lpc vbf workshop
DESCRIPTION
LPC VBF Workshop. Welcome and Introduction Dan Green Fermilab. Welcome. 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 - PowerPoint PPT PresentationTRANSCRIPT
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!