Joint IPPP Durham/Cockcroft Institute/ICFA Workshop on Advanced QED methods for Future Accelerators

Abstract

The joint IPPP Durham/Cockcroft Institute/ICFA workshop on advanced QED methods for futureaccelerators took place at the Cockcroft Institute in early March 2009. The motivation for the workshopwas the need for a detailed consideration of the physics processes associated with beam–beameffects at the interaction points of future high-energy electron-positron colliders.There is a broad consensus within the particle physics community that the next international facility forexperimental high-energy physics research beyond the Large Hadron Collider at CERN should be ahigh-luminosity electron–positron collider working at the TeV energy scale. One important feature ofsuch a collider will be its ability to deliver polarised beams to the interaction point and to provideaccurate measurements of the polarisation state during physics collisions. The physics collisions takeplace in very dense charge bunches in the presence of extremely strong electromagnetic fields of fieldstrength of order of the Schwinger critical field strength of 4.4×1013 Gauss. These intense fields lead todepolarisation processes which need to be thoroughly understood in order to reduce uncertainty in thepolarisation state at collision.To that end, this workshop reviewed the formalisms for describing radiative processes and themethods of calculation in the future strong-field environments. These calculations are based on theFurry picture of organising the interaction term of the Lagrangian. The means of deriving the transitionprobability of the most important of the beam–beam processes – Beamsstrahlung – was reviewed. Theworkshop was honoured by the presentations of one of the founders, V N Baier, of the ‘Operatormethod’ – one means for performing these calculations.Other theoretical methods of performing calculations in the Furry picture, namely those due to A INikishov, V I Ritus et al, were reviewed and intense field quantum processes in fields of different form– namely those present in intense lasers – were also presented. Within the Furry picture the lowestorder physics processes are represented by one vertex Feynman diagrams. Additionally, higher orderprocesses in the Furry picture are thought to be important and are still not fully studied.The Advanced QED methods workshop also benefited greatly from reports on ongoing and plannedexperimental work on quantum processes in intense external fields. Some of the experimentsreviewed were the NA43 and NA63 experiments using the inter atomic fields in aligned crystals atCERN. In the past, evidence has been obtained from successful experiments using an intense laser atthe SLAC experiment E144. The possibility now exists for new experiments with intense laser lightwith the planned XFEL at DESY and the European Extreme Light Infrastructure.For upcoming accelerator projects, computer simulations of the first order processes in the FurryPicture during the bunch-bunch collision are being performed using the programs CAIN and Guinea-Pig++. The implementation of spin dynamics in these simulation programs was reported on at theworkshop.This relatively small workshop generated a very productive intermix of theoretical, experimental andcomputational developments covering this important field of physics. Fruitful discussions took placecovering improvements to the models, estimations of the remaining theoretical uncertainties and futureupdates to the existing simulations. It was felt that ongoing workshops in the same field would be ofbenefit to all those involved.The organisers would like to express their sincere thanks to all of the attendees for their contributions,to the staff of the Cockcroft Institute for hosting the workshop, to the IPPP at Durham for providingsubstantial funding and administrative support, and to ICFA for their sponsorship. We would also liketo thank IOP Publishing for their assistance in publishing our proceedings in the Journal of Physics: Conference Series.