ChPT tests at NA62 Mauro Raggi, Laboratori Nazionali di Frascati On behalf of the NA62 collaboration X Th quark confinement and hadron spectrum Tum campus, Munich 8-12 October

Outline  NA48/2 and NA62 experiments at CERN SPS  K ± ChPT studies history in NA48/2  NA62 measurement of K ±    (new preliminary)  NA62 K ± e   analysis (in progress)  Ongoing investigations  Conclusion Mauro Raggi, INFN Laboratori Nazionali di Frascati 2

NA48/2 & NA62-R K detector Mauro Raggi, INFN Laboratori Nazionali di Frascati 3 Spectrometer - 4 Drift Chambers + Magnet LKr EM calorimeter Muon veto system  NA48/2 data taking  Six months in ’03 ‘04 (K ± )  (60±3) GeV beam  NA62-R K data taking:  Four months in 2007 (mostly K + only)  (74±1.4) GeV beam  NA62 data taking:  Two years starting from 2014? (K +    data)

NA62 experiment K +   Mauro Raggi, INFN Laboratori Nazionali di Frascati 4 Increase intensity of existing NA48/2 beam line by a factor 50 produce an unseparated 75-GeV K + beam: ~750 MHz beam ~ 50 MHz K + ~6 MHz decay in a 60m fiducial volume Collect 5x10 12 Kaon decays/year Tot length 270 m

The ChPT weak chiral lagrangian Mauro Raggi, INFN Laboratori Nazionali di Frascati 5  The basic  S=1 O(p 4 ) chiral lagrangian can be written as:  37 poorly known N i coefficients and W i operators  Combinations of such couplings are accessible by measuring Kaon decays branching fractions and form factors  NA48/2 and NA62 have access all the charged modes in the table with very high precision K2  K +    K 

History of NA48/2 ChPT tests Radiative decays:  K ±      EPJC 68 (2010)  First measurement the DE and INT terms:  Access to the chiral parameters (N 14 -N 15 -N 16 -N 17 )  K ±    e + e - PLB659 (2008)  First BR measurement and first determination of ĉ (N 14 -N 15 -2N 18 ) Non radiative decays:  K ±     e ±  EPJC70 (2010) , PLB 715 (2012)  Determination of the s-wave  scattering length  K ±   e + e -, K ±        PLB 677 (2009) , PLB 697 (2011) )  Discrimination among ChPT models  Access to (N 14 -N 15 ) parameters Mauro Raggi, INFN Laboratori Nazionali di Frascati 6

K     decay theory  The leading O(p 4 ) contribution is given by A(z,ĉ) (loops) which is responsible for a cusp at m  = m 2   C (WZW) corresponds to ~10% of A at O(p 4 )  B, D = O(p 4 )  The ĉ value can be related to fundamental ChPT parameters: Mauro Raggi, INFN Laboratori Nazionali di Frascati 7 In the ChPT framework the differential rate of the decay K ± (p)  ± (p 3 )  (q 1 )  (q 2 ) process (no O(p 2 ) contribution) is: [Ecker, Pich, de Rafael, Nucl. Phys. B303 (1988), 665] [D’Ambrosio, Portoles, PLB 386 (1996), 403] relevant low m  Weak Chiral Lagrangian QCD loop and counterterms

K     decay, ChPt O(p 4 ) vs O(p 6 ) 8 ChPT O(p 4 ) ChPT O(p 6 )  O(p 6 ) loop amplitude correction, evaluated from K3 O(p 4 )  O(p 6 ) A gets y dependence, sizable correction to d  /d z for z <z + Mauro Raggi, INFN Laboratori Nazionali di Frascati [D’Ambrosio, Portolés, PLB386 (1996) 403] O(p 6 ) unitarity corrections may increase the BR by 30÷40%

Present PDG average based on: E787 (1997): BR = (1.10 ± 0.32)× candidates, 5 exp. Bkg ĉ value = 1.6 ± 0.6 O(p 4 ) = 1.8 ± 0.6 O(p 6 ) K     decay experimental status 9 Mauro Raggi, INFN Laboratori Nazionali di Frascati  NA48/2 main data set preliminary 2003/2004: measurement hindered by low trigger efficiency. Abandoned!  New strategy: minimum bias trigger samples from NA48/2 and NA62.  2004 data taking (3 days special minimum bias run)  2007 data taking (3 month control trigger downscaled by 20) [PRL79 (1997) 4079]

Minimum bias data samples Mauro Raggi, INFN Laboratori Nazionali di Frascati : special run (3 days) NA48/2 2007: 3 months trigger downscaled (D≈20) NA62    candidates 147 BG(      11.0±0.8 BG(        5.9±0.7 Signal (    ) 130±12    candidates 175 BG(      11.1±1.0 BG(        1.3±0.3 Signal (    ) 163±13 ~300 candidates 10 times the present world sample

     ChPT fit O(p 6 ) Mauro Raggi, INFN Laboratori Nazionali di Frascati 11  background limits sensitivity to z ≥ data NA48/2 z = (M  /M K ) data NA62 z = (M  /M K ) 2 ChPT O(p 4 ): ĉ = 1.36 ± 0.34 ChPT O(p 6 ): ĉ = 1.67 ± 0.40 ChPT O(p 4 ): ĉ = 1.71 ± 0.30 ChPT O(p 6 ): ĉ = 2.21 ± 0.32

Fit results combined samples Mauro Raggi, INFN Laboratori Nazionali di Frascati 12 BR( K     ) = (1.01 ± 0.06)·10 –6 (NA62-RK+NA48/2 model dependent) ĉ preliminary results for combined samples (NA48/2 and NA62-RK) : Fit to ChPT O(p 4 ): ĉ = 1.56(22) stat (7) syst = 1.56(23) Fit to ChPT O(p 6 ): ĉ = 2.00(24) stat (9) syst = 2.00(26) ChPT O(p 4 ) vs O(p 6 ) models cannot be discriminated so far. Discrimination can be reached by NA62 (~50K-100K events potential) Preliminary E787: BR = (1.10 ± 0.32)×10 -6

K  e  e  decay  The decay K  e  e is highly helicity suppressed (m e 2 /m  2 )≈10 -5  IB of electron or kaon is a pure QED process (very well known)  The SD transition is not helicity suppressed as the e ±  .  SD+ and SD  : same order as IB INT: negligible Mauro Raggi, INFN Laboratori Nazionali di Frascati 13 K+K+ e+e+ e  K+K+ e+e+ e  IB SD s sese ss pp p pepe SD + : positive helicity SD  : negative helicity s sese ss pp p pepe

Decay rate theory and experiments Mauro Raggi, INFN Laboratori Nazionali di Frascati 14 At O(e 2 p 4 ), FF’s F V and F A are constant, O(e 2 p 6 ) F V has a slope : f SD+, f SD- known functions of kinematics F V, F A vector and axial form factors  KLOE measurement 2009  1484±64 events for E*  >10 MeV and p* e >200 MeV:   (SD  )/  (SD  ) ~ 4% with 1500 cts, bkg contributes to error  No sensitivity to SD   Fair agreement with  Pt O(p 4 )  Data favour slope for F V, = 0.38(20) sta (2) syst, but can’t state >2  EPJC 64 (2009) 627

K  e  e  decay NA62 analsys  Selection of SD component, many steps common to the R K analysis     , Ke3 backgrounds photon explicitly detected + tighter e PID  ~10K events with P* e >234 MeV, ~ 7% acc., ~5% bkg  Analysis in progress, plan is to perform a model-independent FF measurement Mauro Raggi, INFN Laboratori Nazionali di Frascati 15 Very preliminary

Next to come… K ±           e + e   As other radiative decays K ±     e + e  is  long-distance dominated:  Electric interference can be used to confirm the measurement made in       Magnetic interference is genuine  ee and can be used to extract the sign of the magnetic term.  P violating observables in the dilepton pair coupling can be used to access short distance physics using K + only (NA62)  Charge asymmetry not contaminated by indirect CP violation (as in K 0 )  Never observed so far:  Few thousand candidates already identified in NA48/2 data sample  Up to ~100K can be expected in NA62 Mauro Raggi, INFN Laboratori Nazionali di Frascati 16 EPJC (2012) 72:1872

Conclusion  NA48/2 and NA62 gave an important contribution to ChPT test at low energies measuring kaon decays:      ,    e + e       e ± v e,  ± e + e ,        Recent preliminary result has been released on    :  BR( K     ) = (1.01 ± 0.06)·10 –6  ĉ = 1.56(22) stat (7) syst = 1.56(23) O(p 4 ) FIT  ĉ = 2.00(24) stat (9) syst = 2.00(26) O(p 6 ) FIT  Advanced analysis is in progress in the e + e  SD  channel  Improved precision in all the channels is possible in the NA62  At least 1 order of magnitude higher statistics (1x10 13 K + in 2 years)  Better particle ID and photon rejection  Due to trigger bandwidth not all decays will be collected  Any theoretical input on interesting measurements is welcome Mauro Raggi, INFN Laboratori Nazionali di Frascati 17