1. VBF H-> in CMS at LHC
Jessica Leonard
University of Wisconsin - Madison
Preliminary Examination
WHO IS MY AUDIENCE??? 735 level
GET STUFF OFF OF CERN COMPUTERS BEFORE END OF WEEK!!! (until Jan. 8)
Wesley may be out of contact from dec jan. 6

2. Outline Motivation for Higgs The Higgs -> tau tau signal
The CMS detector
Monte Carlo
Event Selection
Simulation Results
Future plans
(Add event selection, just “Monte Carlo”, “Simulation Results” -- done)

3. Standard model One particle we haven’t seen yet: Higgs!
Black particles are those whose discovery resulted in a Nobel for a SLAC person (graphic from SLAC website)
SM explains interactions extremely well, but needs a higgs particle!
Deleted first point: How much detail should I get into, in terms of technical/theory stuff? (Lagrangians, whatever)
One particle we haven’t seen yet: Higgs!
Gives mass to W, Z

4. Higgs Physics
More info on Why We Need the Higgs?? Talk about: Higgs required to give mass to W and Z, also couples with most other particles -- coupling strength determines masses of those particles
Theory of Ew interactions but if give mass to w,z directly, violates gauge symmetries -- way out is spontaneous symm breaking. Result: leftover field -- higgs.
Have couple of extra slides on spont. Symm break. For backup: can explain it in words w/o equations, just about longitudinal deg free. Etc.

5. General Higgs Production
Slide before this maybe: higgs couples to all these particles, strength just param of theory, determines mass of part.
Why does cross-section go DOWN as H mass goes up? As H mass goes up, less probable to have gluon/whatever with enough energy to make higher mass particle (also all cross sections proportional to 1/s -- check)
(Just talk about processes, not final state. Talk about backgrounds later, after detector slides)
(Include all production processes pictured? Or just vbf and gg fusion (since dominant)? Not all possible diagrams, but these matter most)
(Focus on vbf because bg of gg fusion is high)
(Split slide)
(Here: various processes are interesting because of different background considerations)
Backgrounds for later: QCD 2 + 2/3j, EW 2 + 2j, t-tbar->WbWb, (b-bbar, Drell-Yan Z/* production,) W+jets
(Why is vbf interesting
Distinct signal: the outgoing quarks form two forward _isolated_ jets of opposite sign eta (can eliminate gluon-radiation jets) -- diagram? Don’t say too much yet on detection -- wait till detector stuff
Relatively high rate)
(Gg fusion has “high QCD background” -- jets)
(Vbf “maybe easier” to pick out of background, or “lower rate but lower background”)
(“General H prod” in title)
Gluon-gluon fusion high rate, but high QCD background
Vector boson fusion lower rate, but lower background

6. Higgs decays Bb~ most prominent signal below ~100 GeV, tau is second
Tau jets easier to identify than b jets
This slide: don’t need to focus on tau tau, just compare and contrast the various decays in terms of ease of seeing them
Next slide: why is VBF interesting (that should be FIRST time VBF is mentioned preferentially), combined with H -> tau tau
Also put both diagrams on that slide
Know: Why is there a dip?
(if REALLY want to, can read djouadi et al paper, but not necessary)
Also “Collider Physics” may have good stuff
Say why
2 tau jets in central detector is distinct signal -- maybe save this until after talk about detector!
VBF H-> Potential discovery channel with ~30 fb-1
Summarize stuff in notes on slide, but don’t put in too much. How much is too much? Don’t shrink the font!
Be prepared to answer why tau easier to id than b’s (put slide number with tau id stuff here, then can jump forward)

7. VBF to di- H-> VBF qqH->: Good potential for discovery!
Relatively high rate for low-mass Higgs
Distinct signal
VBF
Relatively high rate
Identification of Higgs production via tagged jets
qqH->: Good potential for discovery!
(Title: VBF to taus)
(Just say “good potential for discovery” without mentioning luminosity -- do that later: potential discovery channel with ~30 fb-1)
(Put blue feynman diagram from 2 slides ago into this slide, put arrow from “tagged jets” to outgoing quarks, circle quarks!)

8. LHC!
Pick placeholder, have magnet design, put some stuff from “LHC expts” slide on here, get vital stats: circumference, design lumi, energy, etc. Maybe have two slides: one with general stats, one with magnet stuff ???
(Maybe in bruce mellado’s slides -- look. Also smith’s talk: 2-in-1 design, both magnets in same cryostat but fields going in opposite directions (obviously). Didn’t see all that much useful in those talks.)
Go to cern.ch, then “for cern users”
Get summer school talk for magnet stuff
Picture from sept. 06 machine talk -- helpful?? And what’s all this stuff about dipoles, too? -- dipoles are what bend the beam. Quadrupoles focus them, etc. And what exactly is the RF stuff?
Superconducting magnets: niobium-titanium. Nice pictures on showing close-up, field diagram of dipoles
More general info at

9. LHC Startup Stage 1 Stage 2 Stage 3 Stage 4 Starts in 2007
Initial commissioning
43x43156x156, 3x1010/bunch
L=3x x1031
Starts in 2007
Shutdown
Year one (+) operation
Lower intensity/luminosity:
Event pileup
Electron cloud effects
Phase 1 collimators
Equipment restrictions
Partial Beam Dump
75 ns. bunch spacing (pileup)
Relaxed squeeze
Stage 2
75 ns operation
936x936, 3-4x1010/bunch
L= x1032
Stage 3
25 ns operation
2808x2808,3-5x1010/bunch
L=7x x1033
Need picture? Maybe change title? (“Luminosity Profile” was other one)
Put pic on prev slide bigger, has little magnet cartoon!
Know stuff on graphic (“cleaning” refers to momentum dispersion clean-up after collisions. -- how do they do it? CMS get cleanest beam!)
Long Shutdown
Phase 2 collimation
Full Beam Dump
Scrubbed
Full Squeeze
Stage 4
25 ns operation
Push to nominal per bunch
L=1034

10. Experiments at the LHC pp s = 14 TeV Ldesign = 1034 cm-2 s-1
Heavy ions (e.g. Pb-Pb at s ~ 1000 TeV)
ATLAS and CMS :
pp, general purpose
Maybe get rid of heavy ions, tell them I’ll focus on atlas and cms <--
27 Km ring
1232 dipoles B=8.3 T
(NbTi at 1.9 K)
First Collisions 2007
Physics in 2008

11. CMS detector (temp slide)
Components with slides already:
ECAL, HCAL, tracker, trigger, muon
Should other components have slides?
magnet, preshower, . . .

12. CMS Detector CALORIMETERS IRON YOKE MUON ENDCAPS TRACKER
ECAL
HCAL
76k scintillating
PbWO4 crystals
Plastic scintillator/brass
sandwich
IRON YOKE
MUON
ENDCAPS
Cathode Strip Chambers (CSC)
Resistive Plate Chambers (RPC)
TRACKER
Pixels Silicon Microstrips
210 m2 of silicon sensors
9.6M channels
Superconducting Coil, 4 Tesla
MUON BARREL
Drift Tube
Resistive Plate
Chambers (DT)
Chambers (RPC)

13. Tracker Tracker coverage extends to ||<2.5,
with maximum analyzing power in ||<1.6
Strips: reverse-bias diode
Silicon pixel detectors
used closest to the interaction
region
Silicon strip detector used in barrel and endcaps

14. ECAL >80,000 PbWO4 crystals high density
small Moliere radius (2.19 cm)
radiation resistant
Precise measurements of electron/photon energy and position
Each crystal 22mm x 22mm
 x  = x barrel, increases to 0.05 x 0.05 in endcap
Covers || < 3
Resolution:
Reduce words, increase font. Little object in picture: apd (avalanche photodiode) “battery”: vpt vacuum phototriode (better in high-radiation) in ee (like transistor but FAST). How many radiation lengths? Shower max at 4 rad.leng. Interaction length same thing but with hadrons and nuclear interactions

15. sample
80,000 PbWO4 crystals
high density
small Moliere radius (2.19 cm)
radiation resistant
Precise measurements of electron/photon energy and position
Each crystal 22mm x 22mm
 x  = x barrel, increases to 0.05 x 0.05 in endcap
Covers || < 3
Resolution:

16. HCAL HF extends coverage to || = 5
HCAL sampling calorimeter (barrel, endcap)
50 mm copper plates and 4 mm scintillator tiles
Measures energies and positions of central jets
Covers || < 3
Energy resolution:
HF extends coverage to || = 5
Steel plates and 300 m quartz fibers - withstand high radiation
Measures energies and positions of forward jets
Resolution:
115%, hcal cartridge brass. Hf 90%/E + same const. Hf: hybrid photodiode

17. Muon System
Saturated iron is 1.8T. Read about detectors in PDG. Muons > 3 GeV
Muon chambers identify muons and provide position information for track matching.
Drift tube chambers max area 4m x 2.5m cover barrel to ||=1.3
Cathode strip chambers in endcaps use wires and strips to measure r and , respectively. Coverage ||=0.9 to 2.4.
Resistive plate chambers capture avalanche charge on metal strips. Coverage ||<2.1

18. Trigger

19. Seeing Particles in CMS

20. Jets and Hadronization
Produced
Observed
Colored partons produced in hard scatter → “Parton level”
Colorless hadrons form through fragmentation → “Hadron level”
Collimated “spray” of real particles → Jets
Particle showers observed as energy deposits in detectors → “Detector level”
Add charged tracks mention
STOLEN FROM HOMER

21. Jet algorithm Info on how we find Jets and
Tau jets (identification requirements)
Before jet algo, WHAT ARE JETS? Also hadronization/fragmentation -- look in ZEUS people’s slides for examples! HOMER’S -- p. 23 for what are jets! (“Jets and Hadronization”)
Cone algorithm in those slides -- that’s the one we’re using -- HOMER’S pg. 25! (“Jet Finding: Cone Algorithm”) Don’t need to worry about kT? He has both.
Look for tau stuff! -- diagram on p. 78 of dan green’s summer school talk.

22. Calorimeter Trig. Algorithms
From Smith’s talk on cal electronics: NEED MORE THAN JUST CAL ALGOS??? Other subsystem/algorithm stuff??
Split? Need all this stuff? Ex. electron algorithm, etc?
Electron (Hit Tower + Max)
2-tower ET + Hit tower H/E
Hit tower 2x5-crystal strips >90% ET in 5x5 (Fine Grain)
Isolated Electron (3x3 Tower)
Quiet neighbors: all towers pass Fine Grain & H/E
One group of 5 EM ET < Thr.
Jet or t ET
12x12 trig. tower ET sliding in 4x4 steps w/central 4x4 ET > others
t: isolated narrow energy deposits
Energy spread outside t veto pattern sets veto
Jet  t if all 9 4x4 region t vetoes off

23. Jet Finding: Cone Algorithm
Maximize total ET of hadrons in cone of fixed size
Procedure:
Construct seeds (starting positions for cone)
Move cone around until ET in cone is maximized
Determine the merging of overlapping cones
Issues:
Overlapping cones
Seed , Energy threshold
Infrared unsafe
σ diverges as seed threshold → 0 R
STOLEN FROM HOMER
Find out more about this -- all stuff on slide necessary? What about “infrared unsafe” stuff?

24. Tau Triggering
From Dan Green’s summer school talk
Is this necessarily the same as finding an actual tau??
Require a “narrow” jet in the calorimetry. Require confirmation from the tracking, and isolation around the narrow jet.

25. Monte Carlos How do we know all our algorithms actually work?
Simulate the entire event, run it through the actual reconstruction. We know what the “right” answer is, so we can tell how well our reconstruction algorithms work.

26. Monte Carlos (MCs) Parton Level Hadron Level Model Detector Level
QCD Cross section
Hadron Level Model
Fragmentation Model
Detector Level
Detector simulation based on GEANT
Parton Level
Hadron Level
Detector Simulation
STOLEN FROM HOMER
Different picture -- non-ep?
Factorization: Long range interactions below certain scale absorbed into proton’s structure

27. Event Simulation
PYTHIA used to simulate events at parton-level and hadron-level.
FIND OUT MORE ABOUT DET-LEVEL SIM!
On pythia stuff, look at zeus people’s slides again -- lund string algo in homer’s talk for hadronization
-- p in Homer’s talk:
27: MC’s (including parton level, hadron level, det sim level)
28: Leading order MC’s
29: Lund string fragmentation
30: NLO MC’s
Need all of these???

28. Lund String Fragmentation
Used by MCs (or just “PYTHIA”) to describe hadronization and jet formation.
Color “string" stretched between q and q moving apart
Confinement with linearly increasing potential (1GeV/fm)
String breaks to form 2 color singlet strings, and so on., until only on mass-shell hadrons remain.
Cluster, as well, but not using
STOLEN FROM HOMER

29.  decays in detector
Higgs decays isotropically, so signature in general is in central detector (as opposed to forward)
 -> W* + , then
W* -> lepton + l OR
W* -> u + dbar e.g., more hadronization possible (single- and triple-prong events)
What do these look like in the detector?
lepton + l : electron (ECAL energy + track) or muon (muon chamber energy + track) + missing energy
hadrons : hadronic jet (HCAL energy + odd number of tracks), energy deposit must be small and contiguous --> tagged as “ jet”
Put feynman diagram on slide (W*)
Write dominant tau decays as in PDG, with branching fractions:
tau->e + nu_tau + nu_e
Should this slide go after jet reconstruction and tau algorithm slide?

30. Generate events
~50,000 H-> events generated; no constraints on  decays. Higgs mass set to 130 GeV.
Before other stuff

31. Cuts
Get table from zeus slides

32. Plots

33. What next?

34. Conclusions

35. Extras

36. H-> final states and triggers
Note: Here “jet” means energy deposit consistent with 
->jj
L1: single or double  (93, 66 GeV) ???
HLT: double  ???
->j
L1: single 
HLT: single ,  +  jet
->ej
L1: single isolated e, e +  jet
HLT: single isolated e, e +  jet
Need slides before this: monte carlo, hadronization -- how does a tau decay, jets -- what is regular jet vs. tau jet (sasha’s isolation cone pic, or in wesley’s desy talk from dec in 3 slides -- tau tagging, cms electron slide, L2 electron algo)-- why is tau so narrow?, etc
Add branching fractions for each decay, cumulative. BR for single-prong, triple-prong, etc
Mass of tau vs mass of higgs,
Picture of tau isolation cone thing in ptdr also daq tdr

37. H->->l++single-prong event offline selection
e and  candidates identified
Additional electron requirements:
E/p > 0.9
Tracker isolation
Hottest HCAL tower Et < 2 GeV
Highest-pt lepton candidate with pt > 15 GeV chosen
Lepton track identifies the other tracks of interest: within z = 0.2 cm at vertex
Define “single-pronged”

38. H->->l++single-prong event offline selection (cont.)
 candidates identified; jet formed around each and passed through t-tagging requirements
Require -jet charge opposite lepton charge
Hottest HCAL tower Et > 2 GeV if  coincides with electron candidate
-jet Et > 30 GeV

39. H->->l++single-prong event offline selection (cont.)
Jets are the 2 highest-Et jets with Et > 40 GeV, not including e and  candidate
Jets must be within || < 4.5, as well as having different signs in h
Require hj1j2 > 4.5, fj1j2 < 2.2, invariant mass Mj1j2 > 1 TeV
Require transverse mass of lepton-MisEt system < 40 GeV
Don’t need to say as much about their stuff

40. H->->2 1-prong
Backgrounds: ttbar, Drell-Yan Z/*, W+jet, Wt, QCD multi-jet

41. H->->+jet

42. H->->e+jet