ATLAS Calorimetry (Geant)

Transcription

1 signature for New Physics (e.g. compositness, jet multiplicity in SUSY) high of E miss in LHC physics: Importance used in invariant mass reconstruction in decays neutrinos: A=H! fifi, t! lνb, etc. involving in ALAS b-jets, fi -jets and E miss in ALAS Sapiński (INP Kraków) Mariusz Oct 25th, 21 (on behalf of ALAS Collaboration) Importance of jets in LHC physics: QCD studies reconstruction of resonances SUSY and other new physics signature Oct 25th, 21 Mariusz Sapiński (INP Kraków) 1

2 E miss : reconstruction, tails in ALAS Outline ALAS Calorimetry Jet: reconstruction algorithms, calibration Forward jet tagging, low p jet veto b-tagging: vertex & soft, reconstruction of resonances fi-jet: reconstruction Summary Oct 25th, 21 Mariusz Sapiński (INP Kraków) 2

3 Energy resolution E E = 5% p Φ 3% (in j j < 3) E Granularity: ffi ffiffi = :1 :1(for j j < 3) Fast response (few ns of time resolution) in ALAS ALAS Hadron Calorimetry - requirements Good hermecity and coverage up to j j = 5 for E miss! resolution, forward jet tagging in dynamic range from GeV to few ev 1% precision of absolute hadronic energy scale (.1% for electromagnetic scale) At most 2% of nonlinearity up to 4 ev hickness > 9 int (avoid tails in energy deposit for high energy ß) adapted to hadron shower size High radiation resistance (LAr technique in forward part) Oct 25th, 21 Mariusz Sapiński (INP Kraków) 3

4 Pb/LAr EM: Sc/Fe (Barrel) and Cu/LAr (EndCap) HAD: e/h (HAD-ile) = 1.35 Non-compensation: energy (test-beam formula): Etot = Reconstructed in ALAS ALAS Calorimeter Cu/LAr and W/LAr Forward: ALAS Calorimetry (Geant) Hadronic ile Calorimeters EM Accordion Calorimeters Hadronic LAr End Cap Calorimeters Forward LAr Calorimeters ff EEM + fi E 2 EM + fl EHAD+ ffi p EHAD1 EEM3 Oct 25th, 21 Mariusz Sapiński (INP Kraków) 4

5 Minimum Bias (especially at high luminosity) GeV in ffi ffiffi = :1 :1.5 Electronic noise: 2 MeV in tower ffiffi = :1 :1 ffi in ALAS Jet reconstruction Factors related to physics: Initial and Final State Radiation Fragmentation Underlying Event (barrel, electronic noise included) Factors related to detector performance: 1.4 (2.5) GeV in cone of R=.4 (.7), = :3 Magnetic field Non-linearity Lateral shower size, granularity Dead Material and Cracks Longitudinal Leakage (very high-p jets) Oct 25th, 21 Mariusz Sapiński (INP Kraków) 5

6 in ALAS Jet reconstruction (cont.) Cone and clustering approaches: - Cone algorithm: seed + cone iteration of cone direction, jet overlap & energy sharing - Clustering algorithm (QCD inspired): pairing of "particles" (calorimeter towers) starting from closest Choice of algorithm depend on physics channel and luminosity conditions e.g. cone size R : E rec /E kin :4 N :7 1: E kin (GeV) influence of cone size on reconstructed jet energy and on energy resolution Oct 25th, 21 Mariusz Sapiński (INP Kraków) 6

7 1% precision on the absolute jet energy scale Goal: ISR, FSR, out-of-cone energy loss... Systematics: E/p ratio on charged isolated hadrons coming fi decays from! ßν)=11% BR(fi transfer calibration from test-beam inter-calibrate various Calo regions cross-calibrate with Inner Detector Invariant mass constraint on the pair of light jet coming from W decays in tμ t events quark > 3:6 ffi no additional jet and in ALAS Jet energy scale calibration Methods of energy scale calibration: Absolute jet energy scale calibration: p balance between jet and boson in Z + jet fl + jet events and imbalance: fractional < p jet < 12 GeV µ =.33 σ = (p Z-p )/p Z Oct 25th, 21 Mariusz Sapiński (INP Kraków) 7

8 barrel to endcap 1: < j j < 1:8 + scintillator in the crack) (IC in ALAS Dead material and cracks Absorption Length 2 15 Material in front of Muon System 1 5 ile barrel End of active hadronic ile extended barrel Hadronic endcap Forward calorimeter EM barrel EM endcap cryostat walls Pseudorapidity transition regions: endcap to forward 3: < j j < 3: Oct 25th, 21 Mariusz Sapiński (INP Kraków) 8

9 Jet Veto efficiency in ALAS Forward jet tagging and low-p jet veto Jet tagging at large j j - reduction of background in heavy Higgs search vector boson fusion: p of quark agging Efficiency Pseudorapidity ALFAS no pile-up Full simulation no pile-up E >15 GeV Full simulation with pile-up constant fake tag rate 1% Pseudorapidity jet veto: low-p Z+jet(s) events rejection of tμt background Higgs with ALFAS Higgs with DICE Higgs with DICE, High Luminosity Pile-up ttbar with ALFAS ttbar with DICE hreshold (GeV) Oct 25th, 21 Mariusz Sapiński (INP Kraków) 9

10 in ALAS b-tagging Physics motivation: b-jets important for top physics, B-physics, low-mass Higgs (tth), SUSY (A! fifi, bba; A! fifi) vertex method based on long decay path of B-mesons (cfi ο 47μm) and soft-lepton method Oct 25th, 21 Mariusz Sapiński (INP Kraków) 1

11 construct jet weight W = ±log r i in ALAS vertex algorithm likelihood ratio method: for each selected track significance based on signed impact parameter d is calculated S i = d = (d ) compute ratio r i = f b (S i )=f u (S i ) cut on W (depending on the sample). low lumi: σ(d ) (µm) 1 8 xkalman: 3< p <6 GeV ipatrec: 3 < p <6 GeV xkalman: p > 1 GeV R u-jet g-jet c-jet 6 ipatrec: p > 1 GeV η ε b Oct 25th, 21 Mariusz Sapiński (INP Kraków) 11

12 in ALAS soft lepton method BR(b! e) ß 17% (including b! c! e) electron/pion separation is crucial soft electron identification - nine variables (ID and Calo) used to identify electron track jet weight defined by the weight of the most "electron-like" track: low lumi R jet ε b similar method with use of soft muons Oct 25th, 21 Mariusz Sapiński (INP Kraków) 12

13 resonance: simple! bμ b;mh = 1 GeV (full simulation, low and high WH;H resonance chain: in! hh! bμ bb μ b (mh mass constraint applied) and t! jjb H in ALAS Resonance Reconstruction Events/5 GeV lumi) 8 6 Events/5 GeV m bb (GeV) m bb (GeV) Events/8 GeV 4 3 <m bbbb > = 34 GeV σ m = 13.1 GeV Events/4 GeV 2 15 σ = 13.4 GeV m bbbb (GeV) m jjb (GeV) op mass reconstruction accuracy ß 1 GeV (jet and b-jet energy scale is crucial) Oct 25th, 21 Mariusz Sapiński (INP Kraków) 13

14 in ALAS fi-jets Identification: narrow, isolated jet associated to 1(3) track(s) Events/.1 2 Events/ Other variables: for instance electromagnetic radius of jet: R em R em Jet rejection <P <13 5<P <7 3<P <5 15<P < τ efficiency (%) effciency: fi ο 5% with QCD jet rejection ο 1 Oct 25th, 21 Mariusz Sapiński (INP Kraków) 14

15 miss measurement E Important for new physics signatures (SUSY production and decay) particles Invariant mass reconstruction for channels ν: A=H! fifi, t! lνb, involving Contribution from various calorimeters: (5 GeV), end-cap (4 GeV), barrel E miss energy scale in ALAS H! ZZ! llνν Needs calorimeter coverage up to j j ο 5 uses whole calorimeter) (and forward (3 GeV) - because E decreases (Z! fifi events) Measured Z mass (GeV) Scale factor for E miss Oct 25th, 21 Mariusz Sapiński (INP Kraków) 15

16 miss resolution: ff(p miss X;Y ) E Λ - FCAL only Calorimeter calibration (nonlinearity of response Calorimeter coverage (resolution 2.3 GeV for Electronic noise (for 1.5ff cell cutoff resolution in ALAS σ(p xy miss) (GeV) Influence of Minimum Bias events A ττ σ(σp x (p y )) from pile-up (GeV) minimum bias ΣE (GeV) Number of minimum bias Events and electronic noise pile-up (tower) > 1 GeV E at low energy) j j < 5 falls down to 8.3 GeV for j j < 3) - particle level) deteriorates by less then 1%) Oct 25th, 21 Mariusz Sapiński (INP Kraków) 16

17 miss tails E factor of 1 for E miss > 2 GeV - rejection p jet in events with E miss > 5 GeV - highest events /.5 in ALAS events with badly reconstructed jet Z+jet(s) large E miss - - dangerous background! events / 1 GeV E miss (GeV) pseudorapidity of highest E jet achieved in crack region Oct 25th, 21 Mariusz Sapiński (INP Kraków) 17

18 ! fifi rather not observable in SM H MSSM, A=H! fifi enhanced over large region of in in ALAS A=H! fifi reconstruction parameter space: bba=h; A=H! fifi - for high values of tanfi, Events/5 GeV 3 Events/5 GeV m ττ (GeV) m ττ (GeV) σ m (GeV) 6 Associated production Direct production m A (GeV) direct production: b-jet veto (to reject tμt bkg) associated production: at least one b-jet tag Oct 25th, 21 Mariusz Sapiński (INP Kraków) 18

19 jets: reconstruction algorithms, calibration, veto trigger, fi-jets: narrow and isolated jets with 1(3) Can be triggered on. tracks(s). fi-jets with p miss combining E miss reconstruction depend on coverage and in ALAS Conclusions interesting and importnat physics with Very b-jets, fi-jets and E miss jets, b-jets: vertex and soft-lepton algorithms Resonances decay to fifi are reconstructed vector hermicity of calorimeters ALAS is optimised to exploit LHC-physics at the best. Oct 25th, 21 Mariusz Sapiński (INP Kraków) 19