LIB 2DHP@LHC (Myths and Reality)

1. CERN, Sept. 27 2006 LIB2DHP@LHC (Myths and Reality) FP-420 V.A. Khoze (IPPP, Durham) Main aims: -to quantify the mjor sources of theLumi-IndependentBackgrounds, -to the Exclusive Diffractive Hbb Production at the LHC - to recall the backgrounds to the ED H, WWchannels and to the searches of the CP-odd Higgs (based on works : A. Roeck, R. Orava and KMR, EPJC 25:391-403,2002 ; V. Khoze, M. Ryskin and W.J. Stirling, hep-ph/0607134; KMR ,EPJC 26:229-236,2002;C34:327-334,2004) • CEDP- Main Advantages: • - Measure the Higgs mass via the missing mass technique (irrespectively of the • decay channel). • -H opens up(Hbb Yukawa coupling); unque signature for the MSSM sector • -Quantum number/CPfilter/analyzer. • -Cleanness of the events in the central detectors. ☻If the potential experimental challenges are resolved, then there is a very real chance that for certain MSSM scenarios the CEDP becomes the LHC Higgsdiscovery channel !

2. In the proton tagging mode the dominantHcan 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) + soft Pomeron 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) & •  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

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 S² is the prob. that the rapidity gaps survive population by secondary hadrons  soft physics; S²=0.026(LHC), S²/b² -weak dependenceonb.

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

6. RECALL:  for forward going protonsLO QCD bgd  suppressed by Jz=0 selection rule and by the 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 for jet polar angle cut assuming misidentification probability P(g/b)=1%  0.2 (DKMOR-02)

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  ≈ 0.2 • 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 ) •  No 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 some hopes recently… A.Shuvaev + Durham.

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 main suppression : lies within mass interval the overall suppression factor :  bb Background due to central inelastic production mass balance, again subprocess is stronglysuppressed produces asmall tailon the high side of the missing mass H/bb (DKMOR-02)

16.  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)

17. (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

18. Hunting the CP-odd boson, A (LO)selection rule – an attractive feature of the CEDPprocesses, but…… the flip side to this coin: strong ( factor of ~ 10² )suppression of the CED production of the CP-odd boson. A way out : to allow incoming protons to dissociate(E-flowET>10-20 GeV)KKMR-04 pp p + X +H/A +Y +p(CDD) in LO azim. angular dependence: cos² (H), sin² (A), bgd- flat A testing ground for CP-violation studies in the CDD processes (KMR-04) challenges: bb mode – difficult bgd conditions -mode- small (QED)bgd, but low Br

19. CDD results at  (RG) >3, ET>20 GeV within the (MS) MSSM, e.g.mh scenarios with  =±200 (500) GeV, tan=30-50 CDD(A->bb) ~ 1-3 fb, CDD(A->) ~ 0.1-03 fb CDD(H)~-CDD(A) max bb mode –challenging bgd conditions (S/B ~1/50). -mode- small (QED) bkgd, but low Br situation looks borderline at best  ‘best case’ (extreme) scenario mh with =-700 GeV , tan =50, mg =10³GeV max

20. in this extreme case : (Agg) Br(Abb)22-24MeV at MA=160-200GeV ,tan 50, CDD (A bb) is decreasing from 65fb to 25fb (noangular cuts) CDD (A) 0.8-0.3fb A S/B ~ (A->gg) Br (A->bb) / MCD  5.5 /MCD(GeV) currentlyMCD ~ 20-30 GeV… (12GeV at 120 GeV) Prospects of A- searches strongly depend, in particular, on the possible progress with improving MCD in the Rap. Gap environment We have to watch closely the Tevatron exclusion zones There is no easy solution here, we must work hard in order to find way out .

21. Proton Dissociative Production(experimental issues) (thanks to Monika, Michele , Risto & Albert) Can we discriminate between the cos² and sin² experimentally ?  Measurement of the proton diss. system with ET of 20 GeV and 3<<5 -probably OK for studying the azimuthal distributions (HF or FCAL calorimeters)  Trigger is no problem if there is no pile up (Rap Gaps at Level 1); 4jet at 2*10³³ lumi-borderline Maybe we can think about adding RPs into the trigger ( no studies so far) Maybe neutrons triggered with the ZDC (Michele )? From both the theoretical and experimental perspectives the situation with searches for theAin diffractive processes looks at bestborderline, but the full simulation should be performed before arriving at a definite conclusion.

22. Approximate formula for the background 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  detailedstudies of statistical significance for the MSSM Higgs signal discovery , based on the CMS Higgs group procedure – in progress (HKRSTW, hopefully 2006 )

23. To gain insight into the H- mass dependence Crude approximation:  simplified formulae for stat. sign.  neglect M-dependence of (more or less - MSSM with large tan ).  neglect mass dependence of M. • S/B does not depend on thecurrent (theor.) uncertainties in •  theor. uncertaint. ~ 1.5  at large masses M 140 GeV, B is controllable & reliably predicted. is practically independent on M.  at low masses M < 120 GeV theor. uncertaint. in of order 2-2.5, decreaseswith M decreasing (as ).

24. Known (un)knowns • The probability to misidentify a gluon as a b-jet P(g/b) and the efficiency of • tagging b. • In DKMOR we required P(g/b) =0.01 and chose an optimistic value ( )²=0.6. • Does the CEDP environment help ? • Mass window  M≈3  (M) •  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)

25. Unknown unknowns • a complete computation (at least on the SL level ) of the radiative effects for theHNC  Experimental perspectives for the CP-odd Higgs studies in the proton-dissociation modes. Known Unknowns or Unknown Unknowns ?  Going to higher luminosities (up to 10^34) ? Pile-up…. ? -an instructive example P. Bussey et al (long-lived gluinos) hep-ph/0607264

26. 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