Monochromatization for Higgs production A.Faus-Golfe IFIC - LAL March1FCC Week 2015

 Objectives  Monochromatization principle  Energy Resolution and Monochromatization  Monochromatization factor  Standard scheme  Optimized scheme  Monochromatization implementation in FCC-ee Higgs production  Standard and Optimized scheme implementation  Conclusions and Further studies Outline March2FCC Week 2015

Objectives Mars 20153FCC week The aim is to monochromatize the FCC-ee beams at E CM = GeV for the production of e+e ---> H(125.2) in the s-channel, just like a muon collider, but with hopefully much higher luminosity -- and lower cross-section. The Higgs width is 4.2 MeV and the FCC-ee energy spread is about 5x10 -4 at these energies, so one needs to gain a factor 10 in energy spread. We also need to keep the beams polarized to keep track of the beam energy precisely. From previous study we could conclude that there is no fundamental reason against monochomatization, but given the FCC-ee optics configuration (IP dispersion can be generated independently for the two beams since there are two separate e+ / e- channels) horizontal dispersion at the IP (opposite sign) is the more natural option. Based on this option and the related trade-off between horizontal focusing and horizontal dispersion, we have studied the impact on luminosity and the options to avoid losses.

Energy Resolution: Monochromatization principle Energy resolution and Monocromatization Mars 20154FCC week Monochromatization [7] To increase energy spread bending radius longitudinal partition number

Monochromatization: dispersion has opposite sign in the IP Monochromatization principle Energy resolution and Monocromatization Mars 20155FCC week Standard collision: dispersion has the same sign in the IP Enhancement of energy resolution, and sometimes increase of the relative frequency of the events at the centre of of the distribution.

Monochromatization principle Monochomatization factor Mars 20156FCC week 1) Case with: D* x,y =0 2) Case with: D* x+ = - D* x- =D* x D* y+ = - D* y- =D* y Monochromatization factor  Opposite dispersions at the IP enhance energy resolution without detriment of the differential luminosity while dispersion which have the same sign degrade both differential and total luminosity  When   y <<<   x is more efficient to produce dispersion in the vertical plane trying to keep it zero horizontally

23-27 Mars 20157FCC week Monochromatization principle “Standard” Scheme D* x+ = D* x- = 0 D* y+ = - D* y- =D* y   y <<<   x Implementations historical Studies:  VEPP4: one ring, electrostatic quads [3 ][12]  SPEAR: one ring, electrostatic quads, ~8 [9]  LEP: one ring, electrostatic quads (limited strength) and alternative RF magnetic quads, ~3 (optics limitations) [2] [10]  Superconducting RF resonators [33]  Tau-Charm factory: two rings, vertical dipoles,, ~7.5 [3] [4] [6] ]8] [11] [13] [32] Never tested experimentally !!!!!!

23-27 Mars FCC week Monochromatization principle “Standard” Scheme for FCC-ee Higgs factory: choosing Monochromatization factor Luminosity Standard deviation of w

23-27 Mars FCC week Monochromatization principle “Optimized” Scheme D* y+ = D* y- = 0 D* x+ = - D* x- =D* x Optimizing the beam parameters we could gain in energy resolution keeping the luminosity constant and the beam-beam in the standard limits !!!!!! Rewriting some formulas: with horizontal invariant dispersion with dominant term

23-27 Mars FCC week Monochromatization principle “Optimized” Scheme The new condition for an optimized scheme with: The beam-beam parameter could be maximized in the plane where dispersion is zero, keeping lower value in the plane where dispersion is different from zero

23-27 Mars FCC week Monochromatization principle “Optimized” Scheme for FCC-ee Higgs factory: choosing keeping

23-27 Mars FCC week Monochromatization principle “Optimized” Scheme for FCC-ee

23-27 Mars FCC week Monochromatization principle “Optimized” Scheme for FCC-ee

23-27 Mars FCC week Monochromatization principle “Optimized” Scheme for FCC-ee

23-27 Mars FCC week Monochromatization principle “Optimized” Scheme for FCC-ee

Conclusions Mars FCC week There is no fundamental reason against monochomatization. Implementation of a “standard” and even an “optimized” scheme seems not so difficult. But monochomatization has never been tested experimentally these means a flexible lattice with two modes of operation with/without is mandatory.

Drawbacks: Mars FCC week  D x * gives rise quantum excitation which increase horizontal emittance  Residual coupling  Aperture limitation  Dynamic Aperture reduction  Beam-Beam including parasitic crossings  Estimations of the broad band and the narrow band impedances and the current limits  Touschek lifetime  Polarization ring  Background and masking Further studies

New design of the OTR for ATF-ATF2 References 18

New design of the OTR for ATF-ATF2 References 19 [32] A. Faus-Golfe and J. Le Duff, Versatile DBA and TBA lattices for a Tau-Charm Factory with and without beam Monochromatization. NIM A 372 (1996) [33] A. Zholents, Shopisticated Accelerator Techniques for Colliding Beam Experiments. NIM A 265 (1988) Mars 2015FCC week

Thanks for your attention Mars FCC week