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Seeking Supersymmetry

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Title: Seeking Supersymmetry


1
Seeking Supersymmetry
Paul Grannis Escolo Swieca, Campos do Jordao
Jan. 19 23, 2009
2
Susy
Supersymmetry is basically a simple idea.
Translating the idea into a model which can be
confronted with Nature through experiment leads
to a forest of nearly an infinite number of trees
and tangled pathways. Our aim in this lecture is
to examine some of the interesting trees but also
to gain some perspective of the forest as a whole.
My expertise as a forest ranger is limited!
3
Susy outline
  • Supersymmetry phenomenology
  • Susy breaking
  • Present experimental constraints
  • How much Susy space is left unexplored?
  • What can we learn from the LHC?
  • What will ILC add to Susy understanding?

4
Supersymmetry
Supersymmetry is the maximal extension of the
Lorentz group. It has fermionic generators Q, Q
which anticommute with themselves and relates
fermions and bosons (differing by ½ unit of spin)
Q bosongt fermiongt Q fermiongt bosongt
And thus puts boson and fermion into the same
multiplet, with the same mass (in the
supersymmetry limit). (Denote supersymmetry
partners sparticles ( p ) One of the largest
diseases of the SM is the hierarchy problem the
tendency of Higgs and other masses to rise to the
Planck scale without incredible fine tuning.
Supersymmetry solves this for every fermionic
loop diagram there is now a corresponding bosonic
loop with opposite sign. So there is a
cancellation in the mass divergences at every
order, diagram by diagram exact if Susy is a
perfect symmetry, but good enough even if the
fermion boson mass difference is O(1 TeV) EW
scale.


W
W
W
W
(-)
W
W

H
H
5
Sparticles
Every standard model spin ½ fermion (quark,
lepton) has a spin 0 partner e.g. scalar
electron, scalar up quark etc. Note that the SM
fermions have left- and right-handed states which
are degenerate due to Lorentz invariance (a boost
can turn a left handed up quark into a right
handed up quark). The Susy partners (e.g.
selectronL and selectronR), having no spin,
cannot be so related and thus their masses need
not be the same. Every standard model boson
(spin 1 gauge bosons the massless ones before
EWSB and spin 0 Higgs fields) has a spin ½
partner (wino, bino, gluino, higgsino ). For
each massless gauge boson there are two gauginos,
one for each of the 1 helicity states. In
supersymmetry we require at least two complex
Higgs doublet fields to avoid triangle anomalies.
As we have seen, 3 of these 8 degrees of freedom
are eaten to provide the zero helicity states of
W and Z and the other 5 survive as the physical
h, H, A and H. Each of these 8 Higgs fields has
its corresponding higgsino fields, with again 5
surviving as sparticles.
6
Susy/SM particles
particle and sparticle states (only 1st
generation shown)
7
Susy breaking
Recall that the SM does not yield unification of
the forces (SU(3), SU(2) and U(1) couplings do
not become equal at the GUT scale). TeV scale
Susy modifies the renormalization group evolution
so that the couplings can meet at a common
point. Susy must be a broken symmetry. There is
no scalar partner of the electron at M0.511 MeV
and no spin ½ W partner at 80.399 GeV. In the SM,
the gauge bosons in the symmetry limit must be
zero due to gauge invariance it is the EWSB
that generates the masses of W and Z. The Susy
sparticles can however have intrinsic mass terms
in the Lagrangian for squarks, sleptons,
higgsinos, gauginos all presumably at the TeV
scale. Additionally, we introduce ad hoc
trilinear couplings A governing the
squark-squark-Higgs and slepton-slepton-Higgs
vertices and bilinear couplings B of Higgs
supermultiplets. In the general Minimal
Supersymmetric Standard Model (MSSM), these mass
and couplings, and the Higgsino mass term m, are
put in as 105 arbitrary parameters, to be chosen
by Nature, to describe the Susy breaking. The 105
arbitrary parameters (ugly??) mean that it is
effectively impossible to characterize the
phenomenology for the full class of MSSM Susy
models. Thus simplifying assumptions are often
made about relations among the parameters. and,
even more complex versions of Susy than the MSSM
can be invented
8
Susy Lagrangian
For the record, the Susy breaking Lagrangian
And the Higgs potential
9
R-parity and Mixing
  • Susy could violate baryon and lepton number
    conservation. To prevent this, an invariance
    under R parity inversion is often postulated.
  • R ( -1)3B-3L2S (Bbaryon ,
    Llepton , S spin)
  • All particles have R 1 (e.g. quark with B1/3,
    L0, S1/2 ), whereas all sparticles have R -1
    (e.g. squark with B1/3, L0, S0).
  • R-parity invariance then implies that in any
    reaction initiated by SM particles, there are an
    even number of sparticles participating.
  • Thus the lightest of the sparticles LSP
    (lightest Susy particle) is forbidden to decay
    (to all SM particles), and is a good candidate
    for the Dark Matter particle, as it would have
    very small interaction cross sections and would
    be cosmically stable.
  • Sparticles with the same quantum numbers can
    mix, so the observed mass eigenstates are
    mixtures of the Susy states shown in the table
    above.
  • 2x2 mixing matrix for (charged winos and
    higgsinos) ? 2 charginos c1 , c2
  • 2x2 matrix for squarks (L and R) and sleptons (L
    and R) ? 2 q, l states e.g. t1, t2
  • Off diagonal mass matrix elements
    quark/lepton mass, so large mixing for t, t
  • 4x4 matrix for neutral wino, bino, 2 higgsinos ?
    4 neutralinos c10, c20, c30, c40













10
Susy breaking models
Exploring a parameter space with 105 arbitrary
parameters and trying to confront predictions
with experiment is difficult!! Simplified
models are considered, classified by the
mechanism used to break the Susy symmetry. There
seems not to be a way to break the symmetry
through choices of the MSSM parameters. SUGRA
(supergravity) Postulate some high energy
scale, F, for the symmetry with spontaneous
breaking transmitted to the TeV scale by gravity.
The sparticle masses are scaled by the Planck
scale MP as M F2/MP. Implying that F1011
GeV. In SUGRA, assume that all squarks,
selectrons and Higgs have a common mass m0 at the
GUT scale (F) and all gauginos have a common mass
m1/2. These masses evolve and diverge as they
are run down to the TeV scale. Typically squarks
and gluinos are more massive than sleptons and
gauginos, and decay through chains leading
ultimately to the LSP. The c10 is typically the
LSP and is the DM candidate. Also assume the
trilinear Higgs-sfermion-sfermion couplings have
a common value A0. This leaves the bilinear Susy
breaking term B and the higgsino mass m, but B
and m2 can be eliminated by their relation to MZ,
leaving the 5 parameters m0 m1/2
A0 tanb sgn(m) 1 In SUGRA, the lighter
chargino and neutralinos tend to be mainly
gaugino (not higgsino)-like with M(c20) M(c1)
2M(c10).
11
Susy breaking models
GMSB (Gauge Mediated Susy Breaking) Again
postulate a symmetry breaking at F 1010 GeV,
but transmission by SU(3)xSU(2)xU(1) gauge
interactions to the TeV scale. In this
mechanism, the Susy partner of the graviton, the
gravitino, gets its mass only through gravity and
is much lighter than all other sparticles. Now
the next to lightest Susy particle (NLSP) is
either the lightest neutralino or the stau and
decays weakly to the gravitino c10 ? G g or t1 ?
G t. Unless the NSLP is the neutralino and
lives long enough to escape the detectors, GMSB
phenomenology is quite different from SUGRA. The
photon in the NLSP decay is often a good
experimental signature. There are again 5
parameters in the simplified GMSB framework.




Anomaly mediated and Gaugino mediated Susy
breaking schemes have also been postulated. Each
has rather different characteristic sparticle
mass spectra, though even within a specific model
class wide variations can be found. Also, models
in which R-parity is violated, at least for some
of the sparticle fields, are possible (so long as
B and L conservation is retained).
12
What has experiment ruled out?
The mapping between experiment and Susy theory is
not good. Experiments must choose a particular
signature (specific collection of jets, leptons,
MET etc.) and see whether the rates observed
violate the prediction of a particular model.
Thus experimental results tend to be valid for a
specific Susy breaking scheme, but not generally
for the full MSSM. There are MANY specific
searches at LEP, Tevatron, HERA, and other
experiments often difficult to relate to each
other.
Examples of searches Charged slepton search at
LEP LEP operated at energies up to 208 GeV ee-
collisions and produces slepton pairs as shown
The LEP experiments have also ruled out charginos
below 103 GeV for all but a few pathological
parameter choices.
13
What has experiment ruled out?
The final state then consists of several jets
(2-4 depending on the mass hierarchy) and MET
from the LSP. Several optimized searches with
different number of jets and MET were performed
and compared to a series of predictions in the
(m0 m1/2 ) plane.
The plot shows the MET distribution compared to
SM backgrounds dominated by ttbar, Wjets,
Zjets. It shows possible gluino signal (heavier
gluino case). The data is well modeled by the
backgrounds, so limits can be set.
And in the m0 m1/2 plane, extending LEP
somewhat
Limits in the squark-gluino mass plane
14
What has experiment ruled out?
Chargino masses below about 140 GeV are ruled
out. The data are not consistent with tanb lt10
for M(c1)130 GeV.
Limits in the m0 m1/2 plane extend LEP and
previous Tevatron considerably
15
Is Susy still an attractive BSM idea?
There is no experimental evidence to date for
Supersymmetry no sparticles, no convincing
demonstration of new physics hiding in loops in
rare processes. So is it sensible to retain Susy
as a viable model?
  • Nevertheless Susy has many very attractive
    features
  • It cures the hierarchy problem
  • Allows an explanation for EWSB that is not ad hoc
  • Is thought to be an essential feature of
    consistent string theories (though is not
    predicted to be at low mass scale)
  • Provides a dark matter candidate
  • Completes the Lorentz group
  • Retains the agreement of existing precision
    measurements with SM prediction. (many other
    models tend to produce discrepancies with
    experiment), and Susy reduces in many limits to
    the SM at present energies.

So we are reluctant to give up on Supersymmetry
16
How much Susy space is left?
C. Berger, J. Hewett, J. Gainer, T. Rizzo, hep-ph
0812-0980
  • Most experimental searches to date have been in
    some restricted Susy model, not the MSSM.
    Recently, a more general search in a model space
    called pMSSM (phenomenological MSSM) in which
    some simplifications are made
  • No CP violation in Susy parameters
  • Minimal flavor violation
  • Degenerate 1st and 2nd generation squarks and
    sleptons
  • This leaves 19 (not 105) Susy breaking
    parameters
  • Masses for SU(3), SU(2) and U(1) gauginos (50
    GeV lt Mi lt 1 TeV)
  • Higgsino mass m (50 GeV lt m lt 1 TeV)
  • tanb (1 lt tanb lt 50)
  • Higgs CP odd mass, MA (43.5 GeVlt MA lt 1 TeV)
  • 10 masses for squarks and sleptons (100 GeV lt
    Mf lt 1 TeV)
  • Trilinear couplings only for 3rd generation (b,
    t, t) (Aj lt 1 TeV)

Pick parameters randomly with equal probability
in indicated ranges 107 times. Compute the Susy
spectrum and derived quantities. Require that
predictions agree with theoretical constraints or
experimental results, and keep only those models
that are consistent.
17
How much Susy space is left?
Flavor physics/cosmological constraints Agree
(loosely) with limits on b?sg, Bs ?mm
B?tn, gm-2, quark mixing Relic density of LSP no
greater than WDMh2 0.121 (could be non-LSP dark
matter)
Constraints employed
Theoretical constraints No tachyons No false
minima in scalar potential LSP is lightest
neutralino (Grand unification not required)
LEP/Tevatron limits on squark, chargino masses,
Higgs couplings, heavy stable particles are
obeyed.
For the 107 parameter sets chosen, 7x104 survive
all these constraints. For these, plot the
distributions of sparticle masses, Susy
parameters that are thus still compatible with
data
t1 , t2
Sleptons R sleptons tend to be lighter than
L. Stau1lt selectron/smu
e/m L and R
18
How much Susy space is left?
Squarks some solutions are below the Tevtron
limit 300 GeV where the searches made cuts that
eliminated them from sample.
Gauginos lowest c1 and c10 , c20 states are
quite light, often accessible to 500 GeV ILC.
19
How much Susy space is left?
Light Higgs h is almost always below 125 GeV
(recall in decoupling limit, h HSM). Cases
with Mh lt 110 GeV have odd couplings that evaded
the HSM search. H and A nearly degenerate, even
away from decoupling limit.
light Higgs h (log scale)
heavy Higgs H/Ah
Gluino masses rather uniformly distributed up to
upper limit.
gluino
20
How much Susy space is left?
c10 is the LSP by construction what is the NLSP?
Some preference for c1 and c20, but other
possibilities are also possible.
character of NLSP
What are the components in the c10 LSP after
the neutralino mass mixing? Somewhat
surprisingly it tends not be like SUGRA where c10
is mainly bino. There is a rather large fraction
of cases which are higgsino or wino dominated.
Few cases with all three significant in mixture.
LSP higgsino vs. bino fraction
LSP bino vs. wino fraction
21
How much Susy space is left?
tanb distribution
One can ask the probability distributions for
Susy parameters or observables in the selected
models. Most likely value of tanb is 12
Most likely value of Wh2 from the LSP is
significantly lower than observed Wh2, so it
implies there are other DM particles besides
neutralinos (axions?)
Wh2 distribution
In general, the existing constraints on
supersymmetry leave a large amount of parameter
space still unexplored. However the observables
tend to be in a range that is easily explored by
the LHC, and many states have high probability
for being seen at the ILC.
22
Finding Susy at LHC
The LHC produces mainly squark/gluino pairs via
known strong QCD interactions. Other sparticles
then occur in the decay chains that are quite
model dependent, and ultimately end with a
collection of SM particles and the LSP.
The LHC experiments can quickly see Susy and
determine the Susy scale. Define a variable
Meff METpT(1)pT(2)pT(3)pT(4)
from the
missing ET and pT of the four leading jets in the
event (veto on leptons)
Left plot is Meff distribution shaded histogram
is SM bknd and open circles add in Susy (760 GeV
gluino). Note log scale. Right plot is MSUSY
(Minimum of squark or gluino mass) vs. Meff. The
scale of Susy is remarkably well determined.
Most studies of Susy at LHC have been done in the
SUGRA framework, and even here there are very
different signatures over the range of possible
parameters. ATLAS and CMS have sampled this
space to get an idea of what can be done, but
these studies can only be representative.
23
Finding Susy at LHC
Within SUGRA models, one can scan the space to
get an idea of the discovery reach. For 10 fb-1,
requiring at least 2 jets that are not
back-to-back (for SM rejection) and significant
MET, or high pT leptons with transverse mass of
leptons and MET above the W mass, one obtains
discovery (gt10 events, good S/vB)
Lines are for different final state lepton
content.
Visually these plots look like the LEP/Tevatron
exclusion plots shown before. Dont be fooled
the axes are much expanded! (The Tevatron range
is circled) The LHC should see the effects of
Susy if it has anything to do with EWSB.
LHC should see squarks/ gluinos out to gt 2 TeV
24
Determining Susy parameters at LHC
It is easy to see dramatic effects at LHC if Susy
exists. The harder questions are whether one can
determine that it really is Susy, what the masses
of the sparticles are, what are the decay
branching ratios, what are the quantum numbers of
the sparticles, and what is the nature of Susy
symmetry breaking. The answers to these questions
are again very dependent on the exact Susy model
Nature has chosen. Even small changes in
parameters make large qualitative differences in
decay patterns and masses.
Decay chain example At LHCC Point 3,
M(gluino)300 GeV, M(squarks)310 GeV and gluino
pair production is dominant. A representative
decay chain g ? b1 b ( h.c.) (89)
b1 ? c20 b (86) c20 ?
c10 l l- (34)
(Gluino decays to bottom squark (and SM b) since
light squark mass exceeds gluino mass here.)






25
Sparticle masses from end points
End points For 2 body decay of monoenergetic
particle A (e.g. ee ? AA )whose decay A ? X
C (X unseen, C some known SM particle) is
isotropic in its decay frame, the lab frame
energy distribution for C is flat between end
points E- and E.
Knowing s, and measuring E and E-, allows
solving for MX and MA.
At the LHC (e.g. example in previous page), we
typically do not know s due to parton momentum
distribution, and usually are not dealing with a
monoenergetic particle decaying into two final
particles, but the upper end point continues to
carry information about mass differences.
26
Susy
Masses in gluino decay example
For our example c20 ? c10 l l- , the dilepton
mass upper end point determines the c20 - c10
mass difference (here input to be 50 GeV) to
about 0.1. (A favorable case with small
backgrounds and the large BRs.)
dilepton mass
Get M(b1) to 1 1.5DM(c10) M(g) M(b1) 10
This is a favorable scenario for LHC. Typically
get only mass differences, at the level of
10-20. And mass of c10 is known, so the
absolute scale is not fixed.
27
Susy at LHC
Typically LHC experiments will see evidence of
Susy in many channels, so fitting them all
together can give some information about the
underlying model parameters, assuming a
particular Susy breaking scheme. ATLAS estimates
that the precision on m0, m1/2 and tanb range
between a few and 20, after making the
assumption that it is SUGRA. It is unlikely that
the LHC experiments will measure the spins and
parities of new particles. This is critical to
establishing that what you see is Susy if you
say you see a selectron, you had better be able
to demonstrate that it has spin 0!
For example, 4 different models give same final
state particles (a) and (b) are Susy with
different DM particle. (c) and (d) are extra
dimension models with different KK state
character.
The LHC is a wonderful discovery machine, but the
reverse engineering to let us understand clearly
what is seen is difficult. This is the crux of
the argument for the lepton colliders, where the
simplicity of the reactions pays off. (But dont
sell the ingenuity of the LHC physicists short,
once they have data in hand.)
28
Susy at the ILC
For supersymmetry studies, the ILC is very
complementary to the LHC. Whereas the LHC seems
assured to produce most of the Susy particles,
the ILC is limited in energy (500 GeV to 1 TeV)
so if the sparticles are heavy they may be
inaccessible. (recall that sparticles are
produced in pairs) But for those sparticles that
can be produced, much more incisive measurements
are possible at ILC than at the LHC. The
colliding partons (e e-) have a fixed energy
the beam particles can be polarized to enhance
cross sections and reduce backgrounds, the
events are cleaner, and the initial state is
known. The ILC can measure the masses of the
accessible particles accurately, and can usually
determine their quantum numbers (recall that
knowing the spins is crucial for saying that what
we see is Susy). The mixing matrices can be
measured, and CP violations in these mixings can
be sought. Working together, the two machines
amplify the results of each other. For example,
the ILC can measure the mass of the LSP c10 this
allows the mass differences of the heavier
sparticles measured at the LHC to be converted to
mass measurements. And with results from both
machines, the nature of the Susy symmetry
breaking mechanism can be illuminated.
29
ILC smuons
Can measure both the smuon and LSP mass to lt
accuracy from runs at the maximum energy. Once
one knows the mass from the end point spectrum,
one can set the energy of the collider to near
the smuon pair threshold. In this case, the
threshold behavior is b3 (p-wave). From the
location of the threshold, one can measure the
mass more precisely (0.1 in this case).
End point mass measurements for all observable
Susy particles can be done simultaneously at full
energy. But separate threshold scans are
typically needed for each reaction.
30
ILC smuon Qs couplings
The threshold behavior (for smuons, b vs b3) and
the angular distribution of the final ms
determine the quantum numbers of the mR . To
verify it is Susy, the smuons should be spin 0
and there should be (non-degenerate) partners for
both left- and right-handed m. The dominant
particles produced (mR or mL pairs) can be
selected by altering the polarization of the
incident electron. Supersymmetry requires that
analogous couplings between Susy particles and SM
particles are identical. e.g. g(mnW)
g(mnW) The sparticle couplings can be directly
measured from the cross sections to verify if it
is Supersymmetry or some other model. Similar
techniques work for the selectrons (harder
because one can produce eL eR- and eR eL-
also) and staus (harder because final state ts
are harder).










31
ILC selectron studies
Production of selectron pairs -- have two
diagrams typically the t-channel c0 exchange
dominates and allows measurement of neutralino
couplings (gaugino vs. higgsino) to
lepton/slepton. Bkgnd WW production is suppressed
for beam eR- .

e
e
c0

e distributions for both e- polarizations
e-
e-
End point measurements for selectrons are more
complex as can reach eReR-, eReL-, eLeR-, and
eLeL- final states from same initial state.
But can disentangle to get masses.








Scan at threshold for very accurate masses Here
use e-e- since this is s-wave (b1), not p-wave
(b3) as for ee-. Can achieve 20 MeV (0.01).

Angular distributions of decay electrons e ? e
c10 with polarized beams give quantum numbers,
coupling of exchanged c10 and give information on
nature of neutralino mixing (gaugino/higgsino),
hence the underlying Susy mass parameters.
32
ILC chargino studies
Both s-channel and t-channel processes
contribute. Masses are measured to few from
end points in reaction e e- ? c1 c1- with
decays c1 ? c10 W or c10 ln or c10 qq. The
mass values of c1, c2 constrain the parameters
of the mixing matrix taking (WH) to the mass
eigenstates (c1, c2) and determine M2 (mass of
the SU(2) Susy boson) and m (Higgsino mass
parameter).


M2(c1)M2(c2) M22 2MW2 m2 M(c1) x M(c2)
mM2 MW2 sin(2b)
Thresholds for gaugino pairs are b1 (thus better
mass precision than for scalars).
33
ILC neutralino studies




The mass matrix for the 4 J1/2 neutral gauginos
(b, w3, H1, H2) depends on the U(1) and SU(2)
gaugino masses M1, M2, the higgsino mass m and
tanb. The mass matrix can be diagonalized to
give the physical state ci0, i1,4. There
are 14 possible CP violating phases in the
neutralino sector alone (46 overall in the MSSM).
Unitarity relations yield unitarity quadrangles
which in principle can be determined
experimentally, through a combination of
neutralino production cross sections, and
fermion-sfermion-neutralino vertix
determinations. These, together with the
chargino measurents, make it possible to extract
the underlying Susy parameters even in the case
of CP violation. We need to know M1eiF1, M2,
meiFm, tanb to fix the low energy Susy model.

34
ILC gaugino studies
Measurement of cross sections for c1 c1- and
c1 c2- with polarized beams give us M2, meiFm,
tanb
Measurement of c10 and c20 masses and s(c10 c20)
then give M1 and its phase Fm
?
?
?
CP violating observables like pe(p x p-) in
reaction ee- ? c10 c20 ? c10 c10 l l - can
directly signal CP violation.
35
ILC third generation sfermion studies




The (tL , tR) or (tL , tR) states mix to
non-degenerate mass eigenstates (t2 , t1) or (t1
, t2) through SM fermion Yukawa terms hence
the mixing is most pronounced for third
generation sfermions. The mass mixing matrix is
sensitive to the soft Susy-breaking parameters
and trilinear couplings






tLtR
t1t2
cosqt sinqt -sinqt cosqt




Cross sections with polarized e- , and mass of t
s, allow determination of sinqt to 0.03
(100 fb-1). Polarization of t can be determined
to 7 from the t decay asymmetry This
yields information on the c10 and t mixing (and
also yields info on tanb there are many
independent ways to measure the Susy
parameters!) tR- ? tR- Gaugino tL- ?
tL- Higgsino A valuable tool for independent
study of gaugino mixing



Using polarized e- beams, one can measure the
stop mass to 2 GeV and cosqt to 0.02. The
mixing angle can be improved to 0.001 through
measurement of ALR for t t.

Sfermion measurements allow probe of the Yukawa
Susy couplings and departures from simple mSUGRA
models.
36
ILC Susy studies
The Linear Collider can determine the Susy model,
and make progress to understand the high energy
supersymmetry breaking scale. To do this, one
would like to see the full spectrum of sleptons,
gaugino/higgsino states. The question is whether
the full set of Susy particles will be
kinematically accessible.
Thresholds for selected sparticle pair
productions at LHC mSUGRA model points.
Point 1 2 3 4 5
6 GeV GeV GeV GeV GeV
GeV
reaction
RED Accessible at 500 GeV BLUE added at 1 TeV
c10 c10 336 336 90
160 244 92 c10 c20 494
489 142 228 355 233 c1 c1-
650 642 192 294 464
304 c1 c2- 1089 858
368 462 750 459 e e/ m m
920 922 422 1620 396 470 t t
860 850 412 1594
314 264 Z h 186 207 160
203 184 203 Z H/A 1137 828
466 950 727 248 H H -
2092 1482 756 1724 1276
364 q q 1882 1896 630
1828 1352 1010






The pMSSM study above of models that satisfy
theoretical and expt constraints tend to confirm
that low mass c10, c20, c1 are preferred.


It is likely however that in the case that
supersymmetry exists, one will want ILC upgrades
in energy to at least 1 TeV.
37
ILC Susy run plan
The measurements we have outlined at ILC require
running at several different conditions (beam
particles, energies, polarizations), unlike LHC
where one runs the machine only at full 14 TeV
energy. At ILC, one wants runs at full energy to
seek new physics and measure Susy reaction end
points. Then do special runs at the thresholds
for some Susy reactions and tt production. Can
one do this program achieve the sort of precision
we have outlined in a finite time?
Examine a run scenario for the first 1000 fb-1 of
ILC running at 500 GeV (7 years). Take Mh120
GeV. Assume Susy parameters that assure many
particles are accessible, thus many run
conditions are needed. The SM2 SUGRA point gives
masses and BRs as indicated. Remember that all
Susy reactions allowed occur together, so Susy
forms an important background in many studies.
m0 100 GeV m1/2 250 GeV tanb 10 A0
0 sgn(m)
38
ILC Susy run plan
Cross sections are specified given the SUGRA
parameters note that L and R polarized e- XSs
differ (assume Pe- 80).
Propose run plan shown Calibrate detectors with
Z pole runs. Initial running at 500 GeV to get
Susy reaction end points. e e-threshold scans
for
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ILC Susy run plan
We focus on specific decay topologies (e.g. 4
leptons and MET). Take into account that other
Susy reactions provide background and note that
several reactions may feed a particular final
state. For each channel sum the contributions
from all reactions that feed it. We choose the
e- polarization state to enhance particular
reactions of interest. Since the decay BRs and
backgrounds depend sensitively on the specific
Susy model, this exercise is an existence proof
but is not directly translatable to other models.
Sparticle mass precision achieved in 1000 fb-1
Precision on Higgs mass/couplings and top quark
parameters
Sugra parameter precision
Even for a very rich accessible Susy spectrum,
the ILC should be able to make measurements at
the desired precision.
40
ILC and LHC are synergistic
If Susy exists, the LSP provides a dark matter
candidate. The ILC in particular measures its
mass very accurately and the Susy cross sections
allow the calculation of the DM cosmic density.
If these agree with the density measurements from
Cosmic Microwave Background measurements, we have
provided full understanding of the character of
dark matter.
DM cosmic density ?
If the density from colliders disagrees with
mwave background, we know that there are other
contributing dark matter particles.
DM mass ?
41
ILC and LHC synergy
Measurements of the gluino, wino and bino masses
can be extrapolated by renormalization group to
high scales, and we can see if there is a grand
unification, thus telling us about the scale of
Susy breaking.
m1/2
The sfermion mass terms extrapolated to high
scale reveal the nature of the Susy breaking
shown here for Sugra and Gauge mediated symmetry
breaking.
LHC
High mass Sugra and GMSB patterns are distinctive.
m0
ILC
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ILC and LHC synergy
ILC measures masses, couplings and mixings of the
accessible Susy spectrum much more precisely than
LHC. LHC can observe higher mass sparticles.
Either LHC and ILC alone gives an incomplete view
of the new physics. Acting in concert, like
binocular vision, they give a depth of view that
can tell us much more than either alone.
Pardon me, I thought you were much farther away
43
Supersymmetry summary
  • Low mass supersymmetry offers many desireable
    properties
  • Cures the hierarchy problem
  • Provides a dark matter candidate
  • Allows for unification of Strong, EM, Weak gauge
    forces
  • Has possible sources of CP violation that could
    address the baryon-antibaryon asymmetry
  • And Susy is an ingredient of string theories

If Susy provides these explanations, it will
surely be found at the LHC. The ILC, to the
extent that it can access the Susy particles,
will make precision measurements of masses,
quantum numbers, and couplings to tell us which
Susy breaking model is at work.
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