LPC Hosted VBF Workshop, June, 2009 1

LPC VBF WorkshopLPC VBF WorkshopLPC VBF WorkshopLPC VBF Workshop

Welcome

and

Introduction

Dan Green

Fermilab

LPC Hosted VBF Workshop, June, 2009 2

WelcomeWelcomeWelcomeWelcome

• We are pleased to host a LHC Physics Center (LPC) Workshop – especially on VBF since the US physicists took large responsibility for the HF = tag jets

• If we find a “Higgs”, VBF will be an indispensible tool for exploring properties and isolating couplings.

• There is an exciting program at this Workshop – and we hope you enjoy it.

LPC Hosted VBF Workshop, June, 2009 3

QED – “VBF” at a Few GeVQED – “VBF” at a Few GeVQED – “VBF” at a Few GeVQED – “VBF” at a Few GeV

24 / 3s

2 316 ( / )(2 1) ln( / 2 ) ln( / )eM J s m s M

Single s channel photon cross section falls with s. The 2 photon cross section has additional coupling constants but rises with s. At 100 GeV the cross section for dimuon production ( 90 pb) is comparable to the 2 photon production of ηc ( 33 pb). In general the 2 photon cross section exceeds the single photon at a few GeV

Electron-positron annihilation into 1 photon “decaying “ into a lepton pair.

LPC Hosted VBF Workshop, June, 2009 4

Two Photon PhysicsTwo Photon PhysicsTwo Photon PhysicsTwo Photon Physics

• e are light so that WW radiative processes begin to dominate at a few GeV

• Compare 1 photon production of mu pairs to 2 photon production of eta mesons:

• Ratio is ~ 10% at 10 GeV CM energy, rising faster than linearly with s.

3

~ 0.5 , ~ 1

/ ~ (12 / ) ( / ) ln( / 2 ) ln( / )e

M GeV keV

s M s m s M

LPC Hosted VBF Workshop, June, 2009 5

EW – W EmissionEW – W EmissionEW – W EmissionEW – W Emission

2 2/

/

~ / 8 (1/ ) ln(4 / )

~ / 4 (1/ )(1 )T

L

q W W W

q W W

f x E M

f x x

2 2 2 2/

2/

2

ˆ( / ) ~ ( / 8 ) (1/ )[ln( / ) ][(2 ) ln(1/ ) 2(1 )(3 )]

( / ) ~ ( / 4 ) (1/ )[(1 ) ln(1/ ) 2(1 )]

ˆ/

T T

L L

qq W W W W

qq W W W

d d s M

d d

M s

Weizacher-Williams approx – virtual W. Source function has coupling strength, EW, and a radiative 1/x behavior. Transverse virtual W dominate

Luminosity of transverse W >> that for longitudinal W – but H couples preferentially to longitudinal W. Luminosity of WW in quark- antiquark pair, WW mass M

LPC Hosted VBF Workshop, June, 2009 6

WW in ppWW in ppWW in ppWW in pp

min

1 1

/ /

1

/

( / ) ( / ) ( / ) ( ) ( / )( / )

/

( ) ( / ) ( )

pp WW q q qq WW

pp WW X pp WW WW X

d d d dx x f x f x d d

s d d d s

Luminosity of WW in pp system and cross section to produce X through VBF in pp reactions.

2 3/

2 2/

~16 ( / )( / )

~ / ( / )

pp H WW pp WW

pp H W W pp WW

M d d

M d d

VBF of H has a WW width which grows a cube of H mass – cancels the cross section falloff as M cubed. Falloff of H cross section via VBF with energy is slow. At high enough energy VBF is the dominant process.

LPC Hosted VBF Workshop, June, 2009 7

NumericalNumericalNumericalNumerical

For a mass of 0.5 TeV in 14 TeV pp collisions:

tau ~ 0.0013

dl/dtau ~ 0.005

pp cross section via VBF is ~ 1.3 pb. This is a substantial fraction of the total H production cross section.

LPC Hosted VBF Workshop, June, 2009 8

VBF at a Few TeVVBF at a Few TeVVBF at a Few TeVVBF at a Few TeV

The e/p mass ratio is ~ 2000. Radiative processes begin to be important ( e.g. p radiation in the LHC must be carried by the beam pipe) at a few TeV.

LPC Hosted VBF Workshop, June, 2009 9

CALCHEP – VBF, H(180)CALCHEP – VBF, H(180)CALCHEP – VBF, H(180)CALCHEP – VBF, H(180)

Run CALCHEP for H(180) in pp 7+7 TeV. Tag jet separation in y is not all that large. – no cuts made on sample. Need to use all the topological characteristics of the VBF process.

LPC Hosted VBF Workshop, June, 2009 10

Tag JetsTag JetsTag JetsTag Jets

Tag jet Pt ~ MW/2. Tag jets are opposite in azimuth – assuming SM Higgs CP assignment. Mass of tag jet pair is fairly large. Perhaps use more sophisticated statistical methods – NN ?

LPC Hosted VBF Workshop, June, 2009 11

WW ScatteringWW ScatteringWW ScatteringWW Scattering

Use VBF to study WW scattering at all WW masses. If H mass is large, effectively study strong WW scattering as unitarity limit is approached – photon, H and Z - s channel and t channel and W quartic coupling. Can we use VBF to explore strong WW scattering?

LPC Hosted VBF Workshop, June, 2009 12

WW Scattering - H(200)WW Scattering - H(200)WW Scattering - H(200)WW Scattering - H(200)

Sharp t channel peak – photon, Z exchange. Cross section vs E is for H mass of 200 GeV. Large resonant WW peak unitarizes the weak cross section. In this case the resonance is the focus.

LPC Hosted VBF Workshop, June, 2009 13

WW – Heavy Higgs, H(2000)WW – Heavy Higgs, H(2000)WW – Heavy Higgs, H(2000)WW – Heavy Higgs, H(2000)

Set H mass = 2 TeV – WW cross section in SM decreases smoothly. Look for high mass deviations from SM is no Higgs found. Isolate WW -> WW using VBF?

LPC Hosted VBF Workshop, June, 2009 14

Other “VBF” Contributions ?Other “VBF” Contributions ?Other “VBF” Contributions ?Other “VBF” Contributions ?

WWWggs vs 22 ,

HWtWsgg

HWHWWW

MMM

MMM22

2

)/(~

)/(~

Compared to VBF the simple vertex counting gives:

The width are ~

222 )/()/(~ HtWss MMratio

For a light H the ratio of cross sections is of order 1, so there may be other terms in “VBF”. In fact, the strong production backgrounds make a “standard candle” for VBF using Z instead of H not possible – as far as I can tell

LPC Hosted VBF Workshop, June, 2009 15

Evolution of VBF SearchesEvolution of VBF SearchesEvolution of VBF SearchesEvolution of VBF Searches

• More discriminating data driven ( e.g. jet veto uncertainties) methods are going to be used.

• NN or the like will use the distinctive features of VBF to maximum advantage.

• The CMS community for VBF is active and enthused

• Good hunting!