1、Searching for New Physics with Jet Substructure,Shuo Yang (杨硕)/ Dalian University,2013.8.23 Conference of TeV Physics Working Group,Introduction to Jet algorithms Introduction to Jet Substructure. Searching for heavy charged Higgs with jet substructure Searching for heavy b with jet substructure,Out
2、line,I. Introduction to Jet algorithms,p,p,1. Incoming protonParton distribution function,2. Hard processMatrix element calculation , LO or NLO,3. Radiation (Parton Shower)Initial state radiation (ISR) andFinal state radiation (FSR),4. HadronizationUniversal models,5. Underlying event,What is jet?,q
3、uark,gluon,Why do we see jets? Parton fragmentation,Jet Definition,Which? How?,Jet algorithms provide a set of rules for grouping particles into jets. + Parameters,Recombination schemes define how to combine their momenta . (mostly E-scheme),Jets are objects consisting of a collimated spray of parti
4、cles,Jet Algorithms,Cone Algorithm,Recombination Algorithm,UAI,JetCLU,SISCone.,Jade,Kt, Cambrige-Aachen, Anti-Kt.,Based on fixed geometry Idea: Put cone along dominatant direction of flow direction,Idea: Undo branching,Calculate the distance dij between all pairs of pseudo-jets and the beam distance
5、 diB for each pseudo-jet. Find the minimum in the list of dij and diB . If the minimum is dij, recombine i and j into a new particle and then return to step 1. If it is diB, define it as a final-state jet and remove it from the jet list. Return to step 1. Iterate this process until the original list
6、 is empty, i.e., all peudo-jets have been clustered to jets.,The dij and diB in most popular sequential recombine algorithms for use at the LHC can be parameterized as:,P is a parameter, 1 for kt, -1 for anti-kt, 0 for CA,Borrowed from Salams talk,II Introduction to Jet Substructure,Rest frame,Lab f
7、rame,R=0.4,Hadronically decaying EW massive particles at high Pt = 2 jets,Boosted Massive Particles,Jet cone size and fat jet,Fat Jet,Cone size should be chosen flexibly for physical intention. Boosted massive hadronically decaying objects is common at the LHC. M_Z/TeV Fat jet is useful to capture h
8、adronical decay of the highly boosted massive particle. W, H, t . High PT QCD jet could fake the resonance jet. Generally, mass discriminator is not enough!,In order to separate signal, one have to anatomize the Jet Substructure and reconstruct delicate kinematical variables on subjets !,Brief histo
9、ry of Jet Substructure,Michael H. Seymour Searches for new particles using cone and cluster jet algorithms: A Comparative study, Jun 1993, Z. Phys. C62(1994) 127-138 Butterworth, Cox, Forshaw, Jan 2002 WW scattering at the CERN LHC, Phys. Rev. D65 (2002) 096014 Butterworth, Davison, Rubin, Salam, Fe
10、b 2008, Jet substructure as new Higgs search channel at the LHC, Phys.Rev.Lett.100(2008) 242001. Kaplan, Rehermann, Schwartz and Tweedie, Top Tagging: A Method for Identifying Boosted Hadronically Decaying Top Quarks, Phys. Rev. Lett.101(2008) 142001 Grooming :Filtering ,Trimming, Pruning , Variable
11、 R, Nsubjettiness, Dipoloarity. Higgs tagger, top-tagger, W-tagger ,JH Top Tagger,PRL101 (2008)142001,Jet Grooming,Filtering Trimming Pruning,1. Grooming narrows the mass distributions of jet and the reconstructed massive particles.2. It improves both signal purity and the signal significance.3. It
12、can be used to refine any jet.4. Grooming is time consuming but is promising.,Refine the jet resolution,Filtering: break jet into subjets on angular scale Rfilt , take n filtered hardest subjets. Trimming: break jet into subjets on angular scale Rtrim, take all subjets with Pt,subPt,jet Pruning: If
13、the subjets about to be recombined have RRprune and min(Pt1,Pt2) (Pt1+Pt2), discard the softer one.,Exp for Jet Substructure,taggered top,Searching for heavy charged Higgs with jet substructure,Shuo Yang, Qi-Shu Yan JHEP02(2012)074 arXiv: 1111.4530,Hybrid-R Reconstruction Method,CA jet algorithm wit
14、h a large cone and top tagger to capture the highly boosted top t1. Form a jet list J0 . Recluster the pseudo-jets in the event with a small cone (anti-kt R=0.4) and then get a new jet list L0 . If a small-size jet is within the larger cone of the direction of the tagged top jet, remove it and then
15、form a new jet list L1 . We identify the most energetic jet in L1 as the b3 jet. The unused jets in the jet list form L2 . We require there are at lest 3 jets in the list L2. Reconstruct the second top and W by +,1,2,3,4,R size vs. mass distribution,One typical signal event,Searching for b with Jet
16、Substructure,Qi-Shu Yan, Shuo Yang, in preparation,IV Summary,Jet Substructure is helpful to identify highly boosted massive particles or to tell the jet origin.By studying the processes and pp bbtwtw, we find that the combinatorics canbe reduced and backgrounds can be suppressedsignificantly with j
17、et substructure.,Backup,small cone vs. large cone,perturbative fragmentationnon-perturbative fragmentationunderlying event & pile upmulti-hard-parton,Illustration for collinear safety (left) and collinear unsafety in an IC-PR algorithm(right),Borrowed from G.P. Salams talk,Borrowed from G.P. Salams talk,
