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.