physics with cms

Paolo Meridiani - INFN Roma1 1

Physics with CMSPhysics with CMS

Paolo Meridiani (INFN Roma1)

http://www.roma1.infn.it/main/mappa_sito.html


OutlineOutline

Lecture 1 Is SM satisfactory? Open questions in the SM? LHC: the answer to unanswered questions? CMS Detector: a challenging detector for a challenging machine CMS Commissioning: how much time is required to make it work?

Lecture 2 CMS early physics: what should be done at the beginning? SM physics with CMS: known SM physics can be done better in

CMS? Higgs Physics with CMS: if it’s there we will catch it!

Lecture 3 Beyond the SM physics at CMS: hunting new theories



How 2008 should look like...

How 2008 should look like...



What we should do at the begin?

What we should do at the begin?

New territory to be explored. 14 TeV is just an extrapolation from what we already know...

Pre-operations Synchronization (all subdetectors) Pre-Alignment (Tk + Muon) Pre-calibration (HCAL & ECAL)

Next triggering on collision events Next high rate events: from 10 mb to 1b

Minbias Jets, dijet imbalance Direct photons

Then from b to nb W, Z, W/Z + jets, diphoton, dilepton



Pre-operationsPre-operations

Synchronization Set relative timings to better than 1ns using lasers and pulsers

checking with cosmic muons (should be achieved in cosmic global runs)

Pre-calibration ECAL: intercalibration with cosmics (1.5%)+ TB intercalibrated SM

(one quarter of EB at 0.3%) HCAL: radioactive sources + TB 5%

Pre-alignment Muon: Alignment with cosmic muons + optical alignement system

(also MB w.r.t ME). Track motion when field on (already tested in Magnet test 2006)

Tracker: survey + optical alignment + cosmic muons



The collisions start...The collisions start...

We should first understand the trigger table



How to demonstrate that we are looking at collisions?

How to demonstrate that we are looking at collisions?

First thing than one wants to do is to demonstrate that trigger is selecting real beam-beam interactions. How to do this?

Look at position of the reconstructed vertex. z position will give information on the bunch lenght. RMS should

be compatible with the expected bunch lenght / 2. From tails background can be estimated

Transverse position will give information on transverse beam size and its stability



Measure dN/d, dN/dpTMeasure dN/d, dN/dpT

Minbias are the events with the largest xsec

But minimum bias charge multiplicity known only at 50%

Few 104 events needed to get preliminary measurement of dN/d & dN/dpT

Acquire them with the special prescaled trigger

Probably less than half-hour of good data will be sufficient

Useful also to look for beam background First inputs to start tuning MonteCarlo

for pileup and set final trigger strategies (e.g. Isolation)

Probably first article published by CMS...



What else one can do with minimum bias events?

What else one can do with minimum bias events?

Useful to improve ECAL & HCAL calibrations

Charged pions will be used to improve tracker alignment

Use the assumption that energy deposit is uniform in . Possibility to calibrate rings at same . Precision limited by tracker material which is not completely uniform in

Examples with ECAL

Neutral pions will be another source for ECAL intercalibration



Next step: dijetsNext step: dijets Start using prescaled trigger to try to measure jet-cross section For example look at angular distribution, ratio 2J/J to extract trigger and

reconstruction efficiency Also possibility to intercalibrate the HCAL rings, using the 2J balance

After that start investigating MET in dijets MET is dijet is due to energy mismeasures If tails are under control than b and t pairs should dominated for large (>100 GeV)

MET values



Electrons, muons Electrons, muons

Then move to nb processes at LHC, W/Z production. NLO Xsec known at 4-5% level

Many different uses: Lepton energy scale from W &

Z• Goal 0.1% can be achieved

with 1fb-1

Tune detector simulation (model Z mass and W transverse mass)

Efficiencies from Z (tag/probe)



We are starting to undestand detector, beam what we do...We are starting to undestand detector, beam what we do...

We can start measuring SM xsec (W/Z), W mass, top mass but fundamental ingredients for precise meaurements are:



Precise measurement of MW

Precise measurement of MW



How to measure W mass?How to measure W mass?



Ingredients for precise W mass spectrum prediction

Ingredients for precise W mass spectrum prediction



Rediscover the topRediscover the top

With 840pb LHC is a top pait factory

But also single top has a huge xsec 250 pb t-channel, 62pb tW,

10 pb s-channel

•



Top physics: early analysisTop physics: early analysis Top as “commissioning tool”



Top: semileptonicTop: semileptonic



Top: leptonic + hadronicTop: leptonic + hadronic



Triple gauge boson couplings

Triple gauge boson couplings

ZZ also irreducible bkg for H→4l searches



SM HiggsSM Higgs



Higgs production @ LHCHiggs production @ LHC



Higgs SearchesHiggs Searches

“Benchmark” channels: Strongly tied to

detector performance H, HZZ(*)4l Narrow peaks

Event counting No peak Need good control of

background normalization HWW(*)

VBF Take advantage of the

special topology HWW(*), H



HH

very clean signature in mH<140GeV/c2 regionlow branching ratio (0.002)

signature: two isolated high pT photons narrow peak in di-photon invariant mass

backgrounds: pp→gg (irreducible) pp→ g+jets, pp→jets (reducible)

experimental requirements: very good g identification and isolation aiming at 0.5% ECAL energy resolution

signal:mH = 115 GeV/c2 σxBR = 99.3fbmH = 140 GeV/c2 σxBR = 65.5fbbackgrounds: pp → gg σ = 82pb pp → g +jets σ = 5x104pb pp → jets σ = 2.8x107pb

photons (clusters in ECAL)



HH

signalx10

background events normalized to 1fb-1

two approaches:cuts based analysis andneural network analysis

signal: very small contribution to the total number of events (signal efficiency at 120 GeV/c2 ~ 30%)

30fb-1: discovery possible for masses < 140 GeV/c2

using 0.5% resolution



H→ZZ→4lH→ZZ→4l

GOLDEN CHANNEL: cleanest discovery channel over mH>140GeV/c2 range

signature: 2 pairs of opposite-charge, same flavour isolated leptons from primary vertex dileptons invariant mass ~ mZ

backgrounds: pp → ZZ(*) (irreducible, dominant) pp→tt, pp→Zbb (reducible)

main experimental challenges: lepton identification with high efficiency and resolution down to low (~ 5 GeV/c) pT

selection criteria: requirements on vertex, pT(l), isolation, m(ll)

after cuts

2e2μ final state

beforeselections

afterselections

1fb-1

1fb-1



An event H→4e at CMS...An event H→4e at CMS...



discovery channel in 2mW < mH < 2mZ

signature: 2 charged leptons and missing energy no jet activity in the central region

2 neutrinos in the final state: no mass peak, counting experiments →accurate background estimate from data needed

main backgrounds: WW(*) (irreducible, dominant) pp→ tt, pp→ Wtbpp→ W+jets, pp→ Z+jets

crucial for the analysis:reconstruction tools for charged leptons, missing energy and jet veto understanding !!!

H→WW→2l2H→WW→2l2

2 opposite charge leptonsno jet with ET > 15GeV, |η|<2.5MET > 50 GeV12 < m(ll) < 40 GeV30 < pT

max < 55 GeVpT

min > 25 GeVΔΦ(ll) < 45º

cuts and counts analysis

} (reducible)



H→WW→2l2H→WW→2l2

large S/B, 5σ with L<1fb-1 mH=165 GeV/c2

WW control region, no ΔΦ(ll) cut

10fb-1, e

critical: precise background knowledge→ control regions using data ie. WW: inverted kinematic cuts on ΔΦ(ll) and m(ll) ie. tt: extra b-tagged jets



Higgs in VBF and associated productionHiggs in VBF and associated production

associated ttH, WH production: additional leptons/jets in the final statevector boson fusion: two tagging jets, large Δηjj (>4.5), large m(jj) (>1TeV)

despite lower cross section wrt gg fusion increased discriminating power against QCD jets background better main vertex reconstruction

with large statistics: enhance the significance, measure of Higgs couplings some examples in CMS:

VBF with H→ →l+tjet+ ETmiss (5σ with L=60fb-1 if mH<140GeV/c2) VBF with H→(3σ with L=60fb-1 if mH<150 GeV/c2) ttH, WH with H→ (3σ with L=100fb-1 if mH<150 GeV/c2)

ttH with H→ VBF with H→→l+tjet+ ETmiss



CMS Higgs discovery potential: if it’s there we will catch it

CMS Higgs discovery potential: if it’s there we will catch it

all Higgs mass range: significance larger than 5σ with 30 fb-1

mH < 140 GeV/c2 discovery with L < 10 fb-1

mH > 140 GeV/c2 discovery with L < 5 fb-1

5fb-1 enough140<mH<450GeV/c2 discovery with 30fb-

1 in the full range



Measure Higgs mass and width

Measure Higgs mass and width

Higgs mass precision:better than 0.1% if mH<200 GeV/c2

better than 2% up to 600 GeV/c2

Higgs width precision: detector effects dominate if mH < 200 GeV/c2

if mH > 200 GeV/c2 possible measurement with precision better 30% in ZZ channel



End of lecture 2End of lecture 2


physics with cms

Documents

known sm physics

cms early physics

cms detector

sm satisfactory

higgs physics

tb intercalibrated sm

hcal rings

trigger tablehow