Gaugino searches and SUSY constraints

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)


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


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


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

qq

LEP

+


Chargino pair searches

4jets, 2jets+1lepton, 2leptons+ Missing Energy

'ff 'ff ee 01

01

-

heavysfermions

(W* decay)

lightsfermions

)()(

on depends analysissearch The01 mmm


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


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


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


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


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


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


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


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


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


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


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


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.


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:


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


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 ~ ~

Documents

Gaugino searches and SUSY constraints