Research and Study of SUSY
藏京京
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Summary of Supersymmetry
• Supersymmetry (SUSY) is a symmetry that relates elementary
particles of one spin to another particle that differs by half a
unit of spin and are known as superpartners. In other words,
in a supersymmetric theory, for every type of boson there
exists a corresponding type of fermion, and vice-versa.
• Minimal Supersymmetry Standard Model(MSSM)
contains the minimal extension of the Standard Model
particle.
• mSUGRA Because of unknown mechanism for breaking SUSY,
We will only consider a version called mSUGRA, which
guarantees universality of gaugino and scalar masses and of
trilinear couplings at a high scale.
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mSUGRA parameters and spectrum
• Five free parameters: m0,m1/2,A0,tanβ, sign(μ) Then the
sparticle spectrum, decay branching ratios and production
cross sections can be derived.
• gaugino mass parameters:
M3  M g
2.7m1/ 2 ; M 2  M Z  0.8m1/ 2 ; M1  M Z  0.4m1/ 2
•
gluino mass is equal to M3, neutralinos
(i=1-4) and
chargino
(i=1-2) masses are obtained after diagonalising
their mass matrices which are a function of M1,M2, μ.
• The sfermions of the first two generations:
mu2L
m02  5.0m1/2 2  0.35cos 2  M Z2
mu2R
m02  4.5m1/2 2  0.15cos 2  M Z2
md2
m02  5.0m1/2 2  0.42 cos 2 M Z2
md2
m02  4.4m1/2 2  0.07 cos 2  M Z2
me2L
m02  0.49m1/2 2  0.27 cos 2 M Z2
me2R
m02  0.15m1/2 2  0.23cos 2  M Z2
m2
m02  0.49m1/2 2  0.50 cos 2 M Z2
L
•
R
Third family scalars mass are more complicated. Yukawa
couplings ,off-diagonal elements.
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Sparticle Production and Cascade Deacy
Region 1: gluinos heavier than
any of squarks
Region 2: some squarks heavier,
other are lighter than gluino.
q L of the first two generations
are excepted to be among the
heaviest squarks and the b1
(and t1 )among the lightest.
Region 3: gluinos lighter than
any of the squarks.
Regions of the m0 versus m1/2 plane
showering the production cross sections
and with main squark and gluino decays
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Test Point for mSUGRA
test CMS points are indicate by stars and the
point used in the CMS DAQ TDR by triangle
mSUGRA parameter values for the test
points.Massed are given in units of GeV
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Property of 14 Points
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Cross Sections for the test points in pb at
NLO(LO) for PROSPINO1
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Inclusive Analysis with missing transverse energy
and jets
• Search for the production and decay of gluinos and squark
• LM1 test-point(LO cross section 49fb)
• Events selection:
• Major backgrounds and uncertainties:
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Inclusive analysis with missing
transverse energy and jets
• Selected SUSY and Standard Model background events for 1 fb-1
•
Standard Model background components and uncertainties for 1fb-1
• 5σ observation of low mass SUSY at LM1(gluino mass 600GeV/c2) is
achievable with about 6pb-1 in events with large missing energy plus multijets.(significance computed with ScPf)
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Inclusive muons with jets and
missing transverse energy(at least one muon)
Signal selection



leading muon pT >20GeV/c (good reconstruction efficiency)
leading muon isolated with less than 10GeV of calorimeter energy with a cone of radius R=0.3
(reduce fake muons effects)
three leading jets ET>50GeV (good reconstruction efficiency)
Backgrounds Considered




QCD dijet
tt
electroweak single-boson
electroweak dibosons
Optimized Cuts By GARCON
ETmiss  130GeV , ETj1  440GeV , ETj 2  440GeV ,  j1  1.9,  j 2  1.5,  j 3  3, cos   j1, j 2    0.2,
0.95  cos    ETmiss , j1   0.3, cos    ETmiss , j 2    0.85
 Assuming 10 fb−1 of collected data, this set of cuts would expect to select a total of 2.54
background events from the Standard Model and 311 signal events from the mSUGRA
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LM1 benchmark signal point.
CMS discovery reach
CMS discovery reach contours in the m0-m1/2 plane using inclusive muons with jets and missing
energy for 10 fb-1, 30fb-1 and 60 fb-1 including systematics
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Inclusive analysis with same sign dimuons
• Signal Selection
 muon
dimuon trigger efficience 98%, reconstructed muon separated
2
ΔR ≥ 0.01 from the other one. muon track fit   3 ;hit
number >13; same sign &&PT >10GeV/c
Iso  IsoByTk  0.75  IsoByCalo, with Iso1  10GeV , Iso 2  6GeV
 jet
jet number ≥ 3 &&ET > 50GeV
(final optimal cut-set:
ETj1  175GeV , ETj 2  130GeV , ETj 3  55GeV , ETmiss  200GeV )
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Inclusive analysis with same sign
dimuons
• Background Considered
QCD dijet ( 0  pˆ T  4TeV / c )
tt
electroweak signal boson(
electroweak dibosons
0  pˆ T  4.4TeV / c)
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CMS inclusive reach
•
CMS reach contours(systematic uncertainties included) in the (m0,m1/2)plane for
SUSY processes involving two prompt same-sign muons for L= 1fb-1,10fb-1,30fb-1,
100fb-1. The other mSUGRA parameters are fixed to tanβ=10,μ>10 and A0 =0
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Inclusive analysis with opposite sign dileptons
Signal originate from the decay 20  lRl  l l  10 in the cascade decays of
squarks and glunios. The dilepton invariant mass distribution for this decay
is expected to have a triangular shape with a sharp upper edge.
Signal selection:
 the Level-1 and HLT path that requires a single
isolated lepton(muon or electron);
 at least two same-flavour opposite-sign(SFOS)
isolated leptons(e or μ )with pT >10GeV/c and ∆Rll
≥0.2 and 0.15 for ee and μμ,respectively where the
∆Rll is the distance of two leptons in the η-φ space.
miss
E
 T  200GeV
 at least two jets with pT ≥ 100 and ≥60GeV/c within
 3
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Inclusive analysis with opposite sign dileptons
• Background considered: tt , W  jets, Z  jets , WW  jets, ZZ  jets,
Zbb( with leptonic decays of the Z boson),
Drell  Yan leptonic events and QCD dijets
Cross section at NLO, selection efficiencies and number of events
surviving cuts for signal and background processes
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Results for point LM1
the dilepton final state, assuming tan β
= 10,A = a, μ>0 and I,10,30,fb-1
intergrated luminosity (statistical
uncertainties only)
5σ discovery reach for tan β =10 take
into account background systematic
uncertainties
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Inclusive analyses with ditaus
0


0








Signal originate from 2
1
in gluino and squark cascade decay.
Events selection:




•

Missing ET >150GeV (remove large fraction of SM bg)
At least two tau candidates
At least two jet with ET> 150GeV
∆R between any pair of tau’s should be samaller than 2
Background considered
W and Z production and t ¯t which final states may contain several taus
and jets

Because of its huge cross section (1.3 ·10−4 mb) QCD jet production is
also considered.(an important source of fake taus and fake missing
transverse energy due to imprecision in jet energy measurement.)
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Discovery potential of mSUGRA with ditaus final states
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Other Chanel List
• Higgs: supersymmteric Higgs boson h0 -> bb
so at least two b-tagged jets, miss ET and
multiple jets
0
0
0
0
0


Z


• Z: 2
1 with Z decays into SFOS
• top: t1  t   tllR  tll 
0
2
0
1
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Summary of the reach with inclusive analyses
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List of other organization’s work
1.
2.
3.
4.
5.
6.
7.
8.
Bbar+multi-jets+MET Tanja Rommerskirchen University of Zurich (Switzerland)
Ditau+hadronic-jets+MET GEORLACH Ulrich IPHC Strasbourg (France)
Full hadronic channel Christian Autermann
(Germany)
Higgs K. Huitu Helsinki Insitute of Physics HIP (Finland)
4 leptons Pedro Ribeiro, LIP-Lisbon (Portugal) Malgorzata Kazana, SINSWarsaw(Poland)
dilepton_+jets+MET (measurement of X2->x1ll ) Georgia Karapostoli (Univ of
Athens) Paris Sphicas (CERN)
e+ jets + MET Peter Wittich Cornell University (USA)
Muons + Jets + MET Philipp Biallass RETH Aachen University (Germany)
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