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Fisica del b in CMSFisica del b in CMS
N. Magini Università & INFN Firenze
Parma, Parma, 19 Gennaio 200619 Gennaio 2006
Parma, 19/01/06Parma, 19/01/06 Fisica del B in CMSFisica del B in CMS N. MaginiN. Magini 2
The CMS detectorThe CMS detector
4 Tesla Solenoid4 Tesla SolenoidMuon system in return yokeMuon system in return yoke
Staged Scenario for start-up Staged Scenario for start-up 1. 3rd forward pixel disks missing 2. RPC up to || < 1.63. Single muon trigger up to || < 2.1, dimuon up to || < 2.4
ECALECAL & HCAL & HCAL inside solenoidinside solenoid
22 m long, 15 m diameter,22 m long, 15 m diameter, 14.000 ton Detector14.000 ton Detector
Tracker (Pixel + Silicon Microstrip)Tracker (Pixel + Silicon Microstrip) < 2.4< 2.4
Parma, 19/01/06Parma, 19/01/06 Fisica del B in CMSFisica del B in CMS N. MaginiN. Magini 3
B Physics at CMS B Physics at CMS
B-decays program B-decays program Inclusive b productionInclusive b production
CP violation CP violation
BB00ss Mixing Mixing
Rare decaysRare decays
BBcc
b production atb production at LHCLHCStarting luminosity Starting luminosity 10 1033 33 cmcm-2-2ss-1-1
0.5 mb 0.5 mb about about 0.5 x0.5 x 101066 b pairs/s b pairs/s
onlyonly 100 ev/s on tape 100 ev/s on tape for ALL interesting for ALL interesting physics channels physics channels
The trigger strategy is a great challengeThe trigger strategy is a great challenge
Parma, 19/01/06Parma, 19/01/06 Fisica del B in CMSFisica del B in CMS N. MaginiN. Magini 4
Inclusive b productionInclusive b production
bb differential cross sectionbb differential cross section(from b(from b X) X)
Expected CMS reach – up to pExpected CMS reach – up to pTT ~ 1 TeV/c~ 1 TeV/c
bb X rate X rate extracted from extracted from
total total rate rate fitting the fitting the
distributions of distributions of p pTT w.r.t. the w.r.t. the closest B jetclosest B jet
bcudsg
120 < pT < 170 GeV/c
Valery Andreev, David B. Cline, Stan Otwinowski
Parma, 19/01/06Parma, 19/01/06 Fisica del B in CMSFisica del B in CMS N. MaginiN. Magini 5
Benchmark channelsBenchmark channels
Decays into muons (di-muon Lvl-1 Trigger) :
• BS J/ KK (Bs mixing, CPV)
• BS(d) (rare decays)
Fully hadronic channel(Single muon Lvl-1 Trigger from other B + X
) :
• BS DS (KK) (Bs mixing)
Parma, 19/01/06Parma, 19/01/06 Fisica del B in CMSFisica del B in CMS N. MaginiN. Magini 6
ss
ssBB00
ss
BB00ss
BB00s s oscillationsoscillations
BBss are too heavy to be produced at are too heavy to be produced at B factories B factories studied at hadron collidersstudied at hadron collidersStandard Model predictions
mS < 22.2 x 1012 s-1 @ 95% CL , ssssPDG Experimental limits @ 95% CL
mS > 14.4 x 1012 s-1, ssssLatest result by CDFssss
D0ssss
ss
Parma, 19/01/06Parma, 19/01/06 Fisica del B in CMSFisica del B in CMS N. MaginiN. Magini 7
BBs s J/ J/ BR(BsJ/ )=(9.3±3.3)x10-4
J/ℓ+ℓ- (BR≈6%)K+K- (BR≈49%)
CP violation weak phase s= 2= 22
SM predicts s ~ O(0.03)
Main ongoing activity: benchmark channel for B Physics studies in CMS Physics TDR – Vol. 2
Angular distributions of decay products depend on s, s, Ms (B0
s mixing) and s (CP Violation)
ℓ+
ℓ-
K+
K-
p p
N. Magini, V. Ciulli, T. Speer, K. Prokofiev, L. Wilke, S. Shulga, T. IlichevaN. Magini, V. Ciulli, T. Speer, K. Prokofiev, L. Wilke, S. Shulga, T. Ilicheva
Parma, 19/01/06Parma, 19/01/06 Fisica del B in CMSFisica del B in CMS N. MaginiN. Magini 8
Main backgroundsMain backgrounds
at LHC
– Signal B0s J/K+K- 167 fb
– Exclusive bkg BB00dd J/ J/ K* K* K 900 fb
– Inclusive backgrounds :– b b J/J/XX 51.4 nb– Prompt pp Prompt pp J/J/XX 310 nb
– In all samples : pT GeV/c
– In signal + Bd bkg : pT GeV/c
Parma, 19/01/06Parma, 19/01/06 Fisica del B in CMSFisica del B in CMS N. MaginiN. Magini 10
BB00ss J/ J/KK++KK--
Selection strategy
Trigger
L1 : double muon triggerL2 : regional J/reco with fast tracking
L3 : regional + B0s reco with fast
tracking
OfflineKinematic fitting
Optimization performed vs. Optimization performed vs. the following backgrounds:the following backgrounds:
Prompt pp Prompt pp J/J/XX
• Inclusive b Inclusive b J/J/XX•BB00
dd J/ J/ K* K*
Parma, 19/01/06Parma, 19/01/06 Fisica del B in CMSFisica del B in CMS N. MaginiN. Magini 12
CMS Trigger & DAQCMS Trigger & DAQ
Two level trigger: Lvl-1 and HLTTwo level trigger: Lvl-1 and HLT40 MHZ40 MHZ
50 kHz50 kHz
100 Hz100 Hz
HW
SW
4 DAQ slices at start-up 4 DAQ slices at start-up 50 kHZ 50 kHZ
Parma, 19/01/06Parma, 19/01/06 Fisica del B in CMSFisica del B in CMS N. MaginiN. Magini 13
Level 1 Muon Trigger ratesLevel 1 Muon Trigger rates
Low Lumi
< 2.1
16 kHz DAQ16 kHz DAQ3.6 kHz for 3.6 kHz for
14 ; 3,32.7+0.9=3.6 kHzW =90%Z =99%Bs=15%BBs s J/ J/ efficiency 33.3%
Lvl-1 thresholds Lvl-1 thresholds optimized for optimized for
discovery discovery physicsphysics
High - pHigh - pTT processes are processes are
selected selected
b-jets are b-jets are selected mainly selected mainly
byby1 and 2trigger trigger
Parma, 19/01/06Parma, 19/01/06 Fisica del B in CMSFisica del B in CMS N. MaginiN. Magini 14
Using the Tracker at HLTUsing the Tracker at HLT
Muon HLT stream optimized for high pT isolated muons use the Silicon Tracker instead to reconstruct the decay chain at HLT
HLT track reconstruction has to be fast but does not need to be global as the offline one, therefore it can be:– Regional
• Restricted to some phase-space region defined from external Lvl-1 information (e.g. a cone around muon/jet direction or the set of tracks coming from a vertex or above a PT threshold )
– Partial
• Stopped after a number of hits have been assigned to the track
– Conditional
• Stopped when enough resolution is reached or on other conditionFull tracker Full tracker
performanceperformance
ppTT
Parma, 19/01/06Parma, 19/01/06 Fisica del B in CMSFisica del B in CMS N. MaginiN. Magini 18
BBs s J/ J/ HLT L2 strategy
150 MeV/c2 around J/ mass
Transverse decay length resolution ~ 100 m
– 10 and LT/LT)> 3
Rate = 10 Hz, <t> ~ 190 ms~ 80% of L2 J/ are from b
Signal x 10Signal x 1033
b b J/ J/ X X
prompt J/prompt J/
Tracks reconstructed with 5 hits Tracks reconstructed with 5 hits around L1 around L1 muons - |muons - || < 0.15 , || < 0.15 , || |
< 0.5< 0.5
Parma, 19/01/06Parma, 19/01/06 Fisica del B in CMSFisica del B in CMS N. MaginiN. Magini 19
BBs s J/ J/ HLT L3 strategy
Regional tracking around J/ direction ||| < 0.9, || < 0.9, || < 0.9| < 0.9
HLT HLT HLT RateHLT Rate Events/10fbEvents/10fb-1-1
10.1%10.1% 0.05 Hz0.05 Hz 169000169000
mass mass 20 MeV/c 20 MeV/c22
BB00ss mass mass 190 MeV/c 190 MeV/c22
Parma, 19/01/06Parma, 19/01/06 Fisica del B in CMSFisica del B in CMS N. MaginiN. Magini 20
BBs s J/ J/ Offline selection strategy
• Combinatorial decay chain reconstruction• Kinematic fitting – application of constraints from decay
kinematics– J/ mass constraint
M(<12 MeV/c2,M(B0
s) < 67 MeV/c2
Parma, 19/01/06Parma, 19/01/06 Fisica del B in CMSFisica del B in CMS N. MaginiN. Magini 21
BBs s J/ J/
Proper time resolution
Parma, 19/01/06Parma, 19/01/06 Fisica del B in CMSFisica del B in CMS N. MaginiN. Magini 22
Event selectionEvent selection
Events selected per 10 fb-1
Estimated S/B ~ 6, but very limited statistics for backgrounds larger MC sample produced
Vertex pointing (cos > 0.9)m < 12 MeV/c2
m B0s < 67 MeV/c2
Parma, 19/01/06Parma, 19/01/06 Fisica del B in CMSFisica del B in CMS N. MaginiN. Magini 23
BBss J/ J/ AnalysisAnalysis
Two methods may be used to extract parameters of interest from angular distributions
– Unbinned maximum Likelihood fit
Parma, 19/01/06Parma, 19/01/06 Fisica del B in CMSFisica del B in CMS N. MaginiN. Magini 24
Angular moments methodAngular moments method
Time evolution is a function of the transversity amplitudes A0(t), A||(t), A(t) which contain the parameters of interest
Known functions of the three helicity angles 1,2, describing decay product kinematics
),,(
6
1
)(649
coscos),(2121
3
W ii
tidddd
t gb
A set of 6 weighting functions wi(1,2, ) is defined to separate the 6 bi(t) components
Parma, 19/01/06Parma, 19/01/06 Fisica del B in CMSFisica del B in CMS N. MaginiN. Magini 25
Angular moments methodAngular moments method
Statistical error with 64k generator level events
Sources of systematics:• Background contamination• Detector resolution
• effect shown to be negligible• Selection efficiency bias
Taking into account these effects, after 3 years at low luminosity (60 fb-1): error on
ΔΓs /Γs < 0.018
Parma, 19/01/06Parma, 19/01/06 Fisica del B in CMSFisica del B in CMS N. MaginiN. Magini 26
BBs(d)s(d)
• Lvl-1: 2 pT> 3 GeV/c, =15.2%
• HLT strategy:
– Select pixel seeds with pT > 4 GeV/c in - region around trigger ’s
– Conditional tracking:
- stop if pT<4 GeV/c @ 5σ or Nhit= 6 or σ(pT)/pT<0.02
- Bs reconstruction if only 2 track candidates with opposite charge in 150 MeV/c2 window
- Vertex20 and dr> 150 m
FCNC bs or bd only at loop-level in SM
BR(Bs) = (3.5±1.0)x10-9
MSSM enhancement (high tanβ) probe for new physics BR(Bsμμ)=3x10-6(tanβ/50)6(200 GeV/c2 / mA)4
U. Langenegger, A. Starodumov, P. TrübU. Langenegger, A. Starodumov, P. Trüb
Parma, 19/01/06Parma, 19/01/06 Fisica del B in CMSFisica del B in CMS N. MaginiN. Magini 27
BBss
Lvl-1 Lvl-1 HLT HLT Global Global Events / 10fbEvents / 10fb-1-1 Trigger RateTrigger Rate
15.2%15.2% 33.5%33.5% 5.1%5.1% 4747 <1.7Hz<1.7Hz
HLTHLTFull TrackerFull Tracker
Offline analysis (hep-ph/9907256) based on SV cuts (decay length Offline analysis (hep-ph/9907256) based on SV cuts (decay length and direction) + Tk/Calo Isolation: with and direction) + Tk/Calo Isolation: with SM BR=SM BR=3.5x103.5x10-9-9
10 fb10 fb-1 -1 7 signal events with < 1 background 7 signal events with < 1 background 55 observation with 30 fb observation with 30 fb-1-1
and analysis could be perfomed at high lumi tooand analysis could be perfomed at high lumi too
Mass resolution Mass resolution
= 50 = 50 MeV/cMeV/c22
= 74 = 74 MeV/cMeV/c22
Parma, 19/01/06Parma, 19/01/06 Fisica del B in CMSFisica del B in CMS N. MaginiN. Magini 29
BBss D Dss ((KK)KK)
P(b Bs) x Br(Bs DS K K ) ~ 5 x 10-5
• L1 1 trigger: pT > 14GeV/c , R=3.2 kHz
• HLT strategy:- pixel seeds in full acceptance and Primary Vertex- Partial tracking: 2 pixel and 1 strip hits - Topological cuts: R(KK)<0.3, R(<1.2, R(DS<2.0,
(BS,)>0.6
- Kinematical cuts: pT() > 2GeV/c, pT(DS) > 4 GeV/c, pT(BS) > 5 GeV/c
- Mass reconstruction: M<15 MeV/c2, MDs<75 MeV /c2, MBs<270 MeV/c2
- HLT efficiency 9%
BS-BS mixing: mS 14.4 ps-1 @ 95% CL
Parma, 19/01/06Parma, 19/01/06 Fisica del B in CMSFisica del B in CMS N. MaginiN. Magini 30
BBssDDss
BBss D Dss ((KK)KK)
Mass resolutions (only 3 hits are used)Mass resolutions (only 3 hits are used)
= 5 = 5 MeV/cMeV/c22
= 25 = 25 MeV/cMeV/c22
= 95 = 95 MeV /cMeV /c22
1 year low luminosity (20 fb1 year low luminosity (20 fb-1-1): ):
Lvl-1 1 kHz HLT 5 Hz 300-400 signal events Lvl-1 1 kHz HLT 5 Hz 300-400 signal events mmS S up to 20 up to 20 psps-1-1
1000 events are needed to test allowed SM range: mS 26 ps-1 @ 99%CL
Can not be run on full Lvl-1 2.7 kHz because of Can not be run on full Lvl-1 2.7 kHz because of large output rate: still room to improve large output rate: still room to improve
Parma, 19/01/06Parma, 19/01/06 Fisica del B in CMSFisica del B in CMS N. MaginiN. Magini 31
BBcc Physics Physics
Bc→J/ψµν (J/ψ→µµ)
258 evts after 1 fb258 evts after 1 fb-1-1
(+156 for e chan)(+156 for e chan)Bc→J/ψπ(J/ψ → µµ)
70 evts after 1 fb70 evts after 1 fb-1-1,,Mass RMS 76 MeVMass RMS 76 MeV
Decay length residual RMS 25 Decay length residual RMS 25 mm J.Q. Tao, G.M. Chen, C.H. Jiang
But still need to study bkg rejectionBut still need to study bkg rejection
M = 6287.0 ± 4.8 ± 1.1 MeV/cM = 6287.0 ± 4.8 ± 1.1 MeV/c22
= = 0.46+0.18−0.16 ± 0.03 ps
Parma, 19/01/06Parma, 19/01/06 Fisica del B in CMSFisica del B in CMS N. MaginiN. Magini 32
High Level Trigger table for low lumiHigh Level Trigger table for low lumi
TriggerTrigger Threshold Threshold
((=90-=90-95%) 95%) (GeV)(GeV)
Indiv.Indiv.
Rate Rate (Hz)(Hz)
CumCumul ul
raterate
(Hz)(Hz)
1e, 2e1e, 2e 29, 1729, 17 3434 3434
11, 2, 2 80, 80, (40*25)(40*25)
99 4343
11, 2, 2 19, 719, 7 2929 7272
11, 2, 2 86, 5986, 59 44 7676
Jet * Miss-Jet * Miss-EETT
180 * 123180 * 123 55 8181
1-jet, 3-jet, 1-jet, 3-jet, 4-jet4-jet
657, 247, 657, 247, 113113
99 8989
e * jet e * jet 19 * 5219 * 52 11 9090
Inclusive b-Inclusive b-jetsjets
237237 55 9595
CalibrationCalibration//
otherother
1010 105105
Where is B – Where is B – physics ?physics ?
Table optimized in DAQ-Table optimized in DAQ-TDR for discovery physicsTDR for discovery physics
Allocation of additional 50 Hz to “Standard” Physics ? In this case we would like to trigger on the full 10 Hz bJ/X rate
Bandwith for B-physics at LHC start-up will also depend on actual luminosity– Lower luminosity at
startup higher B-bandwith
From From DAQ-TDR (CERN/LHCC DAQ-TDR (CERN/LHCC
2002-26)2002-26)
Parma, 19/01/06Parma, 19/01/06 Fisica del B in CMSFisica del B in CMS N. MaginiN. Magini 33
ConclusionsConclusions
CMS is a competitive detector for B-physics, even if it is not designed specifically for it
Low-pT dimuon L1 Trigger and use of Fast Tracking at HLT are fundamental for B-decay selection
We should profit from LHC starting conditions: Low luminosity for a while lots of B physics
In only a few months: the Physics TDR Vol. 2 will address in deeper detail the CMS B-physics potential, with a chapter dedicated to the full analysis for the B0
s J/benchmarkchannel and sections on the other topics
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