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2013:groups:sm:higgs:photons [2013/06/10 09:39] suzanne.gasconshotkin |
2013:groups:sm:higgs:photons [2013/06/14 00:01] (current) stefan.hoeche |
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They use d0 = 0.38, epsilon = 1 and n = 2 | They use d0 = 0.38, epsilon = 1 and n = 2 | ||
- | ---POWHEG does not include direct photon processes yet either. There had been some work in HERWIG++, see 1106.3939. | + | ---POWHEG does not include direct photon processes yet either. There had been some work in HERWIG++, |
+ | see 1106.3939. | ||
- | ---pp -> AAA at NLO is done by VBFNLO: http://www.itp.kit.edu/~vbfnloweb/wiki/doku.php?id=documentation:proclist | + | --- pp -> AAA at NLO is done by VBFNLO: http://www.itp.kit.edu/~vbfnloweb/wiki/doku.php? |
+ | id=documentation:proclist | ||
- | ===>Slides shown by: Daniel (talk at Paris photon workshop, delta_pt study) | + | ===>Slides shown by (June 5): Daniel (talk at Paris photon workshop, delta_pt study) |
+ | |||
+ | ===>Discussions/conclusions from June 10 meeting: | ||
+ | |||
+ | --Where does the missing data/MC agreement in the LHC diphoton measurements come from? | ||
+ | Fragmentation, missing higher orders, parton shower? Daniel thinks missing orders... Frank K thinks that Sherpa seems to work, so the statement is not completely correct. In Sherpa it is the interplay of merging with fragewmtnation. | ||
+ | |||
+ | |||
+ | --Discussion of eventual possibility of GoSam interfacing to either SHERPA or POWHEG including parton shower | ||
+ | |||
+ | |||
+ | --BTW: NLO corrections and box in SHERPA + OpenLoops available. | ||
===>Studies to be undertaken (People) | ===>Studies to be undertaken (People) | ||
+ | |||
--Redo study of differential cross section vs. delta_pt with 2gammaNNLO, see how 'turnover' at low delta_pt | --Redo study of differential cross section vs. delta_pt with 2gammaNNLO, see how 'turnover' at low delta_pt | ||
- | compares with NLO case and what is minimum 'safe' delta_pt (Daniel et al?) | + | compares with NLO case and what is minimum 'safe' delta_pt (Daniel, Leandro et al) |
- | --Comparisons between GoSam gamma gamma + 1 jet/MG compared to SHERPA/MG/PYTHIA (Gudrun, Nicolas) | + | --Study of k-factor NNLO/NLO as function of delta_pt for (pt_gamma1, pt_gamma2)={(40, 25), (28, 25), (25, |
+ | 25) GeV} (Nicolas et al) | ||
+ | |||
+ | --Comparisons between GoSam gamma gamma + 1 jet/MG (parton-level) compared to SHERPA/MG/PYTHIA | ||
+ | (Gudrun, Nicolas, Nicolas Greiner) | ||
+ | |||
+ | Observables : | ||
+ | Mgg, pT1, pT2, pTj, dR(j,g1), dR(j,g2) | ||
+ | |||
+ | Comparisons: | ||
+ | Diphoton+up to 2jets Madgraph with Pythia parton shower | ||
+ | Pythia Box | ||
+ | Diphoton+up to 3jets Sherpa with shower | ||
Acceptance cuts proposed for the above studies: | Acceptance cuts proposed for the above studies: | ||
Line 53: | Line 80: | ||
anti-kT jets with R=0.5 | anti-kT jets with R=0.5 | ||
- | Comparisons: | + | Add a second set more tailored for Higgs searches. |
- | Diphoton+up to 2jets Madgraph with Pythia parton shower | + | |
- | Pythia Box | + | |
- | Diphoton+up to 3jets Sherpa with shower | + | |
- | Observables : | + | --GoSAM with parton shower (SHERPA, POWHEG)[maybe not for the proceedings] (Gudrun et al) |
- | Mgg, pT1, pT2, pTj, dR(j,g1), dR(j,g2) | + | |
Line 77: | Line 100: | ||
===>Studies to be undertaken (People) | ===>Studies to be undertaken (People) | ||
- | –Make 2d reweighting (mass X Qt) of LO/LO+ codes used for prompt diphoton irreducible backgrounds to | + | –Make 2d reweighting (mass X qT or qT X deltaPhi) of LO/LO+ codes used for prompt diphoton irreducible |
- | 2gammaNNLO (+gamma2MC), should have m_gg distributions in slices of qt (Nicolas) | + | backgrounds (MG) to 2gammaNNLO (+gamma2MC), should have m_gg distributions in slices of qt |
- | + | (Nicolas,Leandro et al) | |
- | –Make 2d reweightings of LO/LO+ codes used for photon + jet and jet-jet (pure QCD) backgrounds to | + | |
- | DIPHOX in gamma-h and h-h modes (Susan) | + | –Make 2d reweightings of LO/LO+ codes used for photon + jet [and jet-jet (pure QCD)] reducible backgrounds |
+ | to DIPHOX in gamma-h and h-h modes [see arxiv.org/abs/hep-ph/0203064](Susan et al) | ||
- | --Use the above for training and test of MVA at particle level (Nicolas, Leandro +...) | + | --Observe shape differences, use the above for training and test of MVA discriminators at particle level |
+ | (Nicolas, Leandro et al...). For both of the above, need unbiased generator-level samples | ||
+ | |||
+ | |||
3. Isolation –For or against trying to use or at least evaluating Frixione isolation on experimental level? Other | 3. Isolation –For or against trying to use or at least evaluating Frixione isolation on experimental level? Other | ||
cones? –Use in Vgamma –Prior LH studies, which Frixione parameters are the best –Same as usual question | cones? –Use in Vgamma –Prior LH studies, which Frixione parameters are the best –Same as usual question | ||
Line 94: | Line 121: | ||
--It was the general conclusion that Frixione isolation is a technique developed to address a theoretical problem | --It was the general conclusion that Frixione isolation is a technique developed to address a theoretical problem | ||
(treatment of collinear divergences) and its use should be limited to theoretical predictions. If not for a criterion like Fx, a large number of additional subprocesses (dijet production, gamma + jet) would have to be calculated at NNLO. But what about Eric's generalized Fx (see Eq. (19.2.1) of 2011 LH proceedings | (treatment of collinear divergences) and its use should be limited to theoretical predictions. If not for a criterion like Fx, a large number of additional subprocesses (dijet production, gamma + jet) would have to be calculated at NNLO. But what about Eric's generalized Fx (see Eq. (19.2.1) of 2011 LH proceedings | ||
- | http://arxiv.org/pdf/1203.6803v2.pdf)? | + | http://arxiv.org/pdf/1203.6803v2.pdf)? Decided it was useful only if to be used by experiment, which we are not |
+ | recommending | ||
+ | |||
--Studies at NLO by Daniel, Leandro et al (LPNHE Photon workshop Paris 2012) showed that inclusive diphoton | --Studies at NLO by Daniel, Leandro et al (LPNHE Photon workshop Paris 2012) showed that inclusive diphoton | ||
cross-section changed by between<1-3% (corresponding to fragmentation component of between 6-16% [but | cross-section changed by between<1-3% (corresponding to fragmentation component of between 6-16% [but | ||
Line 120: | Line 148: | ||
noted as 'delta']), to be discussed in the next (Monday) meeting: | noted as 'delta']), to be discussed in the next (Monday) meeting: | ||
- | "the function giving the E_T profile vs. the cone radius R currently used in the Frixione criterion is... [( 1 - \cos r)/(1-\cos R_max)]^{n} This form is inherited from Stefano's original PRL paper, which illustrated the criterion in the e+e- case. | + | "the function giving the E_T profile vs. the cone radius R currently used in the Frixione criterion is... [( 1 - \cos r)/(1-\cos R_max)]^{n} |
- | + | This form is inherited from Stefano's original PRL paper, which illustrated the criterion in the e+e- case. | |
- | Indeed in this case the motivation is, the collinear pole in the final state read 1/(1-\cos \theta) where \theta was the orthorial angle in spherical coordinates in the e+e- c.m.s.frame, and the diff element of phase space read d | + | Indeed in this case the motivation is, the collinear pole in the final state read 1/(1-\cos \theta) where \theta was the orthorial angle in spherical coordinates in the e+e- c.m.s.frame, and the diff element of phase space read |
- | \theta \sin \theta = d \cos \theta, so Stefano F. found it shrewd to use a function that led to easily handled | + | dtheta \sin \theta = d \cos \theta, so Stefano F. found it shrewd to use a function that led to easily handled |
analytic formulae. | analytic formulae. | ||
In the hadron collider framework the collinear poles instead look conveniently like \propto 2(\cosh \Delta y) - | In the hadron collider framework the collinear poles instead look conveniently like \propto 2(\cosh \Delta y) - | ||
\cos (\Delta \phi)} in terms of rapidity differences and azim angle differences: nothing to do with the e+e- | \cos (\Delta \phi)} in terms of rapidity differences and azim angle differences: nothing to do with the e+e- | ||
- | inspired formula. | + | inspired formula. On the other hand in the nearly colln limit 2 (\cosh( \Delta y) - \cos (\Delta \phi)} ~ [( \Delta y)^2 + (\Delta \phi)^2] = r^2: therefore a E_T profile E_T = E_Tmax * (r / R_max)^{2n) would do the job equally well. Since we seek a simple form, why not adopting this minimalist choice?" |
- | + | ||
- | On the other hand in the nearly colln limit 2 (\cosh( \Delta y) - \cos (\Delta \phi)} ~ [( \Delta y)^2 + (\Delta \phi)^2] = r^2: therefore a E_T profile E_T = E_Tmax * (r / R_max)^{2n) would do the job equally well. | + | |
- | + | ||
- | Since we seek a simple form, why not adopting this minimalist choice?" | + | |
- | ===>Slides/plots shown by: Gudrun (plots from 1303.0824), Daniel (LPNHE slide 12),Leandro | + | ===>Slides/plots shown by (June5): Gudrun (plots from 1303.0824), Daniel (LPNHE slide 12),Leandro |
(https://indico.cern.ch/conferenceTimeTable.py?confId=215483#20130423 slides 12-16), Suzanne(Daniel's | (https://indico.cern.ch/conferenceTimeTable.py?confId=215483#20130423 slides 12-16), Suzanne(Daniel's | ||
presentation at CMS QCD photons group 14dec11, slide 4 but also LH proceedings 11: | presentation at CMS QCD photons group 14dec11, slide 4 but also LH proceedings 11: | ||
http://arxiv.org/pdf/1203.6803v2.pdf pp 165-179 ) | http://arxiv.org/pdf/1203.6803v2.pdf pp 165-179 ) | ||
+ | |||
+ | ===>Discussions/conclusions from June 10 meeting: | ||
+ | |||
+ | --Daniel presented results from he and Leandro showing differential diphoton cross-section behaviour for | ||
+ | kinematical observables m_gg, deltaPhi and costheta* with a) DIPHOX full direct + 1-frag + 2-frag (NLO frags) | ||
+ | with standard solid cone b) DIPHOX with direct and LO frag and c) DIPHOX with direct only and smooth Fx. | ||
+ | Results in the slides but notably the largest difference was between a) and b) (~5%). These were just | ||
+ | preliminary first studies and need more statistics for almost all observables. Need to compare with GoSam | ||
+ | results from Gudrun. A fixed Et limit at the outer cone of 2 GeV (maybe a bit too tight) was taken. They tried | ||
+ | several Et profiles (chi(r)) including Eric's 'hadron-friendly' one, see above. The results for different profiles can be used to determine the uncertainty on the theoretical isolation. Leandro thinks the sensitivity to outer cone | ||
+ | size (from 0,4 to 0,3) is not too significant. | ||
+ | |||
+ | --Gudrun presented results from 1303.0824: in slide 4, stability of inclusive diphoton + jet cross-section as a | ||
+ | function of epsilon_c and Fx_epsilon for scale variations for inclusive and exclusive jet cuts, conclusion is that | ||
+ | the scale variation bands are thicker for lower epsilon values for Fx (but Fx epsilon does not mean the same | ||
+ | thing as cone epsilon. In standard cone, 'upturn' at low values of epsilon may be due to missing NLO frag. On | ||
+ | slide 6, m_gg distribution, the black curve (NLO, z_c=0,1) is the one to compare with Daniel's/Leandro's | ||
+ | results. | ||
+ | |||
+ | --Decision taken to push adoption of Eric's 'hadron-collider-friendly' Et profile for use by TH pending completion | ||
+ | of studies being undertaken by the group | ||
+ | |||
+ | ===>Slides/plots shown by (June10): Daniel (slides), Gudrun (slides linked from main LH program under June | ||
+ | 10 photons meeting) | ||
===>Studies to be undertaken (People) | ===>Studies to be undertaken (People) | ||
- | --Identify zones in differential phase space where fragmentation component is important (NN ) | + | --Identify zones in differential phase space where fragmentation component is important (treated also in 1. ) |
--Check Standard/discretized Fx/annulus cones for total cross-section and differential distributions, frag. | --Check Standard/discretized Fx/annulus cones for total cross-section and differential distributions, frag. | ||
- | component (DIPHOX/Gamma2MC, GoSam) (NN) | + | component (DIPHOX/Gamma2MC, GoSam) (Daniel/Leandro et al.) continuation of above studies, try a few |
+ | more distributions including qTand z and try Eric's 'hadron-friendly' Et profile. Also evaluate change in size of | ||
+ | outer cone from 0.4 to 0.3 [now used more by some experiments like CMS] (Gudrun et al): Consider cases | ||
+ | where renormalisation and factorisation scales are not equal to each other, and check pt_jet dependence as | ||
+ | well) | ||
- | --Discuss and decide on 'LH Fx Accord' for TH (all) | + | --Discuss and decide on 'LH Fx Accord' for TH, a good name is probably 'LH Tight Photon Isolation Accord' (all) |
4. Hgg signal/background –Propagate new knowledge on the gg-ggf background-signal interference | 4. Hgg signal/background –Propagate new knowledge on the gg-ggf background-signal interference | ||
Line 153: | Line 205: | ||
greater S/B sensitivity (using knowledge from 2. above) | greater S/B sensitivity (using knowledge from 2. above) | ||
+ | ===>Studies to be undertaken (People) | ||
+ | |||
+ | --Try to implement Dixon recent code (see 1305.3854v1) and evaluate with experimentally realistic signal | ||
+ | functions (not just a simple Gaussian)...(Philippe) | ||
+ | |||
+ | This has been done in Sherpa and the process will be included in version 2.0.0, as advertised [[http://indico.cern.ch/getFile.py/access?contribId=33&resId=0&materialId=slides&confId=223649|here]] | ||
+ | |||
+ | |||
+ | **Synthesis of Studies to be undertaken/finished for the proceedings (June 11 2013)** | ||
+ | ================================================ | ||
+ | |||
+ | 1. Measurements: gg, gg + jet, gg + 2jets | ||
+ | |||
+ | --Redo study of differential cross section vs. delta_pt with 2gammaNNLO, see how 'turnover' at low delta_pt compares with NLO case and what is minimum 'safe' delta_pt (Daniel, Leandro et al) | ||
+ | |||
+ | --Study of k-factor NNLO/NLO as function of delta_pt for (pt_gamma1, pt_gamma2)={(40, 25), (28, 25), (25, 25) GeV} (Nicolas et al) | ||
+ | |||
+ | --Comparisons between GoSam gamma gamma + 1 jet/MG (parton-level) compared to SHERPA/MG/PYTHIA (Gudrun, Nicolas, Nicolas Greiner) for Observables : Mgg, pT1, pT2, pTj, dR(j,g1), dR(j,g2) | ||
+ | |||
+ | --Interface of GoSAM with parton shower (SHERPA, POWHEG)[maybe not in time for the proceedings] (Gudrun et al) | ||
+ | |||
+ | 2. Understanding finely the background to the H125 or X125 (or 126!) | ||
+ | |||
+ | –Make 2d reweighting (mass X qT or qT X deltaPhi) of LO/LO+ codes used for prompt diphoton irreducible backgrounds (MG) to 2gammaNNLO (+gamma2MC), should have m_gg distributions in slices of qT (Nicolas,Leandro et al) | ||
+ | |||
+ | –Make 2d reweightings of LO/LO+ codes used for photon + jet [and jet-jet (pure QCD)] reducible backgrounds to DIPHOX in gamma-h and h-h modes [see arxiv.org/abs/hep-ph/0203064](Susan et al) | ||
+ | |||
+ | --Observe shape differences, use the above for training and test of MVA discriminators at particle level (Nicolas, Leandro et al...). For both of the above, need unbiased generator-level samples | ||
+ | |||
+ | 3. Isolation | ||
+ | |||
+ | --Check Standard/discretized Fx/annulus cones for total cross-section and differential distributions, frag. component (DIPHOX/Gamma2MC, GoSam) (Daniel/Leandro et al.) for observables cos theta*, mgg, dr(gamma,jet), deltaPhi, qT, z , and try Eric's 'hadron-friendly' Et profile. Also evaluate change in size of outer cone from 0.4 to 0.3 [now used more by some experiments like CMS] (Gudrun et al):stability of inclusive diphoton + jet cross-section as a function of epsilon_c and Fx_epsilon for scale variations for inclusive and exclusive jet cuts, and differential distributions | ||
+ | |||
+ | --Discuss and decide on 'LH Fx Accord' for TH, a good name is probably 'LH Tight Photon Isolation Accord' (all) Fx only to be used for TH in the case of 'tight' isolations. Use Eric's 'hadron-collider-friendly' Et profile. | ||
+ | |||
+ | 4. Hgg signal/background –Propagate new knowledge on the gg-ggf background-signal interference (Martin,Dixon et al) to the exps. signal modelling (mass shifts..) | ||
+ | --Try to implement Dixon recent code (see 1305.3854v1) and evaluate with experimentally realistic signal functions (not just a simple Gaussian)...(Philippe) | ||
+ | --This has been done in Sherpa and the process will be included in version 2.0.0, as advertised [[http://indico.cern.ch/getFile.py/access?contribId=33&resId=0&materialId=slides&confId=223649|here]] | ||