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Future B physics prospects at hadron colliders
Olivier Schneider
5th KEK topical conference“Frontiers in Flavour Physics”November 20–22, 2001KEK, Tsukuba, Japan
O. Schneider, Nov 20, 2001
Future B physics prospects at hadron colliders
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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
O. Schneider, Nov 20, 2001
Future B physics prospects at hadron colliders
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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 …
O. Schneider, Nov 20, 2001
Future B physics prospects at hadron colliders
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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
O. Schneider, Nov 20, 2001
Future B physics prospects at hadron colliders
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€
0
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1
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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
(,)
O. Schneider, Nov 20, 2001
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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
O. Schneider, Nov 20, 2001
Future B physics prospects at hadron colliders
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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
O. Schneider, Nov 20, 2001
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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
O. Schneider, Nov 20, 2001
Future B physics prospects at hadron colliders
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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 …
O. Schneider, Nov 20, 2001
Future B physics prospects at hadron colliders
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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):
O. Schneider, Nov 20, 2001
Future B physics prospects at hadron colliders
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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
O. Schneider, Nov 20, 2001
Future B physics prospects at hadron colliders
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LHCb and BTeV calorimeters
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σEE = 0.10
E / GeV + 0.015
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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
O. Schneider, Nov 20, 2001
Future B physics prospects at hadron colliders
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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
O. Schneider, Nov 20, 2001
Future B physics prospects at hadron colliders
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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
O. Schneider, Nov 20, 2001
Future B physics prospects at hadron colliders
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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
O. Schneider, Nov 20, 2001
Future B physics prospects at hadron colliders
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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
O. Schneider, Nov 20, 2001
Future B physics prospects at hadron colliders
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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)
O. Schneider, Nov 20, 2001
Future B physics prospects at hadron colliders
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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
O. Schneider, Nov 20, 2001
Future B physics prospects at hadron colliders
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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
O. Schneider, Nov 20, 2001
Future B physics prospects at hadron colliders
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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
O. Schneider, Nov 20, 2001
Future B physics prospects at hadron colliders
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Particle identification
ATLAS
LHCb K– separation for true Very important for many exclusive channels
Example: B0
LHCb
O. Schneider, Nov 20, 2001
Future B physics prospects at hadron colliders
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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
O. Schneider, Nov 20, 2001
Future B physics prospects at hadron colliders
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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)
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A CP t( ) = A dir cosΔmd t( ) − sin2β( ) sinΔmd t( )
LHCb
O. Schneider, Nov 20, 2001
Future B physics prospects at hadron colliders
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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
O. Schneider, Nov 20, 2001
Future B physics prospects at hadron colliders
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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
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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 ]
O. Schneider, Nov 20, 2001
Future B physics prospects at hadron colliders
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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*
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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
O. Schneider, Nov 20, 2001
Future B physics prospects at hadron colliders
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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)
O. Schneider, Nov 20, 2001
Future B physics prospects at hadron colliders
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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
O. Schneider, Nov 20, 2001
Future B physics prospects at hadron colliders
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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