1. FCC-ee: Progress in Physics studies
A lot has happened since first LEP3 ‘observation’! arXiv: v1
see presentations by M. Dam, M. Klute, P. Janot, S. Monteil, M. Koratzinos, A. Blondel
at HEP-EPS 2015 in Vienna.
9/18/2018

2. 1. progress on accelerator -- first look at IP design and issues
-- synchrotron radiation
-- global acc. design
-- polarization and Energy calibration
-- review of crab-waist optics
2. progress on physics
-- summary of TLEP paper
-- new studies for Physics
-- rare Higgs decays
-- h-> ee
-- complementarity of FCC-ee and FCC-hh for Higgs
-- alpha_QED and alpha_s
-- summary of parametric errors on mW prediction
-- top quark couplings
-- sterile neutrinos
3. activities, workshops etc.
9/18/2018

3. Future Circular Collider Study - SCOPE
CDR and cost review for the next ESU (2018)
Forming an international collaboration to study:
pp-collider (FCC-hh)  defining infrastructure requirements
e+e- collider (FCC-ee) as potential intermediate step ECM= GeV
p-e (FCC-he) option
km infrastructure in Geneva area
~16 T  100 TeV pp in 100 km
~20 T  100 TeV pp in 80 km

5. possible long-term strategy
FCC-ee ( km,
e+e-, up to
~350 GeV c.m.)
LEP
PSB
PS (0.6 km)
LHC (26.7 km)
HL-LHC
HE-LHC?
(33 TeV c.m.)
SPS (6.9 km)
FCC-hh
(pp, up to
100 TeV c.m.)
60 years of e+e- pp AA ep highest energies
NB if there is an electron ring it will be before the hadron machine !

6. • separate e- and e+ storage rings • very strong focussing: β*y = 1mm
Provide highest possible luminosity from Z to tt by exploiting b-factory technologies:
• separate e- and e+ storage rings
• very strong focussing: β*y = 1mm
• top-up injection
• crab-waist crossing
Overlap in Higgs/top region, but differences and complementarities
between linear and circular machines:
Circ: High luminosity, experimental environment (up to 4 IP), ECM calibration
Linear: higher energy reach, longitudinal beam polarization

7. crab waist optics is being developed by BINP
note very high
-- and variable --
number of bunches
Gain w.r.t. ‘baseline optics’ ~1
AMBITIOUS and CHALLENGING: Excellent luminosity prospects, E aperture OK,
but IR region is a great challenge ! Aim at decision in fall 2015

8. Experimental conditions
IPs L*~2m
-- bunch crossing spacing from 2-5 ns (Z) up to 3s (top)
-- no pile-up (<0.001 at FCC-Z/CrabWaist)
-- beamstrahlung is mild for experiments
-- Beam energy calibration for Z and W running -- IR design with crossing angle is not trivial
 a challenging magnet design issue.
9/18/2018

9. Of particular importance: luminosity monitors
M. Dam
Requirements dominated by Z line shape and peak cross-section measurements
9/18/2018

10. Solenoid compensation and integration (similar to superKEKB)
integration of luminosity monitors
Synchrotron radiation
 creation of dedicated MDI group.
9/18/2018

11. FCC-ee SC RF system
RF system requirements are characterized by two regimes:
high gradients for H and 𝒕 𝒕 – up to ≈11 GV
high beam loading with currents of ≈1.5 A at the Z pole
Main RF frequency of 400 MHz
(as for FCC-hh and LHC)
conversion efficiency (wall plug to RF power) is important for power consumption - aiming for 75% or higher  R&D !
important item for FCC-ee power budget, ≈65% achieved for LEP2
recent breakthrough in klystron efficiency (I. Syratchev)
LHC cavities (400 MHz)

12. FCC-ee layout option K. Oide asymmetric layout -
less bending for incoming beam, stronger bending for outgoing beam; reduced synchrotron radiation towards the IP
K. Oide
a bypass for the injector?
Presently concentrating on design with 2 IR, RF sections at degrees.
 Saw toothing is different in e+ and e- ring (OK)
Will come back with 4 IP option when this works.

13. Input from Physics to the accelerator design
0. Nobody complains that the luminosity is too high (the more you get, the more you want)
no pile up, even at the Z: at most 1ev /300bx
1. Do we need polarized beams?
-1- transverse polarization:
continuous beam Energy calibration with resonant depolarization
central to the precision measurements of mZ , mW , Z
requires ‘single bunches’ and calibration of both e+ and e-
a priori doable up to W energies -- workarounds exist above (e.g. Z events)
large ring with small emittance excellent. Saw-tooth smaller than LEP for Z
need wigglers (or else inject polarized e- and e+) to polarize ‘singles’;
simulations ongoing (E. Gianfelice, M. Koratzinos, I.Kopp)
-2- longitudinal polarization requires spin rotators and is very difficult at high energies
-- We recently found that it is not necessary to extract top couplings (Janot)
-- improves Z peak measurements if loss in luminosity is not too strong
but brings no information that is not otherwise accessible
2. What energies are necessary?
-- in addition to Z, W, H and top listed the following are being considered
-- e+e-  H(125.2) (requires monochromatization A. Faus) (under study)
-- e+e- at top threshold ~20 GeV for top couplings (E_max up to GeV)
-- no obvious case for going to 500 GeV
9/18/2018

14. Beam polarization and E-calibration @ FCC-ee
Precise meast of Ebeam by resonant depolarization
~100 keV each time the meast is made LEP
At LEP transverse polarization was achieved routinely at Z peak.
instrumental in 10-3 measurement of the Z width in 1993
led to prediction of top quark mass ( GeV) in Mar’94
Polarization in collisions was observed (40% at BBTS = 0.04) 
At LEP beam energy spread destroyed polarization above 61 GeV
E  E2/  At TLEP transverse polarization up to at least 81 GeV (WW threshold)
to go to higher energies requires spin rotators and siberian snake (see spares)
TLEP: use ‘single’ bunches to measure the beam energy continuously
no interpolation errors due to tides, ground motion or trains etc…
<< 100 keV beam energy calibration around Z peak and W pair threshold.
mZ ~0.1 MeV, Z ~0.1 MeV, mW ~ 0.5 MeV

15. -- Model independent Higgs couplings and invisible width
First look at the physics case of TLEP, arXiv: v3 scoped the precision measurements:
-- Model independent Higgs couplings and invisible width
-- Z mass (0.1 MeV), W mass (0.5 MeV) top mass (~10 MeV), sin2Weff , Rb , N etc...
 powerful exploration of new physics with EW couplings up to very high masses
 importance of luminosity and Ebeam calibration by beam depolarization up to W pair
So far: simulations with CMS detector (Higgs) -- or «just» paper studies.
Snapshot of novelties appeared in recent workshops
Higher luminosity prospects at W, Z with crab-waist
 sensitivity to right handed (sterile) neutrinos
 s-channel e+e-  H(125.2) production almost possible (  monochromators?)
 rare Higgs Z W and top decays, FCNCs etc...
 top couplings do not require longitudinal polarization
 QED(mZ) can be measured to precision using Z line shape extended scan
Alain Blondel Higgs Factories SACLAY

16. FCC-ee PHYSICS PROGRAM
-- Z and W Electroweak physics (1013Z, 108 WW)
precision energy calibration (100 KeV)  m Z, Z, mW, sin2 W
new possibly precision measurement of QED (mZ)
high luminosity search for rare Z decays
neutrino counting and search for RH neutrinos
-- Higgs Physics at ECM= 240 GeV (ZH) and 350 GeV, ZH events
unique determination of ZH coupling and H width,
all fermion and boson couplings (except ttH and HHH)
rare decays
-- top quark physics at GeV
top quark mass (essential for precision EW tests) to exp. precision of 10 MeV
new top quark couplings (no need for beam polarization!)
-- investigating run at ECM= mH to determine Hee coupling
9/18/2018

17. Activities common to FCC-ee, -hh, -eh (2)
Offline software developments
Conveners: Colin Bernet & Benedikt Hegner
Weekly meetings and monthly tutorials towards enabling physics analyses
Subscribe to
√s = 160 GeV
√s = 240 GeV
√s = 350 GeV -
e+e-→ W+W-
e+e-→ HZ
e+e-→ tt
Overall twiki page :
FCC Week in Washington
23-Mar-2015

18. Commissioning, etc to be added -- but as usual, hard to guess
Run Plan
Assuming 4 IP
With 4 IP can execute Z,W,H,t program in 10 years of full luminosity operation (107 s/year)
Commissioning, etc to be added -- but as usual, hard to guess
Staging is foreseen for RF:
1. low RF (5 GV/beam , 12 MW): begin with Z scan, develop crab waist, energy calibration
+ HZ at low luminosity
2. Complete power for High lumi ZH (and WW)
3. arrange RF to reach 10 GV/beam, run 350 GeV ECM
4. run high statistics Z pole
9/18/2018

19. incl. invisible = (dark matter?) Will improve with Hadronic Z tag
FCC-ee as Higgs factory
(constrained fit
including ‘exotic’)
4 IPs
(2 IPs)
ZH events in 5 years
«A tagged Higgs beam».
sensitive to new physics in loops
incl. invisible = (dark matter?)
NB leptonic tag only.
Will improve with Hadronic Z tag
A big challenge, but unique:
Higgs s-channel production at s = mH
104 events per year. limits or signal?
monochromators?
Aleksan, D’Enterria, Woijcik
 total width
HHH (best at FCC-hh)
Htt (best at FCC-hh)
<1%
28%
13%
from HZ thresh
from tt thresh

20. very accurate precision on threshold cross-section sensitive to loop corrections

21. monochromators can be envisaged,
thanks to different channels for e+ and e-

25. the HL-LHC with a 250-350 GeV e+e- machine.
Measurements of most of Higgs physics and couplings, CP violation etc..
are best made (in the circular machines) with the ZH process at GeV
Top quark and Higgs self couplings can be addressed with a linear collider
of energy above 500 GeV (at least 550 GeV for ttH, at least 1 GeV for HHH).
However for ttH and HHH, similar precisions can be achieved by combining
the HL-LHC with a GeV e+e- machine.
And what about the higher energy pp collider?

26. HIGGS AT FCC-pp

27.  Lots of statistics and ideas for small systematics

29. Precision measurements
Given that we have no idea what is the physics that will explain
-- the dark matter
-- the baryon asymmetry of the Universe
-- the masses of neutrinos
and also why e and p have the same charge at precision
...
we should undertake broadest, most powerful search
Electroweak precision measurements are complementary to
the Higgs measurements and provide a test of the existence
of new, weakly interacting particles up to very high energies
(new physics that violates the SM symmetries does not decouple)

30. A Sample of Essential Quantities: X
Physics
Present precision
TLEP stat
Syst Precision
TLEP key
Challenge MZ
MeV/c2
Input
2.1
Z Line shape scan
0.005 MeV
<0.1 MeV
E_cal
QED corrections Z
 (T)
(no !)
2.3
0.008 MeV Rl
s , b
20.767
 0.025
Z Peak
0.0001 
Statistics N
Unitarity of PMNS, sterile ’s
2.984 0.008
Z+(161 GeV)
0.004
->lumi meast
QED corrections to Bhabha scat. Rb b  
Statistics, small IP
Hemisphere correlations
ALR
, 3 ,
(T, S )
0.1514
0.0022
Z peak, polarized 
4 bunch scheme
Design experiment MW
, 3 , 2, 
(T, S, U)
80385
± 15
Threshold (161 GeV)
0.3 MeV
<1 MeV
E_cal &
QED corections
mtop
173200
± 900
Threshold scan
10 MeV
Theory limit at 100 MeV?
Alain Blondel FCC Future Circular Colliders
9/18/2018

31. 350 GeV: the top mass
Advantage of a very low level of beamstrahlung in circular machines
Could potentially reach 10 MeV uncertainty (stat) on mtop
From Frank Simon, presented at 7th TLEP-FCC-ee workshop, CERN, June 2014

32. G.Abbiendi
8 March 2005

34. 9/18/2018

35. Theoretical limitations
FCC-ee
R. Kogler, Moriond EW 2013
SM predictions (using other input)
0.0002
0.0001
0.0002?
0.0003 ?
0.0000 ? ?
Experimental errors at FCC-ee will be times smaller than the present errors.
BUT can be typically times smaller than present level of theory errors
Will require significant theoretical effort and additional measurements!
Radiative correction workshop July 2015 stressed the need for 3 loop calculations for the future!
Suggest including manpower for theoretical calculations in the project cost.

36. in other words .... ()=  10-5 + several tests of same precision
NB without TLEP the SM line would have a 2.2 MeV width
in other words .... ()=  several tests of same precision

37. NEW
no need for High Energy
or beam polarization!

38. Search for Right-handed neutrinos
(aka Sterile, or Heavy Majorana, etc..)
Arguably the missing particles in the SM
Usually sent to ~GUT scale but not necessary
TeV scale possible  mN  mW
Mixing with light neutrinos 2 ~ mv/mN
(10-12 for mN ~50 GeV)
Decay weakly by mixing
N -> lepton W 55% without missing energy
lifetime becomes long! 
displaced vertex topologies
Decay
Decay length: cm
NB CC decay always leads to
 2 charged tracks
9/18/2018

39. SHIP NZ = 1013 100𝒎 <L<5m region of interest FCC-ee sensitivity N +
W-qq
SHIP
NZ = 𝒎 <L<5m
region of interest
FCC-ee sensitivity
NB very large detector caverns for FCC-hh may allow very large FCC-ee detector (R=15m?)
leading to improved reach at lower masses.
9/18/2018

40. FCC-ee activities mini-workshops
Working groups conveners appointed and regular VIDYO meetings
for physics, accelerator and joined, as well as WG.
mini-workshops
-- detector mini-workshop (C. Leonidopoulos, E. Perez, M. Dam) June 2015
-- precision calculations mini-workshop July 2015 (Heinemyer, Ellis, Grojean) -- Higgs mini-workshop September 2015 (Klute, Peters)
-- alpha_s workshop October 2015 (D’Enterria)
FCC-ee workshop 9-11 November in London (Ellis et al)
General FCC week in Rome April 2016
9/18/2018