Post on 08-Mar-2016
description
ATL
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Higgs Boson parameters at LHCSerena Psoroulas, University of Bonn
on behalf of the ATLAS and CMS collaborationsXXIInd Recontres de Blois, 15th-20th July 2010
1
SM Higgs production
Production cross section for 14 TeV, Standard Model Higgs
Typical uncertainties:
gg fusion: 10 % (NNLO)
VBF: 5 % (NLO)
WH, ZH: 5% (NNLO)
ttH: 15% (NLO)
2
SM Higgs decay
Separation between low (<140 GeV) and high (> 140 GeV) mass:
bb: MH < 130 GeV
γγ: 110 < MH < 140 GeV
ττ: MH < 140 GeV
WW: highest significance in 2 MW < MH < 2 MZ
ZZ: MH > 130 GeV
Excluded by direct searches
Excluded
Bran
chin
g ra
tio
3
Mass
Discovery (14 TeV)
LHC has the potential to discover or exclude the Higgs in the mass range 100-600 GeV
Once a Higgs-like signal is discovered: measure the mass of the new particleuseful channels: H→ZZ and H→γγ
5
(GeV)Hm100 120 140 160 180 200 220
expe
cted
sig
nific
ance
0
2
4
6
8
10
12
14
16
18Combined
4l (*)
ZZ
µ eWW0j µ eWW2j
ATLAS-1L = 10 fb
Mass (14 TeV)
CMS2e2μ
γγ+1jet10 fb-1
Low mass:
powerful channels at low mass: H→γγ and H→ττ
low rate: optimized analysis to increase significance
mass resolution below 1 GeV for CMS ~ 1.5 GeV for ATLAS
uncertainty << 1%, dominated by systematics
luminosity needed: ≤ 30 fb-1
High mass:ZZ production, Z decay into leptons
resolution: 2-3 GeVuncertainty: <1% (MH
up to 500 GeV)luminosity needed: 10-100 fb-1
6
CMS2e2μ
Decay width and couplings
Measurement of decay width
The decay width has a strong dependance on MH
MH < 200 GeV: no direct measurement
ATLAS study: global maximum likelihood fit to determine the coupling parameters in mass range from 110 to 190 GeV
Two studies shown:
M.Duhrssen, Prospects for the measurement of Higgs boson coupling parameters in the mass range from 110 - 190 GeV (ATL-PHYS-2003-030)
Rémi Lafaye et al., JHEP08(2009)009
CMS14 TeV
Expected performance in H→ZZ→4lfrom: CMS Note 2006/107
8
From rates to ratio of widthsAssuming one spin-0, CP-even Higgs: extract ratio of widths fitting the ratio of decay rates
Lowest uncertainty in WW, reference for measurement of ratio of widths
9
Unc
erta
inty
on
rate
:
Unc
erta
inty
on
ratio
of
wid
ths:
N(gg → H → ZZ)
N(gg → H → WW )=
σggBR(H → ZZ)
σggBR(H → WW )=
ΓHZZ
ΓHWW
Assuming only the dominant couplings of SM are present: fit ratio of couplings using theoretical predictions for couplings to production Xsect and BR
New study: couplings extracted using a likelihood mapFit to absolute coupling g, sensitive also to contributions from new physics.
only fast simulation used in these studies other effects not taken into account yet (pileup)
From partial widths to couplings
10
Unc
erta
inty
on
r. of
cou
plin
gs:
estimate with large
uncertaintiesgjjH → gSM
jjH(1 +∆jjH)
30 fb-1
Spin and CP
Measure spin and CP looking at the available channels:
observations from direct searches in several channels:
observation of H→γγ excludes spin-1 object (Yang theorem)
spin-0 Higgs visible in angular correlation of leptons in H→WW→llνν
use a channel that has not any spin/parity assumption: angular distributions and correlation of the decay products. Two examples:
1. polarization of decay products of H→ZZ→4l, in: Prospective analysis of spin- and CP-
sensitive variables in H→ZZ→llll at the LHC, C.P. Buszello, et al., Eur. Phys. J. C 32, 209–219 (2004)
similar analysis from CMS, shown in backup slides
2. topology of VBF H→ττ and H→WW events, in: Prospects for the measurement of the structure of the coupling of a Higgs boson to weak gauge bosons in weak boson fusion with the ATLAS detector, C. Ruwiedel, et al., Eur. Phys. J. C 51, 385–414 (2007)
12
Spin and CP
Spin and CP in H→ZZ→4lLeptons angular distribution for θ, ϕ:
L = longitudinal , T = transverse contribution
Z from Higgs are mostly L-polarized, Z from background are mostly T-polarizedFor MH > 300 GeV, no correlation in phi as Z are L-polarized
Test for spin-0 vs spin-1 hypothesis, and parity +1 vs -1:
F (φ) = 1 + αcosφ+ βcos2φ
G(θ) = T (1 + cos2θ) + Lsin2θ
JONAS STRANDBERG
Observables R, ! and "
• The angle between the 2 Z’s decay planes, !, expected to becorrelated mainly for transversely polarized Z bosons.– Correlation starts to disappear forMH > 300, longitudinal Z’s.
• Angular distributions for " and ! described by:F (!) = 1 + # cos! + $ cos 2!
G(") = T (1 + cos2") + L sin2"
• Define observables #, $ and R = (L ! T )/(L + T ).
• Test for:– Spin 1, CP +1– Spin 1, CP -1– Spin 0, CP -1
OBSERVABLES R, ! AND " 8. SYMMETRIES AND SPIN, JULY 29, 2009JONAS STRANDBERG
Measurement of R
Eur. Phys. J. C32:209-219
ATLAS
• Predicted values of R as afunction of the Higgs mass.
ATLAS
• Expected precision on themeasurement of R (100 fb!1).
• R provides good separation between the SM Higgs boson andthe alternative Higgs bosons forMH > 230 GeV.– ForMH ! 200 GeV, a measurement of R is only able toexclude the pseudo-scalar alternative.
MEASUREMENT OF R 9. SYMMETRIES AND SPIN, JULY 29, 2009
R =L− T
L+ T
13
JONAS STRANDBERG
Measurement of R
Eur. Phys. J. C32:209-219
ATLAS
• Predicted values of R as afunction of the Higgs mass.
ATLAS
• Expected precision on themeasurement of R (100 fb!1).
• R provides good separation between the SM Higgs boson andthe alternative Higgs bosons forMH > 230 GeV.– ForMH ! 200 GeV, a measurement of R is only able toexclude the pseudo-scalar alternative.
MEASUREMENT OF R 9. SYMMETRIES AND SPIN, JULY 29, 2009
R100 fb-1: •exclusion of non-SM cases at high mass
•exclusion of Pseudoscalar case at low mass
Fast Simulation only
General parametrization of the Higgs coupling to vector bosons:
a1 governs SM coupling; a2 and a3 governs CPE(ven) and CPO(dd) coupling
Angle between two highest-pt jets in VBF events is sensitive to structure:
determination of coupling from Δϕ of jets
determination of anomalous contribution to coupling (luminosity ≥30 fb-1 for MH ~ 160 GeV, H→WW)
JONAS STRANDBERG
Higgs Coupling to Weak Gauge Bosons• Generalized parametrization of theHiggs coupling to vector bosons:
T µ!(q1, q2) = a1(q1, q2)gµ!
+a2(q1, q2) [q1 · q2gµ!
! qµ2 q!
1 ]
+a3(q1, q2)!µ!"#q1"q2#
• a1 governs the SM coupling, a2 and a3
the CPE(ven) and CPO(dd) couplings.
• Angle between jets inVBF events sensitiveto T µ!(q1, q2).
• Determine admixturefrom !!(jet, jet).
ATLAS
ATLAS
Eur. Phys. J. C51:385-414
HIGGS COUPLING TO WEAK GAUGE BOSONS 13. SYMMETRIES AND SPIN, JULY 29, 2009
Anomalous coupling in VBF
Tµν
Tµν(q1, q2) = a1(q1, q2)gµν
+a2(q1, q2)[q1 · q2gµν − qµ2 qν1 ]
+a3(q1, q2)eµνρσq1ρq2σ
JONAS STRANDBERG
Small Anomalous Coupling to Gauge Bosons• After establishing dominant coupling is Standard Model-like:– Check for additional small anomalous CPE coupling.
ATLAS ATLAS
• Expected precision on the determination of gHZZe for 30 fb!1:
– !(gHZZe ) = 0.11 in the H ! WW channel forMH = 160 GeV.
– !(gHZZe ) = 0.24 in the H ! !! channel forMH = 120 GeV.
Eur. Phys. J. C51:385-414SMALL ANOMALOUS COUPLING TO GAUGE BOSONS 16. SYMMETRIES AND SPIN, JULY 29, 2009
14
Fast Simulation only
Higgs self-coupling
15
Self-coupling
Self coupling is the missing part to establish the Higgs mechanism: measure HH production
!"#$%&'(()#*+,'-(%+.#,.*#/%00+#1*2.'&%+1#,.*#/%00+#-"+"&#+*($32"45(%&0#.'+#,"#-*#1*'+46*78#
96"++#+*2,%"&+#$"6#//#56"742,%"&8
+1'((#+%0&'(#26"++3+*2,%"&+:#('60*#-'2;06"4&7+#$6"1##,,:#<<:#<=:#<<<:#,,,,:#<,,:>>>
&"#+%0&%$%2'&,##1*'+46*1*&,#5"++%-(*#',#,.*#?/9
&**7#@45*6#?/9####?#A#BCDE 213F +*23B:#GCCC#$-3B
H%IJ#/%00+#-"+"&#+*($32"45(%&0#K#
!"#$%&'(()#*+,'-(%+.#,.*#/%00+#1*2.'&%+1#,.*#/%00+#-"+"&#+*($32"45(%&0#.'+#,"#-*#1*'+46*78#
96"++#+*2,%"&+#$"6#//#56"742,%"&8
+1'((#+%0&'(#26"++3+*2,%"&+:#('60*#-'2;06"4&7+#$6"1##,,:#<<:#<=:#<<<:#,,,,:#<,,:>>>
&"#+%0&%$%2'&,##1*'+46*1*&,#5"++%-(*#',#,.*#?/9
&**7#@45*6#?/9####?#A#BCDE 213F +*23B:#GCCC#$-3B
H%IJ#/%00+#-"+"&#+*($32"45(%&0#K#
!"#$%&'(()#*+,'-(%+.#,.*#/%00+#1*2.'&%+1#,.*#/%00+#-"+"&#+*($32"45(%&0#.'+#,"#-*#1*'+46*78#
96"++#+*2,%"&+#$"6#//#56"742,%"&8
+1'((#+%0&'(#26"++3+*2,%"&+:#('60*#-'2;06"4&7+#$6"1##,,:#<<:#<=:#<<<:#,,,,:#<,,:>>>
&"#+%0&%$%2'&,##1*'+46*1*&,#5"++%-(*#',#,.*#?/9
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H%IJ#/%00+#-"+"&#+*($32"45(%&0#K#
16
small signal cross section, large backgrounds from top and vector boson production
measurement may be possible at the SuperLHC, with high luminosity - more studies needed
luminosity needed: ~ 6000 fb-1
Conclusions
Not only the Higgs’ DISCOVERY but also its IDENTIFICATION will be possible with ATLAS and CMS eventually (>30 fb-1)
most important channels are H→γγ and H→ZZ→4l for accurate measurement of the peak
we will measure
MH to 1%,
Γtot to 15% for MH > 200 GeV
partial widths and couplings (ratios and absolutely)
spin/CP and possible anomalous couplings
the parameters of the Higgs potential need at least the SLHC
17
References
All the plots in this talk (unless otherwise stated) show results presented in:
The CMS Collaboration, CMS Physics Technical Design Report, Volume II: Physics Performance, 2007 J. Phys. G: Nucl. Part. Phys. 34 995
The ATLAS Collaboration, Expected Performance of the ATLAS Experiment, Detector, Trigger and Physics, CERN-OPEN-2008-020, Geneva, 2008
18
Backup
Discovery potential (14 TeV)
LHC has the potential to discovery or exclude the Higgs in the mass range 100-600 GeV
Combination of several channels for low mass range
“golden channel” ZZ for large mass range, MH > 200 GeV
Vector boson decay for very large masses
Once a Higgs-like signal is discovered: measure the mass of the new particleuseful channels: H->ZZ and H->γγ
20
(GeV)Hm100 120 140 160 180 200 220
expe
cted
sig
nific
ance
0
2
4
6
8
10
12
14
16
18Combined
4l (*)
ZZ
µ eWW0j µ eWW2j
ATLAS-1L = 10 fb
Discovery potential (14 TeV)
21
(GeV)Hm100 200 300 400 500 600
expe
cted
sig
nific
ance
0
2
4
6
8
10
12
14
16
18Combined
4l (*)
ZZ
µ eWW0j µ eWW2j
ATLAS-1L = 10 fb
LHC has the potential to discovery or exclude the Higgs in the mass range 100-600 GeV
Combination of several channels for low mass range
“golden channel” ZZ for large mass range, MH > 200 GeV
Vector boson decay for very large masses
In the plot: significance in ATLAS in the whole mass explored by the experiments
Determination of the mass in CMS (14 TeV)
CMS estimate of the statistical precision on the mass measurement for H→γγ and H→ZZ→4l (from Physcs TDR)no systematic uncertainty included in this estimate
22
Resolution on the mass in ATLAS (14 TeV)
23
ATLAS estimate of the RMS on the diphoton invariant mass for Higgs mass measurement for H→γγ (from CSC note)no systematic uncertainty included in this estimate
left: unconverted photons, right: at least one converted photonthe text per box shows the region number, the percentage of events occurring in that region, and the RMS of the diphoton invariant mass
VBF analysis (14 TeV)
MH < 140 GeV
H→ττ is a powerful channel for VBF
production
Contribution in H→WW or H→γγ is not negligible.
Experiments can improve their
analysis using a more VBF-like
selection, thanks to the high precision in reconstructing the
forward jets
24
Forward jets (tag)
Higgs decay
Marco Delmastro (Blois 2009) Searches for the Higgs boson at LHC 21
2 high pT tag jets at large rapidity no color flow between tag
jets implies a rapidity gap, thus the central jet veto effective to reduce backgrounds
Higgs mass is reconstructed using the collinear approximation and the angle between the two
VBF analysis in H→WW (14 TeV)
Leading jets properties in
VBF H→WW and most relevant backgrounds
25
VBF analysis in H→ττ (14 TeV)
26
Leading jet pseudorapidity
Jet reconstruction efficiency in pt and η
Reconstruction of the Higgs peak
Cross section at 7 TeV
Cross section at 7 TeV:
27
Ratio of cross sections at different center-of-mass energies (10 TeV as a reference)
Projection (7 TeV)
Within the expected luminosity for the first run (1 fb-1):
exclusion limit, combining all channels and both experiments, 140 < MH < 200 GeV
high sensitivity in part of the tanβ/MA plane, to discover or exclude h (for MSSM)
NOTE-2010/008 The CMS physics reach in searches at 7 TeV
Similar results to be released by ATLAS
28
Assuming only the dominant couplings of SM are present: fit relative couplings
α, β: coefficients that relate the coupling strenght to the relative production Xsect or BR, calculated from SM predictions
From widths to couplings
29
Unc
erta
inty
on
r. of
cou
plin
gs:
Spin and CP in H->WW->llνν
angular correlation between the two leptons - if the Higgs is a spin-0 particle
Marco Delmastro (Blois 2009) Searches for the Higgs boson at LHC 18
correlation between 2 leptons, preferentially emitted in the same direction in the Higgs rest frame
Marco Delmastro (Blois 2009) Searches for the Higgs boson at LHC 18
correlation between 2 leptons, preferentially emitted in the same direction in the Higgs rest frame
Spin and CP in H->ZZ->4l (ATLAS)Prospective analysis of spin- and CP-sensitive variables in H→ZZ→llll at the LHC, C.P. Buszello, et al., Eur. Phys. J. C 32, 209–219 (2004)
Leptons angular distribution for θ, ϕ:
Observables give test for spin-0 vs spin-1 hypothesis, and parity +1 vs -1
F (φ) = 1 + αcosφ+ βcos2φ
G(θ) = T (1 + cos2θ) + Lsin2θ
JONAS STRANDBERG
Observables R, ! and "
• The angle between the 2 Z’s decay planes, !, expected to becorrelated mainly for transversely polarized Z bosons.– Correlation starts to disappear forMH > 300, longitudinal Z’s.
• Angular distributions for " and ! described by:F (!) = 1 + # cos! + $ cos 2!
G(") = T (1 + cos2") + L sin2"
• Define observables #, $ and R = (L ! T )/(L + T ).
• Test for:– Spin 1, CP +1– Spin 1, CP -1– Spin 0, CP -1
OBSERVABLES R, ! AND " 8. SYMMETRIES AND SPIN, JULY 29, 2009
31
ATLAS
Spin and CP in H->ZZ->4l (CMS)
General structure:
κ momenta of the V(ector) bosons, p = k1 + k2 momentum of Φ (Higgs particle with unspecified CP values)
Case study: SM-like scalar with a pseudoscalar contribution (κ = 1, η ≠ 0 and ζ = 0)
In this case, the decay width will have the SM term (scalar), a pseudoscalar term (~η2) and an interference term (~η, violating CP)SM case: η = 0, pseudoscalar case: η→∞ (or: tanξ = η, -π/2 < tanξ < π/2)
φ, θ permits discrimination
JONAS STRANDBERG
Observables R, ! and "
• The angle between the 2 Z’s decay planes, !, expected to becorrelated mainly for transversely polarized Z bosons.– Correlation starts to disappear forMH > 300, longitudinal Z’s.
• Angular distributions for " and ! described by:F (!) = 1 + # cos! + $ cos 2!
G(") = T (1 + cos2") + L sin2"
• Define observables #, $ and R = (L ! T )/(L + T ).
• Test for:– Spin 1, CP +1– Spin 1, CP -1– Spin 0, CP -1
OBSERVABLES R, ! AND " 8. SYMMETRIES AND SPIN, JULY 29, 200932
CJ=0ΦV V = κ · gµν +
ζ
m2V
· pµpν +η
m2V
· �µνρσk1ρk2σ
Spin and CP in H->ZZ->4l (CMS)
In this case, the decay width will have the SM term (scalar), a pseudoscalar term (~η2) and an interference term (~η, violating CP)SM case: η = 0, pseudoscalar case: η→∞ (or: tanξ = η, -π/2 < tanξ < π/2)
φ, θ permits discrimination
JONAS STRANDBERG
Observables R, ! and "
• The angle between the 2 Z’s decay planes, !, expected to becorrelated mainly for transversely polarized Z bosons.– Correlation starts to disappear forMH > 300, longitudinal Z’s.
• Angular distributions for " and ! described by:F (!) = 1 + # cos! + $ cos 2!
G(") = T (1 + cos2") + L sin2"
• Define observables #, $ and R = (L ! T )/(L + T ).
• Test for:– Spin 1, CP +1– Spin 1, CP -1– Spin 0, CP -1
OBSERVABLES R, ! AND " 8. SYMMETRIES AND SPIN, JULY 29, 2009
33
from CMS Physics TDR
Discrimination SM vs MSSM
If determination of couplings shows a discrepancy with SM predictions: how well LHC can distinguish between SM and another model? example: MSSM
M.Duhrssen et al, Phys. Rev. D 70, 113009 (2004)
considering m_A > 150 GeV, the narrow peak at low mass of the h particle is well separated, similar analysis to SM analysis
5 σ and 3 σ curves in MA - tanβ plane, for different luminosities.
On the left of the curve, the region where the χ2 test can distinguish between SM and MSSM