fisica del b in cms n. magini università & infn firenze parma, 19 gennaio 2006

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


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


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


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)


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


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


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


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*


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


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


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


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


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


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


BBs s J/ J/

Proper time resolution


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


BBss J/ J/ AnalysisAnalysis

Two methods may be used to extract parameters of interest from angular distributions

– Unbinned maximum Likelihood fit


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


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


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


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


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


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


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


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)


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

fisica del b in cms n. magini università & infn firenze parma, 19 gennaio 2006

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