Mass methods

From Wiki Les Houches 09

Revision as of 09:21, 16 September 2009

Variable/Method	Reference(s)/Code	Realm of Applicability	Precision	Good for	Fails for	Unknown/Future directions
MT	(ancient)	one missing particle
Meff	hep-ph/9610544[1], hep-ph/0006276[2]	Discovery of NP with massive particles.	Bad, quoted to be 20%-50% on masses in references, but needs to be interpreted in a specific model.	Discovery above SM contribution and estimating mass scale of particles with dominant cross section.	Does not identify process, but gives some information on particle content of dominant topologies.
HT		always			does not identify process in any way
Edges	hep-ph/9610544[3] (lots)	Cascade decay chains. Gives one relationship between NP masses per pair of visible final state particles.	Quoted as 4% on LSP in fast simulation pheno study of SPS1a, hep-ph/0410303 [4]	Mass differences in leptonic decays.	Dependence on absolute mass scale is weak. Can be fooled by false solutions.	Intermediate 3-body decays? Combinatoric (other side) jets not considered. Calorimeter nonlinearity?
MT2	hep-ph/9906349[5]
MT2 kink ("stransverse" mass)	arXiv:0709.0288[6]	4-body final state, 2 missing		large mass differences and large pT	small mass differences or no pT
MTn		4-body final state, n missing
MTgen	arXiv:0708.1028[7]
M2C	arXiv:0712.0943[8]
M3C	arXiv:0811.2138[9]
	arXiv:0812.1042[10]					See also Eq.5 of arXiv:0902.4864 and Eq.53 of hep-ph/0508097 which may be the same. (thanks K.C. Kong)
Exactly-constrained Polynomials	arXiv:0707.0030[11]	4 on-shell intermediate resonances, 2 missing				Apply to squark-neutralino2-slepton-neutralino1 cascade where other side is squark-neutralino1.
Multi-event Polynomial intersection	arXiv:0802.4290[12]	5 or more on-shell intermediate resonances, 2 missing				Statistics of histograms created with n-event subsets; If mass differences are fixed and the masses are increased, what happens? (Sabine Kraml); Develop methods for asymmetric chains and < 6 intermediate resonances.
"Wedgebox" techniques	arXiv:0802.0022

• How can we define "Precision" in a manner that lets us meaningfully compare different methods? A lot of process-specific assumptions and backgrounds usually enter the application of each method.
• In general, all methods need to be systematically tested in cases where the assumptions needed for the method are not satisfied.
• Appropriate consideration of ISR/FSR jets is not usually considered. Requires 2->3 matrix elements where the hard scattering process includes a possible extra hard quark/gluon radiation.

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Outcome

• Models to be studied

SUSY at SPS1a (Sezen), UED at SPS1a (Tommaso), U(1)_B-L (Lorenzo) for event generation

Technicolor (Sasha; see separate point below)

question 1): what should be used for ued ?? comphep feynrules and madgraph have been validated against each other, but there is contradiction w pythia... tommaso renaud and the others should try to figure out what's going on by contacting claude and benjamin and priscila ([13], arXiv:0906.2474[http://arxiv.org/abs/0906.2474) might be due to different version of ued implemented; if so, should be documented

• Signatures

3 lepton + MET

2 lepton + MET

2 lepton + 2 jets + MET

2 lepton + 4 jet (+ MET) OR 4 lepton + 2 jets + MET

4 lepton + MET

• Methods

polynomial: Sezen, (Bob)

MT2: Chris + Monoranjan

Meff + sqrt(s)_min: Jean-Raphael + Asesh

Edges: Tania

MT: Lorenzo (S.Moretti and A.Belyaev are happy to collaborate)

• Event samples

- Parton level, no shower, no hadronization, no detector

- Parton level, no shower, no hadronization, no detector, 1 extra hard jet

- Parton level + shower + hadronization + detector

question 1): which generator should be used for 2->3 ?? herwig cannot do this

question 2): what about delphes validation ?? sezen works on it

• Parton level cuts (open to discussion)

- Pt: Generic Pt > 20 GeV on all objects including EtMiss

- Eta: eta cut is usually very detector dependent. Which part of the detector can be trusted for which object, excluding "crack region", ... There is also how close to beam pipe you can detect things. So to keep thing simple I would vote to have only a cut on Eta max independently of the objects.

• Data storage

at Cern (people at Cern)

• Deadlines (preliminary)

data generation until mid august

results mid november

• Technicolor model

by A. Belyaev

possible signatures (partly in accordance w above):

A) 1 lepton + ETmiss

B) 1 lepton + ETmiss + jets

C) 2 leptons + ETmiss

D) 2 leptons + ETmiss + jets

E) 3 leptons + ETmiss

F) 4 leptons + ETmiss

Sasha plans to apply basically all methods on this model by himself but is happy to share data and knowledge.

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AVAILABLE DATA SAMPLES

Here people who generated data which is ready for analyses should shortly describe what is available, in which format, and where the data can be obtained. We will put up sth similar later on when first data analyses have been performed.

• U(1)_B-L (Lorenzo)

At the moment, you can find 2 samples of events in my public directory at CERN:

/afs/cern.ch/user/b/basso/public/

called B-L_1k.lhe and B-L_j_1k.lhe, produced with CalcHEP.

In details, they are 1000 events from the process:

pp -> ~n,~n

with ~n = ~n1,~n2,~n3 are the heavy neutrinos further decayed;

where p = u,U,d,D,s,S,c,C,G (gluon).

The same for the extra jet

j = u,U,d,D,s,S,c,C,G,

where the kinematical cuts:

P_T > 20 GeV

|eta_j| < 3 have been applied in the generation.

Inclusive cross-sections (regardless of the final state in which the heavy neutrinos decay) are:

B-L_1k.lhe, parton level, cs = 80.32 fb

B-L_j_1k.lhe, parton level with extra jet, cs = 20.02 fb

Notice that excluding taus means to decrease the above cross-sections at least by a factor 2/3 roughly (no mixing between heavy neutrinos, so ~n3 is almost always excluded).

Finally, I introduced new LHA numbers for neutrinos and Z':

nu_h1 = 9910012

nu_h2 = 9910014

nu_h3 = 9910016

H1 = 9900025

H2 = 9900026

Zp = 9900032

I don't state the masses for the Z' and the neutrinos, so you will have something to work out and enjoy.

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Production of SUSY/UED samples

This section describes how we generated signal samples. For both models, the mass spectrum is corresponding to sps1a point.

• UED model is obtained from FeynRules with R = 1/500 and alpha_s computed at 1/R. This is not relevant for further steps and mass spectrum is overwritten to reproduce susy sps1a one. The new mass spectrum with equivalence between UED and susy particles can be seen [[14][on this link]]. Input files for madgraph are in this [[15][directory]].
• Matrix element generation is done with Madgraph 4.4.24. Madevent was used to generate the following processes : gogo, gogoJ, gosq, gosqJ, sqsq, sqsqJ, neuneu, neuneuJ where go = gluino, sq = (anti-)squark, neu = color neutral gaugino or slepton, J = uu~dd~ss~cc~g. param_card.dat can be found on these directories for[[16][ued]] and similarly for susy.
• SUSY/UED decays chains with possible 3-bodies decays are done with BRIDGE v1.8
• Matching between samples with/without ISR is done using Madgraph MLM matching procedure using k_T jet algorithm and QCUT = 40 GeV. To avoid double-counting in sqsqJ and gosqJ samples, events with an intermediate gluino resonance were removed using EXCRES key. This procedure is at the moment working only when interfacing directly pythia with madgraph. In order to solve this a 3-steps procedure had to be done :

 1- get list of rejected events from matching procedure by running pythia directly on madgraph samples
 2- run pythia on BRIDGE samples in inclusive mode (keeping all events)
 3- rejects events from resulting pythia samples via the step1 list when building Delphes files from STDHEP.