Forward Proton Tagging at the LHC as a Means to Search for New Physics
V.A. Khoze (IPPP, Durham)
main aims
 to illustrate the theoretical motivations behind the recent
proposals to add the Forward Proton Taggers
to the LHC experiments.
 to show that the Central Exclusive Diffractive Processes
may provide an exceptionally clean environment to search
for and to identify the nature of new objects at the LHC
based on works in collaboration with B. Cox, A. De Roeck, A. Kaidalov, A. Martin, R. Orava, M. Ryskin and W.J. Stirling
(New studies of the MSSM Higgs sector with G. Weiglein et al., in progress)
FP-420
1
CMS & ATLAS were designed and optimised to look beyond the SM
 High -pt signatures in the central region
But…
incomplete
• Main physics ‘goes Forward’
•Difficult background conditions.
• The precision measurements are limited by systematics
(luminosity goal of δL ≤5%)
 Lack of :
•Threshold scanning , resolution of nearly degenerate states (e.g. MSSM Higgs sector)
•Quantum number analysing
•Handle on CP-violating effects in the Higgs sector
•Photon – photon reactions
p
matching Δ
X
YES-> Forward Proton Tagging
Rapidity Gaps  Hadron Free Zones
Mx ~ δM (Missing Mass)
p
RG
Is there a way out?
☺
ILC chartered territory
RG
p
p
2
Forward Proton Taggers as a gluonic Aladdin’s Lamp
(Old and New Physics menu)
•Higgs Hunting (the LHC ‘core business’)
K(KMR)S- 97-04
•Photon-Photon, Photon - Hadron Physics
•
‘Threshold Scan’: ‘Light’ SUSY
…
• Various aspects of Diffractive Physics (soft & hard ).
(strong interest from cosmic rays people
High intensity Gluon Factory
KMR-02
KMR-01
)
(underrated gluons)
KMR-00, KMR-01
QCD test reactions, dijet P-luminosity monitor
•Luminometry
•Searches for new heavy gluophilic states
KMOR-01
KMR-02, KMRS-04
FPT
Would provide a unique additional tool to complement the conventional
strategies at the LHC and ILC.
FPT  will open up an additional rich physics menu ILC@LHC
Higgs is only a part of the broad EW, BSM and diffractive program@LHC
wealth of QCD studies, glue-glue collider, photon-hadron, photon-photon interactions…
3
The basic ingredients of the KMR approach
(1997-2005)
Interplay between the soft and hard dynamics
RG signature
for Higgs hunting (Dokshitzer, Khoze, Troyan, 1987). Developed and promoted by Bjorken (1992-93)
Bialas-Landshoff- 91
( Born -level )
rescattering/absorptive
effects
Main requirements:
•inelastically scattered protons remain intact
•active gluons do not radiate in the course of evolution up to the scale M
•<Qt> >>/\QCD
in order to go by pQCD book
-4
(CDPE) ~ 10 *  (incl)
4
High price to pay for such a clean environment:
-4
σ (CEDP) ~ 10 σ( inclus.)
Rapidity Gaps should survive hostile hadronic radiation
damages and ‘partonic pile-up ‘
W = S² T²
Colour charges of the ‘digluon dipole’ are screened
only at rd ≥ 1/ (Qt)ch
GAP Keepers (Survival Factors) , protecting RG against:

the debris of QCD radiation with 1/Qt≥ ≥ 1/M
(T)

soft rescattering effects (necessitated by unitariy)
(S)
How would you explain it to your (grand) children ?
Forcing two (inflatable) camels to go through the eye
of a needle
P
H
P
5
Higgs boson
LHC cost
REWARD
2.5 billion
6
Current consensus on the LHC Higgs search prospects
•SM Higgs : detection is in principle guaranteed for any mass. ☺
•In the MSSM h-boson most probably cannot escape detection, and in large
areas of parameter space other Higgses can be found. ☺
•But there are still troublesome areas of the parameter space:
intense coupling regime of MSSM, MSSM with CP-violation…..

•More surprises may arise in other SUSY
non-minimal extensions: NMSSM……
• After discovery stage (Higgs Identification):

The ambitious program of precise measurements of the Higgs mass, width, couplings,
and, especially of the quantum numbers and CP properties would require
an interplay with a ILC (G. Weiglein ‘s talk)
7
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 ;C

•
H
, P-even)
difficult or even impossible to explore the light Higgs CP at the LHC conventionally.
(selection rule - an important ingredient of pQCD approach,
->bb ‘readily’ available
(gg)CED  bb LO (NLO,NNLO) BG’s -> studied
SM Higgs
S/B~3(1GeV/M)
complimentary information to the conventional studies.
•
For some (troublesome) areas of the MSSM parameter space may become a discovery channel
•
H →WW*/WW - an added value
•
New run of the MSSM studies is underway (with G. Weiglein et al)
•
•
 - ‘an advantageous investment’
especially for SM Higgs with M≥ 135GeV,
New leverage –proton momentum correlations
(probes of QCD dynamics, pseudoscalar ID , CP- violation effects)

LHC : ‘after discovery stage’, Higgs ID……
KMR-02; J.Ellis et al -05
8
☻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.
bb-mode requires special attention.
Uncertainties in the theory
(Unusually) large higher-order effects, model dependence of
predictions (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).
9
Exclusive SM Higgs production
b jets :
MH = 120 GeV s = 2 fb (uncertainty factor ~2.5)
MH = 140 GeV s = 0.7 fb
optimistically
MH = 120 GeV : 10 signal / O(10) background in 30 fb-1 (with detector cuts)
WW* :
MH = 120 GeV s = 0.4 fb
MH = 140 GeV s = 1 fb
H
MH = 140 GeV : 5-6 signal / O(3) background in 30 fb-1 (with detector cuts)
•The b jet channel is possible, with a good understanding of detectors and clever level 1
trigger ( μ-trigger from the central detector at L1 or/and RP(220) +jet condition)
•The WW channel is extremely promising : no trigger problems, better mass resolution at
higher masses (even in leptonic / semi-leptonic channel), weaker dependence on jet finding
algorithms
•The  mode looks advantageous
If we see SM-like Higgs + p- tags  the quantum numbers are 0++
H
10
The MSSM can be very proton tagging friendly
The intense coupling regime is where the
masses of the 3 neutral Higgs bosons are close to
each other and tan  is large
suppressed
enhanced
0++ selection rule suppresses A production:
CEDP ‘filters out’ pseudoscalar production,
leaving pure H sample for study
MA = 130 GeV, tan  = 50
Mh = 124 GeV :70 signal / (3-10) background in 30 fb-1
MH = 135 GeV : 125 signal / (2-5) background in 30 fb-1
MA = 130 GeV : 3 signal / (2-5) background in 30 fb-1
Well known difficult region for conventional channels, tagged proton channel may well be the
discovery channel , and is certainly a powerful spin/parity filter
11
EXPERIMENTAL CHECKS
Up to now the diffractive production data are consistent with K(KMR)S results
Still more work to be done to constrain the uncertainties
•Very low rate of CED high-Et dijets, observed yield of Central Inelastic dijets.
(CDF: Run I, Run II)
data up to (Et)min>50 GeV
• ‘Factorization breaking’ between the effective diffractive structure functions
measured at the Tevatron and HERA.
(KKMR-01 ,a quantitative description of the results, both in normalization and the shape of the distribution)
•The ratio of high Et dijets in production with one and two rapidity gaps
• Preliminary CDF results on exclusive charmonium CEDP. Higher statistics is underway.
•Energy dependence of the RG survival (D0, CDF)
•
CDP of γγ
BREAKING NEWS, CDF
(in line with the KMRS calculations)
12
CONCLUSION
Forward Proton Tagging would significantly extend the physics reach
of the ATLAS and CMS detectors by giving access to a wide
range of exciting new physics channels.
 FPT has the potential to make measurements which are unique at
LHC and challenging even at a ILC.
For certain BSM scenarios the FPT may be the Higgs discovery channel
within the first three years of low luminosity running
 FPT offers a sensitive probe of the CP structure of the
Higgs sector.
 Nothing would happen before the experimentalists &
engineers come FORWARD and do the REAL WORK .
The R&D studies must be completed within 12 months
(only limited time-scale and manpower available)
13
FP420
(58 physicists from 29 institutes in 11 countries)
Sub-detectors of either or both of ATLAS & CMS (common R&D route).
The UK groups lead the studies.
LOI-submitted to the LHCC:
CERN-LHCC-2005-025 LHCC-I-015
FP420 : An R&D Proposal to Investigate the Feasibility of Installing Proton Tagging
Detectors in the 420m Region at LHC.
From the LHCC minutes (November 2005)
The LHCC heard a report from the FP420 referee. In its Letter of Intent,the FP420
Collaboration puts forward an R&D proposal to investigate the feasibility of installing proton
tagging detectors in the 420 m. region at the LHC. By tagging both outgoing protons at 420 m.
a varied QCD,electroweak, Higgs and Beyond the Standard Model physics programme becomes
accessible. A prerequisite for the FP420 project is to assess the feasibility of replacing the
420 m. interconnection cryostat to facilitate access to the beam pipes and therefore allow
proton tagging detectors to be installed.
The LHCC acknowledges the scientific merit of the FP420 physics program and the
interest in its exploring its feasibility.
FP420 detector will replace the 420m interconnection cryostat
First opportunity –autumn 2008 (planned LHC shutdown)
14
FP-420
The LHC start-up is approaching
15