Some Anomalous Results from the CMS

Transcription

1 Some Anomalous Results from the CMS Saha Institute of Nuclear Physics

2 What did LHC find The SM (like) Higgs boson And nothing

3 6 anomalies from CMS A1. Di-lepton edge analysis in SUSY sees 2.6 Sigma excess A2. eejj channel for the WR searches sees 2.8 sigma A3. evjj channel in leptoquark searches (PAS only) A4. The tth cross section: sees a signal at 3.4 sigma when 1.2 sigma would be expected A5. The H µτ decay 2.5 sigma effect (PAS only) A6. The SM WW cross section about 2 sigma effect both at 7 and 8 TeV (also seen by ATLAS but recent NNLO calculations reduce the discrepancy) (all are from 8 TeV data ~20fb-1)

4 Plan of the talk The CMS performance Particle flow Electron,photon Jets MET Muon Pileup and isolation The test statistic for significance Anomalies in SUSY, Exotica (details) Anomalies in Higgs results February, 2015 Outlook

5 The CMS detector

6 Particle flow Reconstruct all stable particles in CMS detector by linking responses of subdetectors Photon, electron, muon, charged and neutral hadrons Resulting list of particles can be used as if they came from a MC generator Composite objects like jets, taus, MET can be reconstructed from the PF candidates

7 PF diphoton mass reconstruction

8 Photons and electrons EGM

9 jets Anti-KT with distance parameter 0.5 CALO, JPT, PF PF jets clustered from PF candidate particles Resolution measured from MC and various energy balancing methods 2011 JINST 6 P11002

10 MET (ET) Magnitude of transverse momentum imbalance Constructed from PF candidates Correted for various detector effects Dominated by jet enrgy resolution Column 1 Column 2 Column Row 1 Row 2 Row 3 Row 4

11 Muons 1-6% relative momentum resolution for pt<100gev > 10% at a TeV > 1% hadron to muon fake probability Single muon trigger rates (much) better than 90% above a few GeV

12 Pileups: jets, and primary vertex 50 ns bunch spacing, in 2011 ~ 15, in 2012 ~ 30 average pileup contribution to pt can be 10/20 GeV/unit area Affects jets, energy in isolation cones Vertex identified from sum(pt2) of charged tracks in CMS

13 Pileup subtraction Fastjet Pileup subtraction is done using the method of jet-area developed by G. Salam et. al. Pt,jetsub = Pt,jet - ρajet Jet area is not the geometric area of a R cone in the η φ plane ArXiv ,

14 Isolation Typical cone size PF based Sum of pt of photons, charged, neutral hadrons - ρa (exclude candidate particle) Relative isolation normalize by candidate particle pt (e.g. rel PF isolation >0.12 for muons in µµjj analysis)

15 Pileup reweighting

16 Pdf and scale uncertainties

17 Higher orders

18 Profile Likelihood ArXiv:physics v2 Histogram of interest, and auxiliary measurement, used to construct Likelihood (Poisson statistics, u is signal strength, theta = nuisance parameters, here theta is b in each bin) Denominator: Likelihood at global minimum, Numerator: at a given mu, conditional maxima w.r.t. nuisance parameters Is between 0,1 by definition tμ broadens due to presence of nuisance parameters

19 p-value and Z statistic p = 2.87 x 10^-7 Z=5 Source: Cowan et.al. Z statistic can be quoted to report significance One needs to know the distribution of t MC trials Analytic formula

20 Profile likelihood for positive μ For non-negative μ a slightly different staistic is proposed A special case for test of μ= 0 hypothesis μ = 0 rejected means discovery Significance Bigger q0 means greater discrepancy Insensitive to downward fluctuations and q0 = 0

21 Test statistic for upper limits Test statistic qμ for upper limit ~ Test statistic qμ for upper limit, for non-negative signal strength Test statistic qμ insensitive to upward fluctuation Higher value of statistic for more downward fluctuation Significance

22 Asimov dataset, median CL, and its variance A hypothetical dataset Defined as a dataset, over which ML estimators of all parameters equal their true value Name inspired by Isaac Asimov's Franchise, in which a single most representative voter of an electorate replaces all the voters

23 CLs To protect against rejection of background only hypothesis, due to downward fluctuation

24 CLs Probability of Q to be more background-like than observed Probability of Q to be less signal like background-like than observed To protect against rejection of background only hypothesis, due to downward fluctuation Optimal in the Neyman Pearson sense Leads to asymptotic formula

25 Look Elsewhere Effect If the location of a local excess is not known an upward fluctuation of background anywhere is a potential candidate One needs to modify the significance of an excess, keeping this in mind this is look elsewhere effect Ref: E Gross, O. Vitells, PoS ACAT(2010)007 To quantify, many background only MC trials are used, in each one the signal-like fluctuation with largest significance is taken. O(107) trials for 5-sigma, time consuming

26 The L-R symmetric model Explains parity violation as a consequence of spontaneous breaking of SUL(2)XSUR(2) Heavy right handed gauge bosons Heavy right handed Majorana neutrinos Explains neutrino mass thrhough see-saw mechanism Predicts direct production of the heavy gauge bosons and neutrinos at the LHC

27 lljj channel Spectrum includes heavy WR's and heavy ZR Also heavy Nτ, Nµ, Ne Same flavor leptons Majorana N same charged leptons (SSSF) No charge requirement in this analysis Mnl>MWR is not considered

28 lljj channel: cross section and branching WR branching: Only one flavour accessible Degenrate mass of flavors Cross section: Strict symmetry gl = gr L-R boson and lepton mixing angles are assumed small FEWZ used for cross section calculation

29 Trigger and simulation Double electron trigger: 2 X ET>33 GeV Single muon trigger pt > 40 GeV Pythia with Z2* tune MNl = 0.5 MWR Background : mainly (~90%)

30 Event selection Isolated leptons, seperated from jets by dr >0.5 Leading leptons and jets taken pt,l1 >60 GeV, pt,l2 > 40GeV pt,jet1, pt,jet2 > 40GeV WR ene candidates formed Mlljj > 600 GeV, Mll>200 GeV Signal acceptance ~ 80% MNl ~ 0.5 MWR

31 Signal and background yield

32 lljj mass spectrum Chi squared 1.4/0.9 for e/mu channel Excess in eejj channel in TeV 14 observed/4 expected 2.8 sigma LOCAL significance Kolkata, Not consistent LHCDM 2015, IACS, 02 with signal No compelling evidence in other mass and pt distributions

33 lljj cross section upper limit (95% CL) 95% upper limit on σxbr for WR Red band is pdf uncertainty

34 Lljj exclusion

35 st 1 generation scalar Leptoquark Pati-Salam, SU(5), technicolor compositeness models Predict fundamental symmetry between quarks and leptons Leptoquarks LQ are bosons, fractional charge, colored,scalar/vector Decays to charged lepton/neutrino and quark (same generation, unknown branching β)

36 LQ decay channels LQ decays to charged lepton+quark with (unknown) branching β Or to neutrino + quark with branching (1-β ) β is free parameter in this search ejej ( 2e + at least 2 jets) ejνj ( 1e + MET + at least 2 jets) Backgrounds: Z+jet, tt_, multijet, diboson, W+jet, photon+jet

37 ejej pre-selection 2 leading e + 2 leading jet passing id e+ dijet HLT Exactly 2 e, pt > 45 GeV, η <2.5 Atleast 1 jet, pt > 125 GeV, η <2.4 Atleast 2 jet, pt > 45 GeV, η <2.4 Mee > 50 GeV ST > 300 GeV (scalar sum of pt of 2 leading e's and j's) Muon veto (no well identified muon with pt> 10 GeV) Optimization on s/sqrt(s+b)

38 ejej selection Based on 3 criteria: Mee > 50 GeV ST > 300 GeV Mejaverage (Mejmin) Which Mej? The one that gives minimum difference between the pairs. The average of the pair masses is then Mejaverage

39 LQ selected events

40 ejvj pre-selection e+ dijet HLT Exactly 1 e, pt > 45 GeV, η <2.1 Atleast 1 jet, pt > 125 GeV, η <2.4 Atleast 2 jet, pt > 45 GeV, η <2.4 MET> 55 GeV φ (MET,e) > 0.8, φ (MET,j) > 0.8, R (e,jets) > 0.7 ST > 300 GeV (scalar sum of pt of e and j's +MET) Muon veto (no well identified muon with pt> 10 GeV) Optimization on s/sqrt(s+b)

41 ejvj selection Optimization based on 4 criteria: MET ST > 300 GeV Mej,MT,vj

42 Limits on LQ pair production Limit with CLS asymptotic modified frequentist

43 Combined exclusion

44 Mej Mej Errors include stat+sys on background + stat on signal Broad excess, most significant for 650 GeV LQ mass optimization 10 events excess in eνjj corresponds to Mej 650 GeV, β = eejj excess is not in ST tail, eνjj excess is in ST tail.

45 LQ conclusion

46 SUSY edge analysis Search for OS SF e or mu + jets + MET Decay from on shell heavy neutral particle rise in dilepton invariant mass spectrum with a sharp fall (edge) Generic signature, isotropic decay Edge not affected by JER,JES

47 SUSY edge event selection

48 Fit models Flavor symmetric Drell-Yan Signal

49 SF dilepton fit Best fit edge: GeV Local p-value with -2logQ statistic is Gaussian one sided tail probability 2.4 sigma No look-elsewhere effect

50 Central OF dilepton No local edge or excess

51 Sbottom decay hypotheses

52 Counting experiment

53 H µτ

54 H µτ

55 tth Best fit mu value is , 3.4 sigma above background only hypothesis 2 sigma upward fluctuation from SM expectation

56 Theoretical speculations Edge analysis: Huang, Wagner, arxiv:

57 Theoretical speculations Allanach et. al. arxiv v2 Dobrescue, Martin, arxiv v2: Golden cascade in MSSM Resonant pair production of vector-like leptons to explain lljj excess arxiv : The flavour violating Higgs decay in terms of Type III 2HDM

58 Wait till the collisions No evidence of new physics There are some intriguing excesses at ~ 2 sigma level Considering look elsewhere effect such fluctuations are consistent with SM expectations We need to wait for the new collisions at 13 TeV (just a few months)

59 ...and a new boson 4th July 2012

60 Our experiment: CMS

61 CMS tracker

62 Electromagnetic Calorimeter

63

64 CMS magnet and muon system

65 Data Acquisition System

66 Higgs to two photons

67 ...and a new boson

68 Our detector: Hadron Outer

69 Backups