SSI-2012 week-1 Questions for Lecturers
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TimestampQuestion to which lecture ?LecturerYour nameYour question on the lectureAnswered ?
7/24/2012 14:29:487/24 (Tuesday) Statistics for Discovery (I)Gross, EilamWhy is the convention to use a less strict boundary of 5% for an exclusion in comparison to a discovery?yes
7/24/2012 14:31:117/24 (Tuesday) Statistics for Discovery (I)Gross, EilamWhen calculating the confidence intervals: how do we know the 'true value' is contained in the intervals from the toys experiments? what exactly is the true value in this case?yes
7/24/2012 16:06:027/24 (Tuesday) Statistics for Discovery (I)Gross, EilamKassaMy question concerns the Brazil plot, more specifically the role of monte-carlo simulation in making the Brazil plot. Is the following line of thought true?

1. Assuming the standard model, and fixing the value of the higgs mass, I can calculate exactly sigma/sigma_{SM}. This would result in a delta function distribution for the value of \mu = sigma/sigma_{SM} for the given higgs mass.
2. Now I claim that this number (\mu) is actually not a fixed number, but a gaussian distributed random number distributed about the mean value that I calculated above.

My confusion is, how do I determine the standard deviation? Do I run a bunch of monte carlo simulations for a given fixed higgs mass and infer the distribution of \mu? If not then how are the 1 \sigma and 2 \sigma (green and yellow) bands determined?
7/24/2012 16:25:027/24 (Tuesday) Statistics for Discovery (I)Gross, EilamWhen computing the look elsewhere effect how do you decide what mass range to use? (eg. why 100-600 GeV instead of 100-1000 GeV?)yes
7/25/2012 11:53:157/25 (Wednesday) Statistics for Discovery (II) Gross, EilamStone, David1. You don't mention much about the dependence of your topics on Bayesian or Frequentist takes on statistics. I don't know much about these two approaches to statistics, so could you comment as to whether or not any of the topics you discuss depend on which approach one takes?yes
7/25/2012 12:31:247/25 (Wednesday) Statistics for Discovery (II) Gross, EilamAaij, RoelTo be able to calculate the likelihood, the shape of distributions for signal and background are required. Particularly for the background or for model-independent searches, this might be non-trivial. How important is the precise knowledge of shapes, also in view of the look-elsewhere effect?yes
7/25/2012 13:01:247/25 (Wednesday) Statistics for Discovery (II) Gross, EilamJiang, YunHow to combine the signal strength with the asymmetric error bars (upper error is not equal to lower error) from different channel? Even in the case where some lower error bar is missing (not zero)? yes
7/25/2012 13:04:067/25 (Wednesday) Statistics for Discovery (II) Gross, EilamJiang, YunRef to slide 112 or 140, could you describe how to weigh the channels (gamgam, bb, ZZ, WW, tautau ...) and then obtain the combined signal strength? yes
7/25/2012 22:24:367/25 (Wednesday) Statistics for Discovery (II) Gross, Eilam1-It's possible to comment a little about analysis in the case of two hypotheses of the type signal1+b and signal2+b ? There's big differences, compared with s / s+b case, in setting the confidence level?

2- Systematics uncertainties that affects only the rate of distributions (e.g. uncertainty in luminosity) or the shape of distributions (e.g. scale of renormalizations) are implemented on the toy models in different ways?
7/26/2012 11:27:077/25 (Wednesday) Statistics for Discovery (II) Gross, EilamJiang, YunRef silde 48, Is q_{obs} obtained from a single real measurement? Since it is not a physical quantity, so I don't think it cannot be directly measured. Am I right? If so,, could you show how to deduce this observed q from a real experiment (not MC)?yes
7/26/2012 17:18:077/24 (Tuesday) Statistics for Discovery (I)Gross, Eilamyou said in the 1st lecture that there is a mathematical reason why you think that the 5-sigma result will not go away. Please explain the reason (again, if you already did).yes
7/24/2012 9:09:037/24 (Tuesday) EWSB Basics (II)Haber, HowardHow do we know f_pi is independent of the Higgs mechanism? Also, how many Higgs bosons do we need to produce to see the admixture of the pion within the physics Higgs boson state - will it show up in decay rates?yes
7/24/2012 9:15:577/24 (Tuesday) EWSB Basics (II)Haber, HowardWhat would be the mass of the H+ if the 20% excess in the Hgg rate is due to an extra loop constribution?yes
7/24/2012 9:33:527/23 (Monday) EWSB Basic (I)Haber, HowardPlease bear with an experimentalist, here. What does "at tree level" or "at loop level" refer to? If possible, can you answer for someone who hasn't had a field theory course? Thank you.yes
7/24/2012 9:57:597/24 (Tuesday) EWSB Basics (II)Haber, HowardYoosoofmiya, RezaAs far as I understand, field theory could be done only in language of Lagrangians. My question is: why do theorists choose to represent symmetries in the Lagrangian as groups, such as SU(3)xSU(2)xU(1) - what is the motivation in involving group theory?
7/24/2012 10:10:557/23 (Monday) EWSB Basic (I)Haber, HowardIn the "Mexican Hat" potential (\mu \phi^2 +\lambda \phi^4), why is it ok to set \mu \rightarrow -\mu?yes
7/24/2012 10:12:097/24 (Tuesday) EWSB Basics (II)Haber, HowardAs you mentioned, theorists are suggesting introducing "stops" in the gg-->h and
h-->gamma-gamma loops to explain the earliest LHS Higgs results. Shouldn't introducing stops also affect the h--> lepton, lepton signal as a higgs can decay into two squarks or sleptons with each of them decaying into a neutralino and a quark or lepton?
7/24/2012 10:12:397/24 (Tuesday) EWSB Basics (II)Haber, HowardWhat do we mean by effective field theory?yes
7/24/2012 12:48:497/24 (Tuesday) EWSB Basics (II)Haber, HowardCan you say something about how the Degrassi paper determines (from the top mass and Higgs mass) whether the vacuum is stable or metastable?yes
7/24/2012 13:05:507/23 (Monday) EWSB Basic (I)Haber, HowardRaval, Aditi 1. In the discussion regarding the WW scattering and unitarity, you wrote that the "most restrictive bound arises from the isospin zero channel (2 W_L^+ W_L^- + Z_L Z_L)". I'm not sure what that state is. I thought that the weak isospin states were W^\pm and W^0 before EWSB. Is (2 W_L^+ W_L^- + Z_L Z_L) a constructed weak-isospin state after EWSB?

2. How does partial wave unitarity imply |M^J|^2 \leq 1? Why is there a restriction on partial wave amplitudes and not the total amplitude (i.e. the sum of all the partial waves)?
7/24/2012 13:12:037/24 (Tuesday) EWSB Basics (II)Haber, HowardRaval, AditiWhen you talked about the stability of the EW vacuum, you talked about how the Higgs potential changes i.e. depends on energy when radiative corrections are included. I have heard (sorry, don't have sources), that the Higgs potential is temperature (Energy) dependent, and before the Electroweak Phase Transition, the potential was parabolic. As the Universe cooled, it changed to the mexican hat potential, after which EWPT (EWSB) took place. Is this temperature dependence somewhat related to radiative corrections, or is this an independent phenomenon? Or am I all wrong in thinking that the potential is temperature dependent? yes
7/24/2012 14:36:467/23 (Monday) EWSB Basic (I)Haber, HowardJiang, YunThe current discovery shows that the actual allow window for Higgs mass(~125 GeV) is somehow deviated from the best global fit. Are we satisfied with this result? If this is acceptable, what's the purpose to repeat such global fit as many paper is doing now?yes
7/24/2012 14:42:237/24 (Tuesday) EWSB Basics (II)Haber, HowardJiang, Yun1) How to precisely measure the relative couplings?
2) Must we impose an additional Z_2 symmetry to remove lam_6, lam_7 terms for the 2HDM? Otherwise, is FCNC bad?
3) What's the spin for this "125 GeV signal"?
4) Could you summarize/comment the deviations between the SM and July 4th's result leads to the new physics?
7/25/2012 10:31:127/24 (Tuesday) EWSB Basics (II)Haber, HowardI have a question on the little hierarchy problem you mentioned to in the last part of your lecture. You said that the problem becomes rather severe for the small Higgs boson mass in the case of composite Higgs boson models. What mechanism causes the feature? Also, do composite Higgs models always have such a feature, or, is the statement valid only for the little Higgs-like models? (I mean, is the discussion applicable to other composite Higgs models like the technicolor models?)
7/25/2012 10:05:327/25 (Wednesday) Precision Higgs Theory (I)Petriello, FrankIs the factorization scale related with the renormalization scale of a given scattering process? If not, how do you determine or define the most favorable factorization scale of the process?yes
7/25/2012 13:06:257/25 (Wednesday) Precision Higgs Theory (I)Petriello, FrankJiang, YunHow to detect high Higgs mass region, say mH>600 GeV? Is it only possible to realize using e+e- collider? yes
7/25/2012 22:44:437/25 (Wednesday) Precision Higgs Theory (I)Petriello, FrankOn slide 25 (lecture 1), you say that Higgs decay width becomes broad for the VV channel -- does it imply that the mass resolution is bad for these channels or something else?yes
7/26/2012 10:04:217/26 (Thursday) Precision Higgs Theory (II)Petriello, FrankPlease explain the terms "inclusive" and "exclusive" in context of cross-sections.yes
7/26/2012 10:07:497/26 (Thursday) Precision Higgs Theory (II)Petriello, FrankCould you elaborate more on why large rapidity separation of two jets is important for search of higgs produced by VBF?yes
7/26/2012 10:21:457/25 (Wednesday) Precision Higgs Theory (I)Petriello, FrankAlthough slightly unrelated, this question is motivated by equation 1 of slide 31. Can you spell out the logical relation between the following terms? Pole mass, constituent mass, current mass, bare mass, physical mass, MS bar mass, running mass. I get confused by the flurry of different terms in the literature, and then it confuses what was originally defined clearly in QFT books. yes
7/26/2012 10:28:357/26 (Thursday) Precision Higgs Theory (II)Petriello, Frank(i) I once heard that in the SM with 4th generation (SM4), the NLO electroweak correction to the h—>gamma gamma branching ratio leads to significantly suppressed partial decay width of the mode, thus, in spite of large gg —> h production rate in the case of SM4, the significance of gg —> h —> gamma gamma in the SM4 is less than that of the SM. Can you explain this feature by using the effective Lagrangian approach you introduced?? (In the lecture, you said that the approach is also applicable to the h gamma gamma coupling.)

(ii) Can you distinguish the effective couplings of the SM Higgs boson to gamma gamma and gg with those of dilaton with the mass of 125 GeV??
7/26/2012 11:23:207/26 (Thursday) Precision Higgs Theory (II)Petriello, FrankWhy is "125 GeV signal" impossible to be spin-1?yes
7/26/2012 11:43:357/26 (Thursday) Precision Higgs Theory (II)Petriello, FrankPellen, MathieuIn dimensional regularization, why scaleless integrals are null?
Is it an "arbitrary" choice?
If yes, why this choice?
7/23/2012 22:32:337/23 (Monday) Historical PerspectiveQuigg, Chrisref : Slide 51 -- 4 tasks for the higgs ---
Can you elaborate on the "Keep EW theory from misbehaving" point?
7/23/2012 22:42:397/23 (Monday) Historical PerspectiveQuigg, ChrisIt seems Higgs Mass Plot from LEPEWWG predicts a Higgs mass below 125 GeV. Does this indicate new Physics beyond the SM?
Does the fact that Higgs mass is not very high as one would expect for a scalar predict new physics beyond the SM?
The fact that the Higgs mass of 125 GeV allows the universe to live in a meta-stable vacuum means that we may not need beyond the SM physics.
Which one of these pictures is correct - new physics or no new physics? What is the correct perspective towards thinking about these questions?
7/25/2012 13:08:137/25 (Wednesday) Higgs Searches (I) Sharma, VivekJiang, YunRef to Slide 25, how to estimate the background? Does it use MC? Could you explicitly show how it works? yes
7/25/2012 22:21:407/25 (Wednesday) Higgs Searches (I) Sharma, VivekWhy can't LHC check for the polarizations of the photons in the H-->YY signal to measure the spin of the particle associated with the 125 GeV resonance?yes
7/25/2012 22:41:297/25 (Wednesday) Higgs Searches (I) Sharma, VivekLecture 1 - Slide 17 -- What is the difference between qqH and ttH production channels?yes
7/25/2012 22:53:457/25 (Wednesday) Higgs Searches (I) Sharma, VivekIt seems that the CMS plots exclude Higgs only till ~580 GeV. So what is the status of the searches beyond that mass? Till what mass range do you keep looking?yes
7/25/2012 23:16:437/25 (Wednesday) Higgs Searches (I) Sharma, VivekIt has been repeated a lot of times that H-->YY is a clean signal. What does "clean" mean here?yes
7/26/2012 11:12:367/26 (Thursday) Higgs Searches (II)Sharma, VivekIt's been mentioned that the current pileup is higher than predicted. Why is that, i.e. what was underestimated?yes
7/26/2012 12:20:497/26 (Thursday) Higgs Searches (II)Sharma, VivekChelstowska, MagdaCan you elaborate on the Wg* bkg estimation in the H->WW channel in CMS? How do you define your control region in this case? And what is the purity? Do you also have a data driven method for the Wg background? yes
7/26/2012 14:32:207/25 (Wednesday) Higgs Searches (I) Sharma, VivekCould you explain the difference between pile ups and underlying events?yes
7/23/2012 21:53:477/23 (Monday) Hadron Collider EnvironmentTully, ChrisHow much is the area (metric units) of the measurement \delta \eta x \delta \phi = 0.1 x 0.1 . Slide 5. yes
7/24/2012 12:05:187/23 (Monday) Hadron Collider EnvironmentTully, ChrisYou mentioned the R9 variable for photons. CMS are reporting diphoton results split into R9 > or < 0.94, and a lot of recent higgs branching ratio papers which focus on the diphoton channel make a point that this distinction allows greater power for testing the SM Higgs. Why is this parameter useful in this context?yes
7/24/2012 12:05:377/23 (Monday) Hadron Collider EnvironmentTully, ChrisCollins, JackYou mentioned the R9 variable for photons. CMS are reporting diphoton results split into R9 > or < 0.94, and a lot of recent higgs branching ratio papers which focus on the diphoton channel make a point that this distinction allows greater power for testing the SM Higgs. Why is this parameter useful in this context?yes
7/24/2012 12:34:007/23 (Monday) Hadron Collider EnvironmentTully, ChrisHow the vertex time is measured? (in reference to slide 10) yes
7/24/2012 14:32:217/25 (Tuesday) LHC: The DetectorsTully, ChrisWhy did CMS and ATLAS assemble their ECALs in different directions? What are the advantages of vertical/horizontal alignment?yes
7/24/2012 14:48:247/25 (Tuesday) LHC: The DetectorsTully, ChrisAs the luminosity increases, both ATLAS and CMS (and LHCb) are already experiencing problems dealing with the ever increasing pile-up - for instance all trigger thresholds are being pushed up and up, and you've shown even then we will have difficulties.

So I was wondering: won't the experiments need to tell the LHC crew at some point 'you've been working amazingly, but can we please keep the lumi flat from now on?'
7/26/2012 10:57:297/26 (Thursday) LHC: The MachineZimmermann, FrankWhat is the biggest challenge for the machine in going from from 8 TeV to 13 or 14 TeV?yes
7/26/2012 11:05:077/26 (Thursday) LHC: The MachineZimmermann, FrankIt is very impressive that the LHC has exceeded expectations in so many areas. Are there any areas in which the LHC performance has been lower than expectations?yes
7/27/2012 20:28:017/25 (Wednesday) Statistics for Discovery (II) Gross, EilamI'm not really an expert on this but as far as I understand there's 5 sigma significance in each experiment, so can we say there is a 10 sigma Higgs discovery at LHC?