Theoretical background: see Francisco’s presentation 4) Experimental strategy 5) Detectors Kristin Schimert 7 December 2010 K + → π + ν  ν

3. Why study rare kaon decays? 7 December 2010 Kristin Schimert 3 1) Explicit violations of the Standard Model (SM) 2) SM parameters 3) CP Violation 4) Strong interactions at low energy Most common kaon decays:

4. The NA62 experiment 7 December 2010 Kristin Schimert 4 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

5. Motivation for using K + → π + ν  ν 7 December 2010 Kristin Schimert 5 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 |V td | Deviation from theory indicates new physics

6. Experimental goals 6 Collect about 80 events with signal:background ratio of 10:1 in two years of data taking  Requires 10 13 K + decays with a branching ratio of 10 -10 Construction criteria: kaon intensity, signal acceptance, background suppression Kristin Schimert 7 December 2010

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 7 Kristin Schimert 7 December 2010

8. CERN SPS 7 December 2010 Kristin Schimert 8 NA62

9. Detector overview 7 December 2010 Kristin Schimert 9 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”

10. Kinematic rejection 7 December 2010 Kristin Schimert 10 rejects more than 90% of K+ decays!

11. Detector overview 11 http://na62.web.cern.ch/na62/Documents/MaterialPresentationSchemas.html Kristin Schimert 7 December 2010

12. Detector layout 7 December 2010 Kristin Schimert 12

13. Large-angle photon veto 7 December 2010 Kristin Schimert 13 γγ

14. Large-angle veto 7 December 2010 Kristin Schimert 14

15. References 1. Proposal to measure the rare decay K + → π + ν  ν at the CERN SPS http://na62.web.cern.ch/na62/D ocuments/Proposal%20spsc- 2005-013.pdf 2. Technical Design Document http://na62.web.cern.ch/NA62/D ocuments/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 25 th birthday http://cerncourier.com/cws/articl e/cern/28470 7 December 2010Kristin Schimert15