ian hinchliﬀe lbnl october 15, 2003conferences.fnal.gov/hadroncollider/talks/hinchliffe.pdf ·...

SUSY at Hadron Colliders

Ian HinchliffeLBNL

October 15, 2003

Outline

• Models and Signatures

• LHC

• Tevatron (a few remarks)

• Future colliders – when to give up.

All plots from ATLAS simulations unless otherwise noted

Ian Hinchliffe – FNAL – Oct, 2003 1

Models and Signatures

Will discuss model with minimal particle contentTwo Higgs doublets (H1 and H2) and SUSY partners for SM fields plus Gravitino

Most general model has many parameters• SUSY breaking masses for scalars(m0) and gauginos (M1/2)• SUSY conserving µ parameter (µH1H2)• Soft A and B terms – BµH1H1 and LEH2 etc.Trilinear term A, important only for 3rd generation as in enters scaled by Yukawas• MZ is given in terms of these.

R parity – neutral LSP stable – all events have 2 LSP’s in them ⇒ missing ET and pairproduction of sparticlesSensible Model has far few parametersMasses cannot be too high or SUSY is irrelevant to EWSB


Hadron Production of Sparticles

LHC is likely to be above threshold for many sparticles

A consistent model must be used for simulation. Most popular is SUGRA

Unification all scalar masses (m0) at GUT scaleUnification all gaugino masses (m1/2) at GUT scaleUniversal A and B| µ | and B are traded off for MZ and tanβ = v1/v2

So five parameters tanβ = v1/v2 sign(µ) A, m1/2 and m0 gives full mass spectrumand decaysGluino mass strongly correlates with m1/2, slepton mass with m0.

Studies have also been done for Gauge, Anomaly mediated, and R-Parity breakingmodels.

Enough cases have now been studied that given a complete set of masses and decayrates, we can usually estimate what can be done at LHC.


SUSY in hadron colliders

Inclusive signatures provide evidence up to 2.5 TeV for squarks and gluinos.

Everything is produced at once; squarks and gluinos have largest rates.

Production of Sparticles with only E-W couplings (e.g sleptons, Higgs) may be dominatedby decays not direct production.

Must use a consistent model for simulationcannot discuss one sparticle in isolation.

Makes studies somewhat complicated and general conclusions difficult to draw.

LHC Strategies different from Tevatron where weak gaugino production probablydominates

Studies shown here are not optimized

Large event rates are used to cut hard to get rid of standard model background.

Dominant backgrounds are combinatorial from SUSY events themselves.

Studies shown here are not optimized; large event rates are exploited to cut hard to getrid of standard model background.

Full program difficult to estimate, depends on masses and branching ratios


Characteristic SUSY signatures at hadron colliders

Not all present in all models

• /ET

• High Multiplicity of large pt jets

• Many isolated leptons

• Copious b production

• Large Higgs production

• Isolated Photons

• Quasi-stable charged particles

N.B.Production of heavy objects implies subset these signalsImportant for triggering considerations in hadron colliders


Inclusive analysis at LHC

These studies tend to be conservative

Reach is shown for various inclusive signalsJets plus missing ET

Multileptons of same and opposite signShown for SUGRAShaded regions excluded by theory or LEPExtends to gluino masses of over 2 TeV for10fb−1

M0 (GeV)

M1/

2 (G

eV)

∫ L dt = 10 fb-1

tan(β) = 10, µ > 0, A0 = 0

ETmiss

0l

1l

2l OS

3l 2l SS

q(500)

q(1000)

q(1500)

q(2000)

q(2500)

g(500)

g(1000)

g(1500)

g(2000)

g(2500)

0

200

400

600

800

1000

1200

1400

0 200 400 600 800 1000 1200 1400 1600 1800 2000


Plot shows evolution of reach with luminosityNotice that a few 0.1fb−1 covers most of theregion favored by fine tuning arguments

∫L dt = 1, 10, 100, 300 fb-1 A

0= 0, tanβ= 35, µ > 0

ET (300 fb-1)

miss

ET (100 fb-1)

miss

ET (10 fb-1)

miss

ET (1 fb-1)

miss

g(1000)~

q(1500)

~

g(1500)~

g(2000)~

q(2500)

~

g(2500)~

q(2000)

~

g(3000)~

q(1000)~

q(500)~

g(500)~Ω

h 2 = 0.4

Ωh 2 = 1

Ωh 2 = 0.15

h(110)

h(123)

1400

1200

1000

800

600

400

200

50000

1000 1500 2000

m0

(GeV)

m1/

2(G

eV)

EX

TH

DD

_210

1

CMS

Catania 18

one year @1033

one year @1034

one month @1033

Fermilab reach: < 500 GeV

one week @1033

cosmologically plausible region


Reach is similar in other modelsExample of anomaly mediated modelShaded pink region is excluded by LEP

In general reach depends mainly on Mg and Mq provided Mχ01

Mg, Mq

rather model independent


Estimating the scale

Select events with at least 4 jets and Missing ET

A simple variable

Meff = Pt,1 + Pt,2 + Pt,3 + Pt,4 + /ET

At high Meff non-SM signal rises abovebackground note scale

(GeV)effM

0 500 1000 1500 2000 2500

-1E

vent

s/50

GeV

/10

fb

10

102

103

104

105


Peak in Meff distribution correlates with SUSYmass scaleMSUSY = min(Mu, Mg)Will determine gluino/squark masses to ∼ 15%in SUGRA, much poorer in a more general MSSM15 parameters were varied

0

400

800

1200 (a)

mSUGRA

(b)

MSSM

0

400

800

1200

0 500 1000 1500 2000 2500

M (GeV)eff

M

(

GeV

)SU

SYef

fM

(G

eV)

SUSY

eff

Note that rate information is difficult to use as BR are not knownMust reconstruct decays to get more informationExamples follow


Identifying typical decays

Assume Mg > Mq ( similar results in reverse case)Then typically

B(qL → χ02q) ∼ 1/3, B(qL → χ±

1 q′) ∼ 2/3, B(qR → χ01q) ∼ 1 .

If channels are open, two body decays such as χ02 → ˜+`−, χ0

2 → Zχ01, χ0

2 → hχ01

usually dominate

Otherwise χ02 → χ0

1`+`− via virtual slepton

So a good idea to look for leptons


Leptonic final states

Isolated leptons indicate presence of t, W , Z, weak gauginos or sleptons

Straightforward caseDecay chain is χ2 → ˜+`− → χ1`

+`−

• 2 isolated opposite sign leptons; pt > 10 GeV• ≥ 4 jets; one has pt > 100 GeV, rest pt > 50GeV• /ET > max(100, 0.2Meff)Mass of opposite sign same flavor leptons isconstrained by decay

M`` =√

(M2χ0

2− M2˜)(M2˜ − M2

χ01)/M˜.

Standard Model background is dominated by ttOther SUSY events (mainly χ±

1 decays alsocontribute)

0

100

200

300

400

0 50 100 150 200

signalSM backgSUSY backg

Eve

nts/

4 G

eV/3

0 fb

−1M (GeV)

ll


Others CMS Plotseµ events arise from τ+τ−

Note that right plot has only χ2 →τ+τ− and χ2 → Zχ0

1 opentypical of large tan β

250

200

200

200

300

300

400

500

100

150

50

100

100 0 0 0200 300100 0

M(I+I-) (GeV)M(I+I-) (GeV)

Eve

nts

/ 4 G

eV /

1 fb

-1

m0 = 150 GeV, m1/2 = 250 GeV

µ > 0, A0 = 0

m0 = 90 GeV, m1/2 = 220 GeV

µ > 0, A0 = 0

tanβ = 2 tanβ = 35

Blois 20

e+e-,µ+µ−

e±µe+e-,µ+µ−

e±µ

SM

Eve

nts

/ 4 G

eV /

1 fb

-1

±±

Flavor subtraction remove the SMbackground and cleans up signalThis example has both χ0

2 → ˜+`−

and χ02 → Zχ0

1,

M(l+l−) (GeV)

Eve

nts/

4 G

eV/3

0 fb

−1

e+e− + µ+µ− − e+µ− − µ+e−


Signal is visible over large part ofparameter spaceAt large m0 rates are suppressed bylarge slepton massCMS plot

104 pb-1

105 pb-1

900

800

700

600

500

400

300

200

100

0 50 100 150 200 250 300 350 400 450 500

m0 (GeV)

m1/

2 (G

eV) tanβ = 2, A0 = 0,

µ < 0

D_D

_106

1n

TH

LEP2 + Tevatron (sparticle searches)

TH

EX

103 pb-1

Must add jets to this to try to get full decay chains


Squark masses

Attempt to find qL → qχ02 → q ˜ → q``χ0

1

Identify and measure decay chain• 2 isolated opposite sign leptons; pt > 10 GeV• ≥ 4 jets; one has pt > 100 GeV , rest pt > 50 GeV• /ET > max(100, 0.2Meff)

Mass of q`` system has max at

Mmax``q = [

(M2qL

− M2χ0

2)(M2

χ02− M2

χ01)

M2χ0

2

]1/2 = 552.4 GeV

and min at 271 GeV (in the example shown)


0

500

1000

1500

2000

2500

0 200 400 600 800 1000Mllq (GeV)

Eve

nts/

20 G

eV/1

00 fb

-1

smallest mass of possible ``jetcombinations largest mass of possible ``jet

combinations

Kinematic structure clearly seenCan also exploit `jet mass


Can now solve for the masses. Note that no model is needed

Very naive analysis has 4 constraints from lq, llqupper, llqlower, ll masses4 Unknowns, mqL

, meR, mχ0

2, mχ0

1

Errors are 3%, 9%, 6% and 12% respectively

0

50

100

150

200

250

300

350

400

0 50 100 150 200 250 300 350 400

S5

O1

correlations meR

vs. mχ01

0

0.005

0.01

0.015

0.02

0.025

50 100 150 200 250

LSP massMass of unobserved LSP is determined


Errors are strongly correlated and a precise independent determination of one massreduces the errors on the rest.


What about qR?

qrqr → qqχ01χ

01 produces clean events

m2T 2(χ) ≡ min

/q(1)T +/q(2)

T = /ET

[max

m2

T (pj(1)

T , /q(1)T ; χ), m2

T (pj(2)

T , /q(2)T ; χ)

]

Event selectionTwo jets with PT > 150 GeV/ET > 200 GeVNo other jets with PT > 40 GeVClear structureDetermines a combination of Mqr and Mχ0

1

13.54 / 13P1 -0.1971 0.6797E-01P2 619.6 8.249P3 0.1320 0.3268E-01P4 374.7 13.46

MT2 (GeV)

dσ/d

MT

2 (E

vent

s/20

GeV

)0

5

10

15

20

25

30

35

40

0 200 400 600 800 1000


Decays to Higgs

If χ02 → χ0

1h exists then this final state followed by h → bb results in discovery ofHiggs at LHC.In these cases ∼ 20% of SUSY events contain h → bb

Event selection/ET > 300 GeV≥ 2 jets with pT > 100 GeV and ≥ 1 with| η |< 2No isolated leptons (suppresses tt)Only 2 b-jets with pT,b > 55 GeV and | η |< 2∆Rbb < 1.0 (suppresses tt)Clear peak in bb massVery small standard model background (pale)Dominant background is other SUSY decays(dark)


Generally applicable

This method works over a large region ofparameter space in the SUGRA ModelHatched region has S/

√B > 5

Contours show number of reconstructed HiggsChannel is closed at low m1/2

tanβ=10, sgnµ=+1, A0=0

m0 (GeV)

m1/

2 (G

eV)

∫Ldt=300 fb-1

10000

1000

100

S/√B>5BR(χ

∼20→χ

∼10h)=0.5

0

200

400

600

800

1000

0 500 1000 1500 2000


Combine with a jet to attempt to getq → qχ0

2 → qhχ01

Take bb around the peak and combine with alljetsPlot the combination with the smallest massAgain we see upper kinematic limit

0

25

50

75

100

0 200 400 600 800 1000mbbj (GeV)

Eve

nts/

20 G

eV

signalSM backgSUSY backg


Importance of Taus

Most models have e/µ universality, but τ ′s are special

τ1 is usually lightest slepton

Two τ mass eigenstates are mixtures of τL and τR.

Need to measure masses and mixings

Therefore τ rates are important

m(τ ) < m(µ)Taus may be the only produced leptons in gaugino decay


Leptonic tau decays are of limited use – where did lepton come from?

Rely on Jet and Et(miss) cuts to get rid of SM background and obtain clean SUSYsample.

Tau background then arises from QCD jets in the SUSY event

Only need rejection O(10)Measure “visible” tau energy. Can infer real end point from measured spectrum.

Real kinematic end point directly constrains masses.

Mmaxττ = Mχ0

2

√√√√1 −M2

τ1

M2χ0

2

√√√√1 −M2

χ01

M2τ1

Then can reconstruct the decay chain by selecting these tau pairs


Use Hadronic tau decays, using jet shape andmultiplicity for ID and jet rejection

1

10

10 2

10 3

10 4

0 20 40 60 80 100τ efficiency (%)

Jet r

ejec

tion

70<PT<13050<PT<70

30<PT<5015<PT<30


Example of decay to tau event

qL → χ02q → qτ+τ−χ0

1

≥ 4 jetsone has pt > 100 GeVrest pt > 50 GeVNo isolated leptons with pt > 10 GeV/ET > max(100, 0.2Meff)Plot mass of observed “tau” pairs

0

1000

2000

100 200 3000

Mττ (GeV)

Eve

nts

/ 7 G

eV /

10 fb

-1

signal

SM bkg

Red Solid’: Signaldashed: b- background from “real+fake”Solid: background from “fake+fake”

In principle polarization information can be extractedVital to determine mixings


Heavier Gauginos

In some cases, heavier gaugino are “Higgsino” like and cannot be produced significantlyin squark/gluino decay

But production of squarks can be huge so that even small BR may be observable

In some cases the Gauginos can all be mixedthen the heavier ones can be produced with significant rates

χ04/χ±

2 decay chains can give OS, SF dileptons:

qL → χ04q → ˜±

R`∓q → χ02`

+`−q

qL → χ04q → ˜±

L`∓q → χ01`

+`−q

qL → χ04q → ˜±

L`∓q → χ02`

+`−q

qL → χ±2 q′ →→` `±q′ → χ±

1 `∓q′

more complicated dilepton signals


1

10

10 2

10 3

0 200 400

OS-SF ALL

OS-OF ALL

OS-SF SM

mll (GeV)

Eve

nts/

10 G

eV/1

00 fb

-1

m0 = 100 GeV, m1/2 = 150 GeV

1

10

10 2

10 3

0 200 400

OS-SF ALL

OS-OF ALL

OS-SF SM

mll (GeV)

Eve

nts/

10 G

eV/1

00 fb

-1

m0 = 100 GeV, m1/2 = 250 GeV

Most events are from χ02 but event rates are large enough for higher end-points to be

measured to ±5 GeV


These heavier gauginos are visible over a large part of parameter space

Plot shows event ratesDark line shows reach for 100fb−1

m0 (GeV)

m1/

2 (G

eV)

100

1000

10000200

400

200 400


Third Generation quarks

Measurement of b gives vital information about SUSY breaking

m0 = 100 GeV, M1/2 = 300 GeV, A0 = −300 GeV, tan β = 10, sgn µ = +

g → tt∗1 → tbχ−

1 , g → bt1 → tbχ−1

0 200 400 600 800 0 200 400 600 8000

200

400

600

800

1000

1200

0

50

100

150

200

Eve

nts

/ 10

GeV

Eve

nts

/ 10

GeV

m (GeV)tb m (GeV)tbReconstruct events with t and b and look for a kinematic end point


Even Messier cases

R-parity breakingImplies either Lepton number or Baryon number is violated and LSP decaysEither χ0

1 → qqq, or χ01 → qq` or χ0

1 → `+`−νFirst two have no /ET , last 2 have more leptons and are straightforwardFirst case is hardest, Global S/B is worse due to less /ET


Example, SUGRA with χ01 → qqq

Leptons are essential to get rid ofQCD background≥ 8 jets with pt > 50 GeV2 OSSF isolated leptons.ST > 0.2, selects “ball like” eventsΣjets+leptonsET > 1 TeVDilepton mass still shows clearstructure with small backgroundfromχ0

2 → `+`−χ01 0 50 100 150

Mll (GeV)

400

200

0

Eve

nts/

3 G

eV/3

0 fb

-1


As nothing is lost, should be possible to reconstruct χ01

Difficult because jet multiplicity is very high and χ01 mass is usually small, so jets are

soft

≥ 8 jets with pt > 17.5 GeV≤ 8 jets with pt > 25 GeV2 jets with pt > 100(200) GeVand | η |< 21 or 2 leptons with pt > 20 GeVSphericity cutcombine 6 slowest jets into 2 setsof 3;require M(jjj)1−M(jjj)2 <20 GeV

mjjj (GeV)

Eve

nts/

10 G

eV/3

0 fb

-1

0

25

50

75

100

0 100 200 300 400 500

Nominal mass 122 GeV SM backgroundsignificant


Can cut around peak and combinewith either leptons or quarksreconstructqR → qχ0

1(→ qqq)) andχ0

2 → ``χ01

Plot shows χ02

Note that tight cuts imply low eventrate

0

10

20

30

0 100 200 300 400

m(χ20) = 212 GeV

Eve

nts/

20 G

eV/3

0 fb

-1

.

m(χ20) = 252 GeV

mjjjll (GeV)

0

5

10

15

20

0 100 200 300 400


Preferred regions?

It would be nice to know where to look

If we really believe in minimal SUGRA thenWMAP provides strong constraintsEven stronger if g − 2 is included (with one valueof R(e+e−) at low energy)

100 200 300 400 500 600 700 800 900 10000

100

200

300

400

500

600

700

800

100 200 300 400 500 600 700 800 900 10000

100

200

300

400

500

600

700

800

mh = 114 GeV

m0 (

GeV

)

m1/2 (GeV)

tan β = 10 , µ > 0

mχ± = 104 GeV


But constraints weaken outside minimal sugra

R = M2/M3 at GUT scale.

350100 350100600 600850 8501100 11001350 13501600 1600

250

0

250

0

500 500

750 750

1000 1000

1250 1250

1500 1500

M1M1

m0 m0

(GeV)(GeV)

(GeV) (GeV)

Stau LSP Stau LSP

GEN

XEN

XEN

r = 1.0 r = 0.6


When to give up

Many arguments based on naturalness indicating that LEP/Tevatron should seesomething.

LHC should find something if squarks/gluinos less than ∼ 3 TeV

You can always cook something up that LHC cannot find (∆M = 1GeV )

0 2000 4000 6000 8000 10000M1/2 (GeV)

0

4000

8000

12000

16000

20000

m0 (

GeV

)

mSUGRA

tanβ=10,Α0=0µ>0

0.094<Ωχh2<0.129

aµ(−1.5σ)


Tevatron

No signal claimed by an experiment

TeV will extend search range with more luminosity Reach is limited nut “the train isalready late”Squark and gluino production may not dominant


Global searches involving /ET canextend search regionPlot from Tevatron study


Best hope is production of χ02χ

+1 → `+`−χ0

1`+νχ0

1Background dominated by WZ∗

Tevatron study hep-ph/0003154

m m

3σ contours.


If this signal is seen thenstructure in the `+`− massdistribution will constrain χ0

2 andχ0

1 masses (see later)Plot shows some typical casesNote event ratescase (1) was ruled out by LEP!


If Tevatron finds SUSY it will determine the mass scale of some particles


Upgrades

Its very likely that LHC will discover SUSY.

But it’s unlikely that it will measure everything

Studies of χ3 and χ4 likely rate limited.

In some models first two generation squarks can be very heavy.

For more on this see Albert’s talk


References

[1] S. Abdullin et al. [CMS Collaboration], “Discovery potential for supersymmetry inCMS,” hep-ph/9806366.

[2] I. Hinchliffe, F. E. Paige, M. D. Shapiro, J. Soderqvist and W. Yao, Phys. Rev. D55, 5520 (1997) [hep-ph/9610544].

[3] S. Abdullin, CMS Note 1997/070.

[4] D. Denegri, W. Majerotto and L. Rurura, Phys. Rev. D60 (1999), 035008;L. Rurua, PhD Thesis, Institute of High Energy Physics, Austrian Academy ofSciences, 1999.

[5] H. Bachacou, I. Hinchliffe and F. E. Paige, Phys. Rev. D 62, 015009 (2000)[hep-ph/9907518]. at the L! JHEP0009, 004 (2000) [hep-ph/0007009].

[6] F. Gianotti, et al., hep-ph/0204087.


[7] ATLAS Collaboration, ATLAS Detector and Physics Performance Technical DesignReport, CERN/LHCC/99-14 (1999).

[8] D. R. Tovey, Phys. Lett. B 498, 1 (2001) [arXiv:hep-ph/0006276

[9] B. C. Allanach, A. J. Barr, L. Drage, C. G. Lester, D. Morgan, M. A. Parker,P. Richardson and B. R. Webber, hep-ph/0102173.

[10] M. Kazana, G. Wrochna, and P. Zalewski, CMS CR 1999/019 (June, 1999).

[11] D. Tovey, Eur. Phys. J. bf C4, N4 (2002)

[12] G. Polesello, http://agenda.cern.ch/askArchive.php?base=agenda&categ=a03395&id=a03395s0t4/transparencies.

[13] J. R. Ellis, K. A. Olive, Y. Santoso and V. C. Spanos, “Supersymmetric dark matterin light of WMAP,” arXiv:hep-ph/0303043.

[14] U. Chattopadhyay, A. Corsetti and P. Nath,


[15] A. Birkedal-Hansen and B. D. Nelson, “Relic neutralino densities and detection rateswith nonuniversal gaugino masses,” Phys. Rev. D 67 (2003) 095006 [arXiv:hep-ph/0211071].

[16] J. R. Ellis, T. Falk, K. A. Olive and Y. Santoso, “Exploration of the MSSM with non-universal Higgs masses,” Nucl. Phys. B 652 (2003) 259 [arXiv:hep-ph/0210205].


ian hinchliﬀe lbnl october 15, 2003conferences.fnal.gov/hadroncollider/talks/hinchliffe.pdf ·...

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