The present theoretical error on the Bhabha scattering cross section in the luminometry region at LEP

We consider the error budget for the calculation of the LEP/SLC luminosity in the Monte Carlo event generator BHLUMI4.04 from the standpoint of new calculations of the exact result for the O(α) correction to the process e + e − → e + e − + γ in the low angle luminosity regime at SLC/LEP energies, for the double bremsstrahlung effect e + e − → e + e − + γγ in this regime, and for the size of the two-loop virtual correction to e + e − → e + e − in this regime in context of Yennie-Frautschi-Suura exponentiation. We find that the error on the O(α 2 ) photonic correction can be reduced from the currently published value 0.1% to the value .027%. This leads to an over-all precision tag for the currently available program BHLUMI4.04 of 0.061%. This reduction of the precision of the calculation is important for the final LEP1 EW precision Z physics tests of the Standard Model. Currently, new luminometers at LEP1 have made measurements of the luminosity process e + e − → e + e − + n(γ) at the experimental precision tags below .1%. This should be compared with the prediction by the Knoxville-Krakow (KK) Collaboration in the program BHLUMI4.04 2 wherein the theoretical precision tag of 0.11% is realized for this process in the ALEPH SICALtype 3 acceptance. If one combines the experimental results, one arrives at an experimental precision of 0.05%. Evidently, for the final EW precision tests data analysis for LEP1, it would be desirable to reduce the theoretical precision tag on the luminosity cross section prediction at least to the comparable .05%-regime in order not to obscure unnecessarily the comparison between experiment and the respective Standard Model of the electroweak interaction. With this as our primary motivation, we have examined the error budget arrived at in Refs.2,4,5 in view of recent exact results impacting both the technical and physical precision of the errors quoted in that budget.More precisely, if one looks into the error budget shown in Table 1 Ref.2,4 , one sees that the largest contribution is associated with the O(α 2 ) photonic corrections, which contribute 0.1% in quadrature to the total 0.11% quoted for the total precision of the BHLUMI 4.04 prediction in these references for the ALEPH SICAL-type acceptance. Accordingly, we have used the exact results in Refs. 6,8,9 and the exact result in Ref.7 to make a more realistic estimate of the true size of this dominant error quoted in Refs.2,4 .In re-examining the photonic corrections used in BH-LUMI 4.04 at the O(α 2 ), which is the relevant order of the corrections, one needs look at the approximations made in the matrix element used in the calculation encoded in the program in comparison to available exact results. This will allow us to re-assess the physical precision of the corresponding part of the BHLUMI 4.04 matrix element, which is the exact O(α 2 ) LL(leading-log) Yennie-Frautschi-Suura (YFS) exponentiated matrix element. The implementation of the Monte Carlo algorithm in BHLUMI 4.04 for two hard photon emission needs also to be checked at ...

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“…This is the main reason we will be able to reduce the estimated precision of the BHLUMI4.04 prediction in comparison to Ref. 2,4 .…”

mentioning

confidence: 88%

“…With this as our primary motivation, we have examined the error budget arrived at in Refs. 2,4,5 in view of recent exact results impacting both the technical and physical precision of the errors quoted in that budget.…”

Section: Currently New Luminometers At Lepmentioning

confidence: 99%

New results on the theoretical precision of the LEP/SLC luminosity

et al. 1999

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“…[11] and its summary published in Ref. [12]) the present program BHLUMI 4.04 features a precision of 0.11% for the best LEP luminometers at the scattering angles 1…”

Section: Introductionmentioning

confidence: 99%

Upgrade of the Monte Carlo program BHLUMI for Bhabha scattering at low angles to version 4.04

Jadach

Płaczek

Richter-Wąs

et al. 1997

Computer Physics Communications

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131

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The new version of the Monte Carlo program for small-angle Bhabha scattering BHLUMI with an overall precision of 0.11% is presented. The main improvements are in the matrix element of the main multi-photon sub-generator based on the Yennie-Frautschi-Suura exponentiation, where the missing second-order terms in the leading-logarithmic (LL) approximation are supplemented and the contribution from the Z resonance is improved. In the LUMLOG sub-generator based on the LL approximation, we implement collinear photon emission in the final state and we also add a down-graded third-order LL matrix element, which has exactly the same incomplete third-order LL contribution as the multi-photon BHLUMI. The new LUMLOG is therefore capable of calculating the missing third-order LL part in the cross sections obtained from the main multi-photon event generator, for arbitrary event selection. The first-order event generator OLDBIS remains unchanged. Nature of physical problem: The small-angle Bhabha scattering process is used in all electron-positron colliders to calculate machine luminosity. This process is subject to QED radiative corrections, which have to be known for arbitrary cut-offs and/or acceptance with a precision at least a factor of 2 better than the pure experimental precision. This means that the level of 0.05% should be reached. A realistic simulation should include multiple emission of the bremsstrahlung photons. Submitted to Computer Physics Communications Method of solution:The Monte Carlo simulation of the small-angle process is an ideal solution. It provides the integrated cross-section for arbitrary cuts. Direct simulation of the final state electrons and photons is precisely what is needed for detector simulation purposes.Restrictions on the complexity of the problem: The overall precision of the QED calculation is restricted to 0.11%, for a typical LEP/SLC luminometer angular range of 1• < ϑ < 3 • , where ϑ is the scattering angle. Typical running time: The efficiency for multi-photon sub-generator is typically 6 million variable-weight events and 4 million constant-weight events per hour for an HP9000-735/100 MHz machine.

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“…[10] in connection with the respective O(α 2 )L corrections needed for the 0.061% (0.054%) total precision tag achieved in Ref. [11] for the LEP1/SLC luminosity process in the Monte Carlo event generator BHLUMI4.04 in Ref. [12].…”

Section: Preliminariesmentioning

confidence: 93%

Exact differentialO(α2)results for hard bremsstrahlung ine+
Jadach
¹
,
Melles
²
,
Ward
³

et al. 2002
Phys. Rev. D
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17
0
57
0
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We present the exact O(α) correction to the process e + e − → ff + γ, f = e, for ISR⊕FSR at and beyond LEP2 energies. We give explicit formulas for the completely differential cross section. As an important application, we compute the size of the respective sub-leading corrections of O(αL) to the ff cross section, where L is the respective big logarithm in the renormalization group sense so that it is identifiable as L = ln |s|/m e 2 when s is the squared e + e − cms energy. Comparisons are made with the available literature. We show explicitly that our results have the correct infrared limit, as a cross-check. Some comments are made about the implementation of our results in the framework of the Monte Carlo event generator KK MC.

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The present theoretical error on the Bhabha scattering cross section in the luminometry region at LEP

Cited by 37 publications

References 1 publication

New results on the theoretical precision of the LEP/SLC luminosity

New results on the theoretical precision of the LEP/SLC luminosity

Upgrade of the Monte Carlo program BHLUMI for Bhabha scattering at low angles to version 4.04

Exact differentialO(α2)results for hard bremsstrahlung ine+
Jadach
¹
,
Melles
²
,
Ward
³

et al. 2002
Phys. Rev. D
Self Cite
17
0
57
0
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The present theoretical error on the Bhabha scattering cross section in the luminometry region at LEP

Cited by 37 publications

References 1 publication

New results on the theoretical precision of the LEP/SLC luminosity

New results on the theoretical precision of the LEP/SLC luminosity

Upgrade of the Monte Carlo program BHLUMI for Bhabha scattering at low angles to version 4.04

Exact differentialO(α2)results for hard bremsstrahlung ine+Jadach1, Melles2, Ward3 et al. 2002Phys. Rev. DSelf Cite170570View full textAdd to dashboardCite

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Exact differentialO(α2)results for hard bremsstrahlung ine+
Jadach
¹
,
Melles
²
,
Ward
³

et al. 2002
Phys. Rev. D
Self Cite
17
0
57
0
View full text Add to dashboard Cite