IntMasterclasses@LHC
First ideas of physics concepts
for the LHC masterclass measurements
Michael Kobel Konrad Jende
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Michael Kobel Konrad Jende
Concepts
W-Path
Structure of the Proton
New Physics with the LHC
Z-Path
Lepton Universality
New Physics with the LHC
1. Concepts of the Measurement
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The aim: Developing concepts that reflect the true motivation for the LHC
(New physics) and allow to get deep insights (fundamental measurements).
Michael Kobel Konrad Jende
The W-Path Concept
1. Introduction of the W: β decay of the neutron
(learning objective: missing energy Neutrino)
2. Measurement on preselected events with missing energy:
Identify and count #leptons (e or mu) and #jets
Determine for single W (+Jets) the ratio
(deduce insight about: structure of the proton)
Search for double W candidates via WW lv lv
reduce tt Wb Wb lv Jet lv Jet requiring 0 Jets
(deduce insight about: rare processes, backgrounds, new physics)
1. The W-Path
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W-Path
Single W + Jets (Structure of the Proton)
WW-Pairs (Search for the
Higgs)
leptons charged negatively ofnumber
leptons charged positively ofnumber :R
expectations for LHC in 2010
Michael Kobel Konrad Jende4
number of expected events during the LHC physics run in 2010(ATLAS; 100pb-1; 7TeV)
Njets
category I: one lepton category II: two leptons
e+ν, µ+ν e-ν, µ-ν e+νe-ν, µ+νµ-νe+νµ-ν, µ+νe-ν
number of expected events in
2010
0 W → lν: 285000tt→ lν+Jets: 2
W → lν: 165000tt→ lν+Jets: 2
H → WW → lνlν: ~1?WW → lνlν : ~1
tt → lνlν + Jets: ~1
1 W → lν: 95000tt→ lν+Jets: 30
W → lν: 55000tt→ lν+Jets: 30
H → WW → lνlν: <1WW +Jets→ lνlν + Jets: 1
tt → lνlν + Jets: 15
>= 2 W → lν: 38000tt→ lν+Jets: 2500
W → lν: 22000tt→ lν+Jets: 2500
H → WW → lνlν: ~1?WW +Jets→ lνlν + Jets: 1
tt → lνlν + Jets: 1000
Sample preparation for students
Michael Kobel Konrad Jende
• Sample preparation (by us!) using missing energy cut eliminate Z+Jets 1(+1 missed) leptons + Jets reduce QCD (minimum bias), but not completely
• Tasks for students:• identify and count isolated leptons (electrons and myons)
• reject events w/o leptons (QCD background, leptons in Jets etc.)• be aware of electric charges
• 1 lepton: count charges separately• 2 leptons: reject same-sign (here SUSY extension possible)
• >3 leptons: reject (here SUSY extension possible)
• count number of jets• enhance new physics (Higgs) for 2 leptons requiring 0 Jets
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CERN COURIER, Apr 1 2003
Deeper background info (mostly for us)(single W)
Michael Kobel Konrad Jende
Charge ratio in events with 1 Lepton & missing Energy
Compton-Process:
Drell-Yan-Process:
Result from processes above, if only valence quarks u,d would be involved: 2:1 (2 u- and 1 d-quark in proton)
Washed out - by above processes with see quarks u, d- by gluon fusion:
g
u
d
W+
leptons charged negativelyof numberleptons charged positivelyof number
:R
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dldWug l uluWdg l
llWud
CERN COURIER, Apr 1 2003
JetslWqqgg l
llWdu
Michael Kobel Konrad Jende
Reducing the washout...
Jana Schaarschmidt, TU Dresden
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R+- as a function of the lepton transverse momentum R+- as a function of η
Jana Schaarschmidt, TU Dresden
Figure 1 Figure 2
…possible by rejecting events with leptons above pt > 20 GeV in sample preparation
Michael Kobel Konrad Jende
njetsllbbWWttgg ll
Jana Schaarschmidt, TU Dresden
Jan Schumacher, TU Dresden
JetsllqqWWqq ll
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Figure 3 Figure 4
Deeper background info (WW pairs)
Distribution of Njets „QCD+EWeak WW“ „ttbar“
Possible after some years or now with simulated events
Michael Kobel Konrad Jende
Search for Higgs via excess over known Eweak process
• Compare observed number of lvlv with expectation from WW (Excess maybe Higgs?)• Check additional information: angle Dfℓℓ between leptons Higgs would have low values
CERN-OPEN-2008-020 (ATLAS, Higgs Boson in Gluon Fusion Higgs Signal not to scale!)
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Michael Kobel Konrad Jende
2. The Z-Path
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Z-PathLepton
Universality
Search for New Physics
1. Introduction of the Z: heaviest messenger particle
(learning objective: couples to all fundamental particles,
making it a tool to study their properties)
2. Measurement on preselected events with at least 1 lepton:
Identify and count #lepton pairs (ee or mumu) and #jets(?)
Determine for single Z (+Jets) the ratio
(deduce insight about: lepton universality)
Search for double Z candidates via ZZ 4l
reduce tt Wb Wb lv l(Jet) lv l(Jet) requiring 0 Jets or no Emiss
(deduce insight about: rare processes, backgrounds)
ee Zofnumber
Zofnumber :/
eR
expectations for LHC in 2010
Michael Kobel Konrad Jende11
number of expected events during the LHC physics run in 2010(ATLAS; 100pb-1; 7TeV)
Njets
category I: two lepton category II: four leptons
e+ e- µ+µ- e+ e-e+ e-, µ+µ-µ+µ- e+e-µ+µ-
number of expected events in
2010
0 Z → ll: 14000tt→ ll +X: 1
Z → ll: 14000tt→ ll+X: 1
H → ZZ → 4l: <1ZZ → 4l: ~1
tt → lνlν + 2l from Jets: ~1(?) 1 Z → ll: 6000
tt→ ll +X: 4Z → ll: 6000tt→ ll+X : 4
>= 2 Z → ll: 2500tt→ ll + X: 250
Z → ll: 2500tt→ ll + X: 250
Sample preparation for students
Michael Kobel Konrad Jende
• Sample preparation (by us!) using 1 identified lepton reduce QCD (minimum bias), but not completely
still a lot of W + Jets background• Tasks for students:• identify and find lepton pairs with opposite charge
• reject events w 1 lepton (W background) or same-sign pairs• be aware of lepton flavor (check universality)
• 1 lepton pair: count flavors separately• 2 lepton pairs: count number of jets? Require no Emiss?
for rejecting ttbar and enhancing new physics (Higgs)• undecided
• build 2-lepton mass Z mass?• maybe build 4-lepton mass Higgs mass ?
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CERN COURIER, Apr 1 2003
Michael Kobel Konrad Jende
Invariant masses
Tasks (how?): - Determine the invariant mass of each di-lepton system- Determine the invariant mass of the 4-lepton system
CERN-OPEN-2008-020 (Di-muon invariant mass distribution in the Z->μμ channel)
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