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03 August 2010

ATL-PHYS-SLIDE-2010-218

Higgs Boson parameters at LHC Serena Psoroulas, University of Bonn on behalf of the ATLAS and CMS collaborations XXIInd 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


Branching ratio

SM Higgs decay

Excluded by direct searches

Separation between low (<140 GeV) and high (> 140 GeV) mass:

E x c l u d e d

bb: MH < 130 GeV γγ: 110 < MH < 140 GeV

ττ: MH < 140 GeV 3

WW: highest significance in 2 MW < MH < 2 MZ ZZ: MH > 130 GeV


Mass


LHC has the potential to discover or exclude the Higgs in the mass range 100-600 GeV

expected significance

Discovery (14 TeV) 18 16

ATLAS

Combined (*) ZZ A 4l aa

-1

14

L = 10 fb

oo WW0j A ei µi WW2j A ei µi

12 10 8

Once a Higgs-like signal is discovered: measure the mass of the new particle useful channels: H→ZZ and H→γγ

6 4 2 0 100

120

140

160

180

200

220

m H (GeV)

5


Mass (14 TeV) 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

γγ+1jet 10 fb-1

High mass: ZZ production, Z decay into leptons

CMS 2e2μ

CMS 2e2μ

6

resolution: 2-3 GeV uncertainty: <1% (MH up to 500 GeV) luminosity needed: 10-100 fb-1


Decay width and couplings


Measurement of decay width The decay width has a strong dependance on MH MH < 200 GeV: no direct measurement

CMS 14 TeV

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

Expected performance in H→ZZ→4l from: CMS Note 2006/107 8


From rates to ratio of widths Lowest uncertainty in WW, reference for measurement of ratio of widths

Uncertainty on rate:

N (gg → H → ZZ) σgg BR(H → ZZ) ΓHZZ = = N (gg → H → W W ) σgg BR(H → W W ) ΓHW W

9

Uncertainty on ratio of widths:

Assuming one spin-0, CP-even Higgs: extract ratio of widths fitting the ratio of decay rates


From partial widths to couplings Assuming only the dominant couplings of SM are present: fit ratio of couplings using theoretical predictions for couplings to production Xsect and BR estimate with large uncertainties

New study: couplings extracted using a likelihood map Fit to absolute coupling g, sensitive also to contributions from new physics.

gjjH â&#x2020;&#x2019;

SM gjjH (1

+ â&#x2C6;&#x2020;jjH )

Uncertainty on r. of couplings:

30 fb-1

only fast simulation used in these studies other effects not taken into account yet (pileup) 10


Spin and CP


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 CPsensitive 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


– Correlation starts to disappear for MH > 300, longitudinal Z’s. • Angular distributions for θ and φ described by:

Spin and CP in H→ZZ→4l F (φ) =

1 + α cos φ + β cos 2φ

G(θ) =

T (1 + cos2 θ) + L sin2 θ

• Define observables α, β and R = (L − T )/(L + T ).

Leptons angular distribution for θ, ϕ: • Test for:

F (φ) = 1 + αcosφ –+Spin βcos2φ 1, CP +1

2 G(θ) = T (1 + cos2 θ)– + Lsin θ -1 Spin 1, CP

L = longitudinal , T = transverse – Spincontribution 0, CP -1

Z from Higgs are mostly L-polarized, Z from background are mostly T-polarized O BSERVABLES R, α AND β S YMMETRIES AND S PIN , J ULY 29, 2009 8. J ONAS S TRANDBER For MH > 300 GeV, no correlation in phi as Z are L-polarized J ONAS S TRANDBE

Measurement ofofRR Test for spin-0 vs spin-1 hypothesis, and parity +1 vs -1: Measurement

L−T R= L+T

Fast Simulation only

100 fb-1: •exclusion of non-SM cases at high mass •exclusion of Pseudoscalar case at low mass

R

ATLAS ATLAS

ATLAS ATLAS

• Predicted values of as R as 13R • Predicted values of a a

• Expected precisionon onthe the • Expected precision


T µν (q1 , q2 )

=

a1 (q1 , q2 )g µν

Anomalous coupling in VBF +a2 (q1 , q2 ) [q1 · q2 g µν − q2µ q1ν ]

+a3 (q1 , q2 )!µνρσ q1ρ q2σ

• a1 governs the SM coupling, a2 and a3 General parametrization of the Higgs coupling to the CPE(ven) and CPO(dd) couplings. vector bosons:

ATLAS

µν • AngleTbetween jets J ONAS S TRANDBERG (q1 , q2 ) = a1 in (q1 , q2 )g µν µ ν µν VBF+aevents sensitive (q , q )[q1 · q2g − q q1 ] 2 1 2 2 Small Anomalous Coupling to Gauge Bosons µν µνρσ q2 ). to T (q1 ,+a q1ρ q2σ 3 (q1 , q2 )e

• After establishing dominant coupling is Standard Model-like: • aDetermine admixture a2 and a3 governs 1 governs SM coupling; – Check for additional small anomalous CPE coupling. CPE(ven) and CPO(dd) from ∆φ(jet, jet). coupling

Angle between two highest-pt jets in VBF events is H IGGS C OUPLING TOto W EAKµν B OSONS 13. sensitive structure: T GAUGE

Eur. Phys. J. C51:385-414

Fast Simulation S YMMETRIES AND S PIN , J ULY 29, 2009 only

determination of coupling from Δϕ of jets ATLAS ATLAS determination of anomalous contribution to coupling (luminosity ≥30 fb-1 for MH ~ 160 GeV, H→WW) • Expected precision on14the determination of geHZZ for 30 fb−1 :


Higgs self-coupling 15


+*($32"45(%&0#.'+#,"#-*#1*'+46*78#

H%IJ#/%00+#-"+"&#+*($32"45(%&0#K#

Self-coupling

!"#$%&'(()#*+,'-(%+.#,.*#/%00+#1*2.'&%+1#,.*#/%00+#-"+"&# 96"++#+*2,%"&+#$"6#//#56"742,%"&8 +*($32"45(%&0#.'+#,"#-*#1*'+46*78#

H%IJ#/%00+#-"+"&#+*($32"45(%&0#K#

!"#$%&'(()#*+,'-(%+.#,.*#/%00+#1*2.'&%+1#,.*#/%00+#-"+"&# Self coupling is the missing part to establish the Higgs mechanism: measure HH production 96"++#+*2,%"&+#$"6#//#56"742,%"&8 +*($32"45(%&0#.'+#,"#-*#1*'+46*78#

96"++#+*2,%"&+#$"6#//#56"742,%"&8

+1'((#+%0&'(#26"++3+*2,%"&+:#('60*#-'2;06"4&7+#$6"1##,,:#<<:#<=:#

small signal cross section, large backgrounds from top and vector boson production

Â&#x; &"#+%0&%$%2'&,##1*'+46*1*&,#5"++%-(*#',#,.*#?/9 &**7#@45*6#?/9####?#A#BCDE 213F +*23B:#GCCC#$-3B

+1'((#+%0&'(#26"++3+*2,%"&+:#('60*#-'2;06"4&7+#$6"1##,,:#<<:#<=:#<<<:#,,,,:#<,,:>>> measurement may be possible at the SuperLHC, with high luminosity - more Â&#x; &"#+%0&%$%2'&,##1*'+46*1*&,#5"++%-(*#',#,.*#?/9 studies needed &**7#@45*6#?/9####?#A#BCDE 213F +*23B:#GCCC#$-3B luminosity needed: ~ 6000 fb-1

+1'((#+%0&'(#26"++3+*2,%"&+:#('60*#-'2;06"4&7+#$6"1##,,:#<<:#<=:#<<<:#,,,,:#<,,:>>> 16


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) expected significance

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

18 16

ATLAS

Combined (*) ZZ A 4l aa

-1

14

L = 10 fb

oo WW0j A ei µi WW2j A ei µi

12 10 8 6

Vector boson decay for very large masses

4 2 0 100

Once a Higgs-like signal is discovered: measure the mass of the new particle useful channels: H->ZZ and H->γγ

120

140

160

180

200

220

m H (GeV)

20


Discovery potential (14 TeV) expected significance

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

18 16

ATLAS

Combined (*) ZZ A 4l aa

-1

14

L = 10 fb

oo WW0j A ei µi WW2j A ei µi

12 10 8

“golden channel” ZZ for large mass range, MH > 200 GeV

6 4

Vector boson decay for very large masses

2 0 100

In the plot: significance in ATLAS in the whole mass explored by the experiments

200

300

400

500

600 m H (GeV)

21


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) 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 photon the text per box shows the region number, the percentage of events occurring in that region, and the RMS of the diphoton invariant mass

23


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

Forward jets (tag)

2 high pT tag jets at large rapidity

Higgs decay

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 

Marco Delmastro (Blois 2009)

Searches for the Higgs boson at LHC

24

21


VBF analysis in Hâ&#x2020;&#x2019;WW (14 TeV)

Leading jets properties in VBF Hâ&#x2020;&#x2019;WW and most relevant backgrounds

25


VBF analysis in H→ττ (14 TeV) Leading jet pseudorapidity

Reconstruction of the Higgs peak

Jet reconstruction efficiency in pt and η

26


Cross section at 7 TeV Cross section at 7 TeV:

Ratio of cross sections at different centerof-mass energies (10 TeV as a reference) 27


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


From widths to couplings Assuming only the dominant couplings of SM are present: fit relative couplings

Uncertainty on r. of couplings:

ι, β: coefficients that relate the coupling strenght to the relative production Xsect or BR, calculated from SM predictions

29


is 2009)

Spin and CP in H->WW->llνν angular correlation

 correlation between 2 leptons, preferentially emitted in the same direction in the Higgs rest frame  correlation between 2 leptons, preferentially between thethetwo leptons - ifin the Higgsrest is frame a spin-0 particle emitted in same direction the Higgs

Marco Delmastro (Blois 2009) Searches for the Higgs boson at LHC

Searches for the Higgs boson at LHC

18 18


Spin and CP in H->ZZ->4l (ATLAS) J ONAS S TRANDBERG

Observables R, α and β

Prospective analysis of spin- and CP-sensitive variables in H→ZZ→llll at the LHC, Buszello, et al.,planes, Eur. Phys. φ, J. Cexpected 32, 209–219to (2004) between theC.P. 2 Z’s decay be

mainly for transversely polarized Z bosons.

Leptons angular distribution for θ, ϕ:

on starts to disappear for MH > 300, longitudinal Z’s.

F (φ) = 1 + αcosφ + βcos2φ

tributions for θ and φ described by: F (φ) =

G(θ) = T (1 + cos2 θ) + Lsin2 θ

1 + α cos φ + β cos 2φ

Observables give test for spin-0 vs spin-1 T (1 + cos2 θ) + L sin2 θ hypothesis, and parity +1 vs -1

G(θ) =

ervables α, β and R = (L − T )/(L + T ).

CP +1

CP -1

CP -1 8.

S YMMETRIES AND S PIN , J ULY 29, 2009

31

ATLAS


Spin and CP in H->ZZ->4l (CMS) General structure: J ONAS S TRANDBERG η ζ J=0 µν µ ν µνρσ · p p + · � k k CΦV = κ · g + 1ρ 2σ V 2 2 Observables R, α and β mV mV • The angle between 2 Z’s decay planes, φ, expected be particle with κ momenta of the V(ector)the bosons, p = k1 + k2 momentum of Φ to (Higgs correlated mainly for transversely polarized Z bosons. unspecified CP values) – Correlation starts to disappear for MH > 300, longitudinal Z’s.

Case study: SM-like scalarfor with a pseudoscalar (κ = 1, η ≠ 0 and ζ = 0) • Angular distributions θ and φ describedcontribution by: F (φ) =

1 + α cos φ + β cos 2φ

In this case, the decay width will have the SM term (scalar), a pseudoscalar term (~η2) and G(θ) = T (1 + cos2 θ) + L sin2 θ an interference term (~η, violating CP) SM• case: η= 0, pseudoscalar case: tanξ Define observables α, β and R η→∞ = (L −(or: T )/(L + T=).η, -π/2 < tanξ < π/2) for: φ,•θTest permits discrimination – Spin 1, CP +1 – Spin 1, CP -1 – Spin 0, CP -1 32


Observables R, α and β

Spin and CP in H->ZZ->4l (CMS)

• The angle between the 2 Z’s decay planes, φ, expected to be correlated mainly for transversely polarized Z bosons. – Correlation starts to disappear for MH > 300, longitudinal Z’s.

• Angular distributions for θ and φ described by: F (φ) =

1 + α cos φ + β cos 2φ

In this case, the decay width will have the SM term (scalar), a pseudoscalar term (~η2) and G(θ) = T (1 + cos2 θ) + L sin2 θ an interference term (~η, violating CP) Define observables R= − T<)/(L + T ). SM case: η = 0, pseudoscalar• case: η→∞ (or: tanξα, = βη,and -π/2 < (L tanξ π/2) φ, θ permits discrimination

• Test for:

– Spin 1, CP +1 – Spin 1, CP -1 – Spin 0, CP -1

O BSERVABLES R, α AND β

8.

S YMMETRIES AND S PIN , J ULY 29, 2

from CMS Physics TDR

33


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


Higgs Boson parameters at LHC by Serena Psoroulas