Ratio of Ke3 to Pipi0

A. Dabrowski, May 26 20051

Anne DabrowskiNorthwestern University

NA48/2 Analysis Meeting26 May 2005

Ratio of Ke3 to Pipi0


Outline

● Data & MC samples

● DATA / MC of final selection

● Trigger Efficiency

● Particle ID efficiency

● Br results

– K+ / K-

● Error analysis

– Statistical contributions

– Inputs from PDG (pizero Br)

– Systematic Errors, stability under variation of selection cuts, and form factor (λ+)

● Final result

● Conclusion


Data:

● Compact 7.2 & Database (database-2005-02-11) pass 5 Min bias 2003 (runs 15745,15746 and 15747)

– Bad burst ● Check: DCH,MBX,HODC,LKR,MUV,PMB and MNP33Current ne 0)● Reject 31 bursts for which momentum = 10.0 GeV ● Total number of bursts after bad burst rejection: 2244

– Alphas and betas– Projectivity and Blue Field (Alan algorithm to remove phi

dependence)

MC Sample:

– Ginsberg correction

– Constants from PDG 2002 for ke3 (λ + = 0.02760)

– Pi0 decays according to its branching ratio– CMC005 corrections including corrections of May 9th 2005 – Result based on sample size of 8 M pipi0 and 8 M ke3– Pipi0 mc has 0.13% pipi0g (IB) included in it at generation level

Data and MC samples


Common Selection for Ke3 and pipi0

● Track Section (no extra tracks allowed):– 1 track after excluding Ghost-tracks – Hodoscope time window (-17. 20. ns)– Track quality > 0.8 CDA < 2.5 , Beta, alpha corrections from

database– x,y vertex (-1.8,1.8) cm , z charge vertex (-500,8000) cm– Blue Field correction applied

● Pi0 Selection (extra gammas allowed for both)– Energy of gamma (3, 65) GeV– Separation between gammas > 10 cm – Time difference between gammas (-5., 5.) ns– Energy scale– Projectivity correction– Calculate neutral vertex for each pair of gammas, and choose

gammas based on best difference between charge and neutral vertex

● Use this neutral vertex in the blue field routine to correct the slopes of the track (reason: phi dependence studies of Alan)


Difference between Ke3Ke3 and pipi0pipi0 Selections

• Kaon Mass < 0.4772 or > 0.5102 (3 sigma from the mean)

• Momentum (5, 35) GeV

• PT track (0.01, 0.2) GeV

• Nu mass (-0.012, 0.012) GeV2

• Dist between track & gammas > 10 cm

• COM Track < 0.22 GeV

• COM pi0 < 0.27 GeV

• Mass (eπ0 ) < 0.425 GeV

• Particle ID for electrons:Particle ID for electrons:

• EOP > 0.95 and shower EOP > 0.95 and shower width rms in x and y (0.65 – width rms in x and y (0.65 – 0.85)0.85)

• Kaon Mass (0.4772,0.5102) GeV

• Momentum (10, 50) GeV

• PT track < 0.215 GeV

• Nu mass (-0.0025, 0.001) GeV2

• Distance between track & gammas > 35 cm

• PT pi0 < 0.220 GeV

• E/P < 0.95


Pipi0 E/P < 0.95

Ke3 E/P > 0.95 andShower shape rms in both x and y 0.65 – 0.850.65 – 0.85

Summary of particle ID used:


Ke3 Data / MC Momentum track


Ke3 Data / MC Energy Pi0


Ke3 Data / MC PT of pi0


Ke3 Data / MC PT of track


Ke3 Data / MC Vertex


Ke3 Data/MC COM energy pi0


Ke3 Data/MC COM energy track


Electron ID

• Selected electrons from tight ke3 selection

• Used same data sample, and timing and fiducial cuts as in analysis

• Used cuts in analysis plus– Mk < 0.465 or mk > 0.525– Pt track < 0.175 GeV– -0.005 < m nu < 0.00025

GeV^2– Mx^2 < -0.0025 GeV^2– ECOMpi0 < 0.23 GeV– ECOMtrk < 0.17 GeV– Mass mupi0 < 0.36 GeV

Global efficiency (96.59 +- 0.14) %

E/P > 0.95 and shower rms cut 0.65 – 0.85 in each of x and y


Electron ID as background for pipi0

• Selected electrons from tight ke3 selection

• Used same data sample, and timing and fiducial cuts as in analysis

• Used cuts in analysis plus– Mk < 0.465 or mk > 0.525– Pt track < 0.175 GeV– -0.005 < m nu < 0.00025

GeV^2– Mx^2 < -0.0025– ECOMpi0 < 0.23 GeV– ECOMtrk < 0.17 GeV– Mass mupi0 < 0.36 GeV

E/P > 0.95 needed for background contribution estimate in pipi0 (pion ID is E/P < 0.95)



Pion ID for background to ke3 estimate

• Selected from tight pipi0 selection:

• 0.485 < mkaon < 0.505• 0.245 < Ecmpi < 0.25• Mx^2 > -0.0015

Same timing, data sample, trigger selection and fiducial volume cuts as selection


E/P > 0.9>5 and shower shape needed for background contribution estimate of pipi0 in ke3


Pion ID E/P < 0.95

• Selected from tight pipi0 selection:

• 0.485 < mkaon < 0.505 GeV• 0.245 < Ecmpi < 0.25 GeV• Mx^2 > -0.0015 GeV^2

Same timing, data sample, trigger selection and fiducial volume cuts as selection


E/P < 0.95 particle ID condition for pions in normalization


Background contributions

Channel Background contributions

Pipi0(E/P<0.95)

Kmu3 (0.280+-0.0058) %Ke3 (0.0100+-0.0015) %

Ke3

(E/P>0.95)

(rms shower shape in x and y)

Pipi0 (0.0043 +- 0.0002) % Pipi0pi0 (0.0070 +-0.0003) %


Acceptance of Signal and Normalisation K+

channel

Raw Acceptance from MC

Acceptance * particle ID

Final acceptance

ke3 0.0750 +- 0.0001 0.0723 +- 0.0002

(E/P > 0.95 for electrons)

0.0723 +- 0.0002

pipi0 0.1473 +- 0.0001 0.1465 ± 0.0001 (E/P < 0.95 for pions)

0.1448 ± 0.0001


Background to ke3 K+

Source ofBackground

Particle ID used

RAW MC acceptance no particle ID (%)

Acceptance* particle ID(%)

Background(Accbk*Br_bk)/(AccS*BR_signal) (%)

Pipi0(note when

pion doesn’t decay)

E/P > 0.95 + shower shape

0.0196 +- 0.0005 0.000072 +- 0.000003

0.0043 +- 0.0002

Pipi0pi0(note when



0.3845 +- 0.0025 0.0014 +- 0.0001 0.0070 +- 0.0003


Sources of background pipi0 K+

Source ofBackground

Particle ID used

Raw Acceptance

(%)

Acc*Particle ID (%)


kmu3 E/P < 0.95 0.2650 +- 0.0018 0.2650 +- 0.0018 0.2800 +- 0.0058

ke3 E/P < 0.95 0.1934 +- 0.0016 0.0100 +- 0.0015 0.0157 +- 0.0024


Acceptance of Signal and Normalisation K-

channel

Raw Acceptance from MC

Acceptance * particle ID

ke3 0.0748 +- 0.0001 0.0724 +- 0.0002

(E/P > 0.95 for electrons)

pipi0 0.1471 +- 0.0001 0.1463 +- 0.0001

(E/P < 0.95 for pions)


Background to ke3 K-

Source ofBackground

Particle ID used

RAW MC acceptance no particle ID (%)

Acceptance* particle ID(%)


Pipi0(note when



0.0197 +- 0.0005 0.000075 +- 0.000004

0.0045 +- 0.0003

Pipi0pi0(note when



0.3844 +- 0.0027 0.0015 +- 0.0001 0.0074 +- 0.0004


Sources of background pipi0 K-

Source ofBackground

Particle ID used

Raw Acceptance

(%)

Acc*Particle ID (%)


kmu3 E/P < 0.95 0.2641 +- 0.0018 0.2641 +- 0.0018 0.279 +- 0.006

ke3 E/P < 0.95 0.1944 +- 0.0018 0.0080 +- 0.0006 0.0127 +- 0.0010


• Main Trigger Q1/4 • Min bias trigger for

trigger efficiency calculation Trackloose/100

channel K+ K-

pipi0 0.9987 ± 0.0002 0.9990 ± 0.0002

Ke3 0.9987 ± 0.0005 0.9983 ± 0.0008

kmu3 0.9986 ± 0.0006 0.9988 ± 0.0007

Result of two charges combined

Trigger Efficiency


Ratio result Main Error contributions

Signal Normalization

Systematics

Ratio Ke3/pipi0 K+

0.24756 +- 0.00126

0.00103 0.00036 0.00062

Ratio Ke3/pipi0 K-

0.24501 +- 0.00163

0.00138 0.00048 0.00075

• The error in the Br includes:– Data sample (signal and normalization)– Systematic

• Trigger efficiency• MC statistics (8 M pipi0 and 8 M kmu3 of each charge)• Errors in particle ID efficiency (particle ID error bin by bin and propagated)• Errors due to background subtraction (including particle ID)

• No systematic errors due to kinematic cuts or form factor changes have been included

Result (Ratio Ke3/pipi0)


Br(Ke3) Main Error contributions

Signal Normalization

Systematics Pizero Br

Br Ratio

Ke3 K+

0.05231 +- 0.00044

0.00022 0.00008 0.00013 0.00035

Br Ratio

Ke3 K-

0.05177 +- 0.00049

0.00029 0.00010 0.00016 0.00034

• The error in the Br includes:– Data sample (signal and normalization)– Systematics

• Trigger efficiency• MC statistics (8 M pipi0 and 8 M kmu3 of each charge)• Errors in particle ID efficiency (particle ID error bin by bin and propagated)• Errors due to background subtraction (including particle ID)

• No systematic errors due to kinematic cuts or form factor changes have been included

Result ( Br Ke3)


Ratio of Ke3/pipi0 K+ 0.24756 +- 0.00126Statistics from signal (number of Ke3 events data) 0.00104 Statistics from normalization (number of pipi0 events data) 0.00036

Background subtraction 0.000006 Trigger efficiency in pipi0 events 0.00005 Trigger efficiency in ke3 events 0.00012 Acceptance * Particle ID ke3 0.00056 Acceptance* Particle ID pipi0 0.00023 Number of ke3 events data 49566

Number of pipi0 events data 466069

Details of error contributions to ratio


Ratio of Ke3/pipi0 K- 0.24501 +- 0.00163

Statistics from signal (number of Ke3 events data) 0.00137 Statistics from normalization (number of pipi0 events data) 0.00048

Background subtraction 0.000014 Trigger efficiency in pipi0 events 0.00005 Trigger efficiency in ke3 events 0.00012 Acceptance * Particle ID ke3 0.00069 Acceptance* Particle ID pipi0 0.00023 Number of ke3 events data 27494

Number of pipi0 events data 258500

Details of error contributions to ratio


Χ2/ndf 11.81 / 12 Χ2/ndf 16.99 / 12

Ratio of Ke3/ pipi0 as a function of momentum

K+ K-


K+ 0.24873 +- 0.00126 K- 0.24622 +- 0.00164

Statistics from signal (# Kmu3 events data) 0.00104 0.00138

Statistics from norm (# pipi0 events data) 0.00036 0.00048

Total Statistical Error 0.00110 0.00146

Background subtraction

Trigger eff for pipi0 events

Trigger eff for kmu3 events

Acc * Particle ID kmu3

Acc* Particle ID pipi0

Combined result =

Combination of both charges


• Systematics considered:– Fiducial volume – z vertex cut– Low energy neutral energy scale– Varying E/P cut for both electrons and pions– Parameter describing energy dependence of form factor (λ +

)

Estimation of Systematic Error


Cut varied Ratio result

Statistical Error

Systematic Error

Difference Br ± correlated error

Default (-500, 8000 cm)

0.24756 0.00109 0.00062

( 0, 8000 cm) 0.24737 0.00110 0.00062 -0.00019 +- 0.00017

(-1000,8000 cm) 0.24761 0.00108 0.00062 +0.00005 +- 0.00015

(-2000,8000 cm) 0.24769 0.00107 0.00062 +0.00013 +- 0.00023

(-500,7000 cm) 0.24825 0.00114 0.00063 +0.00069 +- 0.00033

(-500,6000 cm) 0.24839 0.00125 0.00066 +0.00082 +- 0.00075

Error Assigned 0.0008

Vertex cut K+


Cut varied Ratio result

Statistical Error

Systematic Error


Default (-500, 8000 cm)

0.24501 0.00146 0.00074

( 0, 8000 cm) 0.24492 0.00147 0.00074 -0.00008 +- 0.00023

(-1000,8000 cm) 0.24500 0.00144 0.00074 -0.00001 +- 0.00020

(-2000,8000 cm) 0.24476 0.00142 0.00074 -0.00025 +- 0.00030

(-500,7000 cm) 0.24515 0.00151 0.00075 0.00014 +- 0.00044

(-500,6000 cm) 0.24523 0.00166 0.00078 0.00022 +- 0.00101

Error Assigned 0.0003

Vertex cut K-


Cut varied Ratio Statistical Error

Systematic Error


Default K+ (min g 3 Gev)

0.24756 0.00109 0.00062

( min g 5 GeV) 0.24736 0.00119 0.00064 -0.00020 +- 0.00057

Error Assigned K+ 0.0002

Energy γ 2

Energy γ 1

Low neutral energy scale K+


Cut varied Ratio Statistical Error

Systematic Error


Default K-(min g 3 GeV)

0.24501 0.00146 0.00074

( min g 5 GeV) 0.24416 0.00159 0.00076 -0.00085 +- 0.00077

Error Assigned K-

-0.0009

Energy γ 2

Energy γ 1

Low neutral energy scale K-


Form factor model Ratio result (K+) Difference

0.0276 (PDG 2002,used in

BNL E865 result)

0.24756 +- 0.00109(stat) +- 0.00062 (sys)

0.0278 (PDG 2004 0.0278+-

0.0070)

0.24723 +- 0.00109(stat) +- 0.00070 (sys)

-0.00033

0.0271(PDG 2004 –1 σ)

0.24841 +- 0.00109(stat) +- 0.00070 (sys)

+0.00084

0.0285

(PDG 2004 +1 σ)

Error Assigned

Varying the form factor λ+


Form factor model Ratio result (K-) Difference

0.0276 (PDG 2002,used in

BNL E865 result)

0.24501 +- 0.00146 (stat) +- 0.00074 (sys)

0.0278 (PDG 2004 0.0278+-

0.0070)

0.24586 +- 0.00146 (stat) +- 0.00079 (sys)

+0.00086

0.0271(PDG 2004 –1 σ)

0.24527 +- 0.00146 (stat) +-0.00079 (sys)

+0.00026

0.0285

(PDG 2004 +1 σ)

Error Assigned

Varying the form factor λ+


Summary of Systematic Error Contributions

Cut Systematic Contribution

Vertex Cut

Min Energy Cut

E/P

Parameterization of form factor

Total Systematic Error


Recall PDG:

Br(Ke3) = 0.0487+- 0.0006

Br(pipi0) = 0.2113 +- 0.0014

Ratio(ke3/pipi0) = 0.2305+-0.0032

Final result for ratio Ke3/pipi0 and Br(Ke3)


Conclusion

Documents

Ratio of Ke3 to Pipi0