1. The NA48 Experiment: Lepton Universality Tests and New Prospects (P326) Cristina Biino INFN Torino On behalf of the NA48/NA62/P326 collaboration New Trends in High-Energy Physics Yalta, Crimea, Ukraine, September 15-22, 2007

2. Yalta 2007 2 Cristina Biino Introduction Violation of Lepton Universality is predicted by almost every new physics model. Kaon Physics: So far precision is poor, tests on levels of 1-2% (K l3 ) or even 3-4% (K e2 /K  2 ) K l2 decaysK l3 decays K e2 /K  2 K e3 /K  3, Vus

3. Yalta 2007 3 Cristina Biino Overview NA48 experiment: Recent results and prospectives on Lepton Universality test in K   l  decays Recent results from K    0 l  decays : –CKM matrix element |Vus| –Lepton Universality test CERN P326: A proposal to measure the rare decay K +   + -

4. Yalta 2007 4 Cristina Biino 1. Lepton universality with K   l  decays –Physics motivations –Results from NA48 data collected in 2003/2004 –Run 2007

5. Yalta 2007 5 Cristina Biino Well predicted by the Standard Model, but must include radiative corrections: (Finkemeier, Phys. Lett. B387 (1996):  R K = -(3.78 ± 0.04) % ) R K (SM) = (2.472 ± 0.001) ·10 -5 0.04% precision! The value of R K could be different in case of SUSY LFV. The difference wrt SM could be as large as ± 3% (Masiero, Paradisi, Petronzio, Phys. Rev. D74 (2006) 011701). Measurement of R K test the  /e universality and provides a sensible test of the SM. R K (PDG 2006) = (2.45 ± 0.11) ·10 -5 From three experiments from the 70’s, with kaons at rest. K e2 /K  2 - Introduction

6. Yalta 2007 6 Cristina Biino A sample collected during 2003 data taking –1 month of data taking using a downscaled trigger A sample collected at the end of 2004 data taking in a special run –56 hours of data taking with a very efficient minimum bias trigger NA48 – Recent Data N Ke2raw - N Ke2back Acc(K  2) C  R K = TrEff(Ke2) Acc(Ke2) C e D N K  2raw - N K  2back Where D is the downscaling for the K  2 events and C l represents the correction due to PID. Most of the systematics cancel in the ratio of the partial widths. The dominant contribution, the background subtraction error, scales with the statistics.

7. Yalta 2007 7 Cristina Biino Similar kinematics allows to exploit systematic cancellations –Keep at maximum the same cuts for both modes 1 track topology z of decay vertex Geometric acceptance at chambers and Lkr calorimeter Track momentum –Particle identification using E LKr /P spectr Muons : E/P < 0.2 Electrons: E/P > 0.95 –Cut on the missing mass with the right lepton mass assignment Ke2/K  2: Analysis

8. Yalta 2007 8 Cristina Biino The dominant background is K  2 –A muon loses almost all its energy in the calorimeter, giving the E/p of the electron –It is measured from the data in momentum bins K e3 contribution is obtained by MC DataMC Ke2/K  2: Background

9. Yalta 2007 9 Cristina Biino NA48 - 2004 data sample – 3407 ± 63 st ± 54 sy K e2 events – The bigger systematics is the K  2 background subtraction R K = (2.455 ± 0.045 ± 0.041) 10 -5 NA48 - 2003 data sample – 4670 ± 77 st +29 -8 sy K e2 events – Trigger efficiency is the bigger systematics R K = (2.416 ± 0.043 ± 0.024) 10 -5 KLOE – ~ 8000 K e2 events from 1.7 fb -1 – Different systematics R K = (2.55 ± 0.05 ± 0.05) 10 -5 Ke2/K  2: Recent Results Combine all preliminary results and PDG2006: R K = (2.457 ± 0.032) 10 -5  2 /n dof = 2.44/3

10. Yalta 2007 10 Cristina Biino A dedicated run to measure R K has been approuved for 2007 –4 months of data taking –Collect ~150,000 K e2 –Goal to reach an error of ± 0.3% Optimized beam parameters wrt 2004 –Kaon momentum from 60 GeV/c to 75 GeV/c –Kaon momentum bite from 3 GeV/c to 2.5 GeV/c –p T kick from the spectrometer magnet from 120 to 263 MeV/c All these improve the kinematic separation of K e2 Ke2/K  2: NA62 (ex NA48) 2007 run

11. Yalta 2007 11 Cristina Biino It is mainly K  2 Below 35 GeV/c use kinematic separation –Build M 2 miss with electron assumption equal samples of K e2 and K  2 Above 35 GeV/c use E LKr /p tr to identify the electron - But 510 -6 of muons experience a catastrophic energy-loss in the LKr and are mis-identified as electrons Montecarlo simulation Ke2/K  2: Background to Ke2

12. Yalta 2007 12 Cristina Biino Measure this background during the run Put a 9 X 0 lead bar between the hodoscope planes in front of the LKr –Lose 18 % of acceptance –All electrons are killed –Only muons pass –The E/p distribution of the muons is measured Ke2/K  2: Background to Ke2

13. Yalta 2007 13 Cristina Biino Ke2/K  2: Expectations Expected precision on R k –Statistical 0.28% with 150,000 K e2 decays –Systematic 0.2% Thanks to the measurement of the K  2 background and to the improved beam and spectrometer conditions The 2007 dedicated Run: –It is going on since ~ the end of June –The detector has restarted well after 3 years –Data taking is quite smooth –As a reference, a good shift (8 hours) is giving around 800 K e2

14. Yalta 2007 14 Cristina Biino 2. Lepton universality and CKM matrix element |Vus| with the K   0 l  decays –Measurements of BR(K   0 e  ) and of BR(K   0   ) –Extraction of |Vus| –|Vus| and Lepton Universality r  e

15. Yalta 2007 15 Cristina Biino NA48: Extraction of |Vus| from K  l3  (K l3 ) = BR(K l3 )/  K = GF2GF2 384  3 m K 5 S EW |V us | 2 |f + (0)| 2 I K (1+  K ) Short-distance radiative correction The measured quantity Phase space integral containing form-factor parameterization Long-distance correction (isospin symmetry breaking) NA48 Data sample: ~3 days of dedicated running (very soft trigger) in 2003 Analysis method: measurement of BR(K e3 )/BR(K     0 ), BR(K  3 )/BR(K     0 )  normalization to a large and well-know mode with a similar signature. Decay channelK+K+ K–K– Background level K   0 e  56,19530,898~10 –4 K   0   49,36427,525~0.2% K     0 461,837256,619 Event samples collected

16. Yalta 2007 16 Cristina Biino NA48:K  l3 and |Vus|: results NA48: K  l3 and |Vus|: results BR(K e3 )/BR(K     0 ) = 0.2470  0.0009 stat.  0.0004 syst. BR(K  3 )/BR(K     0 ) = 0.1637  0.0006 stat.  0.0003 syst.  Both measurements above the PDG’06 average, but agree with other experiments normalizing to    0 ;  Comparison to KLOE: a hint that the PDG’06 value of BR(    0 ) is biased (waiting for KLOE    0 ! ) BR(K e3 ) = (5.168  0.019 stat.  0.008 syst.  0.030 norm. )% BR(K  3 ) = (3.425  0.013 stat.  0.006 syst.  0.020 norm. )% BR(K e3 ) measurements PDG’06 BNL E865 2003 KLOE (2007 absolute measurement ) ISTRA+ 2007 NA48/2 2007 % PDG’06 KLOE (2007 absolute measurement ) NA48/2 2007 BR(K  3 ) measurements % Eur. Phys. J. C50 (2007) 329 + erratum Assuming Br(K2  ) from PDG

17. Yalta 2007 17 Cristina Biino NA48:K  l3 and |Vus|: results NA48: K  l3 and |Vus|: results  Errors dominated by those of long-distance corr. |V us | = 0.2277  0.0013 other  0.0019 th. = = 0.2277  0.0023  Combined K e3 and K  3 result: compatible to CKM unitarity  Error dominated by the theoretical uncertainty of f + (0) |V us |f + (0) = 0.2193  0.0012 [K e3 ] = 0.2177  0.0013 [K  3 ] = 0.2188  0.0012 [K l3 ] |Vus| unitarity f + (0) = 0.2185  0.0022 |Vud| = 0.9738  0.0003 |Vub| = (3.60  0.7) 10 -3 f + (0) = 0.961(8) Marciano & Roos ‘84 Leutwyler & Roos ‘06

18. Yalta 2007 18 Cristina Biino |Vus| and Lepton Universality: results  One can evaluate : for the K  mode: r  e = 1.0059(87) using 2004 BRs r  e = 1.019(13) (R  e ) obs   3 I e3 (1+  e3 ) [ |V us | f + (0) ] 2  3,obs ( G  F ) 2 r  e = = = (R  e ) SM  e3 I  3 (1+   3 ) [ |V us | f + (0) ] 2 e3,obs ( G e F ) 2 I : integral of form factors over phase space (1+  ) : form factor corrections for SU(2) breaking and long distance EM interactions for the K LS mode: r  e = 1.0039(56) using 2004 BRs r  e = 1.054(15) for the  l mode: r e  = 0.9966(30) Erler, Ramsey-Musolf ‘06 Results from Flavianet Working Group on Kaon Decays

19. Yalta 2007 19 Cristina Biino 3. P326 : a proposed experiment to measure the rare decay K +     at the CERN SPS –Theoretical prediction and experimental situation –P326 proposal: beam and detector challenges experimental techniques and background rejection

20. Yalta 2007 20 Cristina Biino CP Standard Model predictions BR(K +  + )  (1.6×10 -5 )|V cb | 4 [  2 +(  c -  ) 2 ]  (8.0 ± 1.1)×10 -11 BR(K L  0 )  (7.6×10 -5 )|V cb | 4  2  ± 0.6  ×10 -11 Golden modes  FCNC loop processes  Short distance dynamics dominated  One semileptonic operator, hadronic matrix element related to measured quantities Present measurement (E787/949): BR(K +   ) = 1.47 × 10  10 (3 events) +1.30 -0.89 K + →  + : a theoretical clean environment sensitive to new physics

21. Yalta 2007 21 Cristina Biino P326 a 10% new measurement (100 events ) CERN-SPSC-2005-013 SPSC-P-326 September 2005: presented at CERN SPSC December 2005: R&D endorsed by CERN Research Board Start of test beams at CERN in 2006 2007: prototypes construction and test beams at CERN and Frascati 2008 – 2010: Technical design and construction Start of data taking 2011 Schedule Located in the same hall as NA48 CERN, Dubna, Ferrara, Firenze, Frascati, Mainz, Merced, Moscow, Napoli, Perugia, Pisa, Protvino, Roma, Saclay, San Luis Potosi, Sofia, Torino, Triumf  Proposal to Measure the Rare Decay K    at the CERN SPS

22. Yalta 2007 22 Cristina Biino P326 guidance principles O (100) K +  +  events ~ 10% background Kaon decay in flight technique Intense proton beam from SPS High energy K (P K = 75 GeV/c)  Kaon ID (CEDAR)  Kinematical rejection Kaon 3-momentum: beam tracker Pion 3-momentum: spectrometer KK K+K+  m 2 miss =(P K  P  ) 2  Veto and particle ID  /  detection: calorimeters Charged veto: spectrometer  /  /e separation: RICH  BR(SM) = 8×10 -11  Acceptance 10%  ~ 10 13 K + decays in 2 years

23. Yalta 2007 23 Cristina Biino Kinematics and Backgrounds 92% of total background Allows us to define a signal region K +   +  0 forces us to split it into two parts (Region I and Region II) Span across the signal region Rejection must rely on vetoes Kinematically constrained Not kinematically constrained 8% of total background

24. Yalta 2007 24 Cristina Biino The Beam: narrow band, high intensity P Kaon = 75 GeV/c (  P/P ~ 1.1%) Fraction of K + ~ 6.6% Negligible amount of e + Beam acceptance = 12  str (×25 NA48/2) Area @ beam tracker = 58×24 mm 2 Integrated average rate = 760 MHz K + decays / year = 4.8 × 10 12 P proton = 400 GeV/c Proton/pulse 3.3×10 12 (×3.3 NA48/2) Duty cycle 4.8/16.8 s Primary beam Secondary beam Vertical view DECAY VOLUME VOLUME (~100 m) K+ decay rate: ~11 MHz p Achromat 1 Quadrupoles Radiator Achromat 2 Cedar Scraper Gigatracker 20 mm 5 m Target

25. Yalta 2007 25 Cristina Biino The P326 layout Technical Design Report in preparation VACUUM 10 -6 mbar 50 MHz 800 MHz11 MHz K + ~ 75 GeV ++

26. Yalta 2007 26 Cristina Biino The tracking system The Gigatracker (i.e. the beam spectrometer) The Spectrometer (i.e. the downstream tracker) 3 Si pixel stations across the 2 nd achromat: (60 × 27 mm 2 ) 4 chambers with 4 double layers of straw tubes each (  9.6 mm)  Rate: ~ 45 KHz per tube (max 0.8 MHz)  Low X/X 0 0.1% X 0 per view in vacuum  Good hit space resolution 130  m per view  Moment p measurement 1 magnets (270 pt kick)  Veto for charged particles 5cm radius beam hole displaced in the bending plane according to beam path m 2 miss resolution ~ 1.1×10  3 GeV 2 /c 4 main contribution from θ  K measurement θKθK pp pKpK θKθK θθ m 2 miss resolution 8.8 m 7.2 m 2.1 m Time resolution (ps) Signal/Background  (P K )/P K ~ 0.22%  (  K ) ~ 16  rad ( (  Rate 760 MHz (charged particles) ~ 50 MHz / cm 2  300×300  m pixels  200 Si  m sensor + 100 Si  m chip Low X/X 0  Readout chip bump-bonded on the sensor (0.13  m technology) Excellent time resolution needed for K + /  + association  (t)~200 ps / station Prototype Test Beam in 2007

27. Yalta 2007 27 Cristina Biino The particle ID system 18 m long tube (  2.5 m ), 17 focal lentgh mirrors CEDAR: existing Cerenkov counter at CERN The CEDAR (i.e. the kaon ID) The RICH (i.e. the pion ID ) p K  Beam composition  Adapted to P326 need:  Vary gas pressure and diaphragm aperture to select Kaons H 2 instead of Ne New PMs and electronics  Ne @ 1 atm (  thr = 13 GeV/c)  >3   /  separation up to 35 GeV/c  High granularity (2000 PMTs)  Small pixel size (18 mm PMT)  Disentangle pileup in Gigatracker  (t)~100 ps PMTs tested in 2006 Prototype Test Beam in 2007

28. Yalta 2007 28 Cristina Biino The Veto system Large angle (10-50 mrad): 13 ANTIS Two options under test: Lead-scintillator tiles or blocks or Lead-scintillator fibers (KLOE-like) Photon vetoes Rings calorimeters (in vacuum) Rate: ~ 4.5 MHz (  ) + ~ 0.5 MHz (  ) (OR 12) 10 -4 inefficiency for 0.05 < E  < 1 GeV 10 -5 inefficiency for E  > 10 GeV Medium angle (1-10 mrad): NA48 LKr Calorimeter New Readout Rate: ~ 8.7 MHz (  ) + ~ 4 MHz (  ) + ~ 4 MHz (  ) 10 -4 inefficiency for 1 < E  < 5 GeV 10 -5 inefficiency for E  > 1 GeV Inefficiency for E  > 10 GeV tested on NA48/2 data ( K + →     ) Small angle (< 1 mrad): Shashlik technology Rate: ~ 0.5 MHz (  ) 10 -5 inefficiency for high energy photons Sampling calorimeter + Magnet for beam deflection Muon veto and sweeper Rate: ~ 7 MHz (  ) + ~ 3 MHz (  ) 10 -5 inefficiency for  detection Sensitivity to the MIP em/hadronic cluster separation 5Tm B field in a 30×20cm 2 beam hole: deviate the beam out from the SAC

29. Yalta 2007 29 Cristina Biino Preliminary sensitivity studies Acceptance (60 m fiducial volume):  Region I: 4%  Region II: 13%  Total: 17% To be reduced after analysis cuts (losses due to dead time, reconstruction inefficiencies…) Simulation of the P-326 apparatus Acceptance ~ 10% is achievable Region I and II Momentum range: 15 < P  < 35 GeV/c  Against muons  RICH operational reasons  Plenty of energy in photon vetoes Remind: K  m 2 miss = 0.0182 GeV 2 /c 4 K  m 2 miss < 0

30. Yalta 2007 30 Cristina Biino Signal and Backgrounds Events/yearTotalRegion IRegion II Signal (acc=17%) 651649 K++0K++0 2.71.71.0 K +  + 1.21.1<0.1 K +  e +  +   ~2negligible~2 Other 3 – track decays ~1negligible~1 K++0K++0 1.3negligible1.3 K++K++ 0.50.2 K +  e + (  + )  0, others negligible  Total bckg.93.06  S/B ~ 8 (Region I ~5, Region II ~9)

31. Yalta 2007 31 Cristina Biino Conclusions  P326 experiment: Search for new physics using the rare Kaon decay K + →  +  A new experiment (~10 -12 sensitivity per event) at an existing machine and employing the infrastructures of an existing experiment  General design mostly defined. Overall simulation and performances under review  R&D program: construction of detector prototypes and test in progress. Important results by end of 2007  An accurate measure of Kl2 decays can provide a sensitive test on SM and e/  universality.  NA48 experiment: has presented two measurements compatible with SM predictions.  NA62 experiment: a dedicated run is under way to collect 150,000 Ke2 and measure RK with 0.3% accuracy.  NA48 experiment: measured ratios of decay rates of Ke3 and K  3 to K2  are presented. Both measurements are found to be larger than the current values given by PDG and lead to a larger magnitude for |Vus|. When combined with the latest PDG value of |Vud| the result is in agreement with unitarity of the CKM matrix.  A lepton universality test is computed and a comparison to other kaon channels is done.

32. Yalta 2007 32 Cristina Biino Back-up Slides

33. Yalta 2007 33 Cristina Biino Running conditions –Same minimum bias trigger as in 2004 K e2 : 1 track in the hodoscope + energy in the LKr K  2 : 1 track downscaled From 2004 experience, all systematics below 0.2%, except background to K e2 Tabella di venelin, con freccia error is statistic Event filtering performed in L3 A factor 2.4 reduction K e2, K  2 streams + control triggers and few additional decay modes In 2004 limited by the statistics of the control sample Ke2/K  2: 2007 Run

34. Yalta 2007 34 Cristina Biino Background Rejection K + →   (K  )  Largest BR: 63.4%  Need ~10 -12 rejection factor Kinematics: 10 -5 Muon Veto: 10 -5 MAMUD Particle ID: 5×10 -3  RICH K + →     ( K  )  2nd Largest BR: 20.9%  Need ~10 -12 rejection factor Kinematics: 5×10 -3 Photon Veto: 10 -5 per photon Large angle: 13 ANTIs (10 < acceptance < 50 mrad) Medium angle: NA48 LKr (1 < acceptance < 10 mrad) Small angle: IRC1,2 SAC (acceptance < 1 mrad) Assuming the above veto inefficiencies and an acceptance of 10%, a S/B > 10 is obtained if (  m) 2 ~ 8×10 -3  GeV 2 /c 4

35. Yalta 2007 35 Cristina Biino Trigger  A possible scheme: LevelL0 “hardware”L1-L2 “software” Input~10 MHz1 MHz Output1 MHz O (KHz) ImplementationDedicated hardwareTDAQ farm ActionsRICH 1Track, μ veto, LKr (  ) veto L1 = single sub-detectors L2 = whole event  Software trigger reduction ~ 40

36. Yalta 2007 36 Cristina Biino Irradiated test diode itc-IRST wafer, 200µm Gigatracker: R&D program Readout chip: 1st MPW submission in 0.13  m Submitted in February 07 Analogue FE blocks for the "CFD" option (Torino ) FE amplifier discriminator NINO, LVDS driver (CERN) Wafers delivery ≈ end May 07 ASICs characterization (t resolution, jitter, time walk) Tests card in progress (results by September) Si diode irradiation tests Prototype wafers (200µm thick) produced by itc-IRST using ALICE pixel layout 3 mm × 3 mm and 7 mm × 7 mm test-diodes Test diodes irradiated with n and p (Ljubljana, CERN) Fluences: 1E12 to 2E14 1MeV n cm -2 (range P326) Pre and post irradiation measurements (annealing) to study diode characteristics Si diode characterization with pulsed IR laser system Towards a Technical Proposal

37. Yalta 2007 37 Cristina Biino Chosen technology: tube of mylar (25  m, D=1 cm, L=2.1 m) 100 straws produced in Dubna Tests on gas leakage Tests on tube expansion in vacuum Prototype assembled & cosmic ray tests October 2007: Prototype integration in NA48 set-up and test on beam Spectrometer: R&D program

38. Yalta 2007 38 Cristina Biino CEDAR W-type filled with Ne tested at CERN in November 2006, using a 100 GeV hadron beam with 10 5 – 10 7 ppp (CERN, Firenze, Perugia). Test of fast photomultipliers using Cerenkov light. CEDAR upgrade program CEDAR: R&D program

39. Yalta 2007 39 Cristina Biino pK+pK+ Simulation FWHM 0.375 ps t ns November 2007: prototype integration in the NA48 set up and test with beam RICH: R&D program Full length prototype (17 m, 0.6 m diamater, stainless steel tube at CERN) Mirror built, delivered and under test in Firenze Endcap with 96 Hamatsu PMs readout through Winston’s cones PMs tested at SPS (2006) and Firenze/Perugia (with laser) Measured FWHM per single  per phototube 390ps (150 ps electronics and 110 ps laser included) Design, construction and test of a RICH prototype (CERN, Firenze, Perugia)

40. Yalta 2007 40 Cristina Biino October 2006 test: Tagged photon beam Using the existing NA48 setup vacuum Electron beam (25 GeV/c) Bremsstrahlung Kevlar window Drift chambers Magnet Calorimeter  e- X LKr cm  Energy deposition in LKrelectron Energy GeV 2×10 8 electrons collected 10  ineff.sensitivity below 10 GeV Liquid Kripton Calorimeter Consolidation of the readout Custom boards (FPGA based) sending data directly to PC Farm Test of the new electronics in 2007 NA48 run

41. Yalta 2007 41 Cristina Biino KLOE-type lead/scintillating fiber: prototype constructed in Frascati 1 mm diameter scintillating fibers, 0.5 mm thick lead foils. Readout granularity: 18 cells Very well known and tested technology Under test at the Frascati BTF 16.8 cm8.2 cm All fiber: 8 X 0 Fibers+lead wires: 9 X 0 Studies of the efficiency of detectors built with this technology available Fermilab prototype under test at BTF  Outgassing tests performed at CERN on detectors built with same technology: they can be placed in the vacuum of the decay region (10 -6 mbar) Lead scintillators tiles Aijimura et al. NIM in press Large angle photon vetoes: R&D program

42. Yalta 2007 42 Cristina Biino eeee  Test beam activity at BTF in Frascati (Frascati, Napoli, Pisa, Roma) e - beam (300-500 MeV/c) Both calorimeter prototypes under test 1 st step: test with electrons 2 nd step: test with photons Test beam periods in March, April, June 2007 Work carried on up to now using electrons: Understanding the beam background Calibration of the prototypes First data analysis (efficiency, energy and time resolution) Large angle photon vetoes: R&D program

43. Yalta 2007 43 Cristina Biino MAgnetized MUon Detector Sampling calorimeter + Magnet for beam deflection Em/hadronic clusters separation Sensitivity to MIP 10   detection inefficiency Muon Veto: MAMUD

44. Yalta 2007 44 Cristina Biino LevelL0 “hardware”L1-L2 “software” Input~10 MHz1 MHz Output1 MHz O (KHz) ImplementationDedicated hardwareTDAQ farm ActionsRICH minimum multiplicity, Muon vetoing, LKr vetoing L1 = single sub-detectors L2 = whole event Main work on possible solutions for the L0 hardware TELL-1 board (LHCb) based implementation for all non FADC sub detectors Design of a new 100 ps TDC daughter-card (RICH, Straws, MAMUD,…) Two prototypes under study (Mainz and Pisa) A possible scheme: TRIGGER 1 track ×  ×  → 1 MHz L1 trigger input → PC farm Software trigger reduction ~ 40

45. Yalta 2007 45 Cristina Biino P-326 Kaon Flux ~100 times NA48/2 Kaon Flux Other physics opportunities can be addressed: Lepton – flavor violation: K e2 /K  2,K +  +  + e -, K +  -  + e + Tests of CPT K +  +  - e + Search for new low mass particles: K +    (light RH neutrinos) K +  +  0 P (pseudoscalar sGoldstino) Hadron spectroscopy … Other physics opportunities