1. mSUGRA SUSY Searches at the LHC
Why use mSUGRA and what signals does it give ?
Detector requirements.
SUSY discovery (production via strong interactions):
Squarks & gluinos.
Next-to-lightest neutralino.
SUSY parameter determination:
From Drell-Yan production cross-sections (gauginos & sleptons)
Sparticle masses (neutralinos, squarks & gluinos)
Conclusions
Ian Tomalin
15/01/2019

2. Why use mSUGRA ? Why not just use the MSSM ?
Particles: SM ones + 5 Higgs
Sparticles: Spin 0 partners of SM fermions: qL,qR,lL,lR,nL Spin 1/2 partners of bosons/Higgs: c10,c20,c30,c40,c1±,c2±, g
Nice theory, but 124 free parameters !
Ian Tomalin
15/01/2019

3. Why use mSUGRA ? mSUGRA (minimal Supergravity)
Favourite SUSY theory for LHC studies. (Peter will discuss alternatives).
Only 5 parameters (+ SM ones):
m_ (Scalar mass at GUT scale) ~ Squark & Slepton masses.
m_1/ (Gaugino mass at GUT scale) ~ Gaugino & gluino masses.
tan(b) (VEV ratio of 2 Higgs doublets).
A_ (Higgs-fermion-antifermion coupling)
sign(m) (Higgsino mixing parameter)
Ian Tomalin
15/01/2019

4. mSUGRA Characteristics
m_1/2 (GeV)
lR mass
contours
N.B. lR mass is approximately m_0.
m_0 (GeV)
Ian Tomalin
15/01/2019

5. mSUGRA Signals
R-parity: SUSY particles pair-produced c10 is stable (so missing ET).
Mass (q, g) > mass (t) > mass ( l, c)
SUSY production:
Dominated by q & g (strong interaction) - up to 100M/year.
Some l & c from Drell-Yan (EW interaction) ~ 10K/year.
SUSY decays:
Give ET(miss), many (b-)jets, leptons.
Ian Tomalin
15/01/2019

6. mSUGRA Signals s(q) >> s(g) q ® q’ c ; c20 ® l+ l-1 2
s(q) >> s(g) q ® q’ c ; c20 ® l+ l-
s(q) ~ s(g) q ® q’ c ; g ® t t; c20 ® c10 h/Z
m_1/2 (TeV) ~ mass c & g
s(q) << s(g) g ® t t; c20 ® c10 h/Z
s(q) << s(g) g ® c10 t t; c20 ® c10 l+ l-
m_0 (TeV) ~ mass q & l
Ian Tomalin
15/01/2019

7. Detector Requirements
Calorimeter coverage for |h| < 5 (i.e. q > 10):
Needed for good ET(miss) resolution.
Needed to identify Drell-Yan events - with jet veto.
Tracker:
To identify b jets.
Prove leptons are isolated.
Measure lepton momenta
Ian Tomalin
15/01/2019

8. Detector Requirements
Measured Et(miss) in events with no missing energy.
Ian Tomalin
15/01/2019

9. SUSY Discovery - Squarks and Gluinos
Expect up to 100M q and g per year ! Can discover in days !
Signatures: ET(miss), many (b-)jets, leptons Selection cuts depend on m_0 and m_1/2 …
SM Backgrounds: t t, W/Z + jets. Huge SUSY cross-section means Signal/Background ~ 1.
By end of LHC life, explore q and g masses up to ~3 TeV.
Ian Tomalin
15/01/2019

10. SUSY Discovery - Squarks and Gluinos
Signal and background for events with two like-charge isolated leptons.
N_jet
Pt (lepton)
Pt (jet)
Et (miss)
Et (sum)
Ian Tomalin
15/01/2019

11. SUSY Discovery - Squarks and Gluinos
m_1/2 (TeV) ~ mass c & g
m_0 (TeV) ~ mass q & l 1 2
1 lepton
2 SS leptons
3 leptons
2 OS leptons
c10 = dark matter
Explored region after 1st LHC year.
Various final states help constrain SUSY.
Easily cover region where c10 could be dark matter.
Ian Tomalin
15/01/2019

12. SUSY Discovery Next-To-Lightest Neutralino
q and g often decay to c20.
c20 ® c10 l+ l-
Mass (l+l-) has sharp upper threshold: Clear signal for SUSY Measures m_1/2 !!
If decay proceeds via slepton, also measures m_0.
1 months running !
Ian Tomalin
15/01/2019

13. SUSY Discovery Next-To-Lightest Neutralino
m_0 (TeV) ~ mass q & l 1
m_1/2 (TeV) ~ mass c & g
0.5
c20 ® lL+ l-
c20 ® lR+ l-
c20 ® c10 l+ l-
Reach after 1 year’s high luminosity running.
Ian Tomalin
15/01/2019

14. Constraining SUSY with Cross-Sections
Measure q & g rate to various final states (1, 2, 3 leptons …) (Tend to decrease with increasing m_0 and m_1/2.)
Measure Drell-Yan (EW) production rates of:
c1+ c (3 lepton final state)
l+ l (2 lepton final state)
(Must use jet-veto to suppress q & g SUSY background. Need large luminosity.)
Ian Tomalin
15/01/2019

15. Constraining SUSY with Sparticle Masses
Providing c20 ® c10 l+ l- then:
Can measure m_1/2 using maximum l+l- mass seen in c20 ® c10 l+ l- .
Can also measure m_0, if c20 decays via slepton.
At maximum l+l- mass, know c20 momentum: P(c20) = P( l+l- ) .[M(c20) /M( l+l- ) ] where M(c20) estimated from m_0.
If qL ® qc20 or g ® qq ® qqc20 , can then determine qL and g mass.
Ian Tomalin
15/01/2019

16. Conclusions Many studies use mSUGRA, as better constrained than MSSM.
Detectors must find ET(miss), (b-)jets and isolated leptons. Need excellent solid angle coverage.
SUSY may be discovered within days of LHC start-up via production of squarks and gluinos.
.c20 ® c10 l+ l- decays could determine sparticle masses. Together with cross-section measurements, this helps constrain SUSY.
Ian Tomalin
15/01/2019