Эксперимент ATLAS Научная сессия ученого совета ОФВЭ ПИЯФ декабря 2013 года Олег Федин

24 декабря 2013 научная сессия ОФВЭ 2 LHC shutdown LS1 LHC back for physics in April 2015 with most probably 13 TeV, i.e. 1.6 times enlarged energy ATLAS LS1 activities: repair and revision of all ATLAS sub-systems. installation of the Pixel IBL. Analysis of data accumulated during RUN-I. Preparation for the ATLAS detector upgrade in Phase-I (2018).

24 декабря 2013 научная сессия ОФВЭ 3 RUN-I: ATLAS Luminosity & Data taking 2012 – 8 TeV L ~ 23 fb – 7 TeV L ~ 5 fb – 7 TeV L ~ 0.05 fb -1 ΔL/L = ±2.8 (preliminary) ΔL/L = ±1.8 ΔL/L = ±3.4 Outstanding performance of LHC ! Number of events in RUN-I dataset (~ 28 fb -1 ) after all selection cuts: W l ν ~ 100 M (LEP2: 0.2M pair W + /W - ) Z ll ~ 10 M (LEP 16M ) tt l+X ~ 0.4 M SM Higgs ~ 400 [~1 H γγ (~1 H 4l) produced every 50 (14h) at 7x ]

24 декабря 2013 научная сессия ОФВЭ 4 A challenge in RUN-I - pile up events Experiments design value ~22 Expected to be reached at L~10 34 Peak Luminosity: 7.73 x cm -2 s -1 peak # collisions vs time Numbers of interactions per bunch crossing Strategy: Developed pile-up robust fast triggers; Optimized reconstruction and identification of physics objects; Precise modeling of in-time and out-of-time pile-up in simulation; Flexible computing model to handle x2 trigger rate and x2 event size. Huge efforts invested over the RUN-I to minimise the impact of pile- up on physics

24 декабря 2013 научная сессия ОФВЭ 5 Trigger in 2012 Trigger Menu optimized for 7x10 33 cm -2 s -1 at 8 TeV: improvement of object selection, e.g. isolation to keep single lepton threshold low (in-spite of 2 x lumi and 2 x pile-up with respect 2011) pile-up robust algorithms close to offline selections Operations in 2012 show trigger is coping very well (in terms of rates, efficiencies, robustness,...) with harsh conditions while meeting physics requirements Trigger rates: Level 1 rates ~ 65 kHz Level 2 rates ~ 5 kHz Event Filter(EF) rates ~ 400 Hz Efficiency of inclusive single electron trigger as a function of pile-up PNPI contribution : E T miss trigger optimization for 2012 data; optimization of single electron trigger for RUN-II (efficiency and rate) using 2012;

24 декабря 2013 научная сессия ОФВЭ 6 Electron Performance Electron reconstruction improved More performing track cluster matching Track pattern recognition takes in account of bremsstrahlung losses Achieved ~ 98% reconstruction efficiency, ~ flat vs η and ET Retuning of cuts (shower shape) Identification efficiency achieved ~ 95%, ~ flat vs pile-up Electron identification efficiency Results are from Z ee data and MC tag-and-probe PNPI contribution : s/w development for the tracks refit to account lost of the energy due to brem; measuring electron efficiencies in 2012 data and define SF in Z ee and Υ ee channels; validation of egamma s/w; The work supported by RFBR. 2011

24 декабря 2013 научная сессия ОФВЭ 7 Search for high mass di-lepton resonances Highest invariant mass dielectron event m ee =1.5TeV,p T =0.59/0.58 TeV Highest invariant mass dimuon event m μμ =1.8TeV,p T =0.65/0.65TeV Models: Z(SSM,E6), Z*, G*(RS) etc Signature: l + l (with l=e,μ) two electrons |η| 40/30GeV two muons |η| 25 GeV Benchmark model: Sequential Standard Model (SSM) in which Z has the same coupling to fermions as SM Z.

24 декабря 2013 научная сессия ОФВЭ 8 Search for high mass di-lepton resonances Observable is mass of di-lepton pair normalized to Z-peak Dominant background is Z/γ* ll Backgrounds: From simulation: Drell-Yan, diboson and ttbar Data-driven estimation : W+jet and dijet Signals: From LO simulation

24 декабря 2013 научная сессия ОФВЭ 9 Search for high mass di-lepton resonances In the absence of any significant signal 95% C.L. limits were set using Bayesian approach on cross section time branching ration Z (SSM) observed limit: 2.90 TeV Z* observed limit: 2.85 TeV PNPI contribution : electron channel analysis: cut flow, QCD bkg. estimation, SF for electon efficiencies, Z* MC production and validation, CL for Z* channel.

24 декабря 2013 научная сессия ОФВЭ 10 Search for heavy bosons decaying to lepton and neutrino Many models predict additional heavy bosons that decay to lepton and neutrino Use Sequential Standard Model (SSM) W as benchmark model Search for high mass states with lepton plus missing ET The observable is transverse mass Look for excess above background – counting experiment!! Signature: l ν (with l=e,μ) one electron |η| 125 GeV and missing E T > 125 GeV one muon |η| 45 GeV and missing E T > 45 GeV E T miss electronsE t miss muons

24 декабря 2013 научная сессия ОФВЭ 11 Search for heavy bosons decaying to lepton and neutrino p T electrons p T muons Background: W lν most dominant and irreducible Z ll when one lepton is not reconstructed mimicking real missing E T Dibosons (WW,WZ,ZZ) + ttbar+ single top production are the next largest that have real missing ET QCD multi-jet estimated from data Observed in both channels that MC overestimates data at high p T Should be resolved to be able to unblind

24 декабря 2013 научная сессия ОФВЭ 12 Search for heavy bosons decaying to lepton and neutrino Analysis is still blind: data above 252 GeV (in the limit setting region) is not shown on plots m T electrons m T muons

24 декабря 2013 научная сессия ОФВЭ 13 Search for heavy bosons decaying to lepton and neutrino W (SSM) expected limit: 2.95 TeV W* expected limit: 2.80 TeV PNPI contribution : electron cahnnel analysis: cut flow, QCD bkg. estimation, SF for electon efficiencies, W* MC production and validation, CL for W* channel.

24 декабря 2013 научная сессия ОФВЭ 14 Forward-backward asymmetry in Z ll Due to the V-A nature of the electroweak interaction, the leptons produced in the annihilation process qq Z/γ * l + l - present a forward-backward asymmetry (A FB ) with respect to the quark direction in the rest frame of the dilepton system. Several Standard Model parameters can be extracted from the A FB measurement. One of these is the electroweak mixing angle, sin 2 θ W. At tree level, this is expressed by the ratio of the vector and axial-vector couplings of the fermions

24 декабря 2013 научная сессия ОФВЭ 15 Z-boson polarization Angular coefficients Ai are functions of lepton- pair kinematics: p T ll, y ll, m ll. Contain information about underlying QCD - dynamics, subject to modifications from higher order perturbative and non- perturbative corrections, structure functions, renormalisation/factorisation scale, underlying event, dependent on the subprocess type: annihilation or Compton s cattering. => QCD dynamics can be probed. Aim is to measure all 8 coefficients A0 -A7, which requires simultaneous 2D fitting in (cos θ CS, φ CS ) parameter space. May be used to compare MC generator implementations of hard scatter/parton shower Not explored in TH papers since almost 20 years, last published results on NL O corrections for Tevatron from `94. Differential cross-section represented as of nine helicity cross- sections multiplied by harmonic polynomials in θ,φ angles of lepton in the Collins- Soper frame: LO term A3, A4, A5, A6 - parity conserving A0, A1, A2, A7 - parity violating A4 - related to AFB

24 декабря 2013 научная сессия ОФВЭ 16 Z-boson polarization Angular coefficients are not expressed by analytical formulae (usually). Some expected to be small: A1,A3,A4, or close to zero: A5,A6,A7. At large p T, A0 and A2 grow and saturate at 1. Only A3 and A4 show some dependence on m ll and Y ll.

24 декабря 2013 научная сессия ОФВЭ 17 Z-boson polarization: analysis strategy Standard data analysis in the fiducial volume, after background subtraction an d unfolded to the particle level (from detector effects and QED FSR: use Born- level leptons). Monte Carlo templates (particle level) propagated to the fiducial volume; use reweighting to isotropic events. 2D fit in (cos θ CS, φ CS ) distributions in p T bins, coefficients A0-A7 extracted from the fits. Comparison of measured coefficients with different MC predictions and different PDFs. Interpretation in language of QCD dynamics. Relation between A4 and sin 2 θ W. Prediction power for other observables (e.g. φ *) At this point, we have a handle (in principle) on infinite order QCD in Collins-Soper frame! full phase-space fiducial phase-space Distributions are sensitive to the production sub- process, and the shapes change r apidly with p T Z. In fiducial volum e, the shapes are dominated by kinematic effects

24 декабря 2013 научная сессия ОФВЭ 18 Z-boson polarization: QCD background estimation PNPI contribution : muon channel analysis: cut flow, QCD bkg. estimation, unfolding, closure for unfolding, reweightnig reco to data, template from different MC and fit in 2D space to extract coefficients

24 декабря 2013 научная сессия ОФВЭ 19 TRT detector Фотография одной из трубок для подачи газовой смеси в детектор TRT, сделанная с помощью эндоскопа, на которой видно ее повреждения в месте изгиба под воздействием озона. TR ratio vs # run PNPI contribution : repairing of TRT detector; TRT s/w development

24 декабря 2013 научная сессия ОФВЭ 20 Pixel New Service Quarter Panels (nSQP) and IBL Transfer services from outside world to pixel detectors Problematic opto-couplers on SQP To replace these need new infrastructure and electronics New electronics will allow greater readout bandwidth for > operation PNPI contribution : creation and assembly cables for the nSQP (technicians and engineers); installation of cables and temperature sensors for the Pixel evaporative cooling systev s/w developing for the Pixel DCS.

24 декабря 2013 научная сессия ОФВЭ 21 TDAQ/DCS Software development of the system of control, configuration and monitoring of ATLAS DAQ – 4 new versions have been issued. Improvement of web interface of the Shifter Assistant system for the expert support of operational control of DAQ and detectors. Development of new tools of archiving and graphical representation of operational monitoring information. Upgrade computers, operating systems and base SCADA system of central DCS (11 PC) Development, testing and put in production of new CANOpen OPC server in advanced standard OPC UA. Upgrade and improvements of: – Rack Control system, – DCS Access Control (including remote access), – ATLAS – LHC Communication – Interface to Condition Database – Calorimeters Cooling package DCS Expert on-call (7/7,24/24) > 20 weeks. PNPI contribution to TDAQ: PNPI contribution to DCS: Отдел информационных технологий проф. Рябов Ю.Ф. Scheme of archiving & representation of data of TDAQ operational monitoring

24 декабря 2013 научная сессия ОФВЭ 22 План модернизации (upgrade) LHC ?, IR 4x, bunch spacing 25 ns ~20-25 fb -1 ~ fb -1 ~350 fb -1, bunch spacing 25 ns, bunch spacing 50 ns Go to design energy, nominal luminosity Injector and LHC Phase-1 upgrade to ultimate design luminosity HL-LHC Phase-2 upgrade, IR, crab cavities? s=14 TeV, L=5x10 34 cm -2 s -1, luminosity leveling s=14 TeV, L~2x10 34 cm -2 s -1, bunch spacing 25 ns s=13~14 TeV, L~1x10 34 cm -2 s -1, bunch spacing 25 ns s=7~8 TeV, L=6x10 33 cm -2 s -1, bunch spacing 50 ns LHC startup, s = 900 GeV Towards to High Energy LHC (HE-LHC) -s=33 TeV Peak luminosity observed in ATLAS in cm 2 s -1

24 декабря 2013 научная сессия ОФВЭ 23 ATLAS upgrade – Phase I Новые детекторы в NSW должны: выдерживать загрузки до 15 к Гц/см 2 On-line (триггер) Эффективность 99% Обеспечить набор измерений с точностями R~100 мкм, φ ~2-3 мрад, dθ~1 мрад; Off-line реконструкция обеспечивать трековое разрешение 60 мкм в плоскости R- φ ; угловое разрешение 0.3 мрад; эффективность восстановления сегмента трека не хуже 97%; сохранять работоспособность до 1 К/см 2 накопленной дозы облучения (предполагая 10 лет работы в условиях sLHC). В качестве новых детекторов были выбраны: TGC камеры хорошо, зарекомендовавшие себя в эксперименте ATLAS; новая технология MM (Micro Megas). Possible participation of PNPI : Construction and assembly of sTGC chambers. Development of fast simulation for nSMW; Development trigger s/w and h/w for nSMW.