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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]
stefan.hoeche
@@ Line 28: / Line 28: @@
 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)
 --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,
+) 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:
@@ Line 53: / Line 80: @@
  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)
-–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
-gammaNNLO (+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
 . 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
@@ Line 94: / Line 121: @@
 --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
-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
 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:
-"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.
 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-
-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
 presentation at CMS QCD photons group 14dec11, slide 4 but also LH proceedings 11:
 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
+photons meeting)
 ===>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.
-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)
 . 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)
+===>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)**
+================================================
+. 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)
+. 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
+. 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.
+. 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]]

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