Paolo Valente – INFN Roma – 1 BEACH 2006, Lancaster University Future rare kaon decays experiments How will the UT look like in years >2010?…

Paolo Valente – INFN Roma – 2 BEACH 2006, Lancaster University Why study rare K decays in the LHC era?  Are K rare decays still interesting?  More importantly, will it be worth to study them in the years of LHC? Theory tells us: yes, a few K rare decays are – and will be – still very interesting because:  There could be more degrees of freedom near the electroweak scale, i.e. New Physics beyond the SM  We know very well the flavour mixing, but we still do not understand the underlying mechanism Rare K decays are the ideal tools

Paolo Valente – INFN Roma – 3 BEACH 2006, Lancaster University Why study rare K decays in the LHC era? Rare K decays are the ideal tools:  Mediated by Flavour Changing Neutral Currents  Strongly suppressed by the hierarchy in the CKM matrix  Theoretically clean since dominated by short-distance contributions In other words, from K rare decays we can extract information on the flavour structure of New Physics sd V td V ts *

Paolo Valente – INFN Roma – 4 BEACH 2006, Lancaster University Flavour mixing - 3 generations (implying CP violation is possible) - hierarchy  Quark mixing is described by the Cabibbo-Kobayashi-Maskawa (CKM) matrix  Success of the Standard Model:  Direct CP violation in the K system:  ’   0 [NA48, KTeV]  CP violation in the B sector: A CP (J/  K s ), [BaBar, Belle]  Now we need precise determinations of the CKM parameters:  Use observables with small theoretical errors Im t = Im V ts *V td ≠ 0

Paolo Valente – INFN Roma – 5 BEACH 2006, Lancaster University UT fits  Constraints from |V ub | / |V cb |, Δm Bd and Δm Bs compared with constraints from CP violating quantities in the K (ε K ) and in the B (sin2β) sectors  Constraints from |V ub | / |V cb |, Δm Bd and Δm Bs compared with constraints from CP violating quantities in the K (ε K ) and in the B (sin2β) sectors ρ = ± η = ±  95% confidence regions extracted using |V ub | / | V cb |, ε K, Δm Bd, Δm Bs and sin2β ρ = ± η = ± 0.028

Paolo Valente – INFN Roma – 6 BEACH 2006, Lancaster University K L   e  e  K L   vv UT and rare K decays K L     K    vv  Already strong bounds on the unitarity triangle come from K and B  F=2 and tree level transitions  FCNC transitions can tell us more… Im t = A 2 5  Re t = A 2 5  Enhanced sensitivity to SM violations because of strong CKM suppression ~ Enhanced sensitivity to SM violations because of strong CKM suppression ~ 5

Paolo Valente – INFN Roma – 7 BEACH 2006, Lancaster University New Physics potential  Second order weak interactions sensitive to NP  A deviation from the predicted rates of SM would be a clear indication of NP  Complementary program to the high-energy frontier:  If [When!] new physics will appear at the LHC, rare decays may help to understand the nature of it

Paolo Valente – INFN Roma – 8 BEACH 2006, Lancaster University New Physics scenario VtdVtdVtdVtd Vts*Vts*Vts*Vts* sd sd Is flavour mixing completely governed by universal CKM matrix?Is flavour mixing completely governed by universal CKM matrix?  No extra complex phases  Same operators as in Standard Model, but with different coefficients  High correlation between K and B rare decays yes Minimal flavour violation (MFV)  Extra phases - can lead to large deviations from SM prediction (especially for the CP-violating modes) no New flavour simmetry breaking,  ~ 1 TeV natural scale

Paolo Valente – INFN Roma – 9 BEACH 2006, Lancaster University  Expected improvements NNLO calculation + reduction parametric CKM uncertainties  2 % error expected in the next few years K + →  + : SM prediction The hadronic matrix element can be extracted from the well measured K + →   e + The hadronic matrix element can be extracted from the well measured K + →   e + Small theoretical uncertainty, no long distance contributions QCD NLO Buchalla, Buras 1999 = C + A 4 [       ] = (8.0±1.0)  BR SM (K    )

Paolo Valente – INFN Roma – 10 BEACH 2006, Lancaster University  Expect to be completely dominated by parametric CKM uncertainties [V td and m t ] in the next few years  The cleanest mode! K L →  0 : SM prediction BR SM (K L   ) = C 0 [Im(V ts * V td )/10 -4 ] 2 = (3.0±0.6)  Already at the level of 2 % Already at the level of 2 %

Paolo Valente – INFN Roma – 11 BEACH 2006, Lancaster University So, why study rare K decays in the LHC era? 1.Search for explicit violation of Standard Model Lepton Flavour Violation 2.Study the strong interactions at low energy Chiral Perturbation Theory, Form Factors 3.Test fundamental symmetries CP,CPT 4.Probe the flavour sector of the Standard Model FCNC 1 st ingredient: Physics!  K L →   l  l    K L →    K + →    are the golden modes… BR ~ or below few % precision desirable to match the theoretical error  Need very intense kaon beams  Need dedicated detectors with exceptional background rejection …moreneeded!

Paolo Valente – INFN Roma – 12 BEACH 2006, Lancaster University Rare K decays panorama p K =10 GeV 38M/s separated, p K =22 GeV 9 M/s unseparated, p K =45 GeV 3.5 M/s p K =0.7 GeV 33 M/s unseparated, p K =75 GeV 9 M/s p K =2 GeV 0.6 M/s p K =2 GeV 320 M/s KK KK stopped K separated, p K =15 GeV 0.4 M/s p K =0.6 GeV 2.3 M/s 7 M/s JPARC is coming … you’ve heard from Tadashi Nomura you’ve heard from Tadashi Nomura I will concentrate on P326 in the following

Paolo Valente – INFN Roma – 13 BEACH 2006, Lancaster University P326: K  →   at the CERN SPS… 400 GeV protons from the SPS, producing an high intensity kaon beam 2 nd ingredient: The beam

Paolo Valente – INFN Roma – 14 BEACH 2006, Lancaster University …using part of the NA48 setup… Some pieces [and many physicists] from previous [successful] kaon experiments 3 rd ingredient: A community of physicists 4 th ingredient: A suitable detector!

Paolo Valente – INFN Roma – 15 BEACH 2006, Lancaster University …but P326 is also much more! The P326 project wants to exploit a combination of opportunities: 1.A strong physics case  eagerly waited from theorists  fully complementary to the high-energy frontier 2.The possibility of having an high intensity kaon beam at the CERN SPS, using an existing infrastructure 3.A community of (enthusiast) physicists coming from successful kaon physics experiments (NA48, KLOE, and more) 4.The possibility of using part of an high-performance and highly- specialized detector as NA48 [in particular very valuable parts as the Liquid Kr, the vacuum tank, the hodoscope, the magnet, the muon detector, …] … but it is also a playground for further improving experimental techniques for rare kaon decays studies by dedicated R&D studies

Paolo Valente – INFN Roma – 16 BEACH 2006, Lancaster University Measurement technique: decay in flight KK p  (GeV/c)  p K = 75 GeV/c  At least 10% acceptance  Signal to background  10:1  80 events in 2 years  rejection power needed  Define kinematical cuts...  KK KK

Paolo Valente – INFN Roma – 17 BEACH 2006, Lancaster University Background rejection 92% of total background  Define a signal region  Due to K +    , split signal region in 2  Span across the signal region Kinematically constrained Not kinematically constrained 8% of total background

Paolo Valente – INFN Roma – 18 BEACH 2006, Lancaster University Background rejection Kinematical cuts are not sufficient to bring down backgrounds by a factor ~10 12 Need veto detectors! Rejection 0.05   e  0.03     0.02  0.06  0.21  0.63   BRDecay kinematics chargedveto E/p E/p  veto  veto

Paolo Valente – INFN Roma – 19 BEACH 2006, Lancaster University An experimental challenge!  Track and identify kaons in the beam at 0.8 GHz rate with 0.5% momentum resolution with 150 ps time resolution with a tight material budget  Track decay products in a mbar vacuum with 0.5% momentum resolution with 150 ps time resolution with a tight material budget  Reject   and veto additional  with a single  detection inefficiency E  > 1 GeV  Reject  background at level 10  separation at high p GigaTracker + Cherenkov Liquid Krypton +  vetoes Straw tracker + hodoscope Magnetized Iron + RICH

Paolo Valente – INFN Roma – 20 BEACH 2006, Lancaster University What is already available: NA48 What is already available: NA Total: 5.3M K L  0  0 Magnetic spectrometer 90 m vacuum tank beam Liquid krypton EM calorimeter Hodoscope MagnetizedIron

Paolo Valente – INFN Roma – 21 BEACH 2006, Lancaster University Experiment layout * * * * magnet * * Already available 1 m 200 m0 m 100 m Gigatracker Notice the ~30:1 aspect ratio

Paolo Valente – INFN Roma – 22 BEACH 2006, Lancaster University P326 beam K12 NA48/2 K12 P326 SPS protons/pulse on T10 1× ×10 12 Duty cycle (s./s.) 4.8 / 16.8 Solid angle (msterad)  0.40  16 K + momentum [band] (GeV/c) 60 [4%]75 [1%] Area at Gigatracker (cm 2 )  7.0  20 Total beam/pulse (  10 7 ) [per eff. spill length MHz] MHz/cm 2 (at Gigatracker) Eff. run time / year (pulses) 3× ×10 5 K + decays per year (60 m fiducial region) 1.0  ×10 12 Quadrupoles QuadrupolesDipoles (1 st achromat) Muonsweep CEDAR Dipoles (2 nd achromat) Gigatracker Scraper Collimator Collimator From T10 target Collimator Almost 50× more kaons with present SPS

Paolo Valente – INFN Roma – 23 BEACH 2006, Lancaster University Challenge #1  Track and identify kaons in the beam at 0.8 GHz rate with 0.5% momentum resolution with 150 ps time resolution with a tight material budget GigaTracker + Cherenkov  Beam Cherenkov counter already available (CEDAR)  New photo-detectors  Will be tested at SPS North Area in October

Paolo Valente – INFN Roma – 24 BEACH 2006, Lancaster UniversityGigatrackerSpecifications:  Momentum resolution ~ 0.5 %  Angular resolution ~ 10  rad  Time resolution ~ 100 ps  Minimal material budget  Perform all of the above in 800 MHz hadron beam, 40 MHz/cm 2 36 mm 48 mm Station 1 Station 2 Station 3 Hybrid Detector:  SPIBES (Fast Si micro-pixels)  Momentum measurement  Facilitate pattern recognition in subsequent FTPC  Timing to select the right track  FTPC (NA48/2 KABES micro-megas with FADC readout)  Track direction

Paolo Valente – INFN Roma – 25 BEACH 2006, Lancaster University Gigatracker: Si micro-pixel Timing resolution (ps) Signal/Background ratio  size: 36 mm (X) × 48 mm (Y)  pixel size: 300  m × 300  m  chip thickness 100  m  X/X  << 1%  momentum resolution 0.4% Objective:  (t) ~ 200 ps (per station): Complex readout chip bump-bonded on the sensor 0.13  m CMOS technology (now under development, CERN+INFN)

Paolo Valente – INFN Roma – 26 BEACH 2006, Lancaster University Gigatracker: FTPC T drift1 T drift2 micro-megas gap 25  m  Gas TPC + micro-megas  Coming from NA48/2  R&D on new, fast, readout electronics to improve time resolution

Paolo Valente – INFN Roma – 27 BEACH 2006, Lancaster University Challenge #2  Track decay products in a mbar vacuum with 0.5% momentum resolution with 150 ps time resolution with a tight material budget Straw tracker + hodoscope Uncorrelated Non-Gaussian tails due to Non-Gaussian p  resolution M miss 2 (GeV/c 2 ) 2 Region I Region II

Paolo Valente – INFN Roma – 28 BEACH 2006, Lancaster University Straw tracker in vacuum  6 chambers with 4 double layers of straw tubes 9.6 mm diameter  Rate: ~45 KHz per tube (max 0.5 MHz) (  ) 130  m/hit  (p)/p = 0.23%  0.005% p  (  ) ~ 50  20 mrad 2 magnets 270 and 360 MeV P t kick 5 cm radius beam holes displaced in the bending plane according to the beam path Redundant p measurement Good resolution Low mass Operate in high vacuum X/X 0 ~ 0.1% per view Veto for charged particles up to 60 GeV/c 8.8 m 7.2 m 5.4 m 2.3 m

Paolo Valente – INFN Roma – 29 BEACH 2006, Lancaster University TRT ATLAS Straw diameter – 4 mm, length – 40 and 150 cm 17 end-cap wheels are built in JINR (105 kpc of straws) COMPASS TRACKER Straw diameter – 6 and 10 mm, length up to 3.8 m 15 chambers were built in JINR Straw trackers were already operated in vacuum: COSY-TOF, Juelich, MECO, BNL but … Straw tracker in vacuum … no large straw detector operated in vacuum since now

Paolo Valente – INFN Roma – 30 BEACH 2006, Lancaster University Challenge #3  Reject   and veto additional  with a single  detection inefficiency E  > 1 GeV Liquid Krypton +  vetoes

Paolo Valente – INFN Roma – 31 BEACH 2006, Lancaster University Photon vetoes Large angle vetoes E  GeV Inefficiency < ÷ > Liquid Kripton E  GeV Inefficiency < ÷ ÷ ,10 -5 >  ANTI: Rate ~4 MHz (  )+ ~0.5 MHz (  ) (OR of 13 rings)  Liquid Kripton: Rate ~7 MHz (  ) + ~4 MHz (  )+ ~3 MHz (  )  in veto  in LKr  (rad) E (GeV)

Paolo Valente – INFN Roma – 32 BEACH 2006, Lancaster University Liquid Kripton calorimeter Must achieve inefficiency < to detect photons above 1 GeV Advantages:  It exists  Homogeneous (not sampling) ionization calorimeter  Very good granularity (~2  2 cm 2 )  Fast read-out (Initial current, FWHM~70 ns)  Very good energy ~1%,  Very good time ~ 300 ps, and position ~1 mm resolution Disadvantages:  0.5 % X 0 of passive material in front of active LKr  The cryogenic control system needs to be updated

Paolo Valente – INFN Roma – 33 BEACH 2006, Lancaster University Veto rings  Set of ring-shaped photon vetoes surrounding the decay tank  Extensive R&D performed by American and Japanese groups… … followed by specialized studies for P326 by INFN groups  Inefficiency as low as challenging but possible  Baseline solution: Lead/Plastic scintillator sandwich with WLS fibers readout  Large contribution to the total cost of the P326 project  Small angle calorimeters to close the gap of the beam-pipe Decay tube

Paolo Valente – INFN Roma – 34 BEACH 2006, Lancaster University Challenge #4  Reject  background at level 10  separation at high p Magnetized Iron + RICH

Paolo Valente – INFN Roma – 35 BEACH 2006, Lancaster University MAgnetized MUon Detector Pole gap is 30  11 cm 2 Coils cross section 15  25 cm 2  To provide pion/muon separation and beam sweeping.  150 iron plates, 2 cm thick (260  260 cm 2 )  Four coils magnetize the iron plates to provide a 1.3 T dipole field in the beam region  Active detector:  Strips of extruded polystyrene scintillator (1  4  130 cm 3 )  Light is collected by WLS fibers (1.2 mm diameter)   rejection  About 7 MHz of muons and 3 MHz of pions

Paolo Valente – INFN Roma – 36 BEACH 2006, Lancaster University A RICH for P326  1 atm Ne gas 18 m  Spherical split mirror, f=17 m PMT’s PMT’s  18 m long, 1 atm Neon gas  12 GeV threshold for   >3  separation p 3  separation p<35 GeV beam pipe mirror

Paolo Valente – INFN Roma – 37 BEACH 2006, Lancaster University P326 collaboration Proposal SPSC-P-326 CERN Beam, CEDAR, Gigatracker (SPiBeS), LKr, Trigger & DAQ, Software Dubna Straw tracker INFN Ferrara, Torino Gigatracker (SPiBeS) INFN Firenze, Perugia Hodoscope INFN Frascati, Napoli, Pisa, Roma  -veto large angle, Trigger & DAQ, Software Mainz Straw tracker Moscow MaMuD Protvino MaMuD Saclay Gigatracker (KaBeS) Saint Luis-Potosi RICH Sofia  -veto small angle

Paolo Valente – INFN Roma – 38 BEACH 2006, Lancaster University P326 time schedule  Refine layout, RICH R&D  Gigatracker R&D  Photon vetoes R&D  Vacuum tests  Straw tracker R&D  Liquid krypton test-beam (Oct. ’06)  Approval  Construction, installation and tests  Data taking

Paolo Valente – INFN Roma – 39 BEACH 2006, Lancaster University P326: going on… We have found a fortunate combination where a compelling physics case can be addressed with an existing accelerator, employing the infrastructure (i.e. civil engineering, hardware, some sub-systems) of an existing experiment … … even though this a new initiative And with new, challenging detectors to be designed and built We are looking for new collaborators!

Paolo Valente – INFN Roma – 40 BEACH 2006, Lancaster University Longer term (more protons needed!) K 0 L →  0 e  e   and K 0 L →  0    K 0 L →  0 e  e   and K 0 L →  0     K 0 L →  0K 0 L →  0 See T. Nomura… E391a and JPARC

Paolo Valente – INFN Roma – 41 BEACH 2006, Lancaster UniversityConclusions  Rare K decays are interesting now, since they are sensitive to New Physics effects  They will still be very interesting when results will be coming from the LHC? Yes, maybe even more, since they can give unique information on the flavour structure of New Physics  Very ambitious experimental programs - requiring very intense hadron beams - requiring challenging detectors: hermetic, highly efficient, with PID capabilities  A lively and enthusiastic community - still not tired of many years of success from glorious past kaon experiments… - … even in hard times from the funding point of view!

Paolo Valente – INFN Roma – 42 BEACH 2006, Lancaster University

Paolo Valente – INFN Roma – 43 BEACH 2006, Lancaster University K L →  0 K L →  0  Purely theoretical error:  2%  Purely CP-Violating (Littenberg, 1989)  Totally dominated from t-quark  Computed to NLO in QCD ( Buchalla, Buras, 1999)  No long distance contribution: SM 3   Experimentally: 2/3 invisible final state !!  Best limit from KTeV using   →  ee  decay BR(K 0 →   ) < 5.9  % CL Still far from the model independent limit: BR(K 0 →   ) < 4.4  BR(K + →   ) ~ 1.4  Grossman & Nir, PL B407 (1997)

Paolo Valente – INFN Roma – 44 BEACH 2006, Lancaster University Looking at the far future…  A competitive program can start now for charged kaons at the current SPS  For a very competitive neutral kaon decay experiment, ~ slowly extracted, high energy protons per second would be needed

Paolo Valente – INFN Roma – 45 BEACH 2006, Lancaster UniversityE949 Stopped K technique ~0.1 % acceptance

Paolo Valente – INFN Roma – 46 BEACH 2006, Lancaster University 2 events E event E949

Paolo Valente – INFN Roma – 47 BEACH 2006, Lancaster University E787/E949 result BR(K   →    =   the Standard Model, 2  the Standard Model, but with a large error (3 events…) AGS hep-ex/ PRL93 (2004)

Paolo Valente – INFN Roma – 48 BEACH 2006, Lancaster UniversityE391a CsI calorimeter Front barrel Main barrel Vacuum tank Then going to J-PARC…

Paolo Valente – INFN Roma – 49 BEACH 2006, Lancaster University  Stopped K +  With respect to E787/949:  Lower energy  Separated beam  Spectrometer: higher B field  More compact  Better resolution  Finer segmentation  Improved  veto detector (crystals)  Objective:  50 events  Not in J-PARC phase-1  Needs beamline, room, funding

Paolo Valente – INFN Roma – 50 BEACH 2006, Lancaster UniversityKLOD  IHEP Protvino 60 GeV proton beam  Off-axis angle=35 mrad  K L ’s peak momentum = ~6 GeV/c  Objective:  28 events/9 background in 3 years  Run in 2008