1 LIB (Myths and Reality) V.A. Khoze (IPPP, Durham) Main aims: - to quantify the mjor sources of the Lumi-Independent Backgrounds, -to the Exclusive Diffractive H  bb Production at the LHC - to recall the backgrounds to the ED H  , WW channels and to the searches of the CP-odd Higgs FP-420 (based on works : A. Roeck, R. Orava and KMR, EPJC 25: ,2002 ; V. Khoze, M. Ryskin and W.J. Stirling, hep-ph/ ; KMR, EPJC 26: ,2002 ; C34: ,2004) CERN, Sept ☻ If the potential experimental challenges are resolved, then there is a very real chance that for certain MSSM scenarios the CEDP becomes the LHC Higgs discovery channel !  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/ CP filter/analyzer. -Cleanness of the events in the central detectors.

2 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 & unusually large 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) ŽNLLO one-loop box diagram ( mass- unsuppressed, cut-nonreconstructible)  b-quark mass effects in dijet events – (most troublesome theoretically) still incomplete  In the proton tagging mode the dominant H  can be observed directly.  certain regions of the MSSM parameter space are especially proton tagging friendly (at large tan  and M, S/B )

3 focus on  the same for Signal and Bgds contain Sudakov factor T g which exponentially suppresses infrared Q t region  pQCD new CDF experimental confirmation, 2006 S² is the prob. that the rapidity gaps survive population by secondary hadrons  soft physics; S² = (LHC),  S²/b² - weak dependence on b. KMR technology (implemented in ExHume)

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

6 the prolific LO subprocess may mimic production  misidentification of outgoing gluons as b –jets for jet polar angle cut assuming misidentification probability P(g/b)=1% (DKMOR-02)  0.2  for forward going protons LO QCD bgd  suppressed by Jz=0 selection rule and by the colour, spin and mass resol. (  M/M) –factors. RECALL : for reference purps : SM Higgs (120 GeV)

7 A little bit of (theoretical) jargon Helicity amplitude s for the binary bgd processes g g g (g ( helicities of ‘active gluons’ (double) helicities of produced quarks  convenient to consider separately 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)  for Jz=0 the Born HCA vanishes, (usually, HCA is the dominant helicity configuration.)  for large angles HNCA Symmetry argumts (BKSO-94) (Jz=2, HCA) S – Jz=0, LO B- domint. Jz=2

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

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 very large masses M   at M< 300 GeV still phenomenologically unimportant due to a combination of small factors   appearance of the factor consequence of supersymmetry

10  mass-suppressed Jz=0 contribution  theoretically most challenging (uncomfortably large higher-order effects)  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-Sudakov Double 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. DL effects can be reliably summed up ( FKM-97, M. Melles, Stirling, Khoze ). Complete one-loop result is known (G. Jikia et al ) 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. HNC contribution rapidly decreases with increasing M Fq= 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 + + radiation off b-quarks  potentially a dominant 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., Large-angle, hard-gluon radiation does not obey the selection rules

13 How hard should be radiation in order to override Jz=0 selection rule ? as well known (classical infrared behaviour) 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,  N rises 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 ( ) v iolation of the equality : (limited by the ) contribution is smaller than the admixture of Jz=2. KRS-06 b-direction case (HCA) 0.2  (  R/0.5)² Note :  soft radiation factorizes  strongly suppressed is not a problem,  NLLO bgd  numerically small  radiation from the screening gluon with p t~Qt : HC (Jz=2) LO ampt. ~ numerically very small  hard radiation - power suppressed KMR-02 (  R –separation cone size)

15 Production by soft Pomeron-Pomeron collisions bb main suppression : lies within mass interval the overall suppression factor :  Background due to central inelastic production H/bb mass balance, again subprocess is strongly suppressed produces a small tail on the high side of the missing mass (DKMOR-02)

16  mode ● Irreducible bgds (QED) are small and controllable. ( > GeV) QCD bgd is small if g/  - misidentification is < 0.02 (currently ~0.007 for  -jet efficiency 0.60)

17 WW mode (detailed studies in B. Cox et al. hep-ph/ )  No trigger problems for final states rich in higher p T 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 : the h- rate can rise by about a factor of in some MSSM models (e.g., small  eff scenario). KRS …….

18 Hunting the CP-odd boson, A  (LO) selection rule – an attractive feature of the CEDP processes, 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-flow E T>10-20 GeV ) KKMR-04 pp  p + X +H/A +Y +p (CDD) in LO azim. angular dependence: cos²  (H), sin²  (A), bgd- flat  challenges: bb mode – difficult bgd conditions  -mode- small (QED)bgd, but low Br A testing ground for CP-violation studies in the CDD processes (KMR-04)

19  within the (MS) MSSM, e.g. mh scenarios with  = ±200 (500) GeV, tan  =30-50  CDD (A->bb) ~ 1-3 fb,  CDD (A->  ) ~ 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, m g =10³GeV max CDD results at  (RG) >3, E T >20 GeV

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

21 Proton Dissociative Production (experimental issues) (thanks to Monika, Michele, Risto & Albert)  Measurement of the proton diss. system with E T 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 )? Can we discriminate between the cos²  and sin²  experimentally ?  From both the theoretical and experimental perspectives the situation with searches for the A in diffractive processes looks at best borderline, but the full simulation should be performed before arriving at a definite conclusion.

22 Approximate formula for the background  detailed studies of statistical significance for the MSSM Higgs signal discovery, based on the CMS Higgs group procedure – in progress (HKRSTW, hopefully 2006 ) main uncertn. at low masses S SM /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 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 the current ( 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, decreases with 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  M CD from the Central Detector only (bb,  modes) in the Rap Gap environment? Can we do better than  M CD ~20-30 GeV? Mass dependence of  M CD ? (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 the HNC  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/

26 Conclusion  Luminosity Independent Backgrounds to CEDP of Hbb do not overwhelm the signal and can be put under full control especially at M> 120 GeV.  Luminosity Independent Backgrounds to H  WW &  channels are 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