EuroGDR

1
Focus-Point studies at LHC

• U. De Sanctis, T. Lari, C. Troncon
• University of Milan and INFN
• ATLAS Collaboration

2
SUSY and Dark Matter

• DM ? SUSY
• Non-baryonic matter density, computed from WMAP
  measurements
• 0.094 lt WDM h2 lt 0.129 (2s confidence interval)
• For any specific set of parameters of a SUSY
  R-parity conserving model, it is
• possible to compute the LSP relic density from
  the mass spectrum and the Big-Bang
• cosmology.
• The relic density can be less than WDM (if other
  contributions to the DM).
• The WMAP upper limit is a constrain that defines
  cosmologically interesting
• regions of the SUSY parameter hyperspace.
• I will limit myself to mSUGRA here.

SUSY ? DM Once (if) we will have a
measurement of SUSY mass spectrum mixing angle
etc., one can compute the relic density it
corresponds to.
3
mSUGRA and DM
SUSY spectrum computed with ISAJET 7.69 Relic
density computed with Micromegas 1.3.0
In most of mSUGRA parameter space the predicted
relic density is too large. In the Focus-Point
region (large m0) the lightest neutralino has a
significant Higgsino component, and the relic
density is reduced by s-channel annihilation in
the early universe.
Focus Point
Coannihilation (very narrow)
Selected for a detailed study with ATLAS
simulation.
4
Comparison of RGE codes
m0 scan m1/2 300 GeV tanb 10 A00 m gt0 mt175
GeV
Large differences in the predicted relic density
using different codes to compute SUSY mass
spectrum at the Electro-Weak scale. The study
presented here was made using ISAJET 7.69.
Wh2
m0 (GeV)
3000
4000
5
SUSY mass spectrum
Masses (GeV)
Mass spectrum at the selected point M03400 GeV
m1/2 300 GeV tanb 10 A00 m gt0 mt175 GeV

c01 102.6
c02 157.4
c03 172.3
c04 290.5
c?1 145.4
c?2 282.7
g 854
qL 3416
t1 2041
h 118. 8








Squarks at the limit of LHC reach. Other sleptons
and heavy Higgs too heavy for LHC. Gluino decays
into neutralinos and charginos.
6
Production xSection
Sum of jet and missing transverse energy. using
ATLAS fast simulation

• Production xSections

cc 4.6 pb
gg 0.58 pb
qg 3.7 fb


10 fb-1 (1st LHC year?) Susy/vSM 16

• cc production most abundant,
• but little jet and missing energy
• difficult to separate from SM. We are
• investigating the possibility to use
• c1c02 ? c01 l c01 l l-
• searching for 3 leptonsmissing
• energyno jet events.
• gluino pair production dominant
• after standard SUSY cuts.
• squarks visible with high luminosity

Standard cuts (not optimized for this point) on
jet and missing energy and lepton veto.
7
Gluino decays
Gluino decays g ? c0 qq 7.2 g ? c0 bb
3.7 g ? c0 tt 28.0 g ? c0 g 5.9
g ? c? qq 9.6 g ? c? tb 45.6
Golden channel is the neutralino dilepton decay
(gives neutralino mass difference). In
principle, the leptons from neutralino decays can
be combined with jets to get further mass
relations. However, large number of jets from
gluino decay (heavy combinatory background) and
poor lepton statistics to start with. We have
concentrated on reconstruction of the two main
gluino decays using tt and tb invariant mass
distributions (gives difference between gluino
and gaugino mass scales)
Neutralino dilepton decays c03 ? c01 l l c02 ?
c01 l l
8
Dilepton mass distributions
The c02 edge can be measured (constrain on
neutralino mixing matrix from the shape?) The c03
edge hardly visible even after three years at
design luminosity.
At generator level
ATLAS


c02 ? c01 ll-
Experimental, flavour subtracted




c03 ? c01 ll-
ATLAS

60
40
20
Mll (GeV)
300 fb-1 No SM background
Cuts Meff gt 750 GeV, ETmiss gt 100 GeV,
1 jet with pT gt 100 GeV Leptons with pT gt 10 GeV
60
40
20
80
Mll (GeV)
9
Gluino decays to chargino
Top quark decay into udb or csb fully
reconstructed. tb invariant masses reconstructed.
30 fb-1 No SM background
ATLAS
M(g)-M(c?1)

• 33 fb-1
• no SM backg.

M(g)-M(c?2)
200
400
600
Mtb (GeV)
10
Gluino to neutralino
Invariant mass of two fully reconstructed
tops. Analysis cuts similar to the gluino to
chargino analysis. With high luminosity an
endpoint can be extracted.
Experimental, flavour subtracted
At generator level
ATLAS
ATLAS


g ? c04 tt
300 fb-1 No SM background


g ? c03 tt


g ? c02 tt


g ? c01 tt
400
600
800
400
600
800
Mtt (GeV)
Mtt (GeV)
11
Scan of parameter space
As one moves up the FP strip the SUSY masses
increase and the production cross sections
decrease.
FP2 FP3 FP4 FP5
M0 3400 4200 5720 6000
M1/2 300 500 1000 1000
Wh2 .059 .026 .078 .012
M(g) 854 1334 2453 2468
M(c01) 103 176 401 241
s(gg) 580 21.3 0.05 0.05
s(cc) 4600 1074 57 480
s(gq) 3.7 0.2 0 0
M0-m1/2 scan for mt175 GeV,A00,tanb10,mgt0
FP5
FP4
Gluino mass
FP3
FP2
Cross sections in fb, masses in GeV
12
Neutralino mass differences
The c02 is close in mass to c01 on the right of
the band (where W ltlt WWMAP) while it is close to
the c03 on the left of the band (where W
WWMAP). Almost always m(c02)-m(c01) is below the
threshold for c02 ? c01 Z0 The dilepton edge
would provide a good constrain on W.
M(c02)-M(c01)
M(c03)-M(c02)
13
Effect of top mass
M1/2 (GeV)
M1/2 (GeV)
Mt 175 GeV
500
500
Mt 172 GeV
100
100
2000
5000
2000
4000
M0 (GeV)
As the top mass is increased the FP region moves
to larger values of m0. For the same m1/2 the
gluino/gaugino masses and decays depend very
little on the top mass. Sfermions are within
LHC reach only for a light top.
Mt 178 GeV
500
100
2000
5000
M0 (GeV)
14
Effect of top mass
At fixed m1/2 300 GeV, relation between mtop
and m0 for the FP region. tanb10,A00,mgt0
FP6 FP2 FP7 FP8
mtop 172 175 178 183
M0 1900 3400 7130 30850
M1/2 300 300 300 300
Wh2 .066 .059 .077 .0827
M(g) 814 854 904 1011
M(c01) 102 103 108 106
s(gg) 703 580 412 202
s(cc) 4610 4600 3650 4130
s(gq) 110 3.7 0 0
FP8
FP7
FP2
FP6
15
Effect of tanb
tanb10
tanb54
FP2
FP10
FP11
tanb30
A larger value of tanb pushes the FP band to
lower values of m0 At FP11 abundant squark
production!
FP9
16
Conclusions

• Part of the Focus-Point region is accessible by
  the LHC experiments. A test
• point was studied with the ATLAS detector fast
  simulation. A number of mass
• constrains can be measured m(c02)-m(c01),
  m(g)-m(c) and m(g)-m(c0).
• A scan of mSUGRA focuspoint space has been
  performed with ISAJET to study how the SUSY mass
  spectrum varies and select points for more
  detailed studies.
• The gluino gets heavier as one moves along the
  band in the m0-m1/2 plane. The LHC reach to
  observe gluino pair production should be about
  m1/2 900 GeV. Gaugino production may be used to
  extend this reach, assuming it can be isolated
  from the SM background.
• The neutralino spectrum is sensitive to position
  both along and trasversal to the band.
• The squarks are accessible for low top masses
  and/or high tanb - this would allow to get m0
  (and confirm that sfermions are there)
• The Focus-Point is under active study by the
  ATLAS collaboration. All results are preliminary
  and more are coming.

17
Horizontal line scan (III)

• Not really any good solution with SOFTSUSY

18
Comparison of RGE codes (2)
Comparison for point M03400 GeV m1/2 300 GeV
tanb 10 A00 m gt0 mt175 GeV
ISAJET 7.69 SOFTSUSY 1.86 SPheno 2.22 Suspect 2.3
M(c01) 102.6 126.9 126.9 127.0
M(c02) 157.4 247.7 248.6 247.4
M(c03) 172.3 596.4 665.4 580.8
M(g) 853.7 858.1 807.7 869.0
M(uL) 3419 3481 3431 3481
All masses in GeV
19
One more table
FP12 FP2 FP9 FP10 FP11
mtop 10 10 30 54 54
M0 3400 3400 2400 2300 1400
M1/2 300 300 300 300 180
m -
W .061 .059 .091 .052 .114
M(g) 854 854 829 825 517
M(uL) 3416 3416 2449 2356 1435
M(t1) 2041 2041 1479 1427 860
M(c01) 111 103 107 107 68
s(gggq) 580 580 700 1314 16670
s(cc) 4550 4610 4600 3650 4130
Little effect from changing the sign of m
mh 114.8 GeV