Open issues of the pp ee analysis

Open issues of the ppee analysisMauro Raggi, LNF INFN

30th August 2014

Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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.

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

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

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 28 August 2013


Additional suppression of the BG

28 August 2013


Mee for the two set of cuts

28 August 2013


BG acceptances comparison

28 August 2013

BG type Acc Old Acc New Nbg old Nbg new

K2pD 4E-7 1.9E-7 76 31

K3pD 6.2E-6 9.8E-7 201 36

Total BG 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% 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


Rad. Corr. flux measurement

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)

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)28 August 2013


Rad. Corr models acceptances

28 August 2013

Model p+p0

P0D

modExtra

gNtot GEN

Ntot Sel

Acc Delta

Gatti Photos Yes 1.558E8

5540701

3.555% 0

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%

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)


Rad correction and BG to ppee

28 August 2013

Old selection

P0D

modExtra

gAccBG NBG BG%

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

Maximum difference in the BG evaluation of 29 event ~ 1.1% systematic

new selection

P0D

modExtra

gAccBG 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


Flux calculation results 2003Quantity Present value Value was Rel Error

BR(p+p0D(g)) (2.425±0.073)x1

0-3 (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%

28 August 2013

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(p0

D)=3%Effect of the radiative corrections taken into account


Radiative corrections ppee

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

28 August 2013


Mee systematic check

28 August 2013


Mee systematic check

28 August 2013

0 BR(Ppee) 4.19E-06 +/- 8.84E-08 (Nevent 22470 MinCut 1.00E+00 error 2.11E-02)1 BR(Ppee) 4.24E-06 +/- 3.11E-08 (Nevent 21080 MinCut 2.00E+00 error 2.18E-02)2 BR(Ppee) 4.30E-06 +/- 4.81E-08 (Nevent 19140 MinCut 3.00E+00 error 2.29E-02)3 BR(Ppee) 4.30E-06 +/- 6.09E-08 (Nevent 17140 MinCut 4.00E+00 error 2.42E-02)4 BR(Ppee) 4.32E-06 +/- 6.87E-08 (Nevent 15680 MinCut 5.00E+00 error 2.53E-02)5 BR(Ppee) 4.29E-06 +/- 7.54E-08 (Nevent 14290 MinCut 6.00E+00 error 2.65E-02)6 BR(Ppee) 4.25E-06 +/- 8.06E-08 (Nevent 13120 MinCut 7.00E+00 error 2.76E-02)7 BR(Ppee) 4.26E-06 +/- 8.43E-08 (Nevent 12260 MinCut 8.00E+00 error 2.86E-02)8 BR(Ppee) 4.31E-06 +/- 8.70E-08 (Nevent 11600 MinCut 9.00E+00 error 2.94E-02)

Trigger correction not icludedOffset on the BR

Max effect (4.32-4.19)/4.32 ~ 3%

Preliminary Check with new selection

Result independent of the selection type depend on the MC only


DE component fitting

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.

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

Seems that our acceptance spoils the difference even more

28 August 2013

IB MC GENDE MC GEN

Before the selection After the selection

IB MC GENDE MC GEN


Real life is even harder…

28 August 2013

IB MC RECDE MC REC

Reconstructed MC after correct DE normalization including higher acceptance factor 5

Mee

T*p

Situation in T*pi looks a bit betterbut BG has to be taken into account…

IB MC DE MC

IB MC DE MC


Errors summary table preliminary

28 August 2013

Systematic Value

N of signal events (2450) 2.11% sqrt(2243)/2243

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%

Total Error


BR calculations options

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?

28 August 2013

What error for accTot?


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.

28 August 2013

Thank you for your attention28 August 2013

Open issues of the pp ee analysis

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