V.A. Khoze (IPPP, Durham)

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FP-420
Diffractive processes at the LHC as a means to
study SUSY Higgs sector
V.A. Khoze (IPPP, Durham)
(in collaboration with S. Heinemeyer, M. Ryskin,
W.J. Stirling, M. Tasevsky and G. Weiglein )
Main aims -to demonstrate that Double Proton
Tagging _at_LHC is especially
beneficial for the detailed studies of the MSSM
Higgs bosons
-to illustrate and to compare the salient
features of the three main
decay channels (bb, WW, ??)
for studies in the forward proton mode
- hunting the CP-odd Higgs in the
diffractive environment
?If the potential experimental challenges are
resolved, then there is a very real
chance that for some areas of the MSSM parameter
space the DPT could be the LHC Higgs
discovery channel !
Disclaimer some of the results are (very)
preliminary and should be taken only
as a snapshot of the current
understanding. Studies
are still ongoing.
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Main motivations

• addressing the issues of
• ? current theoretical understanding of the MSSM
  Higgs sector, ( e.g. CHWW-05 )
• ? impact on the CP-even SUSY Higgs searches in
  the DPT mode in
• various regions of the parameter space (
  defining the best case scenarios)
• ? update of attempts to account for the
  real-life reduction factors for the
• observable signal (trigger, tagging
  efficiencies, angular cuts ) help from Monika
  and Albert
• 
  (first studies DKMROR-02 , a lot
  of activity since then )
• ? evaluation of the bb- backgrounds in the more
  realistic
• conditions (e.g., current understanding of
  the RP acceptances...).

(P. Bussey, Manch. wksp-05)
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• The advantages of CED
  Higgs production
• Prospects for high accuracy mass measurements
  irrespectively of the decay mode.
• ( H-width and even missing mass lineshape
  in some BSM scenarios).
• Valuable quantum number filter/analyzer.
• ( 0 dominance CP -even)
• ? difficult or even impossible to explore the
  light Higgs CP at the LHC conventionally.
• (selection rule - an important
  ingredient of pQCD approach,
• H ?bb opens up (Hbb Yukawa coupling)
• (gg)CED ? bb LO (NLO,NNLO) BGs -gt
  studied
• SM Higgs S/B3(1GeV/?M), ?M?
  3 ?
• complimentary information to the
  conventional studies.
• ? MSSM Higgs (with large tan?) ? CED friendly
  .
• H ?WW/WW - an added value
• ?? - potential of an advantageous investment
• ? NMSSM (with J. Gunion et al. ) e. g.,
  H?4 ? (2?- trigger)

to warm-up
? LHC after discovery stage, Higgs ID
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• ?Experimental Advantages
• - Measure the Higgs mass via the missing mass
  technique
• - Mass measurements do not involve Higgs decay
  products
• - Cleanness of the events in the central
  detectors.
• Experimental Challenges
• Tagging the leading protons
• Selection of exclusive events backgrounds
• Triggering at L1 in the LHC experiments
• Uncertainties in the theory
• Unusually large higher-order effects, model
  dependence of
• prediction (soft hadronic physics is involved
  after all)

There is still a lot to learn from present and
future Tevatron diffractive data (KMRS-
friendly so far). BREAKING NEWS, ????-CDF
(Dec.2005)
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Recall
Theoretical Input
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(h ? SM-like, H/A- degenerate.)
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(theoretical expectations more on the
conservative side)
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(KMR- based estimates)

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(more on the pessimistic side, studies based on
the CMS Higgs group procedure still to come)
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(2 jet L1 trigger condition)
-10 muon-rich final states (no RP condition)
-1
, 300fb
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-1
(600fb )
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Current Experimental Understanding and
Assumptions
thanks to Monika, Albert , Michele Peter
bb mode

• ?Triggering on H (120 GeV) currently a
  special challenge.. Necessitates L1 jet ET as low
• as 40 GeV . QCD background saturating the
  available output bandwidth.
• ?2j L1 trigger condition can be kept on
  acceptable level by requiring single-sided 220 m
  RP condition (up to L21033), Signal
  efficiencies 10-15.
• ?10 of the bb events can be retained by
  exploiting muon-rich final states (no RP
  requirements).
• ?At M120 GeV an overall reduction factor
  (combined effect of trigger/tagging efficiencies,
  angular cut) R(120 GeV)13 (more on the
  optimistic side).
• Assume R13 at Mlt180 GeV.
• ?At M?180 GeV we may avoid the RP condition in
  the trigger, and the reduction factor can
  become R? 5. Prospects to work at higher
  luminosities. believable (Albert, Peter)
• Assume R5 at Mgt180 GeV.

? But mass resolution is much poorer when
combining with 220m RP
the situation may be even better though no
detailed studies so far
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Note, the existing estimates assume current
hardware

• ?1/R should rise with increasing M, partially
  compensating decreasing ?(CED).
• (saturation probably somewhere around 200-250
  GeV)
• ?increasing RP acceptance (e.g. factor of
  1.3 when going from 120 to 180)
• ? b-tagging efficiency, mass resolution
  improve for larger masses.
• ? trigger efficiency should increase for
  larger M,
• Mass resolution is critical for the S/B for the
  SM 120 GeV Higgs.
• Less critical at larger masses.

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?? mode ?A sub-sample of the general dijet
sample. ?Assume reduction factor R 13
situation may be (much) better, especially at
larger M.
?Trigger
thresholds are lower than for the general
category. ? Might be possible to find the
signatures allowing to avoid the RP condition.
semileptonic decays, missing ET
..event topology (Monika, Albert)
No
dedicated studies yet. ?Irreducible bkgds (QED)
are small and controllable. QCD bkgd is
small if g/?- misidentification is lt0.02
(currently 0.007 for ?-jet
efficiency 0.60)
?Trigger cocktail - combined statistics
(especially for searches and CP-ID purposes)
bb and ?? are taken on the L1 simultaneously
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WW mode
(detailed studies in B. Cox et al.
hep-ph/0505240)
? No trigger problems for final states rich in
higher pT leptons. Efficiencies 20 (including
Br) if standard leptonic (and dileptonic) trigger
thresholds are applied. Extra 10-15 from L1 jet
RP condition. Further improvements, e.g.
dedicated ? -decay trigger. ?Much less sensitive
to the mass resolution. ?Irreducible backgrounds
are small and controllable. Within 30fb-1 of
delivered lumi about 5 events of SM H(140 GeV)
1.5 events of H(120GeV). Statistics may double
if some realistic changes to leptonic
trigger thresholds are made. The h- rate can
rise by about a factor of 3.5-4 in some
MSSM models (e.g., small ?eff scenario).
(Monika)
? Pile-up is not such a severe problem as one
might expect. The centrally tagged
data may be analysed efficiently even at
1034 lumi, using the timing technique.
FP-420
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h?bb
mhmax scenario, ?200 GeV, MSUSY 1000 GeV
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H?bb
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h???
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H???
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h?WW
small ?eff scenario
mh? 121-123 GeV
for the SM Higgs at M 120 GeV ? 0.4 fb,
at M 140 GeV ? 1 fb
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Current understanding of the bb backgrounds for
CED production
?for reference purposes SM (120 GeV)Higgs in
terms of S/B ratio (various uncrt. cancel)
? First detailed studies by De Roeck et
al. (DKMRO-2002)
? Preliminary results and guesstimates work
still in progress
S/B?1 at ?M ?4 GeV
Four main sources (1/4 each)

• ? gluon-b misidentification (assumed 1
  probability) Prospects to improve in the CEDP
• 
  environment
  ? Better for larger M.
• ? NLO 3-jet contribution
  Correlations, optimization -to be
  studied.
• ? admixture of Jz2 contribution
• ?b-quark mass effects in dijet events
  Further studies of the higher-order QCD
• 
  in progress

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• ? The complete background calculations are
  still in progress
• (unusually large high-order QCD and
  b-quark mass effects).
• ? Optimization, MC simulation- still to be done
• Mass dependence of the ?SM(CEDP) SH1/M³
• Bkgd ?M/M for ???,
• ?M/M for ?
• ? ( ?M ,triggering, tagging etc improving with
  rising M)

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h? bb, assume currently ? S/?SB, mhmax
scenario, ?200 GeV
(MS) MSSM
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H?bb
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h???
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H???
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Resume

• ? H?bb in the high mass range (MA?180-250
  GeV)
• -unique signature for the MSSM,
• cross-sections overshoot the SM case by orders
  of magnitude.
• -possibility to measure the Hbb Yukawa coupling,
• -nicely complements the conventional Higgs???
  searches
• - CP properties, separation of H from A,
• unique mass resolution,
• -may open a possibility to probe the wedge
  region !?
• -further improvements needed ( going to high lumi
  ?....)
• (more detailed theoretical studies required )
• ? h, H?bb, in the low mass range (MA lt 180 GeV)
• -coverage mainly in the large tan ? and low MA
  region,
• -further improvements (trigger efficiency.)
  needed in order to increase
• coverage

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• ? h,H? ?? in the low mass range (MAlt180 GeV)
• essentially bkgd free production,
• need further improvements, better
  understanding..,
• -possibility to combine with the bb-signal
• (trigger cocktail )
• -can we trigger on ?? without the RP condition ?
• ? h? WW
• -significant (4) enhancement as compared to
  the SM case
• in some favourable regions of the MSSM parameter
  space.

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Hunting the CP-odd boson, A
?(LO) selection rule an attractive feature of
the CEDP processes, but ? the flip side to
this coin strong ( factor of 10²
)suppression of the CED production of the A
boson. ?A way out to allow incoming protons
to dissociate (E-flow ETgt10-20 GeV)
KKMR-04 pp? p X H/A Y p
(CDD)
in LO azim. angular dependence cos²? (H), sin²?
(A), bkgd- flat
A testing ground for CP-violation studies in the
CDD processes (KMR-04)
? challenges bb mode bkgd conditions
??-mode- small (QED)bkgd, but low Br
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CDD results at ?? (RG) gt3, ETgt20 GeV
? within the (MS) MSSM, e.g. mh
scenarios with ? 200 (500) GeV, tan?30-50
?CDD(A-gtbb) 1-3 fb, ?CDD(A-gt??) 0.1-03
fb ?CDD(H)-?CDD(A)
max
bb mode challenging bkgd conditions (S/B
1/50). ??-mode- small (QED) bkgd, but low
Br situation looks borderline at best

• ? best case (extreme) scenario
• mh with ?-700 GeV , tan? 50, mg
  10³GeV

max
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in this extreme case ?(A?gg) Br(A?bb) ? 22-24
MeV at MA160-200 GeV ,tan? ?50,
?CDD (A ?bb) is decreasing
from 65fb to 25fb (no angular cuts)

? ?CDD (A???) ? 0.8-0.3 fb
A ?
S/B ?(A-gtgg) Br (A-gtbb) /? MCD ? 5.5
/?MCD (GeV) currently ?MCD 20-30 GeV (??12GeV
at 120 GeV) Prospects of A- searches strongly
depend, in particular, on the possible progress
with improving ?MCD in the Rap. Gap
environment
We have to watch closely the Tevatron exclusion
zones
There is no easy solution here, we must work hard
in order to find way out .
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Proton Dissociative Production (experimental
issues)
thanks to Monika, Michele Albert
Can we discriminate between the cos²? and sin²?
experimentally ?
? Measurement of the proton diss. system with ET
of 20 GeV and 3lt?lt5 -probably OK for
studying the azimuthal distributions (HF or
FCAL calorimeters) ? Trigger is no problem if
there is no pile up (Rap Gaps at Level 1)
4jet at 210³³ lumi- borderline
Maybe we can think about adding RPs into the
trigger ( no studies so far) Maybe neutrons
triggered with the ZDC (Michele )?
? From both the theoretical and experimental
perspectives the situation with searches
for the A in diffractive processes looks
at best borderline,
but the full simulation should be performed
before arriving at a definite conclusion.
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Known Unknowns or Unknown Unknowns ?
(challenges, questions, miscommunication,
misinterpretation, mis ) ?Triggering on the
bb- channel without RP condition at M? 180 GeV
? ? Electrons in the bb trigger ? ?Triggering
on the ??- channel without RP condition at lower
M values ? ?Mass dependence of the signal
reduction factor for the bb-channel ? ? Trigger
cocktail for the searches CP ID purposes.
?Experimental perspectives for the CP-odd Higgs
studies in the p-dissociation modes ? ?Mass
window ?MCD from the Central Detector only (bb,
?? modes) in the Rap Gap environment? Can we do
better than ?MCD 20-30 GeV? Mass dependence of
?MCD ?
?How to trigger on events with both protons in
the 420m RP ? Increase in L1 trigger latency
(SLHC) ? Special running modes ?.... ?Going
to higher luminosities (up to 1034) ?
Pile-up. ?
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CONCLUSION

• ?Forward Proton Tagging would significantly
  extend the Higgs study reach
• of the ATLAS and CMS detectors.
• ? FPT has a potential to perform measurements
  which are unique at LHC and complementary to
  ILC.
• ?For certain BSM scenarios the FPT may be the
  Higgs discovery channel.
• (even with the current hardware)

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? The LHC start-up is approaching
FP-420

• Nothing would happen before the experimentalists
  and engineers
• come FORWARD and do the REAL WORK

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BACKUP