γγ  interac*ons  at  KLOE  

Ivan  Prado  Longhi  on  behalf  of  the  KLOE/KLOE-­‐2  Collabora*on  Università  “Roma  Tre”  and  INFN  -­‐  Sezione  ”Roma  Tre”  

MesonNet2013  -­‐  Prague,  17-­‐06-­‐2013  

2  Ivan  Prado  Longhi@Mesonnet2013  

Electromagne*c  calorimeter  

•   lead/scin*lla*ng  fibers  •   98%  solid  angle  coverage  •   σE/E  =  5.7%/√(E(GeV))  •   σt=57  ps/√(E(GeV))  +  100  ps  • PID  capabili*es  

Dria  Chamber  

•   Gas  mixture  90%  He  +  10%  C4H10  •   δpT/pT  <  0.4%  (450<ϑ<1350)  •   σxy≈150  μm;  σz  ≈  2  mm  

MAGNETIC  FIELD  0.52  T  

KLOE  Detector  

e+e- → e+e-γ*γ* → e+e-X

X �

X: JPC = 0±+ �

(  π0,  η,  η’,  σ(500)  )  

} �

γγ  physics  @  KLOE  

La Thuile 26/2/2013 S.Miscetti@LaThuile 2013

!! physics @ KLOE: "#(!!) measurement

20

KLOE: no e± tagging ! s = 1 GeV

KLOE-2: tagger to reduce background from $ and to close kinematics !s = M$

!  !!!# (!0!0) studied (under-way) at KLOE

!  Data sample: 240 pb%1 @ "s = 1 GeV (reduced bckg contamination from $)

!  Selected channels: #"&+&%&0/&0&0&0'

!  Main background: $!#! with undetected recoil photon

Analyses  on  L=242.5  pb-­‐1  off-­‐peak  data  (collected  at  √s=1  GeV):  •   e+e-­‐  →  e+e-­‐η    •   e+e-­‐  →  e+e-­‐π0π0  (in  progress)  

3  Ivan  Prado  Longhi@Mesonnet2013  

Mo*va*ons:  Γ(X→γγ),  meson  structure,  search  for  σ(500)      

e+e-­‐  →  e+e-­‐  η    

4  Ivan  Prado  Longhi@Mesonnet2013  

e+e-­‐  →  e+e-­‐  η  

5  Ivan  Prado  Longhi@Mesonnet2013  

Two  channels:  

η  →  π0  π0  π0   η  →  π+  π-­‐  π0  

•   6γ  only  with  E>15  MeV,                    230<ϑ<1570,        |t-­‐r/c|<3σt  •   no  tracks  in  the  dria  chamber  •   γγ  pairing  

•   kinema*c  fit  requiring  M6γ=  mη    

•   2γ  only  with  E>15  MeV,                    230<ϑ<1570,        |t-­‐r/c|<3σt  •   2  tracks  with  opposite  charge        from  a  cylinder  ρPCA  <  8  cm,        |zPCA|  <  8  cm,  ρfirst-­‐hit  <  50  cm    •   γγ  pairing  to  renconstruct  π0  •   electron-­‐pion  likelihood  cut    •   kinema*c  fit  requiring  Mππγγ=  mη    

!"" "#$%&%'("""""""""""""""""""""""""""""""""""""""""""""")*"#$%&")+,"-" )*")+,""!"".%',/$)%0"1%)"&,23%&%'(")+,"%'4$&%$')" "/$55")*"6,",23$7,")*")+," "/$55"

!"#

!-"$'8"*'79"-"#+*)*'5":%)+";"<=>"?,@A"BC*D D=>EFA"G)! )""HI")&$0J5"%'")+,"8&%1)"0+$/6,&"

, , " ", , " A" $'$795%5"5)&$),(9""

32

2

)(0

p a irM

MMp a ir

"! !#!$%! "! !#!"&!

B" "K8$)$L"

B" "K?M"5%('$7L"

B" "K8$)$L"

B" "K?M"5%('$7L"

Main  background:  e+e-­‐  →    ηγ  with  γ  at  small  angles,  outside  the  acceptance  

!"#

! ! " "! ! " #" $%"&'(""

!"#$%&'()#!"# ##

!$%%#&'()*#+),)-#../#0'1()*-#%2/# ##0,),'0,'3)*#45565# #78%/###

0'1()*# #9#:!;8%"# #"8!2</###=+6&#9#$$7"=$>.%#

")! ! " "! ! # " " *+,"-!./"+"),0123"4"0125*(6("/"78"

#9:"");!./" ;$<'**"")-!.$/"

e+e-­‐  →  e+e-­‐  η:  2D  fits  

6  Ivan  Prado  Longhi@Mesonnet2013  

η  →  π0  π0  π0  

Variables:  PL  and  M2miss  

!"#

! ! " "! ! " #" $%"&'(""

!"#$%&'()# !" #!"# ## # !"#*+#*,!"##*-*.# !"#/-/.

$%$&#'()*+#,*-*.#!"/#0(1)*+#0-*-(0-(2*+#34454# #%67/###7$/# .#$&/# .#!8/#9 9 .#!!/#9:9;.#</#3 3

0(1)*+# #=#>$&6%7# #&6$?@/###A,5'#=#$B%&A$B%7#

!""#$%&#'())#)*+),-#'.(#

")! ! " "! ! # " " *+,"-!./"+")0123"4"5160*(7("/"89"

#:;"")<!./" <$='**"")-!.$/"

e+e-­‐  →  e+e-­‐  η:  2D  fits  

7  Ivan  Prado  Longhi@Mesonnet2013  

η  →  π+  π-­‐  π0  

Variables:  PT  and  M2miss  

e+e-­‐  →  e+e-­‐  η:  results  

σ(e+e-­‐  →  e+e-­‐  η,  √s  =  1  GeV)    =  (32.0  ±  1.5stat  ±  0.9syst  ±  0.2BR(η  →  3π))  pb  

σ(e+e-­‐  →  e+e-­‐  η,  √s  =  1  GeV)    =  (34.5  ±  2.5stat  ±  1.0syst  ±  0.7FF  ±  0.4BR)  pb  

σ(e+e-­‐  →  e+e-­‐  η,  √s  =  1  GeV)    =  (32.7  ±  1.3stat  ±  0.7syst)  pb  

Neutral  channel,  ≈  720  signal  events:  

Charged  channel,  ≈  390  signal  events:  

Combined  

Γ(η→γγ)  extracted  (see  reference  for  details  on  luminosity  func*on  and  FF  parametriza*on):  

Γ(η → γγ) = (520± 20stat ± 13syst) eV

8  Ivan  Prado  Longhi@Mesonnet2013  

Most  precise  measurement,  In  agreement  with  PDG  value  

(510±26)  eV  

!"#

! ! " " #"$!%&'(""

")%!*"+%"+",-.%($+/.("/."(0!"1/("1-$!! ! " "! ! "! !

"" "2! ! " " 3",+."4!"

/.*!5!.*!.('6"*!$/7!*"+%"+"46"5$-*&,("-1"(0!"8+/."+.+'6%/%"/."(0!",+%!"-1"! ! " "! ! "! ! 9"6/!'*/.:" "2! ! " " 9 %;<"=!>3";"2?@A"B"C@%(+("B"@%6%("B"DEF"3"549"/."+:$!!8!.("G/(0"(0!"7+'&!"-4(+/.!*"/."(0!"*!*/,+(!*"+.+'6%/%H""

"2! ! " " 9 %;<"=!>3";"2?@D"B"?%(+("B"<C%6%("B"<<EF"3"54"$%&'#()(*+,%*&-(#./0,# #-/0((#(+-*&0'#

%2I!>3"

2.43"

!"#

! ! " " #"$!%&'(""

")%!*"+%"+",-.%($+/.("/."(0!"1/("1-$!! ! " "! ! "! !

"" "2! ! " " 3",+."4!"

/.*!5!.*!.('6"*!$/7!*"+%"+"46"5$-*&,("-1"(0!"8+/."+.+'6%/%"/."(0!",+%!"-1"! ! " "! ! "! ! 9"6/!'*/.:" "2! ! " " 9 %;<"=!>3";"2?@A"B"C@%(+("B"@%6%("B"DEF"3"549"/."+:$!!8!.("G/(0"(0!"7+'&!"-4(+/.!*"/."(0!"*!*/,+(!*"+.+'6%/%H""

"2! ! " " 9 %;<"=!>3";"2?@D"B"?%(+("B"<C%6%("B"<<EF"3"54"$%&'#()(*+,%*&-(#./0,# #-/0((#(+-*&0'#

%2I!>3"

2.43"

e+e- → ηγ @ √s = 1 GeV

9  Ivan  Prado  Longhi@Mesonnet2013   !"#

! ! " " #"$!%&'(""

")%!*"+%"+",-.%($+/.("/."(0!"1/("1-$!! ! " "! ! "! !

"" "2! ! " " 3",+."4!"

/.*!5!.*!.('6"*!$/7!*"+%"+"46"5$-*&,("-1"(0!"8+/."+.+'6%/%"/."(0!",+%!"-1"! ! " "! ! "! ! 9"6/!'*/.:" "2! ! " " 9 %;<"=!>3";"2?@A"B"C@%(+("B"@%6%("B"DEF"3"549"/."+:$!!8!.("G/(0"(0!"7+'&!"-4(+/.!*"/."(0!"*!*/,+(!*"+.+'6%/%H""

"2! ! " " 9 %;<"=!>3";"2?@D"B"?%(+("B"<C%6%("B"<<EF"3"54"$%&'#()(*+,%*&-(#./0,# #-/0((#(+-*&0'#

%2I!>3"

2.43"

Studied  as  main  background  for  e+e-­‐  →  e+e-­‐  η      

σ(e+e-­‐  →  ηγ  )  

η→  π+  π-­‐  π0,  SND  

η→  π0  π0  π0,  SND  

KLOE  result  

e+e-­‐  →  e+e-­‐  π0π0    

10  Ivan  Prado  Longhi@Mesonnet2013  

Ivan  Prado  Longhi@Mesonnet2013   11  

e+e-­‐  →  e+e-­‐  π0π0  (work  in  progress)  

Cut-­‐based  and  mul*variate  analysis  

(possible  produc*on  of  σ(500)  as  a  resonant  intermediate  state)  

ANALYSIS  CUTS  

To  reject  annihila*on  processes  e+  e-­‐→  KSKL,  ηγ,  ωπ0,  f0γ,  a0γ,  γγ    

Signal  e+e-­‐  →  e+e-­‐  σ  →  e+e-­‐  π0π0:  complete  matrix  element,  full  phase  space    [Eur.  Phys.  J.  C47  (2006)  65]  

Selected  sample  contaminated  by  low-­‐invariant  mass,  high-­‐pt,  unbalanced  pL  background  (machine  bkg)        

MULTIVARIATE  ANALYSIS  

using  TMVA  package  -­‐>  cut  on  the  MVA  output  

e+  e-­‐  annihila*on  processes  normalized  according  to  Xsec*ons    

machine    background  selected  from  data  by    topological  criteria  

   track  veto,  4γ  only,  no  late-­‐clusters  (to  reject  KSKL  events)    

χ2ππ =

(mπ0 −mij)2

σ2ij

+(mπ0 −mkl)2

σ2kl

12  

e+e-­‐  →  e+e-­‐  π0π0:  analysis  cuts  

   π0π0  selec*on  cu�ng  on  

1

10

10

10

M!! (MeV)

M!!

(M

eV)

1

10

10

10

M!! (MeV)

M!!

(M

eV)

0

25

50

75

100

125

150

175

200

225

250

0 25 50 75 100 125 150 175 200 225 250

0

25

50

75

100

125

150

175

200

225

250

0 25 50 75 100 125 150 175 200 225 250

χ2ππ  <  4  

mγ1γ2  vs  mγ3γ4  

ID 1000000ENTRIES 2854 0.00 0.00 0.00 0.00 0.285E+04 0.00 0.00 0.00 0.00

m4 (MeV)

p T (MeV

)

IDEntriesMeanRMSUDFLWOVFLWALLCHAN

1000000 2854

-24.11 106.6 0.000 0.000 2854.

pL (MeV)

0

50

100

150

200

250

300

350

400

450

500

200 300 400 500 600 700 800 900

0

20

40

60

80

100

120

-400 -200 0 200 400

Low  m4γ,  high  pT  

unbalanced  pL    

“DATA  DRIVEN”  machine  background:    

Selected  studying:  •   d  =  displacement  of  the  reconstructed  photons’  origin  from  the  IP  •   |t-­‐r/c|  of  the  t0  cluster    

Ivan  Prado  Longhi@Mesonnet2013  

ID 1000000ENTRIES 9788 0.00 0.00 0.00 0.00 0.979E+04 0.00 0.00 0.00 0.00

ABS(t-r/c)t0

sqrt(

d 12 +d 22 )

0

10

20

30

40

50

60

70

80

90

100

-0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4

A   B  

C  S  

“DATA  DRIVEN”  BKG:  Normaliza*on  

A   B   C   S  

Data   1418   1611   1375   6213  

a   b   c   S  

KsKL   85   8   24   868  

ηγ   30   3   16   345  

ωπ0   27   2   23   754  

f0γ   -­‐   -­‐   -­‐   58  

γγ   -­‐   -­‐   -­‐   45  

a0γ   -­‐   -­‐   -­‐   9  

#  bkg  events  in  A  +  B  +  C≈  1418+1611+1375  =  4404    with  contamina*on  ≈  218  Bkg(S)  =  (A-­‐a)*(C-­‐c)/(B-­‐b)=  1048  (assuming  uniformely  distributed  bkg  in  the  |d|  vs  |t-­‐r/c|t0  plane)  

13  

33  cm  

0.5  ns  

|d|  vs  |t  –  r/c|t0  

Ivan  Prado  Longhi@Mesonnet2013  

14  

data

EntriesMeanRMSALLCHAN

8398 392.8 114.1 8398.

M4 (MeV)

dN/d

M4

(25

MeV

)-1

0

50

100

150

200

250

300

350

400

450

200 300 400 500 600 700 800 900

 ndata=  8398  

A  fit  to  m4γ  spectrum  is  performed  using  f=n/ndata  as  star*ng  values  

KSKL  

ωπ0  

ηγ  

γγ→  π0π0  

Bkg  (data  driven)  

ε   σ  (nb)   n  =  Lσε  

KSKL   0.003   1.28   985  

ηγ   0.006   0.284   393  

ωπ0   0.006   0.550   806  

f0γ,  a0γ,  γγ    

≈  0   -­‐   120  

AFTER  SELECTIONS:  

e+e-­‐  →  e+e-­‐  π0π0:  cut  based  analysis  

Ivan  Prado  Longhi@Mesonnet2013  

Bkg  (data  driven)   3267  

γγ→  π0π0   2830  

15  

MULTIVARIATE  ANALYSIS  WITH  TMVA  

•   “Data  driven”  machine  background  normalized  by  extrapola*on  •     MC  Distribu*ons  normalized  to  fit  results        

Training  

 Data  to  be  analyzed:  8398  events      

Applica*on  

Applica*on  is  performed  on  each  MC  and  data-­‐driven  bkg  sample  in  order  to  evaluate  the  efficiencies  of  cu�ng  on  

the  MVA  output  

Longitudinal momentum [MeV]-400 -200 0 200 400

18.9

MeV

/ (1

/N) d

N

00.001

0.002

0.0030.004

0.005

0.0060.007

0.008

0.009Signal

Background

Longitudinal momentum [MeV]-400 -200 0 200 400

18.9

MeV

/ (1

/N) d

N

00.001

0.002

0.0030.004

0.005

0.0060.007

0.008

0.009

U/O

-flo

w (S

,B):

(0.0

, 0.0

)% /

(0.0

, 0.0

)%

Input variable: Longitudinal momentum

Transverse momentum [MeV]50 100 150 200 250 300 350 400

6.93

MeV

/ (1

/N) d

N

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

Transverse momentum [MeV]50 100 150 200 250 300 350 400

6.93

MeV

/ (1

/N) d

N

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

U/O

-flo

w (S

,B):

(0.0

, 0.0

)% /

(0.1

, 0.0

)%Input variable: Transverse momentum

t-r/c chi^2 [F]2 4 6 8 10 12

0.20

5 F

/ (1

/N) d

N

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

t-r/c chi^2 [F]2 4 6 8 10 12

0.20

5 F

/ (1

/N) d

N

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

U/O

-flo

w (S

,B):

(0.0

, 0.0

)% /

(0.0

, 10.

1)%

Input variable: t-r/c chi^2

Gaussian  smearing  σ  =  40  MeV  on  px  and  py  for  γγ→  π0π0  MC  

χ2t =

1

4

4�

i

�ti − ri/c

σt,i

�2PL   PT  

Likelihood output0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Effic

ienc

y (P

urity

)

0

0.2

0.4

0.6

0.8

1

Likelihood output0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Effic

ienc

y (P

urity

)

0

0.2

0.4

0.6

0.8

1

Signal efficiencyBackground efficiency

Signal puritySignal efficiency*purity

S+BS /

For 4886 signal and 3512 background isS+Bevents the maximum S /

65.3767 when cutting at 0.2892

Cut efficiencies and optimal cut value

Sign

ifica

nce

0

10

20

30

40

50

60

70

Ivan  Prado  Longhi@Mesonnet2013  

M4 (MeV)

dN/d

M4

(10

MeV

)-1

M4 (MeV)

dN/d

M4

(10

MeV

) -1

0

25

50

75

100

125

150

175

200

225

200 300 400 500 600 700 800 900

0

20

40

60

80

100

120

140

160

200 300 400 500 600 700 800 900

16  

KSKL  

ωπ0  

ηγ  

γγ→  π0π0  MC  

Bkg  (data  driven)  ε   σ  (nb)   n  =  Lσε  

KSKL   0.003   1.28   953  

ηγ   0.005   0.284   374  

ωπ0   0.006   0.550   774  

f0γ,  a0γ,  γγ    

≈  0   -­‐   110  

Cu�ng  on  likelihood  >  0.3  

Subtracted  spectrum  

M4γ  spectra  

Likelihood response0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

dx / (1

/N) d

N

0

10

20

30

40

50

60 SignalBackground

Likelihood response0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

dx / (1

/N) d

N

0

10

20

30

40

50

60

U/O

-flow

(S,B

): (0

.0, 0

.0)%

/ (0

.0, 0

.0)%

TMVA response for classifier: Likelihood

5324  events  

2625  events  

Ivan  Prado  Longhi@Mesonnet2013  

Bkg  (data  driven)   492  

γγ→  π0π0   2625  

Ivan  Prado  Longhi@Mesonnet2013   17  

SUMMARY  

Off-­‐peak  (  √s  =  1  GeV)  data  collected  by  KLOE  are  precious  to  study  meson  produc*on  in  γγ  interac*ons  

2  Analyses:  

 e+e-­‐  →  e+e-­‐  η,  published    [JHEP01(2013)119]  •   Studied  in  both  η→π+π-­‐π0  and  η→π0π0π0  channels  •   σ(e+e-­‐  →  e+e-­‐  η,  √s  =  1  GeV)  evaluated,  Γ(η→γγ)  extracted              (most  precise  measurement)  

 e+e-­‐  →  e+e-­‐  π0π0,  work  in  progress  •   excess  of  events  just  above  π0π0  threshold  •   contamina*on  from  machine  background  handled  using  a  mul*variate              analysis  approach  •   promising  ≈  2600    γγ→  π0π0  candidate  events  sample          

Ivan  Prado  Longhi@Mesonnet2013   18  

SPARES  

d1   d2  

χ2d1,d2

=2�

i

(r�i(d1)/c− ti)2

σ2t,i

+

2�

i

�r�j(d2)/c− tj

�2

σ2t,j

r�i,j =�

r2i,j + d21,2 + 2d1,2zi,j

r1   r2  

r’2  r’1  

1 2

3 4

r3  r4  

r’4  r’3  

MINIMIZE:  

d1  ≠  0  or  d2  ≠  0  could  be  a  signature  for  machine  bkg  events        

19  

e+e-­‐  →  e+e-­‐  π0π0:  selec*ng  bkg  

Ivan  Prado  Longhi@Mesonnet2013  

IDEntriesMeanRMSUDFLWOVFLWALLCHAN

6000 10042

26.47 23.05 0.000 0.000

0.1004E+05

sqrt(d12+d2

2)

IDEntriesMeanRMSUDFLWOVFLWALLCHAN

6000 33794

15.65 13.03 0.000 0.000

0.3379E+05

sqrt(d12+d2

2)

0

100

200

300

400

500

600

700

0 20 40 60 80 100 120 140 160 180 200

0

500

1000

1500

2000

2500

3000

3500

4000

0 20 40 60 80 100 120 140 160 180 200

Data  

MC  ηγ  

|d| =�d21 + d22

CONSIDER:  

20  

e+e-­‐  →  e+e-­‐  π0π0:  selec*ng  bkg  

ID 1000000ENTRIES 2854 0.00 0.00 0.00 0.00 0.285E+04 0.00 0.00 0.00 0.00

m4 (MeV)

p T (M

eV)

IDEntriesMeanRMSUDFLWOVFLWALLCHAN

1000000 2854

-24.11 106.6 0.000 0.000 2854.

pL (MeV)

0

50

100

150

200

250

300

350

400

450

500

200 300 400 500 600 700 800 900

0

20

40

60

80

100

120

-400 -200 0 200 400

PT    VS  m4γ  

CUTTING    |d|>33  cm  

Low  m4γ,  high  pT  

unbalanced  pL    

Ivan  Prado  Longhi@Mesonnet2013  

Alterna*ve  bkg  selec*on  variable  

IDEntriesMeanRMSUDFLWOVFLWALLCHAN

7000 10042

-0.1382 0.4596 0.000 0.000

0.1004E+05

(t-r/c)t0

IDEntriesMeanRMSUDFLWOVFLWALLCHAN

7000 33794

-0.1051 0.2263 0.000 0.000

0.3379E+05

(t-r/c)t0

0

100

200

300

400

500

600

-1.5 -1 -0.5 0 0.5 1 1.5

0

500

1000

1500

2000

2500

3000

-1.5 -1 -0.5 0 0.5 1 1.5

Data  

MC  ηγ  

21  

ID 1000000ENTRIES 2821 0.00 0.00 0.00 0.00 0.282E+04 0.00 0.00 0.00 0.00

m4 (MeV)

p T (M

eV)

IDEntriesMeanRMSUDFLWOVFLWALLCHAN

1000000 2821

-25.77 119.1 0.000 0.000 2821.

pL (MeV)

0

50

100

150

200

250

300

350

400

450

200 300 400 500 600 700 800 900

0

20

40

60

80

100

120

-400 -200 0 200 400

t  –  r/c    of  the  t0  cluster  

PT    VS  m4γ  

Low  m4γ,  high  pT  

unbalanced  pL    

CUTTING    |t-­‐r/c|>0.5  ns  

Ivan  Prado  Longhi@Mesonnet2013  

22  

Longitudinal momentum [MeV]-400 -200 0 200 400

18.9

MeV

/ (1

/N) d

N

00.001

0.002

0.0030.004

0.005

0.0060.007

0.008

0.009Signal

Background

Longitudinal momentum [MeV]-400 -200 0 200 400

18.9

MeV

/ (1

/N) d

N

00.001

0.002

0.0030.004

0.005

0.0060.007

0.008

0.009

U/O

-flow

(S,B

): (0

.0, 0

.0)%

/ (0

.0, 0

.0)%

Input variable: Longitudinal momentum

Transverse momentum [MeV]50 100 150 200 250 300 350 400

6.93

MeV

/ (1

/N) d

N

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

Transverse momentum [MeV]50 100 150 200 250 300 350 400

6.93

MeV

/ (1

/N) d

N

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

U/O

-flow

(S,B

): (0

.0, 0

.0)%

/ (0

.1, 0

.0)%

Input variable: Transverse momentum

t-r/c chi^2 [F]2 4 6 8 10 12

0.20

5 F

/ (1

/N) d

N

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

t-r/c chi^2 [F]2 4 6 8 10 12

0.20

5 F

/ (1

/N) d

N

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

U/O

-flow

(S,B

): (0

.0, 0

.0)%

/ (0

.0, 1

0.1)

%

Input variable: t-r/c chi^2

smearing  σ  =  40  MeV  on  px  and  py  for    γγ→  π0π0  MC  

χ2t =

1

4

4�

i

�ti − ri/c

σt,i

�2

PL  PT  

MULTIVARIATE  ANALYSIS  

INPUT  DISTRIBUTIONS:  “SIGNAL”:  all  simulated  physical  processes  (MC  γγ-­‐>ππ,  KSKL,  ηγ,  ωπ  etc.)  

“BACKGROUND”:  Data  sample  selected  with  |d|>33  cm  

All  contribu*ons  weighted  according  to  previous  fit  results    

Ivan  Prado  Longhi@Mesonnet2013  

23  

htempEntries 8398Mean 0.5671RMS 0.4197

like0 0.2 0.4 0.6 0.8 10

200

400

600

800

1000

1200

1400

htempEntries 8398Mean 0.5671RMS 0.4197

like

Likelihood response0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

dx / (1

/N) d

N

0

10

20

30

40

50

60 SignalBackground

Likelihood response0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

dx / (1

/N) d

N

0

10

20

30

40

50

60

U/O

-flow

(S,B

): (0

.0, 0

.0)%

/ (0

.0, 0

.0)%

TMVA response for classifier: Likelihood

LIKELIHOOD  RESPONSE  

“Training”  on  input  distribu*ons  

“Applica*on”  on  data  sample  

Ivan  Prado  Longhi@Mesonnet2013  

24  

CUTTING  LIKELIHOOD  OUTPUT  >  0.3  

Likelihood output0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Effic

ienc

y (P

urity

)

0

0.2

0.4

0.6

0.8

1

Likelihood output0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Effic

ienc

y (P

urity

)

0

0.2

0.4

0.6

0.8

1

Signal efficiencyBackground efficiency

Signal puritySignal efficiency*purity

S+BS /

For 4886 signal and 3512 background isS+Bevents the maximum S /

65.3767 when cutting at 0.2892

Cut efficiencies and optimal cut value

Sign

ifica

nce

0

10

20

30

40

50

60

70εsig  ≈  97%  

εbkg  ≈  14%  

purity  ≈  90%  

Ivan  Prado  Longhi@Mesonnet2013  

25  

n  before  TMVA     n  aaer  TMVA     Red.  Factor  

KSKL   985   953   0.99  

ηγ   393   374   0.95  

ωπ0   806   774   0.96  

f0γ   61   60   0.98  

γγ   50   41   0.82  

a0γ   9   9   1  

bkg   3512   492   0.14  

γγ→  π0π0  (data)   2722   2625   0.96  

γγ→  π0π0  (MC)   10184   9924   0.97  

CUTTING  LIKELIHOOD  OUTPUT  >  0.3  

Ivan  Prado  Longhi@Mesonnet2013  

26  

EntriesMeanRMSALLCHAN

5324 428.6 118.2 5324.

M4 (MeV)

dN/d

M4

(25

MeV

)-1

0

25

50

75

100

125

150

175

200

225

200 300 400 500 600 700 800 900

EntriesMeanRMSALLCHAN

5884 405.8 115.0 2625.

0

20

40

60

80

100

120

140

160

200 300 400 500 600 700 800 900

CUTTING  LIKELIHOOD  OUTPUT  >  0.3  

Subtracted  spectrum  

γγ→  π0π0  MC  

INVARIANT  MASS  SPECTRA  

KSKL  

ωπ0  

ηγ  

γγ→  π0π0  

bkg  

Ivan  Prado  Longhi@Mesonnet2013  

27  

EntriesMeanRMSALLCHAN

5323 77.25 53.24 5323.

pT (MeV)

dN/d

p T (1

0 M

eV)-1

0

100

200

300

400

500

0 50 100 150 200 250 300 350 400 450 500

EntriesMeanRMSALLCHAN

5723 87.57 65.37 2624.

PT (MeV)

0

50

100

150

200

250

300

0 50 100 150 200 250 300 350 400 450 500

CUTTING  LIKELIHOOD  OUTPUT  >  0.3  

Subtracted  spectrum  

γγ→  π0π0  MC  

 PT  SPECTRA  

KSKL  

ωπ0  

ηγ  

γγ→  π0π0  

bkg  

Ivan  Prado  Longhi@Mesonnet2013  

28  

data

EntriesMeanRMSALLCHAN

8398 392.8 114.1 8398.

M4 (MeV)

dN/d

M4

(25

MeV

)-1

0

50

100

150

200

250

300

350

400

450

200 300 400 500 600 700 800 900

BEFORE  MULTIVARIATE  ANALYSIS  

n  =  Lεσ     f  =  n/ndata   ffit  

KSKL   985   0.117   0.12435  

ηγ   393   0.047   0.04465  

ωπ0   806   0.096   0.0768  

f0γ   61   0.007   0.0056  

γγ   50   0.006   0.0072  

a0γ   9   0.001   0.0012  

bkg   3267*   0.389   0.4182  

γγ→  π0π0   2830   0.337   0.32412  

 ndata=  8398  A  fit  to  m4γ  spectrum  is  performed  using  f=n/ndata  as  star*ng  values  

KSKL  

ωπ0  

ηγ  

γγ→  π0π0  

Bkg  (data  driven)  

*normalized  by  extrapola\on  

Ivan  Prado  Longhi@Mesonnet2013  

!"#

! ! " "! ! " #" $%"&'(""

!"#$%&'()# !" #!"# ## # !"#*+#*,!"##*-*.# !"#/-/.

$%$&#'()*+#,*-*.#!"/#0(1)*+#0-*-(0-(2*+#34454# #%67/###7$/# .#$&/# .#!8/#9 9 .#!!/#9:9;.#</#3 3

0(1)*+# #=#>$&6%7# #&6$?@/###A,5'#=#$B%&A$B%7#

!""#$%&#'())#)*+),-#'.(#

")! ! " "! ! # " " *+,"-!./"+")0123"4"5160*(7("/"89"

#:;"")<!./" <$='**"")-!.$/"

!"#

! ! " "! ! " #" $%"&'(""

!"#$%&'()#!"# ##

!$%%#&'()*#+),)-#../#0'1()*-#%2/# ##0,),'0,'3)*#45565# #78%/###

0'1()*# #9#:!;8%"# #"8!2</###=+6&#9#$$7"=$>.%#

")! ! " "! ! # " " *+,"-!./"+"),0123"4"0125*(6("/"78"

#9:"");!./" ;$<'**"")-!.$/"

e+e-­‐  →  e+e-­‐  η:  2D  fits  

29  Ivan  Prado  Longhi@Mesonnet2013  

η  →  π0  π0  π0  

η  →  π+  π-­‐  π0  

Ivan  Prado  Longhi@Mesonnet2013   30  

! "#$%&'(# #)&%*+#,-.#/0#

12-#34567894:;#63-<#4;#9243#8;87=343#>-;-?89-3#-@-;93#A492#-B8C9#589?4B#-7-5-;9#8CC:?<4;>#9:#D677#E/!:<=#F283-#3F8C-#<439?4!694:;3&#1243#?-36793#4;#92-#F?:<6C94:;#:D# #5-3:;3#A492#;:;#;->74>4!7-#9?8;3@-?3-#5:5-;965&##G--<#9:#98H-#4;9:#8CC:6;9#92-# #9?8;3494:;#D:?5#D8C9:?######

12-#D:?5#D8C9:?#43#F8?85-9?4I-<#83#####A492#

!"

J4567894:;#:D#92-#34>;87##

J7:F-#F8?85-9-?#! #98H-;#83#8@-?8>-#:D#-BF-?45-;987#5-836?-5-;93#

η  TRANSITION  FORM  FACTOR  

Ivan  Prado  Longhi@Mesonnet2013   31  

!""#!$%&!!'())!$%&!'())!$*+!

!"#$%&& !"#''(!"#''(

!"#$%&'()*+#,"#-./&(0.12#2/'#3"#,4%25262+#70*("#849"#:;#<=>?=@#=ABC#D"#E&6+#70*("#849"#=CF+#AGC#<=>HF@#I"$&//42J+#K"I&J%'./#2/'#D"K2%1./+#LJMN"#70*("#$A;#<=>?B@#A?B#

!"#$%&&'#$()$*"#$+(,$)'-.*%(-$γγ  LUMINOSITY  FUNCTION