Research Experience & Interests

Transcription

1 Research Experience & Interests Daniela Paredes Laboratory of Nuclear and Particle Physics Aristotle University of Thessaloniki May 23, 2015 Daniela Paredes Research Experience & Interests 1/ 17

2 Research experience : LPC-Clermont-Ferrand, PhD Student (TOP/Exotics, t th multileptons, TileCal group): Search for New Physics in events with 4 top quarks Main PhD thesis subject. Estimation of the mis-identification rates of the electron charge for the same-sign dilepton group (TOP/Exotics and t th). Study of the calibration by a radioactive source of the photodiodes of the LASER system of the ATLAS Tile calorimeter Present: Aristotle University of Thessaloniki, Post-doctoral researcher (DBL/Exotics group): Search for exotic decays of the Higgs boson. Talks at International Conferences on behalf on the ATLAS Collaboration: Higgs and Beyond the Standard Model Physics at the LHC, Trieste (Italy), June 2013: Searches for exotics with top with the ATLAS detector at 8 TeV. 50th Rencontres de Moriond: EW Interactions and Unified Theories, La Thuile (Italy), March 2015: Search for Higgs decays to BMS light gauge bosons in four-lepton events at s = 8 TeV. ERE2015: Stepping in the second century, Palma de Mallorca (Spain), September 2015: Searches for New Physics with ATLAS (invited talk) Daniela Paredes Research Experience & Interests 2/ 17

3 Outline : LPC Clermont-Ferrand (France) Search for New Physics in events with 4 tops Estimation of the Q Mis-id background at s = 8 TeV Stability of the photodiodes of the LASER system of TileCal Present: Aristotle University of Thessaloniki (Greece) Search for exotic decays of the Higgs boson 3 Interests & Scientific results Interests & future plans Scientific results Daniela Paredes Research Experience & Interests 3/ 17

4 : LPC Clermont-Ferrand (France) 2014-Present: Aristotle University of Thessaloniki (Greece) Interests & Scientific results Search for New Physics in events with 4 tops Estimation of the Q Mis-id background at s = 8 TeV Stability of the photodiodes of the LASER system of TileCal Search for New Physics in events with 4 tops Goal: Find New Physics in 4 top quarks events (t tt t). New Physics Model: Low-energy effective field theory. Channel of decay: Two leptons with the same electric charge. Analysis performed on: Full 2011 dataset at 7 TeV: 4.7 fb 1 Partial 2012 dataset at 8 TeV: 14.3 fb 1 Full 2012 dataset at 8 TeV: 20.3 fb 1 Includes also three lepton events Analysis tests theories that at low energy manifest as a 4-tops contact interaction Daniela Paredes Research Experience & Interests 4/ 17

5 : LPC Clermont-Ferrand (France) 2014-Present: Aristotle University of Thessaloniki (Greece) Interests & Scientific results 4 tops signal Search for New Physics in events with 4 tops Estimation of the Q Mis-id background at s = 8 TeV Stability of the photodiodes of the LASER system of TileCal Model obtained from Degrande et al. JHEP 13:125, General and model-independent approach: Low-energy effective field theory. g t L = L SM Contact interaction operator + C 4t Λ 2 ( t R γ µ t R )( t R γ µt R ) 2 All possible operators with hypotheses: All SM symmetries conserved. Only top-philic new physics. 3 C 4t /Λ 2 : free parameter to put a limit on. 4 Cross-section σ C 4t /Λ 2 2. t t t t g t Introduces a new 4-tops contact interaction Daniela Paredes Research Experience & Interests 5/ 17

6 : LPC Clermont-Ferrand (France) 2014-Present: Aristotle University of Thessaloniki (Greece) Interests & Scientific results Personal contributions Search for New Physics in events with 4 tops Estimation of the Q Mis-id background at s = 8 TeV Stability of the photodiodes of the LASER system of TileCal 1 Full analysis of the four tops signal in the SM and BSM Upper limits on the parameter C 4t /Λ 2 and on σ 4tSM : σ 4tSM < 70 8 TeV, 20.3 fb 1 First public results on the experimental search of 4-top quarks: 4.7 fb 7 TeV: ATLAS-CONF fb 8 TeV: ATLAS-CONF fb 8 TeV: arxiv: [hep-ex] Paper submitted to JHEP. 2 Estimation of the Q Mis-id background at s = 8 TeV (detailed later). 4t C C 4t /Λ 2 < 15.1 ATLAS 95% CL excluded region 95% CL observed limit 95% CL expected limit ± ± s = 8 TeV, 20.3 fb 1σ 95% CL expected limit 2σ 95% CL expected limit Λ [TeV] Daniela Paredes Research Experience & Interests 6/ 17

7 : LPC Clermont-Ferrand (France) 2014-Present: Aristotle University of Thessaloniki (Greece) Interests & Scientific results Search for New Physics in events with 4 tops Estimation of the Q Mis-id background at s = 8 TeV Stability of the photodiodes of the LASER system of TileCal Estimation of the Q Mis-id background at s = 8 TeV Sign of the electric charge of one of the two leptons in selected same-sign pair has been mis-reconstructed: True opposite-sign lepton pair reconstructed as a same-sign pair! It could come from: 1 Incorrect measurement of the sign of the track curvature dominant at high transverse momentum. 2 Hard Bremsstrahlung producing trident electrons: e ± e ± γ e ± e + e (1) Energy cluster assigned to wrong track! Entries Significance ee channel, s=8 TeV ATLAS Preliminary Ldt = 14.3 fb Data Q Mis id Fakes tt+z/w(w) WZ/ZZ ± ± W W N jets Q Mis-id one of the dominant backgrounds in the analysis Q Mis-id rates estimated with data driven techniques in Z e + e + jets events. Daniela Paredes Research Experience & Interests 7/ 17

8 : LPC Clermont-Ferrand (France) 2014-Present: Aristotle University of Thessaloniki (Greece) Interests & Scientific results Contributions Search for New Physics in events with 4 tops Estimation of the Q Mis-id background at s = 8 TeV Stability of the photodiodes of the LASER system of TileCal 1 Official estimation of the Q Mis-id background for the TOP/Exotics same-sign dilepton group: a) Same-sign top production (tt). b) Vector-Like-Quarks. c) 4 th generation b. d) T 5/3 production. e) Four tops produced via: - Standard Model. - Contact interaction. - Sgluon decay. - 2UED/RPP model. Exotic analysis paper submitted to JHEP arxiv: [hep-ex]. 2 Official estimation of the Q Mis-id background for t th same-sign dilepton group t th analysis paper to be submitted to Phys. Lett. B. ATL-COM-PHYS Editor of the internal note explaining the procedure to estimate the charge flip rates ATL-COM-PHYS Official charge flip rates used for the TOP/Exotics and tt H same-sign dilepton groups Daniela Paredes Research Experience & Interests 8/ 17

9 : LPC Clermont-Ferrand (France) 2014-Present: Aristotle University of Thessaloniki (Greece) Interests & Scientific results Search for New Physics in events with 4 tops Estimation of the Q Mis-id background at s = 8 TeV Stability of the photodiodes of the LASER system of TileCal Stability of the photodiodes of the LASER system in TileCal Daniela Paredes Research Experience & Interests 9/ 17

10 : LPC Clermont-Ferrand (France) 2014-Present: Aristotle University of Thessaloniki (Greece) Interests & Scientific results Search for New Physics in events with 4 tops Estimation of the Q Mis-id background at s = 8 TeV Stability of the photodiodes of the LASER system of TileCal Stability of the photodiodes of the LASER system in TileCal Role of the LASER system in TileCal 1 One of the hardware calibration systems. 2 Monitor the stability of the response of the 9852 PMTs and their associated electronics. Four photodiodes measure the intensity of the laser light Important to know if photodiodes are calibrated and if their electronics is linear. Daniela Paredes Research Experience & Interests / 17

11 : LPC Clermont-Ferrand (France) 2014-Present: Aristotle University of Thessaloniki (Greece) Interests & Scientific results Contributions Search for New Physics in events with 4 tops Estimation of the Q Mis-id background at s = 8 TeV Stability of the photodiodes of the LASER system of TileCal 1 Full analysis of the data taken from February, 2011 to February 2013 Data from the photodiodes calibration were not analyzed before ATLAS Internal Tile Calorimeter Photodiode 2 Scale Factor Normalized mean value 2 Proposal of a new method to study the stability of the photodiodes response. 1 3 Editor of the two approved internal notes describing the stability of the photodiodes: ATL-TILECAL-INT and ATL-TILECAL-INT /11 07/11 /11 01/12 04/12 07/12 /12 12/12 04/13 A B C D date Paper to be submitted to JINTS: ATL-COM-TILECAL Daniela Paredes Research Experience & Interests 11/ 17

12 Outline : LPC Clermont-Ferrand (France) Search for New Physics in events with 4 tops Estimation of the Q Mis-id background at s = 8 TeV Stability of the photodiodes of the LASER system of TileCal Present: Aristotle University of Thessaloniki (Greece) Search for exotic decays of the Higgs boson 3 Interests & Scientific results Interests & future plans Scientific results Daniela Paredes Research Experience & Interests 12/ 17

13 : LPC Clermont-Ferrand (France) 2014-Present: Aristotle University of Thessaloniki (Greece) Interests & Scientific results Search for exotic decays of the Higgs boson Search for exotic decays of the Higgs boson Goal: Search for exotic decays of the Higgs boson. New Physics Model: Final state: 4l. SM + U(1) D gauge symmetry. l Z d l H κ s Z d l H Z d Z d 4l l Analysis performed on full 2012 dataset at 8 TeV: 20.3 fb 1. Analyses based on the H ZZ 4l measurement (arxiv: ). Daniela Paredes Research Experience & Interests 13/ 17

14 : LPC Clermont-Ferrand (France) 2014-Present: Aristotle University of Thessaloniki (Greece) Interests & Scientific results Personal contributions Search for exotic decays of the Higgs boson 1 Determination of the final selection of events. 2 Definition of the control region. 3 Comparison data/mc. 4 Co-editor of the support note. 5 Cross-checks... Paper to be submitted to Phys. Rev. D. ATL-EXOT-PHYS I presented this analysis at Moriond 2015 Starting the Run II analysis Upper limits computed in terms of: d 95% CL Upper Bound on µ Signal strength µ d = σ BR(H Z d Z d 4l) [σ BR(H ZZ 4l)] SM ATLAS s = 8TeV, 20.3 fb Final State: 4e+2e2 µ+4µ Observed Expected ± 1 σ ± 2 σ m Zd [GeV] Daniela Paredes Research Experience & Interests 14/ 17

15 Outline : LPC Clermont-Ferrand (France) Search for New Physics in events with 4 tops Estimation of the Q Mis-id background at s = 8 TeV Stability of the photodiodes of the LASER system of TileCal Present: Aristotle University of Thessaloniki (Greece) Search for exotic decays of the Higgs boson 3 Interests & Scientific results Interests & future plans Scientific results Daniela Paredes Research Experience & Interests 15/ 17

16 : LPC Clermont-Ferrand (France) 2014-Present: Aristotle University of Thessaloniki (Greece) Interests & Scientific results Interests & Future plans Interests & future plans Scientific results Searches for New Physics: - Phenomena expected to emerge at the LHC. - In line with my current research and experience. Monojet final states are a clean signature in searches for exotic processes: - SUSY. - Large extra spatial dimensions. - WIMPs. Detector related activities: detector upgrade or performance studies - A highly performing detector is indispensable for any signature. Minimum expected scientific production up to mid Paper publication (using the data taken in 2015) for 2016 Winter conferences. 2 Paper publication (using the data taken in 2016) for 2017 Winter conferences. Contribution to other analyses to be discussed. Contribution to detector related activities to be discussed. Daniela Paredes Research Experience & Interests 16/ 17

17 Scientific results ATLAS collaboration papers: - The ATLAS Collaboration, Search for new light gauge bosons in Higgs boson decays to four-lepton final states in pp collisions at s = 8 TeV with the ATLAS detector at the LHC, ATL-EXOT-PHYS (to be submitted to Phys. Rev. D), ATL-CONF The ATLAS Collaboration, Analysis of events with b-jets and a pair of leptons of the same charge in pp collisions at s = 8 TeV with the ATLAS detector, arxiv: [hep-ex] (submitted to JHEP), The ATLAS Collaboration, The Laser calibration of the ATLAS Tile Calorimeter, ATL-COM-TILECAL (under review to be submitted to JINST), The ATLAS Collaboration, Search for the associated production of the Higgs boson with a top quark pair in multi-lepton final states with the ATLAS detector, ATL-HIGG (to be submitted to Phys. Lett. B.), ATL-CONF ATLAS Conference Notes: - The ATLAS Collaboration, Search for anomalous production of events with same-sign dileptons and b-jets in 14.3 fb 1 of pp collisions at s = 8 TeV with the ATLAS detector, ATLAS-CONF , The ATLAS Collaboration, Search for exotic same-sign dilepton signatures (b quark, T 5/3 and four top quarks production) in 4.7 fb 1 of pp collisions at s = 7 TeV with the ATLAS detector, ATLAS-CONF , ATLAS internal notes (reviewed and approved): - Paredes, D. (editor), and Calvet, D. Stability of the photodiodes and their electronics in the LASER system of the ATLAS Tile Calorimeter in 2012 and 2013, ATL-TILECAL-INT , Paredes, D. (editor), and Calvet, D. Stability of the photodiodes and their electronics in the LASER system of the ATLAS Tile Calorimeter in 2011, ATL-TILECAL-INT , ATLAS internal notes (not reviewed): - Paredes, D. (editor), and Calvet, D. Estimation of the mis-identification rates of the electron charge at 8 TeV, ATL-COM-PHYS , Daniela Paredes Research Experience & Interests 17/ 17

18 BACKUP Daniela Paredes Research Experience & Interests 18/ 17

19 Search for New Physics in events with 4 tops Daniela Paredes Research Experience & Interests 19/ 17

20 Motivation Four tops have never been observed. SM prediction for 4-tops at the LHC is very small: σ SM 0.5 fb at 7 TeV Some models predict an enhancement of the t tt t production rate at the LHC: Top composite 3 σ SM Cross sections for multi-top production in the SM (Barger et al. Phys.Lett.B687:70-74,20) Daniela Paredes Research Experience & Interests 20/ 17

21 New Physics models involving 4 top quarks Some models can be tested by studying events with 4 top quarks: Predicts a 5 th fundamental force. 1 Composite top g t t t 2 Randall-Sundrum g t t t Contribution from a 4-tops operator to 4-tops production Daniela Paredes Research Experience & Interests 21/ 17

22 New Physics models involving 4 top quarks Some models can be tested by studying events with 4 top quarks: Predicts a Universe with 5 dimensions. 1 Composite top g t t t gkk 2 Randall-Sundrum g t t t g KK t t Daniela Paredes Research Experience & Interests 21/ 17

23 Search strategy Look in a region with high H T objects, ET miss and large jet multiplicity. Determine the cut giving the lowest expected upper limit on σ 4t. Events / 0 GeV ATLAS Internal Ldt = 14.3 fb ee channel, Q Mis id Fakes tt+z/w(w) WZ/ZZ ± ± W W s=8 TeV Events / 40 GeV 2 ATLAS Internal Ldt = 14.3 fb ee channel, Q Mis id Fakes tt+z/w(w) WZ/ZZ ± ± W W s=8 TeV tttt C.I. ( 65.3) Uncertainty tttt C.I. ( 65.3) Uncertainty H [GeV] T miss E T [GeV] Events ATLAS Internal Ldt = 14.3 fb ee channel, Q Mis id Fakes tt+z/w(w) WZ/ZZ ± ± W W s=8 TeV Events 2 ATLAS Internal Ldt = 14.3 fb ee channel, Q Mis id Fakes tt+z/w(w) WZ/ZZ ± ± W W s=8 TeV tttt C.I. ( 65.3) Uncertainty tttt C.I. ( 65.3) Uncertainty N jets N b jets Daniela Paredes Research Experience & Interests 22/ 17

24 Final selection TeV: 4.7 fb TeV: 14.3 fb 1 ) Final selection obtained by iterating cuts on the discriminant variables: 1 H T = jets,e,µ p T, 2 N jets, 3 N b jets, 4 E miss T. Goal: determine the cut giving the lowest expected upper limit on σ t tt t : Expected limits computed at 95% C.L. CL s method with the LLR as a test statistic has been used. Each limit is computed using a cut&count experiment. The optimization includes the full systematic uncertainties. Daniela Paredes Research Experience & Interests 23/ 17

25 Final selection: TeV: 4.7 fb TeV: 14.3 fb 1 ) Expected 95% C.L. upper limit [pb] ATLAS Internal N jets 2, N 1 b jets N 2, N 2 b jets Simulation, s= 7 TeV jets N jets 3, N 1 b jets N jets 3, N 2 b jets N jets 3, N 3 b jets N jets 4, N 1 b jets N jets 4, N 2 b jets N jets 4, N 3 b jets Expected 95% C.L. upper limit [pb] ATLAS Preliminary N jets 2, N 1 b jets N 2, N 2 b jets Simulation, s= 8 TeV jets N jets 3, N 1 b jets N jets 3, N 2 b jets N jets 3, N 3 b jets N jets 4, N 1 b jets N jets 4, N 2 b jets N jets 4, N 3 b jets [GeV] Cut on H T [GeV] Cut on H T Final selection s [TeV] HT [GeV] N jets N b jets ET miss [GeV] 7 > > 40 8 > > 40 Final event selection for the signal region Daniela Paredes Research Experience & Interests 24/ 17

26 Limits at 95% C.L. for t tt t contact interaction 95% C.L. upper limit [fb] Channel Obs. Exp. 1σ range 2σ range ee eµ µµ Comb TeV 95% C.L. upper limit [fb] Channel Obs. Exp. 1σ range 2σ range ee eµ µµ Comb TeV C 160 C ATLAS Internal Ldt = 4.7 fb s = 7 TeV ATLAS Internal Ldt = 14.3 fb s = 8 TeV Excluded region at 95% CL 60 Observed limit at 95% CL Expected limit at 95% CL Expected limit ± 1σ 40 Expected limit ± 2σ Λ [TeV] C /Λ 2 < 28 TeV 2 Excluded region at 95% CL 60 Observed limit at 95% CL Expected limit at 95% CL Expected limit ± 1σ 40 Expected limit ± 2σ Λ [TeV] C /Λ 2 < 15 TeV 2 Daniela Paredes Research Experience & Interests 25/ 17

27 Production of the Q mis-id background at s = 8 TeV Daniela Paredes Research Experience & Interests 26/ 17

28 Estimation of the charge flip rates Normalized events ATLAS Internal Same sign events Ldt =20.3 fb Opposite sign events 2 s = 8 TeV [GeV] M ee Charge flip rates estimated with data driven techniques in Z e + e + jets events. GOAL: estimate the contamination from opposite-sign events in the same-sign signal region Daniela Paredes Research Experience & Interests 27/ 17

29 Procedure 1 Rates (ɛ) computed as a function of ( η,p T ) by minimizing the likelihood function: ln(l(ɛ N SS, N)) i,j,k,l where both leptons satisfy p T < 140 GeV. ln[n ij,kl (ɛ i,k + ɛ j,l )]N ij,kl SS N ik,jl (ɛ i,k + ɛ j,l ) (2) 2 Rates corrected using a p T dependent correction factor above 140 GeV correction factor extracted from t t MC. 3 Opposite-sign events reweighted using these rates: estimation of contamination in same-sign events. Systematics: Differences between the measured and true rates in MC. Differences between the true rates extracted for e and e +. Change of the Z peak region. Differences between the rates corrected using other t t samples. Daniela Paredes Research Experience & Interests 28/ 17

30 Apply the p T correction 1 p T correction factor extracted from t t events ɛ( η, p T ) for t t computed using the truth-matching method. 2 Correction factor computed with respect to the highest bin of the low p T region: p T [80, 140] GeV α t t ( η, p T ) = 3 Correction applied if electron satisfies p T > 140 GeV α t t set to 1 if electron p T < 140 GeV. ɛ( η,p T ) ɛ( η,p T [80,140]GeV) mis id 1 ATLAS Internal Simulation tt s = 8 TeV ) T ( η,p tt α ATLAS Internal Simulation tt s = 8 TeV p T p T [15,140] GeV [140,00] GeV Truth matching tt p [15,60] GeV T p [60,80] GeV T p [80,140] GeV T p [140,00] GeV T η η Daniela Paredes Research Experience & Interests 29/ 17

31 Apply the p T correction 1 Rates after correction are defined as: ɛ( η, p T ) Z = ɛ( η, p T [80, 140]GeV) Z α t t ( η, p T ). mis id 1 ATLAS Internal Ldt =20.3 fb s = 8 TeV 2 3 p [15,60] GeV T p [60,80] GeV T p [80,140] GeV T p [140,00] GeV T η Systematics are included Daniela Paredes Research Experience & Interests 30/ 17

32 Improvements 1 Rates p T dependence taken into account Implementation of the likelihood method in 2D. New method developed when lepton p T > 140 GeV. 2 Z peak region redefined differently for M SS Z it takes into account the shift of M SS Z 3 Different sources of systematics considered and MOS Z with respect to MOS Z. before, they were computed just as the differences with respect to other methods (tag&probe and direct extraction). Daniela Paredes Research Experience & Interests 31/ 17

33 Closure test: Z MC and data Events 00 ATLAS Internal Same sign events 800 Simulation Z+jets s = 8 TeV Estimate after p T correction Events 900 ATLAS Internal Same sign events Ldt =20.3 fb s = 8 TeV Estimate after p T correction M ee [GeV] M ee [GeV] Z MC: Same-sign events: Likelihood after correction: Data Same-sign events: Likelihood after correction: Good agreement within uncertainties Daniela Paredes Research Experience & Interests 32/ 17

34 Closure test: Z MC and data Events ATLAS Internal Simulation Z+jets s = 8 TeV Same sign events Estimate after p correction T Estimate without p dependence T Events ATLAS Internal Ldt =20.3 fb s = 8 TeV Same sign events Estimate after p correction T Estimate without p dependence T Ratio Leading lepton p [GeV] T Ratio Leading lepton p [GeV] T Z MC: Same-sign events: 158. Likelihood after correction: Likelihood without p T dep.: 84 ± 4. Data Same-sign events: 152. Likelihood after correction: Likelihood without p T dep.: 72 ± 4. Good agreement within uncertainties Daniela Paredes Research Experience & Interests 33/ 17

35 Stability of the photodiodes of the LASER system of TileCal Daniela Paredes Research Experience & Interests 34/ 17

36 The LASER intercalibration tool: the photodiodes system Important to know if photodiodes are calibrated and if their electronics is linear and stable. Linearity measured by injecting calibrated charges into photodiodes electronics. Calibration done with an alpha ( 241 Am) source. How does the system photodiodes-source work? 1 Source moves and stops in front of each photodiode. 2 Signal digitized after an amplifier. 3 For each event only one photodiode contains energy from the alpha radiation the other three are pedestals. The photodiodes box Daniela Paredes Research Experience & Interests 35/ 17

37 Photodiodes calibration Calibration process includes : 1 Pedestal run Taken before the source scan. 2 Alpha scan Taken while the source is scanning. Pedestal run measures: Response of the electronics without signal Average of these events is the pedestal. Electronic noise RMS of the distribution. Pedestal run Pedestal Daniela Paredes Research Experience & Interests 36/ 17

38 Photodiodes calibration Calibration process includes : 1 Pedestal run Taken before the source scan. 2 Alpha scan Taken while the source is scanning. Alpha scan Alpha scan measures: Response of the photodiodes in presence of the source alpha response. Pedestal and noise when the source is in front of the other photodiodes Pedestal Alpha response Daniela Paredes Research Experience & Interests 36/ 17

39 Stability of the photodiodes and their electronics Stability can be studied by using: Readout electronics from pedestal and alpha runs Alpha response of the alpha scan 1 Stability of the photodiodes electronics: Pedestal Mean value vs. time: compare pedestal extracted from the different runs Ratio should be 1. Noise RMS vs. time: compare noise extracted from the different runs Ratio should be 1. 2 Stability of the alpha response: scale factor vs. time (defined later) Scale factor (SF 0 ) should be 1. Here just results for photodiode 2 (similar results for the other photodiodes) Daniela Paredes Research Experience & Interests 37/ 17

40 Entries Mean 1 RMS Entries Entries Mean 1 Mean RMS RMS Stability of the alpha response: the scale factor method Assumption: variations in the alpha spectra are due to variations of the photodiodes gain and/or readout electronics NEW METHOD rescaling of the spectrum: the amplitude of each event is multiplied by a scale factor. Two methods were tested: 1 Normalized mean value (µ) default. 2 Scale factor (SF ). RMS of each distribution gives precision of the method. Entries SF 1 /SF 0 SF 1 /SF 0 (χ 2 µ /(µ SF 0 ) 1 0 test) (Kolmogorov test) SF 1 /SF 0 Scale factor is more precise than normalized mean value Daniela Paredes Research Experience & Interests 38/ 17

41 Stability of the alpha spectra: results ATLAS Internal Tile Calorimeter Photodiode 2 Scale Factor Normalized mean value /11 07/11 /11 01/12 04/12 07/12 /12 12/12 04/13 A B C D date Scale factor and normalized mean value are well correlated. Maximum deviation for the periods C and D 0.5% Daniela Paredes Research Experience & Interests 39/ 17

42 Search for exotic decays of the Higgs boson Daniela Paredes Research Experience & Interests 40/ 17

43 Motivation Some BSM theories include dark sector states that use the Higgs boson as a portal to look for New Physics. 1 Models add a U(1) d gauge symmetry which introduces: New gauge field Z d with kinetic mixing ɛ with the hypercharge gauge boson Z d : BSM light gauge boson or Dark Z that couples to the dark charge of the new sector. Additional Higgs with mass mixing κ leading to a new Higgs doublet. motivated by DM searches (see arxiv: ). 2 Dark sector can be inferred from: Deviations from the SM-predicted rates. Decays through exotic intermediate states. Open possibilities such as H H ZZ d 4l Z d κ s Z d l l l a) H ZZ d 4l: ɛ κ b) H Z d Z d 4l: κ ɛ My case! H Z d Z d 4l l Daniela Paredes Research Experience & Interests 41/ 17

44 Signal / Background / Data 1 Signal generation: Only gluon fusion for Higgs production is considered. Hidden Abelian Higgs Model is used as a benchmark (arxiv: ) m Zd [15, 60] GeV. 2 Background processes: H ZZ 4l (Higgs coming from ggf, VBF, WH, ZH and t th), ZZ 4l, WW /WZ Obtained from simulation and normalized from theory. Z + jets, t t Estimated from data. J/ψ and Υ Obtained from simulation and normalized using the ATLAS measurements. 3 Data: 20 fb s = 8 TeV. Only electrons and muons are used. All results from ATLAS-CONF Daniela Paredes Research Experience & Interests 42/ 17

45 Event preselection 1 Quality requirements: GRL, detector status, primary vertex. 2 Trigger: single and dilepton triggers. 3 Leptons: Electrons: E T > 7 GeV, η < 2.47 excl < η < 1.52, z 0 < mm. Muons: p T > 6 GeV, η < 2.7, d 0 < 1 mm. 4 Quadruplets: At least 4 leptons containing 2 same-flavor opposite sign leptons (SFOS): p T : p T > 20 GeV, p T > 15 GeV p T > GeV. One(two) lepton(s) match the single(dilepton) trigger. Leptons are paired in SFOS indices 1(3) and 2(4) denote first(second) pair. 5 Quadruplets with minimum m, where m = m 12 m 34, are kept. 6 Additional requirements: Separated leptons: R(l, l) > 0.1, R(l, l ) > 0.2. Track isolation: p cone20 T /p l T < 0.15 Calo Isolation: E cone20 T /E T (p T ) < 0.2 (e), 0.3 (µ). Impact parameter significance: d 0 /σ d0 < 6.5 (e), 3.5 (µ). Daniela Paredes Research Experience & Interests 43/ 17

46 Changes with respect to HSG2 selection Cut H ZZ 4l H Z d Z d 4l 4 leptons Kinematics same Trigger matching 1 quadruplet m 12 closest to m Z m = m 12 m 34 minimal Primary pair mass 50 < m 12 < 6 GeV Secondary pair mass X < m 34 < 115 GeV (X = f (m 4l )) R Track, calo isolation same IP significance Signal region 115 < m 4l < 130 GeV Z and J/Ψ Υ vetoes on all SFOS pairs m 2l m Zd < δm Comparison of the selection applied to the H Z d Z d 4l and H ZZ 4l analyses m 2l m Zd < δm is the reduced form of m 12 m Zd < δm && m 34 m Zd < δm. Daniela Paredes Research Experience & Interests 44/ 17

47 Search strategy 1 Assume the discovered Higgs-like particle around m H = 125 GeV is the lighter of the new Higgs doublet in this extended scenario. 2 Consider only electrons and muons Three different final states: 4e, 2e2µ and 4µ. 3 Consider 15 m Zd 60 GeV: m Zd < 15 GeV to be considered at Run II. m Zd < m H /2 to have two on-shell Z d. 4 Results given in terms of µ d = σ BR(H Z d Z d 4l) [σ BR(H ZZ 4l)] SM. The denominator here is just the SM σ BR(H ZZ 4l). It is constant as function of m Zd µ d = 1 would correspond to the H Z d Z d 4l having a strength equal to the SM rate H ZZ 4l. Daniela Paredes Research Experience & Interests 45/ 17

48 Search strategy Events with at least 4 leptons containing 2 same-flavor opposite-sign leptons (SFOS) are used m 12(34) : Invariant mass of the first (second) SFOS pair. Keep only quadruplets with minimum m = m 12 m 34. m ll has to be consistent with the detector resolution (the two Z d have the same mass). Events / 5 GeV Final state : 2e2µ ATLAS Data 2012 m H = 125 GeV H >Z d Z d >4l (m =20 GeV) s = 8 TeV, 20.3 fb Z d 7 H >Z d Z d >4l (m =50 GeV) Z d ZZ* > 4l H >ZZ* >4l WW,WZ 4 tt Zbb, Z+jets (Z+) quarkonium Total background Significance m [GeV] Absolute mass difference, m, in the 2e2µ channel, after the impact parameter significance requirements Daniela Paredes Research Experience & Interests 46/ 17

49 1 115 < m4` < 130 GeV Remove a lot of ZZ events. 2 Z and J/ψ Υ vetoes ( m2` mz < GeV and m2` < 12 GeV) on all SFOS pairs Remove events with a Z on-shell or low-mass m [GeV] Signal Region 80 Final state : 4e 70 ZZ* 4l 60 H ZZ* 4l H ZdZd 4l (m = 50 GeV) Zd resonances. 3 m`` < mh /2 loose Signal Region. 4 mzd m`` < δm 20 ATLAS Simulation 0 0 mh = 125 GeV δm = 5/3/4.5 GeV for 4e/4µ/2e2µ channel m4l [GeV] ZZ 4`, H ZZ 4` and H Zd Zd 4` (mz = 50 GeV) d Daniela Paredes Research Experience & Interests 47/ 17

50 Data/background comparison in the loose SR: m ll Entries / 5 GeV ATLAS s = 8 TeV, 20.3 fb m H = 125 GeV Final state : 4e Data 2012 ZZ* > 4l H >ZZ* >4l WW,WZ tt Zbb, Z+jets (Z+) quarkonium Total background Entries / 5 GeV ATLAS s = 8 TeV, 20.3 fb m H = 125 GeV Final state : 4µ Data 2012 ZZ* > 4l H >ZZ* >4l WW,WZ tt Zbb, Z+jets (Z+) quarkonium Total background Significance m ll [GeV] Significance m ll [GeV] Entries / 5 GeV ATLAS s = 8 TeV, 20.3 fb m H = 125 GeV Final state : 2e2µ Data 2012 ZZ* > 4l H >ZZ* >4l WW,WZ tt Zbb, Z+jets (Z+) quarkonium Total background Entries / 5 GeV ATLAS s = 8 TeV, 20.3 fb m H = 125 GeV Final state : 4e+4µ+2e2µ Data 2012 ZZ* > 4l H >ZZ* >4l WW,WZ tt Zbb, Z+jets (Z+) quarkonium Total background Significance m ll [GeV] Significance m ll [GeV] Daniela Paredes Research Experience & Interests 48/ 17

51 Data/background comparison in the loose SR: m Events / 5 GeV ATLAS s m H = 8 TeV, 20.3 fb = 125 GeV Final state : 4e Data 2012 ZZ* > 4l H >ZZ* >4l WW,WZ tt Zbb, Z+jets (Z+) quarkonium Total background Events / 5 GeV ATLAS s m H = 8 TeV, 20.3 fb = 125 GeV Final state : 4µ Data 2012 ZZ* > 4l H >ZZ* >4l WW,WZ tt Zbb, Z+jets (Z+) quarkonium Total background 1 1 Significance Events / 5 GeV m [GeV] ATLAS s m H = 8 TeV, 20.3 fb = 125 GeV Final state : 2e2µ Data 2012 ZZ* > 4l H >ZZ* >4l WW,WZ tt Zbb, Z+jets (Z+) quarkonium Total background Significance Events / 5 GeV m [GeV] ATLAS s m H = 8 TeV, 20.3 fb = 125 GeV Final state : 4e+4µ+2e2µ Data 2012 ZZ* > 4l H >ZZ* >4l WW,WZ tt Zbb, Z+jets (Z+) quarkonium Total background 1 1 Significance m [GeV] Significance m [GeV] Daniela Paredes Research Experience & Interests 49/ 17

52 Data/background comparison in the loose SR: m 4l Events / 5 GeV ATLAS s m H = 8 TeV, 20.3 fb = 125 GeV Final state : 4e Data 2012 ZZ* > 4l H >ZZ* >4l WW,WZ tt Zbb, Z+jets (Z+) quarkonium Total background Events / 5 GeV ATLAS s m H = 8 TeV, 20.3 fb = 125 GeV Final state : 4µ Data 2012 ZZ* > 4l H >ZZ* >4l WW,WZ tt Zbb, Z+jets (Z+) quarkonium Total background Significance m 4l [GeV] Significance m 4l [GeV] Events / 5 GeV ATLAS s m H = 8 TeV, 20.3 fb = 125 GeV Final state : 2e2µ Data 2012 ZZ* > 4l H >ZZ* >4l WW,WZ tt Zbb, Z+jets (Z+) quarkonium Total background Events / 5 GeV ATLAS s m H = 8 TeV, 20.3 fb = 125 GeV Final state : 4e+4µ+2e2µ Data 2012 ZZ* > 4l H >ZZ* >4l WW,WZ tt Zbb, Z+jets (Z+) quarkonium Total background Significance m 4l [GeV] Significance m 4l [GeV] Daniela Paredes Research Experience & Interests 50/ 17

53 Systematic uncertainties: H Z d Z d 4l Daniela Paredes Research Experience & Interests 51/ 17

54 Number of events in the Signal Region Process 4e 4µ 2e2µ H Z d Z d 4l (m Zd = 25 GeV) 2.38 ± 0.07 ± ± 0. ± ± 0.12 ± 0.93 (ggf)h ZZ 4l (1.3 ± 0.3 ± 0.2) 2 (0.9 ± 0.3 ± 0.3) 2 (0.2 ± 0.1 ± 0.2) 2 (VBF)H ZZ 4l (.0 ± 2.0 ± 0.7) 4 (8.4 ± 2.3 ± 0.4) 4 (5.1 ± 1.7 ± 0.2) 4 (W)H ZZ 4l (8.4 ± 2.1 ± 0.8) 4 (2.2 ± 1.1 ± 0.1) 4 (2 ± 1 ± 0.1) 4 (Z)H ZZ 4l (2.8 ± 1.0 ± 0.2) 4 (9.8 ± 5.6 ± 0.5) 5 (18 ± 7 ± 1) 5 (t t)h ZZ 4l (5.6 ± 2.0 ± 0.6) 5 (3.8 ± 1.7 ± 0.4) 5 (4.7 ± 1.9 ± 0.5) 5 ZZ 4l (7.1 ± 3.6 ± 0.5) 4 (8.4 ± 3.8 ± 0.5) 3 (9.1 ± 3.6 ± 0.6) 3 WW, WZ < < < t t < < < Zbb, Z+jets < < < ZJ/ψ and ZΥ < < < Total background (1.6 ± 3.1 ± 0.2) 2 (1.9 ± 3.1 ± 0.3) 2 (1.2 ± 3.1 ± 0.1) 2 Data H Z d Z d 4l (m Zd = 20.5 GeV) 2.32 ± 0.07 ± ± 0. ± ± 0. ± 0.96 (ggf)h ZZ 4l (1.1 ± 0.3 ± 0.2) 2 (0.5 ± 0.2 ± 0.2) 2 (0.2 ± 0.1 ± 0.02) 2 (VBF)H ZZ 4l (5.8 ± 1.8 ± 0.4) 4 (6.3 ± 2.0 ± 0.3) 4 (3.6 ± 1.5 ± 0.1) 4 (W)H ZZ 4l (3.3 ± 1.2 ± 0.3) 4 (1.0 ± 1.0 ± 0.0) 6 (9.4 ± 6.7 ± 0.5) 5 (Z)H ZZ 4l (2.4 ± 0.9 ± 0.2) 4 (1.6 ± 0.7 ± 0.1) 4 (1.1 ± 0.6 ± 0.1) 4 (t t)h ZZ 4l (4.1 ± 1.9 ± 0.4) 5 (4.4 ± 2.1 ± 0.5) 5 (4.0 ± 1.6 ± 0.4) 5 ZZ 4l (3.5 ± 2.0 ± 0.2) 3 (4.1 ± 2.7 ± 0.2) 3 (2.0 ± 0.6 ± 0.1) 2 WW, WZ < < < t t < < < Zbb, Z+jets < < < ZJ/ψ and ZΥ < < < Total background (1.6 ± 3.1 ± 0.2) 2 (1.0 ± 3.1 ± 0.2) 2 (2.6 ± 3.1 ± 0.1) 2 Data The expected and observed numbers of events in the signal region for each of the three final states, for the hypothesized mass m Zd = 25 GeV and 20.5 GeV One event in data passes all the selections in the 4e channel and is consistent with 23.5 m Zd 26.5 GeV. One other in data passes all the selections in the 4µ channel and is consistent with 20.5 m Zd 21.0 GeV. Daniela Paredes Research Experience & Interests 52/ 17