Status of Monte Carlo generators for gamma-gamma physics
Transcript of Status of Monte Carlo generators for gamma-gamma physics
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Status of Monte Carlo generators for
gamma-gamma physics
Sergiy Ivashyn
NSC KIPT and V.N.Karazin Kharkiv National University
(Kharkiv, Ukraine)
September 9, 2013
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Outline
Intro tophysics
Monte Carlo for
Rad.corrs
Summary
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Reviews of gamma-gamma physics
[ Terazawa, Rev.Mod.Phys. 45 (1973) 615 ]
[ Budnev, Ginzburg, Meledin, Serbo, Phys.Rep. 15 (1975) 181 ]
[ Wagner, "Photon photon reactions" (1983) ]
[ Berger, Wagner, Rev.Mod.Phys. 146 (1987) 1 ]
main physics problems
basic formulae
equivalent photon approxiamtion (EPA)
basic experimental approaches
(single-tag, double-tag)
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Physics highlights
production of hadrons
Adler-Bell-Jackiw anomaly
( odd number of pseudoscalars)continuum study ( pair of mesons )scalar and tensor mesonsmeson mixing, symmery breaking patterns
polarizabilities
. . .
production of other particles
new particle searches ( X)QED studies (
+
)Intro to physics S. Ivashyn (Kharkiv) 5/ 36
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Gamma-gamma experiment.
Double-tag
detecting (tagging) both leptons
access to both variables: t1 andt2
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Gamma-gamma experiment.
Single-tag
tagging one lepton
measure only one invariant,Q2 = tIntro to physics S. Ivashyn (Kharkiv) 7/ 36
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Different regions of interest
large
sgood EPA, high
low BG from annihilation channel
small sThis is where we live from to
poor EPA, small
BG from annihilation channel
Phenomenology depends on the scale of
s
Intro to physics S. Ivashyn (Kharkiv) 8/ 36
G h i i hi lk
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Gamma-gamma physics in this talk
Gamma-gamma production of hadronsexclusive particle production via thephoton-photon
fusionsub-process of thee+++e scattering.
e+++
e
e+++
e
e+++
e
PFocus on
small
s(up to few GeV)
one, two, at most three particles produced
Intro to physics S. Ivashyn (Kharkiv) 9/ 36
Ph i
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Physics context
Two-photon transition form factors
Shape, slope
[ Czyz, Ivashyn, Korchin, Shekhovtsova, Phys.Rev. D85 (2012) 094010 ]
Asymptotics (the BaBar puzzle)
[ Dorokhov, JETP Lett. 92 (2010) 707 ]
[ Bakulev, Mikhailov, Pimikov, Stefanis, Phys.Rev. D86 (2012) 031501, D87 (2013) 094025 ]
Impact on muong 2(hadronic light-by-light scattering)[ Jegerlehner, Nyffeler, Phys.Rep. 477 (2009) 1 ]
[ Babusci et al., Eur.Phys.J. C72 (2012) 1917 ]
[ Zhevlakov, Radzhabov, Dorokhov, Russ.Phys.J. 53 (2010) 625 ]
Intro to physics S. Ivashyn (Kharkiv) 10/ 36
@ PhiP i 13
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@ PhiPsi 13
Recent/ongoing/planned data analyses
See todays talksD.Babusci KLOE/KLOE-2
s 1.02 GeV
P=0,00,
S.Uehara BELLE s 10.58 GeVP=0,00,+,0,KK
On ThursdayX.Song BES-III
s 3.77 GeV
P=0,,
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M i i t f MC
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Main requirements for MC
High efficiency under a typical event selection
Realistic phenomenology
Realistic QED radiative corrections
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MC d i i t
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MC used in experiments
The collaborations typically use their pivate MC
KLOE (a MC by Nguyen, Piccinini and Polosa)
CLEO (TwoGamby D.Coffman / V.Savinov)
Belle (TREPSby S.Uehara)
BES-III (UDODby V.Bytev and A. Zhemchugov
andTwoGamfrom DELPHI)
Lately: publicly available MC generators (via CPC)
KLOE-2, BES-III (EKHARA)
BaBar (GGRESRC)
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A ailable MC small s I
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Available MC: small s I
GGRESRC[ Druzhinin, Kardapoltsev, Tayursky, arXiv:1010.5969, to appear in CPC (2013) ]
0,,,c
simple VMD form factors
rad.corrs according to modified prescription of
[ Ong, Kessler, Phys.Rev. D38 (1988) 2280 ]
[ Ong, Carimalo, Kessler, Phys.Lett. B142 (1984) 429 ]
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Available MC: small s II
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Available MC: small s II
EKHARAhttp://prac.us.edu.pl/~ekhara
[ Czyz, Ivashyn, Comput.Phys.Commun., 182 (2011) 1338 ]
0,,custom, fine-tuned form-factors
[ Czyz, Ivashyn, Korchin, Shekhovtsova, Phys.Rev. D85 (2012) 094010 ]
rad.corrs not public yet
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Available MC: large s I
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Available MC: large s IGALUGA[ Schuler, Comput.Phys.Commun., 108 (1998) 279 ]
. . . (30 mesons)Based onBudnev formalism
[ Budnev, Ginzburg, Meledin, Serbo, Phys.Rep. 15 (1975) 181 ]
models for . . . const. quark model
VMD
. . .
no rad.corrs
highly effective mapping
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Available MC: large s II
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Available MC: large s IIGaGaRes[ Berends, von Gulik, Comput.Phys.Commun., 144 (2002) 82 ]
1S0(0), 3PJ(J+) (J=0, 1, 2), 1D2(2)resonances ofu,d,s,c,bquarks
Based onDensity matrix formalism(hard scattering)
[ Schuler, Berends, van Gulik, Nucl. Phys. B 523 (1998) 423 ]
no rad.corrsspecial mapping for no-tag, single-tag and
double-tag
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Available MC: large s III
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Available MC: large s III
the phenomenology can be not appropriate
for small
sphysics
the algorithms can teach us a lot
GALUGAmappings GGRESRC,EKHARA
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Types of rad corrs
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Types of rad.corrs
Leading corrections
virtual correction to the vertex
soft photon emissionhard photon emission
self energy / vacuum polarization
box diagrams (extra photon exchange)
Rad.corrs S. Ivashyn (Kharkiv) 19/ 36
Standard approach to rad corrs
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Standard approach to rad.corrs
Approximations for Soft+Virtual
smallt(leading terms inQ2
/m2e)
larget(leading terms inm2e/Q2)
Intergrated hard photon emission
such a way that |THard|2 H |TLO|2
d
dQ2
1+(Q2)
d0
dQ2
or
(1+)
0
Rad.corrs S. Ivashyn (Kharkiv) 20/ 36
Example: approx rad corrs
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Example: approx. rad.corrs
Ong, Kessler (1988)[ Ong, Kessler, Phys.Rev. D38 (1988) 2280 ]
[ Ong, Carimalo, Kessler, Phys.Lett. B142 (1984) 429 ]
In a modified form, implemented in GGRESRC
[ Druzhinin, Kardapoltsev, Tayursky, arXiv:1010.5969 ]
Used in BaBar data analyses
[ Aubert et al., Phys.Rev. D80 (2009) 052002 ]
[ del Amo Sanchez at al., Phys.Rev. D84 (2011) 052001 ]
[ Lees et al., Phys.Rev. D81 (2010) 052010 ]
Rad.corrs S. Ivashyn (Kharkiv) 21/ 36
A safe approach to rad corrs
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A safe approach to rad.corrs
use exact QED formulae
no analytic integration of hard photon spectrum
implement in MC
make it numerically efficient
Under development in EKHARA MC generator
Rad.corrs S. Ivashyn (Kharkiv) 22/ 36
Summary
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Summary
TheMC generators are doing well
Some of them are distributed under CPC licence
The algorithm lessons from LEP era generators
Improvement in rad.corrs is needed and foreseen
2 and 3 meson cases to be implemented
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Summary S. Ivashyn (Kharkiv) 24/ 36
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Spare parts
S P A R E S S. Ivashyn (Kharkiv) 25/ 36
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Virtual. Vacuum polarization
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Virtual. Vacuum polarization
e,,loops are therehadronic vac.pol. is also there
similar correction for the electron line
Appendix S. Ivashyn (Kharkiv) 29/ 36
Hard photon emission. Positron line
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Hard photon emission. Positron line
M0 separation of hard and soft photon
(matching)
+++1particle in the final state
similar correction for the electron line
Appendix S. Ivashyn (Kharkiv) 30/ 36
Pentabox contribution
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e tabo co t but o
contributions of the five-point functions will always benegligible or irrelevant
[ van Neerven, Vermaseren, Phys.Lett. B142 (1984) 80 ]
Appendix S. Ivashyn (Kharkiv) 31/ 36
Ong, Kessler. Final formula
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g,
Rad.corr for single-tag case=V+S+HI+HF
=
ln 1
rmax 17
12
(L 1) + 25
36
depends only onQ2 (viaL) andrmax
L ln Q2m2
rmaxis maximal energy of undetected ISR hard photonnormalized to the beam energy, typically: rmax 1
Appendix S. Ivashyn (Kharkiv) 32/ 36
Example: exact, but integrated
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p , g
[ Landr, Mork, Olsen, Phys.Rev. D36 (1987) 44 ]
Start with theexactformulae for the rad.corrs
Integrate the hard-photon spectrum
Total rad.corr is then given only by the vac.pol.
contributions
(the rest gets fully cancelled)
Final formula=vac.pol.
Appendix S. Ivashyn (Kharkiv) 33/ 36
Why integrated results are bad
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y g
intergrated form is good for analytical exercises
for MC one needs unintegrated expressions
Appendix S. Ivashyn (Kharkiv) 34/ 36
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differential cross section spans more than
five orders of magnitude
integrated rad.corr with small uncertainty
can in fact be dramatically biased in the tail
Appendix S. Ivashyn (Kharkiv) 35/ 36
EKHARA rad.cors. Work in progress
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p g
Check independence of result from
IR regulator Soft-Hard matching scaleM
0
Developing efficient mappings
To compare with GGRESRC
Appendix S. Ivashyn (Kharkiv) 36/ 36