# Presentation: 938426

## CMS – B Physics Reach

- CMS – B Physics Reach

- V. Ciulli
- INFN Firenze
- on behalf of CMS collaboration
-  **IV INTERNATIONAL SYMPOSIUM ON LHC PHYSICS AND DETECTORS**** ****FERMILAB, MAY 1-3 2003**

## B Physics at LHC 

- B Physics at LHC

-  B-decays program
- Rare decays
- CP violation
- B0s Mixing
-  b production at LHC
- peak luminosity: 2x1033 cm-2s-1 -> 1034 cm-2s-1
- 0.5 mb  O(105-106) b pairs/sec
- only 100 ev/sec on tape for ALL interesting physics channels
-  The main challenge is the trigger strategy
- Some benchmark channels analysed
- BS 
- BS J/   KK
- BS DS (KK) 
-  Results from DAQ-TDR (CERN/LHCC 2002-26)

- CMS - b Physics Reach

- LHC 2003, Fermilab

## Trigger & DAQ architecture

- Two level trigger: Lvl-1 and HLT

**40 MHZ**

**100 KHz**

**100 Hz**

- Several staging scenarios possible.
- Each slice allows  12.5 KHz

- CMS - b Physics Reach

- LHC 2003, Fermilab

## Trigger & DAQ architecture

- Two level trigger: Lvl-1 and HLT

**40 MHZ**

**50 KHz**

**100 Hz**

- 4 DAQ slices at start-up => 50 KHZ

- Several staging scenarios possible.
- Each slice allows  12.5 KHz

- CMS - b Physics Reach

- LHC 2003, Fermilab

## A closer look to Lvl-1 trigger 

- A closer look to Lvl-1 trigger

| Trigger | Threshold 
(=95%) (GeV) | Indiv.
Rate (kHz) | Cumul rate
(kHz) |
| --- | --- | --- | --- |
| 1e/, 2e/ | 29, 17 | 4.6 | 4.3 |
| 1, 2 | 14, 3 | 3.6 | 7.9 |
| 1, 2 | 86, 59 | 3.2 | 10.9 |
| 1-jet,3-jets, 4-jets | 177,86,70 | 3.0 | 12.5 |
| Jet * Miss-ET | 88 * 46 | 2.3 | 14.3 |
| e * jet  | 21 * 45 | 0.8 | 15.1 |
| Min-bias |  | 0.9 | 16.0 |

- Total output rate:
-  50 kHz x 1/3 “safety”
- => 16 kHz allocated

- Lvl-1 thresholds optimized for a wide physics discovery program
-  high-pt processes are selected
- b-jets are selected mainly by 1 and 2trigger

- Low luminosity table =>

- CMS - b Physics Reach

- LHC 2003, Fermilab

**Notes:**
Singolo muone 2.7 khz 
Di-muone 0.9 khz

## Lvl-1 Trigger: Muon Stream

- Low Lumi

- < 2.1

- _16 kHz DAQ_3.6 kHz for 

_**14 ; 3,3**__**2.7+0.9=3.6 kHz**_******W****	****=90%********Z ****	****=99%********Bs********=15%**

- Integrated muon rates above threshold** **

- Muon rate dominated by ,K decays up to 4 GeV, then by b-, c-quark decays  up to 25 GeV

- < 2.1

- CMS - b Physics Reach

- LHC 2003, Fermilab

## High Level Trigger 

- High Level Trigger

**100 Hz**

**40 MHZ**

**100 KHz**

- Implemented on a PC farm:
- 300 msec/ev on 1GHz PIII
- (±50% uncertainty)
- _Same software as for offline_

- 30 Hz

- A total of 30 Hz are allocated to muons
- 25 Hz single
- 5 Hz di-muons
- _In addition non-isolated muons are rejected_

- Low lumi

- CMS - b Physics Reach

- LHC 2003, Fermilab

## HLT single muon stream content 

- 25 Hz

- b/c

- W

- Only ~5 Hz are b/c events:  1 Hz -> 107 ev/year at low lumi
- Not enough for decays with BR<10-4 and selection efficiency <10%

- CMS - b Physics Reach

- LHC 2003, Fermilab

## HLT Tracking

- Previous results can be improved by using Tracking in the High Level Trigger
- HLT reconstruction has to be fast but not as global and precise as the offline one
- HLT Tracking can therefore be:
- Regional
- Restricted to some phase-space region defined from external Lvl-1 information (e.g. a cone around muon/jet direction or the set of tracks coming from a vertex or above a PT threshold )
- Partial
- Stopped after a number of hits have been assigned to the track
- Conditional
- Stopped when enough resolution is reached or on other condition

- CMS - b Physics Reach

- LHC 2003, Fermilab

## Primary vertex reconstruction 

- y

- y

- Primary vertex reconstruction

- Hit pairing with a straight line in rz
- IP1 mm
- PT>1 GeV
- Matching with 3rd layer  track candidate
- PV candidate if  3 track cross z-axis
- Signal vertex from PT and Ntracks

- Average time:50msec/1 GHz

- PV efficiency >95% in high luminosity events

-  = 26 m

- CMS - b Physics Reach

- LHC 2003, Fermilab

## Partial reconstruction  

- Good track parameters resolution with 4-5 hits
-  half the time for full reconstruction needed

**Full tracker performance**

- Time vs hits in 100 GeV b-jets

- IP

- Pt

- CMS - b Physics Reach

- LHC 2003, Fermilab

## Benchmark channels

- Di-muons Lvl-1 Trigger:
- BS 
- BS J/   KK
- Single muon Lvl-1 Trigger (second B+X)
- BS DS (KK) 

- CMS - b Physics Reach

- LHC 2003, Fermilab

## Bs

- Lvl-1:  2  PT>3GeV, =15.2%
- HLT strategy:
- Select pixel seeds with PT > 4 GeV in - region around trigger ’s
- Conditional tracking:
- stop if  pt<4 GeV/c @ 5σ or Nhit=6 or σ(pt)/pt<0.02
- Bs reconstruction if only 2 track candidates with opposite charge in 150 MeV window
- Vertex20 and dr> 150 m
- Average CPU Time = 240 msec / 1GHz CPU

**FCNC b->s or b->d only at loop-level in SM****  **
** ****=> BR(B****s********)=(3.5±1.0)x10****-9**

- CMS - b Physics Reach

- LHC 2003, Fermilab

**Notes:**
Se ci sono BR molto piu’ alti questa e’ sicuramente una evidenza di Nuova Fisica.. In qunto nell’ambito dello SM vanno tramite FCNC loops... Ci sono un certo numero di modelli che fornscono branching ratio piu’ alti.

Questa strategia va modificata per High luminosity

Gli studi possono continuare ad alta luminosita’

Flavout changing Neutral current

## Bs

| Lvl-1  | HLT  | Global  | Events/ 10fb-1 | Trigger Rate |
| --- | --- | --- | --- | --- |
| 15.2% | 33.5% | 5.1% | 47 | <1.7Hz |

**HLT**

**Full Tracker**

- Offline analysis results (hep-ph/9907256), using SM BR=**3.5x10****-9**
- (Lvl-1 trigger in ||<2.4 instead of ||< 2.1)
- 10 fb-1  => 7 signal events with <1 background
- 5 observation with 30 fb-1
- and analysis could be perfomed at high lumi too

- Mass resolution

-  = 46 MeV

-  = 74 MeV

- CMS - b Physics Reach

- LHC 2003, Fermilab

**Notes:**
Background proviene dai processi di gluon splitting.

Allo scopo di aumentare
l’efficienza abbassare 
il taglio in Pt usando allo stesso
tempo la carica fornita dal lvl-1
Allo scopo di rendere accettabile il rate

Il rate di 1.7 viene dal fatto che la statistica e’ limitata....

Vecchia analisi 
Numero eventi di segnali 7 dopo un anno a 10^33.
Numero di eventi di fondo <1 at 90% CL.

## BsJ/ 

- BsJ/ 

- BR(BsJ/ )=(9.3±3.3)x10-4
- J/l+l- (BR≈6%)
- K+K- (BR≈49%)

- CP violation weak phase
- s= 2= 22
- SM predicts s ~O(0.03)

- HLT strategy:
- Lvl-2: reconstruct muons as for Bs  
- 100MeV window around  J/ mass, 20 and dr> 200 m
- Rate = 15 Hz,  <t>~260ms
- 90% of Lvl-2 J/ are from b’s
- Lvl-3: reconstruct  and Bs
- Regional tracking around J/ direction
- <t>~800ms

- CMS - b Physics Reach

- LHC 2003, Fermilab

## BsJ/ 

| Lvl-1  | Lvl-2  | Lvl-2 Rate  | Lvl-3  | Lvl-3 Rate | Events/ 10fb-1 |
| --- | --- | --- | --- | --- | --- |
| 16.5% | 13.7% | 14.5 Hz | 8.7% | <1.7Hz | 83800 |

- J/

- HLT mass resolutions

- 

- Bs

-  = 22.4 MeV

-  = 2.2 MeV

-  = 46.5 MeV

- CMS - b Physics Reach

- LHC 2003, Fermilab

**Notes:**
L’elevato tempo di CPU per la ricostruzione della phi e’ dovuto al numero di tracce che vengono ricostruiti anche se sono intorno a 13 per evento... chiaramente e’ necessario qualcosa di piu’ smart!!

Vantaggio di CMS rispetto a Atlas grande valore del campo magnetico.. Consente una maggiore risoluzione in massa.

## BsJ/ 

**l****+**

**l****-**

**K****+**

**K****-**

- Angular analysis of **B****s****->J/******on a sample of 600 K yields:

|  | ΔΓs | s(xs=20) | s(xs=40) |
| --- | --- | --- | --- |
| Value | 0.15xΓs | 0.04 | 0.04 |
| Error | 8.0% | 0.014 | 0.03 |

- CERN-2000-04

- Error on ΔΓs vs stats

- ΔΓs /Γs ~ 15 %
- s(xs=20) ~  0.025 rad
- s(xs=40) ~  0.05 rad

- 30 fb-1

- CMS - b Physics Reach

- LHC 2003, Fermilab

## BsDs (KK) 

- P(b  Bs) x Br(Bs DS   K K  ) ~ 5 x 10-5

- L1 1 trigger: PT>14GeV, R=3.2KHz
- HLT strategy:
- pixel seeds in full acceptance and Primary Vertex
- Partial tracking: 2 pixel and 1 strip hits
- Topological cuts: R(KK)<0.3, R(<1.2, R(DS<2.0, (BS,)>0.6
- Kinematical cuts: PT()>2GeV, PT(DS)>4GeV, PT(BS)>5GeV
- Mass reconstruction: M<15MeV, MDs<75MeV, MBs<270MeV
- HLT efficiency 9%
- <t> = 640 msec

- BS-BS mixing: mS  14.4 ps-1 @95%CL

- CMS - b Physics Reach

- LHC 2003, Fermilab

**Notes:**
Questo canale e’ molto interessante in quanto e’ completamente ricostruibile dal punto di visto dello stato finale ha un branching ratio accettabile ed inoltre 
Da studi fatti in precedenza si e’ visto che  una semplice analisi consente una buona separazione tra segnale e fondo..
Inoltre sono sufficineti 1000 eventi completamente ricostruiti per fornire una misura di delat ms tale da escludere I valori previsti da SM e quindi essere capici di fornire informazioni di Nuova Fisica.

Si ricostruisce il vertice primario,
Utilizzando un algoritmo che considera tutte le coppie di recHits sui pixel che sono consistenti con segmenti di tracce.. 

Nella prossima versione esistera’ una versione piu’ accurata...
Si considera che provengono dal vertice primario se sono conpatibili con un cilindro di raggio 1mm e 30 cm di lunghezza.

Ad LHC si considerano per la produzione bbbar tre meccanismi cioe’ gluon splitting, fusioni dei partoni e flovour excitation. 
Purtroppo non esiste una particolare regione in cui noi possiamo andare a restringere la nostra ricerca per I candidati Bs... Quindi l’unica limitazione che possiamo introdurre e’ quella di utilizzare un numero limitato di strati del tracker al fine di limitare il tempo necessario per la ricostruzione.

## BsDs (KK) 

- 

- Bs

- Ds

- BsDs (KK) 

- Mass resolutions (only 3 hits are used)

-  = 5 MeV

-  = 25 MeV

-  = 95 MeV

- 1 year low luminosity (20 fb-1):
- Lvl-1 1KHz    HLT 5Hz    300-400 signal events => mS up to 20 ps-1

- 1000 events are needed to test allowed SM range: mS  26 ps-1 @99%CL

- CMS - b Physics Reach

- LHC 2003, Fermilab

## B-triggers in HLT table

- Bandwith for B-physics at LHC start-up will depend on:
- Luminosity
- Lower lumi => higher B-bandwith
- Background conditions
- If good factor 3 for safety may have been overestimate
- In addition a possible strategy is introducing B-triggers as the luminosity drops during the fill

- CMS - b Physics Reach

- LHC 2003, Fermilab

## Conclusions

- CMS is a competitive detector for B-physics, even if it is not designed specifically for it
- A key point is B-decay selection in the High Level Trigger thanks to fast tracking
- A proof of concept has been given on few benchmark channels in the DAQ TDR
- Much will depend on LHC starting conditions:                    Low lumi for a while  lot of B physics
- Computing and Physics TDR’s will address in more details the CMS B-physics potential

- CMS - b Physics Reach

- LHC 2003, Fermilab

## Back-up slides

## CMS detector 

- 13x6 m Solenoid: 4 Tesla field
-  tracking up to  ~ 2.4

- Muon system in return yoke

- First muon chamber just after solenoid
-  extend level arm for pt measurement

**Staged Scenario for start-up **
- 1. ME4 staged
- 2. 3rd forward pixel disks missing
- 3. Descoped HCAL (reduced no. of
-      longitudinal samplings)
- 4. Descoped ME1/1a (3 ch in one,
-     muon trigger up to || = 2.1)

- ECAL & HCAL
- inside solenoid

- 22 m long, 15 m diameter,
-  14.000 ton Detector

- CMS - b Physics Reach

- LHC 2003, Fermilab

**Notes:**
Very important is the hermeticity

## CMS software

-  Generazione degli eventi PYTHIA 6.158
-  Detector simulation: Geant3
-  Geometry and Material Budget up-to-date (2002)
-  Multiple interactions and pile-up of out-of-time events included
-  Detector response (digitization, noise ...)
-  First trigger simulation
-  Reconstruction
-  muons
-  calorimetric clusters
-  tracks
-  vertices

- CMS - b Physics Reach

- LHC 2003, Fermilab

## Muon reconstruction

****

- Lvl-1, Lvl-2, Lvl-3

- Coverage limited to 2.1
- (RPC limit and ME1/1a of CSC non-partecipating to L1)

******= 0.11**

******=0.013**

- Lvl-2

- Lvl-3

- barrel

- Muon chambers

- Muon chambers +
- tracker

**(1/P****T****rec -1/P****T****gen) /(1/P****T****gen)**

- CMS - b Physics Reach

- LHC 2003, Fermilab

**Notes:**
Che cosa sono questi plots

## CMS Tracker

- Transverse IP resolution  ~ 20 m for tracks with Pt ~ 10GeV

- Pixel detector: 3 layers
- 4.2 – 15 cm radii
- +- 60 cm in z

- Occupancy ~ 10-4
- Pixel is used for seeding

- Silicon strip : R = 10-60 m, cell size ~ 10 cm2
- Pixel: R, z = 10-20 m, cell size ~ 150 m2

- CMS - b Physics Reach

- LHC 2003, Fermilab

**Notes:**
Dire perche’ e’ importante il pixel.. Ambiente clear etc...

Pixel utilizzato come seeding per il tracking
Normalmente come seeding vengono utilizzati gli strati esterni ma in CMS 8% -15% dei pioni da 1 GeV interagiscono nei primi 8 strati, pertanto si utilizzano gli strati di pixel con bassa occupancy e eccellente risoluzione in 3D.

## Geometry Modeling in Simulation 

**Support structures**

**Care has been taken to model localized heavy material  (e.g. Aluminum for cooling) separately**

**Pixel module**

**How the DAQ TDR data have been simulated**

- CMS - b Physics Reach

- LHC 2003, Fermilab

## Tracker: Track Reconstruction

- Generaton of seeds (Seed Generator)
- Construction of trajectories for a given seed (Trajectory Builder)
- Ambiguity resolution (Trajectory Cleaner)
- Final fit of trajectories (Trajectory Smoother)
- Each component has one or more implementation.
**Three different algorithms are currently fully implemented: **** Combinatorial Track Finding, Deterministic Annealing Filter, Gaussian Sum Filter**

- CMS - b Physics Reach

- LHC 2003, Fermilab

## Tracking efficiency

- Single 

- Single 

- Jets

- Degradation
- due tracker material

- No significant degradation compared to single pions

- Jets ET = 50-200 GeV
-  Fake Rate < 1 %

- CMS - b Physics Reach

- LHC 2003, Fermilab

**Notes:**
Global efficiency:  selected RecTracks/all SimTracks 
Algorithmic efficiency: selected RecTracks/selected SimTracks
SimTrack selection: at least 8 hits, at least 2 in pixel
Global efficiency limited by pixel geometrical acceptance

Efficiency for particles in a 
0.4 cone around jet axis
No significant degradation 
compared to single pions

## Secondary vertex reconstruction

|  | H0 (130)->4  | Bs | BsJ/  |
| --- | --- | --- | --- |
| (x) m | 12.12 ± 0.13 | 47.5 ± 3.63 | 55.3 ±0.95 |
| (z) m | 19.18 ± 0.23 | 71.5 ± 1.3 | 72.7 ±1.4 |
| CPU time  msec | 2.5 | 1.9 | 3 |

- Resolution on secondary vertices

- H0 (130)->4 ****

**B****s******

- CPU time vs tracks

- CMS - b Physics Reach

- LHC 2003, Fermilab

## High Level Trigger table for low lumi

| Trigger | Threshold 
(=90-95%) (GeV) | Indiv.
Rate (Hz) | Cumul rate
(Hz) |
| --- | --- | --- | --- |
| 1e, 2e | 29, 17 | 34 | 34 |
| 1, 2 | 80, (40*25) | 9 | 43 |
| 1, 2 | 19, 7 | 29 | 72 |
| 1, 2 | 86, 59 | 4 | 76 |
| Jet * Miss-ET | 180 * 123 | 5 | 81 |
| 1-jet, 3-jet, 4-jet | 657, 247, 113 | 9 | 89 |
| e * jet  | 19 * 52 | 1 | 90 |
| Inclusive b-jets | 237 | 5 | 95 |
| Calibration/
other |  | 10 | 105 |

- Average CPU time for HLT: 300 msec on 1GHz PIII
- Best up-to-date estimate, ~50% uncertainty

| Physics channel | Efficiency |
| --- | --- |
| H(115 GeV) | 77 % |
| H(160 GeV)WW* 2  | 92% |
| HZZ4 | 92% |
| A/H(200 GeV)2  | 45% |
| SUSY (~0.5 TeV sparticles)  | ~60% |
| With RP-violation | ~20% |
| We  | 67% (fid: 60%) |
| W | 69% (fid: 50%) |
| Top X | 72% |

- CMS - b Physics Reach

- LHC 2003, Fermilab

**Notes:**
Singolo muone 25 hz
Di-muoni 4 herz

## HLT: CPU usage

**All numbers for a 1 GHz, Intel Pentium-III CPU**

| Trigger | CPU (ms) | Rate (kHz) | Total (s) |
| --- | --- | --- | --- |
| 1e/, 2e/ | 160 | 4.3 | 688 |
| 1, 2 | 710 | 3.6 | 2556 |
| 1, 2 | 130 | 3.0 | 390 |
| Jets, Jet * Miss-ET | 50 | 3.4 | 170 |
| e * jet  | 165 | 0.8 | 132 |
| B-jets | 300 | 0.5 | 150 |

**Total: 4092 s for 15.1 kHz ******** 271 ms/event**
**Therefore, a ****100 kHz system requires 1.2x10****6**** SI95**
**Expect improvements, additions.  **Time completely dominated by
- muons (GEANE extrapolation) – will improve
**This is “current best estimate”, with ~50% uncertainty.**

- CMS - b Physics Reach

- LHC 2003, Fermilab