π 0 γγ calibration Savrina Daria, ITEP, Moscow SINP MSU, Moscow Victor Egorychev, ITEP, Moscow Ivan Belyaev

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1 π 0 γγ calibration Savrina Daria, ITEP, Moscow SINP MSU, Moscow Ivan Belyaev Victor Egorychev, ITEP, Moscow

2 Loose cuts for π 0 selection One of the ways to improve the calibration procedure is to increase the number of selected π 0 s. For this purpose the cuts on the π 0 and photon transverese momenta could be loosen so that the error in defining of the π 0 peak position is not very much affected. 1/12 PT γ > 200 MeV PT γ > 300 MeV Loose π 0 transverse momentum (GeV) Loose Tight Tight π 0 transverse momentum (GeV) Number of π 0 s depending on the π 0 transverse momentum Loose π 0 transverse momentum (GeV) Loose Tight Tight π 0 transverse momentum (GeV) Signal to sqrt(sig.+bkg.) ratio depending on the π 0 transverse momentum cut «Tight» cuts (used in previous calibration): PT π0 > 800 MeV PT γ > 300 MeV «Loose» cuts: PT π0 > 550 MeV PT γ > 250 MeV

3 Loose cuts for π 0 selection γγ mass distributions with tight (left) and loose (right) cut on transverse momenta applied 35M of miscalibrated min.bias MC-events No other cuts except the reconstruction ones are applied signal = 2.277x10 5 S/B = signal = 4.14x10 5 S/B = /12

4 Loose cuts for π 0 selection The calibration procedure is also being performed with Kali but different cuts were used for the π0 selection PT π0 > 550 MeV PT γ > 250 MeV On 100M of input MC minimum bias events the same number of pi0's is obtained as for 200M with tighter cuts may be useful for reducing of statistics necessary for the calibration Less cells with low occupancy Lower S/B ratio worse shape of the mass distribution 5924 cells were calibrated after the first pass which is less than with the tight cuts, most of the others had unsatisfactory fit parameters 3/12

5 MC calibration with the loose cuts Less than seven primary iterations were enough to achieve the convergency through the first pass Change of the coefficients at the last primary iteration Deviation of the coefficient from the value on the previous step 4/12 Number of cells with the deviation greater than given > 0.01 % 5816 > 0.05 % 5377 > 0.5 % 4887 > 0.1 % 2300 > 1.0 % 1228 > 5.0 % 125 > 10.0 % 18 > 15.0 % 0 97% of coefficients at the last iteration have deviation less then 5% π0 peak position for each iteration Peak width depending on the iteration number

6 MC calibration: mass distributions γγ mass distributions before (blue) and after (red) the calibration for different preshower energy cuts No preshower energy cut applied Mass: 138.4± ± 0.0 Width: 12.84± ±0.05 Eprs < 10 MeV cut for both photons Mass: 139.7± ± 0.1 Width: 12.97± ±0.32 5/12 Eprs 1 < 10 MeV and Eprs 2 > 10 MeV cut Mass: 138.5± ± 0.1 Width: 13.01± ±0.11 Eprs > 10 MeV cut for both photons Mass: 138.2± ± 0.0 Width: 12.79± ±0.05

7 Some results with loose cuts After the first run of the calibration the coefficients obtained with loose cuts have big differense from those obtained with tight cuts on π0 and γ transverse momenta The alternative set of coefficients is going to be checked The secondary iterations are nevertheless needed to tell if the coefficients became closer to the correct ones than the coefficients obtained with the tight cuts were Loose cuts vs tight cuts coefficients Unfortunately now it takes some time: ~ 2 hours for the re-reconstruction using ganga not taking into account the jobs failed for different reasons (about 10% of such jobs) ~ 2 hours/iteration for the primary iterations on SLC5 CAF but other people are using the machine also, should not interrupt their work 6/12

8 Real 2010 data calibration attempt Schematic view of the cells group subdivision Distribution of the cells with low statistics (violet) and bad fit parameters (blue) 7/12 20M of real events Reco , prod 6234 Subdivided into groups by ECAL area (inner, middle, outer) ECAL side (left,right,up down) ring slices (g = sqrt((i-31.5) 2 +(j-31.5) 2 ) cellid = LHCb.CellID('Ecal', 'area','side','g') Loose PT cuts applied P T γ > 250 MeV P T π0 > 550 MeV 155 coefficients for 172 cells are obtained 15 more have low statistics 2 have unsatisfactory fits

9 «Bad» cells Mass distributions in the cells defined as «bad» ones Ecal-Outer-4-12 Bad number of signal events Bad signal error Bad coefficient presicion Ecal-Inner Bad number of signal events Bad signal error Bad coefficient presicion 8/12 Eprs < 10 MeV cut for both photons Eprs 1 < 10 MeV and Eprs 2 > 10 MeV cut Eprs > 10 MeV cut for both photons

10 Real 2010 data calibration attempt Convergency is fast due to the relatively small number of cell groups Most of the coefficients were obtained from the histograms with (E prs1 > 10 MeV && E prs2 < 10 MeV) or E prs1,2 > 10 MeV cuts π 0 peak position depending on the iteration number Peak width depending on the iteration number 9/12 1 st iteration 5 th iteration 10 th iteration 0.01 % % % % % % % 0 0 0

11 Real 2010 data calibration attempt γγ mass distributions before (blue) and after (red) the calibration for different preshower energy cuts Now the preliminary by-zone preshower coefficients obtained from 2009 data are used. This results in the wrong values of the final pi0 peaks. The betterknown coefficients from the database are needed for the better calibration No preshower energy cut applied Mass: 136.6± ± 0.2 Width: 13.51± ±0.20 Eprs < 10 MeV cut for both photons Mass: 141.0± ± 0.7 Width: 12.09± ± /12 Eprs 1 < 10 MeV and Eprs 2 > 10 MeV cut Mass: 138.2± ± 0.4 Width: 12.77± ±0.53 Eprs > 10 MeV cut for both photons Mass: 135.6± ± 0.2 Width: 13.38± ±0.21

12 Pion kinematic parameters for real 2010 data variable distribution pi0 energy pi0 rapidity pi0 transverse momentum pi0 mass dependance 11/12 The dependance of the mass on the pi0 rapidity, the energy dependance became weaker But the transverse momentum dependance still exists

13 Photon kinematic parameters for real 2010 data variable distribution pi0 mass dependance max photon energy min photon energy max photon pt min photon pt The dependance of the mass on the photons energy became weaker But for some reason the transverse momentum dependance still exists 12/12

14 Summary An attempt was made to introduce some improvements into the calibration procedure by increasing the number of selected events may show some advantages such as decreasing the number of input events, necessary for calibration thus reducing time and size of ntuples and giving more occupied cells needs to be checked Some priliminary results on the real 2010 data were obtained the results are close to what is expected even more events are now available in the bookkeeping have to take them into account too re-reconstruction may be made to watch the further behaviour of the calibration procedure 1/13