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LPC Lectures, Feb., 2010 1
LPC Particle Physics LecturesLPC Particle Physics LecturesLPC Particle Physics Lectures
The Standard Model and Beyond
LHC PhysicsDan GreenFermilab
LPC Lectures, Feb., 2010 2
Outline –
I, The Standard Model
Outline Outline ––
I, The Standard I, The Standard ModelModel
•
Tools•
Comphep
•
Calchep
•
SM Particles and Forces•
V-V Interactions
•
SM Questions•
The LHC
•
ATLAS and CMS•
First Data –
Soft Interactions
•
Hard Scattering
LPC Lectures, Feb., 2010 3
Tools for These LecturesTools for These LecturesTools for These Lectures
http://comphep.sinp.msu.ru/overview
http://theory.sinp.msu.ru/~pukhov/calche p.html
These tools can reside on your desktop. They can be used to compute many fundamental processes. What they lack is only the “hadronization”
of the final state quarks and gluons and the “underlying event”
soft particles. (interface to Pythia)
What they provide is a rapid understanding of the basics of collider physics.
LPC Lectures, Feb., 2010 4
“Particle Physics”
in the 20th
Century
““Particle PhysicsParticle Physics””
in the 20in the 20thth
CenturyCentury•
The e-
was discovered by Thompson ~ 1900. The nucleus was discovered by Rutherford in ~ 1920. The e+, the first antiparticle, was found in ~ 1930. The μ , indicating a second “generation”, was discovered in ~ 1936.
•
There was an explosion of baryons and mesons discovered in the 1950s and 1960s. They were classified in a "periodic table" using the SU(3) symmetry group, whose physical realization was point like, strongly interacting, fractionally charged "quarks". Direct evidence for quarks and gluons came in the early 1970s.
•
The exposition of the 3 generations of quarks and leptons is only just, 1996, completed with the top quark discovery and the observation of the neutrino associated with the tau lepton in 2002 at Fermilab. In the mid 1980s the unification of the weak and electromagnetic force was confirmed by the W and Z discoveries at CERN.
•
The LHC, starting in 2009, will be THE tool to explore the origin of the breaking of the electroweak symmetry (Higgs field?) and the origin of mass itself. The Higgs boson is postulated to be responsible for
the mass of all the known elementary particles.
LPC Lectures, Feb., 2010 5
The Standard Model of Elementary Particle Physics
The Standard Model of Elementary The Standard Model of Elementary Particle PhysicsParticle Physics
•
Matter consists of half integral spin fermions. The strongly interacting fermions are called quarks. The fermions with only electroweak interactions are called leptons. The uncharged leptons are called neutrinos.
•
The forces are carried by integral spin bosons. The strong force
is carried by 8 gluons (g), the electromagnetic force by the photon (γ), and the weak interaction by the W+
Zo
and W-. The g and γ
are massless, while the W and Z have ~ 80, 91 GeV
mass. The postulated Higgs boson is a scalar.
J = 1 g,γ, W+,Zo,W- Force Carriers
J = 1/2
u
d
c
s
t
b
e
νe
μ
νμ
τ
ντ
Q/e=
2/3
-1/3
1
0
Quarks
Leptons
HJ= 0
LPC Lectures, Feb., 2010 6
Fundamental Forces -
Strong Fundamental Forces Fundamental Forces --
Strong Strong
2 / 4 ~ 0.12( ) , ~ 0.2( ) 0
3 3 1 8, 3 3 3 1 8 8 10
s s
s
s
gGeV
α παα
=Λ → ∞ Λ∞ →
⊗ = ⊕ ⊗ ⊗ = + + +
Strong interactions : quarks carry color as do gluons. Because of this non-Abelian
property the strong coupling diverges at low mass scales and vanishes at high mass scales. The latter property makes perturbative
calculation in p-p
possible. There are 3 low mass quark flavors ( u, d, s) that bind into the observed low mass mesons and baryons in SU(3) multiplets.
LPC Lectures, Feb., 2010 7
Forces -
GravityForces Forces --
GravityGravity•Gravitational coupling constant is not dimensionless as in EM, weak and strong. Coupling is universal, however as in EM, e. There are non-Abelian
features –
“gravity
gravitates”
-> non-linear GR.
•
Gravity becomes strong only at a very high mass scale•
Very bad high energy behavior. Not
renormalizable. Impossible for 4-D point particles -> strings, extra dimensions?.
GeVxM
cMGNG19
2
103.1~
4/1.0~ hπα =
LPC Lectures, Feb., 2010 8
Forces -
Weak InteractionsForces Forces --
Weak InteractionsWeak Interactions•Fermi theory –
a universal coupling G between 4
fermions. Use muon
lifetime to find value for G. G is not dimensionless.•[G] –
1/M2
.
Low energy weak interactions grow rapidly with mass scale.
•
Bad high energy behavior. Violates unitarity
at a few 100 GeV
CM energy
πννσ /)( 2sGee =+→+
Gs
s
/2
/42
π
ππσ
<
=< D
LPC Lectures, Feb., 2010 9
Electro -
Weak UnificationElectro Electro --
Weak UnificationWeak Unification•In the 1980’s we found that weak interactions only appear to be weak at low energies.
•At energies above the W and Z mass the electromagnetic and weak forces are ~ equal. The coupling constants are ~ equal and the forces are unified.
8( ) / ( ) ~ 3 10o xμπ γ γ π μ ν+ +Γ → + Γ → +
2 2/W Wg M
2 2 2
2 2 /
1/ , 1/( )/ , /
sin
rW
W W
q q me r g e re g θ
−
+
=
D
LPC Lectures, Feb., 2010 10
Weak Interactions -
IIWeak Interactions Weak Interactions --
IIII•Partially solved by having G arise from a coupling constant (dimensionless, universal) and a propagator for a massive gauge boson
•This is not enough to preserve unitarity. W+W scattering diverges badly. S wave scattering amplitude violates unitarity
at a mass scale ~ 1
TeV
-> hence the LHC. What is EWSB?
2
2
2/
30/1~4/
sin
WW
WW
WW
MG
g
eg
πα
πα
θ
=
=
=
2( ) ~ 3 /16
4 / 3 ~ 1o W W
W W
W W W W s M
M s M TeV
α
α
Α + → +
= <
LPC Lectures, Feb., 2010 11
Strong and Weak are non-Abelian, Photon is Uncharged
Strong and Weak are nonStrong and Weak are non--AbelianAbelian, , Photon is UnchargedPhoton is Uncharged
2 2 2,E P M P P Mμμ= + ⋅ =
2( ) Mφ φ φφ= ∂ ∂ −l
To describe quantum fields we will use ψ for fermion (J = ½) fields, φ for scalar (J = 0)fields, and ϕ for vector (J = 1) gauge fields. For masses, m is used for fermions and M forbosons.
2
( )( ) ( )( )~ ( ) ,I
D Dg g
ϕ ϕ ϕ ϕ
ϕ ϕϕ ϕϕϕϕ
∂ ∂ →
∂l
Pr
by AePrr
−
μμμμ ieAD −∂=→∂
ggggggg, ZWWWW −+−+ ,γ −+−+−−+−+ WWWWZZWWZWWWW ,,, γγγ
Classical
Lagrangian
density
Classical gauge replacement
Quantum gauge replacement
LPC Lectures, Feb., 2010 12
WW Cross Section at LEPWW Cross Section at LEPWW Cross Section at LEP
COMPHEP point shown. Proof that the WWZ triple gauge boson coupling is needed. The LEP result has established the non-
Abelian
nature of the EW coupling of vector bosons.
LPC Lectures, Feb., 2010 13
ZZ at LEPZZ at LEPZZ at LEP
SM has only the single Feynman diagram. There are no relevant triple or quartic
couplings. Use the data to set limits on couplings beyond the SM.
LPC Lectures, Feb., 2010 14
Higgs Width -
WW + ZZHiggs Width Higgs Width --
WW + ZZWW + ZZ
Higgs decays to V V have widths Γ
~ M3
Try this as a COMPHEP example ?
Note that Higgs width ~ Mass at 1 TeV
-> unitarity
violation if Higgs mass is too large.
LPC Lectures, Feb., 2010 15
A Few Unresolved Fundamental Questions in HEP
A Few Unresolved Fundamental A Few Unresolved Fundamental Questions in HEPQuestions in HEP
•
How do the Z and W acquire mass and not the photon?
•
What is MH
and how do we measure it?•
Why are the known mass scales so different? ΛQCD
~ 0.2 GeV
<< EW <φ> ~ 246 GeV
<< MGUT
~ 1016
GeV
<< MPL
~ 1019
GeV•
Why is charge quantized?
•
Why is matter (protons) ~ stable?•
Why is the Universe made of matter?
•
What is “dark matter”
made of? Dark energy?•
Why is the cosmological constant small?
•
How does gravity fit in with the strong, electromagnetic and weak forces? Are there extra dimensions in the Universe, as yet unobserved?
LPC Lectures, Feb., 2010 16
Why the LHC ?Why the LHC ?Why the LHC ?
Higher energy means larger mass –
up to the TeV
mass scale where we know new physics must appear. LHC experimental designs follows from the plan to find the SM Higgs boson.
LPC Lectures, Feb., 2010 18
CERN SiteCERN SiteCERN Site
Lake GenevaLake GenevaLarge Hadron
Collider
27 km circumferenceLarge Large HadronHadron
ColliderCollider
27 km circumference27 km circumference
CMSCMS
ATLASATLAS
LHCbLHCb
ALICEALICE
LPC Lectures, Feb., 2010 19
LHC Accelerator -
DipolesLHC Accelerator LHC Accelerator --
DipolesDipoles
To reach the required energy in the existing tunnel, the dipoles operate at 8.3 T & 1.9 K in superfluid
helium. That makes the LHC the coldest extended place in the entire universe
wrt
Tevatron
(USA)Energy
x 7 luminosity x 20
LPC Lectures, Feb., 2010 20
Detection of Fundamental Particles
Detection of Fundamental Detection of Fundamental ParticlesParticles
Particletype
Tracking ECAL HCAL Muon
γ
e
μ
Jet
Etmiss
EM force
(Bremm
+ pair )
leptons
(ionize)
q, g
ν
LPC Lectures, Feb., 2010 21
The Large LHC ExperimentsThe Large LHC ExperimentsThe Large LHC Experiments
LPC Lectures, Feb., 2010 22
Cosmic Ray CommissioningCosmic Ray CommissioningCosmic Ray Commissioning
Both CMS and ATLAS have taken several 100 million cosmic ray events in order to align and calibrate the detectors while awaiting the LHC collisions.
LPC Lectures, Feb., 2010 24
Cosmic Muon
-
SpectraCosmic Cosmic MuonMuon
--
SpectraSpectra
Magnet test: alignment of the muon
system. Movement in 3.8 T field tracked. Checked to be “elastic”. Extract charge ratio for cosmic rays.
LPC Lectures, Feb., 2010 25
2008 First Events: Collimators Closed
2008 First Events: Collimators 2008 First Events: Collimators ClosedClosed
~2.109
protons on collimator ~150 m upstream of CMSECAL-
pink; HB,HE -
light blue; HO,HF -
dark blue; Muon
DT -
green; Tracker Off
LPC Lectures, Feb., 2010 27
2009 -
Start to Rediscover the SM
2009 2009 --
Start to Rediscover the Start to Rediscover the SMSM
L for 1 month run (106
sec)
Integrated L Trigger Process Comments
1023 100 mb-1 NoneσI
~ 50 mbInelasticnon-diff
Input to tweak Pythia
1024 1 μb-1 Setup Jet Inelasticnon-diff
Calib
in azimuth
1025 10 μb-1 Jetσ(gg) ~ 90 μbσ(ggg) ~ 6 μb
g+g
-> g+gg+g
-> g+g+gEstablish JJ
cross section
1026 100 μb-1 Jet g+g
-> g+gg+g
-> g+g+gDijet balance for polar angle –
Establish MET
1027 1 nb-1 JetSetup Photonσ(qγ) ~ 20 nb
g+g
-> g+gg+g
-> g+g+gq+g
-> q+γ
Dijet masses > 2 TeV, start discovery search.J+γ
calib
LPC Lectures, Feb., 2010 28
Kinematics -
RapidityKinematics Kinematics --
RapidityRapidityOne Body Phase Space
NR
φddPPdPdPdPPd TT||2 =Ω=
r
( ) EPdmPPd /224r
=−δ( )2
TPdydπ=EdPdy /||=
Relativistic
6.9,7.7,14,2@
,0max
cosh
max
222
=
=+=
=
yTeVpp
momentumbeamPatyPmm
ymE
T
TT
T
Rapidity
If transverse momentum is limited by dynamics, expect a uniform distribution in y
Kinematically
allowed range in y of a proton with PT
=0
LPC Lectures, Feb., 2010 29
Rapidity “Plateau”Rapidity Rapidity ““PlateauPlateau””Monte Carlo results are from COMPHEP -
running under Windows or Linux
Region around y=0 (90 degrees) has a “plateau”
with width Δy ~ 6 for LHC
LHC
LPC Lectures, Feb., 2010 30
Rapidity Plateau -
TevatronRapidity Plateau Rapidity Plateau --
TevatronTevatron
Existing data exhibits a plateau in rapidity.
LPC Lectures, Feb., 2010 31
Minbias
Rapidity DensityMinbiasMinbias
Rapidity DensityRapidity Density
Using data from 0.2 to 1.8 TeV
to
extrapolate the plateau rapidity density. For all pions
expect
Note –
2x extrapolation from 0.9 TeV
1/ ( / ) ~ 9o
d dρ σ σ η
π π π+ −
=
= =
LPC Lectures, Feb., 2010 32
Charged Particle RapidityCharged Particle RapidityCharged Particle Rapidity
LPC Lectures, Feb., 2010 33
Minimum Bias EventsMinimum Bias EventsMinimum Bias Events
Use dE/dx
in the CMS tracking system to do particle identification. Extract the charged particle cross section vs. particle type as a function of y and Pt
Useful for overlap to simulate high luminosity pileup. Must tune Monte Carlo models, e.g. for triggering.
LPC Lectures, Feb., 2010 34
Minbias
–
Pt DataMinbiasMinbias
––
Pt DataPt Data
Extrapolations of the Pt distribution and average values.
Expect <Pt> ~ 0.65Note the factor ~ 100 drop in single tracks (tracker alignment) from 14 ->0.9 TeV
for Pt = 6 GeV
LPC Lectures, Feb., 2010 35
First Data, 0.9 TeV, ~5 First Data, 0.9 First Data, 0.9 TeVTeV, ~5 , ~5 1bμ −
LPC Lectures, Feb., 2010 36
The Underlying EventThe Underlying EventThe Underlying Event
Extrapolation of the UE is uncertain. The UE is crucial for trigger strategy –
e.g. lepton isolation. Must tune the CMS Monte Carlo to have a valid representation of the UE and the minbias
pileup.
LPC Lectures, Feb., 2010 37
s Quark Secondary Verticess Quark Secondary Verticess Quark Secondary Vertices
LPC Lectures, Feb., 2010 38
Tracker dE/dx
for K, pTracker Tracker dE/dxdE/dx
for K, pfor K, p
CMS Preliminary CMS Preliminary 20092009
√√s=900GeVs=900GeV
(GeV/c)
LPC Lectures, Feb., 2010 39
Minbias
Pions
and ECALMinbiasMinbias
PionsPions
and ECALand ECAL
~ 0.14 /~ ~ 14 / ( )
o
GeV Pds R cm P GeV
π
π
π γ γθ
θ
→ +
Use charged pions
at moderate Pt to start tracker alignment in 2009 and start in situ HCAL. Neutral pions
can be used for ECAL.
γ
γπo
LPC Lectures, Feb., 2010 41
Jets at 0.9 TeVJets at 0.9 Jets at 0.9 TeVTeV
First seem SM “objects”
are the strongly produced Jets.
LPC Lectures, Feb., 2010 42
“Back to Back Jets”““Back to Back JetsBack to Back Jets””
Start to establish jet resolution by comparing Pt of the 2 jets
LPC Lectures, Feb., 2010 43
Lepton Candidates -
eLepton Candidates Lepton Candidates --
ee
With the luminosity taken at 0.9 and 2.4 TeV
in 2009 one expects only a few leptons from b Jet semi-leptonic
decays. Can start to debug “b tagging”
and electron and muon
id (muons
from CRAFT in place already).
LPC Lectures, Feb., 2010 45
Parton and Hadron
DynamicsParton and Parton and HadronHadron
DynamicsDynamicsFor large ET
, or short distances, the impulse approximation means that quantum effects can be ignored. The proton can be treated as containing partons
defined by distribution functions. f(x) is the probability distribution to find a parton
with momentum fraction x.
LPC Lectures, Feb., 2010 46
Parton Distribution Functions (PDF)
Parton Distribution Functions Parton Distribution Functions (PDF)(PDF)
The LHC data will probe regions of the distribution functions which are not yet explored. It is important to have a reliable set of verified PDF in order to model new physics and SM backgrounds.
LPC Lectures, Feb., 2010 47
p-p
Collisions -Valence?pp--pp
Collisions Collisions --Valence?Valence?
Valence dominates quarks for x > 0.04. Sea dominates at low x for quarks.
Gluons dominate all quarks for x < 0.2.
LPC Lectures, Feb., 2010 48
2-->2 Formation Kinematics22---->2 Formation Kinematics>2 Formation Kinematics
θθ
βγ
τ
τ
tan/1sinhsin/1cosh
:0/,/
)/ln(2~,)/(~,sinh
cosh
/0
,/
,/2
222
||
21
212
21
||
==
===
+=
Δ=
=
===⇒=
=−==
=
yy
mEPmE
Pmm
MsyesMxymP
ymE
sMxxx
xxxsMxx
sPx
TT
yT
T
E.g. for top quark pairs at the Tevatron, M ~ 2Mt ~ 350 GeV. <x> ~ √τ~350/2000 ~ 0.18 -> valence quarks.
x1 x2
2
2 2 2 21 2 1 2
~ 4~ [( ) ( ) ]
s PM P x x x x+ − −
LPC Lectures, Feb., 2010 49
Hadronic
Cross SectionsHadronicHadronic
Cross SectionsCross Sections
( ) )4321(ˆ)()(/
)4321(ˆ)()(//ˆ
/ˆ)4321(ˆ)()(ˆ
210
2211
221
212211
+→+=
+→+===
==+→+==
= στττσ
στστ
τσσσ
dfCfdydd
dyddxfxCfdsMss
dydsdysddxdxddxdxxfxCfdPPd
y
BA
To form the system need x1
from A and x2
from B picked out of probability distributions with the joint probability PA
PB
to form a system of mass M moving with momentum fraction x. C is a color factor (later). On the plateau, the cross section is Δσ
~ (dσ/dy)y=0
Δy. The value of Δy varies only slowly with mass ~ ln(1/M)
LPC Lectures, Feb., 2010 50
Pointlike
Parton Cross Sections
PointlikePointlike
Parton Cross Parton Cross SectionsSections
Point-like cross sections for parton - parton scattering. The entries have the generic dependence already factored out. At large transverse momenta, or scattering angles near 90 degrees (y ~ 0),
the remaining factors are dimensionless numbers of order one.
Process 2A Value at θ = π⁄2 q q q q′ ′+ → + 2 2 24 [ ] /
9s u t+
2.22
q q q q+ → + 2 2 2 2 2 2 24 8[( ) / ( ) / ] ( / )
9 27s u t s t u s ut+ + + −
3.26
q q q q′ ′+ → + 2 2 24 [ ] /9
t u s+ 0.22
q q q q+ → + 2 2 2 2 2 2 24 8[( ) / ( ) / ] ( / )9 27
s u t t u s u st+ + + − 2.59
q q g g+ → + 2 2 2 2 232 8[ ] / [ ] /27 3
t u tu t u s+ − + 1.04
g g q q+ → + 2 2 2 2 21 3[ ] / [ ] /6 8
t u tu t u s+ − + 0.15
g q g q+ → + 2 2 2 2 24 [ ] / [ ] /
9s u su u s t− + + +
6.11
g g g g+ → + 2 2 29 [3 / / / ]
2tu s su t st u− − −
30.4
q q gγ+ → + 2 28 [ ] /9
t u tu+
g q qγ+ → + 2 21[ ] /
3s u su− +
Pointlike
partons
have Rutherford like behavior
σ
~ π(α1
α2
)|A|2/s
s,t,u
are Mandelstam variables. |A|2
~ 1 at y=0.
LPC Lectures, Feb., 2010 51
2-->2 and 2-->1 Cross Sections
22---->2 and 2>2 and 2---->1 Cross >1 Cross SectionsSections
( ) [ ] ( )
( ) [ ]
31 20
1 24 2
0 1 2 1 2
2
2
21 20
2 2 :ˆ ˆ/ 2 ( ) ( )
ˆ ˆ/
( / ) ~ [ ( ) ( )] ( )
2 1:ˆ 4 (2 1),
ˆ ˆ (2 1)( / ), int
/ ( ) ( )
y x
y x
y x
M d dydM C xf x xf x d s
d s
M d dydM C xf x xf x
J partial wave unitarity
ds J M egrate over narrow width
M d dy C xf x xf x
τ
τ
σ σ
σ πα α
σ πα α
σ π
σ π
σ
= =
= =
=
→
=
≈
→
< +
= + Γ
=
∫D
( ) [ ]
2
12
2 21 2 120
(2 1) /
/ ~ " "
/ ( ) ( ) (2 1)
ff
y x
J M
M
M d dy C xf x xf x J
τ
τ
π
α
σ π α
=
= =
⎡ ⎤Γ +⎣ ⎦Γ
⎡ ⎤= +⎣ ⎦
“scaling”
behavior –
depends only on τ
and not M and s separately
LPC Lectures, Feb., 2010 52
2--> 2 Kinematics -
“Decays”22----> 2 Kinematics > 2 Kinematics --
““DecaysDecays””
y
y
esMx
yyyesMx−=
+==
]/[
2/)(,]/[
2
431
x1 x2 x,y,M
y3
, y4 y*, θ*
Formation System Decay CM Decay
The measured values of y3
, y4 and ET
allow one to solve for the initial state x1
and x2 and the c.m. decay angle.3 4ˆ ( ) / 2
ˆ ˆcos tanh( )
y y y
yθ
= −
=
LPC Lectures, Feb., 2010 53
CM Energy and Discovery “Reach”
CM Energy and Discovery CM Energy and Discovery ““ReachReach””
For masses below ~ 1 TeV
the loss of luminosity of the fundamental interactions is modest in going from 10 to 14 TeV.
LPC Lectures, Feb., 2010 54
2010 -
Typical Statistics for a 10 TeV
Run
2010 2010 --
Typical Statistics for a Typical Statistics for a 10 10 TeVTeV
RunRun
Assume 200 pb-1, include acceptance, initial reconstruction and id efficiency
Establish Standard Model cross sections and distributions
Log ~ 200 pb-1
at 10 TeV
in 2010. This should be reliable data taking without Physics penalty for masses < 1 TeV.
Fir 1 /fb
~ scales ( 5 x ) the factor in parton
luminosity from 10 -> 7 TeV
min bias 2 x1013
Jet Et>25 6 x 1011
Jet Et>140 6 x 107
γ+Jet
Et>20 6 x 107
W ->lν 600,000
Z -> ll 60,000
tt-> lν4q 2000
LPC Lectures, Feb., 2010 55
Problems -
IProblems Problems --
II
1.
Download Calchep. Read the Users manual.
2.
Compute g+g->g+g
at low Pt.3.
Compute e+E->W+W and compare to LEP data.
LPC Lectures, Feb., 2010 56
Hand EstimatesHand EstimatesHand Estimates
0
2 ' 30
3
4
8
'
~ /~ ln(1/ )
~ ( / )
( / ) ( )(2 1)[ ( ) ( )] /
~ 1.8 (1 )
~ 0.7 (1 )
~ 0.2(1 )
( ) ~ / 4~ 2( 2 )
y
y
v
v
s
W
v v s
x M sy x
d dy y
d dy q q M J xf x xf x M
xu x x
xd x x
xq xq x
M q q MPDF xu xq xd xq xq xq
σ σ
σ π
α
=
=
ΔΔ
= Γ + → +
−
−
= −
Γ → ++ +
Just to get started make tree level LO hand calculations for a 2 -> 1 DY process.x is the minimum value, assume a plateau cross section and a plateau width. Take simple formula for valence and sea quark distributions. Assume EW coupling and width
LPC Lectures, Feb., 2010 57
Cross Sections -
EstimatedCross Sections Cross Sections --
EstimatedEstimated
Note that valence quarks dominate over sea for masses above ~ 1 TeV. Line is 1/M2
scaling –
not too far off simply extrapolating for inclusive W production
LPC Lectures, Feb., 2010 58
Estimate vs
Theory @ NLOEstimate Estimate vsvs
Theory @ NLOTheory @ NLO
Estimate assuming allowed EW transitions to
Width in formation assumed to be SM. For decays, SM EW gives a ¼
BR of W’
-> t+b
and a 1/9 BR of W -> u + v.
At 1 TeV
( ~ CDF limit ) LHC cross section into muon
+ MET + 2 b jets is 1.7 pb. Therefore, this search is “early physics”.
3( ) ( )ud cs tb eν μν τν+ + + + +
top related