Higgs Production at LHC
Transcript of Higgs Production at LHC
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Higgs Production at LHC
Vittorio Del DucaINFN Torino
Roma 21 ottobre 2004
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In proton collisions at 14 TeV, and for the Higgs is produced mostly via
MH > 100 GeV
gluon fusion
weak-boson fusion (WBF)
Higgs-strahlung
associated production
largest rate for all
proportional to the top Yukawa coupling
second largest rate (mostly initial state)
proportional to the WWH coupling
third largest rate
same coupling as in WBF
same initial state as in gluon fusion, but higher range
proportional to the heavy-quark Yukawa coupling
gg → H
qq → qqH
qq̄ → W (Z)H
tt̄(bb̄)H
yt
u d
MH
x
yQ
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in the intermediate Higgs mass range
gluon fusion cross section is
WBF cross section is
yield cross sections ofWH, ZH, tt̄H
∼ 20 − 60 pb
∼ 3 − 5 pb
∼ 0.2 − 3 pb
MH ∼ 100 − 200 GeV
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proportional to the Yukawa coupling squared, and thus to
but dominated by top quark Yukawa coupling
dominated by EW coupling
proportional to αW
m2
f
proportional to m4
f/m4
H
Decay width into W ∗W
∗ plays a significant role
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total width branching fractions
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≈ 10−3Small BR:
Large backgrounds from pp → γγ
CMS and ATLAS have very good photon-energyresolution: O(1%)
Search for a narrow γγ invariant mass peak, with
Background is smooth: extrapolate it into the signal region from the sidebands
mH < 150 GeV
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Gold-plated mode: cleanest mode for 2mZ < mH < 600 GeV
Smooth, irreducible background from pp → ZZ
Small BR:
at threshold
BR(H → ZZ) is a few %
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Fully reconstructed invariant mass of the leptons
Silver-plated modeuseful for
H → ZZ → l+l−
νν̄
mH ≈ 0.8 − 1 TeV
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Exploit l+l−
angular correlations
Signal and background have similar shapes: must know background normalisation well
mH = 170 GeV
integrated luminosity: 20 fb−1
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Search channel for mH = 120 − 130 GeV
Measure h2
tBR(H → bb̄) with ht = Htt̄ Yukawa coupling
must know background normalisation well
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WBF can be measured with good statistical accuracy:
σ × BR ≈ O(10%)
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WBF featuresenergetic jets in the forward and backward directions
Higgs decay products between the tagging jets
sparse gluon radiation in the central-rapidity region,due to colourless exchange
NLO corrections increase the WBF production rate by about , and thus are small and under control
W/Z
10 %
A WBF event Lego plot
Campbell, Ellis; Figy, Oleari, Zeppenfeld 2003
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hep-ph/0203187
hep-ph/0402254
QCD/p.d.f. uncertainties:
O(20%)
O(5%) for WBF
for gluon fusionluminosity uncertainties: O(5%)Statistical significance:
NS√NS + NB
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The properties of the Higgs-like resonance are itscouplings: gauge, Yukawa, self-couplings
quantum numbers: charge, colour, spin, CP
assuming -universality, WBF and gluon-fusion ratesyield measurements of combinations of partial widths
W/Z
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Ratios of Y/X cancel uncertainties on initial state luminosities andp.d.f.’s, and allow for the determination of the ratio of the Yukawa/gaugecoupling
Zeppenfeld et al. hep-ph/0002036
The gauge coupling has also CP properties and a tensor structure. Info on that can be obtained by analysing the final-state topology of Higgs + 2 jet events (more on this later)
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a QCD loop + an EW loop
Aglietti Bonciani Degrassi Vicini 04 (light fermion loop)
Degrassi Maltoni 04(heavy fermion loop)
Relative corrections to production and decay through gluon fusion(with light fermion loop)
For the total electroweak corrections are5 to 8 % of leading order
O(α2
Sα2
W )
115 GeV ≤ MH ≤ 2MW
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O(α4
S)
2-loop1-looptree
R. Harlander hep-ph/0007289
total cross section forinclusive Higgs productionat LHC
Harlander Kilgore 02Anastasiou Melnikov 02
Ravindran Smith van Neerven 03
The band contours arelower
upper
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S. Frixione hadron collider wksp MSU 2004
Higgs distribution
difference at large is due to different default scale for NNLO + NNLL, for MC@NLO
pT
pT µ = µR = µF
µ2= M2
Hµ2
= M2
H + p2
T
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a fully differential cross section:bin-integrated rapidity distribution, with a jet veto
jet veto: requireR = 0.4
|pjT | < p
vetoT = 40 GeV
for 2 partons
R2
12 = (η1 − η2)2 + (φ1 − φ2)
2
if
if
R12 > R
|p1
T |, |p2
T | < pveto
T
R12 < R
|p1
T + p2
T | < pveto
T
MH = 150 GeV (jet veto relevant in the decay channel)H → W+W
−
K factor is much smaller for the vetoed x-sect than for the inclusive one:average increases from NLO to NNLO: less x-sect passes the veto|pj
T |
C. Anastasiou K. Melnikov F. Petriello 2004
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CaveatOdagiri hep-ph/0212215
Including parton showers and hadronisation through HERWIG, Odagiri finds much less correlation between the jets, but the plot has been obtained by generating also the jets through the showers
A better analysis would require the generation of the basic final-state topology (i.e. Higgs + 2 jets) through the exact matrix elements, and the additional radiation through showers and hadronisation
ALPGEN Collab & VDD, in progress
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In WBF no colour is exchanged in the t channel
The central-jet veto is based on the different radiation pattern expected for WBF versus its major backgrounds, i.e. production and WW + 2 jet production
The central-jet veto can also be used to distinguish between Higgs production via gluon fusion and via WBF
tt̄
Barger, Phillips & Zeppenfeld hep-ph/9412276
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Distribution in rapidity of the third jet wrt to the rapidity average of the tagging jets
Ratio of Higgs + 3 jet to Higgs + 2 jet production as a function of
Frizzo, Maltoni, VDD hep-ph/0404013
pT
min
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In Higgs + 2 jets, the azimuthal angle correlation between the two jetscan be used as a tool to distinguish between WBF and gluon fusion,and to investigate the tensor structure of the WWH coupling
Higgs + 2 jets via gluon fusion is known at leading order, including thetop mass dependence
Higgs + 2 jets via WBF is known at NLO, which increases theWBF production rate by about
it has a strong renormalisation scale dependence
the large limit is accurate if and , and is valideven when the dijet, or jet-Higgs, invariant masses are much larger than
Large-rapidity (WBF) cuts can be used to deplete gluon fusion wrt WBF
A central-jet veto can be used to further deplete gluon fusion wrt WBF; a study of the veto can be performed through Higgs + 3 jets, which has been computed at leading order in the large limitMt
Mt MH ! 2Mt pT ! Mt
Mt
10 %