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Physics with KLOE at DAFNE phase 2

Physics with KLOE at DAFNE phase 2. F. Bossi, LNF. Frascati September 16, 2005. The purpose of this talk is to discuss some relevant physics issues that can be studied at the new machine using the KLOE detector. I will emphasize:.

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Physics with KLOE at DAFNE phase 2

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  1. Physics with KLOE at DAFNE phase 2 F. Bossi, LNF Frascati September 16, 2005

  2. The purpose of this talk is to discuss some relevant physics issues that can be studied at the new machine using the KLOE detector I will emphasize: What KLOE has achieved up to now and what part of this can be improved with further statistics Which portion of the original KLOE program can be addressed only with an integral luminosity ≥ 20 fb1 What are the possible ways to improve the detector performance Much of this talk has to be taken as a guideline for discussion and does not pretend to be exhaustive

  3. KLOE has proven to be perfectly suited to cover a wide variety of physics issues, spanning from charged and neutral K decays, to low-energy hadron spectroscopy, to quantum interferometry studies This is demonstrated by the number of published results which have given to KLOE worldwide reputation

  4. KLOE physics papers KS ePLB 535, 37 (02) KS PLB 538, 21 (02) KL lifetimeaccepted byPLB KL PLB 566, 61 (03) KL mainsubmitted toPLB K+ +00PLB 597, 49 (04) KS 000PLB 619, 61 (05)   0 PLB 536, 203 (02)   00 PLB 537, 21 (02)    PLB 591, 49 (04)   ' PLB 541, 45 (02)   + PLB 606, 12 (05)   +0 PLB 561, 55 (03)   + PLB 606, 12 (02)   l+l PLB 608, 199 (05)

  5. The ingredients of success E.M: Calorimeter: Drift Chamber: Full angular coverage Good momentum resolution Large tracking volume Exceptional timing capabilities Minimization of materials Large lever arm Excellent e/ separation based on t.o.f. Good 0 reconstruction capabilities Full kinematical reconstruction of events Maximization of efficiency for long-lived particles (K± ,KL)

  6. KL decays at KLOE KL 30 decay time e  +0 6 – 24.8 ns 40 – 165 cm 0.37 L + L/βc (ns) Lesser of pmiss-Emiss in  or  hyp. (MeV)

  7. Measurements of kaon partial rates provide at present by far the most accurate test of Unitarity (i.e. of Universality as P.F. points out) | Vud|2+ |Vus|2 + |Vub|2 = 0.9998 ± 0.0011

  8. The study of KL decays has been the driving force in the design and operation of KLOE. However DANE has proven to be almost without competitors under other respects. KS decays: 3x105taggedKS mesons delivered / pb1 No way to obtain the same purity at any hadron machine: some decays can be studied only here. Quantum interferometry KLOE reached the highest sensitivity on decoherence effects decays: 4x104 mesons delivered / pb1 KLOE has already the largest sample of  mesons collected to date.

  9. I will discuss all of the three items above, but, because of personal preparation and prejudice, I will emphasize KS decays mostly

  10. Sensitivity to CPT violation through the charge asymmetry: • ASAL signals CPTin mixing and/or in SQ decay amplitudes • Sensitivity to CP violation in K0-K0 mixing: • AS = 2 Re  assuming CPT symmetry • (KS  e) provides test of S= Q rule: • S(e)/L(e) = 1 + 4 Re x • Can obtain |Vus| from measurements of G(KS  e) KS e decays (KSL +e)  (KSL e+) AS,L = (KSL +e) + (KSL e+)

  11. KS e decays Use of TOF and kinematics to reject the huge + background Need to associate DC tracks to calorimeter’s clusters t  texp (e+) (ns) Non negligible loss in signal acceptance Present overall efficiency ~ 6% t  texp (+e) (ns)

  12. KS e decays KLOE current results ( ~ 400 pb1) : BR( KS +e) = ( 3.53 ± 0.05 ± 0.03) x 104 BR( KS e+) = ( 3.54 ± 0.06 ± 0.04) x 104 BR( KS e) = ( 7.06 ± 0.08 ± 0.06) x 104 AS = ( 1.5 ± 10 ± 5 ) x 103 Present KLOE run aims at AS~ 3 x 103 i.e ~ 2 Re  A 3 measurement of AS requires ~ 20 fb1

  13. KS e decays e (KLCrash + Ks DC selection) Can we do better than that? 0.2 T. Spadaro Magnetic field value dramatically affects signal acceptance. Can improve up to a factor ~ 2 0.15 0.1 Present analysis, MC with detailed field map 400 pb-1 MC with LSF=0.5, with uniform axial B field Proper balancing with consequent loss in momentum resolution yet to be studied 0.05 0 3 5 4 B (kG)

  14. KS  decays • Same motivations of the KSe3, but more difficult: • Lower BR: expect 4×10-4 • Background events from KS  pp, p mn: same PIDs of the signal • Troublesome charge identification for the signal • Anyway, measurement never done before • 2002 data • MCm+p- n • MC ppg • MC pp Can reach a statistical accuracy of ~ 3% with present data This channel begs for more statistics ! 20 0 20 Emiss Pmiss ( hyp) (MeV)

  15. KS 30 decays This decay violates CP. SM branching ratio is 2 x 109 MC Eff. Stat. = 5.3 data Analysis based on  counting and kinematic fit on 20 and 30 hypotesis 22 Nbck (MC) = (3.13 ± 0.82 ± 0.37) 23 KLOE 450 pb1 Nobs = 2 450 pb-1 ’01+’02 data BR ≤ 1.2 x 107 90% C.L. 22 Cf. NA48 (05): BR ≤ 7.4 x 107 90% C.L. 23

  16. KS 30 decays Background mostly due to photon clusters double splittings Preliminary studies show that there is room for “algorithmic” improvements in background rejection without big losses in signal efficiency Study of the entire KLOE data set crucial for a better assessment of the real potentialities of the analysis Ideally, with 20 fb1 one can reach a limit ~ 5x109

  17. KS +0 decays Decay mainly CP-conserving (I = 3/2) BR useful to constrain K 3 amplitudes PDG ’04: BR = (3.2+1.2-1.0)  10-7 2 from kin. fit  MC background  MC signal (L x 100) Never observed directly • Preliminary results with 740 pb-1: • Signal efficiency: ~ 1.5% • Candidates: 6 events • Background (sidebands): ~ 3.5 events • Number of events observed consistent with expectation • Statistical error: ~ 100% • Evaluation of systematic error in progress

  18. KS +0 decays Scaling above numbers: With 20 fb1 one can reach a statistical precision of ~ 15% Note: At least one of the two tracks has low momentum: 36% efficiency due only to acceptance Use lower magnetic field could potentially greatly increase efficiency

  19. KS 0 e+edecays Fundamental to assess indirect CPV contribution to parent KL decay Measured by NA48 on the basis of 7 events (plus 6+) BR = (5.8 ± 3) x 10-9 Theoreticians’ dream: measurement at 15% accuracy What efficiency can reasonably be expected for KLOE? Quoting my presentation at a previous meeting ( May 2005): “Based on 3 experience, Matthew bets for 4%”

  20. KS 0 e+edecays Feasibility study performed on the basis of ~ 480 pb1 equivalent MC all- events, and 2x105signal events ( M. Moulson, M. Palutan, T. Spadaro) sig~ 13% First step: usual Ks tagging plus preselection criteria Surviving background events accounted by: 115 KS + 6095 KS 20+ 10 dalitz decay 16 KS 20+ 20 dalitz decay (double dalitz) 277 KS 20+ conversion 93 Badly reconstructed K+K events 2 Badly reconstructed  0 events

  21. KS 0 e+edecays Further selection based on cuts on 5 independent variables signal MC MC signal DATA 400 pb1 DATA 400 pb1 2 kinem. fit e+e inv. mass

  22. KS 0 e+edecays Cuts tuned on MC: 0 events retained  < 4.8 ev / fb1 @ 90% CL Detailed studies of problematic topologies: single dalitz : 880 pb1 : 0 events  < 2.6 ev / fb1 double dalitz: 4200 pb1 : 0 events  < 0.55 ev / fb1 K+K : 880 pb1 : 0 events  < 2.6 ev / fb1 Overall efficiency on signal: 4.3% Check on data (~ 400 pb1) : 0 observed (0.12 expected) Optimistically (no further bkg) ~ 5 events observed in 20 fb1

  23. Quantum Interferometry Measurements of decay time differences between KS and KL decays into various combinations of +, 00, l can determine the entire set of parameters describing the neutral kaon system From fit on KSKL ++ (380 pb1) m = (5.34 ± 0.34) x109 hs1 At 20 fb1 m = 0.05 x 109 hs1 Data Fit result Compare with : PDG 04 : m = 0.016 x 109 hs1 Best (KTeV 03) : m = 0.043 x 109 hs1

  24. Quantum Interferometry interference term modified introducing a decoherence parameterz. From fit on KSKL ++ (380 pb1) KLOE preliminary result: At 20 fb1 Compare with : (from CPLEAR data)

  25.  meson decays With 20 fb1 as many as 6x108 mesons produced Channels presently studied with KLOE: With 20 fb1, can largely improve UL’s on   0l+l,  e+e,  +

  26. A note on tracking In most of the above mentioned decays, low-momentum charged particles are produced A too high magnetic field not only affects the acceptance, but also worsens the pattern recognition and the track reconstruction performance, producing higher splitting probabilities and non-gaussian resolution tails Further complications are posed by the coarse cell granularity and the z-coordinate reconstruction in the full-stereo geometry pions from KS +0 decays

  27. A note on tracking – an explicative example from K+K Split track, no VTX reconstructed Split track

  28. A digression – measurment of the neutron FF Many people have asked whether KLOE can be used to perform the measurement of nucleon form factor. The key issue here is to know the efficiency of the calorimeter in detecting low energy neutrons. At present nobody can really state how large it is. A dedicated test is needed. In the meantime we are following the idea (B. Sciascia) of searching for neutrons in hadronic interactions of K on the beam pipe and the inner DC wall (a background for her analysis!). The method is still under developement but has shown promising preliminary results.

  29. Conclusions and remarks A f factory delivering 20 fb-1 allows an interesting and various physics program to be pursued KLOE has proven to be perfectly tailored for it, although improvements can still be considered: Beside this, the goal of keeping KLOE running beyond 2010 is by no means trivial: careful maintenance and precise studies have to be undertaken to prove the feasibility of this • ♣ Insertion of a vertex chamber closer to the IP • ♣ Implementation of better z coordinate reconstruction by charge division • ♣ Optimization of the magnetic field value with respect to Ks physics and interferometry • ♣ Improvement of reconstruction algorithms, both for charged and neutral particles • ♣ Redesign of the IR and the connected instrumentation

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