Higgs Factory Workshop
Fermilab, 14-16 Nov.2012
RAL seminar Alain Blondel 13-02-2013
The Higgs Boson Discovery
4th July 2012
CMSCMS
HCP
Nov’12
Discovered Higgs-like Boson: Clear mass peak in gg and ZZ*4l
– observed: 6.9; expected: 7.8
Is this the SM one ? From searches to measurements
November/14/2012
2
2
F.Cerutti - Higgs Factory
LHC has done better than projected:
here is a plot from ATLAS in 2005,
expected ~4 with 10fb-1 at 14TeV
HCP 2012 (Kyoto):
-- mass (125.90.4 GeV/c2) (my average)
-- spin parity (0+ preferred at 2.45 -- CMS)
already measuring couplings at 20% level …
(with a number of assuptions)
gH-gluon
gSM
=g
fermion
H-gluon
Vector boson
Photon
RAL seminar Alain Blondel 13-02-2013
When mH is known the EW precision measurements have no more freedom!
EW precision measurements, rare decays (BS, etc… )
-- 4th generation
-- SUSY
-- Higgs triplets
-- etc. etc.
Strong incentive to revisit and improve Z pole measurements and mW…
RAL seminar Alain Blondel 13-02-2013
The questions
Is this the Standard Model Higgs?
A Higgs beyond the SM?
Measure the properties of this new particle with high
precision
your Banker’s question:
What precision is needed to see something interesting?
RAL seminar Alain Blondel 13-02-2013
Once the Higgs boson mass is known, the Standard Model is entirely defined.
-- with the notable exception of neutrino masses, nature & mixings
***the only new physics there is***
but we expect these to be almost completely decoupled from Higgs
observables. (true?)
Does H(125.9)
Fully accounts for EWSB (W, Z couplings)?
Couples to fermions?
Accounts for fermion masses?
Fermion couplings ∝ masses?
Are there others?
Quantum numbers?
SM branching fractions to gauge bosons?
Decays to new particles?
All production modes as expected?
Implications of MH ≈ 126 GeV?
Any sign of new strong dynamics?
your Banker’s question:
What precision is needed to see something interesting?
RAL seminar Alain Blondel 13-02-2013
Some guidance from theorists
New physics affects the Higgs couplings
SUSY
, for tanb = 5
Composite Higgs
Top partners
Other models may give up to 5% deviations with respect to the Standard Model
Sensitivity to “TeV” new physics needs per-cent to sub-per-cent
accuracy on couplings for 5 sigma discovery
LHC discoveries/(or not) at 13 TeV will be crucial to understand the
strategy for future collider projects
R.S. Gupta, H. Rzehak, J.D. Wells, “How well do we need to measure Higgs boson couplings?”, arXiv:1206.3560 (2012)
H. Baer et al., “Physics at the International Linear Collider”, in preparation, http://lcsim.org/papers/DBDPhysics.pdf
RAL seminar Alain Blondel 13-02-2013
The LHC is a Higgs Factory !
1M Higgs already produced – more than most other Higgs factory projects.
15 Higgs bosons / minute – and more to come (gain factor 3 going to 13 TeV)
Difficulties: several production mechanisms to disentangle and
significant systematics in the production cross-sections prod .
Challenge will be to reduce systematics by measuring related processes.
if
observed
 prod (gHi )2(gHf)2 extract couplings to anything you can see or produce from
H
if i=f as in WZ with H ZZ  absoulte normalization
RAL seminar Alain Blondel 13-02-2013
Conclusions
Approved LHC 300 fb-1 at 14 TeV:
HL-LHC 3000 fb-1 at 14 TeV:
•
Higgs mass at 100 MeV
•
Higgs mass at 50 MeV
•
Disentangle Spin 0 vs Spin 2 and
main CP component in ZZ*
•
More precise studies of Higgs CP
sector
•
Coupling rel. precision/Exper.
•
Couplings rel. precision/Exper.
• Z, W, b, t
• t, 
• gg and gg
10-15%
3-2  observation
• Z, W, b, t, t, 
2-10%
• gg and gg
2-5%
• HHH >3  observation (2 Exper.)
5-11%
Assuming sizeable reduction of theory errors
LHC experiments entered the Higgs properties measurement era: this is just the beginning !
LHC Upgrade crucial step towards precision tests of the nature of the newly-discovered boson
November/14/2012
9
F.Cerutti - Higgs Factory
Couplings at HL-LHC: ATLAS
MC Samples at 14 TeV from Fast-Sim.
Truth with smearing: best estimate of physics
objects dependency on pile-up
Validated with full-sim. up to ~70
Analyses included in ATLAS study:
H gg 0-jet and VBF
H  tt VBF lep-lep and lep-had
H  ZZ  4l
H WW  lnln 0-jet and VBF
WH/ZH  gg
ttH  gg (ttH  ) Direct top Y coupling
H   Second generation fermion coupling
HH bb gg Higgs Self-Couplings
November/14/2012
10
ttH  gg
Very Robust channel
Good S/B
Statistically limited
F.Cerutti - Higgs Factory
2021
2030
HL-LHC will already be a Higgs factory, able to
perform precise measurements on the relative values
of the gg, gluon-gluon,tt, bb, , tt, W and Z
couplings. and even some hint (30% or 3) of Higgs
self-coupling.
Missing : absolute value of the Higgs total width (or
overall strength of couplings) which could play
against possible invisible or exotic decay mode in
(fortuitous) cancellation.
Precision not sufficient for sensitivity to TeV scale in
Higgs couplings
2 values of expected errors:
1. assume same analysis and systematics
2. assume theory systematics will reduce by 2 and exp errors as 1/sqrt(N)
recall :LEP reduced by factor 10 several theory systematics
RAL seminar Alain Blondel 13-02-2013
H
Full HL-LHC
Relative
W
b
t

RAL seminar Alain Blondel 13-02-2013
Z
t
RAL seminar Alain Blondel 13-02-2013
RAL seminar Alain Blondel 13-02-2013
gg collider
RAL seminar Alain Blondel 13-02-2013
RAL seminar Alain Blondel 13-02-2013
+- Collider vs e+e- Collider ?

A +- collider can do things that an e+e- collider cannot do
[16,17]
Direct coupling to H expected to be larger by a factor m/me
  + -,jh
 H  40000   e + e -  H[peak = 70 pb at tree level]
 Can it be built + beam energy spread dE/E be reduced to 3×10-5 ?

(
)
(
)
4D+6D Cooling needed!
 For dE/E = 0.003% (dE ~ 3.6 MeV, H ~ 4 MeV)
 no beamstrahlung, reduced bremsstrahlung
 Corresponding luminosity ~ 1031 cm-2s-1
Expect 2300 Higgs events in 100 pb-1/ year
Using g-2 precession, beam energy and energy spectrum
 Can be measured with exquisite precision (<100 keV)
 From the electrons of muon decays
Then measure the detailed lineshape of the Higgs at √s ~ mH
 Five-point scan, 50 + 100 + 200 + 100 + 50 pb-1
H→bb and WW
m Precision from

 :



H
Peak
, W, …
 (pb)
√s
(mH), TLEP
H
0.1 MeV
0.6 pb
0.2 MeV
10-6
2.5%
5%
Patrick Janot
, W, …
HF2012 : Higgs beyond LHC (Experiments)
14 Nov 2012
17
MICE
Neutrino Factory
MICE is one of the critical R&D experiments
towards neutrino factories and muon colliders
With the growing importance of neutrino physics
+ the existence of a light Higgs (125 GeV)
physics could be turning this way very fast!
Cooling and more generally the initial chain
capture, buncher, phase rotation and cooling
rely on complex beam dynamics and technology,
such as
High gradient (~>16 MV/m) RF cavities embedded
in strong (>2T) solenoidal magnetic field
MANY CHALLENGES!
MUON COOLING  HIGH INTENSITY NEUTRINO FACTORY
HIGH LUMINOSITY MUON COLLIDER
RAL seminar Alain Blondel 13-02-2013
COOLING -- Principle is straightforward…
Longitudinal:
Emittance exchange involves ionization
varying in space which cancels the dispersion
of energies in the beam.
This can be used to reduce the energy spread
and is of particular interest for
+ -  H (125)
since the Higgs is very narrow (~4.2 MeV)
HF2012 summary Physics-- Alain Blondel 16-11-2012 Fermilab
COOLING -- Principle is straightforward…
Longitudinal:
Transverse:
Similar to radiation damping in an electron storage
Practical
realization
ring:
muon momentum
is reducedis
in not!
all directions
by going through liquid hydrogen absorbers,
and restored longitudinally by acceleration in RF
cavities. Thus transverse emittance is reduced
progressively.
Emittance exchange involves ionization
varying in space which cancels the
dispersion of energies in the beam.
This can be used to reduce the energy
spread and is of particular interest for
+ -  H (125)
since the Higgs is very narrow (~5MeV)
Because of a) the production of muons by pion
decay and b) the short muon lifetime,
MICE
cooling
channel
(4D cooling)
ionization
cooling
is only practical
solution
to produce high brilliance muon beams
6D candidate cooling lattices
HF2012 summary Physics-- Alain Blondel 16-11-2012 Fermilab
RAL seminar Alain Blondel 13-02-2013
The Higgs was barely missed at LEP2
LEP2: 26.7km circumference
4 IPs : L3, ALEPH, OPAL DELPHI
20MW of synchrotron radiation (scales as E4/R)
b* = 5cm
 luminosity lifetime ~ few hours
L = 1032 /cm2/s H=20%; 240fb 50 Higgses per exp per year!
able to do discovery, but not study!
What else?
RAL seminar Alain Blondel 13-02-2013
ILC in a Nutshell
Polarised electron source
Damping Rings
Ring to Main Linac (RTML)
(inc. bunch compressors)
Polarised
positron
source
Beam Delivery System
(BDS) & physics
detectors
e- Main Linac
not too scale
29.10.12
RAL seminar Alain Blondel 13-02-2013
e+ Main Linac
Beam dump
CLIC Layout at 3 TeV
Goal: Lepton energy frontier
Drive Beam
Generation
Complex
Drive beam time structure - initial
240 ns
140 s train length - 24  24 sub-pulses
4.2 A - 2.4 GeV – 60 cm between bunches
Main Beam
Generation
Complex
D. Schulte, CLIC, HF 2012, November 2012
Drive beam time structure - final
240 ns
5.8 s
24 pulses – 101 A – 2.5 cm between bunches
24
Latest reference:
The Higgs at a Linear e+e- Collider has been studied for many years
Community is large and well organized
At a given Ecm and Luminosity, the physics has marginally
to do with the fact that the collider is linear
--specifics:
e- (80%) and e+ (30%) polarization is easy at the source for ILC
(not critical for Higgs)
very small beams  very small beam pipe (b and c physics)
pulsed at 5-10Hz  can pulse detector and save on cooling need (X0)
Luminosity grows as ECM , 1-2 1034/cm2/s at 500 GeV, one IP.
cost grows as A+BECM, both A and B are very large.
‘ready’. 10 years from approval to operation
 start 2025… if all goes very well
RAL seminar Alain Blondel 13-02-2013
Higgs production mechanism
Assuming that the Higgs is light, in an e+e– machine it is produced by
the “higgstrahlung” process close to threshold
Production xsection has a maximum at near threshold ~200 fb
1034/cm2/s  20’000 HZ events per year.
e-
H
Z*
e+
Z – tagging
by missing mass
Z
For a Higgs of 125GeV, a centre of mass energy of 240GeV is sufficient
 kinematical constraint near threshold for high precision in mass, width, selection purity
RAL seminar Alain Blondel 13-02-2013
best for tagged ZH physics:
Ecm= mH+11110
W. Lohmann et al LCWS/ILC2007
take 240 GeV.
27
ILC
Z – tagging
by missing mass
total rate  gHZZ2
ZZZ final state  gHZZ4/ H
 measure total width H
empty recoil = invisible width
‘funny recoil’ = exotic Higgs decay
easy control below theshold
e-
H
Z*
e+
Z
RAL seminar Alain Blondel 13-02-2013
New: 250 GeV (HZ)
allows to disentangle
ambiguity (intrinsic to LHC)
between invisible width
and total width
+precision better to HL-LHC
in bb andcc
high energy running
allows Hvv channel
+access to ttH and HHH…
… not better than HL-LHC
Can we get sub-% precision  sensitivity to TeV new physics?
29
H
Full HL-LHC
W
b
t

RAL seminar Alain Blondel 13-02-2013
Z
t
How can one increase over LEP 2 (average) luminosity by a factor 500
without exploding the power bill?
Answer is in the B-factory design: a very low vertical emittance ring with
higher intrinsic luminosity
electrons and positrons have a much higher chance of interacting
 much shorter lifetime (few minutes)
 feed beam continuously with a ancillary accelerator
LEP3 day introduction -- Alain Blondel
prefeasibility assessment for an 80km project at CERN
John Osborne and Caroline Waiijer ESPP contr. 165
LEP3, TLEP
(e+e- -> ZH, e+e- → W+W-, e+e- → Z,[e+e-→ t𝑡] )
key parameters
LEP3
circumference
26.7 km
max beam energy
120 GeV
max no. of IPs
4 2-8 times
luminosity at 350 GeV c.m. - ILC lumi
-2s-1
luminosity at 240 GeV c.m. 10
cmthresh.
at34ZH
luminosity at 160 GeV c.m. 5x1034 cm-2s-1
luminosity at 90 GeV c.m. 2x1035 cm-2s-1
TLEP
80 km
175 GeV
410-40 times
0.7x10
cm-2s-1
ILC34lumi
34 cm
-2s-1
5x10
at ZH
thresh.
2.5x1035 cm-2s-1
1036 cm-2s-1
at the Z pole repeating LEP physics programme in a few minutes…
TLEP tunnel in the KEK area?
SuperTRISTAN in Tsukuba: 40 km ring
Proposal by K. Oide, 13 February 2012
80 km ring in KEK area
12.7 km
KEK
105 km tunnel near FNAL
(+ FNAL plan B
from
R. Talman)
H. Piekarz, “… and … path to the future of high energy particle physics,” JINST 4, P08007 (2009)
China Higgs Factory (CHF)
What is a (CHF + SppC)
• Circular Higgs factory (phase I) + super pp
collider (phase II) in the same tunnel pp collider
e-e+ Higgs Factory
2012-11-15
HF2012
37
LEP3, TLEP
(e+e- -> ZH, e+e- → W+W-, e+e- → Z,[e+e-→ t𝑡] )
key parameters
LEP3
circumference
26.7 km
max beam energy
120 GeV
max no. of IPs
4 2-8 times
luminosity at 350 GeV c.m. - ILC lumi
-2s-1
luminosity at 240 GeV c.m. 10
cmthresh.
at34ZH
luminosity at 160 GeV c.m. 5x1034 cm-2s-1
luminosity at 90 GeV c.m. 2x1035 cm-2s-1
TLEP
80 km
175 GeV
410-40 times
0.7x10
cm-2s-1
ILC34lumi
34 cm
-2s-1
5x10
at ZH
thresh.
2.5x1035 cm-2s-1
1036 cm-2s-1
at the Z pole repeating LEP physics programme in a few minutes…
Circular machine revisited after super-b and synchrotron light source:
e.g. TLEP  sub % precision and sensitivity to TeV-scale physics.
RAL seminar Alain Blondel 13-02-2013
gHZ
gHb
gHc
gHg gHW gHt
gHg
gH
RAL seminar Alain Blondel 13-02-2013
H
H,inv
LEP3, TLEP
(e+e- -> ZH, e+e- → W+W-, e+e- → Z,[e+e-→ t𝑡] )
key parameters
circumference
max beam energy
max no. of IPs
luminosity at 350 GeV c.m.
luminosity at 240 GeV c.m.
luminosity at 160 GeV c.m.
luminosity at 90 GeV c.m.
LEP3
26.7 km
120 GeV
4
1034 cm-2s-1
5x1034 cm-2s-1
2x1035 cm-2s-1
TLEP
80 km
175 GeV
4
0.7x1034 cm-2s-1
5x1034 cm-2s-1
2.5x1035 cm-2s-1
1036 cm-2s-1
at the Z pole repeating LEP physics programme in a few minutes…
Circular e+e- Collider as a Higgs Factory
•
Advantages:
 At 240 GeV, potentially a higher luminosity to cost ratio than a linear one
 Based on mature technology and rich experience
 Some designs can use existing tunnel and site
 More than one IP
 Tunnel of a large ring can be reused as a pp collider in the future
•
Challenges:
 Beamstrahlung limiting beam life time requires lattice with large
momentum acceptance
 RF and vacuum problem from synchrotron radiation
 A lattice with low emittance
 Efficiency of converting wall power to synchrotron radiation power
 Limited energy reach
 No comprehensive study; design
study needed.
42
ICFA workshop on Higgs Factories, Fermilab 14-16- November 2012
beamstrahlung:
reducing b* and increasing current leads to radiation of particles
in the field of the colliding bunch.  increase energy spread and produce tails
luminosity spectrum LEP3 & ILC:
M. Zanetti (MIT)
circular HFs – beamstrahlung
• simulation w 360M macroparticles
• t varies exponentially w energy acceptance h
• post-collision E tail → lifetime t
TLEP at 240 GeV:
t>2 s at h=1.0% (4 IPs)
t>37 s at h=1.5%
t>11 min at h=2.0%
t>3h at h=2.5%
TLEP at 350 GeV:
t>6 s at h=2.0% (4 IPs)
t>37 s at h=2.5%
t>3 min at h=3.0%
t>20 min at h=3.5%
RAL seminar Alain Blondel 13-02-2013
M. Zanetti (MIT)
Extension possibilities
1. LEP3 (C=27km) is limited to the ZH threshold at 240 GeV
+ complicated (and unlikely) to integrate in the LHC tunnel
 keep it as backup if all else fails
2. TLEP (C=80km) is the favorite:
superb physics performance, revisit all EW energy scale 90-370 GeV.
with up to 4 collision points
80km ring e+e- collider can be 1st step to O(100 TeV) pp collider,
and ~100GeV<-> 50 TeV ep collider
thereby offering long term vision at CERN
3. linear machines can be upgraded to energies up to ~1 or even 3 TeV
(upgrade path from ILC to CLIC in same tunnel has been discussed)
4. A muon collider remains the most promising option for the very high
energy exploration with point-like particles.
RAL seminar Alain Blondel 13-02-2013
possible long-term strategy
Zimmermann
TLEP (80 km,
e+e-, up to
~370 GeV c.m.)
PSB PS (0.6 km)
SPS (6.9 km)
LHC (26.7 km)
VHE-LHC
(pp, up to
100 TeV c.m.)
same detectors?
(E. Meschi)
also: e± (100 GeV) – p (7 & 50 TeV) collisions
≥50 years of e+e-, RAL
pp,seminar
ep/A
physics
at
highest
Alain Blondel 13-02-2013
all of this is for TLEP/VHE-LHC
RAL seminar Alain Blondel 13-02-2013
Conclusions
-- The newly discovered H(126) candidate is a fascinating particle of a
new nature (elementary scalar!) that deserves detailed measurements
-- There is much more to understand about Higgs physics measurements
and their potential to test physics beyond the SM. This should be
discussed in a dedicated and detailed Higgs Physics workshop.
-- LHC is/will be an impressive Higgs factory. This must be taken into
account in any future machine discussion!
-- The linear collider ILC can perform measurements at few% level for
the Higgs invisible width, search for exotic decays, and improvement of
bb, cc, couplings wrt LHC by factors ~2
-- for gg, tt, , ttH, HHH, HL-LHC will do ~ as well or better
-- There is a strong motivation to investigate if one could do better
-- more precise or/and cheaper
-- Now that the Higgs mass is known, a new round of precision EWRC
measurements is strongly motivated. (Predicted mtop, mHiggs, now sensitive
inclusively to EW-coupled new physics)
RAL seminar Alain Blondel 13-02-2013
Conclusions(2)
-- e+e- ring collider offer a potentially better luminosity/cost ratio
than the linear one and the possibility to have several IPs.
-- Much progress has been brought about by the experience of LEP2
B factories and Synchrotron light sources.
-- The main point of the HF2012 workshop was to understand whether
the performance of circular machines could be as high as advertised
The answer is ‘maybe’ but there is lots of work to do to establish this.
There are also ideas to push the luminosity further.
This calls for a design study of circular e+e- Higgs Factory
-- If the luminosities advertised can be reached, the resolutions
on several Higgs couplings can be improved from a few % to below
percent precisions, opening the possibility of discovery of TeV scale new
physics.
-- Revisiting Z pole and W threshold is now a must. This can be done
at both circular machines with extreme precision using the virtues of
excellent calibration and polarization.
RAL seminar Alain Blondel 13-02-2013
RAL seminar Alain Blondel 13-02-2013
RAL seminar Alain Blondel 13-02-2013
TLEP design study –preliminary structure
for discussion
Institutional board
Accelerator
1. Optics, low beta,
alignment and feedbacks
2. Beam beam interaction
3. Magnets and vacuum
4. RF system
5. Injector system
6. Integration w/(SHE)-LHC
7. Interaction region
8. Polarization &E-calib.
9. Elements of costing
Steering group
web site, mailing lists,
speakers board, etc..
Experiments
1. H(126) properties
2. Precision EW
measurements at the Z
peak and W threshold
3. Top quark physics
4. Experimental
environment
5. Detector design
6. Online and offline
computing
International
Advisory board
Physics
1. Theoretical
implications and
model building
2. Precision
measurements,
simulations and
monte-carlos
3. Combination +
complementarity
with LHC and other
machines ; global fits
CONCLUSIONS(3)
With the discovery of H(126) a new chapter is open in Particle
physics. It will take a long time and should be planned carefully.
Depending on the outcome of LHC run at 14 TeV, a dedicated
machine to study with great precision the Electroweak scale 90-350
GeV, will be very strongly motivated.
An e+e- collider situated in a new 80km tunnel, offers outstanding
luminosity and precision.
It can serve as a precursor for a high energy exploratory pp machine
at ~100 TeV
There are many challenges! A design study has been recommended
and you are very welcome to participate
https://espace.cern.ch/LEP3/
RAL seminar Alain Blondel 13-02-2013