# Presentation: 804456

## Status and prospects for b Physics at ATLAS and CMS

- S. Tarem, Technion
- For the ATLAS and CMS Collaborations

**A REMINDER: ATLAS AND CMS DO NOT COLLECT DATA YET ALL “RESULTS” ARE MC**

## Introduction-1

**There is still a lot to be learned from flavour/CP physics **

## Introduction-2

- LHC is geared towards “Discovery Physics”
- B physics is a side show
- A limited trigger bandwidth is available for it
- We need to use it to the best advantage
- B jet tagging is an important tool
- For low mass Higgs and for Top Physics
- For this too the trigger level is crucial
- B’s cannot be triggered by a simple jet trigger
- Detector calibration depends on channels that are also good for B Physics - J/Ψ and μ
- Initially we expect expanded bandwidth

## What measurements?

| CP Violation |  | sin(2) |
| --- | --- | --- |
|  |  | s L; s; A||; A┴; the strong phase difference  the weak phase s |
| Measurement of Bs oscillations:  |  | ms= mH – mL |
| Rare decays |  | Precise measurements of the branching ratios and asymmetries |
| b polarization measurements |   | Asymmetry parameter b, Pb, life time measurements |
| Bc mesons |  | Precise determination of Bc mass, Bc life time |

## Event rate is too high to collect

| Object | What physics? |
| --- | --- |
| e | Higgs, B-physics, new gauge bosons, extra dimensions, SUSY, W, top |
|  | Higgs, extra dimensions, SUSY, B-physics |
|  | B-physics, Higgs, new gauge bosons, extra dimensions, SUSY, W, top |
| Jets | SUSY, compositeness, resonances, B-physics |

- The selection of physics signals requires the identification of objects that can be isolated from the high particle density environment.

**Event rate**** ******

**Level-2**** ******

**Level-1**** ******

**Offline Analyses****  **

## The ATLAS Trigger and ROI mechanism

- LVL1
- Uses muon trigger chambers and calorimeter
- Finds  e, **** jet, ****** **candidates above thresholds
- Identifies Regions of Interest
- Processing time 2.5 s
- LVL2
- Uses Region of Interest data
- Combines information from  detectors
- Processing time 10 ms
- Output rate ~2kHz
- Event Filter
- Processing time 1s
- Output rate ~200Hz

**hardware**

**software**

## Level-1 Muon trigger

- Muon chambers layout and trigger scheme

- Minimal threshold for Level-1 is 6GeV
- For low luminosity (L ~1033 cm-2s-1)
- Reduces background from decay in flight of π/K

|  | Process | Barrel | End-Cap | Combined System |
| --- | --- | --- | --- | --- |
| Low 
pT
6GeV | /K | 7.0 | 9.8 | 16.8 |
|  | b | 1.9 | 2.1 | 4.0 |
|  | c | 1.1 | 1.3 | 2.4 |
|  | W | 0.004 | 0.005 | 0.009 |
|  | Total | 10.0 | 13.2 | 23.2 |

**Trigger rate (kHz) expected in Muon Spectrometer L= 10****33****cm****-2****s****-1**

**Only 4 kHz of these are b events!**

## Level-1: Calorimeter

- Calorimeter Trigger
- looking for e/ + Jets + t objects
- Using trigger towers of Hadronic and Electromagnetic calorimeters
- The requirement for a trigger object:
- The RoI cluster – local maximum
- The most energetic cluster > ET
- Total ET in EM isolation < EM Isolation Threshold
- Total ET in Hadron < Hadronic isolation threshold

** **Example of e/ trigger algorithm**:**

## The CMS trigger

- CMS has a 2 level trigger
- LVL1
- Uses muon chambers and calorimeter
- Finds  e**, ******** **jet**, ******** **candidates above thresholds
-  40 MHz  100 KHz
- Envisioned B physics trigger is 2 x μ(>3 GeV?) | μ(>14 GeV)
- HLT
- Uses algorithms similar to offline
- 100 KHz  100 Hz
- Inclusive b,c, trigger (high pT jet)
- Partial reconstruction of exclusive decays around μ ROI

##  Trigger issues for b-physics performance

- B-physics performance is impacted strongly by trigger menu
- Characteristic B-physics triggers are at low pT
- The experiments have multilevel triggers
- Level-1 is in hardware – designed for 40MHz100KHz
- The level-1 trigger for B-physics is based on one or more muons
- Acceptable trigger rates in ATLAS and CMS have been reduced due to “staging” of high level trigger processing power
- Envisioned trigger menus include 2 low pT μ or one higher pT μ
- Algorithms are developed for recovery of events at level-2
- First luminosity is expected to be lower and that will enable collecting 6 GeV single muons at the beginning

## Algorithms to recover events at level-2

- Triggers based on di-μ at level-1
- Most rare bμμX expected to pass this
- Triggers based on a single muon at level-1
- Dimuons with the second below level-1 threshold (J/Ψ)
- J/Ψe+e- from events with level-1 μ from other b
- Both strategies are necessary – depends on level-1 thresholds

**single-muon**

**di-muon**

**all**

**all**

**h**

**h**

**b**

**b**

**c**

**c**

**J/******

**@10****33****cm****-2****s****-1**

**Cross section, (nb)**

- Dimuonrecovery at level 2

**LVL1 p****T****(********) > 6GeV**

## Dimuonrecovery at level 2

- LVL1:	1 RoI pT (μ) > 6GeV

- LVL2
- Confirm μ RoI
- Open the region (Δη x Δφ) around μ ROI in order to find J/Ψ
- Find ID tracks in selected region
- M (μ+μ-) > 2.8 GeV
- Extrapolate track to MS
- Associate track with MS hits – select di-μ, J/**Ψ** etc
- Vertexing

**Efficiency for both ********+********-**** from J/******** to be found in enlarged ******** RoI**

## J/Ψe+e- using EM RoI

- J/Ψe+e- using EM RoI

- LVL1:	μ(pT  > 6GeV )+
-               ≥1 EM RoI (ET > 2GeV)

- LVL2
- Confirm  and e RoIs
- If only one level-1 e
- Find ID tracks in extended ROI – apply mass Cuts
- Associate track with EM Calorimeter information
- If 2 level-1 e
- confirm at LVL2 inside small region around each e

## Level 2 for specific channels 

- Bs  Ds ( φπ ) π
- Level 1: μ+jet
- Level 2: Tracking inside enlarged jet ROI at level 2
- Rate at L=10^33 310 Hz
- Bd  K*0 , Bs  φ 
- Level 1: μ+EM
- Level 2: Reconstruct K*0K+π- or φ K+ K- around g ROI
- Rate at L=10^33 23 Hz  (0.5 after event filter)
- B μ+μ- , B K* μ+ μ-
- Level 1: 2μ (or μ)
- Level 2 confirm, combine with ID tracks, vertex
- Rate at L=1034 < 10 Hz

## Estimates of Trigger Efficiencies - ATLAS

|  | LVL1+LVL2 | Event
Filter | Overall Efficiency |
| --- | --- | --- | --- |
| B  μμ  | ~ 75% | 95% | ~70%
Events with + and - pT > 6 GeV |
| B μμ K* | ~ 75% | 85% | ~65%
Events with + and - pT > 6 GeV |
| BdJ/Ψ (μμ ) Ks | First : ~ 85%
J/Ψ(μμ): 77%
Overall: ~ 65% | ~100% | ~65%
Events with one  pT>6 GeV and other  pT > 3 GeV |
| Bd  J/Ψ (e+e-) Ks | Muon: ~ 85%
J/Ψ( e+ e- ): 72% 
Overall: ~ 60% | ~100% | ~60% Ev. with e+ and e- pT > 5 GeV
~40% 1st e pT>5 GeV, 2nd e pT>2 GeV |
| Bs  Ds π   
Ds  φ (K+K-) π | Muon: ~ 85%
Ds (φπ): 50%
Overall: ~ 40% | ~100% | ~40%
Events with Bs pT>10GeV
and pT > 1.5 GeV |

- Rough Estimates of efficiencies for some example channels

## Online b-tagging - CMSinclusive b-jets trigger

- Enormous QCD production drives the inclusive jet trigger thresholds for 1st, 3rd and 4th jet to 657,247,113 GeV
-  Two tracking options
-  Pixel-only,  3 hits in 3 layers required
-  Regional algorithm on complete tracker
-  L1 : hadronic streams, but also muon and e/ streams
-  L2 : jet ET thresholds, 350, 150, 55 GeV
-  L2.5 : pixel-only b-tag >2 tracks with D0>2 in leading or next-to-leading jet
-  L3 : regional b-tag >3 tracks with D0>2.5
- QCD di-jet rate for selection is 16 Hz, only 7 Hz are exclusive
- Timing: t = 50 kHz x tjet + 1 kHz x tpixel + 200 Hz x ttracker

## Sample channel: BsJ/Ψ φ

- This final state is an admixture of CP-even/CP-odd eigenstates
- The 2 components have different angular dependencies
- Extracting mixing parameters requires separation of CP eigenstate amplitudes
- Determine from the angular distribution of the decay, proper decay times and flavour tag
- Decay Parameterized by
- 3 transversity amplitudes
- 2 independent magnitudes and 2 independent phases:
- 	|A║|   |A┴|    δ1    δ2
- 3 mixing parameters, 1 weak mixing phase
- 	ΓL      ΓH    ΔMs     S
- 	 8 parameters to be extracted from the data

## The BsJ/Ψ φ analysis

- The differential decay rate may be written as a sum of products - amplitudes X time dependent terms X angular terms
- With
- Θ – 3 angles describing kinematics
- Fi(Θ) – angular distribution functions
- α – the decay parameters from previous slide
- fi(α,t) – time dependent functions of the parameters to be measured
- The angular and decay time distributions are fit to obtain the decay parameters

## Trigger for BsJ/Ψ φ  - CMS

- Level  1 - muons
- 2 muons with pT>3 GeV ε=57.6% rate 900 Hz
- Opposite charge requirements ε=45.8%
- Main background from direct J/Ψ

## Level 2 - J/Ψ search
Primary vertex reconstruction ε=96.9% 
Tracking in region Δη=±0.15 Δφ==±0.5 around muon candidates
Partial track reconstruction with 5 hits
pT(μ)>2.5 GeV, pT(J/Ψ)>4 GeV, m(J/Ψ)±150 MeV 
Secondary vertex fit
Χ2<10
transverse decay significance>3
Cos(momentum/decay-length)>0.9
L2 ε = 28.7%, rate = 15 Hz
80% bJ/Ψ 

- Primary vertex reconstruction ε=96.9%
- Tracking in region Δη=±0.15 Δφ==±0.5 around muon candidates
- Partial track reconstruction with 5 hits
- pT(μ)>2.5 GeV, pT(J/Ψ)>4 GeV, m(J/Ψ)±150 MeV
- Secondary vertex fit
- Χ2<10
- transverse decay significance>3
- Cos(momentum/decay-length)>0.9
- L2 ε = 28.7%, rate = 15 Hz
- 80% bJ/Ψ

- Signal * 1000

- bJ/Ψ

- Direct J/Ψ

## Level 3 – φ search
Tracking in region Δη=±0.9 Δφ==±0.9 around J/Ψ 
Partial track reconstruction - max 5 hits
pT(K)>0.7 GeV, pT(φ)>1 GeV
 m(φ)±20 MeV, m(Bs)±200 MeV
Vertex fit on 4 tracks, similar to previous requirements
L3 ε = 20.5%
Rate < 0.1 Hz

- Tracking in region Δη=±0.9 Δφ==±0.9 around J/Ψ
- Partial track reconstruction - max 5 hits
- pT(K)>0.7 GeV, pT(φ)>1 GeV
-  m(φ)±20 MeV, m(Bs)±200 MeV
- Vertex fit on 4 tracks, similar to previous requirements
- L3 ε = 20.5%
- Rate < 0.1 Hz

## Offline selection results - CMS

- Efficiency:
- Statistics:
- Not using Bs mass cut

## Offline selection results - CMS

- Decay time resolution
- Decay time dependent efficiency
- Arising from HLT selection
- This affects the time dependent fit
- Care must be taken to verify actualresults in the data

- Decay length significance cut

- Lower tracking efficiency fortrack from displaced vertex

## ATLAS sensitivity in Bs→ J/Ψ φ

| For integrated luminosity 30 fb-1 |  |  |
| --- | --- | --- |
| Signal events within kinematic cuts |  | 810 000 |
| Signal events passing L1 and L2 di-muon triggers |  | 623 700  |
| Signal events after offline reconstruction, and successful Bs vertex fit |  | 333 000 |
| Signal events after signal selection cuts |  | 270 700 |
| Bs proper-life time resolution |  | 83 fs |
| Tag efficiency / wrong tag fraction | jet charge | 63%  /  38% |
|  | electron | 1.2%  /  27% |
|  | muon | 2.5%  /  24% |
| Background |  | 15% |
| Results of simultaneous 7 parameters fit  |  |  |
|  (s)   (for ms = 20 ps-1) |  | 0.046 |
|  ( ΔΓs ) / ΔΓs |  | 13% |
|  ( Γs) / Γs |  | 1% |
|  ( A║) / A║ |  | 0.9% |
|  ( A┴ ) / A┴  |  | 3% |

|  | Гs | ΔΓs | δ1 | δ2 |
| --- | --- | --- | --- | --- |
| Гs |  | 70% |  |  |
| ΔΓs |  |  |  |  |
| δ1 |  |  |  | 98% |
| δ2 |  |  |  |  |

- σ(Bs)=83fs
- ΔГs=0.1

**Correlations:**

**CMS also has such ****estimates**

## ATLAS  sensitivity  to SUSY in CPV Bs mixing phase in Bs  J/Ψ φ  

** ****Expected  ATLAS sensitivity**
**after 3 years (30 fb-1)**

**  ****SUSY model**
**Ball,Khalil,2004**

**  ****ATLAS    final detector**

- SM – is already OUT of experimental sensitivity (would need 30 years ...)

## ΛbJ/ΨΛ - ATLAS

- Prepare to measure lifetime and polarization
- Λ efficiency depends strongly on track impact parameter cut at reconstruction
- J/Ψ efficiency good with (second) muons > 2.5 GeV pT
- Lifetime prospects – with a D0 like analysis:
- For the polarization analysis
- fits distributions and correlations of 5 decay angles
- obtain the polarization, asymmetry parameter and 4 helicity amplitudes

| Luminosity | Expected Number of Λb | Statistical uncertainty in the lifetime measurement |
| --- | --- | --- |
| 0.2 fb-1 | 521 | 75 fs |
| 1 fb-1 | 2604 | 33 fs |
| 5 fb-1 | 13021 | 15 fs |

**Current uncertainty in world average: 72 fs****.**

## Angular resolutions are found in full MC

                                                                        ...

and used in toy MCto estimate our sensitivity to thepolarization P and the asymmetry param. 
 can be estimatedeven if P is very small

-                                                                         ...
- and used in toy MCto estimate our sensitivity to thepolarization P and the asymmetry param. 
-  can be estimatedeven if P is very small

**30 fb****-1**

**5 fb****-1**

**σ****P**

**σα**

## Beauty with 100 pb-1, first measurements, preparations

| Inclusive B and Onia | Direct J/ | 1000 k | R =  bb → J/pp → J/
R =  pp → pp → J/ |  |
| --- | --- | --- | --- | --- |
|  | bb  J/ X | 400 k |  |  |
|  |  | 100 k |  |  |
|  | B  J/ X  b  X  | 25 k | b-b correlations |  |
| Exclusive B
Tree decay
 | B+→J/K+ | 17000 | Important reference channel. New channels (B→) relative to this   |  |
|  | B0→ J/K0* | 8700 |    
   Masses, Lifetimes
Sensitive checks for understanding Inner Detector |  |
|  | B0→ J/Ks | 1300 |  |  |
|  | Bs→ J/ | 900 |  |  |
|  | b→ J/ | 260 |  |  |
|  | Bs → Ds  | 25 | Hadronic channels – only prepare methods for later measurements |  |
| Rare exclusive B
Sensitivity limits | B+→K+ | 23 |  Belle today 80
      |  |
|  | B0→ K0* | 12 |  |  |
|  | Bs→  | 9 |  |  |
|  | b→  | 3 |  |  |
|  | B→ | 1 * 10-7  90%CL |  | Tevatron today 1.2  10 -7 |

- Beauty with 100 pb-1, first measurements, preparations

## Expected measurements - ATLAS 

|  |  |  | Signature after 500 pb-1 |  | Signature 
after 30fb-1  |  |
| --- | --- | --- | --- | --- | --- | --- |
|  |  |  |  |  | Signal          Background |  |
| B=2, B=1 | Bs→J/ | Lifetimes, s / s | 5000 |  | 300k |     30%
 |
|  | Bs→Ds 
Bs→Dsa1 | 
Δms | - |  | 6900 
3600 | <100%
<100% |
|  | B0→J/Ks | Lifetime
sin2 | 4500 |  | 270k |    15% |
|  | B+→J/K+ | Lifetime,
QCD tests
systematics | 60000 |  | 3.6M | 15%    |
|  | b→ J/ | Lifetime | 1250 |  | 75k |  |
| gluon,  penguin | Bd→K
Bs→ | Br.fraction | 220
- |  | 13200
 2400 | S/√B >5  
S/√B >7
 |

- Expected measurements - ATLAS

## Semi-muonic exclusive rare B-decays in ATLAS

| BR used in the MC |  | Signal 
after trigger + offline reconstruction 3y@1033cm-2s-1 |
| --- | --- | --- |
| 


2.0 10-6 | Bd→
Bd → 
Bs → 
b→  | 3000
 300 
 900 
1500 |

**SM events after trigger and reconstruction**

**MSSM ****C****7geff****>0 ****events after trigger and reconstruction**

- ATLAS statistics errors

**Notes:**
Also will analyze the differential distributions like the invariang mass of the dimuon in radiative decays

## ATLAS performance summary for B   decays

| BR used in MC |  | Detector version | Luminosity | Signature after trigger +offline reconstruction |  |
| --- | --- | --- | --- | --- | --- |
| 3.5 10-9
 | Bs → 
 | Final 
Detector studies 2005-2006 | 3y@
1033cm-2s-1
(30fb-1) | 21 
Signal | ~60 
background bb->X |
|  |  |  |  | Upper limit 6.6×10-9 | 90%CL |
|  |  |  | 10 fb-1
 | 7           Signal | ~20 
background bb->X |
|  |  |  |  | Upper limit
7.0×10-9 | 90%CL |
|  |  |  | 100 pb-1 | Upper limit
6.4×10-8 | 90%CL |
|  |  | Early detector studies 2000 | 1y@
1034cm-2s-1
(100fb-1) | 92
Signal | ~900
background bb->X |
| 0.9 10-10
 | Bd →  | Early detector studies 2000 | “ | Upper limit 
3 × 10-10 
SM 1.6x10-10 | 95%CL
   |

- ATLAS performance summary for B   decays

**Notes:**
Also will analyze the differential distributions like the invariang mass of the dimuon in radiative decays

## Summary

- We’d better wait a few years for the summary...
- But there is plenty of work to do in the mean time.