gaugino searches and susy constraints
DESCRIPTION
Gaugino searches and SUSY constraints. Paolo Azzurri CERN. On behalf of :. 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 - PowerPoint PPT PresentationTRANSCRIPT
Gaugino searches andSUSY constraints
On behalf of :
Aachen, July 18, 2003EPS HEP 2003 - International Europhysics Conference
on high energy physics
Paolo AzzurriCERN
EPS Aachen 18.07.03 P.Azzurri - Gaugino searches and SUSY contraints 2
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)
EPS Aachen 18.07.03 P.Azzurri - Gaugino searches and SUSY contraints 3
MSSM parameters
• GUT universality of gauginos and sfermions reduces the number of fundamental MSSM parameters (C-MSSM)
Mixing in the first two sfermion families constrained by smallness of FCNC and CP violation .
The third family is less constrained:
AmmAbmbm
Atmtm
b
t
),~(),~( :Stau ),
~(),
~( :Sbottom
),~(),~( :Stop
21
21
21
AmmAm ,tan,,,, 2/100 • Gaugino and sfermion mass relations:
GUTmMMM :::::: 1232/1123
WZmmAmffm ,,tan,,,)~
( 2/100
21tan3
5 2
2
1 WMM
EPS Aachen 18.07.03 P.Azzurri - Gaugino searches and SUSY contraints 4
Precision measurements of Z width
MeV 1.7 MeV 6.2 invZ
totZ
No limit on massesj ~ ,~ ,b
~ ,t~
as they can have very small
Z couplings
lower mass limits for particles with large and stable Z couplings
GeV 34 )~,~(GeV 41 )~,
~(
GeV 37 )~,~( GeV 43 )~( GeV, 45 )(
RR
RR
RR
emsdm
cummm
Impact of LEP1 data
Higgsino region
Mixed region
Gaugino region
The plane scenario 2,M
EPS Aachen 18.07.03 P.Azzurri - Gaugino searches and SUSY contraints 5
Susy signal searches at LEP2
But… No signal found MSSM exclusions(quoted at 95% CL)
~light with ceinterferen ...
(pb) )252(
ee : pairs Chargino
2
negativeLEP
_
.e~light with ceinterferen ...
(pb) )101(
ee : pairs Neutralino
2
0j
0i
positiveLEP
+
scalarsfor )(soft and
gauginosfor rise-)(abrupt
: 4m
-1
3
2
s
.e~e~for light with ceinterferen ...
(pb) )55.0(
~~,~~
ee : pairsSfermion
0
32
positive
LEP
+
EPS Aachen 18.07.03 P.Azzurri - Gaugino searches and SUSY contraints 6
Chargino pair searches
4jets, 2jets+1lepton, 2leptons+ Missing Energy
'ff 'ff ee 01
01
-
heavysfermions
(W* decay)
lightsfermions
)()(
on depends analysissearch The01 mmm
EPS Aachen 18.07.03 P.Azzurri - Gaugino searches and SUSY contraints 7
Chargino pair candidate
P(μ)=8.5 GeV/c
M(hadr)=16 GeV/c2
M(miss)=148 GeV/c2
ECM=196 GeV
No forwardactivity
transverse missingenergy in the detector
ET(miss)=21 GeV
ΔM=26-30 GeV/c2
SM: WW*→τνqq
EPS Aachen 18.07.03 P.Azzurri - Gaugino searches and SUSY contraints 8
Chargino pair results
with heavy sfermions (W* decays) combined ADLO results:
)( 01m
)( m
smallΔM
largeΔM
excluded production cross-section(down to a fraction of pb)
)~(m
excluded chargino masses in C-MSSM
near the kinematic
production threshold
)( m
2)( sm 2GeV/c 103.5m
EPS Aachen 18.07.03 P.Azzurri - Gaugino searches and SUSY contraints 9
M1 and M2 degenerate: small ΔM in the gaugino region (|µ| << M2)
2GeV/c 91.9m
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
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)
2GeV/c 92.4m
EPS Aachen 18.07.03 P.Azzurri - Gaugino searches and SUSY contraints 10
Neutralino pair searches
Acoplanar jetsAcoplanar leptons
'ff ee 01
01
001
- j
01
01
002
- 'qq ee j
01
01
002
- 'qq'qq ee j
Multi-jets andmissing energy Multi-jets + photon and
missing energy
excluded production cross-sections
to a fraction of pb
EPS Aachen 18.07.03 P.Azzurri - Gaugino searches and SUSY contraints 11
Lower LSP mass limit (with heavy sfermions)
The
LS
P li
mit
grow
s as
(s
)/4
O-L-D-A
GeV/c 38.0-39.4-39.2-39.6 )( 201 m
95% CL exclusions from gaugino pair productions close to the kinematic limit
2)( sm 2)()( 00 smm ji
The lowest not-excluded neutralino-LSP masses are found in the
mixed region at tan=1 and μ<0
EPS Aachen 18.07.03 P.Azzurri - Gaugino searches and SUSY contraints 12
What changes with light sfermions
Chargino pair cross sections decrease and newdecay channels are opened (cascade or invisibledecays as for the “corridor” where is dominant).
)~()( mm
~ l
Both the cross sections and sensitivityincrease. For example in the case of dominantleptonic decays as 0
10 ~ j
+
_
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
)( 0m
EPS Aachen 18.07.03 P.Azzurri - Gaugino searches and SUSY contraints 13
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
The limit derived in the case of heavy sfermions remains similar for light sfermions
under mass unification assumptions
O-L-D-A
GeV/c 36.3-39.4-39.2-39.6 )( 201 m
Lower LSP mass limit (with light sfermions)
region in the 1tan
and 0for stillLimit
mixed
region) (signals ~ ~by excludednot
)~()(
gauginoeecorridormm
RR
EPS Aachen 18.07.03 P.Azzurri - Gaugino searches and SUSY contraints 14
Impact of Higgs searchesmh<mZ |cos2β| + radiative corrections from top and stop:
2
2~
22
4
2
22 log
sin8
3
t
t
W
th
m
m
m
mgm
limitslower into
es translatsearches Higgs SM
:m ,tan,mgiven
2
0t
M
At mA and mixing), (stop
over scan
The LSP mass limit with Higgs constraints
moves at higher tan regions20
1 GeV/c 46 )( m
LSP limit in higgsino region
LSP
lim
it in
mix
ed
regi
on
LSP
lim
it in
gau
gino
reg
ion
EPS Aachen 18.07.03 P.Azzurri - Gaugino searches and SUSY contraints 15
Impact of mixing on MSSM exclusions (DELPHI)
Previous limits with no-mixing scenario : tan ,tan ,tan tb AAA
Stau mixing leads to chargino blind spots when 11011
~ )()~( mm
Search for SUSY signals from :011
02
02
02
01
02
~ ,
: , and t~ ,b~
h,
combine and 0 set : DELPHI02
02
01
02
tb AAA
)0(A with )0Aor (Asector stopor stau in mixing free ofimpact thestudied Also
bt
GeV/c 45.5 )( 201 m
EPS Aachen 18.07.03 P.Azzurri - Gaugino searches and SUSY contraints 16
without higgs
constrants
GeV/c 37 )( 201 m
Impact of stau mixing on MSSM exclusions (ALEPH)
More general approach:Stau mixing decoupled from other families.
Study the effects vs mixing angle
4545
) (large mhigh at tagsISR ~~by
:45 extremeat
) (large m lowat signals ~by
:40 largeat
coveredcorridor LSP-Stau
001
011111
o
0011
01
02
o
gaugino region
mixed region
EPS Aachen 18.07.03 P.Azzurri - Gaugino searches and SUSY contraints 17
Other lower mass limits
From the same scan of the C-MSSM parameter space lower mass limits on other SUSY particles can be obtained
Small χ+ M sensitivity is covered with special searches (ISR tags, stable)
Invi
sibl
e ch
argi
nos
corr
idor
in th
e ga
ugin
o re
gion
.
GeV/c 100-90 )( 21 m
GeV/c 110 )e~(
GeV/c 95-75 )e~(2
L
2R
m
m
GeV/c 95-85 )~( 2m
EPS Aachen 18.07.03 P.Azzurri - Gaugino searches and SUSY contraints 18
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.
J.Ellis, T.Falk, G.Ganis, K.Olive, M.Schmitt
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.
EPS Aachen 18.07.03 P.Azzurri - Gaugino searches and SUSY contraints 19
Exclusions in minimal SuperGravity (mSUGRA)
,...)tan,m,(m fixed 210
0 i tounified AA
,...tan, fixed m 0A m
Scan of the plane:
(LEP-208 GeV)
Regions excluded by:1. Theory2. Z width ()3. Charginos4. Selectrons/Staus5. Higgs6. Stable heavy charged
021 ,mm
LSP ~
LSP ~ 01
• Dynamic EWSB :
• GUT unification of scalar and Higgs sector:
• GUT unification of trilinear couplings:
EPS Aachen 18.07.03 P.Azzurri - Gaugino searches and SUSY contraints 20
Lower LSP mass limit in mSUGRA(L
EP
-20
8 G
eV)
space ,tan,, in theScan 0021 Amm
201 GeV/c 60-50 )( m
7. Neutralino stau cascades
s.production or
in signals by Covered
small. is - when mixing) (large
stauslight for tan largeat problemsAgain
02
02
01
02
01
02
~ 01
mm
EPS Aachen 18.07.03 P.Azzurri - Gaugino searches and SUSY contraints 21
Conclusions• The absence of MSSM signals at LEP2 translate into strong constraints on
the domains of the model parameters and on the gaugino masses
• higgs searches exclude low tan m(χ0)>45 GeV/c2 (gaugino).
• 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.
• The exclusions are robust for stau mixing effects
• With full mSUGRA constraints m(χ0)>50-60 GeV/c2 (gaugino -mixed).
• In the same framework m(χ+)>90 GeV/c2 , m(eR)>90 GeV/c2, m(ν)>90 GeV/c2 ~ ~