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Proton and kaon timelike form factors from Babar
Sergey Serednyakov (on behalf of Babar Collaboration) Novosibirsk State University Budker Institute of Nuclear Physics, Novosibirsk

The XXII International Workshop High Energy Physics and Quantum Field Theory June 24 July 1, 2015 Samara, Russia

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OUTLINE 1. 2. 3. 4. 5. 6. 7. Proton FF description Babar detector, ISR method Proton FF data Nucleon threshold Charged kaon FF description Kaon FF data Conclusion

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pp quantum numbers
JPC = 1-- , J = L+S, P=(-1)L+1=-1, L=0,2 , C=(-1)L+S=-1, S=1, S, D waves, two form factors e.g. GE , GM

_

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e+e- NN cross section
Differential cross section (N=p,n) : Total cross section:
(e e NN ) C 4m 2
2 2

GM (1 cos

2

2

2 4 mB ) G 2 m

2 E

(1 cos

2

)

(e e

NN )

4

2

C
2

3m

GM

2

2 2mB G 2 m

2 E

Effective form F factor

2

GM

2

G

2 E

/2

1 1/ 2

,

m2 2 4mB

Two measurable values: 1 effective FF, 2 |GE/GM |

C for protons : C y /(1 e y ), y

/,

1/137,

v/c

Function C (Coulomb factor ) is significant at ~ 1 MeV above threshold

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Expectations for the nucleon form factors
-- |GE|=|GM| at threshold, S-wave only -- -> const at threshold, C ~ 1/v -- proton polarization ~ (GE-GM)

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Reactions to study e.m. TL form factors
1. e+e- annihilation, e+e- colliders Adone,DCI, CLEO, BES, VEPP-2000 2. Antiproton annihilation, proton-antiproton colliders CERN, FNAL -N
e+

Form factor

N

e

-

3. ISR Initial State Radiation, e+e- colliders - Babar

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ee

pp

Two latest BABAR works:
1 - PhysRevD.87.092005(2013), m < 4 GeV - LA ISR 2 - PhysRevD.88.072009(2013), m =3 6 GeV - SA ISR

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PEP-II e+e- collider, Babar detector
E+ = 3.1 GeV, E- = 9 GeV PEP-II
BaBar IFR: resistive plate chambers

Babar

e+

ECM = M( (4S))=10.6 GeV 2000 2008 yrs Lins=10 nb-1/sec L = 500 fb-1 N(B) = 109

e

-

BaBar SVT and DCH precision tracking BaBar EMC: 6580 CsI(Tl) crystals, E resolution ~1-2 % at high E.

BaBar DIRC Particle ID up to 4-5 GeV/c

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e+ehadrons in ISR
ISR

ISR Initial State Radiation or Radiative Return

e

+

d (s, x ) dx d (cos )
Hadrons

H (s, x, )

0

(s (1 x ))
x2 ,x 2 2E s

H - radiation function

e
Mhadr <

H (s, x, )

2 2x x x sin2

2

s
L
with L0 ~ 0.5 ab
ISR

~ 0.3% L0 ,
-1

---> L

ISR

~ 1.5 fb-1 !

Advantages of ISR 1. Full energy range from 2m up to s is available 2. Detection efficiency is independent on the reaction mechanism 3. No large radiative corrections
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Large/small angles kinematic in ISR

~10% ISR events, Mh<3 GeV
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~90% ISR events, because of ISR boost Mh> 3 GeV
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ee

pp analysis, SA ISR kinematics
_

Main selection 1 two tracks : p, p criteria, SA case 2 M 2 miss 1GeV / c
3 Pt
rans .

2

0.15 GeV / c 5 GeV / c

4 Pp

Backgrounds 1 Two photon e e
2 ISR with
0

e e pp, ~ 3% pp 0 , ~ 5%

:e e

Systematics: ~3%
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ee

pp
2.15

LA ISR kinematics
Babar: PhysRevD.87.092005(2013)

Fit:
Fpp ~

p (1232)?

S

(m ) C ~422 m4 m ln ( m /

2

2

)

FF ~ 1 at threshold

N(1520)N(1520)?

2.9

Babar results are in agreement with previous data and more precise
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ee
Cos

pp

distribution and |GE/GM| ratio (Babar)

G

M

G
E

Babar: PhysRevD.87.092005(2013)
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ee
Babar: PhysRevD.88.072009(2013)

pp

SA ISR kinematics

Scaled FF

QCD fit

F(q2) -> F(-q2) ! Babar results are in agreement with previous data at E<4 GeV, And have a tendency to approach spacelike FF at E>4 GeV
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e+e-

hadrons cross section near nucleon-antinucleon threshold e+ e- 6

_ -e e pp + nn
+ -

e+e- hadrons

arXiv:1402.5225v1 [hep-ph] 21 Feb 2014

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Comparison of baryons form factors p-n p-

Fn=0.47Fp

F =-.24Fp

pProton: PhysRevD.87.092005(2013) - Babar Neutron :PhysRevD. 90, 112007 (2014) - SND : PhysRevD. 76, 092006 (2007) - Babar pQCD : Z.Ph. C42 569 (1989) Chernyak,Zhitn.

F =0.33Fp

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The charged kaon form factor

Two BABAR works : 1 - Phys.Rev.D88 032013 (2013) - E < 5 GeV/c 2 Preliminary - E < 7.5 GeV/c2 - SA ISR

2-

LA ISR

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The charged kaon form factor

e+e- K+K-, JPC=1--, L=J=1
P-wave

2 KK

3

(s)

3s

| FK | 2 ,

FK
(K

8

s

f

K

s
l) GF f 8
2 2 K

S

~

C ln( m 2

2

)
2

M

2 K

ml 2 2 (1 ( ) ) | Vqs | mK

f

K

156MeV

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The history of kaon TL form factor above
1. e+e- -> K+KVEPP-2 (1970), Adone, DCI, VEPP-2M

(1020)

1970

~ 5 nb 2. e+e- -> K+K- (ISR) Babar ( 2013 )
Phys.Lett. 41B 205 (1972)

2013

in 40 years 106 times in Lum.!

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e+e- -> K+K- analysis, SA ISR
Main selection criteria 1 two tracks : K , K
2M 3 Pt 4 PK
2 miss

1 GeV / c

2

rans .

0.15 GeV / c 5 GeV / c

Background 1 Two photon e e
2 ISR with
0

e e K K , ~ 3% KK
0

:e e

, ~ 5%

3 ISRmisID : e e

, ~ 5%

Systematics ~ 3%

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e+e- -> K+K- cross section

Phys.Rev.D88 032013 (2013)

Babar data

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Kaon form factor , LA ISR

Phys.Rev.D88 032013 (2013
CZ: Z.Ph. C42 569 (1989)

)

Data are higher the QCD prediction by 4 times

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Kaon form factor, SA ISR, Babar preliminary
SA LA ISR comparison
Scaled form factor

The kaon form factor with SA ISR technique agrees with LA ISR data and more precise. At E > 5 GeV/c2 the tendency to approach to the QCD limit is seen.
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Conclusions on the proton timelike form factor (FF)
1. Using the ISR method in Babar the proton FF has been measured from the threshold up to 6 GeV 2. Near the threshold the proton FF is close to the pointlike value 1. 3. The e+e- >p- cross section is nearly constant from the p threshold up to 2.2 GeV. 4. A resonance structure in proton FF is seen in the region 2-3 GeV 5. Beginning from q=5 GeV the proton FF reveals the tendency to approach to the QCD prediction F(q2)=F(-q2).

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Conclusions on the charged kaon timelike form factor (FF)
1.Using the ISR method in Babar the charged kaon FF has been measured from the threshold up to 7 GeV 2. Below 2 GeV in the kaon FF the resonance structure is seen. 3. At E<4 GeV the kaon FF is ~ 4 times higher than the QCD limit 4. At E>5 GeV the kaon FF approaches to the QCD limit

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Thank you for attention

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