vadym zhuravlov
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Vadym Zhuravlov
ATLAS MDT seminar 27 Nov 2007
Contents:
1.Introduction: what is SUSY and why SUSY2.Models, points, spectra3.Quasi-stable NLSP4.Missing Et signature5.Background6.Spin measurement7.Conclusion
•A symmetry which relates bosons and fernions and represented by operator
Q |BOSON> = |FERMION> and Q |FERMION> = |BOSON>
• Generalization of Poincare algebra links together representation with different spin
{Q Q} = 2σ P
• Q does not change the particle quantum numbers, except spin
• Even if there is no “WHY” still there is a question:
why there are two classes of particles in nature – bosons and fermions
• Invented more then 30 years ago and still not discovered ( Higgs also)
• Provides unification of gauge coulings: (requires SUSY masses below few TeV)
• Provides a good candidate for Dark Matter – lightest neutralino (R-parity is conserved)
ΔMHiggs ~ log Λ
ΔMHiggs ~ Λ2
ΔMHiggs ~ Λ• Solves “hierarchy” problem SM is effective theory at E<<Λ (~1019 GeV)
MHiggs(tree level) ~ 1038 GeV
Fine tuning needed!“Not natural…”
SUSY: = 0
Barnett Newman “Broken Obelisk”
SUSY fields and particles
•SM: 28 bosonic and 96 fermionic DOF – highly non-supersymmetric! •Fields -> superfields• 2 complex Higgs fields: h, H, A, H+, H- tanb = V1/V2
MSSM – 124 parameters.
SUSY is a broken symmetry.
• Non of MSSM fields can develop non-zero VEV to break SUSY. Hidden sector where SUSY is broken.
• Messenger: transmit broken SUSY to visible sector.
1. Gravity mediated SUSY breaking: gravitino mass ~ EW mass
mSUGRA parameters: m0, m1/2, A0, tanb, sign(m)1. Gauge mediated SUSY breaking: messinger sector
consists of particles with SU(3)xSU(2)xU(1) quantum numbers
2. Gaugino mediation: SUSY is broken in another brane.
Our braneHidden
sector
BULK
gaugino
R = (-1)3(B-L)+2s
“+” for ordinary particles“-” for supersymmetrical partners
If R-parity is conserved, SUSY-particles are created in pairs, LSP is stable
Under R-parity the lepton and barion numbers are conserved
Rule to create SUSY Feynman vertex: take SM vertex and replace 2 legs by super-legs
GeV
Renorm. GroupEquations
Ellis et al. hep-ph/0303043
tanβ=10, μ>0
Old constrain0.1 < Ώh2 < 0.3
New constrain0.094 < Ώh2 <
0.129Favorite by g-2
STAU is NLSP
excluded by b→sγ
excluded by LEP
'Bulk' region: t-channel slepton exchange - LSP mostly Bino. 'Bread and Butter' region for LHC Expts.
'Focus point' region: significant h component to LSP enhances annihilation to gauge bosons
Slepton Co-annihilation region: LSP ~ pure Bino. Small slepton-LSP mass difference makes measurements difficult.
SUSY Dark Matter
Quasi- stable STAU
Production:
10 fb-1 Mτ = 160 GeV tanβ=10340 STAUs
Experimental signatures:
1. Lifetime > 10-8 : slow muon-like particle
2. 10-10 < Lifetime < 10-8 : kink tracks
3. Lifetime < 10-10 : muons with large impact parameter
A.Gladyshev hep-ph/0509168
• A charged particle passing the MDT will leave clusters of ionized atoms
• The electrons drift to the wire in the center of each tube
• The radius from which the electrons drift to the wire is calculated from a time measurement
• t0 is estimated for a muon traveling at the speed of light
• The segment is tangent to the radii
• Some hits from “noise” are ignored
t0
tmeasured=t0+tdriftR=R(tdrift)=R(tmeasured-t0)
tdrift
Segment reconstruction
S. Bressler
• The long time window of the MDT guarantees that data of low particles will be saved.
• The measured hit radius is incorrect
• We want to estimate t
• Larger radii result in
• Badly fitted segment
• Wrong direction of segment
t0(slow particle)
=t0+ttmeasured=t0+t+tdri
ft
Rmeasured = R(tmeasured-t0) = R(tdrift+t) > R
tdrift
Segment reconstruction
S. Bressler
• Relies on long time window of MDT and BCID from ID
• Identify penetrating particle by associating muon hits and segments with extrapolated ID track
• Loop over possible t
• Change MDT digits’ time and hence radii
• Create MDT segments from the re-timed digits• Estimate t0 (TOF) from the t that minimizes the 2
• Include information from segmentsin trigger chambers• RPC tof
• TGC direction
• Calculate and M
S. Bressler
misal1_mc12.005414.GMSB5_jimmy.susy.digit.RDO.v12000502part of MuGirl
M=P/βγ
Hiroshi Nomoto
0-lepton mode
MET > 100 GeV1 jet with Pt>100 GeV4 jets with pt>50 GeVTransv. Spher. > 0.2
1-lepton mode
MET > 100 GeV1 jet with Pt>100 GeV4 jets with pt>50 GeVTransv. Spher. > 0.2m or e pt > 20 GeV
2-lepton mode
MET > 100 GeV1 jet with Pt>100 GeV4 jets with pt>50 GeV2 m or e pt>20 GeVTransv. Spher. > 0.2
TDR cuts – 10 years old!!!
pg
Lq 02
R
01
no interaction with detector ET,miss
qX
Meff = Sjjets|Pt| + Et miss correlated to MSUSY
MSUSY = SMisi / Ssi
ATLAS TDR
S/B = 10S/B = 2
Matrix Element calculation VS Parton Showering
No lepton mode
Estimate background from data
Bad knowledge of:
• Underlined Event
• Cross-sections
• Parton Distribution Functions
• Detector Calibration (jets, MET)
• statistics of Monte Carlo
QCD Background
• Two main sources:– fake ET
miss (gaps in acceptance, dead/hot cells, non-gaussian tails etc.)
– real ETmiss (neutrinos from b/c quark decays)
• Simulations require detailed understanding of detector performance (not easy with little data).
• Huge cross-section – need of Fast Shower Simulation
• Estimate background using data: jet smearing function
Pythia dijets
SUSY SU3
QCD Background• Step 1: Measure jet smearing function from data
– Select events: ETmiss > 100 GeV, (ET
miss, jet) < 0.1
– Estimate pT of jet closest to EtMiss as
pTtrue-est = pT
jet + ETMiss
• Step 2: Smear low ETmiss multijet events with
measured smearing function
MET
jets
fluctuatingjet
Njets >= 4, p
T(j1,j2) >100GeV,
pT(j3,j4) > 50GeV
ETmiss
NB: error bars expected errors on background.
ATLAS
Preliminary
ATLAS
Preliminary
No lepton channel: Z→νν background
Get Z from Zee, what are the steps :1. Take Zee events2. Correct for electron identification efficiency (measured with real data)3. Correct for acceptance cuts (with MC)4. Get Z distributions
Below is the formula summarizing the different steps :
)(
)())(())((
),(),(
))(()(
2,21,1 eeZBr
ZBrZPCZPC
PeffPeff
ZPNMETN TFiducialTKin
TT
TRawCorr
20.00%
3.36%
Z MET distribution
Correct for electron id efficiency (measured with data)factor 2
# branching ratios from PDGFactor 6
Correct for kinematics cuts (PT(lept) > 20 GeV/c) from MC20%
Correct for fiducial cuts (|(lept)| < 2.5) from MC15%
Background: ttbar -> lnln (one l is missing) and ttbar -> qqbar ln
How to get rid of semi-leptonic ttbar background?
MT (GeV) MT (GeV)
bbqql bbll
Transverse mass: Minv(Missing Pt and PtLepon)
W mass
di-leptonic ttbar: decay resimulation
1. Select pure biased di-leptonic ttbar sample: small MET (no susy signal) – seed events
2. Reconstruct kinematics. How? → coming soon
3. resimulate top decay (as many times as needed) and count events with large MET
no susy with susy
Background: ttbar->bblnln Bbqqln with second lepton from b/c decay
dileptonic ttbar background: clean bb lνlν sample
Clean di-leptonic ttbar sample
Missing ET
Number of pairs
Background in D = A x C/B
A
B C
D
N_pairs = 0
N_pairs > 0
No strong correlation between MET and N_pairs
ttbar background for 2 lepton search
background+
SUSY
1 lepton search: main background – dileptonic top.Why one lepton is missing?
• it is tau. Take one of the leptons of clean di-leptonic ttbar sample and replace it by tau. Decay tau and see what happens – change of MET, Njets, nLeptons. • it miss-identified. Drop on the two leptons of clean di-leptonic sample, re-weight events by miss-identification efficiency
Inclusive reach in mSUGRA parameter space
Reach sensitivity only weakly depends on tanb, A0 and m
SUSY spin measurement
ll
llA
Spin-0 flat
•If SUSY signals are observed at the LHC, it will be vital to measure the spins of the new particles to demonstrate that they are indeed the predicted super-partners•Angular distributions in sparticle decays lead to charge asymmetry in lepton-jet invariant mass distributions. The size of the asymmetry is proportional to the primary production asymmetry between squarks and anti-squarks
•charge asymmetry of lq pairs measures spin of c0
2
•shape of dilepton invariant mass spectrum measures slepton spin
Spin-½, mostly winoSpin-0
Spin-½
Spin-0
Spin-½, mostly bino
Polarise
MeasureAngle
stransverse mass
Transverse mass Mt– endpoint is a mass of decaying particle (W)Stransverse mass Mt2– endpoint is a mass of c
stransverse mass – direct slepton production
Signature: two opposite sign same flavor leptons and missing Et
Endpoint of stransverse mass is a function of mass difference of slepton and LSP
MT2
Other topics:
1. R-hadrons2. Tau-signatures3. Gaugino direct production4. Study of gauge-mediated SUSY5. R-parity violating processes6. Spectroscopy
Conclusion:
• LHC is last chance to discover SUSY• SM uncertainties in the BG estimation is a limiting factor• Many models, parameters, preferable points: lot of work
Backup slides
electri
“SUSY was invented more then 30 years ago and still not discovered”
but
Electron was invented more then 2 500 years before
Vision of Ezekiel… et a lumbis eius et sursum quasi aspectus splendoris ut visio
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