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M. Palutan, T. Spadaro, P. Valente Laboratori Nazionali di Frascati

Status of the analysis of K S semileptonic decays Update on BR ( K S  p - p + )/ BR ( K S  p 0 p 0 ). M. Palutan, T. Spadaro, P. Valente Laboratori Nazionali di Frascati. C. Gatti Università Statale di Pisa  Università di Roma “La Sapienza”. e + p - n H WK  K 0  = a + b

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M. Palutan, T. Spadaro, P. Valente Laboratori Nazionali di Frascati

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  1. Status of the analysis of KS semileptonic decaysUpdate on BR(KS p-p+)/BR(KS p0p0) M. Palutan, T. Spadaro, P. Valente Laboratori Nazionali di Frascati C. Gatti Università Statale di Pisa  Università di Roma “La Sapienza”

  2. e+p-nHWKK0 = a+b e-p+nHWKK0 = a*-b* e-p+nHWKK0 = c+d e+p-nHWKK0 = c*-d* Physics motivations • Two clean predictions within the Standard Model: • Transition rates: G(KS  pen) = G(KL  pen)  DS=DQ rule • Charge asymmetries: AS = AL CPT symmetry eS = eK+dK eL = eK-dK CPT violation in decay CPT violation in mixing

  3. Test of the DS=DQ rule. The relevant parameter is: e+p-nHWKK0 Re x+ Re c*/a  KLOE statistical error on Re x+ e+p-nHWKK0 KLOE 2000: Phys. Lett. B535 (2002) (assuming d=0) CPLEAR measurement (-1.86.1)10-3 GSsemi = 1 + 4 Re x+ GLsemi BR(KSpen) tL BR(KLpen) tS BR and DS=DQ rule (I) Re x+ can be extracted by measuring the ratio of semileptonic KS and KL decay widths summing up both charge final states 810-3 710-3 110-3

  4. Charge asymmetry (I) G+S,L - G-S,L AS,L = G+S,L + G-S,L AS = 2Re eK + 2Re dK+ 2Re b/a - 2Re d*/a AL = 2Re eK - 2Re dK+ 2Re b/a + 2Re d*/a No measurement CP CPT in mixing CPT in decay DSDQ and CPT AS -AL0 implies CPT (AS +AL  4Re eK) Re dK = (2.9  2.7) 10-4 CPLEARPhys Lett B444 52 (1998)

  5. Charge asymmetry (II) G+S,L - G-S,L AS,L = G+S,L + G-S,L • 3 levels of accuracy can be considered: • In order to test if AS is consistent with 2Re eK , need 2 fb-1 • In order to measure AS with O(30%) significance, need 20 fb-1 • In order to improve limits on dK=(AS – AL)/4 , need 50 fb-1 • + precise measurement ofALe from KTeV ALe = (3322  58stat  47syst ) 10-6 KTeV Phys Rev Lett 88 (2002) KLOE is able to improve on the measurement ofALe, using the whole 500 pb–1 data set

  6. t+ p+0BR+- MK02 tSp+-BR+0 MK+2 1 + 1/ w2 =(1+p+-/ p00R) 1 + w2/2 + w 2 cos(d0-d2 ) R p00/p+- = 1 + 2 w2-w 22 cos(d0-d2 ) KS p+p- and KS p0p0 decays Both the isospin (I=0 and 2) amplitudes and the pp phase-shifts can be estimated from the measured K pp branching ratios: A(K0 p+p-) = A0 eid0+ 2A2 eid2 A(K0 p0p0) = A0 eid0- A2 eid2/2 A(K+ p+p0) = 3/2 A2 eid2

  7. KS p+p- and KS p0p0 decays • Using the PDG values for the branching ratios, one gets: • d0-d2  (56.73.8) (and w=0.045) • This value is inconsistent with the prediction from O(p2) cpT (456), the measurement from pp scattering (45.21.3 1.5), and the estimate from the KL decays • With the KLOE published measurement of • R = G(KS p+p-)/G(KS p0p0)=2.239 based on 17 pb-1 • (R = 2.1857 PDG): • d0-d2  (483)(while w is unchanged) • In pipeline, planned for mid 2003: • Measurement of R with an error of 10-3 • Measurement of both the absolute branching ratios

  8. KS beam KL • A pure KS beam can be selected by identifying the KL in the opposite hemisphere  KS tag • Due to the very different lifetimes lS  0.6 cm, lL 350 cm, a very efficient tag is given by KL’s that reach the calorimeter and interact therein (Kcrash) • ecrash 30% • The Kcrash cluster is cleanly identified by its low velocity, b  0.2, as measured from the time of the e+e- interaction (t0). • This also provides an estimate of the KL direction (s  2) and momentum (s  3MeV) Pf KS

  9. Ks beam KSp0p0 Events tagged by a ‘Kcrash’ cluster KSp+p- Looser cut on b*, from (0.195, 0.2475) to (0.17, 0.28) Higher tagging efficiency, from 0.3 to 0.35 at 100 MeV Lower systematic error in the estimate of the ratio of p+p-/p0p0 and p+p-/pen tagging efficiencies, especially for Kcrash energy cut above 200 MeV

  10. Measurement method ‘Kcrash’ cluster N a BR(KS a) ea =  N b BR(KS b) eb Events tagged by a ‘Kcrash’ cluster p p Selection of KSp+p- events 2 tracks close to the IP, impact on the EmC At least one track associated to an EmC “T0” cluster (0.2% loss) Less than 3 prompt EmC clusters, not associated to any track (0.08% loss)

  11. Measurement method ‘Kcrash’ cluster N a BR(KS a) ea =  KL N b BR(KS b) eb Events tagged by a ‘Kcrash’ cluster e boost p KS Selection of KSpen events 2 tracks and 1 vertex close to the IP, to EmC n Reject events with invariant mass Mpp close to the K0 mass Use time information from calorimeter clusters to perform PID for charged tracks

  12. p/e identification • Time of flight e/p identification (Dt  2 ns) : • dt(m) = tcluster – t.o.f.calculated with mass hypothesis m • Sign of the charge is determined  semileptonic asymmetry accessible e-p+ MC KS  p+p- MC KSpen Data pesignal dt(me1)dt(mp2) dt(me2)dt(mp1) 6 ns e+p-

  13. pen final selection Close the kinematics, by using: KLOE 2000: PLB B535 (2002) 1) e-p identification from t.o.f. 2) KS momentum from KL crash direction and momentum: N(pen) = 627  30 Emiss = ES - Ee- Ep Pmiss = |PS - p1- p2|

  14. Entries 62738 e+p- e-p+ Entries 48917 Data 166 pb-1 (2001) Emiss-Pmiss (MeV) Charge-selected pen spectra Form of signal distribution approximately independent of sign of charge

  15. e+p- e-p+ Data 166 pb-1 (2001) Charge-selected pen spectra Emiss-Pmiss (MeV) Substantial charge dependence of the KSp+p- background spectrum far away from the signal peak

  16. N(p-e+n) = 3854  92  Data 166 pb-1 (2001)  MC fit result c2/n.d.f = 1.5 Event yields by sign of charge Fitting to data unselected by charge gives a result compatible with the sum: N(pen)=7732127 N(p+e-n) = 3863  88  Data 166 pb-1 (2001)  MC fit result c2/n.d.f = 1.1

  17. Efficiency estimates (I) epen = e(fiducial cuts) e(t.c.a) e(t0trigger) e(t.o.f.) 1) “Natural” data control sample: KLpendecays close to the IP • 2) Correction obtained by weighting Monte Carlo kinematics with single-particle efficiencies extracted from data: • KSp +p- (p and m efficiencies) • fp +p- p0 (p and m efficiencies) • Radiative Bhabha (e efficiencies) • KLpen (p, m, and e efficiencies) Pion calorimeter clusters needed for t.o.f PID, correct parametrization of calorimeter response to low-energy (100 MeV) pions is therefore a crucial task

  18. Efficiency estimates (II) 3) Data control sample of KLp+p-p0decays to tag the KS (Rtag) • 4) Data control sample of KSp0p0 and KLpen close to the IP to study vertex efficiency: • The vertex requirement led to the biggest source of systematic error in the 2000 anaysis (1% uncertainty) • Official routine has 2% inefficiency. • A new recovery algorithm has been implemented, which releases the quality cuts of VTXMIN on the c2 (it just looks for a mimimum) • New vertex efficiency practically 100%

  19. Data of year 2000: branching ratio measurement e(fiducial cuts) = (29.70.5)% e(t.c.a.) = (92.50.6)% e(t0trigger) = (92.20.4)% e(t.o.f.) = (82.00.7)% epen= (20.80.4)% N(pen) = 627  30 N(p+p-) = 1.6106 Normalizing to the KS p+p- channel, one gets: BR(KS pen) = (6.910.37)10-4 From the KL semileptonic decay width and assuming Re x+=0,BR(KSpen)=(6.700.07)10-4 Published year 2000 result based on 17 pb-1 is 5 times more accurate than the only existing measurement

  20. Data of year 2001: efficiencies by charge Systematic and statistical uncertainties nearly equally contribute to the error on the pen total selection efficiency

  21. Data of year 2001: branching ratio measurement N(pen) = 7732  127 N(p+p-) = 21.354 106 epen = (23.170.14)% Normalizing to the KS p+p- channel, one gets: BR(KS pen) = (6.610.110.070.040.03)10-4 Statistical Fit syst Effi syst BR(pp) error From the KL semileptonic decay width and assuming Rex+=0, BR(KSpen)=(6.700.07)10-4 Result based on 166 pb-1 of 2001 data

  22. N+ e+-N- e- AS = N+ e++N- e- Charge asymmetry To get the asymmetry, one has to correct the e+p- and e-p+ event yields using the efficiencies for each sign of charge… Present PRELIMINARY result is based on 166 pb-1 AS = 0.012 0.017stat 0.004systwith an overall error of 2% BR(KS p-e+n) = (3.3300.0810.0330.0180.014)10-4 BR(KS p+e-n) = (3.2490.0760.0320.0170.013)10-4

  23. Conclusions and prospects on KSpen Present preliminary result for the branching ratio has an overall error of 2%, allowing an accuracy on Re(x) of 0.5% Present preliminary result (2001 data) for the charge asymmetry has an overall error of 2% and is compatible with 0 Work is needed to improve the MC simulation for the Emiss-Pmiss background spectrum • Full analysis of year 2001-2002 sample will allow measurement of: • Re x with an accuracy better than 5 10-3 • Charge asymmetry to within 1.%

  24. Status of KSp+p- / KSp0p0 • Selection efficiency for KSp+p- is evaluated by folding data/MC tracking, TCA, T0 efficiencies into the MC simulation • Efficiencies have been extracted for the whole 2001 sample and for a selected sample of 60 pb-1 of 2002 • Ratio of tagging efficiency with the new b* window is now stable at 0.1% level throughout the samples • Work is needed to address the selection efficiency for KSp0p0: • Photon efficiencies • Calorimeter response Run over the whole data set to check stability and to measure data/MC corrections over the entire detector • Effect of accidental clusters on the prompt counting

  25. Measurement method ‘Kcrash’ cluster N a BR(KS a) ea =  N b BR(KS b) eb g Events tagged by a ‘Kcrash’ cluster g g Selection of KSp0p0 events At least 3 prompt EmC clusters not associated to any track

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