# Measurement of Br of D s â†’ € 0 l ½, D s â†’ K...

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### Transcript of Measurement of Br of D s â†’ € 0 l ½, D s â†’ K...

Measurement of Br of Ds 0 l , Ds Ks l , Ds l decays in Signal Monte Carlo and Generic Monte Carlo

Sudeshna Ganguly Anze ZupancGiovanni Bonvicini

Based on my presentation to Belle General meeting, February 201404/30/2014

IdeaIn standard model ( leptonic decay of Ds ):

A c quark decays into a s quark via a virtual w boson which annihilates into a and a , In semi-leptonic decay of Ds ,

Ds can make hadrons without any s-quark by: 1) Focks development : Ds > = c0 | c s > + c1 | c s q q > + c2 | c s q q q q > +.. 2) hadron mixing 3) higher order QCD processesThis analysis probes all that by looking for the decay Ds 0 /() l

5. For Ds Ks l Ds Ks l is a Cabbibo suppressed decay and it shares the same final state as l

w

Obtaining inclusive Ds sample Fully reconstruction in charm: e+ e- cc DtagKXfragDs*

Dtag (See backup for details) D0, D+, C+ (18 tag modes: involving kaons, pions, neutral pions, protons etc.) or excited D*0, D*+

K = K+/- , Ks0

Xfrag = nothing, +/- , 0 , +/- +/- , +/- 0 , +/- +/- +/- , +/- +/- 0

All possible reconstructed DtagKXfrag combinations are made so that there total charge is +(-) 1 and these candidates do not overlap with each other. Then we calculate MR(DtagKXfrag) closest to nominal Ds* mass.

Ds*Ds ; Ds signal candidates are identified as a peak in recoil mass spectrum: = MR (DtagKXfrag ) =

All DtagKXfrag combinations with MR > 1.83 GeV and PR >2.8 GeV are retained for further analysis

*

Best Inclusive Ds sample: Mmiss(DtagKXfrag )Inclusive Ds reconstruction done as described inBN1244 Ds 0 l Ds l Ds Ks l * Mmiss distributions for correctly reconstructed inclusive Ds (with cate1 only) with Signal MC

Reconstruction of exclusive Ds0 l / Ks l / l decay and data sample used for analysis Selection Criteria:

For each DtagKXfrag candidate, exactly 1 charged track and one additional 0 / Ks / in the rest of the event. Ks and candidates do not overlap with inclusive Ds candidates. 1.95 < MR (Ds ) < 1.99 GeV

Selection of 0 (nominal mass 134.9 MeV) : 117.8 < m < 150.2 MeV

*

Selections used for good Ks (nominal mass 497.6 MeV) + - :|m-MKS|< 20 MeV The dominant decay mode of : + - and all + - combinations with invariant mass within +/-250 MeV around the rho's nominal mass (770MeV)are accepted

Signal MC samples have been generated for each of the Ds decay modes : No. of events generated 4X10^7

To determine the reconstruction efficiencies and to study backgrounds six streams of generic MC samples are used(all 4 types: charged, mixed, charm, uds).

Yield determination procedureEach final stage candidate in the exclusive decay mode of Ds is reconstructed explicitly except for the neutrino candidate.

The signal yield from fit to the MM2 (Dtag K Xfrag l 0 /Ks /) = [Pmiss(DtagKXfrag l 0/Ks/)]^2 distribution between -0.3 and +0.3 GeV.

The missing 4-momenta is given as Pmiss(DtagKXfrag l 0/Ks/) = pe+ +pe-pDtag-pK-pXfrag-p-pl-p0/Ks/

First the Eecl variable ( energy of the ECL cluster) with a selection of Eecl

Eecl Eecl is the asymmetric energy between the signal photon candidate and any other photon candidate defined as:

This extra energy is not associated to the Dtag K Xfrag l 0 (Ks / ) system in our analysis. Eecl cluster with energy >50 MeV in barrel, >100 MeV in forward and >150 MeV in backward end cap are used to calculate Eecl.

*

With Eecl

Black line with Eecl

- Conclusions with Eecl
Neutrino energy The neutrino energy for a Dtag K Xfrag l Ks ( ) system in the rest frame is defined as : E l = (MDs 2 - MKs()l2)/ 2 MDs *The low E background events correspond to |MM2| == 0 region, we can obtain a significant background loss by choosing events with lower E Conclusions with Eecl=0.2 selection:

The problem of a peaking background at |MM2| = 0 in Ds Ks decay can be removed applying this selection criteria.

For Ds l channel, the high background with a shoulder near |MM2| = 0 is reduced.

2-dimensional scatter plots(y axis: MM2; x axis: Eecl_ks)*Ds Ks e Signal MCDs Ks e Backgrounds (6 streams of generic MC)Ds Ks Signal MCDs Ks Backgrounds (6 streams of generic MC)

2-dimensional scatter plots(y axis: MM2; x axis: Enu_lepton_ks)*Ds Ks e Signal MCDs Ks e Backgrounds (6 streams of generic MC)Ds Ks Signal MCDs Ks Backgrounds (6 streams of generic MC)

2-dimensional scatter plots(y axis Enu_lepton_ks; x axis: Eecl_ks)*Ds Ks e Signal MCDs Ks e Backgrounds (6 streams of generic MC)Ds Ks Signal MCDs Ks Backgrounds (6 streams of generic MC)

*Ks Ks e Ks e : Very low background; No Cut

Selection criterion No. of signal events No. of background events_signal_backgroundFOM(S/S+44.6B)1Eecl < 6.9 *Enu -1.53422 (out 3778)29(out of 169)0.9060.17249.8

Selection criterion No. of signal events No. of background events_signal_backgroundFOM(S/S+44.6B)1Eecl < 6.5 *Enu +1.74355(out of 4361)13( out of 14)0.9980.92861.9

MM2 for a Dtag K Xfrag e Ks system fitted with a Crystal ball and two Gaussian functions(Signal MC:4X10^7)Ds Ks e Ds Ks *2 = 0.6632 = 1.416with Eecl < 6.9*Enu 1.5 with no cut MM2 for a Dtag K Xfrag Ks system fitted with a Crystal ball and two Gaussian functions(Signal MC:4X10^7)MM2 fitted with the signal function combined with a background linear polynomial function (Generic MC-6 streams: signal mode : number 7 : anti-K0 e+ e )MM2 fitted with the signal function combined with a background linear polynomial function (Generic MC-6 streams: signal: number14 anti-K0 + )2 = 0.6682 = 0.329

MM2 for a Dtag K Xfrag l Ks system fitted with a Crystal ball added to a linear polynomial function for the muon mode and with a Gaussian added to a linear function for the electron mode (Generic MC-6 streams: background modes)

Ds Ks e Ds Ks *2 = 0.3892 = 0.359with no cut with Eecl < 6.9*Enu 1.5

Cross-checking of the Branching ratio of D s Ks l+ e decay in MC(using the best selection criteria)

Branching fraction of D s Ks e decays:

Expected Branching ratio of D s Ks l+ e ; B = 3.7 X 10-3 *Estimated combined Belle Stat. error is 1.5X 10-4Branching fraction of D s Ks decays:

B B (Statistical only) = (3.630.23)X10-3 B B (Statistical only) = (3.720.20)X10-3

* e e : low background: No Cut2-D scatter plots are in the backup slides

Selection criterion No. of signal events No. of background events_signal_backgroundFOM(S/S+44.6B)1Eecl < 4.8 *Enu 0.44058(out 4413)762(out of 1031)0.9190.73920.8

Selection criterion No. of signal events No. of background events_signal_backgroundFOM(S/S+44.6B)1Eecl < 5.1*Enu +1.05308(out of 5351)405( out of 422)0.9910.95934.7

MM2 plot for Ds with 6 streams of Generic MC: only background modesEfficiency = 74%Efficiency = 92%*MM 2 plot for Ds with Signal MCMM2 for l : Blue line with Eecl < 4.8*Enu 0.4 cut and Red line without Enu cut, only Without this cut.Backup slides

MM2 for a Dtag K Xfrag e system fitted with a Crystal ball and two Gaussian functions(Signal MC:4X10^7)Ds e Ds *with Eecl < 4.8*Enu 0.4 with no cut 2 = 1.4162 = 2.267MM2 fitted with a Crystal ball and a landau function (Generic MC-6 streams: background modes) 2 = 0.967MM2 for a Dtag K Xfrag system fitted with a Crystal ball and two Gaussian functions(Signal MC:4X10^7)MM2 fitted with a Crystal ball and a landau function (Generic MC-6 streams: background modes) 2 = 0.757

*0 0 e

Selection criterion No. of signal events No. of background events_signal_backgroundFOM(S/S+44.6B)1Eecl < -4.6 *Enu + 4.2 2185(out 2473)52(out of 87)0.880.59732.6

Selection criterion No. of signal events No. of background events_signal_backgroundFOM(S/S+44.6B)1Eecl

- Ds 0 MM2 for a Dtag K Xfrag 0 system fitted with a background linear function and a signal function(Generic MC-6 streams)* Fit results are shown in the next slideWith Eecl
Fit result : MM2 for a Dtag K Xfrag 0 system fitted with a background linear function and a signal Gaussian function(Generic MC-6 streams) EDM=3.65521e-05 STRATEGY= 1 ERROR MATRIX ACCURATE EXT PARAMETER PARABOLIC MINOS ERRORS NO. NAME VALUE ERROR NEGATIVE POSITIVE 1 a0 1.21310e-02 9.10972e-01 at limit 2.76888e-01 2 a1 -1.31653e+00 1.88251e+00 -1.75494e+00 2.04943e+00 3 fO -3.71207e-02 2.47444e-02 -2.39079e-02 2.55819e-02 4 yld 3.73024e+02 1.93141e+01 -1.90057e+01 1.96242e+01 ERR DEF= 0.5MINOS: status = 0

*So N_s( Signal Yield) = -13.8+(-) 9.23With Eecl

- Ds 0 e MM2 for a Dtag K Xfrag e 0 system fitted with a background linear function and a signal function(Generic MC-6 streams)* Fit results are shown in the next slideWith Eecl
Fit result : MM2 for a Dtag K Xfrag e 0 system fitted with a background linear function and a signal Gaussian function(Generic MC-6 streams)

NO. NAME VALUE

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