A proposal to Study Rare Kaon Decays at the CERN SPS Augusto Ceccucci/CERN

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1 A proposal to Study Rare Kaon Decays at the CERN SPS Augusto Ceccucci/CERN Physics Introduction Rare Kaon Decays in the SM. and Beyond Flavour as a probe of New Physics complementary to the high energy frontier Experimental state-of-the-art Recent Results and world-wide perspectives Description of the CERN proposal P-326 Technique Status February 27, 2006 Lausanne 1

2 Quark Mixing and CP-Violation Cabibbo-Kobayashi-Maskawa (CKM) matrix: Non-diagonal (e.g. V us 0) Flavour Violation 3 or more quark generations CP-Violation in SM (KM) N g =2 N phase =0 No CP-Violation N g =3 N phase =1 CP-Violation Possible ubcbtduduscdcststbvvvvddssbbvv e.g., Im t = Im V ts *V td 0 CPV GIM mechanism No FCNC at tree level Violation at one loop depending on quark masses and CKM couplings February 27, 2006 Lausanne 2

3 CKM Unitarity and Rare Kaon Decays The unitarity of the CKM matrix can be expressed by triangles in a complex plane. There are six triangles but one is more triangular : V ud V ub *+V cd V cb *+V td V tb *=0 It is customary to employ the Wolfenstein parameterization: V us ~ V cb ~ 2 V ub ~ 3 ( i ) V td ~ 3 (1 i ) Sensitive to V td Im t = 2 5 Re t = 2 5 February 27, 2006 Lausanne 3

Status of Unitarity Triangle 95% confidence regions extracted using V ub / V cb, _ K, _m Bd, _m Bs and sin2 = 0.214 ± 0.047 _ = 0.343 ± 0.

4 Status of Unitarity Triangle 95% confidence regions extracted using V ub / V cb, _ K, _m Bd, _m Bs and sin2 = ± _ = ± Constraints from V ub / V cb, _m Bd and _m Bs compared with constraints from CP violating quantities in the kaon (_ K ) and in the B (sin2_) sectors _ = ± _ = ± Rare kaon decays are loop-dominated. Assuming SM they provide strong independent constraints to the UT February 27, 2006 Lausanne 4

5 K 0 L 0 The four golden modes of Kaon Physics Short-distance contrib ( sd / ) >99% Irreducible theory err. on amplitude 1% Total SM BR K % 3% K 0 L 0 e + e 38% 15% K 0 L 0 μ + μ 28% 30% Short distance dynamics: W-top quark loops constitute the dominant contribution: The EW short-distance amplitude is common in the SM but potentially different beyond SM Important to address all these decays Adapted from G. Flavour in the LHC era, 5-7 Nov 05, CERN February 27, 2006 Lausanne 5

6 K : Theory in Standard Model LL5ImReRe()()()()Im()()ttcttcttBKXxXxPXBKXx usccscdttstdv ()2sinKWBrKer ++++ top contributions charm contribution The Hadronic Matrix Element is measured and isospin rotated February 27, 2006 Lausanne 6

7 Predictions in SM () ()0.012()0.009()cccsPXmμ This used to be the largest theoretical error (+/ ). It was reduced by a NNLO calculation A. Buras, M. Gorbahn, U. Haisch, U. Nierste hep-ph/ ) Standard Model predictions BR(K + + ) (1.6_ ) V cb 4 [ 2 +( c - ) 2 ] (8.0 ± 1.1)_10 BR(K L 0 ) (7.6_10-5 ) V cb 4 2 (3.0 ± 0.6)_ The errors are mostly due to the uncertainty of the CKM parameters and not to the hadronic uncertainties February 27, 2006 Lausanne 7

8 Theory vs. Experiment SM Observable B(K 0 L 0 ) B(K + + ) A FB (B X s l + l ) B(B X s ) B(B X s l + l ) A FB (B K ( * ) l + l ) B(B (K ( * ),, ) ) B(B s μ + μ ) B(B K*l + l ) Theoretical error ~3% ~6% ~8% ~10% ~13% ~15% ~25% ~30% ~35% Experimental error?? ~75%?? ~9% ~20% ~30% ~40%?? ~13% Adapted from U. Flavour in the LHC era, 6-8 Feb 06, CERN February 27, 2006 Lausanne 8

9 Intrinsic theory error Combining information from BR(K + + ) and BR(K 0 0 ) one obtains: (Buras et al. hep-ph/ ) ()()()()()() 0.41sin20.34 So for a 10% uncertainty on P c, one can extract, in priciple, a 3.4% exp. determination of sin2 from kaon decays. It is currently 4.6% from B decays February 27, 2006 Lausanne 9

10 Beyond Standard Model Compare two scenarios: Minimal Flavour Violation All mixing governed by universal CKM matrix No Extra Complex Phases Same operators as in SM Different coefficients Stringent correlation with B rare decays New sources of Flavour Symmetry Breaking ~ TeV scale Extra phases can lead to large deviations from SM predictions, especially for the CP-Violating modes February 27, 2006 Lausanne 10

11 MFV: Sensitivity to Z 0 Penguin from Bobeth et a. (2005) February 27, 2006 Lausanne 11

12 New Sources of Flavour Symmetry Breaking Generic MSSM Enhanced EW Penguins February 27, 2006 Lausanne 12

13 Experimental State-of-the-art February 27, 2006 Lausanne 13

1 % acceptance BR(K + + ) = 1.47 +1.30-0.

14 K + + hep-ex/ PRL93 (2004) AGS Stopped K + ~0.1 % acceptance BR(K + + ) = _ Compatible with SM within errors February 27, 2006 Lausanne 14

89 _ 10-10 Current constraint on, plane?

15 Setting the bar for the next generation of K + + experiments E787/E949: BR(K + + ) = _ Current constraint on, plane? 100 events Mean=SM 100 events Mean=E787/949 February 27, 2006 Lausanne 15

16 K 0 L 0 : E391a Upper Limit 10% of RUN I Pencil beam Expected background from K 0 L decays: 0.02 Acceptance: 0.73% BR(K 0 L 0 )< %CL Preliminary (Ken Sakashita@KAON2005) 6 improvement over KTeV one day special run 2 improvement over published limit (KTeV Dalitz technique) For the future: JPARC LOI-05 Recently, J-PARC made a call for proposals February 27, 2006 Lausanne 16

17 K 0 S,L 0 e + e and K 0 S,L 0 μ + μ BR(K S 0 ee) 10-9 = (stat) ± 0.8(syst) BR(K S 0 μμ) 10-9 = (stat) ± 0.2(syst) PLB 576 (2003) PLB 599 (2004) K S 0 μμ 7 events, expected back NA48/1 NA48/1 6 events, expected back BR(K L 0 ee ) < 2.8 _ KTeV PRL93, (2004) BR(K L 0 μμ ) < 3.8 _ KTeV PRL86, 5425 (2001) February 27, 2006 Lausanne 17

18 (Isidori, Unterdorfer, Smith, EPJC36 (2004)) Constructive 00L00L K K 0 L 0 ee (μμ) in SM With the K S measurements, the K L BR can be predicted * Interference between short- and long-distance physics* ()012L(K)10Br+ μμ now favored by two independent analyses* Destructive *G. Buchalla, G. D Ambrosio, G. Isidori, Nucl.Phys.B672,387 (2003) *S. Friot, D. Greynat, E. de Rafael, hep-ph/ , PL B 595 * ()012L()10Bree+ February 27, 2006 Lausanne 18

19 Summary K + + Already 3 clean events are published (E787/E949) Experiment in agreement with SM within errors Next round of exp. need to collect O(100) events to be useful Move from stopped to in flight technique (FNAL Proposal turned down by P5) Proposal for in-flight decays: CERN P-326 Letter of Intent at J-PARC to continue the study with decays at rest K 0 L 0 Large window of opportunity exists. Upper limit is 4 order of magnitude from the SM prediction First results E391a (proposed SES~ ) LOI to continue at J-PARC KOPIO TERMINATED K 0 L 0 ee(μμ) Long distance contributions under good control Measurement of K S modes has allowed SM prediction K S rates to be better measured Background limited (study time dep. Interference?) 100-fold increase in kaon flux to be envisaged February 27, 2006 Lausanne 19

20 CERN-SPSC SPSC-P-326 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 February 27, 2006 Lausanne 20

21 NA48: / / / no spectrometer K L NA48/1 K S / lower inst. intensity NA48/1: K S NA48/2: K ± NA48/2: K ± NA48@CERN Direct CP-Violation established 1996 Re / = 14.7 ± K L Rare Decays Ave: Re / = 16.7 ± First observation of K 0 S 0 e + e and K 0 S 0 μ + μ Search for Direct CP-Violation in charged kaon decays scattering: PLB 633 (2006) (a 0 -a 2 )m + = / February 27, 2006 Lausanne 21

22 Status of P-326 (a.k.a. NA48/3) Presented at the CERN SPSC in September 2005 R&D Endorsed by CERN Research Board on December 2005 (subject to funding) Beam Test foreseen in August 2006 Still seeking groups to fund the RICH counter Seeking full approval by end of to be able to start data taking some time in February 27, 2006 Lausanne 22

23 Background rejection P K P π P ν θ πk Guidance: S/B = 10 ~10-12 rejection 1) Kinematical Rejection m 2 miss m 2) Photon vetoes and PID ( μ) Basic idea to reject K K P(K + ) = 75 GeV/c Require P( + ) < 35 GeV/c P( 0 ) > 40 GeV/c It cannot be missed in the calorimeter/photon veto February 27, 2006 Lausanne 23 P P ν m P 1 P 2 K 2 1 K K PK + P P

24 Backgrounds kinematically constrained Decay K + μ + (K μ2 ) K K K BR % of K + decays Allows us to define the signal region K 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 February 27, 2006 Lausanne 24

25 Backgrounds not kinematically constrained K(K μ3 e3 ) K 5.5_10 - μ2 K _10-3 4_10-5 e4 K e4 K μ4 Decay K + 0 e + BR _10-5 8% of K + decays They span accross the signal regions Must rely on Particle ID and veto February 27, 2006 Lausanne 25

26 P-326 Detector Layout K + + Gigatracker K + + ~11 MHz 75 GeV/c 800 MHz beam /K/p (KABES) February 27, 2006 Lausanne 26

27 P-326 Detector Layout K Gigatracker + K + ~11 MHz 75 GeV/c 800 MHz beam /K/p (KABES) February 27, 2006 Lausanne 27

28 Signal & backgrounds from K decays / year K and other 3-tracks bckg. 2 K μ2 K e3, K μ3,others Total bkg Total Signal K ± ± ±0.1 K μ2 1.2± ±0.3 <0.1 K e4 2±2 negligible 2±2 1±1 1.3± ±0.1 negligible 9±3 Region I negligible negligible 0.2± ±0.2 Region II 1±1 1.3± ±0.1 6±3 February 27, 2006 Lausanne 28

29 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 For Comparison: In the written proposal we quoted 40 events/year@br=10-10 to account for some reconstruction and deadtime losses February 27, 2006 Lausanne 29

30 New high-intensity K + beam for P-326 Already Available Beam: Present K12 (NA48/2) New HI K + > 2006 Factor wrt 2004 SPS protons per pulse on T10 1 x x Duty cycle (s./s.) 4.8 / Solid angle (μsterad) Av. K + momentum <p K > (GeV/c) K + ~ 1.5 Mom. band RMS: ( p/p in %) 4 1 ~0.25 Area at Gigatracker (cm 2 ) Total beam per pulse (x 10 7 ) ~45 (~27) per Effective spill length MHz MHz/cm 2 (gigatracker) ~45 (~27) ~24(~15) Eff. running time / yr (pulses) 3 x x K + decays per year 1.0x x February 27, 2006 Lausanne 30

Decay Tank Specification: 10-6 mbar Study performed with Monte Carlo using Fluka and Gheisha to simulate the hadronic interactions with the residual gas.

31 Decay Tank Specification: 10-6 mbar Study performed with Monte Carlo using Fluka and Gheisha to simulate the hadronic interactions with the residual gas. Measurements: Vacuum test performed on the existing tube of NA48. A 10-5 mbar level reached with only 1 pump. With a few l/s diffusion or cryogenics pumps the requested vacuum level can be achieved Conclusions: The existing decay tank can be used February 27, 2006 Lausanne 31

32 Gigatracker Provide precise measurements on all beam tracks (out of which only ~6% are K + ) Provide very good time resolution Minimise mass (multiple scattering and beam interactions) Sustain high, non-uniform rate ( 800 MHz total) Two Silicon micro-pixel detectors (SPIBES) Timing Pattern Recognition FTPC (Improved KABES) To minimise scattering in the last station SPIBES: P K P X/X 0 << 1% Pixel size ~ 300 x 300 mm (p)/p ~ 0.4% excellent time resolution to select the right kaon track Dependence of the signal to background (from K ) ratio as a function of the gigatracker time resolution February 27, 2006 Lausanne 32 32

SPIBES (Hybrid Pixel) 200 μm Silicon sensor (>11 000 e/h mip) Following Alice SPD Bump-bonding Read-out chip Pixel 300 μm x 300 μm Thinned down to ~100 μm (Alice SPD 150 μm) Beam surface ~ 14 cm 2

33 SPIBES (Hybrid Pixel) 200 μm Silicon sensor (> e/h mip) Following Alice SPD Bump-bonding Read-out chip Pixel 300 μm x 300 μm Thinned down to ~100 μm (Alice SPD 150 μm) Beam surface ~ 14 cm 2 Adapted to the size of the SPIBES r-o chips ~125 μm Cfibre for cooling & support y 2mm/bin 2mm/bin x Front End and R/O considerations based on the experience of the CERN-PH/MIC and PH/ED Groups with the ALICE SPD G. Anelli, M. Scarpa, S. Tiuraniemi Station 1(pixels) 2(pixels) 3(FTPC) February 27, 2006 Lausanne 33 MeV

34 FTPC (KABES) KABES principle: TPC + micromegas E drift T drift2 Pioneered in NA48/2 Tested in 2004 at high intensity with 1 GHz FADC Micromegas Gap 25 _m Micromegas Gap 25 _m In NA48/2 KABES has achieved: Position resolution ~ 70 micron Time resolution ~ 0.6 ns Rate per micro-strip ~ 2 MHz T drif t1 E drift New electronic + 25 m mesh strip signal occupancy divided by 3 February 27, 2006 Lausanne 34

35 Straw Tracker 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 μm/hit for 9.6 straw) small amount of material (~0.1% X 0 per view) but no previous large straw system has been operated in high vacuum February 27, 2006 Lausanne 35

36 Straw Elements and Design 12 ns rise time 100 ns total width Polycarbonate spacer, 25 mg Glue 5μm 12.5 μm 0.2 μm Al 9.6 mm 25 μm Gold plated Tungsten wire 30 μm Two double layers form a view Gas mixture: 20%Ar+80%CO 2 3 coordinates 2300 mm To fit easily into decay volume an octagonal shape is proposed 4 coordinates 2 coordinates 10 cm 1 coordinate 5.4 m 5.4 m k12hika+ (Niels) m from T0 8.8 m 7.2 m 7.2 m About 2000 * 6 -> straws in total February 27, 2006 Lausanne 36

37 RICH Layout February 27, 2006 Lausanne 37

38 RICH as velocity spectrometer. Resolution of a 17m P-326 RICH (CKMGEANT) accepted events 10 3 K + (μ2) reconstructed as K + (πx) in the Velocity Spectrometer K + (μ2) K + (π2) Signal Regions Missing Mass [GeV/c 2 ] February 27, 2006 Lausanne 38

39 and RICH for -μ separation February 27, 2006 Lausanne 39

NA48 LKr as Photon Veto Energy of photons from K + + 0 hitting LKr: > 1 GeV

40 NA48 LKr as Photon Veto Energy of photons from K hitting LKr: > 1 GeV Consolidation of the safety/control system and read-out under way GeV February 27, 2006 Lausanne 40

41 LKr efficiency measured with data Events are kinematically selected. + track and lower energy are use to predict the position of the other K collected by NA48 in 2004 Photon E=11 GeV Pion P=42 GeV/c Cluster not reconstructed E = 22 GeV Expected position February 27, 2006 Lausanne 41

Measured LKr inefficiency per photon (E g > 10 GeV): = (2.8 ± 1.

42 Example: hadronic cluster of a photon Expected energy: ~29 GeV Deposited energy: ~9 GeV Maximum energy ~300 MeV Expected position Measured LKr inefficiency per photon (E g > 10 GeV): = (2.8 ± 1.1 stat ± 2.3 syst ) _ 10-5 (preliminary) 1.1 stat 2.3 syst February 27, 2006 Lausanne 42

43 Beam test 2006 Idea for measuring inefficiency in the range 2 GeV < E < 10 GeV Use of the NA48 set-up. Beam test foreseen during Photons produced by bremsstrahlung. the 2006 SPS run SPS can provide a suitable electron beam. vacuum Kevlar window Electron beam (25 GeV/c) Bremsstrahlung Magnet Drift chambers e - Calorimeter Calorimeter inefficiency below E < 5 GeV is not critical February 27, 2006 Lausanne 43

44 ANTI-Photon Rings From: Ajimura et al., NIMA 552 (2005) 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 February 27, 2006 Lausanne 44

45 MAMUD To provide pion/muon separation and beam sweeping. Iron is subdivided in cm thick plates ( 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) Pole gap is 2 x 11 cm V x 30 cm H Coils cross section 10 cm x 20cm Light is collected by WLS fibres with 1.2 mm diameter February 27, 2006 Lausanne 45

46 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 3% L0 output: 3% x 11 MHz = 330 KHz Keep: L0 + Control + Calibration + Spin-offs < 1 MHz L1 in PC farm (à la LHCb) to keep as much flexibility as possible Software trigger reduction ~40 Important synergies with LHC to be exploited: for instance, the LHCb TELL1 board February 27, 2006 Lausanne 46

47 Other Physics Opportunities The situation is similar to NA48, which was designed to measure 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 + + μ + e, K + μ + e +, (K e2 /K μ2 ) 3. Search for new low mass particles K + + X K P (pseudoscalar sgoldstino) 4. Study rare + & 0 decays 5. Improve greatly on rare radiative kaon decays 6. Compare K + and K - (alternating beam polarity) K +/ +/ 0 (CPV interference) T-odd Correlations in K l4 7. And possibly, given the quality of the detector, topics in hadron spectroscopy February 27, 2006 Lausanne 47

48 Summary Clear physics case The discovery of New Physics will dramatically increase the motivation for searches of new flavour phenomena Healthy competition worldwide: J-PARC SPS Exploit synergies and existing infrastructures NA48 / NA48/1 K S rare decays NA48/2 g/g in K 3 P SPS SPS used as LHC injector (so it will run in the future) No flagrant time overlap with CNGS P-326 fully compatible with the rest of CERN fixed target because P-326 needs only ~1/20 of the SPS protons Join us! February 27, 2006 Lausanne 48

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