LIB 2DHP@LHC (Myths and Reality)

1. FP-420 LIB2DHP@LHC (Myths and Reality) Dec. 10th, 2006 V.A. Khoze (IPPP, Durham) Main aims: -to quantify the mjor sources of theLumi-IndependentBackgrounds, -to Exclusive Diffractive Higgs Production at the LHC. (based on works : A. De Roeck, R. Orava and KMR, EPJC 25:391,2002 ; V. Khoze, M. Ryskin and W.J. Stirling, hep-ph/0607134; B. Cox et al. EPJC 45:401,2006; KMR:EPJC 26:229,2002;C34:327,2004 ) • CEDP- Main Advantages: • - Measure the Higgs mass via the missing mass technique (irrespectively of the • decay channel). • -H opens up(Hbb Yukawa coupling); unique signature for the MSSM Higgs sect. • -Quantum number/CPfilter/analyzer. • -Cleanness of the events in the central detectors. ☻If the potential experimental challenges are resolved, then there may be a real chance that for certain MSSM scenarios the CEDP becomes the LHC Higgsdiscovery channel !

2. In the proton tagging mode the dominantHin principlecan be observeddirectly . • certain regions of the MSSM parameter space are especiallyproton tagging friendly (at large tan  and M , S/B ) Myths For the channel LIBs are well known and incorporated in the (DPE )MCs: Exclusive LO - production (mass-suppressed) + gg misident+ soft PP collisions. Reality The complete background calculations are still in progress (uncomfortably & unusuallylarge high-order QCD and b-quark mass effects). • About a dozen various sources : known (DKMOR, Andy, Marek) & •  admixture of |Jz|=2 production. •  NLO radiative contributions (hard blob and screened gluons) • NLLO one-loop box diagram (mass- unsuppressed, cut-nonreconstructible) •  b-quark mass effects in dijet events – (most troublesome theoretically)still incomplete • (similar problems in photon-photon collisions).

3. KMR technology (implemented in ExHume) focus on  the same for Signal and Bgds contain Sudakov factor Tg which exponentially suppresses infrared Qt region  pQCD new CDF experimental confirmation, 2006 (Koji’s talk) S² is the prob. that the rapidity gaps survive population by secondary hadrons  soft physics; S²=0.026(LHC), S²/b² -weak dependenceonb.

4. Good ExHume description KMR analytical results CDF preliminary outside-cone energy (Koji) (Rjj includes different sources : Centr. Inclus. + soft PP + (rad. ) tail of Centr. Exclus. + experim. smearing)

5. effect. PP lumi (HKRSTW, work in progress).

6. RECALL:  for forward going protonsLO QCD bgd  suppressed by Jz=0 selection rule and by colour, spin and mass resol. (M/M) –factors. forreference purps : SM Higgs (120 GeV) misidentification of outgoing gluons as b –jets may mimic production the prolific LO subprocess SM Higgs for jet polar angle cut misidentification prob. P(g/b)=0.01  B/S 0.06 (DKMOR WishList) (difference in a factor of 2 ? )

7. A little bit of (theoretical) jargon Helicity amplitudes for the binary bgd processes g( g g helicities of ‘active gluons’ S – Jz=0, LO B- domint. Jz=2 (double) helicities of produced quarks • convenient to considerseparately • q-helicity conserving ampt (HCA) and q-helicity non-conserving ampt(HNCA) • do not interfere, can be treated independently, • allows to avoid double counting (in particular, on the MC stage) Symmetry argumts (BKSO-94) forJz=0 the Born HCAvanishes, (usually, HCA is the dominant helicity configuration.)  for large angles HNCA (Jz=2, HCA)

8. in terms of the fashionable MHVrules (inspired by the behaviour in the twistor space) only (+ - ; + -) J_z=2, HCA (-+ ; -+ /+-) an advantageous property of the large angle amplitudes • allHNCA (Jz=0, Jz=2, all orders in ) are suppressed by • all HC ampts ((Jz=0, Jz=2, all orders ) are \propto  vanish at rotational invariance around q-direction (Jz=2, PP-case only) recall:we requirein order to suppress t-channel singl. in bgd processes, also acceptance of the CD..  an additional numerical smallness ( ) LOHCAvanishes in the Jz=0 case (valid only for the Born amplitude)  Jz=0 suppressionisremovedbythe presence of an additional (real/ virtual) gluon (BKSO-94)

9. Classification of the backgrounds  |Jz|=2 LO production caused by non-forward going protons. HC process,suppressed by and by ≈ 0.02 * ( ) estimate  NLLO (cut non-reconstructible) HC quark box diagrams. result ≈ • dominant contribution at verylarge masses M • at M< 300 GeV stillphenomenologicallyunimportant due to a combination of small factors  appearance of thefactor consequence of supersymmetry

10. mass-suppressed Jz=0 contribution  theoreticallymost challenging(uncomfortablylarge higher-ordereffects) • naively Born formula would give0.06  • however, various higher-order effects are essential :  running b-quark mass Single Log effects ( ) the so-called non-SudakovDouble Log effects , corrections of order (studied in FKM-97 for the case of at Jz=0 ) Guidance based on the experience with QCD effects in . •  DLeffects can be reliably summed up(FKM-97 , M. Melles, Stirling, Khoze 99-00 ). •  Complete one-loop result is known (G. Jikia et al. 96-00 ) • complete calculation of SL effects ( drastically affects the result) F=

11. bad news:violently oscillating leading term in the DL non- Sudakov form-factor: • (≈2.5) •  DL contribution exceeds the Born term; strong dependence on the NLLO, scale, • running mass…. effects • No complete SL calculations currently available. Fq= HNC contribution rapidly decreases with increasing M Currently the best bet: : Fq ≈ with c≈1/2. Taken literally factor of two larger than the ‘naïve’ Born term. Cautiously : accuracy, not better than a factor of 5 A lot of further theoretical efforts is needed

12. NLO radiation accompanying hard subprocess Large-angle, hard-gluon radiation does not obey the selection rules + radiation off b-quarks potentially adominant bgd :( ) strongly exceeding the LO expectation.  only gluons with could be radiated, otherwise cancel. with screening gluon ( ).  KRS-06complete LO analytical calculation of the HC , Jz=0 in the massless limit, using MHV tecnique. Hopefully, these results can be (easily) incorporated into more sophisticated MC programmes to investigate radiative bgd in the presence of realistic expt. cuts. ,

13. How hard should be radiation in order to override Jz=0 selection rule ? (classical infrared behaviour) as well known neglecting quark mass (a consequence of Low-Barnett-Kroll theorem, generalized to QCD ) the relative probability of the Mercedes –like qqg configuration for Jz=0 radiative bgd process becomes unusually large  marked contrast to the Higgs-> bb (quasi-two-jet- like) events.  charged multiplicity difference between the H->bb signal and the Mercedes like bbg – bgd: for M120, N ≈7, Nrises with increasing M. hopefully, clearly pronounced 3-jet events can be eliminated by the CD,  can be useful for bgd calibration purposes. Exceptions:radiation in the beam direction;  radiation in the b- directions. could be eliminated DKMOR-02

14. beam direction case if a gluon jet is to go unobserved outside the CD or FD ( ) • violation of the equality : (limited bythe ) contribution is smaller than the admixture of Jz=2. KRS-06 b-direction case (HCA) 0.2 ( R/0.5)² (R –separation cone size) Note :  soft radiation factorizes strongly suppressed is not a problem,  NLLO bgd numerically small  radiation from the screening gluon with pt~Qt: KMR-02 HC (Jz=2) LO ampt. ~ numerically very small  hard radiation - power suppressed

15. Production by soft Pomeron-Pomeron collisions from DKMOR-02 (WishList) main suppression : lies within mass interval z the overall suppression factor : bb PS Background due to central inelastic production mass balance, again subprocess is stronglysuppressed produces atailon the high side of the missing mass H/bb (DKMOR-02)

16. A.Pilkington, CERN 27th Sept.2006 What else should be done/checked? 1.New MRW(2006) diffractive pdf should be used, which are close to H1 fit B: much lower gluon density at large z (MRW fitavailable in Durham HEPDATA). 2. Appropriate value of survival factor. 3.Proper cuts on low ET. . 4. Possibility to veto the ‘Remnant Pomeron’ jets (CD extra jets, maybe T1, T2 detectors …to be studied) Risto , Marek.

17. Not the end of the story….. in terms of Feynman graphs: Central Inelastic Soft PP- Fusion (Pomwig) Studied by KMR 02-06 formally suppressed by • In ‘theoretical jargon’ : CI - ‘kT- factorization, Soft PP – collinear factorization. • CDF inclusive diffractive dijet data – evidence of manifestation of the CI dijet production (both RunI and RunII). Preliminary estimates :We should be fine : B/S(DPE) <0.1-1. Currently, in the description of the Rjj <0.8 distr.ibution, normalization to models (Pomwig...) is fixed by the CDF data! Normalization at Rjj>0.8 (Exhume) comes from the theory.

18. (recall also Pomwig normal. to CDF Run I Dif. Inel data (0.27-0.1) )

19. MAKE HISTORY DPEMC

20. (detailed studies in B. Cox et al. hep-ph/0505240) WW mode • No trigger problems for final states rich in higher pT leptons. • Efficiencies ~20% (including Br) if standard leptonic (and dileptonic) • trigger thresholds are applied. • Further improvements, e.g. dedicated -decay trigger. • Statistics may double if some realistic changes to leptonic trigger • thresholds are made. • Much less sensitive to the mass resolution. • Irreducible backgrounds are small and controllable. • . • Recall : theh- rate can rise by about a factor of 3.5-4 in some MSSM • models (e.g., smalleff scenario). + + ……. KRS-05 Currently : trigger situation is more optimistic.

21. Lepton TriggerEfficiency Cox et al (e or )ATALS (e, , 2e, 2, e) M=120 GeV 8.7%20.3% M=140 GeV 12.8% 26.9% M=160 GeV 16.6%28.8% (Sandra Horwat, MPI) Pile-Up situation is hopefully bettter  mode ● Irreducible bgds (QED) are small and controllable. ( >0.1-0.2GeV)  QCD bgd is small if g/- misidentification is < 0.02 (currently ~0.007 for-jet efficiency 0.60) Lepton trigger efficiency looks optimistic: ATLAS ((e, , 2e, 2, e) M=120 GeV 22.1% M=140 GeV 25.8% M=160 GeV 28.3%

22. Approximate formula for the background assuming DKMRO-2002 wishlist input main uncertn. at low masses SSM/B1 at ΔM 4 GeV Four major bgd sources(~1/4 each at M≈120 GeV)  gluon-b misidentification (assumed 1% probability)  NLO 3-jet contribution Correlations, optimization -to be studied.  admixture of |Jz|=2 contribution + NNLO effects b-quark mass effects in quasi-dijet events Recall : large M situation in the MSSM is very different from the SM. HWW/ZZ - negligible; H bb/- orders of magnitude higher than in the SM

23. Four years on M=120 GeV WishList DKMOR (2002) currently (87% signal catch ) 5.76 GeV  30-40 GeV   2.5% (CMS fast simulation.) Marek 1.3% (ATLAS) Andy misidentification prob.P(g/b)=1% (b-tag efficiency)0.6 0.36 A.Rozanov (ATLAS) PA (Monika, Marek, Andy, Andrew..)  no Pile-Up studies

24. MSSM Recall : large M situation in the MSSM is very different from the SM. HWW/ZZ - negligible; H bb/- orders of magnitude higher than in the SM  detailedstudies of statistical significance for the MSSM Higgs signal discovery , based on the CMS Higgs group procedure – in progress (HKRSTW, hopefully first part of 2007.. )

25. mhmax scenario, =200 GeV, MSUSY =1000 GeV hbb M. Tasevsky et al. (preliminary)

26. Hbb

27. hWW smalleff scenario PRELIMINARY mh 121-123 GeV for the SM Higgs at M = 120 GeV  = 0.4 fb, at M= 140 GeV  = 1 fb

28. Conclusion LuminosityIndependentBackgrounds to CEDP ofHbbdo not overwhelm the signal and can be put under full control especially at M> 120 GeV.  LuminosityIndependentBackgrounds to HWW &channelsare controllable and could be strongly reduced. The complete background calculation is still in progress (unusually & uncomfortably large high-order QCD effects). Further reduction can be achieved by experimental improvements, better accounting for the kinematical constraints, correlations….. Optimization, complete MC simulation- still to be done Further theoretical & experimental studies are needed

29. (Misha’s talk) PU (a naïve theorist’s view) Overlap background: hard event (bb,WW, ...) +2 SD events in the same bunch Xing Roughly : we have to achieve reduction of in 6-7 orders: correlations between measurements in CD and RPs (1, 2, M...),  correlations inazimuthal angles, pt- cuts, use of fast timing detectors (~40-100) ( Andrew, Monika….) Nc, cuts (~100, Andy)  veto in T1, T2 detectors - Risto

30. Known (un)knowns • The probability to misidentify a gluon as a b-jet P(g/b) and the efficiency of • tagging b. • Does the CEDP environment help ? • Mass window  M≈3  (M), any further improvement ? •  Correlations, optimisation -to be studied •  S² (S²/b²),further improvements, experimental checks. •  Triggering issues: • Electrons in the bb –trigger ? • Triggering on the bb/without RP condition at M 180 GeV ? •  Mass window MCDfrom the Central Detector only (bb,  modes) in the Rap Gap environment? • Can we do better than MCD ~20-30 GeV? Mass dependence of MCD ? • (special cases: inclusive bgds, hunting for CP-odd Higgs)

31. BACKUP

32. (KMR- based estimates) 8 (more on the pessimistic side, studies based on the CMS Higgs group procedure –still to come)

33. PU (a naïve theorist’s view) PU? Overlap background: hard event (bb,WW, ...) +2 SD events in the same bunch Xing Roughly :