PHOTOS MC Event Generator Simulating QED radiative correctio n in decays 徐徐徐 Xu Qingjun 徐徐徐徐徐徐徐徐徐 Collaboration with Z.Was 徐徐徐徐徐徐徐徐徐徐徐徐徐, 2010 徐 4 徐 19 徐 徐徐 ,
Jan 18, 2016
PHOTOS MC Event Generator Simulating QED radiative correction in decays
徐庆君 Xu Qingjun杭州师范大学理学院
Collaboration with Z.Was
中国高能物理学会第十次会议, 2010 年 4 月 19 日,南昌
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Outline
Recent Development of PHOTOS MC
Introduction PHOTOS MC Event Generator
Summary and Outlook
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Introduction
Theory
σ,Γ, Br and Distributions
Very Important!!Tell the experiment where to go
Events written in 4-momentum
MC Simulation with detector effects MC Events in 4-momentum
Exp.Compare
Ph
eno
men
olo
gy
Theory Exp.= Or not!!Conclusion:
MC Integration
Further discussions
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Introduction: MC Integration vs.
Simulation For an integral:
MC Integration
MC Simulation Use approximation Instead of , following steps of MC Integration,
events are saved for future useCalculate weight
Events are accepted if W is the maximum weight,
Otherwise we reject them. Statistical error
Rejection
density
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Introduction
MC Event Generator
QCD QED New Physics
PHOTOS MC Event Generator
PHOTOS is used to simulate QED effects in decays
It is widely used (LEP. LHC, DESY, KEK, SLAC, BEPC, BELLE, BARBAR)and has 300+ citations
PHOTOS can be combined with other main process generators
Process independent kernel is used in PHOTOS
Systematic error needs to be controlled process by process
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PHOTOS MC: simulate QED effects
Using Feynman rules, calculate
Calculate virtual QED corrections
Calculate soft and collinear photon contribution
+ + free of IR and collinear divergences=
Calculate non-collinear photon contribution, add corrections of virtual and real photon together, we get one-loop level result
Normal way to study QED radiative correction
(1 + ) + non-collinear
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PHOTOS MC: simulate QED effectsPHOTOS MC simulates hard photon emission from final states
A process independent kernel is used instead of exact matrix element,
it satisfies: in soft and collinear limits, Lim =
= remaining part+
Phase space is exact, factorized into
Born level Amplitude and phase space
Process independent kernel and exact phase space
Events (suppose to be events with and without hard photon)
Events with hard photon
Affects the precision
Affects the precision
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PHOTOS MC: study the precision
How to increase the precision (important for exp. systematic error )
Write it into two parts, one is same as the kernel in PHOTOS, another is remaining part (it is small normally).
The remaining part is process dependent and decide the precision of PHOTOS
Compare results using
Consist, OK
Not consist,
Should the remaining part be considered at two-loop order?
Calculate QED corrections, implement it into PHOTOS Study the amplitude of hard photon emission
help to build other generators
1. Increase the precision of PHOTOS
2. find the similarity of processes in different theory framework (QCD, QED, Scalar QED)
Study the underlying theory
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Status of PHOTOS MC Original references
QED, Scalar QED decay processes in PHOTOS
At this moment PHOTOS kernel is a very good approximation. Multi-photon emission can be simulated.
G. Nanava, Qingjun Xu and Z. Was , arXiv: 0906.4052 [hep-ph]
Qingjun Xu and Z. Was, arXiv:1001.0070[hep-ph]
At work
At workdecay
decay
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Recent Development:
Consider
For precision measurement of g-2
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Recent Development:
Similar factor in QCD Ampli
tude
Similar to Sca
lar QED kern
el
Born level amplitude
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Recent Development: , fraction of events with
,hard photons
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Recent Development:Conclusion:
for the integration and invariant mass distribution,not well for the angular distribution!!
agrees with the scalar QED kernel very well
Compare complete amplitude with the kernel Differences in some range of phase space
Numerical results are consistent with POKAHARA MC Event Generator
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Recent Development:Following approximations in Eur.Phys.J.C64 (2009)47-54, neglecting diagrams with photons emission from hadronic and weak blocks
For precison m
eas
urement of p
ipi scat
ering le
ngths
Part of
diagrams
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Recent Development:
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Recent Development:
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Recent Development:Implement QED correction to PHOTOS MC, compare it with Coulomb correction
used by CERN NA48 (K meson experiment)
Solid line: Coulomb correctionDashed line: QED correction
Difference of Coulomb correction and QED correction
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Recent Development:Compare result from analytical expression for hard photon with result from PHOTOS kernel
Ratios of result from PHOTOS to results using soft-photon and hard-photon expression for hard photon emission.
, where we set
varies from
Note that
Conclusion: the agreement is good for hard photon expressionDifferences in harder photon energy range can be seen
Next step: photon emission from hadronic blocks will be considered!!
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Recent development:Precise measurement of
decay (no numerical results)
form factor and CKM mixing angle
Helpful for simulating B → D e ν(γ), D → pi (K) e ν(γ) For B
exp. a
nd BESIII
Consider at low energy
neglected
Rewrite it into three gauge invariant parts
Collinear singularity
Soft and collinear singularities
No singularity, dropped by previous references
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Summary and Outlook PHOTOS is a widely used MC event generator which simulates QE
D radiative correction in decaysControlling the precision is necessary and important
process
at work, simulating B and D meson semileptonic decays
Future work: D, J/Ψ , Ψ(2s) semileptonic decays
If you have a new idea and/or find something very interesting, it is better to simulate your process and send the code to the experimentalist directly.
Exchange Idea and CodeExchange Idea
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