Post on 05-Jan-2016
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
LHC Physics 3P. Sphicas/ISHEP2003
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
LHC Physics 4P. Sphicas/ISHEP2003
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
2
22
34
expH
H Mv
M
LHC Physics 5P. Sphicas/ISHEP2003
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
LHC Physics 6P. Sphicas/ISHEP2003
Expected Fermilab ReachExpected Fermilab Reach Reach has been updated. Also Tevatron luminosity
profiles; expect 5-10fb-1 by LHC start (+ a bit)
LHC Physics 7P. Sphicas/ISHEP2003
SM Higgs at the LHCSM Higgs at the LHC Production mechanisms & cross section
LHC Physics 8P. Sphicas/ISHEP2003
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)
LHC Physics 9P. Sphicas/ISHEP2003
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
LHC Physics 10P. Sphicas/ISHEP2003
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
LHC Physics 11P. Sphicas/ISHEP2003
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
LHC Physics 12P. Sphicas/ISHEP2003
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
LHC Physics 13P. Sphicas/ISHEP2003
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
LHC Physics 14P. Sphicas/ISHEP2003
HHWWWW(*)(*); also a prime discovery mode; also a prime discovery mode Large backgrounds from top production, WW SM
production
LHC Physics 15P. Sphicas/ISHEP2003
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
LHC Physics 16P. Sphicas/ISHEP2003
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
LHC Physics 17P. Sphicas/ISHEP2003
Weak Boson Fusion (I)Weak Boson Fusion (I) WW interaction -> Higgs
Main characteristic: the two forward “tag” jets
LHC Physics 18P. Sphicas/ISHEP2003
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 )
LHC Physics 19P. Sphicas/ISHEP2003
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
LHC Physics 20P. Sphicas/ISHEP2003
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
LHC Physics 21P. Sphicas/ISHEP2003
SM Higgs properties (II): widthSM Higgs properties (II): width Width; limitation:
Possible for MH>200 Using golden mode (4)
CMS
LHC Physics 22P. Sphicas/ISHEP2003
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
LHC Physics 23P. Sphicas/ISHEP2003
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
LHC Physics 24P. Sphicas/ISHEP2003
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%
P. Sphicas/ISHEP2003
MSSM Higgs(es)MSSM Higgs(es)
LHC Physics 26P. Sphicas/ISHEP2003
Remark on SUSY studies (I)Remark on SUSY studies (I)
LHC Physics 27P. Sphicas/ISHEP2003
Remark on SUSY studies (II)Remark on SUSY studies (II)
LHC Physics 28P. Sphicas/ISHEP2003
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
LHC Physics 29P. Sphicas/ISHEP2003
MSSM Higgses: massesMSSM Higgses: masses Mass spectra for MSUSY>1TeV
The good news: Mh<135 GeV/c2
LHC Physics 30P. Sphicas/ISHEP2003
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
LHC Physics 31P. Sphicas/ISHEP2003
MSSM Higgs productionMSSM Higgs production Cross section prop to tan2
Third-generation fermions e.g., bbA production
LHC Physics 32P. Sphicas/ISHEP2003
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
LHC Physics 33P. Sphicas/ISHEP2003
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
LHC Physics 34P. Sphicas/ISHEP2003
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
LHC Physics 35P. Sphicas/ISHEP2003
H, A reach via H, A reach via decays decays Contours are 5; MSUSY=1 TeV
LHC Physics 36P. Sphicas/ISHEP2003
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
LHC Physics 37P. Sphicas/ISHEP2003
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
LHC Physics 38P. Sphicas/ISHEP2003
Can one separate A & H?Can one separate A & H?
LHC Physics 39P. Sphicas/ISHEP2003
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
LHC Physics 40P. Sphicas/ISHEP2003
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
LHC Physics 41P. Sphicas/ISHEP2003
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
LHC Physics 42P. Sphicas/ISHEP2003
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
LHC Physics 43P. Sphicas/ISHEP2003
Measurement of tanMeasurement of tan: bbA with A: bbA with A
LHC Physics 44P. Sphicas/ISHEP2003
Only h found; is it SM or MSSM?Only h found; is it SM or MSSM?
LHC Physics 45P. Sphicas/ISHEP2003
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…
P. Sphicas/ISHEP2003
Strong “EWK” interactionsStrong “EWK” interactions
LHC Physics 47P. Sphicas/ISHEP2003
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
LHC Physics 48P. Sphicas/ISHEP2003
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
LHC Physics 49P. Sphicas/ISHEP2003
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
–
–
P. Sphicas/ISHEP2003
SummarySummary
LHC Physics 51P. Sphicas/ISHEP2003
Higgs SummaryHiggs Summary