1. Diffractive Higgs production at the LHC
Alan Martin (Durham)
October 2007

2. Exclusive Higgs production at the LHC
Khoze, Martin, Ryskin
O(1 GeV) ?
far
from IP
The price for rapidity gaps ? 

4. calculated from multi-Pomeron
multi-channel eikonal analysis
of soft pp data
S2 = 0.02 at LHC
S2 = 0.05 at Tevatron
no emission when (l ~ 1/kt) > (d ~ 1/Qt)
i.e. only emission with kt > Qt

5. Description of ‘soft’ high energy pp interactions
DL: aeff = t ---but nothing about inelastic intn
Inclusion of multi-P effects essential: new analysis N*
KMR 2007
abare ~ t + +
+ ….
full multi-Pomeron
2-ch eikonal
+ …. + =
where
stotal(LHC) ~ 90 mb
S2Higgs(LHC) ~ 0.02

7. Prediction of s(pp  p + H + p)
contain Sudakov factor Tg which exponentially
suppresses infrared Qt region  pQCD H
S2 is the prob. that the rapidity gaps survive population
by secondary hadrons  soft physics  S2=0.02 (LHC)
S2=0.05 (Tevatron)
s(pp  p + H + p) ~ 3 fb at LHC for SM 120 GeV Higgs
~0.2 fb at Tevatron

8. s(ppp+H+p) ~ 3 fb at LHC for 120 GeV Higgs
if L = 60 fb-1, then 180 events
efficiency of p taggers 54
BR(Hbb) 36
b,b tag efficiency 18
polar angle cut 9
mass window
6 events

9. Background to ppp + (Hbb) + p signal
assuming DMmiss ~ 3sM ~ 5 GeV
B/S
LO (=0 if mb=0, forward protons)
gg  gg mimics gg  bb (P(g/b)=1.3%)
after polar angle cut 
Irreducibe bb 
HO (gg)col.sing  bb+ng
Soft emissions still suppressed by Jz=  ~ 0
Hard emissions if g not seen:
extra gluon along beam Mmiss > Mbb  ~ 0
extra g from initial g along b or b 
Pomeron-Pomeron inelastic 
for M=120 GeV
total B/S~1
S~1/M3, B~DM/M6 : triggering, tagging, DM better with rising M

10. hard P soft P ds/dy|y=0 units 10-3 fb kT<5 GeV DMdijet/Mbb=20%
signal
backgd
hard P
150 20 70 5
soft P
ds/dy|y=0
units 10-3 fb
kT<5 GeV
DMdijet/Mbb=20%
DMmissing=4GeV 9
0.14

11. conventional
signal for SM
GeV Higgs

12. enhanced
eikonal
S2 =0.02
BBKM. (first)
corrn could be
large and -ve,

13. BBKM  (first) corrn could be large and -ve,

14. BBKM (pQCD analysis) find first corrn could be large and –ve.
BUT…need to sum complete set of diagrams.
terms alternate in sign
Amp
70%
sum
Analogous new “soft”
non-perturbative
analysis finds that even
at low QT, amp. is not
completely suppressed
QT~2GeV
ln QT2
1st term
corrn affects mainly small QT
(large size dipoles)

15. New global fit to “soft” data
The full set of enhanced diag. are included in stot, sSD …
in global soft fit
The fit to “soft” data including enhanced rescatt.
--redistributes abs. effects between eik. and enh.
--find total S2 same
Analogously predn for stot(LHC) has v.weak model dep.
since model fits existing soft data and there is
log s energy behaviour
sSD, sensitive to enh. effects, ~flat from 100 GeV,
so expect no extra suppression of diffraction at LHC

16. Leading neutron prod. at HERA eikonal “enhanced” seen not seen g g g
KKMR ‘06
gap due to p exchange
~ exclusive Higgs
eikonal
“enhanced”
yi > 2 – 3
correction prop. to rap. interval
prop. to g energy
(negative)
Prob. to observe leading neutron
must decrease with g energy
But expt.  flat
 small enhanced correction g g g g
seen
not seen

17. Level 1 trigger 420 220 220 420 veto veto
veto-trigger spoiled by pile-up
420-trigger spoiled by c buffer ?
At present, plan to use 2 high ET jets/m (+ 420)
+…?

18. LHC every bunch crossing ! Note N = 3.5  1.7 N = 35  17
as above numbers include elastic
and low mass inelastic in pile-up

19. ~0.01N for 420m
~0.03N for 220m
Note: much recent progress (Tasevsky, Cox, Brandt,….)
using timing, dijet 4-mom = missing 4-mom., checking
multiplicity transverse to b jets, etc….much more optimistic

20. SUSY Higgs: h, H, A, (H+, H--)
There are parameter regions where the
pp  p + (h,H) + p
signals are greatly enhanced in comparison to the SM
Selection rule favours 0++ diffractive production

22. decoupling
regime:
mA ~ mH > 150
h ~ SM
bbH ~ tanb
VVH ~ 0
H,A tt (bb)
intense coup:
mh ~ mA ~ mH
gg,WW.. coup.
suppressed

23. exclusive signal
5s signal at LHC
100 fb-1

24. Adapted from a preliminary plot of Tasevsky et al. (HKRSTW)

25. Possible checks of exclusive rates at the Tevatron
“standard candles” at Tevatron to test excl. prod. mechanism
ppp + c + p high rate, but only an ord.-of-mag.estimate
ppp + jj + p rate OK, but jet algorithm, hadronization etc
ppp + gg + p low rate, but cleaner signal
“standard candles”

26. ppp + gg + p
KMR+Stirling

27. Measurements with Mgg=10-20 GeV
could confirm sH(excl) prediction
at LHC to about 20% or less

28. CDF, Albrow et al. one appears due to p0gg 3 events observed
CDF Blessed this morning!
one appears
due to p0gg
CDF, Albrow et al.
3 events observed
16 events observed
~0.09pb
~0.04pb
It means exclusive H must happen
(if H exists) and probably ~ 10 fb
within factor ~ 2.5.
higher in MSSM
QED: LPAIR Monte Carlo
s(gg) = 10 fb for ETg>14 GeV at LHC

29. Albrow 16 events were like this: 3 events were like this: one appears
due to p0gg

30. ppp + jj + p sexcl~Rjj>0.8 sexcl(M>Mjj)
Exptally more problematic due to
hadronization, jet algorithms, detector
resolution effects, QCD brem…
ppp + jj + p
Exclusive events have Rjj = Mjj/MX =1, but above effects
smear out the expected peak at Rjj = 1 (ExHuME MC)
sexcl~Rjj>0.8
sexcl(M>Mjj)

31. Conclusion The ppp+H+p cross section prediction is robust----factor 2
S/B~1 for SM h -----can be more for SUSY h, H.
Checks are starting to come from Tevatron data (gg,dijet…)
There is a strong case for installing proton taggers
at the LHC, far from the IP it is crucial to get the
missing mass DM of the Higgs as small as possible.
Need more exptal and theoretical work on L1 trigger
The diffractive Higgs signals beautifully complement the
conventional signals. Indeed there are SUSY Higgs
regions where the diffractive signals are advantageous
---determine DMH, Yukawa Hbb coupling, 0++
---searching for CP-violation in the Higgs sector