Exclusive Higgs signals at the LHC
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Exclusive Higgs signals at the LHC. SM Higgs detection at the LHC inclusive signals – a brief review exclusive diffractive signals pp  p + H + p calculation of H bb bar signal and background Exclusive SUSY Higgs signals Calibration processes at the Tevatron

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Exclusive Higgs signals at the LHC

  • SM Higgs detection at the LHC

    inclusive signals – a brief review

    exclusive diffractive signals pp  p + H + p

    calculation of H bbbar signal and background

  • Exclusive SUSY Higgs signals

  • Calibration processes at the Tevatron

    pp  p + dijet +p, pp  p + gg + p

Alan Martin (IPPP,Durham)

also gg H

A low mass Higgs (<130 GeV) will challenging

to identify

Hbb is dominant decay, but is swamped by

the QCD background

Best chance is Hgg

even though BR(Hgg) ~ 2. 10-3


signal for SM

110-130 GeV Higgs

exclusive Higgs production at the LHC

If the outgoing forward protons are measured

far from the interaction point then it is possible

to identify the Higgs and to make an accurate measurement of the

missing mass = MH




…but we must calculate the price for rapidity gaps ?

pp p + H + p

Khoze, Martin, Ryskin

If outgoing protons are tagged far from IP then s(M) = 1 GeV

(mass also from H decay products)

Very clean environment

Hbb: QCD bb bkgd suppressed by Jz=0 selection rule

S/B~1 for SM Higgs M < 140 GeV

L(LHC)~60 fb-1~10 observable evts after cuts+effic

Also HWW (L1 trigger OK) and Htt promising

SUSY Higgs: parameter regions with larger signal S/B~10,

even regions where conv. signal is challenging and

diffractive signal enhanced----h, H both observable

Azimuth angular distribution of tagged p’s spin-parity 0++

 FP420 --- letter of intent

Reliability of predn the cross section is crucial

Khoze, Martin, Ryskin

no emission when (l ~ 1/kt) > (d ~ 1/Qt)

i.e. only emission withkt > Qt

calculated using detailed

2-channel eikonal global

analysis of soft pp data

S2 = 0.026 at LHC

S2 = 0.05 at Tevatron


Monte Carlo

S2 = 0.026

S2 = 0.040


In summary, s(pp p + H + p)

contain Sudakov factor Tg which exponentially

suppresses infrared Qt region  pQCD


S2 is the prob. that the rapidity gaps survive population

by secondary hadrons  soft physics  S2=0.026 (LHC)

S2=0.05 (Tevatron)

s(pp  p + H + p) ~ 3 fb at LHC for SM 120 GeV Higgs

~0.2 fb at Tevatron



to sH(excl)?



S2 =0.026

KMR: using 2-channel eikonal


Lonnblad, Sjodahl,


BBKMuse pert.thy.corrn could

be large and negative,

 s H(excl) reduced ?

KMR  small effect

Arguments why “enhanced” correction is small

KMR ‘06

DY threshold

Original Regge calc. required DY ~ 2-3 between Regge vertices

(Recall NLL BFKL:

 major part of all order resum has kinematic origin

 DY ~ 2.3 threshold implied by NLL  tames BFKL)

Applying to enhanced diagram

need 2DY > 4.6, but at LHC only

log(sqrt(s)/MH) available for yH=0



= 4.6 for MH=140 GeV

Higgs prod. via enhanced diagram

has v.tiny phase space at LHC

Background to ppp + (Hbb) + p signal


assuming DMmiss~3 GeV

LO (=0 if mb=0, forward protons)


gg  gg mimics gg  bb (P(g/b)=1%)

after polar angle cut 0.2

|Jz|=2 admixture (non-forward protons) 0.25

mb2/ET2 contribution <0.2

HO (gg)col.sing bb+ng

Still suppressed for soft emissions.

Hard emissions if g not seen:

extra gluon along beam Mmiss > Mbb 0

extra g from initial g along b or bbar 0.2

Pom-Pom inel. prod. B/S<0.5(DMbb/MPP)2 <0.004

for M=120 GeV 

total B/S~1

S~1/M3, B~DM/M6 : triggering, tagging, DM better with rising M

s(ppp+H+p) ~ 3 fb at the LHC

For LHC integrated L = 60 fb-1

after allowing for:

efficiency of the proton taggers


b, b identification efficiency

polar angle cut

180 events  10 observable exclusive evts

with S/B~1

BSM: motivation for weak scale SUSY

Can stabilize hierarchy of mass scales: dMh2 ~ g2(mb2-mf2)

Gauge coupling unification (at high scale, but < Planck)

Provides a candidate for cold dark matter (LSP)

Could explain the baryon asymmetry of the Universe

SUSY effects at present energies only arise from loops--

so the SM works well

Provides an explanation for Higgs mechanism (heavy top)

The Higgs sector is the natural domain of SUSY. Higgs vev induced

as masses are run down from a more symmetric high scale

There must be a light Higgs boson, Mh < 140 GeV

SUSY Higgs: h, H, A, (H+, H--)

There are parameter regions where the exclusive

pp  p + (h,H) + p

signals are greatly enhanced in comparison to the SM

Selection rule favours 0++ diffractive production

Mh < 140

Mh in GeV

ppp1 + higgs + p2




mA ~ mH large

h = SM

intense coup:

mh ~ mA ~ mH

gg,WW.. coup.


SM: pp  p + (Hbb) + p S/B~10/10~1

with DM = 3 GeV, at LHC with 60 fb-1

e.g. mA = 130 GeV, tan b = 50

(difficult for conventional detection,

but exclusive diffractive favourable)


mh = 124.4 GeV 71 10 events

mH = 135.5 GeV 124 5

mA = 130 GeV 1 5


exclusive signal

5s signal at LHC

30 fb-1

300 fb-1

Tasevsky et al

Diffractive: H bb

Yuk. coupling, DMH, 0++



H,A tt

wide bump

L=60 fb-1



Motivation for cp violation in susy models
Motivation for CP-Violation in SUSY Models

  • In low energy SUSY, there are extra CP-violating phases beyond the CKM ones, associated with complex SUSY breaking parameters.

  • One of the most important consequences of CP-violation is its possible impact on the explanation of the matter-antimatter asymmetry.

  • Electroweak baryogenesis may be realized even in the simplest SUSY extension of the SM, but demands new sources of CP-violation associated with the third generation sector and/or the gaugino-Higgsino sector.

  • At tree-level, no CP-violating effects in the Higgs sector---CP violation appears at loop-level

CP violation in the Higgs sector

h, H, A mix  H1, H2, H3

mixing induced by

stop loop effects…

H1 could be light


Br.s in (fb) for H1, H2, H3 production at the LHC



cuts: (a) 60<q(b or t)<1200, (b) piT>300 MeV, (c) 45<q(b)<1350

ppp + gg + p


Measurements with Mgg=10-20 GeV

could confirm sH(excl) prediction

at LHC to about 20% or less

CDF II Preliminary

CDF Blessed this morning!


3 events observed

16 events observed

It means exclusive H must happen

(if H exists) and probably ~ 10 fb

within factor ~ 2.5.

higher in MSSM

QED: LPAIR Monte Carlo

16 events were like this:


3 events were like this:

Exptally more problematic due to

hadronization, jet algorithms, detector

resolution effects, QCD brem…

ppp + jj + p

Data plotted as fn. of Rjj = Mjj/MX, but above effects

smear out the expected peak at Rjj = 1(ExHuME MC)

Better variable:

Rj = (2ET cosh h*)/MX

highest ET jet h,ET

with h*=h-YM

Rj not changed by O(aS) final state radiation,

need only consider extra jet from initial state.

Prod.of other jets have negligible effect on Rj

due to strong ordering

We compute exclusive dijet and 3-jet prod

(and smear with Gaussian with resolution s=0.6/sqrt(ET in GeV))


Exclusive dijet and 3-jet prod




dijets dominate Rj>0.8

3-jets dominate Rj<0.7

KMR, in prep.



The exclusive diffractive signal is alive and well.

The cross section predictions are robust.

Checks are starting to come from Tevatron data (gg,dijet…)

There is a very strong case for installing proton taggers

at the LHC, far from the IP ---- it is crucial to get the

missing mass DM of the Higgs as small as possible

The diffractive Higgs signals beautifully complement the

conventional signals. Indeed there are significant SUSY

Higgs regions where the diffractive signals are advantageous

---determining DMH, Yukawa Hbb coupling, 0++ determinn

---searching for CP-violation in the Higgs sector

Expect a depletion of

pp  p + bb + p

events as Rjj 1


Diffractive c production









only order-of-magnitude estimates possible for c production


Proton tagging is a valuable weapon in LHC Higgs physics

pp  p + (H bb) + p: S/B~1 if DMmiss~3 GeV, Mmiss = Mbb

especially for the important MH < 130 GeV region

SUSY Higgs: unique signals in certain domains of MSSM

tan b large (i) mh~mH~mA (s enhanced), (ii) mA large

Exclusive double diff. prod. strongly favours 0+

Azimuthal correlations are valuable spin-parity analyzer

Distinguish 0-- from 0+ Higgs

Possibility of detecting CP-violating Higgs

“standard candles” at Tevatron to test excl. prod. mechanism

ppp + c + p high rate, but only an ord.-of-mag.estimate

ppp + jj + p rate OK, but excl. evts have to be separated

ppp + gg + p low rate, but cleaner signal

Allow p’s to dissociate

Larger signal---but no sQCD(bb) suppression,

so use H1 tt (…) EiT>7 GeV





1 + a sin 2j + b cos 2j if CP cons. then a=0, |b|=1