Thomas Hebbeker RWTH part II WS 2003/20042 b jets + leptons/jets/missing energy W →qq,l ... Run II...
Transcript of Thomas Hebbeker RWTH part II WS 2003/20042 b jets + leptons/jets/missing energy W →qq,l ... Run II...
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T.Hebbeker
p p
physics
Tevatron 2002
CMS 2007
UA1 1983
LHC 2008 ? 1.0
part II
Thomas HebbekerRWTH
WS 2003/2004
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T.Hebbeker
p p
physics
Part I Introduction
Part II Standard Model Physics
Part III Higgs
Part IV New PhenomenaReferences
• cross section calculation• QCD and jets• W and Z• charm and bottom• top
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T.HebbekerCross Section
Total inelasticcross section
Pointlike cross section
pp
2252 1010 cmfm −≈≈σ
2362
10 cms
−≈≤ασ
BACKGROUND
SIGNAL
strong
electroweak
p
p
Elastic cross section
strong, electromagnetic
Xsection relatively smallscattering angle tinyLUMINOSITY
LHCSignal / Background 1110−<
LUMINOSITY
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T.HebbekerStructure FunctionsMeasurements:
F2 , F3 ... in DIS
(n,p,elm.,weak, Q2-depend.)
valence, sea, gluons...
Fits/parametrisations:• CTEQ
• MRST
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T.HebbekerCross section calculation in pp
VdQsd F ),( 2σWanted:
Calculable:
Known:
VdQxxd ji
ijF ),,( 2σ
),( 2Qxf ii
kinematicalvariable
final state
sxx 21='s
),(),(),( 22
,
2
QxfQxfdxdxVdQsd
jjji
iijiF ∑∫=
σ
2Q
VdQxxd ji
ijF ),,( 2σ
Spectator jet
Q2 = („momentum transfer“)2
depends on final state
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T.HebbekerCross Sections
at Hadron
Colliders
Note:
may trade:
energy luminosity
Example:
In principle top discovery at SPS !
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Estimate of Xsection p p → W −X
Ansatz:
d u → W − (valence quarks)
σW (√
s) =∫ ∫
fd(x1) f u(x2) σdu(√
s′) dx1 dx2
s′ = x1 x2 s
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Structure Functions:
Rough parametrisation:
fd(x) =0.2
xfu(x) = 2 fd(x)
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Cross section (quark level):
σdu(√
s′) = σ0 ·
s Γ2W
(s′ − m2W )2 + m2
WΓ2W
σ0 =12π
m2W
·Γqq
ΓW
≈12π
m2W
·6
9≈
25
m2W
σdu(√
s′) ≈
25
m2W
·{
1 mW − ΓW /2 <√
s′ < mW + ΓW /20 else
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Calculate:
σW (√
s) = 25 · 0.2 · 0.4·1
m2W
·∫ 1
xmin2
1
x2
[∫ xmax1
xmin1
1
x1dx1
]dx2
xmin2 ≈
m2W
s
xmin1 =
(mW − ΓW /2)2
x2 sxmax
1 =(mW + ΓW /2)2
x2 s
σW (√
s) ≈ 25 · 0.2 · 0.4 ·1
m2W
·∫ 1
xmin2
1
x2
[2
ΓW
mW
]dx2
σW (√
s) = −4 ·1
m2W
·ΓW
mW
· lnm2
W
s
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Results:
1/GeV = 2 · 10−16 mmW = 80 GeVΓW = 2 GeV
σW (√
s) ≈ 4 nb · ln sm2
W
FERMILAB :σp(
√s) ≈ 25 nb
LHC(pp!) :σp(
√s) ≈ 40 nb
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T.HebbekerQCD = Quantum Chromodynamics
Gauge theory: • quarks with 3 colors (r,g,b)
• 8 gluons (color + anticolor r,g,b) SU(3)spin 1
spin 1/2
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T.Hebbekerself coupling, running, confinementnonabelian:
„Running“:
~ 1/distance
mesons and baryons „white“:
qqqqq
strongcoupling„constant“ Zm
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T.HebbekerHadronization = Fragmentation
time
„string“
String model:
QCD:
soft
uud
d
Hadronization: non-perturbative
need models!
jet(to be defined)
hadrons
g q
q
hadrons
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T.HebbekerCalculation of QCD processes
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T.HebbekerHigher Order Corrections
Often: higher order corrections to differential cross section
modeled by LO prediction and „K factor“ (typ. 1 ... 2)
can be large in particular for QCD processes!
LO = Leading Order
NLO = Next to Leading Order
Difficulties for p p reactions:
• parton densities and fragmentation functions depend on order!
• factorization scale, renormalization scale, fragmentation scale
(Q2 parton density) (Q2 hard process) ....
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T.Hebbekerjets
jets reveal hard processs (direction, energy)
experiment and theory must use the same language:
jets need to be defined: „jet algorithm“
parton (quark, gluon)
theory
Typical: 100 particles total
(14 TeV)
2-5 jets per event
hadrons
experiment
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T.Hebbeker
Jet ev
ents
eta
3.7
0.0
-3.7
-1.2
1.2
phi
0.0
2PI
ET GeV
55
Max: 52.4
CDF
D0
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T.Hebbekercone jets
potential problems: seed dependence, infrared sensitivity ...
several variations exist
Cone defined in projection, radius R = (typ = 0.7)
Isolated low energy particles are ignored
Sum of 4-momenta of objects inside cone = jet 4-momentum
ϕη , 22 )()( ϕη ∆+∆
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T.HebbekerkT jets Example:
... several variations exist
b) each cluster:
2,iTi pd =
22,
2, ),min( ijjTiTij Rppd ⋅=
a) list of hadrons = clusters
each pair of clusters:
c) minimum of
combine or remove from list)
d) iterate: goto b)
till list empty
iij dd ,
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T.HebbekerInclusive jet production
D0 1.8 TeV cone radius 0.7
)( 3
sO α
Conclusion: agreement with QCD over many orders of magnitude!
=NLO
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T.Hebbekermultijet events
Measurealphas fromrelative fraction of events with2,3,... jets
CDF 1.8 TeV
cone radius 0.7
Test QCD
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T.HebbekerSoft hadronic processes (LHC)
Elastic
(20 mb)
Inelastic
(80 mb)
(zero quantum numbers!)
diffractive (25 nb)
non-diffractive (55 nb)
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T.HebbekerDouble-Diffractive Event
D0„r
apid
ityga
p“
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T.HebbekerW and Z
measured at LEPreference for W mass measurement
• production cross section
• decay modes
• W mass
• W width
• (W polarization in top decays)
• ...
WWZ
W
mm
θθ 222
sin1cos −==
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T.HebbekerW and Z discoveryDiscovery:
UA1, UA2
(1983)
Precision measurement
Z mass at LEP:
91.1876 +- 0.0021 GeV
νeW →
eeZ →
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T.HebbekerW,Z: production and decay
W decay probability:
)(~ 22AVC ggNBr +
20%
70%
3%
3%
3%eeµµττ
bbccssdduu ++++νν
CNBr ~
33%
33%
11%
11%
11%νeνµντudcs
Z decay probability:
Clearsignature
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T.HebbekerW,Z: mass
D0
1.8
TeV
Tevatron combined: GeV059.0456.80 ±GeV015.0±LHC:
LEP: GeV042.0±Run I
)cos1(22ν
ν φlTlTT EEM −=
)cos1(2 12212 φ−= ll EEM
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T.HebbekerW: width
... difficult...
GeV047.0160.2 ±
D0 1.8 TeV
Monte Carlo
Tevatron combined: (indirect+direct)
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T.HebbekerW,Z: production cross section
theory theory
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T.Hebbekerpp-physics with charm and bottom
cross section huge !
• cross section
• new mesons/baryons/hybrids/... ?
• hadron masses
• hadron lifetimes
• branching fractions (rare decays ?)
• B0 mixing
• CP violaton
s
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T.HebbekerExample: D meson masses
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T.HebbekerReconstruction of decay vertices
D0
bbZ →
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T.HebbekerExample:
decay length
L
)/(βγL
decay length:
Lab frame:
βγctL =
++ +→ KJB ψ/
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T.HebbekerTop Discovery
Fermilab, 1995 CDF, D0
m ~ 175 GeV
GeVpp 1800
CDF
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T.Hebbeker
)ln,(1sin1
2
2/1
HtWFW mmrGm
∆−⋅
=
θαπ
Top Physics• cross section
• decay modes
• top mass
• spin correlations
• ...
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T.HebbekerTop Identification
cross section small (at 2 TeV)
l
b
b
ν
p p
E T
jet jet
jet
ldecay:
production:
ttpp →
bWt→Signature:
2 b jets+ leptons/jets/missing energy
νlqqW ,→
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T.HebbekerTop event in D0
µ -
MTC
Jet 1
IP
SV
Jet 1
IP
SV
Jet 2
Run II(~ 100 events)
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T.Hebbeker
Top event in CDFRun II
(~ 100 events)
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T.HebbekerTop Pair Production
gg contributes
• 15% at 2 TeV
• 95% at 14 TeV
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T.HebbekerTop Mass
CDF
Run I
νbbqqltt→
GeV1.53.174 ±
Tevatron Run I
CDF + D0:
Using massconstraints
...νlW →
LHC: +- 1 GeV
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T.HebbekerTop Cross Section and Top Mass
cross section measurement = indirect mass determination!
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T.Hebbeker
Spin of top related to lepton direction in
due to parity violation!
Top quark lifetime
much shorter than „hadron formation time“
Spin Correlations - introduction
smG tF
t25
32 10528 −⋅≈≈π
τ
scfmh24103~/1 −⋅>τ
If is produced in a certain spin state, e.g.
spins of the two quarks are correlated!
lbWbt ν→→
01 Stt
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T.HebbekerTop Spin Correlations simulation
LHC
direction
lepton 1 direction lepton 2
ttqq →mostly
in
13 S
ttgg →mostly
in
01 S
(Tevatron)
(LHC)
can distinguish!
![Page 45: Thomas Hebbeker RWTH part II WS 2003/20042 b jets + leptons/jets/missing energy W →qq,l ... Run II (~ 100 events) Top Pair Production T.Hebbeker gg contributes •15% at 2 TeV •95%](https://reader034.fdocuments.in/reader034/viewer/2022052008/601d90529c1d8969cb3b1ef8/html5/thumbnails/45.jpg)
T.Hebbeker
p p
physics
Part I Introduction
Part II Standard Model Physics
Part III Higgs
Part IV New PhenomenaReferences
• cross section calculation• QCD and jets• W and Z• charm and bottom• top