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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 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: 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 fb1 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
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
KLOE physics papers KS ePLB 535, 37 (02) KS PLB 538, 21 (02) KL lifetimeaccepted byPLB KL PLB 566, 61 (03) KL mainsubmitted toPLB K+ +00PLB 597, 49 (04) KS 000PLB 619, 61 (05) 0 PLB 536, 203 (02) 00 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)
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)
KL decays at KLOE KL 30 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)
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
The study of KL decays has been the driving force in the design and operation of KLOE. However DANE has proven to be almost without competitors under other respects. KS decays: 3x105taggedKS mesons delivered / pb1 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 / pb1 KLOE has already the largest sample of mesons collected to date.
I will discuss all of the three items above, but, because of personal preparation and prejudice, I will emphasize KS decays mostly
Sensitivity to CPT violation through the charge asymmetry: • ASAL signals CPTin mixing and/or in SQ 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+)
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)
KS e decays KLOE current results ( ~ 400 pb1) : BR( KS +e) = ( 3.53 ± 0.05 ± 0.03) x 104 BR( KS e+) = ( 3.54 ± 0.06 ± 0.04) x 104 BR( KS e) = ( 7.06 ± 0.08 ± 0.06) x 104 AS = ( 1.5 ± 10 ± 5 ) x 103 Present KLOE run aims at AS~ 3 x 103 i.e ~ 2 Re A 3 measurement of AS requires ~ 20 fb1
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)
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)
KS 30 decays This decay violates CP. SM branching ratio is 2 x 109 MC Eff. Stat. = 5.3 data Analysis based on counting and kinematic fit on 20 and 30 hypotesis 22 Nbck (MC) = (3.13 ± 0.82 ± 0.37) 23 KLOE 450 pb1 Nobs = 2 450 pb-1 ’01+’02 data BR ≤ 1.2 x 107 90% C.L. 22 Cf. NA48 (05): BR ≤ 7.4 x 107 90% C.L. 23
KS 30 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 fb1 one can reach a limit ~ 5x109
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
KS +0 decays Scaling above numbers: With 20 fb1 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
KS 0 e+edecays 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%”
KS 0 e+edecays Feasibility study performed on the basis of ~ 480 pb1 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 20+ 10 dalitz decay 16 KS 20+ 20 dalitz decay (double dalitz) 277 KS 20+ conversion 93 Badly reconstructed K+K events 2 Badly reconstructed 0 events
KS 0 e+edecays Further selection based on cuts on 5 independent variables signal MC MC signal DATA 400 pb1 DATA 400 pb1 2 kinem. fit e+e inv. mass
KS 0 e+edecays Cuts tuned on MC: 0 events retained < 4.8 ev / fb1 @ 90% CL Detailed studies of problematic topologies: single dalitz : 880 pb1 : 0 events < 2.6 ev / fb1 double dalitz: 4200 pb1 : 0 events < 0.55 ev / fb1 K+K : 880 pb1 : 0 events < 2.6 ev / fb1 Overall efficiency on signal: 4.3% Check on data (~ 400 pb1) : 0 observed (0.12 expected) Optimistically (no further bkg) ~ 5 events observed in 20 fb1
Quantum Interferometry Measurements of decay time differences between KS and KL decays into various combinations of +, 00, l can determine the entire set of parameters describing the neutral kaon system From fit on KSKL ++ (380 pb1) m = (5.34 ± 0.34) x109 hs1 At 20 fb1 m = 0.05 x 109 hs1 Data Fit result Compare with : PDG 04 : m = 0.016 x 109 hs1 Best (KTeV 03) : m = 0.043 x 109 hs1
Quantum Interferometry interference term modified introducing a decoherence parameterz. From fit on KSKL ++ (380 pb1) KLOE preliminary result: At 20 fb1 Compare with : (from CPLEAR data)
meson decays With 20 fb1 as many as 6x108 mesons produced Channels presently studied with KLOE: With 20 fb1, can largely improve UL’s on 0l+l, e+e, +
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
A note on tracking – an explicative example from K+K Split track, no VTX reconstructed Split track
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.
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