PreBlessing

Open issues of the ppee analysis
Mauro Raggi, LNF INFN
30th August 2014
Outline
 Possible analysis strategies


Addition BG suppression
BG evaluation for different strategy
 Radiative correction treatment


Signal (no correction vs Photos+coulomb)
Normalization (Photos+gatti vs Gatti only)
 Measuring the BR

Total OR IB only or model independent?
 Mee systematic checks

New cuts vs old cuts.
Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy
28 August 2013
Analysis definitions cuts (presel)
 Good Vertex

-1000 < ZVTX < 8000

NVTXtrk = 3
 Good Track

TrackQual >0.75 new

2 GeV <TrackP< 60 GeV

12 cm <RDCH1<135 cm

12 cm <RDCH4<135 cm

Ddead > 2 cm

Track to track dist > 2cm
 Good Clusters

2GeV < ECl <60 GeV

accep(LKR) routine for geometrical acceptance

Cluster to cluster > 10cm

Cluster status <4 new
Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy
28 August 2013
Common preselection
 Preselection cuts (common to PPD and signal analysis)

NgoodVertex=1

3 < NgoodCluster < 8

3 < NgoodTracks < 8

Ellipse 3pc cut

116ns < Track time <154ns

3 good track are the same used in vertex fitting
Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy
28 August 2013
Signal selection
 ngoodCl ≥4
 N electrons =2 E/P>0.85
 N pions =1
E/P<0.85
 N gammas =2 cluster with no associated track &Ecl>3 GeV
 COG < 2 cm
 abs(ETOT-pk)< 6 GeV
 abs(Mpi0-MPI0PDG)<10 MeV
 Mee > 0.001022 GeV
 Distance of electrons @ DCH1 > 0.25 against conversions
 Total charge of electrons = 0
 abs(Meeg-MPI0PDG)>0.005 moved to 7MeV) cut on Dalitz decays
 Mpp > 0.12 GeV new rejects most of 3pD
 abs(MK-MKPDG) < 10 MeV
Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy
28 August 2013
Additional suppression of the BG
Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy
28 August 2013
Mee for the two set of cuts
Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy
28 August 2013
BG acceptances comparison
BG type
Acc Old
Acc New
K2pD
4E-7
1.9E-7
76
31
K3pD
6.2E-6
9.8E-7
201
36
277.7±17
67±8
DE events
176±13
103±11
Nppee-BG
2540
2175
BG % of sig
~11%
3.1%
Syst error
0.68%
0.37%
Total BG
Nbg old
Nbg new
 Adding the Mpp>120 MeV and abs(Meeg) >7 MeV
Background is reduced by factor 3.5
 The acceptance loss is ~15%
 Data MC comparison improves
 BG systematics to the BR goes down to 0.37%

 Becomes a BR(ppee)Mpp>120
Needs extrapolation in the full kinematic range to be performed
 Introduce a cut in the definition of Ntot for the acceptance

Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy
28 August 2013
Rad. Corr. flux measurement
Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy
28 August 2013
The Kaon flux measurement
 Used the decay K±->p±p0D(g) (PPD) means K±->p±ge+e-(g)

Same trigger chain of the signal
 MonteCarlo generator used:

Due to radiative correction issue sing several MC generators

We have KLOE, MS, Prague with no extra photons

We have Gatti+Photos with extra photons generation

ppD selection very sensitive to extra photons

BG to ppee very sensitive to extra photons as well
 Normalization BR used in the calculation:

BR(K->2p(g))xBR(p->Dalitz)=(20.66*1.174)x10-2=(2.425±0.073)x10-3
 Flux measurement formula:

(NPPD - NBGPPD)/(ePPD x AccPPD x BRPPD)
Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy
28 August 2013
PPD selection cuts
 N electrons = 2 (0.9<E/p and P > 3 GeV) with different charges
 Pion charged = 1 (E/p<0.85 P > 10 GeV)
 N gammas = 1 (no ass cluster and E >3 GeV)
 COG< 2 cm
 abs(M(eeg)-MPI0(PDG)) < 10 MeV
 Distance of e+e- tracks at DCH1 > 0.25 cm
 abs(ETOT-PK)< 6 GeV
 Track and clusters in 5ns (data only)
 abs(MK-MK(PDG)) < 10 MeV
 T*p > 85 MeV
 Mee>10 MeV (new improve data MC agreement)
 Trigger (2VTX or 1VTX or 1TRKP)
Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy
28 August 2013
Rad. Corr models acceptances
Model p+p0
P0D mod
Extra g
Ntot
GEN
Gatti
Ntot Sel
Acc
Delta
Photos
Yes
1.558E8
5540701 3.555%
Gatti only
None
No
3.87E8
1.421E7
3.669%
3.2%
Gatti
MS
No
3.77E8
1.392E7
3.682%
3.6%
Gatti
Prague
No
3.78E8
1.392E7
3.695%
3.9%
0
 Rad. Correction systematic

Generation of extra photons give a 3.2% difference in the acceptance

Assuming photos to have a 10% accuracy we propose 0.35% systematic
 Absence of the Dalitz plot reweighting on our MC

We assume the maximum effect is None-Prague (0.7% systematic)
Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy
28 August 2013
Rad correction and BG to ppee
Old
selection
P0D mod
Extra g
AccBG
Gatti
Photos
Yes
4.04E-7
76
3%
Gatti only
None
No
2.5E-7
47
1.9%
Gatti
MS
No
2.8E-7
53
2.1%
Gatti
Prague
No
2.6E-7
49
1.9%
 With the old selection we have

NBG
BG%
Maximum difference in the BG evaluation of 29 event ~ 1.1% systematic
new selection
P0D mod Extra g
AccBG
NBG
BG%
Gatti
Photos
Yes
1.9E-7
36
3%
Gatti only
None
No
2.6E-7
49
1.9%
 With the new selection we have

Maximum difference in the BG evaluation of 13 event ~ 0.6% systematic
Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy
28 August 2013
Flux calculation results 2003
Quantity
Present value
Value was
Rel Error
BR(p+p0D(g))
(2.425±0.073)x10-3
(2.425±0.073)x10-3
3%
Acceptance
(3.555±0.0015)%
(8.00± 0.002)%
0.02%
Trigger efficiency
(97.64± 0.044)%
97.15 ± 0.042
0.046%
BG in PPD sample
3365
13130
0.1% (Sys)
Ntot events
6714917±2591
14654994
0.038%
Syst rad correction
0.76%
0
0.76%
Kflux=(7.971±0.03Stat±0.06Sys±0.24Ext)x1010=(7.971±0.25)x1010
was (7.766±0.23)x1010
Error completely dominated by external error dBR(p0D)=3%
Effect of the radiative corrections taken into account
Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy
28 August 2013
Radiative corrections ppee
Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy
28 August 2013
Radiative corrections on ppee
 D’ambrioso papers does’nt include any kind of radiative
corrections in the IB martix element and BR evaluation
 We implemented the Photos into the IB generator of ppee
(many thanks to Brigitte)

Include the radiative corrections due to e+e- interaction

We also included Coulomb corrections which are constant
 We will estimate the systematic due to radiative correction by
comparing the acceptance of corrected and non corrected MC

The acceptance are:

Rad corr (new sel)= 6.61E-3 with no rad 6.92E-3 -> 4.5% difference

Rad corr (old sel) = 7.44E-3 with no rad 7.81E-3 -> 4.7% difference
 Assuming photos to have a 10% accuracy we propose 0.45%
systematic
Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy
28 August 2013
Mee systematic check
Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy
28 August 2013
Mee systematic check
Trigger correction not icluded
Offset on the BR
Max effect (4.32-4.19)/4.32 ~ 3%
Result independent of the
selection type depend on the MC
only
Preliminary Check with new selection
0 BR(Ppee)
1 BR(Ppee)
2 BR(Ppee)
3 BR(Ppee)
4 BR(Ppee)
5 BR(Ppee)
6 BR(Ppee)
7 BR(Ppee)
8 BR(Ppee)
4.19E-06 +/- 8.84E-08 (Nevent 22470 MinCut 1.00E+00 error 2.11E-02)
4.24E-06 +/- 3.11E-08 (Nevent 21080 MinCut 2.00E+00 error 2.18E-02)
4.30E-06 +/- 4.81E-08 (Nevent 19140 MinCut 3.00E+00 error 2.29E-02)
4.30E-06 +/- 6.09E-08 (Nevent 17140 MinCut 4.00E+00 error 2.42E-02)
4.32E-06 +/- 6.87E-08 (Nevent 15680 MinCut 5.00E+00 error 2.53E-02)
4.29E-06 +/- 7.54E-08 (Nevent 14290 MinCut 6.00E+00 error 2.65E-02)
4.25E-06 +/- 8.06E-08 (Nevent 13120 MinCut 7.00E+00 error 2.76E-02)
4.26E-06 +/- 8.43E-08 (Nevent 12260 MinCut 8.00E+00 error 2.86E-02)
4.31E-06 +/- 8.70E-08 (Nevent 11600 MinCut 9.00E+00 error 2.94E-02)
Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy
28 August 2013
DE component fitting
Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy
28 August 2013
DE and IB in the Mee spectrum
 Difference on the spectrum is very little in the NA48/2
acceptance
 G. D’Ambrosio theoretical paper does’nt provide proper
treatment of radiative corrections for the IB that are greater
than the DE effect itself due to the 2 electrons in the final state
 BG is 3 times bigger than the DE component need a fit with

Data, IB, DE, INT, BG(2pd), BG(3pD) too many distributions
 Much better conditions expected in NA62

104 rejection of the BG due to photon veto

10-20 times more statistics expected
 Needs in any case improved theoretical description to get a
result.
Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy
28 August 2013
Fitting the DE
 Fitting the DE using Mee is quite hard for different reasons:

IB and DE distributions of Mee are very similar much more wrt ppg

Regions where the DE is dominant are populated by 10% BG

The low statistics does’nt allow to have a very hard selection cuts
Before the selection
IB MC GEN
DE MC GEN
After the selection
IB MC GEN
DE MC GEN
 Seems that our acceptance spoils the difference even more
Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy
28 August 2013
Real life is even harder…
IB MC REC
Mee
DE MC REC
Reconstructed MC after correct
DE normalization including
higher acceptance factor 5
IB MC
DE MC
T*p
IB MC
DE MC
Situation in T*pi looks a bit better
but BG has to be taken into
account…
Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy
28 August 2013
Errors summary table preliminary
Systematic
Value
N of signal events (2450)
2.11%
Signal acceptance
0.2%
Total Statistical
2.12%
Difference of 2 analysis
0.45%
Back ground subtraction
0.7% +0.6% (0.35% new selection)
Trigger efficiency
0.65% (From data loose sample)
Non linearity
<1%
Radiave correction
0.5 %
Mee
3% to 1% depending on the cut
Total systematics
1.32% + Mee
BR(p0D) external Flux
3.1%
Total external
3.1%
sqrt(2243)/2243
Total Error
Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy
28 August 2013
BR calculations options
BR( ppee)Tot =
BR( ppee)IB =
N ppee - N BG
K Flux × AccTot
ppee × e ppee
N ppee - N BG - N DE
AccTot
ppee =
Acc(IB) +1/ 71× Acc(DE) +1/128× Acc(INT )
1+ 71+128
What error for accTot?
IB
K Flux × Acc ppee
× e ppee
 Theoretical prediction from G. D’Ambrosio et al (Eur. Phys. J. C (2012) 72:1872):

BR(ppee)IB= 4.19 x 10-6 IB only no isospin correction (PUBLISHED)

BR(ppee)IB= 4.10 x 10-6 IB only isospin breaking correction (PRIVATE)
 In the IB only BR we considered DE as a BG we subtracted:

DE systematic subtraction to be understood
 Model independent BRtot?
Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy
28 August 2013
Conclusions
 We improved a lot the analysis agreement between me and
Milena
 We developed new strategy for BG subtraction
 We included the treatment of radiative corrections in both
analysis
 The comparison with theory is biased by absence of radiative
correction in the theoretical paper.
Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy
28 August 2013
Thank you for your attention
28 August 2013