Hadronic physics “experimental” issues M. Sozzi NA62 Physics Handbook meeting CERN – 10/12/2009

You said hadronic decays? Hadron (/hædr:on/): thick, stout, tough, hard, messy, complicated In principle the place where most interesting things can happen But hard to make sense of them

General experimental remarks In recent times, most “important” hadronic K decay results were obtained from dedicated precision experiments, not as byproducts of experiments designed for something else. This is due to what goes under the name of “systematics” Some K experiments are more “general-purpose” than others An impressive amount of K decaying into the detector is not all

Hadronic K decays in NA62? A performing and diverse detector is there (to suppress very different decay modes) BUT you need to trigger on interesting events NA62 is (being) designed for K +  π + νν decay measurement using an unseparated hadron beam. Requirements: O(10 10 ) suppression of backgrounds Large control samples for background control Simple trigger conditions (“factorization”) Aim: trigger on (single) charged-track events with no muons, no photons and no electrons. K→πνν:17 nm Kμ2Kμ2

RICHMUVCEDARLKRSTRAWSLAV L0 CTP GbE switch PC CDR L0 trigger Trigger primitives Data EB 1 MHz O(10 MHz) O(KHz) NA62 TDAQ - OVERVIEW 1 MHz L0 L1/2 O(<1ms) 2K 1K 200 8K 13K 2.5K 60K Event rate is comparable to LHC. Trigger rate can be even higher.

Hadronic K decays? Hadronic decay modes left through the trigger? HOPEFULLY NONE So: (1) A second phase of NA62 OR (2) Think hard about trigger improvements to accommodate a few potentially very interesting modes during πνν data-taking (we ARE actively pursuing this) ALSO (3) What about a neutral K high-intensity beam?

K + hadronic decays

CP/CPT violation in ∆  Need twin beams Need absolute flux normalization: probably not possible (but see later for 2πγ) Anyway generally suppressed asymmetries

CP violation in Dalitz plot Need twin beams ∆g not necessarily the best quantity (what is “g”?) Measured interference in ππγ opens up new possibility: Δ(∂σ/∂Eγ)

∆g CPV (NA48/2) 91M events 3.1G events π±π+π–π±π+π– π±π0π0π±π0π0

∆g CPV Significant interest in a 10 –4 level experiment (NA48/2) A 10 –5 level experiment: - could possibly be achieved in terms of statistics - would require > x100 control samples - would require a new dedicated design for systematic control - questionable interest? (in view of order-of-magnitude uncertainties in SM predictions, maybe except for Δg C ) Could think of better observables in the Dalitz plot

K  2π γ Reminder: INT could give (direct) CPV O(10 -4 ) in SM (among the largest) Also one of the few places where (exploiting CPT) we might get a combined π + π 0  and π + π 0 CPV rate asymmetry with cross-normalization Separation by photon spectrum K±  π±π0K±  π±π0 Don’t forget the “usual trick”: K ±  π ± π 0 e + e – opening up the possibility for E/M interference (CPV) Added bonus: K + /K – FSI elimination with twin beams New from NA48/2:

CPV in K ± →  ±    oAsymmetry can manifest itself in rates A N and Dalitz plot A W oIf  ≠0 then  + ≠   the number of events K + →      ≠ K - →      oTheoretical range 2·10 -6 to 1·10 -5 with 50<E  * <170 MeV. oSUSY contributions can push the asymmetry to in specific region of the Dalitz plot oPresent experimental knowledge: (0.9±3.3)% PDG08 oNA48/2 limit < 1.4x % CL based on 1.08 Million events INT M. Raggi

CPV in      at NA62 Assuming K + K – beam flux (no downscale) In NA62      events: 150M K M K – Can measure rate asymmetry down to precision Can measure Dalitz plot asymmetry T *  and W Can measure the  angle in the interference term K+/K– ratio measurement can use     normalization Systematic can be pushed down to by using 4 ratio as for       M. Raggi

CPV in K ± →  ±  Present PDG have no limit on asymmetry NA48/2 can reach a % limit NA62 might get (no downscale !!!): – K+ and K- –No evidence of systematic limit on the measurement –Can push the asymmetry limit down to M. Raggi

K± →π±e+e– K± →π±μ+μ–K± →π±e+e– K± →π±μ+μ– NA48/2 reached a limit of 2.1x10 −2 at 90% CL NA62 might collect: K + and K  Can reduce present limit by 1 order of magnitude The SUSY upper limit on the range of Can measure forward backward asymmetry M. Raggi

K  3π γ Dominated by IB at O(p 4 ) for unsuppressed decays (prediction only limited by knowledge of 3π), unlikely to extract direct weak part (low-energy constants)

2π  2π2π  2π - The “classic” hard way (K e4 ) - The “new” hard way (cusps) (see G. Colangelo, B. Bloch and D. Madigojine talks) However: here also some help from our theory colleagues is needed

What about neutral K ? (the land where CP violation rules) Nothing very well thought, but NA48 switched from neutral to charged during its life, while keeping most of the setup In principle an intense neutral beam is possible Again: when speaking about neutral K non-hadronic modes come to mind: π 0 νν, π 0 e+e–, π 0 μ+μ–. Each of them (if at all feasible) would be a new experiment in itself BUT

K 0 hadronic decays KSKS KLKL

K  3π EM cluster reconstruction inefficiency 0.7% systematic error K S (CPV): CPLEAR, NA48, KLOE – different techniques “Trivial” indirect CPV expected BR(K S  3π 0 ) ≈ BR(K L  3π 0 ) |ε| 2 (τ S /τ L ) ≈ 1.9·10 −9 Direct CPV small (?) (and however not precisely predictable)

K  2π:  © P. Boyle (or <2% Re(  ) semileptonics)

K  2π:  ’ χ 2 =5.3/3, consistency 14% (was 6.2/3, consistency 10%) Re(  ’/  ) = (16.4 ± 1.9) · 10 –4 Including Δ I=3/2 correction [EPJ C36 (2004) 37] [PDG scaled error] Direct CPV at ≈ 9 σ Despite the prime importance of this 10% measurement, it is not (yet) what you would choose as a quantitative test of the SM

CPT KSKS KLKL

Bell-Steinberger KLOE+ JHEP12(2006) 011 No direct CPT assumption π+π– phase dominates No significant contribution from 3π

Guinness Book of Records CPT Á la CP/T (1999): 0.5% (KTeV, KLOE, NA48) BR 1.5% (KTeV) reg. interference 1.5% using φ00, no dir CPT and no CPV outside 2π, or use Im(x) and Im(η 3π ) (CPLEAR, NA48, KLOE) 0.3% (KTeV) reg. interference

Vacuum interference experiment (hadronic environment close to target, as done in NA48) using π+π– only: pure K 0 beam best, e.g. low energy CEX: σ(K + n → K 0 p) ~ 40mb (120 MeV/c) → 40 μb (12 GeV/c) (CP/T proposal: 25 GeV/c separated K + beam) “Planck scale” test of CPT questionable (but nice and “durable” result) CPT limit experiment As a bonus: Lorentz symmetry violation with high-energy K decays

The Next Great Hadronic K Decay Experiment is not in sight (you knew that) (Tentative) conclusions However: many interesting K measurements were not foreseen at the beginning Worth keep trying, and you can help on this