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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

&**7#@45*6#?/9####?#A#BCDE 213F +*23B:#GCCC#$-3B

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

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r. of

cou

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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