(Forward Look at) Physics at the LHC

LHC Physics 1P. Sphicas/ISHEP2003

(Forward Look at) Physics at the LHC(Forward Look at) Physics at the LHC

Outline The LHC – quick introduction/reminder The detectors Higgs physics – in the SM and the MSSM Supersymmetry:

Sparticles (squarks/gluinos/gauginos) Precision measurements

Other (possible) new physics TeV-scale gravity Current status Summary

Paris Sphicas

CERN and Univ. of Athens

International School on High Energy Physics

Crete, October 2003

P. Sphicas/ISHEP2003

Standard Model HiggsStandard Model Higgs


Limits on MLimits on MHH (I): EWK vaccum stability (I): EWK vaccum stability Central to the Higgs mechanism:

that point with vev0 is stable (genuine minimum) Radiative corrections can change this

V

For large top masses, potential can curve back down; two terms fighting:

4 vs ~ - (mt/v)4

And since MH2~v2, get a lower bound

on MH (~ 130 GeV)

422

42)( V

2244444

4 /log12361

~ vHHmMMMv

V tZWH

V


Limits on MLimits on MHH (II): triviality bound (II): triviality bound From previous discussion: need a high value of (i.e.

self-coupling) to protect the vacuum However, the running of the coupling results in an increase

with Q2:

So, as Q2, Alternative: if is normalized to a finite value at the pole then

it must vanish at low Q2. Theory is non-interacting “trivial” Way out: assume that analysis breaks down at some scale

(clearly, when gravity gets added, things will change)

2

0222

0

202

/log16/)(1 QQQ

QQ

2

22

34

expH

H Mv

M


Information (limits) on MInformation (limits) on MHH: summary: summary Triviality bound <0>0

Precision EWK measurements

2

22

34

expH

H Mv

M 22

22 /log

823

vFG

M FH

LEP direct search:

MH>114 GeV/c2


Expected Fermilab ReachExpected Fermilab Reach Reach has been updated. Also Tevatron luminosity

profiles; expect 5-10fb-1 by LHC start (+ a bit)


SM Higgs at the LHCSM Higgs at the LHC Production mechanisms & cross section


SM HiggsSM Higgs Decays & discovery

channels Higgs couples to mf

2

Heaviest available fermion (b quark) always dominates

Until WW, ZZ thresholds open

Low mass: b quarks jets; resolution ~ 15%

Only chance is EM energy (use decay mode)

Once MH>2MZ, use this W decays to jets or

lepton+neutrino (ETmiss)


Low mass Higgs (MLow mass Higgs (MHH<140 GeV/c<140 GeV/c22)) H: decay is rare (B~10-3)

But with good resolution, one gets a mass peak

Motivation for LAr/PbWO4 calorimeters Resolution at 100 GeV, 1GeV

S/B 1:20


Intermediate mass HiggsIntermediate mass Higgs HZZ+–+– ( =e,)

Very clean Resolution: better than 1

GeV (around 100 GeV mass) Valid for the mass range

130<MH<500 GeV/c2


High mass HiggsHigh mass Higgs HZZ +–jet jet

Need higher Branching fraction (also for the highest masses ~ 800 GeV/c2)

At the limit of statistics


Higgs discovery prospects @ LHCHiggs discovery prospects @ LHC The LHC can probe the entire set of “allowed” Higgs

mass values in most cases a few months at low luminosity are adequate

for a 5 observation

CMS


A closer look at the discovery lumiA closer look at the discovery lumi Significance for 30 fb-1

No K factors

Luminosity (in fb-1) for 5 discovery of MH<160 NLO K factors for ggH


HHWWWW(*)(*); also a prime discovery mode; also a prime discovery mode Large backgrounds from top production, WW SM

production


Status of HStatus of H bb bb (I) (I) Low mass Higgs; useful for coupling measurement

H bb in t t H production .Br=300 fb Backgrounds:

– Wjjjj, Wjjbb

– t t jj

– Signal (combinatorics) Tagging the t quarks

helps a lot– Trigger: t b(e/)– Reconstruct both t quarks

In mass region

90GeV<M(bb )<130GeV, S/B =0.3


Status of HStatus of H bb bb (II) (II) H bb in WH production

Big background subtraction Mainly: Wjj, t t (smaller: tX,WZ) Example (below) at 105:

– in mass region

88GeV<M(bb )<121GeV,

S/B =0.03

After bkg subtraction


Weak Boson Fusion (I)Weak Boson Fusion (I) WW interaction -> Higgs

Main characteristic: the two forward “tag” jets


Weak Boson Fusion (II)Weak Boson Fusion (II) Observation of qqH, HWW(*) 22

WBF cuts Angle between leptons (against top and WW backgrounds) B-jet VETO (against top) Tau-jet veto (against jj) Cuts on:

M() ET

miss

MT(ETmiss) (against DY)

Top background extractible

from the data (using semileptonic

top events: tt jets )


WBF + HWBF + H In addition to WBF cuts:

Tau-id (for +h mode) Tau reco (xtl,xth>0)

MT()<30 GeV

ETmiss, mass window

Systematics: Z+tt background; 10% on

shape

ATLAS; ++ETmissCMS; +h+ET

miss


SM Higgs properties (I): massSM Higgs properties (I): mass Mass measurement

Limited by absolute energy scale

leptons & photons: 0.1% (with Z calibration)

Jets: 1% Resolutions:

For & 4 ≈ 1.5 GeV/c2

For bb ≈ 15 GeV/c2

At large masses: decreasing precision due to large H

CMS ≈ ATLAS


SM Higgs properties (II): widthSM Higgs properties (II): width Width; limitation:

Possible for MH>200 Using golden mode (4)

CMS


SM Higgs; (indirect) width for MSM Higgs; (indirect) width for MHH<2M<2MZZ

Basic idea: use qqqqH production (two forward jets+veto on central jets) Can measure the following: Xj = Wj/from qqqqH qqjj

Here: j = , , W(W*); precision~10-30% One can also measure Yj= gj/from ggHjj

Here: j = , W(W*), Z(Z*); precision~10-30% Clearly, ratios of Xj and Yj (~10-20%) couplings

But also interesting, if W is known:

= (W)2/XW

Need to measure H WW* =1-(Bb+B+BW+BZ+Bg+B)<<1

(1-)W= X(1+y)+XW(1+z)+X+Xg

z= W/Z; y= b/3QCD(mb/m)2

Zeppenfeld, Kinnunen, Nikitenko, Richter-Was


SM Higgs properties (III)SM Higgs properties (III) Biggest uncertainty(5-10%): Luminosity

Relative couplings statistically limited Small overlap regions

M e a s u r e E r r o r M H r a n g e B H B H b b 3 0 % 8 0 – 1 2 0

B H B H ZZ 1 5 % 1 2 5 – 1 5 5

t t H WH

2 5 % 8 0 – 1 3 0

B H WW B H ZZ 3 0 % 1 6 0 – 1 8 0


SM Higgs: properties (IV)SM Higgs: properties (IV) Self-coupling

From HH production

Cross sections are low Relevant for MH<200 GeV/c2

Need higher statistics, i.e. luminosities; for example, WW(*) with +jetjet channel visible (with 10x the statistics)Measures to 20-25%


MSSM Higgs(es)MSSM Higgs(es)


Remark on SUSY studies (I)Remark on SUSY studies (I)


Remark on SUSY studies (II)Remark on SUSY studies (II)


MSSM Higgs(es)MSSM Higgs(es) Complex analysis; 5 Higgses (H±;H0,h0,A0)

At tree-level, all masses & couplings depend on only two parameters; tradition says take MA & tan

Modifications to tree-level mainly from top loops Important ones; e.g. at tree-level, Mh<Mzcos, MA<MH;

MW<MH+; radiative corrections push this to 135 GeV. Important branch 1: SUSY (s)particle masses

(a) M>1 TeV (i.e. no decays to them); well-studied

(b) M<1 TeV (i.e. allows decays to them); “on-going” Important branch 2: stop mixing; value of tan

(a) Maximal–No mixing

(b) Low (≈2-3) and high (≈30) values of tan


MSSM Higgses: massesMSSM Higgses: masses Mass spectra for MSUSY>1TeV

The good news: Mh<135 GeV/c2


MSSM: h/A decayMSSM: h/A decay

h is light Decays to bb (90%) & (8%)

cc, gg decays suppressed

H/A “heavy” Decays to top open (low tan) Otherwise still to bb & But: WW/ZZ channels suppres-

sed; lose golden modes for H

–

No mixing–

g(uu) g(dd) g(VV)

h cos/sin1

-sin/cos 1

sin() 1

H sin/sin1/

tan

cos/costan

cos() 1

A 1/tan tan 0


MSSM Higgs productionMSSM Higgs production Cross section prop to tan2

Third-generation fermions e.g., bbA production


Higgs channels consideredHiggs channels considered

Channels currently being investigated: H, h, bb (Hbb in WH, t t H) h in WH, t t h ℓ h, H ZZ*, ZZ 4 ℓ h, H, A e/)+ + h + ET

miss

e+ + + ETmiss inclusively and in bb HSUSY

h+ + h + ETmiss

H+ + from t t

H+ + and H+ t b for MH>Mtop

A Zh with h bb ; A

H, A

i j i j H+ qq qqH with H

H , in WH, t t H

fairly new and promising

(very) important and hopeful


The tau: the LHC-SUSY leptonThe tau: the LHC-SUSY lepton Taus are the new element of the LHC

Most SUSY models have e/ universality but -leptons are special

Usually: 1 is the lightest slepton implies that ’s may be the only leptons

produced in gaugino decays

What the b-quark (and the associated tagging) was to the Tevatron experiments


H,AH,A; 3; 3rdrd-generation lepton the LHC-generation lepton the LHC Most promising modes for H,A

’s identified either in hadronic or

leptonic decays Mass reconstruction: take

lepton/jet direction to be the direction


H, A reach via H, A reach via decays decays Contours are 5; MSUSY=1 TeV


HH++ detection detection Associated top-H+ production:

Use all-hadronic decays of the top (leave one “neutrino”)

H decay looks like W decay Jacobian peak for -missing ET

In the process of creating full trigger path + ORCA analysis

ET(jet)>40

||<2.4

Veto on extra jet, and on second top

Bkg: t t H


Other modes: HOther modes: H in bbA production in bbA production Pros: clean signature, good mass resolution (1-2%) Cons: Br(A/H)~410-3

BUT: cross section enhanced by tan Backgrounds:

Z/* : suppressed with b-tagging: vertex+ip; no cut on PT(b) ttX: suppressed with jet-veto + ET

miss


Can one separate A & H?Can one separate A & H?


SUSY reach on tanSUSY reach on tan-M-MAA plane plane Adding bb on the modes can “close” the plane

Wh

bb(e/)

No stop mixing

maximal stop mixing with

30 fb-1 maximal stop mixingwith 300 fb-1


Observability of MSSM HiggsesObservability of MSSM Higgses

4 Higgs observable3 Higgs observable2 Higgs observable

1 Higgs observable

MSSM Higgs bosons

h,A,H,H

h,A,H,H

Assuming decaysto SM particles only

h,H

h

h,H

h,A,H

H,H

h,,H,H

h,H

5 contours


If SUSY charg(neutral)inos < 1 TeV (I)If SUSY charg(neutral)inos < 1 TeV (I) Decays H0 02 02, +i -j become important

Recall that 02 01ℓ+ℓ_ has

spectacular edge on the

dilepton mass distribution Example: 02 02. Four (!) leptons

(isolated); plus two edges

Four-lepton mass

100 fb1


If SUSY charg(neutral)inos < 1 TeV (II)If SUSY charg(neutral)inos < 1 TeV (II) Helps fill up the “hole”

Wh

bb(e/)

No stop mixing

maximal stopmixing with

30 fb-1 maximal stop mixingwith 300 fb-1

Area coveredby H0 02 02,4ℓeptons

100 fb-1


Measurement of tanMeasurement of tan: bbA with A: bbA with A


Only h found; is it SM or MSSM?Only h found; is it SM or MSSM?


MSSM: Higgs summaryMSSM: Higgs summary At least one will be found in the entire MA-tan plane

latter (almost) entirely covered by the various signatures Full exploration requires 100 fb–1 Difficult region: 3<tan<10 and 120<MA<220; will need:

> 100 fb–1 or hbb decays Further improvements on identification?

Intermediate tan region: difficult to disentangle SM and MSSM Higgses (only h is detectable)

Potential caveats (not favored) Sterile (or “invisible”) Higgs

Still doable – but invisible…


Strong “EWK” interactionsStrong “EWK” interactions


Strong boson-boson scatteringStrong boson-boson scattering Example: WLZL scattering

W, Z polarization vector satisfies: p=0;

for p=(E,0,0,p), =1/MV(p,0,0,E) P/MV+O(MV/E)

Scattering amplitude ~ (p1/MW) (p2/MZ) (p3/MW) (p4/MZ), i.e. ~s2/MW

2MZ2

Taking MH the H diagram goes to zero (~ 1/MH2)

Technicalities: diagrams are gauge invariant, can take out one factor of s

but the second always remains (non-abelian group) Conclusion: to preserve unitarity, one must switch on the H at some

mass Currently: MH700 GeV


The no Higgs case: VThe no Higgs case: VLLVVLL scattering scattering Biggest background is Standard Model VV scattering

Analyses are difficult and limited by statistics

L=300 fb-1

Resonant WZ scattering at 1.2 & 1.5 TeV Non-resonant W+W+ scattering

MH=1 TeV

WTWT


Other resonances/signaturesOther resonances/signatures Technicolor; many

possibilities Example: T

±W±Z0 ±+– (cleanest channel…)

Many other signals (bb,

t t resonances, etc…) Wide range of

observability

ATLAS; 30 fb–1

–

–


SummarySummary


Higgs SummaryHiggs Summary

(Forward Look at) Physics at the LHC

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