Transcript Gaugino searches and SUSY constraints Paolo Azzurri CERN

Gaugino searches and
SUSY constraints
On behalf of :
Paolo Azzurri
CERN
Aachen, July 18, 2003
EPS HEP 2003 - International Europhysics
Conference
on high energy physics
R-parity conserved MSSM
• Minimal Supersymmetric extension of the Standard Model
• R-parity conserves lepton and baryon numbers.
⇨ Stable and weakly interacting LSP (WIMP)
★ The lightest neutralino is assumed to be the LSP
☼ Candidate for non-baryonic Cold Dark Matter (CDM)
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MSSM parameters
• GUT universality of gauginos and sfermions reduces the number
of fundamental MSSM parameters (C-MSSM)
m
0
, A0 , m1/ 2 ,  , tan  , m A

• Gaugino and sfermion mass relations:
M 3 : M 2 : M1 : m1/ 2   3 :  2 : 1 :  GUT
M1
 5 tan 2  W  1
M2
3
2

~
m ( f )  f m 0 , A0 , m1/ 2 , tan  , m Z , W

Mixing in the first two sfermion families constrained by smallness of FCNC and CP violation .
The third family is less constrained:
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Stop : m(~
t1 ), m(~
t ), A
~ 2 ~t
Sbottom : m(b1 ), m(b2 ), Ab
Stau : m(~1 ), m(~2 ), A
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Impact of LEP1 data
Precision measurements of Z width

tot
Z
 6.2 MeV

inv
Z
 1.7 MeV
The
 , M 2 
plane
scenario
Higgsino region
lower mass limits for particles with
large and stable Z couplings
m (   )  45 GeV, m (~ )  43 GeV
m ( u~ R , c~R )  37 GeV
~
m(d R ,~
s R )  41 GeV
m ( e~R , ~ R )  34 GeV
No limit on
~ ~ ~ ~
t , b,  ,  j
Mixed region
masses
as they can have very small
Z couplings
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Gaugino region
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Susy signal searches at LEP2
Chargino pairs : e  e      
 LEP 2  (2  25)  (pb)
_
... negative interferen ce with light ~
Neutralino pairs : e  e    i0  j0
+
 LEP 2  (1  10)  (pb)
... positive interferen ce with light ~e .
~ ~ ~
Sfermion pairs : e  e       , q~q
 LEP 2  (0.5  5)  3 (pb)
+
... positive interferen ce with light  0 for ~e ~e .
4m 2
:
s
abrupt (  ) - rise for gauginos
  1-
But… No signal found
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MSSM exclusions
(quoted at 95% CL)
P.Azzurri - Gaugino searches and SUSY contraints
and soft (  3 ) for scalars
5
Chargino pair searches
e  e -       f f ' 10 f f ' 10
heavy
sfermions
(W* decay)
light
sfermions
4jets, 2jets+1lepton, 2leptons
+ Missing Energy
The search analysis depends on
m  m(   )  m( 10 )
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Chargino pair candidate
ΔM=26-30 GeV/c2
ECM=196 GeV
No forward
activity
M(miss)=148 GeV/c2
M(hadr)=16 GeV/c2
transverse missing
energy in the detector
ET(miss)=21 GeV
P(μ)=8.5 GeV/c
SM:
WW*→τνqq
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Chargino pair results
excluded production cross-section
(down to a fraction of pb)
with heavy sfermions (W* decays)
combined ADLO results:
m( 10 )
excluded chargino masses in C-MSSM
m(   )
near the
kinematic
production
threshold
small
ΔM
   103.5 GeV/c
m
m(   )
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
2
m(   )  s 2
m (~ )
large
ΔM
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Low ΔM chargino searches
The standard searches
cover the region
ΔM>3GeV/c2
Searches for soft events
with an ISR photon
cover 0.2<ΔM<3GeV /c2
 
m    92.4 GeV/c 2
Searches for events with
tracks displaying kinks,
impact parameter offsets,
heavy stable charged particles
cover ΔM< 200MeV /c2
GUT unification: small ΔM in the
higgsino region (|µ| << M2)
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 
m    91.9 GeV/c 2
M1 and M2 degenerate: small ΔM in the
gaugino region (|µ| << M2)
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Neutralino pair searches
e  e-  10  0j  f f ' 10 10
excluded production
cross-sections
to a fraction of pb
e  e-   20  0j  qq' qq' 10 10
e  e-   20  0j  qq'  10 10
Acoplanar jets
Acoplanar leptons
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Multi-jets and
missing energy
P.Azzurri - Gaugino searches and SUSY contraints
Multi-jets + photon and
missing energy
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95% CL exclusions from
gaugino pair productions
close to the kinematic limit
The LSP limit grows as (s)/4
Lower LSP mass limit (with heavy sfermions)
m(   )  s 2
m(  i0 )  m(  0j )  s 2
The lowest not-excluded neutralinoLSP masses are found in the
mixed region at tan=1 and μ<0
m( 10 )  39.6 - 39.2 - 39.4 - 38.0 GeV/c 2
A-D-L-O
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What changes with light sfermions
_
Chargino pair cross sections decrease and new
decay channels are opened (cascade or invisible
decays asfor the m (   )  m (~ ) “corridor”
~
where   l  is dominant).
+
Both the cross sections and sensitivity
increase. For example in the case of dominant
~
leptonic decays as  0     0 
j
1
Need to identify the new decay topologies taking into account different BR
Need to include the sensitivity of direct searches
of sfermion pair productions !
Inclusion of slepton signal exclusions under the
assumption of scalar mass unification
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( m0 )
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Lower LSP mass limit (with light sfermions)
Combined exclusions from LEP1 data (1)
charginos(2)
neutralinos(3)
sleptons(4)
the (μ,M2,tanβ) space is covered in a similar way for low
m0 values as in the case of heavy sfermions
m (   )  m (~ ) corridor
not excluded by e~R e~R signals
( gaugino region)
The limit derived in the case of heavy
sfermions remains similar for light sfermions
under mass unification assumptions
Limit still for   0 and
tan   1 in the mixed region
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m( 10 )  39.6 - 39.2 - 39.4 - 36.3 GeV/c 2
A-D-L-O
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Impact of Higgs searches
mh<mZ |cos2β| + radiative corrections from top and stop:
m 
2
h
3g 2
8
2
 m ~t2
log  2
2
2
m
mW sin 
 t
m t4




given m t , tan , m0 :
SM Higgs searches translat es
into M 2 lower limits
LSP limit in mixed region
LSP limit in gaugino region
LSP limit in
higgsino region
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scan over
At (stop mixing), and mA
The LSP mass limit with Higgs constraints
moves at higher tan regions
m(  )  46 GeV/c
0
1
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Impact of mixing on MSSM exclusions (DELPHI)
A   tan  , Ab   tan  , At   tan 
Previous limits with no-mixing scenario :
Stau mixing leads to chargino blind spots when
Search for SUSY signals from :
m (~1 )  m (  10 )
 20  10 ,  20  20
 1  ~1 
 20  ~1       10
DELPHI : set A  Ab  At  0 and combine
~ ~
h, b , t and  20  10 ,  20  20 :
m( 10 )  45.5 GeV/c 2
Also studied the impact of free mixing in stau or stop
sector (A  or A t  0 ) with (A b  0 )
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Impact of stau mixing on MSSM exclusions (ALEPH)
More general approach:
Stau mixing decoupled from other families.
Study the effects vs mixing angle
 45    45
gaugino region
mixed region
m( 10 )  37 GeV/c 2
Stau - LSP corridor covered
at large   40 :
by  20 10  ~1 10 signals at low m 0 (large  )
o
at extreme   45o :
by 1 1  ~1~1 10 10 ISR tags at high m 0 (large  )
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without
higgs
constrants
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Other lower mass limits
From the same scan of the C-MSSM parameter space
lower mass limits on other SUSY particles can be obtained
m(~)  85 - 95 GeV/c 2
m(~eR )  75 - 95 GeV/c 2
m(~e )  110 GeV/c 2
L
Small χ+ M sensitivity is covered with
special searches (ISR tags, stable)
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Invisible charginos corridor
in the gaugino region.
m( 1 )  90 - 100 GeV/c 2
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Robustness of the neutralino-LSP limits
•The unification relation M1/ M2 ≃1/2 is driving the final result.
If M1/ M2 <1/2 the LSP limits deteriorate.
If M1/ M2≫1 (AMSB) we can find very low not-excluded LSP masses
(E.g. small chargino M in gaugino and mixed regions)
•Sfermion mass unification is important in the case of light sfermions.
Even with the standard assumptions the precision is not better than 1 GeV
•Higher order corrections to the GUT relation
M1=f(M2) are of the order of~3%.
•Radiative correction to to gaugino masses
decrease the limit of 1-2 GeV.
J.Ellis, T.Falk, G.Ganis, K.Olive, M.Schmitt
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Exclusions in minimal SuperGravity (mSUGRA)
• Dynamic EWSB :
  fixed (m 0 , m 1 2 , tan  ,...)
(LEP-208 GeV)
• GUT unification of scalar and Higgs sector:
 m A fixed  m 0 , tan  ,... 
• GUT unification of trilinear couplings:
 Ai unified to A0
Scan of the
m
12
~  LSP
, m0  plane:
Regions excluded by:
1. Theory
2. Z width ()
3. Charginos
4. Selectrons/Staus
5. Higgs
6. Stable heavy charged
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~10  LSP
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Lower LSP mass limit in mSUGRA
(LEP-208 GeV)
Scan in the m1 2 , m 0 , tan  , A0 space
7. Neutralino stau cascades
Again problems at large tan  for light staus
(large mixing) when m~1 - m 0 is small.
Covered by  20     10 signals in
 20 10 or  20  20 production s.
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m(  )  50 - 60 GeV/c
0
1
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Conclusions
• The absence of MSSM signals at LEP2 translate into strong constraints
on the domains of the model parameters and on the gaugino masses
• If sfermions are heavy, direct gaugino searches yield a mass limit for the
neutralino LSP:
m(χ0)>38-39 GeV/c2
at tan=1 (mixed region)
• Same limit with universal light sfermions using selectron searches.
• higgs searches exclude low tan
m(χ0)>45 GeV/c2
(gaugino).
• The exclusions are robust for stau mixing effects
~
• In the same framework m(χ+)>90 GeV/c2 , m(e~R)>90 GeV/c2, m(ν)>90
GeV/c2
• With full mSUGRA constraints m(χ0)>50-60 GeV/c2 (gaugino -mixed).
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