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K charged WG activity report (part I)

Next talk. This talk. K charged WG activity report (part I). P.Branchini, E. De Lucia, P. De Simone, E.Gorini, M.Martemianov, L.Passalacqua, M.Primavera, B.Sciascia, A.Ventura, R.Versaci, V.Patera. K mn : first absolute BR evaluation K pp 0 decay: selection efficiency study

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K charged WG activity report (part I)

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  1. Next talk This talk K charged WG activity report (part I) P.Branchini, E. De Lucia, P. De Simone, E.Gorini, M.Martemianov, L.Passalacqua, M.Primavera, B.Sciascia, A.Ventura, R.Versaci, V.Patera • Kmn : first absolute BR evaluation • Kpp0 decay: selection efficiency study • Ratio kmn/Kpp0: analisys refinement • Kl4, Ke3 ; analysis on going • K decay vertex eff. under way • Background on K tag: first look • K tracking efficiency measurement • DE/DX : test of new hardware setup

  2. dE/dx upgrade • The ADC system has been completely revised and upgraded • ADC integration time stretched from 1.8 to 3.1 ms to collect most of the released charged in the cell • Unefficiency in collecting charge released at short distance from the wire fixed • Data with cosmic and magnetic field finally collected last week (!!) • Analisys in progress: preliminary results on efficiency and resolution

  3. dE/dx : ADC signal RED = 2.2 ms (short) BLUE = 3.1 ms (long) BLACK = 1.8 ms (old) (adc count/cm) New dE/dx distribution from cosmic taken with two different ADC gate value (2.2 and 3.1 ms) compared with 2002 cosmic data (1.8 ms) (adc count/cm)

  4. dE/dx : efficiency The longer gate improved the ADC sampling efficiency by more then 30% OLD NADC/Nhit NOW cosq cosq

  5. dE/dx : average energy loss The comparison between old 2002 cosmic and the newly collected cosmic shows a substantial agreement of the B.B. energy loss NEW OLD

  6. dE/dx : resolution The resolution with respect the number of samples in the truncated mean is improved by 30% @ 10 samples and by  25% @ 20 samples ( Nsampletrmean = 0.82 NsampleADC). At Nsample >20 the resolutionis almost flatten noise ? Resolution NOW OLD Prototype resolution Nsampletrmean Nsampletrmean

  7. dE/dx : noise? To test the noise hypothesys we use the pedestal runs. We sum the charge over a road trough 58 planes that fakes a track. The RMS of this sum is compared to the incoherent sum of the sifor each ADC of the road. We find a very little difference…. This amount of noise cannot be responsible for the resolution behaviour. (Maybe the noise analysis should not be done on ped runs ??)

  8. dE/dx upgrade summary • The efficiency loss of the ADC sample has been fixed • The resolution with respect to the T.M. sample is now better by 30 % for track with 20-30 hits • For track with a given hit number the gain is twofold: more ADC samples and better resolution with respect of the T.M. sampling • Yet the prototype resolution has not been achieved • There is a flat behaviour in the resolution at high sample value • The analysis is in progress

  9. K tracking efficiency & geometrical acceptance : aK(pK,qK) • We use the tag in the handle emisphere to have in the signal emisphere a “pure” beam of K+(K-) • The signal is flagged as Kaon with standard cut on momentum and IP distance • Background to the signal is mainly due to early 3 body decay of the K, where a low momentum doughter mimic a K coming from the IP • We use the minimum distance between the candidate K track and the extrapolated K track from the handle as check parameter • The shape of the Dr distribution forbackgroundis taken fromMC • “ “ for signal is taken from MC and from double tagged event

  10. Handle: K+ track with tagged decay K- candidate K- extrapolated aK(pK,qK) signal vs background Once found a “candidate” K we compute the distance of closest approch between the first hit of its track and the track extrapolated from the handle: K definition cuts : 1) q opposite to the “handle” 2) 70 < PK < 130 MeV 3) Rpca < 10 cm 4) -20 < zpca < 20 cm We monitor the background contamination of the signal looking at the tracks minimum distance Dr computed at the point of closest aproach.

  11. K- with tag decay K+ with tag decay K- extrapolated K track eff. = fit to Dr The fit to the Dr distribution between the candidate track and the extrapolated track is made using MC or 2 tag shape for the signal and MC for the background shape BLUE  K from MC RED  K from 2 tag GREEN  bck from MC Signal shape from DATA: Dr (cm)

  12. K shape uncertainties The Dr distribution in the K region is slightly overestimated by the fit with K shape from MC and underestimated by the fit with the K shape from 2 tag. The differences between the 2 fits gives the sistematic on the K shape Fit – signal : MC shape Dr (cm) signal Fit – signal : 2tag shape Dr (cm) Dr (cm)

  13. aK- 2001 2002 IntLum/6 (pb-1) aK-versus time and shape systematic Handle : K+ Signal : K- BLUE = MC shape RED = 2Tag shape We check the stability of aK versus time. The 2001-2002 data were divided in chunk of  6 pb-1each. The two different results account for the 2 different shape choice for the K contribution. Systematic due to the shape uncertainty  2x10-3

  14. aK- IntLum/5 (pb-1) aK sistematic : tag bias Systematic on the K tracking eff. can also be due to what happen in the opposite emisphere. Thus we measured the tracking efficiency with respect to the kind of tagged decay of the other K ( the “handle”) The maximum bias found on aK was between opposite tag :  (7.5 ± 2.0) x 10-4 BLUE: Kpp0 RED : Kmn BLACK: all tag

  15. aK+ with respect qK and pK We divide the qK in 6 bin in the range 30< qK <90 and the K momentum in 6 bin in the range 70< pK<130 (Mev/c) aK- pK100 MeV/c q  900 Nevents qbin Pbin qbin qbin = 10 deg Pbin = 10 MeV/c Pbin

  16. aK: average 2001-2002 values We show the value of the aK for both charge, relative to the full 2001 2002 data set, based on the dst production version 16 and 15, with the corresponding evaluated systematic errors MC : aK+ = 46.98 % truth = 46.97 % MC : aK+ = 46.27 % truth = 46.27 % Still missing a quantitative evaluation of the Tag background… seems to be negligible even at few per mill level, but we are working on it.

  17. aK DaK IntLum/6pb-1 DaK IntLum/6pb-1 aK+vsaK- The nuclear interactions of K- in the beam pipe and in the DC wall reduce aK-in comparison to aK+ by more than 1 % BLUE = aK+ RED = aK- The DaK integrated over q and pK is  (10.4 ± 4) x10-3

  18. DaK d2 2 q d1 1 cosq K- nuclear interactions from DaK (??) If we assume that DaK is totally due to K- nuclear interactions, then it should contain a costant term due to BP, plus a bigger term proportional to 1/sinq due to DC wall (and BP) Work in progress…it is just a first look PnuclK C1 + C2/sinq

  19. aK summary • The K tracking efficiency times the geometrical acceptance aK has been measured using the tag tecnique at fraction of % level • The aK has been measured independently for positive and negative K • The sistematics due to the uncertainty on shape of the signal and due to tag bias have been evaluated • The aK has been measured versus the time in step of  6pb-1 • A memo is in preparation

  20. First look at tag background evaluation The use of the K+(K-) tag decay ( Kmn and Kpp0) allow us to select a pure K-(K+) beam. Eventual pollution of the tag reflects in a systematic underestimation of the absolute BR measured on the other emisphere. We made a first attempt to estimated this background using a sample of 4 pb-1 of 2002 data • We assumed that the background fraction in the events with one tag decay is small. • There is no background in the events where both K+ and K- undergo a tag decay (double tagged events) • We compare the single and double tag kinematic distribution: the differences can be due to the background ( and , to some extent, to slightly different acceptance ) • The statistical power of this analysis is limited by the rate of double tagged decay in K+K- events ( 10% of the total in the stream)

  21. Tag bck: Kinematic variables • The control variables was chosen both in the lab and in the center of mass frame: • Momentum of the K charged secondary in the K frame • Angle between the K flight path and the charged secondary in the K frame • Angle between the charge secondary and the K in the lab • Number of clusters associated at the K decay product ( ≤1 for Kmn and ≤3 for Kpp0) • Energy of the cluster associated to the charged secondary • Time of flight of the charged secondary Only the shape can be compared due to the different yelds of single and double tag events

  22. Charged secondary momentum in K frame Linear scale Log scale Mev/c Mev/c Normalized comparison between single and double tag events Red = difference of the 2 histo Blue = statistic uncertainty Mev/c

  23. Cos(q) between K and secondary in K frame Linear scale Log scale Red = difference of the 2 histo Blue = statistic uncertainty

  24. Cos(q) between K and secondary in lab frame Linear scale Log scale

  25. Number of secondary cluster associated Linear scale Log scale Ncluster ≤1 for Kmn Ncluster ≤3 for Kpp0 Red = difference of the 2 histo Blue = statistic uncertainty

  26. Energy of the cluster associated to the charged secondary Log scale Linear scale MeV MeV MeV

  27. Time of flight of the charged secondary Linear scale Log scale ns ns ns

  28. What about dE/dx ? • dE/dx is a very powerful PID for K± but: • Was not available in 2001 data • Due to low efficiency of ADC sampling in 2002 the DE/dx measurement select the K with q  900 K with dE/dx K with no dE/dx Non Kaons Kaons qK Truncated mean (count/cm)

  29. Background statistic estimator To build a conservative background estimator I have to measure the deviation from statistic fluctuation of the difference of the two sets of histos. We define: d(n) = abs [ his2tag(n) – his1tag(n) ] For bin n sd(n)2 = ( shis1(n))2 + (shis2(n))2 For each bin I consider the quantity e(n) = d(n) - sd(n) . This variable gives the deviation of d(n)from the statistical fluctuation and is > 0 if the bin is bigger then statistica fluctuation and < 0 is underfluctuate. The sum over all the bins of e(n) is a upperlimit to the background.

  30. First results on  3 pb-1 of 2002 Positive Tag

  31. First results on  3 pb-1 of 2002 Negative Tag

  32. Backgroung on negative tag? The difference between the 1 tag and the 2 tag distribution settles on the signal region.. True background ??? • Conclusion: • There is no evidence for a clear background contamination in the single tag events, at least at % level • We are working out a robust statistic estimator for the background level (or limit) • Work in progress..

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