Marie-Hélène Genest, Wien 2005 Extended LHC Reach in Focus Point Region of MSSM Marie-Hélène Genest with Alexander Belyaev*, Claude Leroy, Rashid Mehdiyev.

Marie-Hélène Genest, Wien 2005

Extended LHC Reach in Focus Point Region of MSSM

Marie-Hélène Genestwith

Alexander Belyaev*, Claude Leroy, Rashid Mehdiyev

Université de Montréal*Florida State University


Searching for CDM at LHCWMAP Results

Constraints on cold dark matter

Constraints on supersymmetric parameter space

What is the portion of this constrained parameter space accessible at LHC?

Monte Carlo generation of events in ATLAS

Analysis optimization and results


WMAP• Wilkinson Microwave Anisotropy

Probe measures anisotropies in the cosmic microwave background

• The position and relative heights of the peaks in the multipole moment representation of these anisotropies give information about the geometry of the universe, its composition, …

• Puts constraints on dark matter models


Dark matter constrains

The non-baryonic cold dark matter component of the energy density in the universe :

Matter content

Baryonic contentHubble constant (h = 0.71±0.04)


Supersymmetric candidate

If the R-parity is conserved:R = (-1)B+2L+S with B, L, S the baryon number, lepton number and spin

the lightest supersymmetric particle (LSP) can’t decay to SM particles (is stable)

In some models, the LSP is the lightest neutralino ) a non-baryonic, electrically neutral, weakly interacting massive particle (WIMP) with 10 GeVc-2 < M< 1 TeVc-2 defined as the combination of the supersymmetric partners of the U(1) and SU(2) gauge bosons:


SUSY parameter spaceMinimal Supersymmetric Standard Model (MSSM) Most popular choice: minimal supergravity (mSUGRA)

scenario of SUSY breaking in which MSSM is valid from weak scale up to GUT scale (~1016GeV), where gauge couplings unify

Universal parameters at GUT scale: scalar masses (M0)

Gaugino masses (M1/2)

a-terms (A0) (tri-linear couplings in the soft-breaking Lagrangian)

Two other parameters to fix: tanRatio of the two Higgs vacuum expectation values)Sign( is the mass parameter of the Higgs)

In most mSUGRA parameter space, the relic density obtained is way beyond the WMAP bound


Neutralino relic densityCalculated using ISARED (part of ISATOOLS package in ISAJET v.7.72)

Green regions in agreement with WMAP results:

1- Bulk annihilation region :

pair annihilation at large rate via slepton exchange

Excluded regions:

- Theoritical exclusion in red (no radiative electroweak symmetry breaking or charged LSP)

- Too high relic density for WMAP in blue and unshaded

- Too low relic density for in yellow

2- Stau co-annihilation region stau and mass almost the same; co-annihilation between them in the early universe

3- Hyperbolic branch/focus point region (HB/FP) ’s have a significant higgsino component which facilitates annihilations in WW and ZZ pairs

4- A-annihilation funnel (not shown here, only for very large tan (>45)) mA~2m annihilation through A0 resonance into a fermion/antifermion pair


s = 14 TeV p on p collider

• Luminosity– “low” : 1033 cm-2 s-1, 10 fb-1 /year

– “high”: 1034 cm-2 s-1, 100 fb-1 /year

• 25 ns bunch crossing (BC) (40 MHz)

• High luminosity and large inclusive

at LHC implies:

– ~ 23 minimum bias events per BC

– ~ 70 charged tracks/event with

pT > 1 GeV/cc for || < 2.5

– Detector response speed (t < 50 ns)

– Radiation hardness

• ~ 100 Hz trigger rate

• LHC is a factory of everything: t, b, Z, W,Higgs, SUSY, … etc.

• Some processes at Low L

• Mass reach up to 5 TeV

• Precision measurements dominated by systematic errors

Process Events/year

W l Z ee

gg(m=1 TeV)

H(m=0.8TeV)

15 nb

1.5 nb

800 pb

500 b

1pb

1pb

108

107

107

1012

104

104

ttbb

The Large Hadron Collider


The ATLAS Detector• Tracking in 2T solenoid:

– SCT Si pixel + strips (3+4 layers)– TRT particle id.– B = 2 Tesla

/ pT ~ 5 10-4 pT 0.001

• EM calorimeter: Pb – liquid Argon presampler + segmented EM calo.

/ E ~ 10% / E(GeV)

• Had. Calorimeter:– Fe –scintillator (barrel)

/ E ~ 50% / E(GeV) 0.03 – Cu/W – liquid Argon(endcaps/Forwd) / E ~ 60% / E(GeV) 0.03

• Muons: instrumented large toroid magnet

/ pT ~ 10 % at 1 TeV/c


SUSY reach of CERN LHC

Can explore (Baer, H. et al., JHEP06 (2003) 54.)– all the bulk region– all the funnel region– all the stau co-annihilation corridor (unless tan is really large)

– Up to M1/2 ~ 700 GeV via conventional SUSY search channels

for the HB/FP region

The HB/FP region extends indefinitely to large M1/2, M0 values ultimately well beyond LHC reach.

A careful study can extend the LHC reach into this region…


Actual LHC reach (Baer, H. et al)

Region in this study to improve actual limit

M1/2/M0 is observable if (for 100fb-1):

- the significance S>5, where S = Signal/sqrt(Background)

- the number of signal events left >10

Monte Carlo generation method:

- Signal & BG events: ISAJETv7.64

-CMSJET v4.801 to model the CMS detector

Analysis:

Best cut combination for cuts on:

Number of jets, missing transverse energy, transverse energy of two most energetic jets, circularity, muon isolation and


SUSY Monte Carlo Generation

• For each SUSY point (i.e. M1/2/M0 value) 5x104 - 2x105 signal events were generated with ISAJETv7.72 (PDF CTEQ-5L, mtop=175 GeV) taking into account all SUSY subprocesses

• ATLFAST code to simulate the experimental condition prevailing at LHC for ATLAS detector. Detector dependent parameters tuned to values expected from full simulation

• Signal signature: SUSY in FP/HB region dominated by production of

gluino, neutralino and chargino one isolated lepton (from W decay in chargino decay chain) associated with multi-jet production and a large missing transverse energy


SUSY points studied

With production cross section ranging from 36 to 699 fb


Background Monte Carlo Generation

Various types of SM background can mimic SUSY signature

(1 lepton+multi-jet+large ET,miss) :

top quark pairs, single top quark production, W+jets, WW, QCD jets events.

These BG were generated using PYTHIA, the significant ones turning out to be top quark pairs and W+jets events (1.5x108

events generated for each with prodandpb respectively for partonic transverse momentum cut used)


Optimizing the analysis• To separate signal from background:

– Pre-selection cuts:• 1 lepton• At least one jet with a minimum transverse momentum pT(jet)>20

GeV• A minimum transverse missing energy ET,miss>200 GeV in the event

– Cuts to tune to get the best significance while maintaining at least 10 signal events:

• minimum number of jets Nj

• minimum transverse mass of lepton and missing energy given by MT2

= 2pT(lepton)ET,miss(1-cos• maximum transverse momentum of the lepton• minimum transverse missing energy ET,miss

Cuts tuned first on point M0 ,M1/2: 3500,600

(which allows direct comparison with previous study)

correlation


Chosen cut value to maximize significance while keeping reasonable number of events

For all values of other cuts (maximum pT(l), MT, ET,miss)

The significance always go up with the number of jets

Number of jets cut


MT and pT(l) cuts

Nj>9


Different sets of cuts for parts of the HB/FP region

M0 , M1/2 Nj pT(l)

(GeV)

MT

(GeV)

ET,miss

(GeV)3500,600 4670,880 9 160 160 200

4670,930 4850,1050 9 260 130 250

For reachable points, the observability criterion (S>10, S/sqrt(B)>5) was fullfilled using those optimized sets of cuts:

A significance greater than 5 can be achieved for some other points, having a number of signal events 5<S<10 by fine-tuning the cut values for each point.


Cut efficiency example

Cut

SUSY point M0,M1/2: 4500,900

Top quark pair events

W + jets events

Fraction passing preselection (%)

4.8 4.7x10-1 3.8x10-2

Fraction of preselected events passing the Nj≥9 cut (%)

13.3 14.8 8.0

Fraction of events passing the Nj cut that pass the MT≥160 GeV cut (%)

23.7 2.5x10-2 1.1

Fraction of all events passing all cuts (%)

1.5x10-1 1.7x10-5 3.3x10-5


New preliminary LHC reachBlue x:

S/sqrt(B)>5, S>10

White dots:

S/sqrt(B)>5, 10>S>5

(3<S<5 for 4850,935 and 5000,1080)

Red cross:

S/sqrt(B)<5 or S<3

For now, reach seems to be extended and competitive with LC1000 to some extent

preliminary


Future prospects

• Results are encouraging, but more work is in progress to check the validity of this analysis by performing a direct comparison using the previous study cuts on point 3500,600 in ATLAS detector, with ISAJETv7.64

Marie-Hélène Genest, Wien 2005 Extended LHC Reach in Focus Point Region of MSSM Marie-Hélène Genest with Alexander Belyaev*, Claude Leroy, Rashid Mehdiyev.

Documents

supersymmetric parameter

wmap bound slide

pair annihilation

co annihilation

dark matter models

msugra parameter space

bulk annihilation region

neutralino relic density