MHV rule, (Super)Symmetries and

1
?
?
QCD and High Energy InteractionsLa Thuile
(Italy) , March 8-15 2008 
MHV rule, (Super)Symmetries and Diffractive
Higgs
V.A. Khoze (IPPP, Durham PNPI)
Main aims MHV rules and SUSY at the service
of diffractive Higgs
major QCD backgrounds to H?bb production at the
LHC in the forward proton mode (based on works
with M.G. Ryskin, A.D. Martin and W.J. Stirling)
Higgs sector study- one of the central targets
of FP420 physics menu
ADR
(X. Rouby)
2
The LHC is a discovery machine !

• CMS ATLAS were designed and optimised to look
  beyond the SM
• ? High -pt signatures in the central region
• But
• Main physics goes Forward
• Difficult background conditions, pattern
  recognition, Pile Up...
• The precision measurements are limited by
  systematics
• (luminosity goal of dL 5 , machine 10)
• Lack of

The LHC is a very challenging machine!
The LHC is not a precision machine (yet) !
ILC/CLIC chartered territory
p
p
RG
Is there a way out?
X
YES ? Forward Proton Tagging Rapidity
Gaps ? Hadron Free Zones matching ? Mx dM
(Missing Mass)
RG
p
p
(X. Rouby)
3
For theoretical audience
For experimental audience
MHV rules, Super (symmetry) and Diffractive
Higgs at the LHC
Irreducible Physics Backgrounds to Diffractive
Higgs Production at the LHC
(K.G)
Forward Proton Mode- Main Advantages for Higgs
studies Measurement of the Higgs
mass via the missing mass technique
(irrespectively of the decay
channel) Direct H ?bb mode opens up (Hbb
Yukawa coupling) unique signature for the
MSSM Higgs sector. Quantum number/CP
filter/analyzer Cleanness of the events in the
central detectors.
4
(Khoze-Martin-Ryskin 1997-2008)
-4
?(CDPE) 10 ? (incl)
(A.Dechambre)
New CDF Excl. dijet results A killing blow to
the wide range of theoretical models.
not so long ago between Scylla and
Charibdis orders of magnitude differences in the
theoretical predictions are now a history
5
Studying the MSSM Higgs Sector
without clever hardware for H(SM)?bb at
60fb-1 only a handful of events due to severe
exp. cuts and low efficiencies, though S/B1 .
But H-gtWW mode at Mgt135 GeV. (ADR,B.Cox et
al-06) ? enhanced trigger strategy improved
timing detectors (FP420, TDR)
MSSM
situation in the MSSM is very different from
the SM
SM-like
gt
Conventionally due to overwhelming QCD
backgrounds, the direct measurement of Hbb is
hopeless
The backgrounds to the diffractive H bb mode
are manageable!
6
some regions of the MSSM parameter
space are especially proton tagging friendly
(at large tan ? and M , S/B
)

KKMR-04
HKRSTW, 0.7083052hep-ph
B. Cox, F.Loebinger, A.Pilkington-07
Myths
MC
For the channel bgds are well known and
incorporated in the MCs Exclusive LO -
production (mass-suppressed) gg misident soft
hard PP collisions.
Reality
The background calculations are still not
fully complete (uncomfortably unusually
large high-order QCD and b-quark mass effects).
About a dozen various sources (studied by Durham
group) ? admixture of Jz2 production.
? NLO radiative contributions (hard blob
and screened gluons) ? NNLO one-loop box
diagram (mass- unsuppressed, cut-non-reconstructib
le) ? Central inelastic backgrounds (soft
and hard Pomerons) ? b-quark mass effects in
dijet events still in progress
potentially, the largest source of theoretical
uncertainties!

coming soon
7
for Higgs searches in the forward proton
mode QCD backgrounds are suppressed by
Jz0 selection rule and by colour, spin and
mass resolution (?M/M) factors.
(KMR-2000)
There must be a god
Do not need many events to establish cleanly
that the Higgs is a scalar and to measure
the mass
8
(D. Kosower)
9
NNLO
(CF?CA)
10
(No Transcript)
11
Works is progress W.J. Stirling et al, A.
Shuvaev et al Preliminary results of
calculations with the SL accuracy- very
promising a factor of 8 lower than the Born
expectation (A. Shuvaev et al )
Good
12
( n soft gluons)
13
(angular brackets)
14
?kills soft gluon log
?no collinear logs
Conventional MC algorithms cannot be used
15
LO irreducible
signal
SM (120 GeV) Higgs
backgd
hard P
150
20
70
5
X 1/8
soft P
9
0.14
ds/dyy0 units 10-3 fb kTlt5 GeV DMdijet/Mbb20 D
Mmissing4GeV
16
Conclusion

• Strongly suppressed and controllable QCD
  backgrounds in the forward proton
• mode provide a potential for direct
  determination of the Hbb Yukawa coupling,
• for probing Higgs CP properties and
  for measuring its mass and width.
• In some BSM scenarios pp ?p (H?bb)
  p may become a Higgs
• discovery channel at the LHC.
• Further bgd reduction may be
  achieved by experimental improvements, better
  
• accounting for the kinematical
  constraints, correlations..
• The complete background calculation
  is still in progress
• (unusually uncomfortably large
  high-order QCD effects, Pile-Up at high lumi).
• A clear downward tendency.
• 
  
  
• 
  

?
17
?
UK

Such opportunities come rarely lets not
waste this one!
FP420, It is now or never
18
11. Thou shalt not delay, the LHC start-up is
approaching.
19
BACKUP
20
Visualization of QCD Sudakov formfactor
A killing blow to the wide range of theoretical
models.
d
21
(No Transcript)
22
? beam direction case
if a gluon jet is to go unobserved outside the
CD or FD ( )

• violation of the equality
  (limited by the )
• contribution is smaller than the admixture
  of Jz2. KRS-06

b-direction case (HCA)
0.2 ?( ?R/0.5)²
(?R separation cone size)
Note ? soft radiation factorizes ? strongly
suppressed ?is not a problem, ? NLLO
bgd ? numerically small
? radiation from the screening gluon with ptQt
KMR-02
HC (Jz2) LO ampt.
?numerically very small ? hard radiation -
power suppressed
MHV results for gg(Jz0)?ggg(g) amplitudes
(dijet calibration, b-mistag)
23
Approximate formula for the background
main uncertn. at low masses
?M- mass window over which we collect the
signal ? b-jet angular cut (

) ? both S and B should be multiplied by the
overall efficiency factor ? (combined
effects of triggers, acceptances, exp. cuts,
tagging efficienc., .), ? 4.2 (120 GeV) ?
g/b- misident. prob. P(g/b)1.3 (ATLAS)
Four major bgd sources (1/4 1/4 (1.3)²/4
1/2 ) at M120 GeV, ?M 4GeV
24
(No Transcript)
25
(No Transcript)
26
mb0