First one-two years Physics at LHC

Workshop on LHC Physics

TIFR, September4-8,2006

Monoranjan GuchaitTIFR

CMS,ATLAS notes, talks from ICHEP06,

Many papers, review articles, presentations,

Home pages….

Compilation…

The LHC Experiment

Proton Proton Collsion

Center of Mass energy :14 TeV

Luminosity 1034cm-2s-1

New energy domain( ~8 times)

New luminosity domain(~100 times)

The LHC Experiment

• Physics Goals:

- Testing Standard Model at 14 TeV

Complete with Higgs discovery

- New Discovery? SUSY, Quantum Gravity…

- Anything else?

LHC Schedule

Machine and Experiments closed : 31 st August, 2007

First collisions at cm: 900 GeV with L ~ 1029cm-2s-1, November 2007. - Static run, mainly to debug machine and detectors - Commissioning run at Injection energy until end 2007, then shutdown.

First Collision at cm =14 TeV : Spring 2008 2808 X 2808 bunches, 25 ns bunch crossing,

Expected to achieve few fb-1 by the end of 2008

Interesting Physics….

Experimental Challenges• The total p-p cross section ~100 mb

• At design luminosity about 109 inelastic events/second

• Trigger should reduce this event no more than about 100 events/s for storage and analysis within an interval 25ns, needs a very efficient design of the readout and trigger systems.

Needs a good synchronization among different channels.. …………..many more

Computation.. And Computation 15petabyte(PB) per year, professing them and

making the information available to thousands of Physicists all round the world.

For Comparison: ALEPH: Total data 3.5 TB D0 1992-’96 stored 30 TB( “Farm” came up) LHC 15PB/year ( 1PB = 103TB) Model: Tiered structures, 100,000 processors multi-PB disk, tape

capacity(co-processors estimation 2004)

Pre-Collision Phase

First detector understanding before commisioning with real collision

Detector Alignment and Calibration

Both ATLAS and CMS has developed simulation studies in order to better understand how to use data.

On going Study.. In CMS this month there will be a Workshop to decide

the strategy for 2007 run.

CMS Detector

Initial Detectors • CMS will start without muon RPC in the region 1.6 < < 2.1• Fourth layer of the end cap muon chambers will be absent during

the pilot run• NO EE and pixel detector, but will be installed during the shut down

after the 2007 run----thinking the psossibility to install all these for new two months delay.

• ATLAS will start with two pixel layers (instead three) and without Transition Radiation Tracker in the region 2 <eta<2.4.

What about Trigger and DAQ: Initial L1 rate 50kHz(instead of 100) and 35 kHz(instead of 75) in ATLAS.

Performances Good muon identification and momentum Resolution over a wide range of momenta in the region || < 2.5 ( about 1%

at 100 GeV/C2).

Good charged particle momentum resolution (~ 1% at 100 GeV/c2) and rec. eff. in the inner tracker. Eff. b/tau tagging and triggering on taus

Good electromagnetic energy resolution,good diphoton,dielectron resolution(<1 %) wide geometric coverage(eta <2.5), measurement of the direction of photons and/or correct localization of the promary interaction vetext, pi0 rejection.

Good missing ET and dijet mass resolution with fine lateral segmentaion ( X φ < 0.1 X 0.1) in HCAL.

First Data• 1 fb-1(100 pb-1)= 6 months(few days) at L=1032cm-2sec-1

with 50% data taking efficiency a few 1/fb per experiment at the

end of 2008

W,Z events will be used for calibrationTop events also will be used to for JES,..

Calculations and tools

• For many of the interesting physics processes, higher order calculation exist, still there is a wish list..

Event Generators: PYTHIA, HERWIG,ISAJET

Physics process; ALPGEN,MC@NLO,MCFM,NLOJET++, Madgraph,Comphep….

Outline

SM at 14 TeV

- UE events studies

- Jet Studies

- W/Z studies

- PDF

- Early Top Physics

New Physics

- Zprime

- Higgs

- SUSY..

Cross sections

Min Bias and UE events

• MB events: Events collected with a trigger that is not very restrictive are referred as MB events.

• UE is everything else accompanying the hard scattering component, consists of “beam-beam remnants” and from particles arising from soft or semi-soft multiple interactions(MPI). UE receives contribution from

ISR and FSR

Hard Scattering

PT(hard)

Outgoing Parton

Outgoing Parton

Initial-State Radiation

Final-State Radiation

Hard Scattering

PT(hard)

Outgoing Parton

Outgoing Parton

Initial-State Radiation

Final-State Radiation

Proton AntiProton

Underlying Event Underlying Event

Proton AntiProton

Underlying Event Underlying Event

“Hard Scattering” Component

“Underlying Event”

TheTH

The UE is an unavoidable background to most collider observables, requires good understanding

MB and UE modeling

The Multiple parton interaction model extending pQCD to the soft regime, describe the physics of MB and UE

• MPI models are implemented in the general purpose simulation program lik

General purpose simulation programs PYTHIA, JIMMY, SHERPA, HERWIG are modeled for MB and UE.

Tunned with data from UA5 and Tevatron

Hard scattering events are having different topological structures in the -φ regions.

Regions sensitive to UE components of the interaction.

UE event studies :Jet Production

Charged Jet #1Direction

“Toward”

“Transverse” “Transverse”

“Away”

Charged Particle Correlations PT > 0.5 GeV/c || < 1

• Look at charged particle correlations in the azimuthal angle relative to the leading charged particle jet.

• Define || < 60o as “Toward”, 60o < || < 120o as “Transverse”, and || > 120o as “Away”.

• All 3 regions have the same size in - space, x = 2x120o = 4/3.

UE at CDF

Extrapolation to LHC

Example: top physics

Different UE models shift top mass by about ~ 5 GeVNeeds very good tunning!

Inclusive Jets

• The measurement of jet production cross section at LHC will provide a stringent test of pQCD at a regime which was not probed before so far.

• The first data will be used to provide systematics connected

to measurements.

QCD is a background to almost all New physics scenarios.

A high pT tails to inclusive jets are sensitive to new physics A bad estimations of errors may lead to fake as a new physics

Computed using NLOJET,CTEQ6.1

Different Sub processes

Jets at Tevatron

Uncertainties:JES ~10% for low pT and ~60% at High pT

Energy resolution below 10%, UE: -22% to 4%Hadronisation:13% to 4%

LHC:Statistical Errors

• Statistics is not a problem..

e.g for pT ~ 1 TeV, about 1%

for large pseudorapidty region

it is ~10% for L = 1fb-1

Assuming one month luminosity

@1032cm-2sec-1 and 40% trigger

efficiency

Theoretical Errors

Main Sources µR and µF

Parton distribution Function(PDF)

~10% for pT ~ 1 TeV

For PDF, mainly g(x), at low x,e.g. ~15% for pT =1 teV

Experimental Errors

• Main Source

- Jet Energy Scale(JES)

- Luminosity Measurements

- resolution, triggering efficiency

UE subtraction….

Detector effects:Jet Reconstruction

- R and ET threshold

- Calo Jet to Particle level jet,

jet Calibration 1% uncert. In JES→10% on σ(Jet)5% uncert. In JES→30% on σ(Jet)

Gamma+jet CalibrationDifferent available processes for calibration (/Z+jet, Wjj (from top decay))

Example:make use of the PT balance in +jets

Event selection: selection of events with isolated photons, no high-PT secondary jet, photon and jet well separated in the transverse plane (Et

isol < 5 GeV, ETjet2 < 20 GeV,

φγ,jet > 172°)

Trigger efficiencies included in the analysis,stat error smal (well below 1%) after 10 fb-1

The main systematics is due to non leading radiation effects, QCD backgrounds, gluon-light jet difference, etc.

W/Z at LHC

• LHC is a W and Z factory • For L=1/fb

σ(W→lν)~ 15 nb, ~107 events

σ(Z→ll) ~1.5nb, ~106 events

Theory cross section 2-4% accuracy

Mass, width, W/Z+jets

PDF constraining.

Detector Performances

ECAL calibration using Z→ee

Alignment using Z→µµ

Lepton identification

Luminosity measurements

W/Z at Tevatron

Very good agreement with theoryLuminosity error dominates ~5-6%

W/Z at LHC

σ(W→µν+X)=14700±7(stat)±485(syst)Systematic ~3.3% (dominated by theory)

σ(Z→µµ+X)=1160±2(stat)±27(syst.)heory)Systematic 2.3%( dominated by theory)

Theoretical prediction ~4%Luminosity measurement~6-7%

expected

Luminosity measurement

• Theory accuracy about 2-3%Strategy:I. Count the number of events within

some sets of cutsII. Compare against a theoretical

simulation subject to same cuts OR Take a MC and evaluate the

acceptance (A) of the cuts, to get the cross section

σ = 1/A N/Lum

Accuracy of the calculation dependence of accuracy of calculation A.

6-7% accuracy expected..

PDF

Parton Distribution Function

Proton StructureNeed to understand for testing SM and BSM

PDFs are determined by global analyses of dataFrom DIS,DY and jet production

Two major groups regularly update whenever new data available:MRS,CTEQ

ALL the above groups provide a way to estimate the error on the central PDF

LHAPDF : calculates the PDF uncertainties for any observables

Parton Distribution Function(PDF)

Proton Structure

Need to understandFor testing SM and BSM

very low x

X1,2=(M/14TeV)exp(±y)y:rapidity

Q=M, mass of the final state

Parton Distribution:HERA

HERA PDF: fair agreement

PDF: W/Z process

The experimental uncertainty small to

Distinguish the PDF sets.

PDF errors are sensitive to e rapidity

Distributions

ATLAS studies shows it is possible to distinguish different PDF if Exp. Uncertainty ~3-5% CTEQ61

MRST02 ZEUS02

CTEQ61 MRST02 ZEUS02

e- rapidity e+ rapidity

GeneratedGenerated

y

d(W

e

)/dy

y

d(W

e

)/dy

Reconstructed Reconstructed

W±→e±ν rapidity distributions

eWud

eWdu

Constraining PDF : ATLAS

ZEUS-PDF BEFORE including W data

e+ CTEQ6.1 pseudo-data

ZEUS-PDF AFTER including W data

W rapidity events, CTEQ6.1, ATLFAST, 4% syst err(by hand),100/pbUncertainties is reduced, error low x gluon by 50% are reduced

Top Physics

Early top Physics

• Top cross section ~840pb(1±5%(scale)+3%(pdf))• gg fusion : 90%• qq annhilation:10% For low L=1033cm-2sec-1, every 4 second one

“lepton+jet” event, and one second one top pair.

~ 0.1 m top events for L=1fb-1

Top mass and cross section

Top production is one of main SM background for most of the new physics signal. Top events can be used for estimating JES, b-tagging,

One lepton modeDilepton modeHadronic mode

J/psi mode

Top Physics: Dilepton mode

• Two OS lepton with pt>20GeV, at least two b-tagged jets with pt>30GeV,Etmiss>30GeV

• Upper cuts on the number of high pt jets.

• Backgrounds: Z+jets,

Top Physics: Single lepton mode

• Single muon trigger, at least one muon with pt > 20 GeV,

• Four non-overlapping jets with Et>30,

• Two of them b –jets• And the other two non b-tagged

jets• Etmiss>40GeV• Upper cuts on the multiplicity of

jets

tt → bWbW →bbqqµν

mt(semi-leptonic,1fb-1)=±0.7(stat.)±1.9(syst.)GeV/C2

Top Physics: Hadronic Final states

• Four Partonic jets, two b-jets, huge QCD backgrounds challenging

• Selection inclusive jet trigger, b-jet trigger,

• Events shape variables like centrality,aplanarity

• Used to supres the QCD backgrounds.

mt(semi-leptonic,1fb-1)=±0.6(stat.)±4.2(syst.)GeV/C2

tt → bWbW →bbqqqq

Top Physics: J/psi meson

• J/psi arises mainly from B quark fragmentation

• Reconstruction of J/psi gives significant information about b flight direction.

• Top reconstruction is done taking lepton from W decays and leptons from J/psi

• Rate is too low, Br ~ 10-5

• => 4500 events for 10/fb• Systematic uncert.

contributes:

mt=1.47 GeV/c2

Single top production

• Direct measurement of vtb2

• V-A structures,polarised top, Spin of top,good candidate

• Background for new physics• Coupling structures tWb, can

indicate some new physics

• Results: t-channel• Bg W+jets, • Signal events survived 7000 for

L=30/fb, S/B=3• Result s-channel:• Signal events 2050, S/B=0.15

tw channel:Bg top pairSignal events 4700 events,S/B~1/7

Top Physics: summaryCMS

• A combined top mass accuracy ~ 1GeV/C2

for 10-20/fb data will be feasible

Z’

Zprime:Very Easy to Discover• Additional Z’ boson predicted by

Superstring inspired, GUT, Dynamical Symmetry breaking

model, little Higgs.. Current limit >0.6-0.7 TeV Tevatron reach ~ 1 TeV pp →Z’ →µ+ µ-,

Main Dominant SM: DY

Z prime(contd.)

Large enough to find up tp ~1 TeV, for 0.1 /fb, signal as a mass peak, DY is very easily managable

New Discovery: SUSY

SUSY at TeV Scale, m~ 1 TeVLarge cross section

~10 events/day

Decision for ILC!!

SUSY Discovery

Understanding Etmiss is one of the Experimental Challenge!

Higgs?

Please See talk by A.NikitenkoLooks like difficult case for 1/fb

Is Tevatron a competitor?

Outlook• With first data 1-10/fb

• Detector Understanding..

• Measure charge particle multiplicity ( within few hours of data taking)

Measure QCD jet cross section ~ 30%

W/Z cross section.. Top signal with 100/pb and top

cross section and mass PDF constraining UE events ……..

Z’ prime studiesNew Discovery

Higgs!

International meetings in 2009Exciting news!