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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

MC Event Generator, 徐庆君 2

Outline

Recent Development of PHOTOS MC

Introduction PHOTOS MC Event Generator

Summary and Outlook


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


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


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


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


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


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


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


Recent Development:

Consider

For precision measurement of g-2


Recent Development:

Similar factor in QCD Ampli

tude

Similar to Sca

lar QED kern

el

Born level amplitude


Recent Development: , fraction of events with

,hard photons


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


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


Recent Development:


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


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!!


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


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

photos mc event generator simulating qed radiative correction in decays 徐庆君 xu qingjun...

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