IntMasterclasses@LHC First ideas of physics concepts for the LHC masterclass measurements Michael...

IntMasterclasses@LHC

First ideas of physics concepts

for the LHC masterclass measurements

Michael Kobel Konrad Jende

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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

2

The aim: Developing concepts that reflect the true motivation for the LHC

(New physics) and allow to get deep insights (fundamental measurements).


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

3

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


• 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)


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


JetslWqqgg l

llWdu


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


Figure 1 Figure 2

…possible by rejecting events with leptons above pt > 20 GeV in sample preparation


njetsllbbWWttgg ll


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


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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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


• 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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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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IntMasterclasses@LHC First ideas of physics concepts for the LHC masterclass measurements Michael...

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