1. Update of diffractive Higgs production at the LHC V.A. Khoze, A.D. Martin, M.G. Ryskin A.B. Kaidalov and W.J. Stirling DIS2006, Tsukuba, Japan 20-24 th April, 2006 H p p

2. pp  p + H + p If outgoing protons are tagged far from IP then  (M) = 1 GeV (mass also from H decay products) Very clean environment H  bb: QCD bb bkgd suppressed by J z =0 selection rule S/B~1 for SM Higgs M < 140 GeV L(LHC)~60 fb -1 ~10 observable evts after cuts+effic Also H  WW (L1 trigger OK) and H   promising SUSY Higgs: parameter regions with larger signal S/B~10, even regions where conv. signal is challenging and diffractive signal enhanced----h, H both observable Azimuth angular distribution of tagged p’s  spin-parity 0 ++ FP420: tagging, L1 trigger, pile-up…..see Cox

3. Reliability of pred n of  (pp  p + H + p) crucial contain Sudakov factor T g which exponentially suppresses infrared Q t region  pQCD S 2 is the prob. that the rapidity gaps survive population by secondary hadrons  soft physics  S 2 =0.026 (LHC) S 2 =0.05 (Tevatron)  (pp  p + H + p) ~ 3 fb at LHC for SM 120 GeV Higgs ~0.2 fb at Tevatron H

4. Background to pp  p + (H  bb) + p signal LO (=0 if m b =0, forward protons) gg  gg mimics gg  bb (P(g/b)=1%) after polar angle cut 0.2 |J z |=2 admixture (non-forward protons) 0.25 m b 2 /E T 2 contribution <0.2 HO (gg) col.sing  bb+ng Still suppressed for soft emissions. Hard emissions if g not seen: extra gluon along beam M miss > M bb  0 extra g from initial g along b or b bar 0.2 Pom-Pom inel. prod. B/S<0.5(  M bb /M PP ) 2 <0.004 B/S total B/S~1 assuming  M miss ~3 GeV DKMOR S~1/M 3, B~  M/M 6 : triggering, tagging,  M better with rising M for M=120 GeV 

5. conventional signal for SM 110-130 GeV Higgs

6. 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

7. decoupling regime: m A ~ m H > 150 h = SM H,A   (bb) intense coup: m h ~ m A ~ m H ,WW.. coup. suppressed

8. e.g. m A = 130 GeV, tan  = 50 (difficult for conventional detection, but exclusive diffractive favourable) S B m h = 124.4 GeV 71 10 events m H = 135.5 GeV 124 5 m A = 130 GeV 1 5 SM: pp  p + (H  bb) + p S/B~10/10~1 with  M = 3 GeV, at LHC with 60 fb -1 enhancement

9. Diffractive: H  bb Yuk. coupling,  M H, 0 ++ Inclusive: H,A   wide bump m H =140 m H =160 L=60 fb -1 55 Tasevsky et al

10. 55 L=60 fb -1 Tasevsky et al

11. KMR: using 2-channel eikonal Gotsman,Levin,Maor.. Lonnblad, Sjodahl, Bartels,Bondarenko,Kutak,Motyka BBKM  use pert.thy.  corr n could be large and -ve,   H (excl) reduced ? KMR  pQCD invalid  strong coup regime  small effect eikonal enhanced S 2 =0.026 “enhanced” correction to  H (excl)?

12. BBKM use pQCD to calculate enhanced diagram LLBK eq.  x 4 can be v.small    Infrared stability only provided by saturation momentum, Q S (x 4 ). Hope is that at v.low x 4, Q S allows use of pQCD. Gluon density is unknown in this region! BUT multi-(interacting)-gluon Pomeron graphs become important. These can strongly decrease the effective triple-Pomeron vertex V 3P, see for example Abramovsky. MOREOVER enhanced graphs also relevant for  tot,  inel …pp, so fit to existing data will lead to same eikonal---extrapol. to LHC will not lead not lead to extra suppression of diffraction.

13. Other arguments why “enhanced” correction is small  Y threshold Original Regge calc. required  Y ~ 2-3 between Regge vertices (Recall NLL BFKL:  major part of all-order resum has kinematic origin   Y ~ 2.3 threshold implied by NLL  tames BFKL) Applying to enhanced diagram need 2  Y > 4.6, but at LHC only log(sqrt(s)/M H ) available for y H =0 YY YY = 4.6 for M H =140 GeV Higgs prod. via enhanced diagram has v.tiny phase space at LHC KMR ‘06

14. True expansion is not in  s, but in prob. P of additional inter ns This estimate, and that of BBKM, uses simplest Regge graphs, whereas P  1 in saturation region. Pert. theory  strong coupling regime dominated by rescatt. of “wee” partons (but already included in phen. pp amplitude used in eikonal) enhan excl 10mb 100mb18 4.5 Rough estimate

15. Leading neutron prod. at HERA eikonalenhanced gap due to  exchange ~ exclusive Higgs     y i > 2 – 3 correction prop. to rap. interval prop. to  energy (negative) Prob. to observe leading neutron must decrease with  energy But expt.  flat  small enhanced correction KKMR ‘06

16. Tevatron can check exclusive Higgs prod. formalism

17. pp  p +  + p KMR+Stirling

18. Measurements with M  =10-20 GeV could confirm  H (excl) prediction at LHC to about 20% or less

19. It means exclusive H must happen (if H exists) and probably ~ 10 fb within factor ~ 2.5. higher in MSSM 16 events observed QED: LPAIR Monte Carlo 3 events observed CDF Blessed this morning! Albrow 100  evts per 100 pb -1 at LHC!

20. 16 events were like this: 3 events were like this: Albrow

21. pp  p + jj + p Exptally more problematic due to hadronization, jet algorithms, detector resolution effects, QCD brem… Data plotted as fn. of R jj = M jj /M X, but above effects smear out the expected peak at R jj = 1 (ExHuME MC) Better variable: R j = (2E T cosh  *)/M X with  *=  -Y M highest E T jet ,E T R j not changed by O(  S ) final state radiation, need only consider extra jet from initial state. Prod.of other jets have negligible effect on R j due to strong ordering We compute exclusive dijet and 3-jet prod (and smear with Gaussian with resolution  =0.6/sqrt(E T in GeV))

22. Exclusive dijet and 3-jet prod 3-jet dijet E T >20GeV dijets dominate R j >0.8 3-jets dominate R j <0.7 RjRj KMR, in prep.

23. Conclusion The exclusive diffractive signal is alive and well. The cross section predictions are robust. Checks are starting to come from Tevatron data ( ,dijet…) There is a very strong case for installing proton taggers at the LHC, far from the IP ---- it is crucial to get the missing mass  M of the Higgs as small as possible The diffractive Higgs signals beautifully complement the conventional signals. Indeed there are significant SUSY Higgs regions where the diffractive signals are advantageous ---determining  M H, Yukawa H  bb coupling, 0 ++ determin n ---searching for CP-violation in the Higgs sector