September 27, Proposal to Measure the Rare Decay K     at the CERN SPS CERN, Dubna, Ferrara, Florence, Frascati, Mainz, Merced, Moscow, Naples, Perugia, Protvino, Pisa, Rome, Saclay, San Luis Potosi, Sofia, Turin CERN-SPSC SPSC-P-326

September 27, Physics Introduction: CKM matrix and CP-Violation N g =2 N phase =0  No CP-Violation N g =3 N phase =1  CP-Violation Possible Quark mixing is described by the Cabibbo-Kobayashi-Maskawa (CKM) matrix e.g., Im t = Im V ts *V td ≠ 0  CP KM mechanism: =V us Im t = A 2 5  Re t = A 2 5  The unitarity of the CKM matrix can be expressed by triangles in a complex plane. K + →  + is sensitive to |V td |

September 27, Physics Motivation The Kobayashi-Maskawa mechanism appears to be the main (only?) source of CP-violation Now look for inconsistencies in SM using independent observables affected by small theoretical uncertainties and different sensitivity to new physics The rare process K     belongs to the theoretically cleanest decays in the field of K- and B-mesons It allows one to determine |V td | independently from B 0 -B 0 mixing, thus providing a decisive test of the Standard Model

September 27, K→  : Theory in Standard Model charm contribution top contributions The Hadronic Matrix Element is measured and isospin rotated (~10% correction)

September 27, Predictions in SM This used to be the largest theoretical error (+/ ). It was reduced by a NNLO calculation (Buras et al. hep-ph/ ) The errors are due to the uncertainty of the CKM parameters and not to the hadronic uncertainties

September 27, Setting the bar for the next generation of K + →  + experiments 100 events Mean=SM 100 events Mean=E787/949 Current constraint on  plane ? E787/E949: BR(K + →  + ) = ×

September 27, Some BSM Predictions SM8.0 ± ± 0.6 MFV hep-ph/ EEWP NP B ± ± 10 EDSQ hep-ph/ MSSM hep-ph/

September 27, Other Physics Opportunities The situation is similar to NA48, which was designed to measured “only”  ’/  but produced many more measurements Accumulating ~100 times the flux of NA48/2 will allow us to address, for instance: 1.Cusp like effects (  scattering) –K       e  2.Lepton Flavour Violation K        e , K       e +, (K e2 /K  2 ) 3.Search for new low mass particles –K      X –K       P (pseudoscalar sGoldstino) 4.Study rare     decays 5.Improve greatly on rare radiative kaon decays 6.Compare K + and K - (alternating beam polarity) –K        (CPV interference) –T-odd Correlations in K l4 7.And possibly, given the quality of the detector, topics in hadron spectroscopy

September 27, Principle of the measurement Collect ~ Kaon decays/year from a secondary SPS hadron beam (K12) high energy kaons: 1.high acceptance 2.good resolution 3.good photon detection efficiency 4.redundancy  pions and protons cannot be separated: 1.large rate in the beam tracker

September 27, P-326 Detector Layout 800 MHz beam  /K/p K+K+ ++ ~11 MHz

September 27, Background rejection Guidance: S/B = 10 ~ rejection 1)Kinematical rejection based on the missing mass: 2) Veto and Particle ID , , charged particles  –  e separation

September 27, Backgrounds kinematically constrained DecayBR K +    K  2 )0.634 K +  +  K +  +  +  - K +    0  % of K + decays Allows us to define the signal region K   +  0 forces us to split it into two parts Region I: 0 < m 2 miss < 0.01 GeV 2 /c 4 Region II: < m 2 miss < GeV 2 /c 4

September 27, Backgrounds not kinematically constrained Decay BR K +  0 e + (K e3 ) K3K3K3K K2K2K2K2 5.5×10 -3 +0K++0+0K++0 1.5×10 -3 K e4 4×10 -5 K4K4K4K4 1× % of K + decays They span accross the signal regions Must rely on Particle ID and veto

September 27, Signal Acceptance Acceptance (5 m < Z vertex < 65 m) REGION I: 4% REGION II: 13% Total: 17% For safety, a 10% acceptance is quoted in the proposal

September 27, Signal & backgrounds from K decays / year TotalRegion IRegion II Signal K++0K++0 2.7±0.21.7±0.21.0±0.1 K2K2 1.2±0.31.1±0.3<0.1 K e4 2±2negligible2±2 K   +  +   and other 3-tracks bckg. 1±1negligible1±1 22 1.3±0.4negligible1.3±0.4 K2K2 0.4±0.10.2±0.1 K e3, K  3,others negligible  Total bkg9±33.0±0.26±3

September 27, Summary Signal events expected per (16 Region I, 49 Region II) Background events ~9 (3 Region I, ~6 Region II) Signal/Background ~ 8 S/B (Region I) ~5 S/B (Region II) ~ 9 Backgrounds from beam scattering and interactions not included For Comparison: In the written proposal we quoted to account for some reconstruction and deadtime losses

September 27, Choice of K + momentum : (for 400 GeV/c proton momentum) At 75 GeV/c from 400 GeV/c protons K + /K - per proton ~ 2.1 (K + /  + )/(K - /  - ) ~ 1.2 (K + /Total +ve)/(K - /Total –ve) ~ = 5 x (reg. 1, no p  cut) Choice of positive beam

September 27, Beam: Present K12 (NA48/2) New HI K + > 2006 Factor wrt 2004 SPS protons per pulse on T101 x x Duty cycle (s./s.)4.8 / Solid angle (  sterad)  0.40  Av. K + momentum (GeV/c)6075 K + ~ 1.5 Mom. band RMS: (  p/p in %)  4  1 ~0.25 Area at Gigatracker (cm 2 )  7.0  14  2.0 Total beam per pulse (x 10 7 ) per Effective spill length MHz MHz/cm 2 (gigatracker) ~45 (~27) ~24(~15) Eff. running time / yr (pulses)3 x * K + decays per year1.0x x10 12  48 New high-intensity K + beam for P-326 Already Available

September 27, Required vacuum in the decay tank A FLUKA simulation led us to conclude that the vacuum should be better than 6  mbar to keep the background to less than one event per year This figure can be relaxed by an order of magnitude by positively tagging the kaons The best vacuum achieved in the current tank is about mbar, compatible with the outgassing of painted steel To reach the specified vacuum either a stainless steel tank or a new pumping system is required

September 27, CEDAR Positive identification of Kaons is important to avoid mistaking a beam pion interaction in the residual gas as signal Upgraded version of an existing West type CEDAR Use H 2 (3 bars) to reduce multiple scattering Excellent time resolution (< 100 ps) is required Use, for example, 8 Hamamatsu Linear Array H7260 (32 pixel/unit) as photon detectors to stand the high rate (50 MHz) 6 m

September 27,

September 27, Gigatracker 22 X/X 0 << 1% Pixel size ~ 300 x 300  m  ( p)/p ~ 0.4%  ( t) GT ~100ps on the track: time coincidence to select the right kaon track Provide precise measurements on all beam tracks (out of which only ~6% are K + ) Provide very good time resolution Do not spoil beam and downstream measurements Sustain high, non-uniform rate ( 800 MHz total) PP PKPK   Instrument the 2 nd beam achromat for redundant momentum and angular measurement: Two Silicon micro-pixel detectors (SPIBES) Timing Pattern Recognition One FTPC (Improved KABES) To minimise scattering in the last station SPIBES:

September 27, Required Gigatracker time resolution P(>1hit in  t) =1-exp(-  t*rate)  t ( ± % 33% % 39% % 45% Dependence of the signal to background (from K +      ) as a function of the gigatracker time resolution K+ K+ 

September 27, Gigatracker: SPIBES Front-End p-sub p+ n-sub n+ p+ n+ h e- h ➊ ➋ Simulation of signal collection: Alice pixel size (425 * 50  m) ➊ ➋ MeV Signal simulation: G4 v GeV/c K Si sensor 200  m thick (e.g. ALICE SPD) at least e - /holes Front End and R/O considerations based on the experience of the CERN-PH/MIC and PH/ED Groups with the ALICE SPD

September 27, SPIBES Read out Chip mm N chips To achieve the time resolution a very complex read-out chip bump-bonded on the sensor is needed (technology choice required: 0.25 vs  m CMOS) Photolithographic process max 20-21mm wide chip Beam spot adjusted to fit maximum chip size GT area per pixel station: 36mm(X) x 48mm(Y) - 2 half detectors to cover the area w/o overalp beam rate: high and not uniform 2-3mm I/O Maximum rate in the hottest regions : (Normalized to total rate of 1GHz) ~1.5MHz/mm 2 in sation1, ~1.6MHz/mm 2 in station2, ~1.9MHz/mm 2 in station3 y x 2mm/bin Station 1(pixels) 2(pixels) 3(FTPC) 25

September 27, FTPC (KABES) T drif t1 T drift2 Micromegas Gap 25 μm Micromegas Gap 25 μm KABES principle: TPC + micromegas Pioneered in NA48/2 Tested in 2004 at high intensity (see Villars) Latest Developments: Signal occupancy with Gas Compass 50µm strip + V1 = 30 ns 50µm strip + FAMMAS = 22 ns 25µm strip + V1 = 22 ns 25µm strip + FAMMAS = 10 ns New electronic + 25µm mesh strip signal occupancy divided by 3

September 27, Advantages: can (in principle) operate in vacuum decay volume can be designed without internal frames and flanges can work in high rate of hits good space resolution (~130  m/hit for  9.6 straw) small amount of material (~0.1% X 0 per view) but no previous straw system has been operated in high vacuum Straw Tracker

September 27, Glue – 5  m 12.5  m 0.2  m Al 9.6 mm25  m Gold plated Tungsten wire 30  m Straw Elements and Design 8.8 m186.3 m from T0 5.4 m 7.2 m k12hika+ (Niels)  About 2000 * 6 -> straws in total 3 coordinates 4 coordinates 2 coordinates 1 coordinate 10 cm 2300 mm To fit easily into decay volume an octagonal shape is proposed Two double layers form a view Gas mixture: 20%Ar+80%CO 2 12 ns rise time 100 ns total width Polycarbonate spacer, 25 mg

September 27, Layout of the Straw Tracker P(   ) = 60 GeV/c P(K + ) = 75 GeV/c Holes in Straw-Chambers 5 cm radius Chambers 3, 4, 5 and 6 are off-axis Magnets: p t kick 270 and 360 MeV/c The off-axis layout in the bending plane is essential to reject K        e   decays in which the e  is lost and the   carries most of the kaon momentum

September 27, RICH Layout

September 27, RICH as velocity spectrometer…. Resolution of a 17m P-326 RICH (CKMGEANT)

September 27, …and RICH for  -  separation

September 27, MAMUD Pole gap is 2 x 11 cm V x 30 cm H Coils cross section 10 cm x 20cm To provide pion/muon separation and beam sweeping. –Iron is subdivided in cm thick plates (260  260 cm 2 ) Two coils magnetise the iron plates to provide a 5 Tm field integral in the beam region Active detector: –Strips of extruded polystyrene scintillator (as in Opera) –Light is collected by WLS fibres with 1.2 mm diameter

September 27, Photon Vetoes

September 27,

September 27, Photon Vetoes E rangeInefficiency ANTI < 50 MeV1 (0.5, 1) GeV10  4 > 1 GeV10  5 LKR < 1 GeV1 (1,3) GeV10  4 (3,5) GeV10  4  10  5 > 5 GeV10  5 IRCs, SAC All10  6 P-326 Simulation: Allowed inefficiency/photon From: Ajimura et al., NIMA, in press

September 27, NA48 LKr as Photon Veto Energy of photons from K       hitting LKr: > 1 GeV GeV Urgent consolidation of the safety/control system is needed

September 27, Large Angle Vetoes (ANTI) Two designs under test: –spaghetti (KLOE) –lead/scintillator sandwich (CKM) Extensive simulation under way A tagged photon beam is available in Frascati to test existing prototypes

September 27, Fast Hodoscope (MGG-RPCs) To make tight time coincidence with gigatracker Propose to use the Multi-gap Glass RPC (ALICE-TOF technology) High rate test are mandatory to validate performance up to 5 kHz/cm 2 A prototype PCB suitable for P-326 application is under fabrication ALICE-TOF

September 27, Trigger & DAQ Total input to L0: 11 MHz L0 (example): – > 1 hit hodoscope  73% – muon veto  24% – Photon Veto  18% – <2 EM quadrants & E<50 GeV  2% L0 output: –2% x 11 MHz = 220 KHz Keep: L0 + Control + Calibration + Spin-offs < 1 MHz L1 in PC farm (à la LHCb) to keep as much flexibility as possible

September 27, Cost Estimation (Materials) ElementCost (MCHF)Comments BEAM LINE0.4Modified K12 line CEDAR0.5 GIGATRACKER MCHF if 0.25  m CMOS can be used VACUUM1.0Upgrade of vacuum system ANTI4.2 STRAW2.4 MNP33/ MCHF + He extension CHOD0.9MGG-RPC RICH4.0Indication LKR2.0New supervion system and R/O MAMUD1.5 SAC & IRC0.4 TRIGGER & DAQ1.5 TOTAL24.0

September 27, Strengthening P-326 The demise of the US kaon programme has triggered negotiations with members of KOPIO/CKM to join P-326 The following groups have signed up since the proposal submission: –San Luis Potosi (Mexico, J. Engelfried) –Moscow, INR Interest to join has been expressed by the following groups: –Fermilab (P. Cooper) –BNL (L. Littenberg, S. Kettell) –British Columbia (D. Bryman) –George Mason (P. Rubin) It is our understanding that a possible participation of US groups is subject to: –DOE support towards a strong contribution to the construction of the detector (notably the RICH counter) –The involvement of US University in addition to National Labs

September 27, Status of R&D A talk in itself, but in a nutshell: –Gigatracker (CERN/INFN TO/FE) Study of sensors for fast signal collection Study of chip architecture –Straw Tracker (Mainz/Dubna) Study of prototype in vacuum –Photon vetoes (INFN, CERN, Protvino, Sofia) Tests of existing prototypes with photon sources (Frascati) Construction of prototypes for IRC/SAC Use of LKr as photon detector (more data needed in 2006) –Fast Hodoscope (INFN FI/PG) Investigation of MGG-RPC operated at high rate (≤5 KHz/cm 2 ) –CEDAR (CERN) Fast photon detectors

September 27, SPS Availability There are two approved competitors for beam: LHC and CNGS P-326 requires ~ SPS pulses/year with 4.8 s flat top For comparison, the Fixed Target request quoted in the Villars Report (SPSC-M-730) is pulses/year P-326 is completely compatible with the simultaneous running of COMPASS in the M2 beam line and with experiments and tests in the H2, H4, H6 and H8 beams

September 27, Beam Request 2006 We request 30 days of K12 beam in 2006 to operate the NA48/2 hardware as P-326 test facility in order to: –Measure beam induced backgrounds –Measure LKr inefficiency collecting K       –Test prototype elements of the new detectors In addition we request that a standard (nitrogen gas-filled) CEDAR-W counter is made available in a beam to test the device with new, high rate, photon detectors

September 27, Timeline 2006 –Tests in the present K12 beam –Construction, installation and tests of the new beam (2007) and new detectors ( ) –Data Taking

September 27, Spares

September 27, Possibly the Cleanest SM test In The phase  derives from Z 0 diagrams (  S=1) whereas in A(J/  K S ) originates in the box diagram (  B=2) Any non-minimal contribution to Z 0 diagrams would be signalled by a violation of the relation: A deviation from the predicted rates of SM would be a clear indication of new physics Complementary programme to the high energy frontier: –When new physics will appear at the LHC, the rare decays may help to understand the nature of it

September 27, Kaon Rare Decays and the SM Kaons provide quantitative tests of SM independent from B mesons… …and a large window of opportunity exists! |V td | G. Isidori Im t = A 2 5  Re t = A 2 5 

September 27, K + →  +  : State of the art BR(K + →  + ) = × Compatible with SM within errors hep-ex/ PRL93 (2004) Stopped K ~0.1 % acceptance AGS

September 27,

September 27, 100.0±0.48 mm 102.3±0.45 mm

September 27, Possible Photon detector

September 27, Sigma = ~ 80 ps ~ e - Simulation of average channel response

September 27, The simulations by Lau G. shows that the average rate per channel is ~ 3 MHz. This gives an average current/ch = 0.4 uA or 13 uA in total. But if the pulsed operation of the beam is taken into account. The averaged current over 30 sec is 1/3 of these values! Safety factor of 24 is OK!