1 / 28

Non-PU backgrounds to diffractive Higgs production at the LHC

Non-PU backgrounds to diffractive Higgs production at the LHC (HERA-LHC Workshop, Hamburg, 12-16.03 2007). V.A. K hoze (IPPP, Durham). ). hep-ph/0702212. FP-420. In the proton tagging mode the dominant H  in principle can be observed directly .

abel
Télécharger la présentation

Non-PU backgrounds to diffractive Higgs production at the LHC

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Non-PU backgrounds to diffractive Higgs production at the LHC (HERA-LHC Workshop, Hamburg, 12-16.03 2007) V.A. Khoze (IPPP, Durham) ) hep-ph/0702212 FP-420

  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&hard PP collisions. Reality (very small) 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, CMS-Totem note ) &  admixture of |Jz|=2 production. (Not in MCs)  NLO radiative contributions (hard blob and screened gluons) (Not fully in MCs)  NLLO one-loop box diagram (mass- unsuppressed, cut-nonreconstructible)(Not in MCs)  b-quark mass effects in dijet events – (most troublesome theoretically)still incomplete potentially, the largest source of uncertainties!(LO in Exhume) (Andy ?)

  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 (CDF’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. K. Goulianos,Diffraction at the Tevatron: CDF results, FERMILAB-CONF-06-429-E

  6. effect. PP lumi (HKRSTW, work in progress). (GeV)  in the MSSM at large tan  the Higgs width effects should be properly accounted for

  7. 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 …. gluon identity ? (Andy ) )

  8. 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)

  9. 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 (z) rotational invariance around q-direction (Jz=2, PP-case only)  an additional numerical smallness ( 0.1-0.2 ) recall: to suppress t-channel singularities in the bgds LOHCAvanishes in the Jz=0 case (valid only for the Born amplitude) Jz=0 suppressionisremovedbythe presence of an additional (real/ virtual) gluon (BKSO-94)

  10. 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

  11. 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) 3F=

  12. 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 4 A lot of further theoretical efforts is needed A.Shuvaev et al., E.W.N. Glover et al.

  13. 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. , (Current situation, Andy ? )

  14. 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. DKMOR-02, KMR-07

  15. Production by hard and soft Pomeron-Pomeron collisions (KMR hep-ph/0702213) Requirement: lies with mass interval Suppression: (soft PP and qualitatively for hard PP)

  16. 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

  17. Production by soft Pomeron-Pomeron collisions main suppression : lies within mass interval suppr. factor bb (HI 2006 Fit B and http://www.hep.ucl.ac.uk/~watt/DDIS/ additional factor of ~100 suppression as compared to the ‘old DPDFs’ Background due to central inelastic production mass balance, again subprocess is stronglysuppressed produces asmall tailon the high side of the missing mass H/bb

  18. H1 2006 data show that diffractive gluon densities at  1 are (much) much lower than in the previous analyses. The new MRW2006 fits (which are close to H1 fit B) dpdf are readily availiable at Durham HEPDATA, http://www-spires.dur.ac.uk/  With theMRW2006 partons and M ≈ 20 GeV in the Central Detector the soft DPE bb cross section is less then 0.05 of the Higgs signal (for M_H=120 GeV) The overall suppression of the soft/hard Central Inelastic contributions ~ with N>4. (HI 2006 Fit B and http://www.hep.ucl.ac.uk/~watt/DDIS/ additional factor of ~100 suppression as compared to ‘old DPDF’- based results(CMS-Totem note)

  19. Approximate formula for the background main uncertn. at low masses M- mass window over which we collect the signal b-jet angular cut : ( ) bothSand Bshould be multiplied by the overall ‘efficiency’ factor (combined effects of triggers, acceptances, exp. cuts, tagging efficienc., ….),  ~5% (120 GeV)  g/b- misident. prob.P(g/b)=1.3% (ATLAS) Four major bgd sources ~(1/4 +1/4 + (1.3)²/4 + 1/2 ) at M≈120 GeV, M= 4GeV

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

  21. 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.. )

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

  23. Hbb

  24. Conclusion LuminosityIndependentBackgrounds to CEDP ofHbbdo not overwhelm the signal and can be put under full control especially at M> 120 GeV. 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

  25. 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 ? • RP -mass resolution  (M), further improvement ? • (Risto- conservative estimate) •  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)

  26. FP420 still needs theorists after all Hbb, higher order effects Pile-Up

More Related