ATLAS: Collisions! Vivek Jain Indiana University Apr 5, 2010

Transcription

1 ATLAS: Collisions! Vivek Jain Indiana University Apr 5, 2010

2 ATLAS: Collisions! Vivek Jain Indiana University Apr 5, 2010

3 Outline Introduction A brief tour of the detector Detector Performance 900 GeV data Tracking, jets, e/mu, b-tagging, Physics result GeV data Inclusive charged-particle multiplicities Future Plans Conclusion Vivek Jain 2

4 The Large Hadron Collider Proton-proton collider 7-14 TeV c.m energy 27 km circumference At 4 interaction points, detectors measure the outcome of the collisions: Alice, LHCb ATLAS, CMS Multi-purpose detectors to study high energy collisions: Standard Model Physics top, bottom, QCD, Higgs Beyond Standard Model SUSY, Extra Dimensions, Z, W Vivek Jain 3

5 The ATLAS detector is the result of ~20 years of activity by a worldwide community of scientists and engineers 1992 ATLAS Letter of Intent 1997 Construction starts 2003 Installation at Point 1 starts 2008 Installation completed (Cosmics) 20 Nov 2009 Single Beam Splash 23 Nov 2009 Collisions at 900 GeV Vivek Jain 4

6 From last week! Vivek Jain 5

7 Vivek Jain 6

8 ATLAS: A tour of the experimental hall is truly awe inspiring Vivek Jain 7 ~7800 tons

9 Inner Detector Tracking detector in 2 Tesla solenoid field ID contains 3 sub-detectors (resolutions) Pixel detector: 10/115 µm in Rϕ/z Silicon strip detector: 17/580 µm Transition radiation tracker: 130µm Rϕ The ID provides around 3 pixel, 8 SCT and ~30 TRT measurements per charged track at η = 0. Coverage: η < 2.5 (2.0 for TRT) Allows for accurate track and vertex reconstruction. Resolution goal: σ pt /p T = 0.05% p T 1% è σ ~ 1% for 100 GeV, GeV Vivek Jain 8

10 Calorimeters Measure energy deposit Missing transverse energy is a very important discriminant for Beyond SM physics, e.g., SUSY Electromagnetic (Pb/Cu/W + LAr) Precision measurements of photons, electrons & hadrons η coverage up to 4.9 Hadronic Barrel (Steel + Scint. Tiles) Measure energy deposit of hadrons η coverage up to 1.7 Vivek Jain 9 9

11 Muon Spectrometer Precision tracking chambers and trigger chambers Monitored drift tubes Cathode drift chambers Thin-gap chambers Resistive plate chambers η coverage up to 2.7 Magnetic field produced by 3x8 air-core toroids Barrel/End Cap toroids Complex field map B ~ 0.5T, but varies in R/Z Bend in barrel is in Z Bend in ECap is along R Vivek Jain 10

12 Trigger L2 and EF are software Average event rate of collision trigger (MBTS + BPTX) in Dec ~ 10 Hz Primary physics trigger in 2009: Beam pickup timing devices (BPTX) Electrostatic beam pickup located at ± 175 m from IP Minimum Bias Trigger Scintillators (MBTS) located at ± 3.56m in z (in front of EC calorimeters) 32 scintillating counters covering 2.09 < η < 3.84 Vivek Jain 11

13 Commissioning prior to Test beam data (2004) Understand detector response, calibration procedures, tuned simulation Cosmics ( ) Preliminary calibration, alignment, timing Single Beam splash events Timing, trigger studies Data challenges to stress-test computing & grid infrastructure Well prepared for collisions Vivek Jain 12

14 Data Taking in Nov 2009: single beam splash 23 Nov 2009: First collisions 900 GeV 6 Dec 2009: First collisions with stable beam. Full detector switched on! 8 Dec 2009: First collisions at 2.36 TeV 16 Dec 2009: end of 2009 data taking Recorded data samples # of events Integrated Luminosity Total µb -1 (syst. uncertainty 900 GeV with Full Detector On µb -1 up to 30%) 2.36 TeV ATLAS data-taking efficiency during this time ~90% Vivek Jain 13

15 Data Taking in Nov 2009: single beam splash 23 Nov 2009: First collisions 900 GeV 6 Dec 2009: First collisions with stable beam. Full detector switched on! 8 Dec 2009: First collisions at 2.36 TeV 16 Dec 2009: end of 2009 data taking Max peak luminosity seen by ATLAS : ~ 7 x cm -2 s -1 Recorded data samples # of events Integrated Luminosity Total µb -1 (syst. uncertainty 900 GeV with Full Detector On µb -1 up to 30%) 2.36 TeV ATLAS data-taking efficiency during this time ~90% Vivek Jain 13

16 Detector Hardware Status in 2009 Now % 100% High operational fractions of all detector systems! Pixels and Silicon strips (SCT) at nominal voltage only with stable beams Vivek Jain 14

17 APS 2/13/2010 ATLAS Status & First Results - A.J. Vivek 15Jain 15 Lankford

18 APS 2/13/2010 ATLAS Status & First Results - A.J. Vivek 15Jain 15 Lankford

19 Many ATLAS detector performance results: Only show a few results APS 2/13/2010 ATLAS Status & First Results - A.J. Vivek 15Jain 15 Lankford

20 View of the Inner Detector all systems were ON in this run Vivek Jain 16

21 Results from cosmics Divide a track to its upper and lower half and refit both hit collections. Get 2 collision-like tracks originating from the same cosmic muon. Compare the two tracks to obtain resolutions. Differences from MC mainly due to residual misalignments Vivek Jain 17

22 Tracking in Collision data Inside-out tracking. Start with tracks found in the Si detectors, and extend them out to the TRT Outside-in tracking Use leftover hits in the TRT, and make standalone tracks. Extend them back into the Si detectors and look for hits, and re-fit Currently, pt threshold is 500 MeV/c, and many on-going studies to lower it Vivek Jain 18

23 Tracking (I) Tracks used here have cuts on number of Pixel ( 1) and total number of Silicon hits ( 6), these plots show that track reconstruction in data is well understood. pt>500 MeV/c and Impact Parameter cuts to select primary tracks # hits in Pixels as function of η, φ # hits in SCT as function of η, φ Vivek Jain 19

24 Tracking (II) Efficiency to extend a Pixel only track into the SCT. Main source of inefficiency is interactions in the ID material. In general, data is well represented by MC, but some discrepancies in the high eta region. Mainly related to not knowing the material very well. Use γ Conversions to look at material (Radiation lengths) + other studies Vivek Jain 20

25 TRT and electron identification Intensity of the transition (=photon) radiation in the TRT α to the Lorentz Factor γ = E/m 0 c 2 of the traversing particle. Use # of high threshold hits to separate e/π! conversion Cross-check: the tail towards high-threshold hits is due to electrons from conversion candidates! Vivek Jain 21

26 Final Tracking Efficiency vs. pt, η for use in Charged particle multiplicity paper ATLAS Preliminary ATLAS Preliminary An overall systematic uncertainty of 3.9% for η=0 was assigned Green bands include both statistical and systematic uncertainties Largest contribution comes from description of material in ID Used in result on Charged Multiplicities in pp collisions Investigating lowering pt threshold for the future Andreas Wildauer Vivek Jain 22

27 Pixel Detector: Energy Deposit Analogue readout of pixel detector allows measurement of energy deposit de/dx Band for p, K, pions can be seen Cross-check with confirms bands π K p Andreas Wildauer Vivek Jain 23

28 Primary Vertex: Beam Spot is stable within run X position: X width: Vivek Jain 24

29 Flavour tagging of jets Plenty of heavy flavour jets in top events, SUSY, Higgs ( bb), Z Need good efficiency to tag b-jets and high rejection of light quark/gluon jets Use variety of algorithms that exploit the fact that b/ c hadrons have detectable lifetimes and their daughters have large impact parameters In early data, use simpler algorithms - not as powerful as more sophisticated ones. Less sensitive to systematics Tracking is the critical element in b-tagging Only jet direction is needed Vivek Jain 25

30 b-tagging basics High mass m B ~ 5 GeV Hard fragmentation of b quarks Soft lepton Lifetime of B hadrons: cτ ~ 470 µm (mixture B + /B 0 /B s ), ~ 390 µm (Λ b ) for E(B) ~ 50 GeV, flight length ~ 5 mm, d 0 ~ 500 µm Spatial tagging: Signed impact parameter of tracks (or significance) Secondary vertex Secondary Vertex B Jet axis a 0 >0 a 0 <0 y x Laurent Vacavant Primary vertex Soft-lepton tagging: Low p T e/mu from B (D) (limited by Br: around 20% each) Vivek Jain 26

31 Significance of Transverse IP of tracks rel. to PrVrtx JetProb Algorithm: (for early data) ve values (from MC) to make resolution function and +ve (from data values) for tagging Data agrees well with MC. With more statistics get Res. Func. from data Determine probability of track to come from PV Make prob. for jet to be light quark/gluon jet. Heavy Flavour jets are at low probability (also other long-lived particles) Slight bias towards low probability values Related to tails in Significance plots MC assumes perfectly aligned detector Vivek Jain 27

32 SV0 Tagger based on secondary vertices within jet (for early data) Since in data we expect very few b-quarks, loosen cuts to keep K s, Λ, γ, hadronic interactions. 70 SV within jets in data, ~ 63 in MC (2.4 bjets in MC) This event also tagged by JetProb 2 nd jet in event (Δφ= 3.0) has SV w/ L/σ ~ 0.9 Vivek Jain 28

33 Calorimeter Vivek Jain 29

34 Calorimeter Performance (I) LAr LAr LAr Vivek Jain 30

35 Early Performance of Level 1 Calorimeter Trigger Comparison of E T (L1 tower) and E T (offline) (separate trigger & readout processing) using halo events from single beam Level 1 E T resolution meets requirement (<5% at high energy) ATLAS Status & First Results - A.J. Lankford Vivek Jain 31

36 Calorimeter Response to Isolated Tracks Sample of isolated hadrons 0.5<p T <10 GeV, η <0.8 <pt> ~ 0.8 GeV No other track within ΔR=0.4 Plot: E(ΔR<0.1)/p Test simulation of calorimeter response to single hadrons. π 0 signal Vivek Jain 32

37 Early Performance of Electron ID E(cluster) / p(track) Check of electron ID variables EM cluster matched to track, E/p Fraction of high threshold hits in TRT calorimeter shower shape variables Sample: EM clusters E T >2.5 GeV + track 783 candidates in 330k events Dominated by: hadron fakes ~ 70% electrons from γ-conversions ~ 30% Transition Radiation hits (TR from electrons yield more hi-thresh hits Shower shape cluster radius in η ATLAS Status & First Results - A.J. Lankford Vivek Jain 33

38 JETS Vivek Jain 34

39 Missing ET is a very important discriminant in (R-parity conserving) SUSY searches χ~ 0 1 Missing E T MC (14 TeV) ~ χ 0 1 Data Vivek Jain 35

40 Muons: Muon Toroid was OFF here Vivek Jain 36

41 Combined Muon Performance: Mu Spectrometer (TOROID ON) + Inner p > 4 GeV pt > 2.5 GeV η < cands. In general, ATLAS is working very well. All the pre-collision commissioning has paid off Vivek Jain 37

42 First Physics result from 900 GeV data - Charged Particle Multiplicities in pp Constrain phenomenological models of soft-hadronic interactions and to predict properties at higher centre-ofmass energies. These models include multiple-parton scattering, partonic matter distributions, scattering between the unresolved protons and colour reconnection. Pythia incorporates many of these models: parameters have been tuned to describe charged-hadron production and the underlying event in pp and p p data at CM energies between 200 GeV and 1.96 TeV Vivek Jain 38

43 A specific set of optimised parameters, the ATLASMC09 PYTHIA tune [18], which employs the MRST LO* parton density functions [19] and the pt-ordered parton shower, is the reference tune throughout this paper. These parameters were derived by tuning to underlying event and minimum bias data from Tevatron at 630 GeV and 1.8 TeV. The MC samples generated with this tune were used to determine detector acceptances and efficiencies and to correct the data. For the purpose of comparing the present measurement to different phenomenological models describing minimum-bias events, the following additional MC samples were generated: the ATLAS MC09c [18] PYTHIA tune, which is an extension of the ATLAS MC09 tune optimising the strength of the colour reconnection to describe the hpti distributions as a function of nch, as measured by CDF in p p collisions [3]; the Perugia0 [20] PYTHIA tune, in which the soft-qcd part is tuned using only minimum-bias data from the Tevatron and CERN p p colliders; the DW [21] PYTHIA tune, which uses the virtuality-ordered showers and was derived to describe the CDF Run II underlying event and Drell-Yan data. Finally, the PHOJET generator [22] was used as an alternative model. It describes low-pt physics using the two-component Dual Parton Model [23, 24], which includes soft hadronic processes described by Pomeron exchange and semi-hard processes described by perturbative parton scattering. PHOJET relies on PYTHIA for the frag mentation of partons. The versions used for this study were shown to agree with previous measurements Vivek Jain 39

44 At higher luminosities will get many such events/beam crossing (at design parameters ~ 23/crossing) Our approach is to measure distributions of primary charged particles in events with 1 charged particle (p t > 500 MeV and η < 2.5) Single arm, minimum bias trigger Single/Double Diffractive + Non Diffractive A In general, past experimentst hi detected only the ND part (mainly due to trigger effects) thus requiring many modeldependent corrections Vivek Jain 40

45 Minimum Bias Trigger Min. Bias Trigger Scintillators Mounted in front of the EC calorimeters Require at least 1 hit on either side Measure trigger efficiency from data with orthogonal trigger which requires colliding proton bunches in ATLAS require > 6 hits in Pixel/SCT & loose track with p T > 200 MeV (L2 & EF) Trigger Efficiency wrt. the analysis selection is extremely high MBTS Vivek Jain 41

46 Analysis Overview Use all data taken at 900 GeV with stable beams and where trigger, tracking detectors, and solenoid were operational Measure fully inclusive inelastic distributions to avoid any model dependence Study events with a reconstructed primary vertex and 1 reconstructed track with p T > 500 MeV, η < hit in pixel, 6 hits in SCT d 0 PV < 1.5 mm, z 0 PV sin(θ) < 1.5 mm Correct for trigger, vertex & track efficiency But do not extrapolate outside our phase space This leaves ~326k events for analysis Beam background estimated from unpaired bunches is < 10-4 Vivek Jain 42

47 Primary Vertex Reco & Secondaries The reconstructed primary vertex must contain 3 tracks with p T > 150 MeV, d 0 BS < 4 mm Vertex reconstruction efficiency is derived entirely from data ~100% for events with 4 or more tracks η dependence for (n>1) is ~ flat Systematic uncertainty < 0.1% ATLAS Preliminary Cut on d 0 and z 0 removes secondaries Estimate remaining secondaries from the impact parameter distribution 2.20% ± 0.05 (stat) ± 0.11 (syst) of selected tracks Vivek Jain 43

48 Charged particle density versus η and p T ATLAS Preliminary N ch : number of primary charged particles corr. to hadron level Normalized to # of selected events N ev p T > 500 MeV η < 2.5 N ch 1 (left) ATLAS data shows higher values than all MC tunes But: MCs are tuned in different region of phase space (right) data/mc agrees well only for p t < 0.7 GeV Vivek Jain 44

49 Results (II) N ch : number of primary charged particles corr. to hadron level Normalized to # of selected events N ev p T > 500 MeV η < 2.5 N ch 1 (left) MC excess of events at N ch = 1 but always lower for N ch 10 (right) increase of <p T > with higher N ch Change in slope around N ch = 10 as seen by CDF (used in MC09c tune) Vivek Jain 45

50 Comparison of Results Compared to CMS: N ch consistently lower than measured by ATLAS. This is expected because of CMS definition of NSD, where events with n ch =0 enter the normalization, and a subtraction of SD events Compared to UA1: N ch 20% higher than ATLAS UA1 used a double arm trigger which rejects events with low charged particle multiplicities ATLAS Preliminary <N ch > η < ± 0.003(stat.) ± 0.040(syst.) NSD η < ± NSD obtained using the Pythia DW tune (Tevatron) CMS NSD (p t > 0.5 GeV) ± Andreas Wildauer Vivek Jain 46

51 Physics Prospects for We are scheduled for a long data-taking run at E cm = 7 TeV in : ~ 1 fb -1 Physics reach is less than at E cm =14 TeV, ~0.2x rate for ttbar; ~0.1x rate for W-prime (1.5 TeV) But more than at 2 TeV for high mass objects ~20x rate for ttbar; ~200x rate for W-prime (1.5 TeV) Vivek Jain 47 47

52 LHC planning and scenario for the coming 8 years This scenario is based on the outcome of the recent Chamonix meeting (one month ago) where the machine experts, the experiments and the CERN Management have reviewed the current LHC situation (cm -2 s -1 ) (integrated luminosities in fb -1 ) 4 Note: Moriond EW, 7- March-2010 Peter Jenni (CERN) - Long shutdown in 2012 for preparing design-energy running - 6 months shutdown in 2015 to bring in LINAC4 - Nominal LHC design performance aimed at Likely a long shutdown in 2017 (or around that time) Discoveries Vivek at Hadron Jain Colliders 48 48

53 Three steps in physics program: Understand detector & reconstruction: using physics samples: Z ee, µµ (σ~ 0(20 nb)), ttbar (0(100 pb)), Re-discover Standard Model measure at LHC energies Minbias, W/Z + jets/γ, Drell-Yan, W mass, Dibosons Understand as background to BSM searches Search for new physics Most of the plots shown in the next few slides used fast simulation studies to go from 14/10 TeV to lower c.m. energies Vivek Jain 49

54 Some of the projections shown here are from Chamonix 2009, which assume a very well-understood detector and use fast simulation to go from 14 to lower energies Ecm (TeV) W Projections assume similar S/B ATLAS can trigger and reconstruct leptons up to η <2.5 Signal cross-section rises faster than W+ n-jets background Vivek Jain 50

55 Standard Model Higgs at the LHC s=14 TeV SM Higgs branching ratios M. Duehrssen, La Thuile WH / ZH (Tevatron) tth GF Vivek Jain 51 WBF/ VBF

56 Combined 1 fb -1 H WW significance extrapolated from the 14 TeV studies simple cut analyses will improve over time ~4σ discovery potential possible with 1 fb -1 at 7 TeV Combination of gg (0-jets), VBF (2-jets) 7 TeV Tevatron currently excludes Will improve with more data and analysis ideas Systematics still uncertain Limits on ZZ will be weaker with the same dataset Other modes, e.g., ττ, γγ, bb will need more data Vivek Jain 52

57 Supersymmetry R-parity conserving SUSY could be found rather quickly if it is at ~1 TeV mass scale Large cross-section for e.g. expect ~ 100 evts for 1000 pb -1 ( s=7 TeV) in the spectacular golden dilepton channel (for benchmark SU3 msugra point) Dark matter candidate χ~ 0 1 Missing E T ~ χ 0 1 Vivek Jain 53

58 SUSY reach with pb 10 TeV 1 TeV? Many channels (n jets + m leptons) being investigated: Jets + E T miss channel: highest reach 1-lepton + jets + E T miss channel: more robust against Background uncertainties SU3 SU4 Discovery up to m ~ 750 GeV discovery reach beyond Tevatron expected exclusion (~400 GeV) for s 7 TeV Requires very good understanding of backgrounds, in particular fake missing Et coming from instrumental effects (noise, cracks, ) Vivek Jain 54

59 Summary ATLAS is performing very well All sub-systems are operational Started collecting data at 7 TeV on Mar 30 Data collection efficiency is close to 100% Start of a long marathon! Thanks to colleagues from whom I borrowed slides Andi Wildauer, Andy Lankford, Claude Guyot, Michael Duehressen, Peter Jenni, Laurent Vacavant. P.A. Delsart Vivek Jain 55

60 Road Map of Expected Hadron Collider Performances Now Tevatron 2 TeV 5 fb -1 (analysed) LHC 0.9 and 2.4 TeV µb -1 End 2011 Tevatron 2 TeV 10 fb -1 LHC 7 TeV 1 fb -1 End 2014 LHC 14 TeV 25 fb -1 End 2016 LHC 14 TeV 100 fb -1 Early 2020ies LHC 14 TeV 500 fb (s)lhc 14 TeV 3000 fb -1 (ultimately ) (These are round numbers and estimates, just to give a rough idea ) Many LHC simulations have been made for 10 TeV, an energy previously (before Chamonix 2010) considered as an intermediate operation point for LHC on its way to the design collision energy Moriond EW, 7- March-2010 Peter Jenni Vivek Jain 56 56

61 More information Vivek Jain 57

62 Vivek Jain 58

63 ATLAS LAr Calorimeters LAr Calorimeters: EM Barrel : ( η <1.475) [Pb-LAr] EM End-caps : 1.375< η <3.2 [Pb-LAr] Hadronic End-caps: 1.5< η <3.2 [Cu-LAr] Forward: 3.2< η <4.9 [Cu,W-LAr] ~190K readout channels Vivek Jain 59

64 EM Barrel Segmentation Fine segmentation for Position/direction measurement Shower shape Min. 22 X0 Segmentation in η and depth by etching cells on Cu electrode Basic cell: Δη Δφ= Segmentation in φ by summing signals over electrodes: 16 in strips, 4 in mid, 4 in back Vivek Jain 60

65 Tile Calorimeter Sampling calorimeter made of plastic scintillator and steel Light signal proportional to energy deposity in plastic PMT WLS fiber Notice orientation of scintillator plates Plastic scintillator inside steel absorber structure Vivek Jain 61

66 Vivek Jain 62

67 P.A. Delsart Vivek Jain 63

68 Triggering on Muons Vivek Jain 64

69 Cross Sections at LHC σ tot = 100 mb (huge!) Exploration of TeV scale physics (e.g. Higgs) requires high beam energy, luminosity Probability of interaction N = Lσ Channel LHC is a W, Z, t, b factory LHC bkgd for # events discovery for 100 fb physics -1 Vivek Jain 65 Total statistics previous expts W µ ν ~10 9 ~10 4 LEP ~10 6 Tevatron Z µ µ ~10 8 ~10 6 LEP ~10 5 Tevatron tt W b W b µ ν X ~10 7 ~10 4 Tevatron 1 design luminosity

70 Most of the previous charged-particle multiplicity measurements were obtained by selecting data with a double-arm coincidence trigger, thus removing large fractions of diffractive events. The data were then further corrected to remove the remaining single-diffractive component. This selection is referred to as non-single-diffractive (NSD). In some cases, designated as inelastic non-diffractive, the residual doublediffractive component was also subtracted. The selection of NSD or inelastic non-diffractive charged-particle spectra involves model-dependent corrections for the diffractive components and for effects of the trigger selection on events with no charged particles within the acceptance of the detector. The measurement presented in this paper implements a different strategy Vivek Jain 66

71 msugra - generic searches in RG evolution of scalar and gaugino masses in a typical SUGRA msugra is merely a convenient framework to account for SUSY breaking (only 4 free parameters + 1 sign) for assessing the discovery potential for R- conserving SUSY with χ 0 1 as Lightest Supersymmetric Particle (LSP, Dark matter candidate). The search strategy is largely motivated by the cosmological constraints on the DM relic density. Taking into account LEP and Tevatron results, define benchmark points in the (m 0,m 1/2 plane): m 1/ 2 SU8 SU1 SU3 SU4 SU6 SU2 Cape Town 01/02/2010 Vivek Jain Beyond2010 ATLAS 67 67