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Rare decays program @KLOE

Rare decays program @KLOE. LNF, INFN May 26 th -27 th 2005. Matteo Martini INFN Laboratori Nazionali di Frascati On behalf of the KLOE Collaboration. DA F NE: the Frascati f - factory. e + e - collider @  s = M f = 1019.4 MeV 2 interaction regions (KLOE – DEAR/FINUDA)

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Rare decays program @KLOE

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  1. Rare decays program @KLOE LNF, INFN May 26th-27th 2005 Matteo Martini INFN Laboratori Nazionali di Frascati On behalf of the KLOE Collaboration

  2. DAFNE: the Frascati f - factory • e+e- collider @s = Mf= 1019.4 MeV • 2 interaction regions (KLOE – • DEAR/FINUDA) • Separate e+, e- rings to minimize beam-beam • interactions • Crossing angle: 12.5 mrad ( px(f)12.5 MeV ) 1 M. Martini, K rare decays

  3. KLOE: data taking 2002 Integrated luminosity (pb-1) 2001 2000 Days of running 2000: 25 pb-1 80×106f decays First published results 2001: 176 pb-1 550×106f decays 2002: 296 pb-1 920×106f decays Analysis in progress • New KLOE running in progress: • Lpeak= 1.4 × 1032 cm-2s-1 • 2004: integrated Lum.: 700 pb-1 Goal: collect 2 fb-1 by Dec. 2005 2 M. Martini, K rare decays

  4. The KLOE detector Superconducting coil(B = 0.52 T) Al-Be beam pipe (spherical, 10 cm , 0.5 mm thick) Instrumented permanent magnet quadrupoles (32 PMT’s) sp/p = 0.4 % (tracks with q > 45°) sxhit = 150 mm (xy), 2 mm (z) sxvertex ~1 mm s(Mpp) ~1 MeV sE/E = 5.7% /E(GeV) st= 54 ps /E(GeV)  50 ps svtx(gg) ~ 2 cm(p0 from KLp+p-p0) Drift chamber  Gas mixture: 90% He + 10% C4H10  4 m   3.75 m, CF frame  12582 stereo–stereo sense wires  almost squared cells Electromagnetic calorimeter  lead/scintillating fibers (1 mm ), 15 X0  4880 PMT’s  98% solid angle coverage 3 M. Martini, K rare decays

  5. Kaon production and properties KS (K+) f KL (K-) The f meson decays at rest providing monochromatic and pure kaon beams KSKL (K+K-) produced in pure JPC = 1-- state: Contamination ~10-10 Tagging: observation of KS,L (K+,-) signals presence of KL,S (K-,+) precise measurement of absolute BR’s and interference measurement of KS KL system lS = 6 mm: KS decays near IP lL = 3.4 m: Appreciable acceptance for KL(~0.5lL) NSL ~106 /pb-1; p* = 110 MeV/c l= 0.9 m: 60% acceptance for kaon tracking N+- ~ 1.5106/pb-1; p* = 127 MeV/c 4 M. Martini, K rare decays

  6. Tagging of KS and KL “beams” • KL“crash” • = 0.22 (TOF) KS p+p- KS p-e+n KL 2p0 KL tagged by KS  p+p- vertex at IP Efficiency ~ 70% KL angular resolution: ~ 1° KL momentum resolution: ~ 1 MeV KS tagged by KL interaction in EmC Efficiency ~ 30% KS angular resolution: ~ 1° (0.3 in f) KS momentum resolution: ~ 1 MeV 4x105 tags/pb-1 3x105 tags/pb-1 5 M. Martini, K rare decays

  7. Rare Kaon physics at KLOE hep-ex/0505012 submitted to PLB Paving the road analysis in progress Outlook: • KS 3p0 • - final results • - prospects @2 fb-1 • KSp+p-p0 • - status of the analysis • - prospects @2 fb-1 • KSgg • - preliminary study 6 M. Martini, K rare decays

  8. Search for KSp0p0p0 CP CPT Observation of KS  3p0 signals CP violation in mixing and/or in decay: Uncertainty on KS  3p0 amplitude limits precision of CPT test from unitarity (Bell-Steinberger): CPLEAR ’99 : Imd = (2.4  5.0)x10-5 3p0 uncert. dominates after NA48 meas. : Imd = (-0.2  2.0)x10-5 error now dominated by h+- 7 M. Martini, K rare decays

  9. Search for KSp0p0p0 -- KS3p0 (MC) -- MC BKG  DATA • A kinematic fit is applied on the • Ks side requiring the conservation • of 4-momentum (NDOF=11). •  c2FIT DATA=450pb-1 (2001+2002); MC =0.9fb-1 (all available statistics) • Preselected signal sample (KLCRASH and 6 photons):39538 events • Normalization Sample (KLCRASH • and 4 photons): 23.5x106 events c2FIT/NDF< 3is not enough (2/3 of bkg rejected)! Other discriminating variable have to be used: (z2, z3) 8 M. Martini, K rare decays

  10. Search for KSp0p0p0 Rejection of bkg: KS p0p0 + 2 accidental/split g’s Define signal box in (z2, z3) plane:  z3  pairing of 6g clusters with best p0 mass estimates  z2best pairing of 4g’s out of 6: p0 masses, E(KS), P(KS), c.m. angle between p0’s z2 Data MC KS 3p0 In the (z2 , z3) plane we define a signal and five control boxes. The agreement between DATA and MC, after each analysis step, is better than 10% in each region. z3 Signal generated with BR=10-5 (SND) 9 M. Martini, K rare decays

  11. Search for KSp0p0p0 z2 Data MC KS 3p0 Signal generated with BR=10-5 (SND) z3 • Other analysis cuts: • Track veto to reject events with tracks coming from IP • - Final cut on residual KS energy: E(KS)-SEp 10 M. Martini, K rare decays

  12. Search for KSp0p0p0 Nsel(data) = 2 events selected as signal, with efficiency e3p= 24.5% Nsel(bkg) = 3.130.82stat0.37sys bkg events expected from MC Can state: N3p < 3.45 @ 90% CL Measuring e3p=24.5% from MC generated signal and normalizing signal counts to KS  p0p0 in the same data set we obtain @90% c.l.: NA 48 Which translates into a limit on |h000| @90% c.l.: KLOE 11 M. Martini, K rare decays

  13. Search for KSp0p0p0 • Increased statistics: x 6.5 improvement • Luminosity  x 5 • Add tagging by KL vertex in DC  x 1.3 • Increased background rejection • Largest bkg source after all cuts is the splitting of e.m. clusters • Merging procedure removes bkg but leaves signal untouched • Candidates in data go from 2 to 0, in MC from 3.13 to 2 • Optimization of kinematic fit in progress • Overall better reduction of the known background expected If we will be able to suppress the background to a ~negligible level UL will improve by6.5 x 1.5 ~ 10 12 M. Martini, K rare decays

  14. Search for KSp+p-p0 Present status for the BR(KSp+p-p0): • Decay amplitude is composed of CPC (3x10-7) and CPV (1.2x10-9) parts • Direct measurement of the BR is possible using the entire KLOE data set. • Measurement can be used to verify cPT predictions. These predictions are poorly • tested. Currently, we have performed the search using a sample of 740 pb-1 of data: - 373 pb-1 from 2001-2002 data taking - 367 pb-1 from 2004 data taking Assuming BR(KSp+p-p0) = 3x10-7 230 signal events produced 13 M. Martini, K rare decays

  15. Search for KSp+p-p0 g KL p- p+ g Selection: KL-crash tag with 2 low momentum tracks from IP • Preselection algorithm: • Require vertex at origin with zero net charge • Require 2 prompt neutral clusters • Each pair of clusters is a p0 candidate. For each: • close 3-body kinematics using m(p0), m(KS) • set t0 using pair of clusters • use p(KS) and p(f) to search KL-crash cluster in 20° cone • choose p0 pair that best agrees with reconstructed KL momentum 14 M. Martini, K rare decays

  16. Search for KSp+p-p0 c2 after preselection for MC signal and background MC gives 93 bkg events after kinematic fit   The t’ bkg are due to charged kaon events    K+  +  Application of kinematic fitto reject bkg. Using c2<30 (NDOF = 8): - Cut efficiency = 48.5% - 98.8% of bkg rejected - eMC(SIG) = 3.3% 3.9 events expected 15 M. Martini, K rare decays

  17. Search for KSp+p-p0 • We studied more in detail the various background classes • and developed a set of cuts to reduce them: • K± events • K±p±p0 has monochromatic p± momentum at 206 MeV; • cut on p* • Dalitz • dedicated MC production of Dalitz events; • require TCA cuts for significant reduction of this background • After these cuts we still have 3 t’ bkg events • t’ • dedicated MC production of K± (Ke3 + Km3 + t’), K  all • Cut on the energy of prompt clusters not associated to any • tracks or to p0 (Efree) ± 16 M. Martini, K rare decays

  18. Search for KSp+p-p0 DATA Standard Background MC Compare DATA and MC: DTOF p* 25130 events in the data with no cuts applied c2 EFREE 17 M. Martini, K rare decays

  19. Search for KSp+p-p0 At the end of analysis  signal efficiency 1.5% Preliminary results with 740 pb-1: -candidates: 6 events - background: ~3.5 events - observed events consistent with expectation within the statistical error (100%) - evaluation of systematic error in progress • Scaling the values of signal and background to 2 fb-1 we expect: • 16 events, of which 9 background • 60% statistical accuracy on BR(KSp+p-p0) 18 M. Martini, K rare decays

  20. Paving the road for KSgg BR differs from CHPT O(p4) by 30%, useful to fix one O(p6) counterterm Projections based on • 150 pb-1 of 2001 background MC • 10K events of signal MC With 2+0.5 fb-1 we expect • 500x106 KS events tagged by Klcrash • N(KSgg, tagged) = 500x106 x 2.8x10-6 = 1400 events • acceptance 0.4 • Nsig = 560 events 2 fb-1: with good background rejection  ~ 4% statistical error 19 M. Martini, K rare decays

  21. MC distributions, no data yet N. of events in A.U. bkg signal A.U. A.U. bkg signal Recons. After fit Paving the road for KSgg • Strategy of analysis • No recover splitting and large angular acceptance • Kinematic fit to exploit two body kinematics • Distribution of kinematic variables after fit • Background separation looks promising 20 M. Martini, K rare decays

  22. Conclusion A direct search for KS3p0decay has been performedusing the whole statistics collected at KLOE during 2001- 2002 data taking. We set an upper limit on the branching ratio at: BR(KS3p0) < 1.2x10-7 @ 90% C.L. We have started the direct search of theKSp+p-p0. For the moment we have analyzed only 740 pb-1 of data. Now we are analyzing the other 300 pb-1 already on disk. The prospects at 2 fb-1 is promising. A statistical accuracy of 60% can be reached. We are paving the road to study KSgg. With 2 fb-1 we can reach a statistical error of 4% and contribute to test the cPT prediction for the branching ratio. 21 M. Martini, K rare decays

  23. Backup

  24. Search for KSp0p0p0 Adding in quadrature all the sources of systematic error, we obtain: Using these results and the efficiency on trigger and cosmic veto, we can calculate the number of events of the normalization sample: This value enters directly in the upper limit calculation. M. Martini, K rare decays

  25. Search for KSp0p0p0 The c22p is built selecting 4 out of 6 clusters which satisfies better the kinematics of KS  2p0 • The parameters used are: • mass distribution • opening angle between pions in • KS C.M. frame • 4-momentum conservation The calibration is done using KS2p0sample (see next slide) The c23p is based only on the 3 “best reconstructed” pion masses M. Martini, K rare decays

  26. Search for KSp0p0p0 DATA MC Mp Mp MC DATA DE DE In the construction of c2 we use a different sigma for each sample. DATA and MC (OLDMC, NEWMC) (2001 ,2002 ). M. Martini, K rare decays

  27. Search for KSp0p0p0 • To better calibrate data and MC, we have also questioned how well the MC reproduces the amount of double shower fragments and double accidental clusters. To understand and calibrate this we have divided the MC KL-crash events into 2 further classes: • 2A: events of Ks2p0 in overlap with 2 accidental (~ 60% ) • 2S: events of Ks2p0 with 2 splitted clusters or 1 accidental + 1 splitted cluster (~ 35%) To do this, we perform a 3 components fit (2S, 2A and fake events) M. Martini, K rare decays

  28. Search for KSp0p0p0 c22p c22p DATA 2 S c23p c23p c22p c22p Fake 2 A c23p c23p M. Martini, K rare decays

  29. Search for KSp0p0p0 Sbox CSbox UP Cup Down CDown Back Summing up 2001-2002 for each MC, we can compare DATA with the two different MC productions. NEW OLD A reasonable data-MC comparison is found for both samples at the beginning of the analysis. M. Martini, K rare decays

  30. Search for KSp0p0p0 ALL c22p<14 c23p c23p 14<c22p<40 c22p>40 c23p c23p  DATA -- MC ALL We apply a track veto to reject events with tracks coming from IP. We reject events with: rPCA < 4 cm |ZPCA| < 10 cm M. Martini, K rare decays

  31. Search for KSp0p0p0 ALL c22p down c23p c23p c22p central c22p up c23p c23p  DATA -- MC ALL TRK veto + DE/sE M. Martini, K rare decays

  32. Search for KSp0p0p0 ALL c22p down c23p c23p c22p central c22p up c23p c23p  DATA -- MC ALL END OFANA M. Martini, K rare decays

  33. Search for KSp0p0p0 Sbox CSbox UP Cup Down CDown Comparison between DATA and MC after the optimization procedure. Nobs = 2 Bexp = 3.13 ± 0.82 M. Martini, K rare decays

  34. Search for KSp0p0p0 Adding in quadrature all the contribution found, we obtain: Bexp = 3.13 ± 0.82stat ± 0.37sys M. Martini, K rare decays

  35. Search for KSp0p0p0 For each sample we generate 3 poissonian centered around N2S, N2A and Nfake. Weighting each distribution for the proper calibration factor, obtained with the 2D-fit, we sum them up to build our PDF for the background. The obtained PDF is reasonably similar to a Gaussian with average 3.15 and with equivalent to the ext. stat. Folding the previous PDF with a Gaussian distribution centered around 0 and with a width equivalent to the whole systematic uncertainty we obtain the PDF for bkg that we use on the upper limit calculation. The RMS include statistic and systematic uncertainty. M. Martini, K rare decays

  36. Search for KSp0p0p0 Back THE UNIFIED APPROACH: when Bexp is greater than Nobs, the classical method does not provide a perfect coverage. In this condition is better to use Feldman-Cousin-Neyman method based on likelihood ratio. We observe Nobs = 2 candidates on data and we estimate: Bexp = 3.13 ± 0.82stat± 0.37sys In our case, the exp. background is greater than Nobs. With this counting we obtain the following UL @ 90% C.L.: M. Martini, K rare decays

  37. Search for KSp+p-p0 Current values for the BR Decay amplitude is composed of CPC (3x10-7) and CPV (1.2x10-9) • Selection requiring KL-crash, 2 tracks from IP (zero net charge), 2 prompt neutral clusters • Data 740 pb-1 (2001+2002+ some 2004 runs) • Assuming BR=3x10-7 230 signal events produced • Major bkg: charged kaons, dalitz, t’ • bkg reduced using: TCA , DTcut, P* • Use kinematic fit to select events kinematically closed (c2 cut) • veto events with additional neutral prompt clusters below acceptance. • The set of cuts designed grants eSIG 1.38% with very high background rejection • We expect to measure this BR integrating the whole collected data so far. M. Martini, K rare decays

  38. Search for KSp+p-p0 Back M. Martini, K rare decays

  39. Search for KSp+p-p0 Back M. Martini, K rare decays

  40. Search for KSp+p-p0 Back M. Martini, K rare decays

  41. Search for KSp+p-p0 Back M. Martini, K rare decays

  42. Search for KSp+p-p0 Summary of signal efficiency: M. Martini, K rare decays

  43. Search for KSp+p-p0 Because of Data/MC discrepancies, especially in DTOF, we want to obtain Nbkg from sidebands in data after cuts on DTOF and p*. Assuming no correlation beween c2 and EFree, A/B=C/D Study systematics by inverting cuts, varying acceptances M. Martini, K rare decays

  44. Search for KSp+p-p0 M. Martini, K rare decays

  45. Search for KSp+p-p0 M. Martini, K rare decays

  46. Conclusion • With the data collected during 2001-2002 data taking, KLOE has: • determined the best upper limit on KS3p0 • measured the main KL BR’s with 0.5% accuracy • measured in two independent ways the KL lifetime • with 0.5 % accuracy •  Important contribution to the measurement of Vus • Next in line: • Direct search for BR(KSp+p-p0) • Final result on KSpen BR • Analysis of KL semileptonic form factor slopes • KLOE expects to collect 2 fb-1 by the end of 2005: • thus allowing to improve the search for rare KS decays and KSKL interference studies. M. Martini, K rare decays

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