future b physics prospects at hadron colliders olivier schneider 5th kek topical conference...

Future B physics prospects at hadron colliders

Olivier Schneider

5th KEK topical conference“Frontiers in Flavour Physics”November 20–22, 2001KEK, Tsukuba, Japan

[email protected]

O. Schneider, Nov 20, 2001


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B physics and CP violation in 2006 Experimental results from

—Tevatron Run IIa: CDF + D0, each 2 fb-1

—Asym. B factories: BABAR + Belle, each 300–500 fb-1

—“Equivalent” to several 108 B mesons

Direct measurements of angles of unitarity triangle:— (sin(2)) ≈ 0.03 from B0 J/ KS asymmetry— no precise measurement of other angles

Knowledge on sides of unitarity triangle— (|Vcb|) ≈ few % error— (|Vub|) ≈ 5-10 % error— (|Vtd|/|Vts|) ≈ few-5 % error

(assuming ms < 40 ps-1)

€

sin2 tan−1 η1−ρ

⎛

⎝ ⎜

⎞

⎠ ⎟

⎡

⎣ ⎢

⎤

⎦ ⎥

indirectly known to < 0.03



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€

0

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1

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0

CKM triangle in 2006 (SM)

First stringent test of CKM ansatz !—Sides dominated by theoretical uncertainties—More statistics would improve sin(2)

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ρ

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η

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(1−ρ )2+η 2 from ΔmdΔms

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ρ 2+η 2 fromΓ(b→u)Γ(b→c)

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β from B→ J /Ψ KS

(,) … or CKM picture might already appear inconsistent …



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Most extensions to SM imply … … new physics in decays

(b =1)—Penguin loops

… new physics in mixing(b=2)—Box diagrams—Tree diagrams

Note: SM tree processes are not affected

newparticles

newparticles

b d, s

b d, s

newparticles

d,s b

b d, s

d,s b

lor l

lor l



5

€

0

€

1

€

0

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ρ

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η

CKM triangle in 2006 (new physics)

In this case, a precise measurement of , independent of possible new physics in the mixing, is needed to provide evidence for the new physics

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(1−ρ )2+η 2 + new physics

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β + new physics

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ρ 2+η 2

(,)



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Measuring new physics in B mixing

Cannot be measured at current experimentsNeed much higher statistics, including Bs decays, and PID

(b u)/ (b c)

CP asym. in Bs DsK

CP asym. in Bs DsK

CP asym. in Bs J/ J/

CP asym. in Bd D CP asym. in Bd D

CP asym. in Bd J/ KS

md

atan

SM values ofand

rnew

new physics parametersrnew andnew

2eff

2eff

+ 2eff

2eff

= 2 atannew



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(dis)advantages of hadron collidersfor B physics

Large bottom production cross section bb 100–500b (for √s 2–14 TeV)

Triggering is an issuebb / inelastic 0.2–0.6% (for √s 2–14 TeV)

All b hadrons produced Bu (40%), Bd (40%), Bs (10%), Bc, and b-baryons (10%)

Many primary particles to determine b production vertex

Many particles not associated to b hadrons

b hadron pairs don’t evolve coherently mixing dilutes tagging

1012 bb / yearat 21032 cm2s1



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Hadron colliders ( 2006)Tevatron LHC

proton-antiproton proton-proton√s 2 TeV 14 TeV bb 100 b 500 b cc 1mb 3.5 mb inelastic 60 mb 80 mb total 75 mb 100 mb bunch crossing 7.6 MHz 40 MHzt bunch 132 ns 25 nsz (luminous region) 30 cm 5.3 cm

L [cms] 21032 21032 1033 (1034 )

<n inelastic pp interactions / bx> 1.6 0.53 ~2 (20)@LHCb @ATLAS/CMS

Cross sectionsnot measured yet:large uncertainties



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B physics’ future at hadron colliders

High pT central detectors—CDF+D0 @ Tevatron run II started

• See talk from V. Papadimitriou

—ATLAS+CMS @ LHC ready in 2006• Construction well underway

• Most B physics during LHC’s initial low luminosity period (1033)

(forward) detectors dedicated to B physics—LHCb @ LHC ready in 2006

• Proposed and approved in 1998; TDR phase, some construction started

• Designed to do B physics at 2x1032 (even when ATLAS+CMS at 1034)

—BTeV @ Tevatron ?• Proposed in 2000, more aggressive approach than LHCb (technology & funding)

• approved (stage I) at FNAL, R&D phase; waiting for funding decision …



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ATLAS and CMS

Central detectors ( 2.5) B physics trigger:

—high pT leptons—no purely hadronic trigger

(must rely on tagging lepton) Mostly B physics using J/ decay modes

(+ rare decays with leptons, Bs +- …)

pT thresholds (GeV/c):



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LHCb and BTeV

Forward detectors (1.9 4.9)—still very good acceptance for bb pairs—large pB, use of RICH detectors for PID—vertex detectors inside beam vacuum

Leptonic and hadronic/vertex triggers



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LHCb and BTeV calorimeters

€

σEE = 0.10

E / GeV + 0.015

€

σEE = 0.80

E / GeV + 0.10

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σEE = 0.016

E / GeV + 0.0055

Tasks:—Level-0 ET trigger (e, , hadron)—Electron ID, reconstruction

Preshower:—scintillator + 2X0 Pb + scintillator

ECAL:—Pb + scintillator tiles (“shashlik”)

HCAL:—Fe + scintillator tiles

Tasks:— Electron ID— , reconstruction

ECAL only:—PbWO4 crystals

(developed by CMS)with PMT readout

—2 11850 crystals of ~2.6~2.6 22 (25 X0) cm3 with pointing geometry

—very good resolution



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25 stations (50 Si planes)

LHCb vertex locator Online: pile-up veto

+ vertex trigger Offline: proper time resolution

sufficient for Bs physics

Many stations for full coverage,but only ~200k channels

Inside vacuum tank Sufficiently rad-hard to be very

close to beams—Active Si at 8 mm

where ~1014 neq/cm2/y is expected Sensors on each side retractable

during beam setup Each half in Al box (250 m

thick) acting as RF shield



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LHCb vertex locator

r- and -measuring small Si strips ( “striplets” )

varying pitch, occupancy < 1% 300 m, n-on-n, double metal layer Analogue readout with

STCA–VELO (DMIL) orBEETLE (0.25m)

r sensor

sensor

shortest strip: 6.3 mm



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BTeV pixel detector31 stations (62 Si planes)

Located in dipole field “3-dimensional” hits Radiation hardBut ... 30M channels ! Electronics inside acceptance

larger radiation length (~2% per station)

Heart of BTeV trigger, used at first level of triggering

vacuum tank

Two planes per station:one with “vertical” pixelsone with “horizontal” pixels



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BTeV pixel detectorSi pixels

FPIX0 chip

3 bit analogue readout 200 m thick bump bonded chip (FPIX2)

Test beam

250 m thick 15 cm2 pixel detector 25k rectangular 50400 m pixels



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Vertexing resolutionImpact parameter resolution vs pT

Decay length resolution [cm] for B decays

Excellent proper time resolution avoids significant damping of Bs oscillations(5 measurement of ms up to 48 ps1 using one year of Bs Ds

data with t=43 fs)



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Trigger schemes

Final state reconstructionLHCb

40 kHz1 MHz40 MHz 200 Hz

Detachedvertex+ IP of pT candidate

Medium pT hadron,,e,+ pileup veto

Decay topologyBTeV

80 kHz7.6 MHz 3 kHzDetached vertex+ dimuon

Event selection

ATLASCMS

40 MHzHigh pT , e

pT and ET triggers(muon + calorimeters)

vertex triggers(Si vertex detector)

confirmationand event filters

75 kHz 100 Hz



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Low-level triggers

Si pixels: 3107 channelshardware+processors, asynchronousvariable latency ~150 sreduction factor ~100

calo++pileup veto: 5104 channelshardware, synchronousfixed latency =4 sreduction factor ~40 (only ~10 from pT cut)

Si strips: 2105 channels processors, asynchronousfixed latency =1.7 msreduction factor ~25

1 MHz

40 MHz

Detached vertex+ IP of pT

candidate *

Medium pT hadron,,e,+ pileup veto

(12.4 MHz of inel. interactions)

LHCb

40 kHz

7.6 MHz

Detached vertex+ dimuon

BTeV

80 kHz

* added since TP (LHCb event yields not updated yet for new L1 efficiencies)

L0

L1

L1



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LHCb RICH1

Ring Imaging Cherenkov detectors BTeV:

2 radiators in 1 RICH to cover 3 < p < 70 GeV/c

LHCb: 3 radiators in 2 RICHes to cover 1 < p < 100 GeV/c

LHCb pixel HPD (baseline option)

87 mm diam. phototube with pixel detector bump-bonded to encapsulated binary electronics

1024 Si pixels(500m x 500m)

Prototype chip available



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Particle identification

ATLAS

LHCb K– separation for true Very important for many exclusive channels

Example: B0

LHCb



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Flavour tagging at production Needed for many CP violation measurements Methods used/studied so far:

LHCb and BTeV expected to reach similar tagging power:—LHCb TP: D2=6.4% based on study of lepton and kaon tags alone—BTeV TP: D2=10% assumed

Still to be studied



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from B0 J/ KS Huge statistics (especially ATLAS & CMS) Can also fit for Adir (expected ≈ 0 in SM)

LHCb & BTeV: compare with Penguin decay B0 KS

ATLASee (3 years)

CMS (1 year)

€

A CP t( ) = A dir cosΔmd t( ) − sin2β( ) sinΔmd t( )

LHCb



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Bs mixing phase from Bs J/ , J/ Strange counterpart of B0 J/ KS

SM prediction of Bs mixing phaseis small s = 2 = 22 = O(102)

Sensitive probe for new physics

J/ is not pure CP final state— can reach (s) ≈ 0.02 in 1 year,

under assumptions on the strong phases— need angular analysis for clean extraction

J/ is pure CP=1— need photon detection— BTeV: (s) = 0.033 in 1 year

NP-LR: left-right symmetric model with spontaneous CP viol.NP-DQ: iso-singlet down quark mixing model



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B0 asymmetry, etc ...

Adir and Amix can be measured—e.g. ±0.08 with 1 year at LHCb

but Penguin “pollution” hampers extraction

Study of B0 (, , ) (time-dependent analysis of Dalitz plot)to extract , Penguin and tree terms—BTeV/LHCb claim 10.8/>3.3k untagged per year—more study needed to quote –

Measure Adir and Amix for Bs KK

—e.g. ±0.11 with 1 year at LHCb (if ms=20 ps1)

and combine with B0 resultsto extract assuming U-spin symmetry—LHC claim ~ 5after 1 year

€

A CP t( ) = A dir cosΔmd t( ) + A mix sinΔmd t( )B0 ’ +−annu alyield

Tagged Untagged S/BATL AS .3k .7CMS .9k .LHCb 4.9k >.3 k >BTeV 3.8 k 3

proposed bySnyder&Quinn

proposed byFleischer

M2() [GeV2]

M2 (

) [G

eV2 ]



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from B0 D* , D*

Small interference between two tree decays, with and without prior B0 mixing

Extract and strong simultaneouslyfrom the two time-dependent asymmetries

Use from J/ KS to obtain value of insensitive to possible new physics in mixing

LHCb study: — use both exclusive and inclusive

reconstruction of neutral D from D*

€

Vcb*Vud ∝ λ2

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Vub*Vcd ∝ λ4eiγ

+ strong phase difference

1 year

(degrees)

erro

r on

(d

egre

es)

10% error on no error on

5 years

assumed amplitude ratio = 0.02

strong

= O(10)depends on and strong

(1 year)

Need high stats



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from Bs DsK, Ds

K

Strange counterpart of B0 D*, D*

Here measure and take from J/ Important differences:

— Asymmetry larger because two tree amplitudes of similar order (3)

— Proper time resolution more important— Background from Cabibbo-allowed Ds

* using common BR assumptions (as in LHCb TP)

Sensitivity on depends on:• amplitude ratio• strong phase difference• • ms

For ms = 20 ps1:

(1 year, each expt)

Need very good hadronic trigger efficiency K/ separation proper time resolution

= O(10)



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B Xs,d involve loop & box with Vtd,Vts

Ratio of inclusive rates with “non-resonant” dimuon mass allows extraction of VtdVts with small theoretical error of O(1%)

After several years, this method may become competitive with md/ms

New preliminaryLHCb study

Relative error on Vtd Vts of ~11%

VtdVts from B Xs,d



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Summary

B physics at hadron colliders, currently performed at Tevatron, will get a big boost once LHC turns on (2006) huge statistics: 1012 bb / year at 21032 cm2s1

including Bs mesons Dedicated detectors (LHCb, BTeV) aim for best

…trigger efficiency (hadron and vertex triggers)…proper time resolution…particle identification

Clean extraction of angle after one year several independent measurements with O(10) precision

Confront with other measurements involving loops/boxes if new physics shows up, measure its parameters

future b physics prospects at hadron colliders olivier schneider 5th kek topical conference...

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