Status of the pp ee analysis

Status of the ppee analysis

Mauro Raggi, LNF INFN

29th August 2013

NA48/2 rare decay session

NA62 Collaboration meeting Liverpool

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

Outline Introduction to ppee decay

Status of the MC generators The CMC DE generator vs theory

Review of the analysis strategy List of cuts Data and MC sample

BG evaluation technique Likelihood method Meeg cut and side band evaluation

Data MC comparison (ppee IB) Resolutions and energy scales (charged neutral and global) Mee resolution vs mee

Measurement of the Kaon Flux BG evaluation in K2pDg

Trigger efficiency

BR values and systematic checks

28 August 2013


Introduction to ppee decay

28 August 2013

The interference thanks to the possibility of measuring the plane of polarization of the e+e- pair is splitted into 3 terms: IB/E, IB/M and E/B. IB/M cancels when integrated over f as in ppg, while E/B is only

non-zero if CP violation is allowed.

Short and long distance parity violation contributions

Theoretical paper on ppee are currently: H. Pichl, ``K --> pi pi0 e+ e- decays and chiral low-energy

constants,'’Eur. Phys. J. C 20, 371 (2001) [arXiv:hep-ph/0010284].

L. Cappiello, O. Cata, G. D'Ambrosio and D. GaoEur. Phys. J. C (2012) 72:1872

Never observed so far


BR IB isospin breaking correction

28 August 2013

Cut IB Pub. IB isospin

Cut IB stand IB isospin

The isospin breaking correction only changes the absolute value of the BR (-2%) not the shape of the Q distribution.

Values are not published (G. D’Ambrosio private communication)


DE matrix element

28 August 2013

New set of form factors including unknown parameters

Combination are the same as K±->p±p0g Need to implement the T3 components

From NA48/2 K±->p±p0g

While

Thanks to P. Massarotti


Table of comparison MC theory

28 August 2013

Q>MeV IB th IB MC DE th DE MC

2*me 1 1.000000 1 1

2 MeV 0.736 0.736 0.857 0.865

4 MeV 0.466 0.467 0.689 0.693

8 MeV 0.262 0.263 0.517 0.519

15 MeV 0.134 0.135 0.366 0.363

35 MeV 0.0371 0.0373 0.164 0.167

55 MeV 0.0134 0.0136 0.080 0.082

85 MeV 0.00328 0.00332 0.026 0.026

100 MeV 0.00160 0.00154 0.014 0.013

120 MeV 0.00057 0.00051 0.005 0.005

140 MeV 0.000096 0.00015 0.0007 0.0016

Both IB and DE generators have been implemented in a private version of CMC007For both components all 2003 MC sample has been generated with a statistics which exceeds 10 time the data one.


Analysis strategy Use only the full 2003 data sample (SS0-1-2-3)

Use p+p0D(g)IB as normalization channel

Use: (1Vtx or 2Vtx or 1TrkP) as trigger sample

Perform the BRIB and possibly charge asymmetry measurements

Leave the enlargement of the sample and P violation for final result

28 August 2013

Correction name Data MC

Non linearity (1) X

Projectivity X X

Alpha and Beta X X

Blue Field X X


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 new! 3 good track are the same used in vertex fitting

28 August 2013


Signal selection ngoodCl ≥4

N electrons =2 E/P>0.85 new

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) cut on Dalitz decay mass

abs(MK-MKPDG) < 10 MeV

28 August 2013


Data MC comparison ppee

28 August 2013


MK for data and MC (no BG sub)

Data MC comparison is non good due to 10% BG in the data sample

MK(MC) media = 493.30 MeV Sigma = 5.6 MeV

MK(data) media = 492.69 MeV Sigma = 5.85 MeV

28 August 2013


MK for data and MC (BG sub)

Data MC comparison is good after BG subtraction in the data sample

MK(MC) media = 493.30 MeV Sigma = 5.6 MeV

MK(data) media = 493.29 MeV Sigma = 5.37 MeV

28 August 2013


ZV data MC for signal

28 August 2013


Data MC Mee no BG sub

28 August 2013

Region above 100 MeV dominated by p+p0p0D BG

Bad agreement between data and MC


Data MC Mee BG sub

28 August 2013

Good agreement in between D’Ambrosio and data

Data peak at 120MeV due to 3PD BG almost disappeared

Is the remaining discrepancy due to DE events? Or only insufficient MC statistics in 3pD?


BG estimate signal

28 August 2013


Final set of cuts except MK

28 August 2013

Integrating in the mass plot BG(3PD)= 190.5±11

BG(2PD)= 100±5


Flux normalization

28 August 2013

Use the flux measurement and BRs to estimate BG value

Scale the MC to: NToT(BG)=Kflux x Acc(BG) x Eff x BR(BG)

Compute the integral in the region MK±10MeV

BG(3PD)= 192±12.5stat ± 6ext

BG(2PD)= 75±10stat ±2.4ext


BG estimate summary table

Method 3PD 2PD Total

TfractionFitter

190.5±11 100±12 290.5±23

Flux norm. 195± 13 sta ± 6 ext

75 ± 10 stat ± 2.2ext

270.0 ±17stat±7ext

28 August 2013

The BG measurements agree very well on the 3PD

The value for PPD is not soo good due to low MC statistics in the plot

The value we will use for the BG subtraction is:

280±17stat±7syst

The systematic assigned is the 0.5*difference between the 2 estimates 10


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 Very similar final state in the charged trigger (e+e-p+)

MonteCarlo generator used: According to Evgueni suggestion using the KLOE generator (CMC

51) 1 times full 2003 data set 222 Million events generated run by run 165 in the ZV region 1.3 time the data

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

No cut applied to minimum E* g assuming that generator is fine

Flux measurement formula: (NPPD - NBGPPD)/(ePPD x AccPPD x BRPPD)

28 August 2013


PPD selection cuts N electrons = 2 (0.9<E/p) with different charges

Pion charged = 1 (E/p<0.85)

N gammas = 1 (no ass cluster)

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

Trigger (2VTX or 1VTX or 1TRKP)

28 August 2013


T*p PPD data BG estimate

28 August 2013

Unknown BG source: NBG=65*(130-85)*4+30*(140-130)*4+734=13634 < 0.1% Systematic on the flux measurement (0.1%)

Km3D BG from MC estimate (subtracted from data) NBG=7109

65 events/binKm3D


Data MC for PPD selection

28 August 2013

Data Mass fit resultsMean 493.09 MeV Sigma 3.83 MeV

MC Mass fit resultsMean 493.18 MeV Sigma 3.93 MeV

Mass are very close to each other <100 KeVThey are apart from the PDG by 0.5 and 0.4 MeV


T*p data MC for PPD

28 August 2013

Data T*p fitMean 1085.56 ±1.23x10-6 Sigma 3.83 MeV

MC T*p fitMean 108.587 MeVSigma 3.91 MeV

The T*p is perfectly on it’s place 108.5The difference in data to MC is order 30KeV only

The scale of the spectrometer is really in the right place!


Flux calculation results 2003

Quantity Value Rel Error

BR(p+p0D(g)) (2.425±0.073)x1

0-3 3%

Acceptance (8.00± 0.002)% 0.02%

Trigger efficiency 97.15 ± 0.042 0.046%

BG in PPD sample ?? 13130 0.1% (Sys)

Ntot events 14654994 0.026%

28 August 2013

KFlux=(NPPD - NBGPPD)/(ePPD x AccPPD x BRPPD)=(7.766±0.23)x1010

Error completely dominated by external error dBR(p0

D)=3%BG in PPD sample set to 0 and added 0.1% systematic


Trigger efficiency measurement

28 August 2013


General remarks on trigger

Control trigger : CPRE & !WDOG (TRGW)

Sample Trigger : 1VTX or 2VTX or 1TRK-P 1TRK-P: NT-PK (LvL 0) and 1TRK-P (Mfake<475 MeV)

We expect the trig eff to be different for the 2 decays due to 1TRK-P component in fact: The ppee has 1 more cluster (NT-PK more efficient) The ppee has lower value of T*p (Mfake) 1TRK-P is more efficient In the MC the efficiency of LvL0 NT-PK is not simulated correctly

Problems of low statistics for signal measurement (27 events) Try to use BG enriched sample (330 events sample) Cannot use efficiency measured using PPD

28 August 2013


Trigger efficiency analysis Control trigger : CPRE & !WDOG (TRGW)

Sample Triggers: (1VTX or 2VTX or 1TRKP) (1VTX or 2VTX)

Measured with both the signal and the normalization in data and MC with loose and tight cuts

Difference in between loose and tight cuts is < 0.1% in MC

Data shows the same agreement at least in PPD

Can we use the data loose cuts determination for trigger efficiency?

28 August 2013

Trigger Loose cuts PPD PPD MC ppee ppee MC

1VTX or 2VTX 94.97±0.055

97.03±0.0046

97.7±0.85

97.00±0.027

1VTX or 2VTX or 1TRK-P

97.15±0.042

98.48±0.0033

98.7±0.65

98.95±0.016Trigger Tight cuts PPD PPD MC ppee ppee MC

1VTX or 2VTX 95.08±0.056

97.10±0.0047

92.6±5.0 97.44±0.032

1VTX or 2VTX or 1TRK-P

97.25±0.042

98.55±0.0033

96.3±3.6 99.07±0.019

Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy 31

Trigger efficiency MC vs data PPD

Different absolute value due to bad simulation of NT-PK but same behavior as function of Mee (Mee>2MeV) Difference increasing at low Mee

23 April 2013

DataMC

Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy 32

Trigger efficiency ppee vs PPD MC

This difference is expected and due to MBX cut is small due to electrons in the MC NT-PK is not simulated The difference in data comes from NT-PK (3 clus PPD 4clus ppee)

23 April 2013

PPD(MC)ppee(MC)


Trigger efficiency loose to tight

28 August 2013

Efficiency comparison for ppee MC.

Tight 98.95Loose 99.07

389197 control sample events247440 control sample events


Total BR result for 2003 raw value

Quantity Value

Acceptance (7.80±0.028)x10-3

Trigger efficiency (raw data value) (98.7±0.65) see systematics

N background 270±16

Nppee BG subtracted 2540±49

Kflux (7.766±0.23ext)x1010

28 August 2013

Stat: Includes only the error on Nppee

External error: only Kflux coming from BR(p0)D

Trig: 0.65% error on 98.7% measured from data loose selection

What about DE?


DE component fitting

28 August 2013


DE and IB in the Mee spectrum

Generated 13 Million events of ppee DE run by run 9.6M in ZV acceptance

Acceptance measurement: Acc(DE) = (3.876± 0.006)% Acc(IB) = (0.782± 0.0015)%

The ratio of acceptance is Acc(DE)/Acc(IB)~5 which meansthat the DE is a order ~6% in the data (according to D’Ambrosio prediction 1/77*BR(IB) )

Using G. D’Ambrosio theoretical BR leads to a BG evaluation of: N(ppee)DE =155±20 events ( includes a 10% error on the BR(DE)

)

This number can be subtracted as a BG to get the N(ppee)IB

N(ppee)IB =N(ppee)TOT - N(ppee)DE = 2540-155 = 2385 IB events 28 August 2013


Fitting the DE

Fitting the DE using Mee is quite hard for different reasons: Distributions of Mee is really very similar much more that in ppg Regions in which 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


T*p BG distributions

28 August 2013

3pD MC DE MC


Results of fitting attempts

28 August 2013

Fit with 3 MC only: IBMC, 3pD, 2pDgMC IB frac (86.9±2.2)% 2445±62 ev BG 3pD frac (9.39±1.2)% 264±34 ev BG 2pDg frac (3.7±1.0)% 104±28 evEstimate from BG fit measurement are:NBG 3PD 190.5 ± 13.0 NBG 2PD 100.0 ± 9.8

Residuals look quite good even without the DE. The enhancement of the 3PD bg +74 events is masking the presence of the DEFits with DE does’nt converge!


Systematic checks

28 August 2013


Cut variation systematics

I did many cuts variation that you can see in my April talk MK, M , p COG, Mee, Mee ,g Egmin, PeMin

No effect has been seen except for the PeMIN

This has been redone This misses still the correction of trigger efficiency point to point

28 August 2013


Minimum electron energy

28 August 2013

Max difference (4.34-4.24)/4.24=2.3% max differencePart of this will be due to absence of trigger efficiency I propose to use the 0.5*Max Difference=1.2% systematicI’ll investigate this more soon.


Errors summary table

28 August 2013

Systematic Value

N of signal events (2450) 2.09% sqrt(2811)/2540

Signal acceptance 0.2%

Total Statistical 2.1%

Difference of 2 analysis 0.45%

Back ground subtraction 0.72% (error on BG 18.4/2540)

Trigger efficiency 0.65% (From data loose sample)

Non linearity <1%

Energy scale No effect

Cut Variation 1.2% (PeMIN) see april talk

Total systematics 1.74%

BR(p0D) external 3%

Total external 3%


Preliminary BR result

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 = Kflux*AccDE*Eff*BRDE(Th) =155±20 events (+0.8% syst or

EXT)

28 August 2013


Conclusions

We performed the first measurement of the BR for K±->ppee We reached less than 1% agreement between the two analysis Total and IB only BR can be measured

The Background is very well under control (~9.6%)

First attempt to fit DE is showing many obstacles Small difference in the spectrum BG domination in favored DE regions Low statistics in the data sample

The result is in good agreement with isospin breaking corrected theory

First systematic check does’nt reveal important contribution Trigger efficiency to be added to systematic check routine

28 August 2013

Thank you for your attention28 August 2013

Status of the pp ee analysis

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