The LHCb Flavour Physics Experiment - AGH University of ... · PDF fileThe LHCb Flavour...

The LHCb Flavour Physics Experiment

Eduardo Rodrigues University of Glasgow

AGH, University of Science and Technology, Krakow, Poland, 4 March 2010

AGH, UST, Krakow, Poland, 4 March 2011 2/65 Eduardo Rodrigues

Outline

Motivation

LHC @ CERN @ Geneva

The LHCb experiment

The 2010 LHC(b) run

Prospects for 2011-12

Motivation Universe, matter and antimatter, CP violation


Universe, matter and antimatter

Matter

dominates !

Equal

amounts

of matter

and

Antimatter ?


Matter-antimatter asymmetry in the universe

Common belief:

For every billion ordinary particles annihilating with antimatter

in the early Universe, one extra was left “standing”


How to generate a matter-antimatter asymmetry?

No definitive answer to this question yet!

In 1967 A. Sacharov formulated a set of general conditions

that any mechanism of B-asymmetry generation has to meet :

1) Need a process that violates the baryon number B:

(Baryon number of matter=1, of antimatter = -1)

2) Both C and CP symmetries should be violated

3) Conditions 1) and 2) should occur during a phase in which there is no

thermal equilibrium

(CP violation has far more interest than “solely” cosmological considerations)

Violation of the CP symmetry has been a major field of research

in High Energy Physics since already the 1950s …

Flavour Physics is the “grand picture”


On the 3 big search paths in High Energy Physics

CP

Violation


Flavour Physics programme (not comprehensive!)

CP violation

Flavour Physics

Discovery channels

CKM matrix

n-body baryonic

Hadronic

Dynamics of

heavy flavour decays

Theory

Experiment

Rare decays

Radiative decays

Time-(in)dependent measurements

CP asymmetries

Quark mixing

Branching ratios Lifetimes

Semi-leptonic

LHC @ CERN @ Geneva A multi-purpose lab & accelerator complex

Geneva, CERN and the LHC

LHC

CERN:

European laboratory for high energy physics

CERN – aerial view (old-ish picture)

CERN accelerator complex

Section of the LHC

The Large Hadron Collider – LHC

Pt5

Pt1

Pt2 Pt8

Pt3 Pt7

Pt4 Pt6

Betatron

cleaning

RF Dump

CMS Totem

ATLAS LHCf

ALICE LHCb

Momentum

cleaning

LHC: proton-proton collider, circumference of 27 km

PS, SPS: old accelerators now used as pre-accelerators for the LHC

Nominal energy of 14 TeV, 1.1x1011 protons per bunch

- At 7 TeV a proton has

99.999999% speed of light

LHC beams formed from

counter-rotating bunches

of protons (clever two-in-one design : 2 beam-pipes

inside same magnet with opposite B field

in each pipe)

LHC stored energy

360 MJ

Nominal LHC

A factor 2 in magnetic field

A factor 7 in beam energy

A factor 200 in stored energy!

4x72x1.1 1011p

2808x1.1 1011p

LHC

2010-

2011

target

Done

to

date

In 2010 the LHC reached ~ 20 MJ, close to 5kg TNT !


LHC increase in stored energy over 2010

linear Y scale log Y scale

apr may jun jul aug apr may jun jul aug

3 MJ

The LHCb Experiment The flavour physics experiment at the LHC

LHCb – an international collaboration

15 countries

Over 50 universities

and laboratories

Over 700 scientists

Cavern 100 metres below ground


LHCb physics roadmap

Mission statement

- Search for new physics probing the flavour structure of the SM

- Study CP violation and rare decays with beauty & charm hadrons

Measure processes strongly suppressed in the Standard Model but

- Sensitive to new physics (e.g. contributions from new heavy particles in loop processes)

- Poorly constrained by present data

Measure the sides and angles of the unitarity triangle which is

at the heart of the CKM description of CP violation in the Standard Model

- Over-constrain the system with various related measurements

- Look for inconsistencies among various independent measurements of the

same quantity using decay modes sensitive or non-sensitive to new physics (modes dominated by tree-level or loop diagrams, respectively)

Measure CP violating quantities that probe the flavour structure of the SM


At the heart of «indirect searches» for new physics

Tree diagram

t,c,u

t,c,u

WW

s,d

b s,d

b

0B0B

0B

,K0

s

b

s,d

ss,d

ss

t,c,u

W

cW

d u

s,d s,d

0B

π

D, Ds b

?

?

New

Physics

Virtual particles

appear in

loop mediated processes

Box diagram

Penguin diagram

Loop diagrams


Can one do flavour physics at the LHC ?

Large production of heavy flavour hadrons in proton-proton collisions :

- At the LHC @ E=14 TeV sppbb ~ 500 mb (compared with seebb ~ 1 nb @ E=10 GeV)

- In nominal conditions (LHC luminosity & data taking time of 107 s) this translates to

~ 1012 b-quark pairs produced per year !

- All species of b-/c-flavoured hadrons produced: B0, B±, Bc±, Bs, Lb, etc.

BUT :

- b and anti-b highly correlated, either produced very forward or very backward

with respect to the p-p beam-line

need for a forward detector

- sbb/stotal < 1 % and decay branching ratios

(interesting modes) only ~ 10-9 - 10-4

need for extremely efficient selection (trigger)

with high background rejection power b

b

b

b


Characteristics of heavy flavour hadrons :

- High mass high transverse momentum decay daughters

- “Large” lifetimes typically ~ 10-13 - 10-12 seconds

measurable decay length ~ 1 cm thanks to the relativistic boost

Can one do flavour physics at the LHC ?

btag

Bs

K

K

K

+

Ds

B-production at pp-collision primary vertex

B-decay displaced vertex

B

Key ingredients to high physics performance

1. Trigger efficiency :

- Fast, efficient, flexible selection of interesting physics events

while rejecting as early as possible the undesired “background”

2. Vertex reconstruction and excellent impact parameter resolution :

- Precise reconstruction and separation of primary and secondary vertices

- Identification of long-lived heavy flavour decays

3. Tracking performance :

- Efficient determination of charged track trajectories

- Precision determination of their momentum and angles

4. Particle identification :

- Differentiation of hadrons, muons, electrons, photons over large momentum spectrum

5. Invariant mass resolution :

- High mass resolution easier separation of decay modes with same topology

6. Detector alignment :

- Minimise biases introduced by non-precise knowledge of positions of sub-detectors

The LHCb detector

Forward spectrometer

Acceptance ~10-300 mrad

21 m long

10 m high, 13 m wide

5600 tonnes in total

Each sub-detector has one of several particle measurement purposes : - Particle identity

- Trajectory

- Energy or momentum

Reconstruction: - muons: easy - hadronic tracks: fine - electrons: OK - 0’s, KS, L: OK; 0’s difficult - neutrinos, neutrons, KL: no


The LHCb cavern and detector (May 2009)


1. Two-level trigger system

Level 0

Custom hardware trigger

pp crossing rate

High Level Trigger

Software trigger

High ET particles - Fast decision in ~ 4 ms

- Partial detector information

Search for physics signatures - Software trigger run in PC farm (several thousand CPU nodes)

- Full detector information

- Increasing level of complexity in

event reconstruction and selection

- Decision in ~ 1/20 s

- Typical throughput ~ 70 MB/s

250 GB per hour Storage

~ 2 kHz

1 MHz

~ 30 MHz

- Distinguish interesting physics - Reject asap the “background”

Fast, efficient, flexible

70 MB/s

= 250 GB/h

2. A precision vertex detector – the VELO

2 halves of 21 stations

2 silicon strip sensors

per station

Only 8 mm from beams

VELO – Vertex LOcator : - Precise determination and separation of

primary and secondary vertices

- Identification of long-lived hadron decays

Close-up of the VELO sensors


The VELO – schematics


VELO performance

mm

Nz

Power

)03.0(1.14/N

Epsilon/Const-Zres

0.96

Primary vertex resolution in Z

Vertex detector – 2 retractable halves

Long-lived heavy flavour particles vertex displaced by typically ~ 1cm with respect to the primary vertex

Best primary vertex resolutions at the LHC !

s(x,y,z) ~ (14,13,80) mm for PVs with 25 tracks

Precise primary and secondary

vertex resolutions

+

precise momentum resolution

excellent propertime resolution

~ 50 fs !

Beam


Impact parameter resolution

-

Primary vertex Direction of B

+

IP = Impact Parameter

IP resolutions as low as 15-20 mm

Better resolutions expected

with better alignment

Daughters of long-lived particles tend to have a large IP


VELO – beam-beam collisions and beam-gas events

Green : vertices in beam1-beam2 events

Blue : beam1 – empty collisions

Red : empty - beam2 collisions

(z-axis is scaled compared to

transverse dimensions to see

clearly the beam angle)


VELO – close-up of event display with real tracks


A multi primary vertex event


Event display – primary and secondary vertices


3. Efficient and precise tracking system

Precise determination of track parameters

- Momentum and angles (+ full covariance matrix)

Vertex detector :

- Silicon micro-strip detector

- Provides track “seeds”

Silicon trackers :

- Silicon micro-strip detectors

- Used closer to the beam-pipe where track density is higher

- TT / IT before/after the magnet

Outer tracker :

- Thousands of gas-filled straw tubes

Magnet

The magnet (during installation, end 2004)

Warm dipole magnet

2 huge 27 tonnes coils

1450 tonnes iron yoke

Curving charged tracks allowing for the measurement of their momentum

Magnet and beampipe


Efficient track pattern recognition

- Ex.: VELO cluster finding efficiency of 99.7%

High momentum resolution needed to

separate topologically similar decay modes

Excellent momentum resolution

dp/p = 0.35% to 0.55% achieved

Silicon strip and straw-tube detectors for tracking

- long lever arm ~ 10 m

- hit resolutions ~ 55 and 250 mm, respectively

Together with precise determination of track slopes

provides very good mass resolutions

LHCb

Preliminary

Outer tracker (straw tubes)

Tracking system performance

2 RICH detectors :

- Ring Imaging Cherenkov detectors with photo-diodes

- Differentiate pions, kaons and protons over large momentum spectrum [ 2, 100 ] GeV

Calorimeter system :

- A preshower, a scintillator pad detector, an electromagnetic and a hadronic calorimeter

- Measure particle energies for electrons,

photons, hadrons

- Identify electrons and photons and

differentiate them from hadrons

Muon chambers :

- 5 stations in total

- Identify and measure muons

4. Particle identification systems

Separation of e/g/m//K/p over large momentum range

- Heavy flavour hadron mass peaks with similar topology often overlap


The 2 Ring Imaging CHerenkov detectors

RICH1 RICH2

C4F10 gas

n=1.0014

Up to ~70 GeV/c

CF4 gas

n=1.0005

Beyond ~100 GeV/c

Silica Aerogel

n=1.03

1-10 GeV/c

RICH1 :

- Before the magnet

- For low momentum tracks

RICH2 :

- After the magnet

- For high momentum tracks


PID with the RICH detectors

PID

→ K+ K- decay with kaon identification → 2 opposite charged tracks

?


2 particles with same final state but different mass

D+→KK Ds→KK

PID with the RICH detectors

B- → D0 (→K) K-

Luminosity: ~ 34 pb-1

B- → D0 (→KK) - B- → D0 (→) -

B- → D0 (→K) -

«RICH PID» – example of B- → D0 (→hh) - / K- decays


Installation of calorimeters and muon chambers

The electromagnetic calorimeter (during installation, 2005)

- Measure energy of electrons, photons - Distinguish e/g from hadrons

6 x 7 m2 wall

3300 blocks of

scintillator, fibre

optics and lead


ECAL is calibrated to 2% level

0 resolution is better than expected

0gg

s = 7.2 MeV

D0 K0

s = 23.5 ± 2.5 MeV

L ~ 150 nb-1

J/y e+e-

PID with the calorimeters


PID with the calorimeters

Rare radiative decay B0 → K* g


PID with the muon chambers – → m+ m- modes

5. Invariant mass resolution

2 particles with same final state

but different mass : imagine a very poor mass resolution

and no RICH PID …

D+→KK Ds→KK

Separation of decay modes with same topology

Evolution of mass resolution over time: for J/ψ μμ ; ideal resolution σMC=12 MeV

May: σ~18 MeV August: σ~16 MeV November: σ~13 MeV

Invariant mass of a 2-body decay

M2 = m12 + m2

2 + 2(E1E2 p1p2 cosq )

need precise knowledge of momentum p and angle

q of decay products (as well as their particle type)


6. Detector alignment

Best VELO hit resolution is 4 mm

Great achievement !

Module and sensor alignment

known to better than 5 mm

VELO is opened during injection !

Fill-to-fill variation of two halves

relative alignment < 5mm

Better alignment minimises biases and improves resolutions

The 2010 LHC(b) run A very successful start !

LHC efficiency in the 2010 (proton) run

Plot taken from talk

S. Redaelli, “LHC performance in 2010 and prospects”

LHC end-of-year jamboree, 17/12/2010 http://indico.cern.ch/conferenceDisplay.py?confId=113139

65 %

availability !

Great achievement (specially for a 1st year of run)

http://indico.cern.ch/conferenceDisplay.py?confId=113139


LHC luminosity in the 2010 (proton) run

2010 goals achieved ! Luminosity delivered: almost 50 pb-1

Peak instantaneous lumi.: ~1.61032 cm-2s-1

Operation – LHCb control room

Shift Leader Data Manager

2 main shifters + many experts on call

Operation – LHCb control room


LHCb 2010 data taking – luminosity recorder

1 pb-1 on

7th August

Over 3 pb-1

20 days later!

• Luminosity delivered by the LHC

• Luminosity recorded by LHCb

~ 38 pb-1 recorded

2010 data taking – efficiency

Excellent efficiency ~ 90%

Stable data taking

High efficiency of all sub-detectors, increasing with time (experience)

94%

Running with

high average #

of visible

interactions

per crossing


LHCb sub-detector efficiencies

Detector efficiencies > 99% !

Mass = (5326.7±10.9) MeV/c2

Momentum: p = 62.7 GeV/c, pT = 10.48 GeV/c Muons are magenta, kaon is red

Full spectrometer, top view

VELO region, top view

First B candidate seen in LHCb !

B+ → J/ψ K+

J/ψ → μ+ μ–

Transverse plane (looking from CALO to VELO)

First B+ J/Y K+ candidate event


«Seeing» CP violation with B0/Bs → K modes

K- + K+ -

RAW asymmetry is visually obvious !

Note: No corrections for production/detector asymmetries

B0

Bs

Prospects for 2011-12 The future is bright …


LHC operation in 2011 – prospects

Plot taken from talk

S. Redaelli, “LHC performance in 2010 and prospects”

LHC end-of-year jamboree, 17/12/2010 http://indico.cern.ch/conferenceDisplay.py?confId=113139

Re-start of physics runs in mid-March

Energy : 7 TeV collisions

Integrated luminosity :

Reach 1 fb-1 by end 2011

(we got ~0.04 fb-1 in 2010!)

http://indico.cern.ch/conferenceDisplay.py?confId=113139


LHCb 2010 & 2011 running conditions

2010 running conditions :

Collisions at 7 TeV

~ 38 pb-1 collected

Expectations for 2011 :

Reach 1 fb-1 = 1000 pb-1 by end 2011

Discussion ongoing for 8 TeV run

LHCb design specifications

Average number of visible pp interactions per crossing

(80% of design luminosity reached with 344 colliding bunches instead of 2622)


In short …

LHCb has already proven to be a

heavy flavour experiment at a hadron machine

Excellent and promising results are coming out - This was just the beginning

Many world-class measurements just around the … year - And many competitive with the TeVatron results

Stay tuned …

Thumbs up !

The LHCb Flavour Physics Experiment - AGH University of ... · PDF fileThe LHCb Flavour...

Documents

Transcript of The LHCb Flavour Physics Experiment - AGH University of ... · PDF fileThe LHCb Flavour...