olivier schneider 6th international conference on b-physics at hadron machines beauty ’99 bled,...

Olivier Schneider

6th International Conference on B-physics at Hadron Machines

BEAUTY ’99Bled, Slovenia, June 21-25, 1999

[email protected]

Overview of the

LHCb experiment

LHCb collaboration

Finland: Espoo-Vantaa Inst. Tech.

France: Clermont-Ferrand, CPPM Marseille, LAL Orsay

Germany: Humboldt Univ. Berlin, Univ. Freiburg, Tech.

Univ. Dresden, Phys. Inst. Univ. Heidelberg,

IHEP Univ. Heidelberg, MPI Heidelberg,

Italy: Bologna, Cagliari , Ferrara, Genoa, Milan,

Univ. Rome I (La Sapienza) ,

Univ. Rome II (Tor Vergata)

Netherlands: Univ. Amsterdam, Free Univ. Amsterdam,

Univ. Utrecht, FOM

Poland: Cracow Inst. Nucl. Phys., Warsaw Univ.

Spain: Univ. Barcelona, Univ. Santiago de Compostela

Switzerland: Univ. Lausanne, CERN

UK: Univ. Cambridge, Univ. Edinburgh,

Univ. Glasgow, IC London, Univ. Liverpool,

Univ. Oxford

Brazil: UFRJ (Rio de Janeiro)

China: IHEP(Beijing), Univ. Sci. and Tech.(Hefei),

Nanjing Univ., Shandong Uni.

Russia: INR, ITEP, Lebedev Inst., IHEP,

PNPI (Gatchina)

Romania: Inst. of Atomic Phys. Bucharest

Ukraine: Inst. Phys. Tech. (Kharkov),

Inst. Nucl. Research (Kiev)

U.S.A.: Univ. Virginia, Northwestern Univ., Rice Univ.

O(500) participants from 49 institutes (11.6.99)

Why one more B-physics experiment

?

and then how ...

O. Schneider, Beauty 99 4

Introduction

Before 2005, various experiments will explore unitarity triangle:

well measured

with Bd J/ KS, (sin 2) < 0.05

no good/direct measurement

low statistics measurement with Bd ,theoretical uncertainty

Bd and Bs mixing measured

b u measured,hadronic uncertainty

Constraints on triangle will indicate:– consistency with SM within errors,– or inconsistency with SM (which will not be fully understood)

In any case:

Next generation experiments at LHC needed for full investigation of CP violation:– precision (high stat.) measurements on many Bd and Bs decay channels– aim for theoretically clean channels (not necessarily easiest experimentally)– overconstrain CKM matrix, including terms beyond O(3)


CKM matrix (in SM)

CP violation is due to ≠

i

iV(3)

VCKM V(3) + V

VudVusVub

VcdVcsVcb

VtdVtsVtb

iii

V


Unitarity triangles

O(10-2) in SM


Effect of new physics in Bd mixing

Within Standard ModelWithin Standard Model

Bd → J / KSdecay∝ Vcb* Vcs

arg Vcb* Vcs( ) =

Bd − Bbmixing∝ Vtb* Vtd( )

∝ −( )+ ⎡

⎣⎤⎦exp−i( )

extracted from md measurement

extracted from J/KS CP asymmetry

In presence of new physics in Bd mixingIn presence of new physics in Bd mixing

Bd − Bbmixing

∝ −( )+ +rnew

⎡⎣

⎤⎦exp−i +φnew( )( )

extracted from md measurement

extracted from J/KS CP asymmetry


Effect of new physics in Bd mixing (cont.)

triangle looks consistent with SM because

sides and J/K agree within experimental uncertainties

Possible scenario in 2005Possible scenario in 2005

need precise measurements of to realize that sides ≠ andhence discover new physics

1

−( )

+ + rnew from measuredmd

−( )

+ from SM

+

from SM

+ from

measuredb → u

0

+φnew from measuredCP asymmetry inJ / KS

sides

J/K

sides


Bd D*-n+, D*+n-

arg(mixing) =− +φnew( )

arg(Vcb* Vud ) =

arg(Vub* Vcd ) =

CP asymmetries in these decays allow to extract

new J/K and hence using already measured J/K

Similar story with Bs decaysSimilar story with Bs decays

snew from CP in Bs J

snew from CP in Bs Ds

K, Ds

K

clean extraction of (~ insensitive to new physics in Bs mixing)


Dedicated B physicsexperiment at LHC

Requirements for LHCb:

• reasonable acceptance for bothb-hadrons in event(needed for tagging)

• good proper time resolution (ability to resolve fast Bs oscillations)

• include hadronic final states of interest in trigger (e.g. Bd )

• ability to reduce background– good mass resolution– good particle identification

b b ≈μb b b ≈μbLHC’s advantage:

• large b production cross section• large luminosity

L > cm- s− L > cm- s−

possibility to study many Bs,d,u decayswith branching ratios as low as 10-7


LHCb acceptance

forward geometry with single-arm spectrometer OK

• beauty production predominantlyat low polar angle

• two b-hadrons close in

15 mrad < < 300 mrad

4.9 > > 1.9

bb acceptance similar to large central detector


Detector layout

open geometry easy access to all components

View in bending plane (horizontal)as proposed in 1998:


Layout in LHC cavern

• overall size of LHCb determined by existing experimental hall

• beam crossing point displaced by ~ 11 m (LHCb operates in collider mode)

Side view at interaction point 8:


Si detectors single-sided 150 μm thick r- and -strips active radius 1–6 cm analogue readout

Si detectors single-sided 150 μm thick r- and -strips active radius 1–6 cm analogue readout

Vertex detector

17 silicon stations (disks) installed in vacuum pipe

retractableby 3 cmduring

injection

(details from C. Parkes tomorrow)

towards spectrometer

40 μm resolution on interaction point

(along beam axis)


RICH detectors(details from A. Go on Thursday)

Pattern recognition on photo-detector planesPattern recognition on photo-detector planes

CF4 ringssmallC4F10

rings

largeaerogelrings

Aerogel C4F10 CF4threshold .6 /GeV c .6 /GeV c . /GeV c

K threshold . /GeV c 9. /GeV c .6 /GeV c


K/ separation

K– separation > 3 over full momentum range

1<p< 150 GeV/c

K– separation > 3 over full momentum range

1<p< 150 GeV/c

highest momentum pion from Bs Ds

highest momentum pion from Bd

kaon from b c s(tagging kaon)


Particle identification

… without using RICH information

… without using RICH information

… with RICH fast parametrization

… with RICH fast parametrization

.. with RICHfull simulation andpattern recognition

.. with RICHfull simulation andpattern recognition

84% efficiency96% purity

82% efficiency89% purity

Two-body background:Bs KK (BR=1.5 105)Bs K (BR=0.7 105) Bd K(BR=1.5 105)

Signal:Bd (BR=0.7 105)

mass in GeV/c2

Example: Bd analysis


Other systems

warm dipole magnet– 4 Tm bending power

inner tracking (40 cm x 60 cm)

– Micro Strip Gas Chambers +Gaseous Electron Multipliers (MSGC+GEM), or Micro Cathode Strip Chambers (MCSC)

– fall-back solution:Si

outer tracking– drift chambers with straw-tube geometry

Main trackerMain tracker

CalorimetersCalorimeters

pre-shower– single layer Pb + scintillators

ECAL (details from A. Jacholkowska tomorrow)

– shashlik type, 25 X0

HCAL– Fe + scintillating tiles, 5.6

Muon chambersMuon chambers

p /p =.% <p < GeV / c

mB→ ( ) =MeV /c

mDs → KK( ) = MeV/ c

– Resistive Plate Chambers (RPC) + Cathode Pad Chambers (CPC) for high rate regions

– 22 for calorimeters and muon system


Running luminosity

Aiming for single pp interactionsper bunch crossing

– radiation damage– detector occupancy– pattern recognition

LHCb chosen running luminosity

2 x 1032 cm2 s1

LHCb chosen running luminosity

2 x 1032 cm2 s1

Tune luminosity bydefocusing beams

Constant luminositythroughout LHCb’s

lifetime

5.61011 bb pairs per yearin single pp interactions

assuming inel ≈8 mb andb b ≈μb

30%


Level-0 trigger

40 MHzInput rate

1 MHzOutput rate

4.0 μs

Latency

Pile-up veto – 2 dedicated Si disks to reject multiple pp

interactions (i.e. primary vertexes)

– size of luminous region: z ~ 5 cm

pT or ET single track triggers– muon muon chambers ~ 20 %– electron ECAL ~ 10%– hadron ECAL+HCAL ~ 60%– photon ECAL– ...


Level-1 trigger

1 MHzInput rate

40 kHzOutput rate

512–2048 μs

Latency

(details from C. Parkes tomorrow)

Topological identification of secondary vertexes

– find tracks in silicon (only)– reconstruct primary vertex– form secondary vertexes with

large impact parameter tracks


Higher level triggers

• software only, full event buffer

• farms of commercial processors

Level-2: reconstruct large impact parameter tracks in Si and first tracking chambers, and use measured momenta to refine secondary vertex requirement

Level-3: reconstruct specific b-hadron decay modes (loose cuts)using all information, incl. RICH

10 ms

Latency

40 kHzInput rate

5 kHzOutput rate

5 kHzInput rateof which

25% b-events

200 HzOutput rate

written to tape(20 MBytes/s)

200 ms

Latency


Trigger stability

• trigger is flexible, robust, andwell balanced between levels

• operating point can be adjusted to running conditions without significant loss in physics

point maximizingoverall CP sensitivity

Example: Adjustment of L0 thresholdswith fixed total (μ+e+h) retention of 9%

Example: Adjustment of L0 thresholdswith fixed total (μ+e+h) retention of 9%

CP reach withBd

relative to its maximum


Trigger efficiencies

in %, for useful events, reconstructed and correctly tagged offline

L0 L1 L2 Totalμe h all

BdJ/(ee)KS + tag 17 63 17 72 42 81 24

BdJ/(μμ)KS + tag 87 6 16 88 50 81 36

BsDsK + tag 15 9 45 54 56 92 28

BdDK831

99

Bd + tag 14 8 70 76 48 83 30

“High pT” track firing L0 trigger can be: – track from B decay of interest

– track from other b-hadron useful for tagging

Tags considered (so far): – muon or electron from other b-hadron

b lepton– charged kaon from other b-hadron

b c s

Overall tag efficiency = 40% Overall mistag rate = 30%

Tags considered (so far): – muon or electron from other b-hadron

b lepton– charged kaon from other b-hadron

b c s

Overall tag efficiency = 40% Overall mistag rate = 30%

importance of hadron trigger

efficiency dominatedby kaon tag

importance of hadron trigger


DAQ architecture

Level-0 buffer: on-detector electronicsall data digitized after Level-0 yes

Level-1 buffer: off-detector electronicszero-suppressed data transferred to DAQ after Level-1 yes

event size: 100 kB

Read-out Network (RN)

RU RU

Control &

Monitoring

RU

2-4 GB/s

4 GB/s

20 MB/s

Variable latencyL2 ~10 ms

L3 ~200 msL

AN

Read-out units (RU)

Timing&

FastControl

Front-End Electronics

Si-VTX TRACK ECAL HCAL MUON RICH

LHCb detector

L0

L1

Level 0Trigger

Level 1Trigger

40 MHz

1 MHz

40 kHz

Fixed latency 4.0 μs

Variable latency 512-2048 μs

Datarates

40 TB/s

1 TB/s

Front-End Multiplexers (FEM)1 MHz

Front End Links

Trigger Level 2 & 3Event Filter

SFC SFC

CPU

CPU

CPU

CPU

Sub-Farm Controllers (SFC)

Storage

3 GB/s


Schedule

1998

1999

2000

2001

2002

2003

2004

2005

Inner Tracker

Vertex Detector

RICH, Calorimeters

Muon System

L0 & L1 Trigger, DAQ

Magnet

Computing

Outer Tracker

Technical Proposal

LHCb approved

LHC and LHCb readyfor many years of B physicsat “nominal LHCb luminosity”

TechnicalDesignReports

Magnet installation

Detector and DAQ installation


Bd D*-+, D*+-

• need large stat. (CP asymmetry very small)• efficient hadron trigger essential

Extraction of from 4 time-dependent decay rates, use from J/KS

to get

– reconstruct D* inclusively (using slow pion) ~ 270 k events / year with S/B ~ 7– add D*a1 channels ~ 320 k events / year

in degrees

in

deg

rees

1 year

5 years ~ 4o

• no strong phase difference assumed• no uncertainty on ratio of BRs assumed


Bd D0K*0

• visible BR’s 10–8 –10–7

• hadron trigger and K/ separation essential

K tags flavourof decaying Bd

→ K+ − → K− +

→ K+K−, + −

Extraction of from the measurements of 6 time-integrated rates

m 13 MeV/c2

~ 400 signal

events total

S/B ~ 1

~ 10o

in one year

only Bd → DK *

signal events


Bs oscillations

• good proper timeresolution t essential

t ~ 43 fs

Need to resolve ms oscillations to measure time-dependent CP asymmetry in Bs decays

damped like

exp −

ms t( )⎡

⎣⎤⎦

Bs Ds :

~ 34500 rec. and tagged events/year

> 5 measurement of ms up to 48 ps1 (xs = 75)


• counter part of Bd J/ KS

• CP asymmetry allows to extract the phase of Bs mixing, i.e. angle

Bs J/

• decay into spin-1 particles:J/ can be CP-odd or CP-even(depending on angular orbital momentum)

additional dilution on CP asymmetry

• need angular analysis to separate contributions

• good proper time resolution needed• good proper time resolution needed

can also be done in ATLAS/CMS with similar sensitivity

~ 0.01

in one year

depends ms and r=A(CP-odd)/A(CP-even)(will be extracted as well)


Bs Ds-K+, Ds

+K-

• hadron trigger• proper time resolution• mass resolution• K/ separation (RICH)

• hadron trigger• proper time resolution• mass resolution• K/ separation (RICH)

kill Bs Ds background

Essential features:

Extraction of from 4 time-dependent

decay rates, use from J/ to get

~ 2.5 k events / year with S/B > 10

~ 6–13o

in one yeardepends on , ms,and strong phase(will be extracted as well)


Conclusion

LHC offers unique opportunity to probe CKM sector in depth

To go beyond what other experiments can do, LHCb will rely on– efficient, robust, and

flexible triggering scheme

– high performanceparticle identification

– excellent mass and proper time resolutions

LHCb will operate at its full potential from the first day of LHC running and for many years

LHCb can study many different B decay modes and, with high precision and efficiency, including fully hadronic channels

Ability of measuring CKM elements accurately implies good sensitivity to physics beyond the Standard Model

olivier schneider 6th international conference on b-physics at hadron machines beauty ’99 bled,...

Documents

v ud v

b d mixing

v skip

d measurement

theoretical uncertainty

bphysics experiment

mixing slide

b s mixing measured