Reference processes
Machine parameters -
Basic Standard Model -
W pairs -
Top quark -
Higgs -
SUSY -
Two-photon physics -
Links to other LC web pages
The content of this page was defined at the Lund meeting June 28-30.
Coordination:
One of the objectives of the current linear collider workshop
is to establish a list of reference processes. These processes,
motivated from the physics point of view, have been selected
to test the performance of a detector design from complementary
aspects at the high TESLA luminosity of
5.1034cm-2s-1.
The
list is minimal but comprehensive enough to cover all interesting
signatures that one might expect, and to allow reasonable
extrapolations to "the unexpected".
The list is not to be viewed as a complete list of "all" interesting
physics processes at a linear collider. The physics case contains
a wealth of further processes, and a wide parameter space to be
explored, as evident e.g. for supersymmetry.
All of this will be
covered in the physics section of the final report which will extend
the Physics Chapter of the CDR (DESY 1997-048, ECFA 1997-182) //
Phys. Rep. 299 (1998) 1 (hep-ph/9705442).
Machine parameters
To be used as common guidelines unless otherwise specified.
- Energies:
The possibility to have energy points down
to LEP1/2 and energies up to 2 TeV
should also be kept in mind.
- Luminosity:
- 500 fb-1
This should be taken as reference number for
one to two years of TESLA high-luminosity
running at each energy, so one could assume
a total integrated luminosity of a few ab-1.
- Polarization:
- electron polarization: 80...90% for high...low luminosity
- positron polarization: 60% (uncertain)
- Beam spectra and beamstrahlung:
-
CIRCE program
(with the high-luminosity TESLA option
and 350, 500 or 800 GeV energy)
- e-e- collisions:
- energies and integrated luminosities assumed
to be the same as above
- gamma-gamma:
- use spectra from Compton back-scattering of
laser light as suggested in the literature
Basic standard model process: Bhabha scattering
- Subprocess:
- Key questions:
- how large a cross section can be accessed and with what accuracy?
- Detector relevance:
- geometric coverage and cracks, energy resolution
- Physics case:
- Bhabha scattering for luminosity measurement
- cross sections and asymmetries for Z' searches
- limits of electron radius
W pairs
W pair production has a very large cross section and will
therefore be important both as signal and background process.
- Subprocesses:
- e+ e- -> W+ W- -> q qbar l nu
- Key questions:
- with what precision can the total cross section and
angular distributions be measured?
- Detector relevance:
- detection of W's, especially in the forward direction
- mass reconstruction and resolution for jet pairs
- missing momentum reconstruction for neutrinos
- Physics case:
- anomalous couplings in gauge boson sector
- runs at lower energies: W mass measurements
Top quark
Top production will be studied in dedicated threshold runs and
at high energies. This process will form a major background to
final states of new physics reactions involving multijets and
WW pairs.
- Subprocesses:
- Parameters:
- top pole mass = 175 GeV
- alpha-strong = 0.120 at Z energies
- SM top width = 1.4 GeV
- Key questions:
- experimental precision with which the threshold
cross section can be measured (precision of
beam energy measurement)
- top-quark production at high energies
- Higgs bremsstrahlung off top quarks
- Detector relevance:
- disentangling of complicated jet topologies
- stepwise mass reconstruction: 2 jets give W, 3 jets top
- b tagging
- Physics case:
- top mass (from threshold scan)
- top production (and decay) form factors
- Higgs-top Yukawa coupling
- Comments:
- the fully hadronic decay mode is the most important one for the
threshold analysis and also the most demanding in terms of
jet combinatorics
- above threshold, physics tests can be made on anomalous
couplings (from angular distributions)
- the process e+ e- -> t tbar H -> 4 b's + 4 q's
is very demanding and therefore interesting for the TESLA
high-luminosity analyses
Higgs (SM and extended)
The detection of the SM Higgs boson will obviously be
given high priority. A study of Higgs properties can also be
used to test the MSSM scenario and other possible extensions
of the SM.
- Subprocesses:
- e+ e- -> H Z0
- e+ e- -> HH + X
- Parameters:
- Higgs mass = 120 GeV
- Higgs couplings according to Standard Model
- machine energies at max. cross section, 350,
500 and 800 GeV
- Key questions:
- how well can Higgs properties (mass, branching ratios
(frequent and rare), total decay width, spin/parity) be
measured?
- can Higgs pair production be measured at high luminosity?
- Detector relevance:
- b tagging (also c, tau detection)
- mass reconstruction
- missing energy/momentum
- Physics case:
- Higgs mass
- couplings to Z and W (through production and decay)
and to b, c, tau and gamma (through decay)
- measurement of Higgs self-couplings
- Comments:
- the determination of the Higgs properties is the main
physics point, since discovery either at LEP2, Tevatron, or LHC is
likely; the possibility of a dedicated run at lower
energies, where the cross section is maximal, should not
be excluded
- the process gamma gamma -> H(SM) and h,H,A(MSSM) is
interesting for the exploration of the Higgs couplings
once the mass is known, and possible extensions of the
Higgs mass windows
- several interesting new Higgs production mechanisms occur
in the MSSM, including e+ e- -> Ah, e+ e- -> HA
and e+ e- -> H+H-; these processes do not, in general,
contribute any significant new aspects to the designing
of a detector, however
- Special Higgs analysis: e+e- -> HA
The associated production AH of Higgs particles gives rise
to bbbb and bb+tautau final states. The following
parameters may be used in the experimental simulations for
large tan(beta):
- m(H) = m(A) = 300 GeV
- BR(H/A;b) = 90%
BR(H/A;tau) = 10%
(other BR's are very small)
- E(tot) = 800 GeV
SUSY
Supersymmetry is a broad area, that covers many processes
and a large parameter space. It is therefore necessary to be
rather restrictive.
- Subprocesses:
- e+ e- -> chargino chargino
- e+ e- -> neutralino neutralino
- e+ e- and e- e- -> selectron (anti)selectron
- e+ e- -> stop antistop
- set of parameters for SUSY particles:
- mSUGRA(1):
tan(beta)=3 / m_0=100 / M_1/2=200 / A_0=0 / sgn(mu)=+
- mSUGRA(2):
tan(beta)=30 / m_0=160 / M_1/2=200 / A_0=600 / sgn(mu)=+
- light stop:
tan(beta)=3 / m_0=100 / M_1/2=200 / A_0=-715 / sgn(mu)=+
m_t~R=150 / m_chi^0=120
masses, xsections, decays:
mSUGRA parameters
- photonic decays of SUSY particles in GMSB
RP violation in SUSY particle decays
- Key questions:
- which mass/parameter ranges are detectable
- Detector relevance:
- complicated cascade decays with jets, leptons and
missing energy/momentum
- Physics case:
- discovery of supersymmetric particles
- masses of SUSY particles
- couplings of SUSY particles
- RP violation
- phases and CP violation
- measurement of the low-energy SUSY parameters (mod.independent)
- study underlying theories (mSUGRA, GMSB, ...)
Two-photon physics
Some gamma-gamma reactions are interesting in their own right, but
they can also form an important background to other processes.
- Subprocesses:
- gamma gamma -> q qbar (gluon(s))
- e gamma -> e X
- Parameters:
- pT/jet > 10 GeV in second process
- Key questions:
- how well can hadronic gamma(*) gamma(*)
cross section be measured?
- how well can jet pT spectrum be measured?
- how well can F2gamma be measured?
- Detector relevance:
- e tagging in forward direction
- particles and jets at low transverse momenta
- improved understanding of a large background
- Physics case:
- study QCD in a poorly-understood domain (including
soft/hard QCD transition region, e.g. BFKL)
Links to other LC web pages
Links to some other web pages of interest for the linear collider community:
Back to the
ECFA/DESY workshop home page.
Back to the
Physics home page.