Download - Why B physics at pp collider
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B physics at the Tevatron
S. Donati University and INFN Pisa
April 2003 Meeting of the American Physical Society
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Why B physics at pp collider
CDFCLEO
Open wide spectrum of B hadrons B, B0, Bs, Bc, b, b
bb cross section is 50-100 b ~O(105) larger than @(4S)/Z0
BUT: B hadrons are hidden in a 103
largerbackground (inelastic(pp) 50 mb)
Events more complicated than at (4S)
Crucial detector components:- Tracking system Excellent pt resolution/Vertexing- Trigger Large bandwidth Strong background reduction- Particle identification
CLEO
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Tevatron pp colliderMain Injector (new injection stage for
Tevatron)
Ability to accelerate and deliver higher intensity of protons
More efficient anti-proton production
Collision rate: 396 ns crossing time
(36x36 bunches) ~ 2M collisions/sec
Center of Mass energy: 1.96 TeV
Today: luminosity ~4.0 x 1031 cm-2s-1
4 to 7 pb-1/week delivered
Goal: luminosity: ~1032 cm-2s-1
16 pb-1/week delivered
In this talk: results with 70 pb-1 for CDF and 40 pb-1 for D0
CDF Integrated Luminosity
Mar 02
Jan 03
130 pb-1 (delivered)
100 pb-1 (to tape)
B/Charm: ~ 70 pb-1
commiss
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CDF Detector in Run II
Tracking System - 3D Silicon Tracker (up to ||~2)
- Faster Drift ChamberTime-of-Flight (particle ID) Plug and Forward Calorimeters DAQ & Trigger system (Online Silicon Vertex Tracker: trigger on displaced vertices, first time at hadron collider)
Completely New:
Inherited from Run I:Central Calorimeter (||<1) Solenoid (1.4T)
Muon system (extended to ||
~1.5)
Partially New:
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D0 detector in Run II
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B Triggers and data samplesDisplaced trk + lepton (e, )IP(trk) > 120m
Pt(lepton) > 4 GeV
Semileptonic modes
2-Track Trig.Pt(trk) > 2 GeV
IP(trk) > 100 m
Fully hadronic modes
Di-Muon (J/)Pt() > 1.5 GeV (CDF)
J/ modes down to low Pt(J/) (~ 0 GeV)
- CP violation
- Masses, lifetimes
- Quarkonia, rare decays
- High statistics lifetime
- Sample for tagging
studies, mixing
- BS mixing
- CP asymmetry in 2-body charmless decays
(New in CDF/Short term upgrade in D0)
(Conventional)
Primary Vertex
Secondary Vertex
d = impact parameter
BDecay Length
Lxy
Lxy 450m
PT(B) 5 GeV
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Sanity check with
known signals:
D0 and
Detector calibration:p scale & B-field
correction
Raw tracks
Add B scale correction
Tune missing material
Correct for material in GEANT
1S
2S
3S
MASS SCALE: MCDF = MPDG-M(Pt)
Use J/ to correct for B field and energy loss:
(scale)/scale ~ 0.02%
D0
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Mass measurementsCDF mass (only~20
pb-1)
B+ 5280.6 1.7 1.1 0.8
Bd5279.81 1.9 1.4 0.2
Bs5360.3 3.8 -2.1
(2S) 3686.43 0.54 0.9
CDF
PDGσ
Δ
Ds± - D± mass
differenceBoth D (KK)
m = 99.28 ± 0.43 ± 0.27MeV
PDG: 99.2 ± 0.5 MeV (CLEO2, E691)
Systematics dominated by background modeling
M(Bs) is already the second best in the world (after CDF RunI)
FIRST CDFII
PAPER
2.12.9
See A. Korn’s talk
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Background is subtracted
Conventional way to B: J/
L ~ 40 pb-1
75k J/
CDF triggers on stopped J/ : pt() 1.5 GeV/c, pt(J/) 0
CDF can measure cross section down to pT = 0 (first
at hadron collider)
(ppJ/; pT>0; ||<0.6) =
240 1 (stat) 35/28(syst) nb
See Y. Gotra’s Talk
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First step: Inclusive B J/X Lifetime
Estimate Estimate B B through through
)(
TT
xyBPFP
ML
MCMC
CDF July 2002 (18 pb-1): =1.5260.0340.035 ps
D0 March 2003 (40 pb-1): =1.5610.0240.074 ps
PDG 2002: = 1.674 0.018
D0 Run II Preliminary
B
D0 Run II Preliminary
J/
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B LifetimesHeavy Quark Expansionpredicts the lifetimes
for
different B hadron species
(Bc) << (b0) ~ (b)
< (B0) ~ (Bs) < (B-)
< (b-) < (b)
– (B+)/(B0) = 1.03-1.07
– (Bs)/(B0) = 1.00 + 0.01
– (b)/(B0) = 0.9-1.0
B+/B0 and Bs/B0 measurements agree with prediction
Small discrepancy for b
lifetimes
– LEP + CDF Run I
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Exclusive B J/KLifetime (1)
Use exclusively reconstructed B B+ J/ K+
B0 J/ K0* (K0* K)
Bs J/ ( KK)
bJ/ (p)
Simultaneous fitting of
MB: Extract signal fraction
ct: Extract the lifetime
CDF March 2003 (70 pb-1): (B+ )=1.570.070.02 ps
D0 March 2003 (40 pb-1): (B+ )=1.76 0.24 ps
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Exclusive B J/K lifetime (2)
(Bs Unique to Tevatron)
CDF Preliminary
B+ 1.57 0.07 0.02
(ps)
Bd1.42 0.09 0.02
(ps)
Bs1.26 0.2 0.02
(ps)
Systemat. & statist. errors already @ Run I level
Use control channels: Bu J/ K+
and Bd J/ K0*
Measurement limited only by statistics
Important for simultaneous measurement
)τ(B)τ(B
d
s
)τ(B)τ(B
d
s
)τ(B)τ(B
d
= 0.89 0.15
= 1.11 0.09 c, [cm]See K. Anikeev’s Talk
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CDF: largest fully reconstructedsample in the world: 74 11 evts Yield/Lumi = 2 x RunI
CP asymmetry measures the weak phase of Vts (angle s = 2s )Expected to be very small: sin(2s ) O() 0.03Complicated analysis: requires xs and angular analysis to disentangle CP even/odd final statesCDF reach : sin(2 s )0.1 with 2fb–1 (0.03-0.06 with 10fb–1)
If asymmetry observed with 2fb–1 signal for NEW Physics
We also want to measure the lifetime difference: s = BsH- Bs
L
Current limit (LEP): s / s <0.31 (S.M.: = 0.05 - 0.20)
Physics with B0s J/
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More about BJ/ signals
0bJ/ Br.Ratio and Lifetime meas. in
progress (see T. Yamashita, R. Madrak’s Talk)
CDF
D0
B0J/K0s
CDF~220 events
0bJ/
First steps towards sin(2)
Measurement
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B+/B0 from lepton+displaced track
CDF: high statistics semileptonic B samplesExcellent calibration samples for B+/B0 lifetime,tagging and B0 mixing BlD0X (D0K): ~10,000 eventsBlD*+X (D*+D0): ~1,500 eventsBlD+X (D+K): ~5,000 events
Run II yieldssignificantly larger,
lower lepton pt threshold possible
thanks to i.ptrigger
CDF CDF CDF
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Yield/Lumi ~ Run I x 3 S/N ~ Run I x 2
BS from lepton + displaced track
HIGH STATISTICS SAMPLE:
• Inclusive lifetime:
• Mixing (moderate xs):
good S/N, limited time resolution: back-up sample
Bs Dsl [] l [[KK] ]l ONLY @ Tevatron
Efficiency vs c
MC
AR
BIT
RA
RY
UN
ITS
Systematics of trigger bias
)τ(B)τ(B
d
s
385 22 Ds
(muon only)
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b from lepton+displaced track
• Branching Ratio
• Measure
Q2 = m(l)
important for theory
Experimental challenge:
disentangle from decays through excited baryons
b cl [pK] l
Yield/Lumi = 4 x RunI
S/N ~ 2 x Run I
2dQdΓ
Γ1
Time of flight
dE/dx +
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Physics with the hadronic trigger
Reconstructed large (0.5M) D mesons:D K, D0 K, D* D0, Ds D0 KK, D0 See K. Stenson’s (Charm Physics review), C. Chen (D x-section), S. Vallecorsa (D Cabibbo supp. decays), M. Campanelli (D orb. excited states) talks for CDF Charm results
D’s from Primary Vertex have d 0
Direct Charm
D0K 86.5 0.4 %
(stat)
D*D0 87.6 1.1 % (stat)
DK 89.1 0.4 %
(stat)
Ds 72.4 3.4 % (stat)
B fraction 10 - 20
%
D mesons I.P. (d) distribution
D
d(D)
D
B
CDF: open access to fully hadronic D and B signals
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Ingredients for B0s mixing
Nunmix(t) – Nmix(t)
Nunmix(t) + Nmix(t)= Dcos(mst)Amix(t) =
1. Reconstruct the final state (use fully rec. B0s → D-
s
π+(3π))with good S/B (thanks to precise tracking, vertexing, PID)
60 fs (SVX II detector)45 fs (also Layer 00 is used)
3. Identify the flavor of Bs at production: B-flavor tagging algorithms
2. Measure proper decay time: ; = PT(B) / M(B) c = Lxy
Error on B momentum, ~ 15% (semileptonic)negligible (~ 0.5%) forfully reconstructed final states
Current limit:
ms 14.4 ps-1
ms/md
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First steps towards B0s mixing in
CDF Bs Ds
(*) [] [[KK] ]
Fully reconstructed
Bs is consistent with
Bd D control sample
Collect more data and understand tagging
See S. DaRonco’s Talk
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B Flavor Tagging
OST (opposite side tagging): B’s produced in pairs measure flavor of opposite B
“Identify the flavor of B at production”
JETQ: sign of the weighted average charge of opposite B-JetSLT: identify the soft lepton from semileptonic decay of opposite BSST (same side tagging):
B0 (B0) is likely to be accompanied close by a + ()
Search for the track with minimum PTREL
Figure of merit:
= efficiency ;
Effective size of sample is reduced by D2
D = “Dilution” = 1 – 2Pmistag
D2 “tagging effectiveness” 2%
bd
du
u
B0
+
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NEW in CDF: “Kaon b-taggers”• Exploit K/ separation of new TOF
• Well suited for strange B mesons
Same Side K: a B0s (B0
s) is likely to be accompanied close by a K+ (K) from fragmentation
bs
su
u
B0s
K+
Jet charge tag Muon tag
63.0 3.6 %
= 8.3 1.9%
D=15.8 8.3 % D=44.4 21.1 %
2.4 1.7% 3.3 1.8 %
D0 Run II Preliminary
For CDF studies see A. Ratikin and T. Moulik’s Talks
Opposite Side K: due to bcs it is more likely that a B meson contains in final state a K than a K+ to identify a B0
s look for a K from the decay of the opposite B
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Strategy for disentangling channels:- Invariant mass shape (M ~25 MeV)- Kinematical variables- Particle Identification - Oscillation of CP asymmetry
300 events in 65 pb-1 of CDF Hadronic Trigger data with very good S/B
B0 h+h- is a mixture of
Bd; BdKBsKBsKK
Physics with B0 h+h-
Can soon perform interesting measurements:• Relative B. Ratios: Bd /; Bs KK/K• Direct CP asymmetries in Bd Kself tagging)• CP asymmetries in Bd (with b-tagging)
Later on: CKM angle
CDF II simulation
—sumBdKBsKK
Bd
BsK
( inv.mass)
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Use K/ separation dE/dx
1.16
Disentangling the B0h+h-
contributionsUse M vs (1-p1/p2)q1
See M. Morello’s talk
B0d B0
d K- B0d K+
B0s K+ B0
s K-B0s KK
Expected fraction res. (MC 65 pb-1)B0
d K(0.6): 0.062 (stat)
B0 d(0.15): 0.056 (stat)
B0sKK(0.2): 0.045 (stat)
B0 sK(0.05): 0.036 (stat)
ACP(B0d
K): 0.14 (PDG-2002: 0.06)
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Angle from B0h+h-
B0 + has two (comparable) decay amplitudes:
Tree Penguin
b
d
W+u
d
u
+
B0 d
ACP(t) = ACP dir cos(md t) + ACP
mix sin(md t)
ACPdir, ACP
mix functions of , , d, (d ei P / T decay amplitude)
direct CP CP from mixing alone
R. Fleischer (PLB 459 (1999) 306): Assume U-spin symmetry (d s)Similar relation holds for Bs K+K (md replaced by ms)The 4 asymmetries can be expressed as function of , and P/T amplitude ratio
Parameters can be extracted from fit of meas. of ACP(t) for Bd and BsKK
d
b W+
u
+
B0 u,c,t
d
d
u
(SU(3) breaking effects)Expected (2fb-1) accuracy: () = ±10(stat) ±3(syst)
g
ms/md
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Hadronic b c signal
• Measure mass, lifetime, polarization
• Precise Lifetime
Discrepancy with theory:Is it valid for baryons ?
b c [pK]
Largest fully rec. hadronic channel
)τ(B)τ(Λ
0b
NO PID YET
pK Mass [GeV]
pK Mass [GeV]
See Y. Li’s Talk
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Conclusions The upgraded CDF/D0 detectors are taking new data Great B physics potential, we have results on:
- Masses, lifetimes in the BJ/K exclusive channels and production cross sections- New impact parameter trigger (CDF-only): huge/clean semileptonic/all hadronic B signals (and also Charm):
- Large and clean BlDX reconstructed in CDF (excellent for lifetime, tagging and md
meas.)
- B0s → D-
s π+: first ingredient towards ms
- B0h+h-: important results awaiting on our
way to (B0
sKK, CP in B0dK)
Lots of Beauty (and Charm) at the Tevatron
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Backup Slides
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CDF Integrated Luminosity
Mar 02
commissioning
Data used for Today’s results Mar 02 – Jan 03
130 pb-1 (delivered)
100 pb-1 (to tape)
B/Charm: ~ 70 pb-1
Jan 03
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B physics prospects(with 2fb-1)
Bs mixing: Bs →Dsπ(Ds3π) (xs up to 60, with xd meas. one side of U.T.)
Angle : B0→ J/ψ Ks (refine Run1 meas. up to (sen2) 0.05)
CP violation, angle γ : B0→ ππ(πK), Bs → KK(Kπ)
Angle s and s/ s : Bs→ J/ψ (probe for New Physics)
Precise Lifetimes, Masses, BR for all B-hadrons: Bs, Bc, Λb … (CDF observed: Bc → J/ψ e(). Now hadronic channels Bc → Bs X can be explored)
HF cross sections (beauty and charm)
Stringent tests of SM … or evidence for new physics !!
Both competitive and complementary to B -factories
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Sin(2) in B0J/Ks
N(B0)(t) - N(B0)(t)
N(B0)(t) + N(B0)(t)=Dsin(2)sinmd
tACP(t) =
N(J/ Ks) from scaling Run I data:• x 20 luminosity
8,000• x 1.25 tracks at L1 trigger 10,000• x 2 muon acceptance 20,000• Trigger on J/ e+e + 10,000
In Run1 measured:
sin(2)=0.79±0.39±0.16
B0 J/ Ks ; J/
(400 events)(+60 B0 (2S) Ks)
sin(2)=0.91±0.32±0.18
Combined D2: from 6.3% to 9.1% (Kaon b-tag)
Same S/B = 1
Expect: s(sin2b) 0.05
With 2fb-1 can refine this measurementAlthough: no way to compete with B-Factories !
)) (2 sin( S B
ND1
2
1Stat. Error:
Systematic ~ 0.5xStatistical
(scales with control sample statistics)
ms/md
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Tevatron Performance
July ‘01
Now
Tevatron operations • Startup slow, but progress steady !
• Now: L ~3.5 x 1031 cm-2s-1
integrating ~ 6. pb-1/week• … still factor 2-3 below planned valuesadditional improvements (~10-20%) expected from Jan. 3weeks shutdownCDF operations
• Commissioning: Summer 2001• Physics data since February 2002• Running with >90% Silicon integrated
since July 2002
Initial Luminosity3.8 x 1031
110 pb -1
July ‘02
On-tape Luminosity
Luminosity (on-tape): ~20pb-1 until June (analyses in this talk) Additional 90pb-1 July – December Reach 300- 400 pb-1 by October 2003
Feb ‘02
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Quadrant of CDF II Tracker
LAYER 00: 1 layer of radiation-hard silicon at very small radius (1.5 cm) (achievable: 45 fs proper time resolution in Bs Ds )
COT: large radius (1.4 m) Drift C.
• 96 layers, 100ns drift time • Precise PT above 400 MeV/c
• Precise 3D tracking in ||<1
(1/PT) ~ 0.1%GeV –1; (hit)~150m
• dE/dx info provides 1 sigma K/ separation above 2 GeV
SVX-II + ISL: 6 (7) layers of double-side silicon (3cm < R < 30cm)• Standalone 3D tracking up to ||= 2• Very good I.P. resolution: ~30m (~20 m with Layer00)
TOF: 100ps resolution, 2 sigma K/ separation for tracks below 1.6 GeV/c (significant improvement of Bs flavor tag effectiveness)
TIME OF FLIGHT
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CDF II Trigger System3 levels : 5 MHz (pp rate) 50 Hz (disk/tape storage rate) almost no dead time (< 10%)
XFT: “EXtremely Fast Tracker” 2D COT track reconstruction at Level 1
• PT res. pT/p2T = 2% (GeV-1)
• azimuthal angle res. = 8 mrad
SVT: “Silicon Vertex Tracker” precise 2D Silicon+XFT tracking at Level 2
• impact parameter res. d = 35 m
Offline accuracy !!
CAL COT MUON SVX CES
XFT XCES
XTRP
SVTL2
CAL
L1CAL
GLOBALL1
L1MUON
L1TRACK
GLOBALLEVEL 2 TSI/CLK
CDF II can trigger on secondary vertices !! Select large B,D samples !!
Matched to L1 ele. and muonsenhanced J/ samples
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SVT: Triggering on impact parameters
d
beam spot
COT track ( 2 parameters) 5 SVX coordinates
Impact Parameter (transverse projection)
• Combines COT tracks (from XFT) with Silicon Hits (via patternmatching) • Fits track parameters in the transverse plane (d, , PT) with offline res.• All this in ~15s !• Allows triggering on displaced impact parameters/vertices• CDF becomes a beauty/charm factory
~150 VME boards
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B triggers: conventional
Suffer of low BR and not fully rec. final state
Need specialized triggers(bb) / (pp) 10-3
CDF Run1, lepton-based triggers:
Di-leptons (, PT 2 GeV/c): B J/ X, J/ Single high PT lepton ( 8 GeV/c): B l D X
Now enhanced, thanks to XFT (precise tracking at L1) :• Reduced (21.5 GeV/c) and more effective PT thresholds • Increased muon and electron coverage• Also J/ ee
Nevertheless, many important measurements by CDF 1: B0
d mixing, sin(2), B lifetimes, Bc observation, …
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XFT performance
XFT: L1 trigger on tracks better than design resolution
pT/p2T = 1.65% (GeV-1)
= 5.1 mrad
XFT track
Offlinetrack
Efficiency curve: XFT threshold at PT=1.5 GeV/c
= 96.1 ± 0.1 % (L1 trigger)
53.000 J/
11 pb-
1
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SVT performance
D0 K used as online monitor of the hadronic SVT triggers
I.P. resolution as planned
d = 48 m = 35 m 33 m
Efficiency
80%
90%
soon
transverse beam size
intrinsic
S/B 1
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TOF performance TOF resolution (110ps)
within 10% of design value
with TOF PID
S/N = 1/40
S/N = 1/2.5
Background reduction in KK:Low PT (< 1.5 GeV/c) track pairsbefore and after a cut on TOF kaon probabilityx20 bkg reduction, 80% signal efficiency
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CDF J/cross section
0<pt<0.25
GeV 5.0<pt<5.5 GeV10.0<pt<12.0 GeV
(ppJ/; pT>0; ||<0.6) =240 1 (stat) 35/28(syst) nb
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Lots of charm from hadronic triggers:
Foresee a quite interesting charm physics program:• D cross sections, • CP asymmetries and Mixing in D sector, Rare decays, …
56320490
K mass
D0 K
KK mass mass
D0 KK D0
5670180 2020110
(DKK)/(DK) = 11.17 0.48(stat) 0.98 (syst) %(D )/(DK) = 3.37 0.20(stat) 0.16(syst) %
Relative Br. Fractions of Cabibbo suppressed D0 decays :
Already competitivewith CLEO2 results(10fb-1 @ (4S))
!!!!!
With ~10 pbWith ~10 pb-1-1 of “hadronic trigger” data: of “hadronic trigger” data:
O(107) fully reconstructed decays in 2fb-1
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B0s mixing: expectations with
2fb-1
Signal: 20K ( only) - 75K (all) events• with SVT hadronic trigger
• BR (Ds ) = 0.3 % ; BR (Ds ) = 0.8 %
Resolution: (c) = 45 fs (with Layer00)
D2 = 11.3% (with TOF)
S/B: 0.5-2 (based on CDF I data)
5 sensitivity up to:
Xs = 63 (S/B = 2/1)
Xs = 53 (S/B = 1/2)
S.M. allowed range: 20. < Xs < 35.
Can do a precise measurement… or evidence for new physics !
xs = ms(B0s)Bs Ds, Ds
Ds , K*K,
2( m )22
1 1 S B( x )
N D Ss t
s e
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Projections for xs reach with 2fb-1
Xs = 42-63
Optimistic: S/B =2/1 Conservative: S/B =1/2
MC simulation: accounts also for SVT cuts on proper time acceptance,non-Gaussian tails in proper time resolution function
Xs = 32-53