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Diffractive Higgs production at the LHC
Alan Martin (Durham)31st John Hopkins WorkshopHeidelberg, August 2007
H
p
p
Prod. of Higgs in diffve
hadron-hadron collisionsOtto Nachtmann et al.Phys,Lett. (1990)
Exclusive Higgs production at the LHC
The price for rapidity gaps ?
Khoze, Martin, Ryskin
O(1 GeV) ?
farfrom IP
no emission when ~ 1/kt) > (d ~ 1/Qt)i.e. only emission with kt > Qt
calculated from multi-Pomeronmulti-channel eikonal analysisof soft pp data S2 = 0.02 at LHC S2 = 0.05 at Tevatron
Description of ‘soft’ high energy pp interactions
DL: eff = 1.08 + 0.25t ---but nothing about inelastic intn
Inclusion of multi-P effects essential: new analysis
bare ~ 1.25 + 0t+ + ….
KMR 2007
2-ch eikonal
full multi-Pomeron
total(LHC) ~ 95 mb
S2Higgs(LHC) ~ 0.02
N*
+
+ ….+ +=where
Prediction of (pp p + H + p)
contain Sudakov factor Tg which exponentiallysuppresses infrared Qt region pQCD
S2 is the prob. that the rapidity gaps survive populationby secondary hadrons soft physics S2=0.02 (LHC) S2=0.05 (Tevatron)
(pp p + H + p) ~ 3 fb at LHC for SM 120 GeV Higgs ~0.2 fb at Tevatron
H
(ppp+H+p) ~ 3 fb at LHC for 120 GeV Higgs
if L = 60 fb-1, then 180 events
efficiency of p taggers
BR(Hbb)
b,b tag efficiency
polar angle cut
mass window
54
36
18
9
6 events
Background to ppp + (Hbb) + p signal
LO (=0 if mb=0, forward protons)
gg gg mimics gg bb (P(g/b)=1.3%) after polar angle cut 0.3Irreducibe bb 0.5
HO (gg)col.sing bb+ng
Soft emissions still suppressed by Jz=0 ~ 0Hard emissions if g not seen: extra gluon along beam Mmiss > Mbb ~ 0 extra g from initial g along b or b 0.2
Pomeron-Pomeron inelastic 0.06
B/S
total B/S~1
assuming Mmiss ~ 3M ~ 5 GeV
S~1/M3, B~M/M6 : triggering, tagging, M better with rising M
for M=120 GeV
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
conventionalsignal for SM110-130 GeV Higgs
BBKM. (first)corrn could be large and -ve,
eikonal enhanced
S2 =0.02
BBKM find first corrn could be large and –ve.BUT…need to sum complete set of diagrams.terms alternate in sign
ln QT2QT~2GeV
Analogous new “soft”analysis finds that evenat low QT, amp. is notcompletely suppressed
Amp
corrn affects only small QT
(large size dipoles)
1st term
sum
70%
The full set of enhanced diag. are included in tot, SD … 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 tot(LHC) has v.weak model dep. since model fits existing soft data and there is log s energy behaviour
SD, sensitive to enh. effects, ~flat from 100 GeV, so expect no extra suppression of diffraction at LHC
New global fit to “soft” data
Leading neutronprod. at HERA
eikonal “enhanced”
gap due to exchange ~ exclusive Higgs
yi > 2 – 3
correction prop. to rap. interval prop. to energy(negative)
Prob. to observe leading neutronmust decrease with energyBut expt. flat small enhanced correction
KKMR ‘06
seen not seen
Level 1 trigger
420 420220220
veto veto
veto-trigger spoiled by pile-up420-trigger spoiled by c ------------- buffer ?
At present, plan to use 2 high ET jets/+ 220 (+ 420)
LHC
every bunch crossing !
~0.01N for 420m~0.03N for 220m
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
decouplingregime:mA ~ mH > 150h ~ SMbbH ~ tanVVH ~ 0H,A (bb)
intense coup:mh ~ mA ~ mH
,WW.. coup.suppressed
100 fb-1
5signal at LHC
exclusive signal
Adapted from a preliminary plot of Tasevsky et al. (HKRSTW)
“standard candles”
Possible checks of exclusive rates at the Tevatron
“standard candles” at Tevatron to test excl. prod. mechanismppp + + p high rate, but only an ord.-of-mag.estimateppp + jj + p rate OK, but jet algorithm, hadronization etc ppp + + p low rate, but cleaner signal
ppp + + p
KMR+Stirling
Measurements with M=10-20 GeVcould confirm H(excl) prediction at LHC to about 20% or less
It means exclusive H must happen(if H exists) and probably ~ 10 fbwithin factor ~ 2.5. higher in MSSM
Exclusive pairse e Exclusive pairs
16 events observed
+0.6-0.3
0.5. 0.3
-8
Estimated background = 2.1
(mostly p-dissociation)
1.6 (stat) 0.3 (syst) pb
Poisson Prob. = 3 10 5.5
MEAS
QED: LPAIR Monte Carlo
QED (1.711 0.008) pb
12Note : 2 10 !MEAS INEL
3 events observed
+0.3-0.0
0.14. 0.04
-3
Estimated background = 0.0 events
(p-dissociation, exclusivity, fakes)
0.14 (stat) 0.03 (syst) pb
Poisson Prob.(0.3 3) = 3.6 10
(conservative)
KMR (Durham) prediction = 0.04 (3-5) p
MEAS
b
CDF Blessed this morning!CDF, Albrow et al.
(= 10 fb for ET>14 GeV at
LHC
one appearsdue to 0
~0.09pb
~0.04pb
16 events were like this:0 0: 180 2
( )10 38 GeV
small ( resolution)T
e e
M e e
p
3 events were like this:0: 170
( )10 20 GeV
smallT
M e e
E
Albrow
one appearsdue to 0
ppp + jj + p Exptally more problematic due tohadronization, jet algorithms, detectorresolution effects, QCD brem…
Exclusive events have Rjj = Mjj/MX =1, but above effectssmear out the expected peak at Rjj = 1 (ExHuME MC)
excl~Rjj>0.8
excl(M>Mjj)
Conclusion
The ppp+H+p cross section prediction is robust----factor 2S/B~1 for SM h -----can be more for SUSY h, H.Checks are starting to come from Tevatron data (,dijet…)
There is a strong case for installing proton taggersat the LHC, far from the IP ---- it is crucial to get the missing mass M of the Higgs as small as possible.Need more exptal and theoretical work on L1 trigger
The diffractive Higgs signals beautifully complement theconventional signals. Indeed there are SUSY Higgs regions where the diffractive signals are advantageous---determine MH, Yukawa Hbb coupling, 0++ ---searching for CP-violation in the Higgs sector
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