ATLAS, CMS B-Physics Reach UK HEP FORUM The Cosener's House, Abingdon, 24th-25th April 2004 'From...
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Transcript of ATLAS, CMS B-Physics Reach UK HEP FORUM The Cosener's House, Abingdon, 24th-25th April 2004 'From...
ATLAS, CMS B-Physics Reach
UK HEP FORUM The Cosener's House, Abingdon, 24th-25th April 2004
'From the Tevatron to the LHC'
M.Smizanska, Lancaster University, UK
ATLAS-CMS 2
ATLAS,CMS: b-events from central pp LHC collisions
230b
100b
ATLAS.CMS, LHCb three different strategies to measure B production within partially overlapping phase space
LHC pp total = 100 mb inelastic = 80 mb bb = 500 b
ATLAS/CMS Central detectors
LHCb Forward detector
pT
after triggerand offlineone B ‘in’
|| < 2.5
pT >10 GeV = 100 b
1.9 < <4.9
pT > 2 GeV = 230 b
Luminosity
for B physics
L = 2 × 1033 cm-2 s-1
rare B 1034 cm-2 s-1
L = 2 × 1032 cm-2 s-1
Statistics
exclusive B
1 y @ 1033 cm-2 s-1
2.6 × 106
dominated by B J/But all hadronic with muon tag
1 y @ 2 × 1032 cm-2 s-1
1.7 × 106 B J/
1.7 × 106 hadronic
ATLAS-CMS 3
b-events: LHC vs Tevatron
bb-
ATLAS/CMS LHCb
CDF
Bjorken x1 vs x2 for events that passed trigger&offline
for at least one of B hadrons
ATLAS-CMS 4
ATLAS/CMS
ATLAS
b-events: LHC vs Tevatron, cont
In hadron-hadron collisions b and anti b quarks are produced with
angular distances (0-At LHC a contribution of topologies with b
anti b different from ‘back-to back’ is expected to be even higher
than in Tevatron.
CDF
Implications:
B-Trigger strategies
Tagging uncertaintes
ATLAS-CMS 5
ATLAS,CMS B – physics Trigger strategies
ATLAS-CMS 6
ATLAS Trigger Architecture
Hardware (FPGA)
General Purpose Processors : offline
type algorithms
General Purpose Processors optimised
algorithms
Implementation
Higher LevelTrigger
108 109 Hz2 x
< 2.5 s
~ 10 ms
~ few sec
Decision times
FPGA = Field Programmable Gate Array
High Level Trigger
ATLAS-CMS 7
ATLAS,CMS B – physics Trigger strategies Different scenarios for diff. luminosity
conditions & rates
single-muon
di-muon
all
all
h
h
b
b
c
c
J/
@1033cm-2s-1
1. Di-muon trigger:L1 2 + L2 full precision trackingBd(Bs,Bc ) J/Ks
0 (K0*,),
b (bb) J/() , B b s
2. Muon-electron() trigger: L1 + L1 E/cluster (ET>2GeV)+ L2 tracking in regionBd(Bs,Bc ) J/ (ee) + Ks
0 (K0*,) + B b (b, b) J/ (ee) + B b s + B
3. Muon-hadron triggers:L1 + L1 Jet (ET>5GeV) + L2 tracking in regionL1 + L2 full-scan tracking in Inner DetectorB pure hadronic decays + B
ATLAS-CMS 8
ATLAS LVL1 Jet RoI LVL1 Jet RoI ET > 6 GeV
ET GeV
LVL1 Jet RoI ET > 6 GeV
Bs pT GeV
For hadronic final states use LVL1 Jet RoI (events with LVL1 muon)
• LVL1 Jet Clusters in EM & Hadron Calorimeters.
• Threshold of ET > 6 GeV (efficient for Bs with pT > ~ 16GeV)
• Final threshold chosen will depend on RoI multiplicity
• Preliminary simulation studies gives a mean multiplicity of 2 for a 6 GeV threshold (final value may be higher).
ATLAS-CMS 9
CMS High-Level Trigger Tracking
Limited amount of CPU time available for trigger decision: 500 ms on a 1GHz machine possibly 50 ms in 2007
Reduce # of track seeds # of operations per seed
Regional seed generation
Regional seed generation
Partial/Conditional Tracking
Partial/Conditional Tracking
Limited to some region identified by Lvl1 objects
(e.g. cone around direction)
Stopped when: N hits are reconstructed PT resolution resolution given given
thresholdthreshold PT value given thresholdgiven threshold …………………………………… ……………………………………....
HLT Tracking does notneed to be as accurate as
in the offline
ATLAS-CMS 10
CMS BS -+
@ L1: 2 trigger, PT 3 GeV, || 2.1
@ High Level Trigger: Regional tracking look for pixel seeds only in a cone around the 2, with PT 4 GeV and d0 1mm, and compatible with PV
Conditional tracking reconstruct tracks from good seeds Stop reconstruction if PT 4 GeV @ 5 Keep only tracks with σ(PT)/PT 2%, N 2%, Nhit =6 hit =6
IF 2 Opposite Signs tracks found Calculate the invariant mass Retain pairs with a) |M-MBS
| 150 MeV
b) Vertex 2 20 & d0 150 m
Lvl-1 HLT Global Events/ 10fb-1 Trigger Rate
15.2% 33.5% 5.1% 47 <1.7Hz
ATLAS-CMS 11
ATLAS,CMS Inner detector and B-phys performance
ATLAS-CMS 12
CMS Tracker Design and Performances
Pixel around interaction point Pixel around interaction point 4.2, 7, 10 cm and +- 60 cm in z4.2, 7, 10 cm and +- 60 cm in z
Radius ~ 110cm, Length/2 ~ 270cm
3 disks TID
6 layersTOB
4 layersTIB
9 disks TEC Silicon strip : R = 10-60 mPixel: R, z = 10-20 m, cell size ~ 100x150m
ATLAS-CMS 13
The ATLAS Inner Detector
Sub-Detector r(cm) element size resolution hits/trackPixel 5.0; 8.8 50m x400m 12m x 60m 3 (Silicon) 12.2 (3D) SCT 30-52 80m x 12cm 16m x 580m 4 (Silicon Strip) (stereo)Barrel: 4 cylinders; End-cap: 9 Wheels
TRT 56-107 4 mm x 74cm 170m 36 (Straw Tubes) (projective)
Initial LHC may be without: 1 pixel layer at 8.8cm, one of 3 endcap pixel disks and forward TRT wheels: so called ‘Initial layout’
Three sub-detectors using different technologies to match the requirements of granularity and radiation tolerance
ATLAS-CMS 14
ATLAS: Inner detector performance
B proper time resolutions
Single-Gauss fit [fs]
Com plete
Initial 1998
Bs Ds 100 98 67
B 99 98 69
Bs J/ 85 82 63
Bd J/K 89 86 69
b J/ 101 95 73
ATLAS-CMS 15
Comparison of ATLAS and CMS
impact parameter resolutions
ATLAS-CMS 16
ATLAS particle identification in B-physics events
Low pT electron identification
Combined EM calorimeter-TRT electron identification
Rejection of bb 6X events without electron vs efficiency of events bb 6e5X. Eff=70%,R=570, level-2 rate of signal is 40Hz, fake rate 10Hz due to hadrons misidentified as electrons.
TRT electron identification
Invariant mass for all track pairs in bb J/ (ee)K0 events before and after TRT selection cuts. Electrons have pT>1GeV.
ATLAS-CMS 17
ATLAS particle identification in B-physics events, cont.
Low and medium-pT muon performanceLowest pT muon identification & reconstruction efficiency
Inner detector + Muon spectrometer
Inner detector + Muon spectrometer+ Hadron calorimeter
J/) reconstruction in the environment of b-jet with pT~(50-80) GeV (for QCD b-production studies)
the same in log scale
Even in high pT jet a mass reconstruction is negligibly affected by fake pairs when a muon identified in Muon spectrometer match to a wrong track in Inner Detector.
ATLAS-CMS 18
1year@1033cm-2 s-1 CMS ATLAS
TriggerOfflineS/B
4400k430k8
800k170k31
sin2statisticalLepton tagJet/charge tagTotal
0.0310.0210.015
0.0390.0260.017
Combined ATLASand CMS sin23y@1033cm-2s-1 0.007ATLAS, CMS3y@1033cm-2s-1 &LHCb 5y@1032cm-2s-1
0.005
The statistics used in the table includes: ‘dimuon triggers mu6mu3’, using LVL1 efficiency 80%/per muon. ‘di-electron LVL2 trigger e1e1’. With more realistic e4e4 the precision of ATLAS, CMS degrade by factor 1.2.
Method: maximum likelihood fit using experimental inputs: • proper time resolution• tag probability • wrong tag fraction• background contribution and composition
Neglected at present stage:Direct CP violation term Any new physics contributions Production asymmetry – possibly fcn of (pT Wrong tag fraction – as fcn of (pT
Precise measurements of Bd J/Ks0 decay
ATLAS-CMS 19
Exact: |P/T|2
Approx: |P/T|%0|| TP
%30|| TP
%100|| TP
Signal yields3y @1033cm2s-1
Atlas CMS LHCb5y
First trigger level 46k 52k 150k
Offline 2-boby select. 2.3k 2.6k 4.9k
Mass resol [MeV] 70 27 17
Signal/2-body bck 0.19 0.33 15Signal/other bck 1.6 5 >1Adir 0.16 0.11 0.09Amix 0.21 0.14 0.07correlation 0.25 0.51 0.47
Max.likelihood computedfrom: *Proper time *Invariant mass *Flavour at production *Specific ionisation:
Simulateous fit of 6 contributingdecays parametrized by 9coefficients, constrained bycurrent experimental limits.
Signal decay parametrized in terms of Adir , Amix:
Adir cos( m t) + Amix sin( m t) Adir , Amix in SM depend on or eff
PTwere used to derive sensitivity to
1. Divergencies appeare as sin or cos->1
2. Linear |P/T| approximation is not justified for value 0.36 suggested by current evaluations.
3. The current theoretical uncertainty |P/T|~30% dominates other systematical and statistical errors of full LHC potential.
1. Divergencies appeare as sin or cos->1
2. Linear |P/T| approximation is not justified for value 0.36 suggested by current evaluations.
3. The current theoretical uncertainty |P/T|~30% dominates other systematical and statistical errors of full LHC potential.
sensitivity in dB
ATLAS-CMS 20
Physics of Bs meson
ms from Bs Dsand Bs Ds a1
already after 1 year sensitivity up to ms - 36 ps-1 fully explore SM allowed range ms (14.3 - 26) ps-1
Program for precise measurements of Bs-anti-Bs system parameters : s, ms and probing Bs mixing phase s allowing to investigate new physics
s and s= - from Bs J/ or Bs J/ both sensitive, but precision
sufficient only in Bs J/
Angular analyses of cascade decay Bs J/determine s, s and s simultaneously with 4 parameters of 3 helicity amplitudes A||, AT, A0 :
A||(t=0), AT(t=0), 1, 2. Parameter ms will be measured by flavor specific decays.
Bs
ATLAS-CMS 21
CP - violation weak phase in Bs J/
Standard Model region-updated 2003
New physics Left-right symmetric model (NP-LR) - needs update (2000 version used here).
ATLAS (3y): 1st level trigger 1 only. 2 1st trigger under investigation, not included. TDR Detector, 240Evts.
ATLAS - same – as above with Initial Detector
CMS updated for realistic trigger in 2004 3y@1033 : 252k Evts. The estimated precision between the two ATLAS curves.
LHCb(5Y): full 1st Level trigger, performance parameters as given in 2000
Experimental potential of both experiments not yet fully exploited: more studies on additional triggers, tagging.
ATLAS-CMS 22
Potential for Rare decays
Before LHC
B can be seen before LHC only if drastically enhanced.
BK*will be measured but mass and angular distributions detailed enough to show New Physics only at LHC.
A study proved good performance at nominal LHC luminosity. After 1 year 1034cm-2 s-1
3 years at 1033cm-2 s-1
B Will measure branching ration of Bs which is in SM of order Br < (10-9 Perform high sensitivity search on Bd
Signal Bs->
Signal Bd->
BG
CMS 26 4 <6.4
ATLAS 92 14 660
SignalBs->
BG
CMS 21 3
ATLAS 27 93
Different conclusions about BG: 1.CMS - already exploit isolation cuts in calorimetry 2. Different
assumptions about tails in VTX resolution.
ATLAS-CMS 23
Exclusive Rare decays of B mesons
ATLAS statistics will allow angular analyses that can carry evidence for new physics. E.g. forward-backward asymmetry: *0
d KB
SM
MSSM C7 >0
MSSM C7 <0
Lowest mass region: sufficient accuracy to separate SM and MSSM if Wilson coefficient C7 <0
)cos(
0
1 )cos()cos(
1
0 )cos(
1)(
22
ddsd
dd
dsd
d
dsdsAFB
Three points: mean values of AFB in three q2/MB
2 experimental regions with error bars
ATLAS-CMS 24
Undergoing physics studies not mentioned here:
1. Double heavy flavor mesons (b,c)
2. QCD tests of beauty production at LHC central region. Correlations bb.
3. Physics of Beauty baryons, production polarizations, decays.
4. Rare decays of b s gamma.
5. Rare decays of b
other studies of ATLAS, CMS b-physics group
ATLAS-CMS 25
ATLAS, CMS b-physics-related software
1. ATLAS, CMS – B-related online software under development: reconstruction Algorithms, trigger simulations.
2. ATLAS: offline MC simulation, reconstruction software, physics analyses software.
• Within a successful Data Chalenges-1 period 2002-2003 B-physics group studied B-performance for the Final version of detector layout.
• Data Chalenges-2 started 2004: grid production, Geant 4, databases, new Event Model
3. ATLAS, CMS: B-event Generators software
• For bb production we use Pythia tuned to Tevatron data. Herwig – we never tried. NLOQCD ( MNR code) does not give whole events.
• Installation of B-decays dedicated package ‘EvtGen’ in common use and development with BaBar (main developer) , LHCb, CDF, D0.
ATLAS-CMS 26
B-physics prospects with ATLAS, CMS - conclusions
1. General purpose central LHC detectors are preparing a multi thematic B-physics program - including B-decays and B-production.
2. ATLAS, CMS B-physics trigger strategy rely on dimuon trigger for luminosity 2*1033 cm-2s-1 - extend selection menue at lower luminosities when there is spare processing capacity.
3. In CP violation the main emphasis will be on underlying mechanisms and evidence of New physics. ATLAS, CMS is especially precise in measurement of LHC ‘gold-platted’ mode is also Bs J/
4. Rare decays B have the most favorable experimental signature allowing to measure also at nominal LHC luminosity 1034cm-2 s-1. Will measure branching ration of Bs and sensitivity test for Bd . Precision measurements will be done for B K*.
5. Beauty production at central LHC collisions will be measured for QCD tests.