mhv rule, (super)symmetries and ‘diffractive higgs’
DESCRIPTION
. . QCD and High Energy Interactions La Thuile (Italy) , March 8-15 2008 . MHV rule, (Super)Symmetries and ‘Diffractive Higgs’. V.A. K hoze ( IPPP, Durham & PNPI ). Main aims • MHV rules and SUSY at the service of ‘diffractive Higgs’ - PowerPoint PPT PresentationTRANSCRIPT
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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 Hbb 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
QCD and High Energy InteractionsLa Thuile (Italy) , March 8-15 2008
ADR
(X. Rouby)
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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 δL ≤5% , machine ~10%)
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 , …
YES Forward Proton Tagging
Rapidity Gaps Hadron Free Zones
matching Δ Mx ~ δM (Missing Mass)
RG
RGX
p
p p
p
The LHC is a very challenging machine!
Is there a way out?
The LHC is a discovery machine !
ILC/CLIC chartered territory
The LHC is not a precision machine (yet) !
(X. Rouby)
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For theoretical audience
MHV rules, Super (symmetry) and‘Diffractive Higgs’ at the LHC
Irreducible Physics Backgrounds toDiffractive Higgs Production
at the LHC
For experimental audience
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.
(K.G)
4 not so long ago: between Scylla and Charibdis:orders of magnitude differences in the theoretical predictions are now a history
(CDPE) ~ 10 (incl) -4
(Khoze-Martin-Ryskin 1997-2008)
New CDF Excl. dijet results: A killing blow to the wide range of theoretical models.
(A.Dechambre)
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MSSMwithout ‘clever hardware’: for H(SM)bb at 60fb-1 onlya handful of events due tosevere exp. cuts and low efficiencies,though S/B~1 . But H->WW mode at M>135 GeV. (ADR,B.Cox et al-06)
enhanced trigger strategy & improved timing detectors (FP420, TDR)
The backgrounds to the diffractive H bb mode are manageable!
situation in the MSSM is very different from the SM
Conventionally due to overwhelming QCD backgrounds, the direct measurement of
Hbb is hopeless
>
Studying the MSSM Higgs Sector
SM-like
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Myths
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 |Jz|=2 production. NLO radiative contributions (hard blob and screened gluons)
NNLO one-loop box diagram (mass- unsuppressed, cut-non-reconstructible)’ ‘Central inelastic’ backgrounds (soft and hard Pomerons) b-quark mass effects in dijet events – still in progress potentially, the largest source of theoretical uncertainties!
bb
bb
some regions of the MSSM parameter space are especially proton tagging friendly (at large tan and M , S/B ) KKMR-04 HKRSTW, 0.7083052[hep-ph] B. Cox, F.Loebinger, A.Pilkington-07
250 20
coming soon
MC
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for Higgs searches in the forward proton mode QCD backgrounds are suppressed by Jz=0 selection rule and by colour, spin and mass resolution (M/M) –factors.
There must be a god
Do not need many events to establish cleanly that the Higgs is a scalar and to measure the mass
(KMR-2000)
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(D. Kosower)
9(CFCA)
NNLO
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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
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(+ n soft gluons)
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(angular brackets)
14‘Conventional’ MC algorithms cannot be used
kills soft gluon log
no collinear logs
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hard P
soft P
150 20 70 5
0.14 9d/dy|y=0
units 10-3 fbkT<5 GeVMdijet/Mbb=20%Mmissing=4GeV
signal backgd
X 1/8
SM (120 GeV) Higgs LO irreducible
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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 +(Hbb) +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.
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FP420, It is now or never
Such opportunities come rarely –let’s not waste this one!
UK
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11. 11. Thou shalt notThou shalt not delay, thedelay, the LHC start-upLHC start-up isis approaching.approaching.
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BACKUP
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dA killing blow to the wide range of theoretical models.
Visualization of QCD Sudakovformfactor
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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 Jz=2. KRS-06
sinmis g bbM M
b-direction case (HCA)
0.2 ( R/0.5)²
Note : soft radiation factorizes strongly suppressed is not a problem, NLLO bgd numerically small
bbgg
radiation from the screening gluon with pt~Qt :HC (Jz=2) LO ampt. ~ numerically very small
hard radiation - power suppressed
KMR-02cos
2( / )t tQ p
(R –separation cone size)
bbM
t tM p Q
MHV results for gg(Jz=0)ggg(g) amplitudes (dijet calibration, b-mistag)
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Approximate formula for the background
bb
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)
1 2|60 12 .0 1| 1
main uncertn. at low masses
Four major bgd sources ~ (1/4 +1/4 + (1.3)²/4 + 1/2 ) at M≈120 GeV, M= 4GeV
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mb=0