Advanced Study Institute“Symmetries and Spin”

Prague, 26 July 2001

Claudia-Elisabeth WulzInstitut für Hochenergiephysik der Österreichischen Akademie der Wissenschaften

Nikolsdorfergasse 18, A-1050 Vienna, Austria

CMSPhysics Overview

Open Questions in Particle Physics

Origin and hierarchy of particle massesOrigin and hierarchy of particle massesIs there a Higgs particle and what is its mass?

How must the Standard Model be extended?How must the Standard Model be extended?Supersymmetry, Grand Unified Theories, …

Is there a substructure of quarks and leptons?Is there a substructure of quarks and leptons?Are there more than three light generations?Are there more than three light generations?Are there heavy neutrinos?Are there heavy neutrinos?Asymmetry between matter and antimatterAsymmetry between matter and antimatter

Stability of the protonWhat is the cosmological dark matter made of?What is the cosmological dark matter made of?Origin of QCD ConfinementOrigin of QCD Confinement

Quark Gluon PlasmaHow can gravity be included?How can gravity be included?

CERN’s accelerator complex

LHC/LEP

SPS

Parameters of the Large Hadron Collider

Proton- ProtonCircumference: 27 kmBunches: 3564 + 3564 Protons / bunch: 1011

Beam energy: 2 x 7 TeVPeak luminosity: 1034 cm-2s-1

Bunch crossing interval: 25 nsCollision rate: 107 … 109 HzDipole field: 8.4 TNumber of dipoles: 1104

Heavy Ions (Pb-Pb, S-S, etc.)Beam energy: up to 5.5 TeV/nucleon pairPeak luminosities:1027 cm-2s-1 for Pb-Pb3.1031 cm-2s-1 for O-OBunch crossing interval: 125 ns

Parton

Bunches

CMS Detector

Physics Goals of CMS

Standard Model physicsStandard Model physicsQCD, electroweak theory (Higgs, W, Z, Top, Jets, …)

SupersymmetrySupersymmetrySUSY Higgses, sparticles, ...

Other extensions of the Standard ModelOther extensions of the Standard ModelCompositeness, technicolor, leptoquarks, new heavy vector bosons, extra dimensions, ...

B-physicsB-physics CP violation, B0-B0 oscillations, rare B-decays, ...

Heavy Ion physicsHeavy Ion physicsQuark-Gluon Plasma

Soft physicsSoft physics total, elastic scattering, diffraction

New phenomenaNew phenomena

Cross sections and production rates for various processes vary by many orders of magnitude

• inelastic: 109 Hz• W l: 100 Hz• tt: 10 Hz• Higgs (100 GeV): 0.1 Hz• Higgs (600 GeV): 0.01 Hz

Required selectivity 1 : 10 10 - 11

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Cross sections

Experimental Challenges

Pile-upPile-uptot tot 80 mb, 80 mb, high luminosity -> up to 25 p-p collisions per bunch crossing, 1000 charged particles in || < 2.5Consequences for detectors:Short response times (typically 25 to 50 ns)High granularity (> 108 channels)Radiation resistance (1017 neutrons/cm2 flux,integrated radiation dose up to 107 Gy after 10 years’ operation close to beam)

QCD backgroundQCD backgroundRate dominated by jet production (qq -> qq, gg -> qq etc.), therefore in practice generally only decays with leptons and photons are usable leading to small event rates.

Where is the Higgs?

18 superimposed p-p collisions in the inner part of the CMS tracker, 18 superimposed p-p collisions in the inner part of the CMS tracker, including 4 muon tracks from a Higgs decayincluding 4 muon tracks from a Higgs decay

Here!

Transverse momentum cut of pTransverse momentum cut of pTT > 2 GeV after track reconstruction > 2 GeV after track reconstruction

Standard Model Higgs

Branching ratios Total decay width

Discovery Strategy for the Standard Model Higgs

100 GeV < mH < 150 GeV H -> in incl. prod.,WH, ttH 90 GeV < mH < 120 GeV H -> bb in WH, ttH130 GeV < mH < 200 GeV H -> ZZ* -> 4l (leptons)140 GeV < mH < 180 GeV H -> WW-> ll200 GeV < mH < 750 GeV H -> ZZ-> 4l 500 GeV < mH < 1000 GeV H -> ZZ -> 2l + 2 mH ~ 1 TeV H -> WW -> l + 2 JetsmH ~ 1 TeV H -> ZZ-> 2l + 2 JetsRecently the following channels have been investigated:

H -> ZmH ~ 130 GeV qq -> qqH with H ->

At LHC the SM Higgs is accessible in the entire mass range from the present LEP limit of ~ 115 GeV up to 1 TeV.

Depending on mass different decay channels are traditionally used:

--

-

H ->

The crystal electromagnetic calorimeter has been optimized for this channel.Mass resolution mH/mH < 1% needed.

Irreducible backgrounds at m = 100 GeV:qq -> gg -> Isolated bremsstrahlung

Main reducible background: + jet with “jet” = 0 -> less than 15% of irreducible background

H ->

H -> bb _

This channel and H -> are only way to explore the 115 GeV mass region!NB: WH production perhaps accessible for very high luminosities (300 fb-1).

Only associated production is feasible! Problems with background and trigger!

Event selection:1 isolated e or , 6 jets of which 4 must have a b-tag. Reconstruction of both t’s by kinematic fit necessary to suppress combinatorial bb background.

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H -> ZZ* -> 4l

Need good tracker, ECAL and muon system as Higgs width is small (mH < 1 GeV) for mH < 2mZ. In this mass range the main backgrounds are tt, Zbb (reducible) and ZZ*/Z continuum production (irreducible). Lepton isolation, dilepton mass cuts and impact parameter cuts are used for background suppression.

100 fb-1

- -

H -> WW -> l + lfor mH ~ 2mW

For mH = 170 GeV the BR is about 100 times larger than in H->ZZ*->4l. Can make use of W+W- spin correlations to suppress “irreducible” background. Look for l+l- - pair with small opening angle.

H -> WW -> l + l

The mass can only be determined indirectly from rates and shapes.

The tt and Wtb backgroundscan be reduced by a jet veto.

- -

H -> WW -> l + l

5 discovery can be made with 30 fb-1 in the mass range 130 to 190 GeV.

H -> ll,lljj, ljj

As Higgs width increases and production rates fall with higher masses one must use channels with larger branching ratios.Need to select leptons, jets and missing energy.

CMS 5

5 - ContoursSignificance for 100 fb-1

Summary of Standard Model Higgs in CMS

Supersymmetry

SUSY Particle Production

The Higgs Sector in the MSSM

The MSSM has 5 Higgs bosons: h0, H0, A0 and H±. 2 parameters needed to fix properties: mA, tan. In the limit of large mA the couplings of h0 are similar to SM. Couplings of A and H to quarks of 1/3 charge and leptons enhanced at large tan. A does not couple to WW, ZZ. Couplings of H to WW and ZZ for large mA and tanare suppressed.

The following decay channels can be used as for the SM Higgs:h, A -> (for mA < 2 mt due to branching ratio)H -> ZZ* (no H -> ZZ at large mass since BR too low)

The following decay channels open up:H, A -> (-channels enhanced over SM for large tan)H, A -> hhA -> ZhA ->

N.B. Decays into sparticles will be discussed later.

tt H -> tt bb

tt

H/A ->

Due to high rates this channel can be observed over a large region of parameter space.

Useable final states: (-> ee) (-> ) (-> h± 0’s ) (-> ll) (-> h± 0’s ) (-> hm 0’s )

Main backgrounds:Z, *bb, tt, W + jets, Z + jets, QCDlepton + jet misidentified as (for lepton + hadron final state)

-

-

Mass Determination for H/A ->

Mass reconstructed assuming directions parallel to lepton and -jet.

H/A ->

BR smaller than that for -channel by (m/m)2. This is somewhat compensated by better resolution for ’s. Useful for large tan.

H -> hh

Dominant decay to . Problem is triggering: need soft muons in jets. Sensitivity for tan < 3 and 250 GeV < mA < 2 mt.

Easier to trigger is the channel H -> hh -> +-. In MSSM most of the accessible region is excluded by LEP, but in more general models this channel might be relevant.

H -> hh -> can be triggered on, but rates are low. Background is small, however, and there is a convincing sharp peak in the mass distribution.

bb bb

bb

bb

A, H -> tt

This is the dominant decay channel for large masses. Background comes from QCD tt production. It is large, but significant signal can be extracted if background can be correctly estimated. The search is based on the WWbb final state, with one W decaying leptonically. The trigger requires an isolated lepton. In the analysis 2 b-jets are required in addition.

Determination of mass will be difficult as there is no observable mass peak. The mode is likely to be used as a comfirmation of a signal seen in other channels.

-

-

-

A -> Zh

Can use the leptonic decay of the Z in the trigger. In the analysis 2 electrons (muons) with ET > 20 GeV (pT > 5 GeV) of invariant mass within ± 6 GeV of the Z peak and 2 jets with ET > 40 GeV are required. One or two b-tags are also required. Background comes mainly from tt and Zbb events (for smaller mA).

Signal to background ratio is quite good for moderate mA and small tan, but this region is already excluded in MSSM by LEP.

- -

Charged Higgs

In the MSSM the decay t -> bH± may compete with the Standard Model t -> bW± if kinematically allowed. H± decays to or cs depending on tan. Over most of the range 1 < tan < 50 the mode H± -> dominates. The signal for H± production is therefore an excess of ’s in tt events.If mass of H± is larger than mt it cannot be produced in t-decays. It can be produced by gb -> H-t. Again the search focusses on the decay H± -> . One can use the decay t -> bqq so that ET

miss gets contribution only from H±  decay resulting in a Jacobian peak. The polarization leads to harder pions from -> than from W decays.

-

-

Charged HiggsE

ven

ts f

or 3

x104

pb

-1 /

40 G

eV

Eve

nts

for

3x1

04 p

b-1 /

40 G

eV

mT (-jet, ETmiss) / GeV

mT (-jet, ETmiss) / GeV

100 200 300 400 500

50 100 150 200 250 300 350

Transverse mass reconstructed from -jet and ET

miss for pp -> tH± with m(H±) = 400 GeV

tan = 30

tan = 20

Transverse mass reconstructed from -jet and ET

miss for pp -> tH± with m(H±) = 200 GeV

H± -> , t -> qqb

SUSY Higgs to Sparticles

If neutralinos/charginos are light the branching ratios of H and A into these sparticles is sizeable. Most promising with respect to background are channels with leptonic decays of the sparticles:2

0 -> 10 l+ l- and 1

+ -> 10 l +

Signal: A, H -> 2

0 20 -> 4l + X

Backgrounds:SM: ZZ, Zbb, Zcc, tt, WtbSUSY: q/g, ll, , q,

In the following only the case m(l) > m(20) will be considered.

~ ~ ~ ~

~ ~

~ ~ ~~ ~~ ~ ~ ~~- - - -

~

SUSY Higgs to Sparticles

100 fb-1

Signal

Background(mainly SUSY)

tan = 5mA = 350 GeV

SUSY Higgs to Sparticles

Excluded by LEP

tan

mA (GeV)

5 significance contours

MSSM parameters: M(10) = 60 GeV,

M(20) = 120 GeV, = - 500 GeV,

m(l) = 250 GeV, m(q,g) = 1000 GeV~ ~ ~

30 fb-1

100 fb-1

A, H -> 20 2

0 -> 4l + X~ ~

~~

SUSY Higgses in CMS5 significance contours

Sparticles

If SUSY is relevant to electroweak symmetry breaking then gluino and squark masses should be of order 1 TeV.

As in general many SUSY particles are produced simultaneously, a model with a consistent set of masses and branching ratios must be used in the simulations.

Traditionally CMS uses the Supergravity (SUGRA) model, which assumes that gravity is responsible for the mediation of SUSY breaking.

Another possible model is the Gauge Mediated SUSY Breaking Model (GMSB) which assumes that Standard Model gauge interactions are responsible for the breaking -> see J. Krolikowski’s talk at this workshop.

Sparticles

Supersymmetric particles may have striking signatures due to cascade decays, leading to final states with leptons, jets and missing energy.

Shown here is a qq event:

q -> 20 q

q -> 1± q

10~

~

~

e

10e~

~

~

~~

~

~

Squarks and Gluinos

They dominate the SUSY production cross section and contribute about 10 pb for masses around 1 TeV.

In minimal SUGRA they give rise to ET

miss from 10’s plus

multiple jets and a variable number of leptons from the gauginos. The charges of the leptons can be used to extract signals, even in the CMS level-1 trigger.

The figure shows results for the channelsn leptons + ET

miss + > 2 jets

~

Squarks and Gluinos

The figure shows the q, g mass reach for various luminosities in the inclusive ET

miss + jets channel.

~ ~

1 year at 1034 cm-2s-1

1 year at 1033 cm-2s-1

1 week at 1033 cm-2s-1

1 month at 1033 cm-2s-1

Charginos, Neutralinos, Sleptons

Example for Drell-Yan production of 1± 2

0:

qq -> W* -> 1± 2

0 -> 10 l + 1

0 l+l-

Search in 3l and no jets channels, possibly also with ETmiss.

Backgrounds: tt, WZ, ZZ, Zbb, bb, other SUSY channels

In SUGRA the decay products of SUSY particles always contain 10’s.

Kinematic endpoints for combinations of visible particles can be used to identify particular decay chains.

Examples: l+l- mass distribution from 2

0 -> 10 l+l- has endpoint which measures

m(20 ) - m(1

0 );2

0 -> l±lm -> 10 l+l- has different shape with a sharp edge at the

endpoint which measures the square root of:[m2(2

0 ) - m2 (l)] [m2(l) - m2 (10)]

m2(l)

~

~ ~~

- - -

~ ~ ~ ~

~ ~~ ~

~ ~

~ ~

~

~ ~

Neutralino Mass Determination

Final state with:

3l, no jets, ETmiss

Overview of physics not discussed

• If electroweak symmetry breaking proceeds via new strong interactions many resonances and new exotic particles will certainly be seen

• New gauge bosons with masses less than a few TeV can be discovered

• Signals for extra dimensions will be revealed if the relevant scale is in the TeV range

• Standard Model physics involving the top quark will be explored in detail (e.g. top mass measurement, rare top decays)

• A Beauty physics programme is foreseen provided that adequate financial resources can be found! Precise determination of sin2, study of Bs-Bs oscillations and rare B-decays (e.g. B -> ) can be performed.

• Quark-Gluon-Plasma signatures can be studied within the Heavy Ion programme

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Conclusions

• The Standard Model Higgs can be discovered over the entire expected mass range up to about 1 TeV with 100 fb-1. The most plausible part below 200 GeV mass can be explored with several channels.

• Most of the MSSM Higgs boson parameter space can be explored with 100 fb-1, all of it can be covered with 300 fb-1.

• The mass reach for squarks and gluinos is in excess of 2 to 2.5 TeV (m0 < 2 to 3 TeV, m1/2 < 1 TeV) for all tan within mSUGRA

• Sleptons can be detected up to 400 GeV mass in direct searches and probed indirectly up to 700 GeV

• 10 canbe found up to 600 GeV mass. The dark matter hypothesis will

be systematically tested and should be within reach for tan < 20.

~

Conclusions

The CMS experiment at the LHC accelerator will enable us to explore physics in the TeV region.

We are eagerly We are eagerly awaiting the first awaiting the first data!data!