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
“search for higgs at the lhc in vector boson fusion”

2. Outline Motivation for Higgs Higgs Physics The Higgs ->   Signal
The Large Hadron Collider
The Compact Muon Solenoid Detector
Monte Carlo
Event Selection
Simulation Results
Future Plans
(Add event selection, just “Monte Carlo”, “Simulation Results” -- done)
How to look for higgs, lhc, simulating detector

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)
Emphasize that the whole standard model depends on the higgs (but we haven’t seen it), maybe clarify “depend on higgs”
One particle we haven’t seen yet: Higgs!
Gives mass to W, Z
Higgs coupling strength determines masses of other massive particles
Standard Model depends on Higgs!

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.
Look in h+m for material for this one slide -- chapter 14 headings! Combine em and weak; weak bosons need mass -- photon massless; higgs mechanism does that. Implies 1 scalar particle, not found yet -- higgs. We’d better find higgs! Why do we really believe it’s here? Predictive power of standard model!
Put this slide into bullets

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)
Gg fusion picture -- reverse arrow in t loop!
Plot from hep-ph/ “QCD Effects in Higgs Physics”, M. Spira.
Gluon-gluon fusion high rate, but high QCD background
Vector boson fusion lower rate, but lower background

6. Higgs decays Low Higgs mass: Higher Higgs mass:
Bb~ most prominent signal below ~100 GeV, tau is second
Tau jets easier to identify than b jets
Higher Higgs mass:
WW most prominent decay
ZZ second
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?
Plot from hep-ph/ “QCD Effects in Higgs Physics”, M. Spira.
(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)
Most prominent “decay”; also say WW dominates for higher higgs mass, ZZ second
Next slide -- show latest prediction of where we think it is (parabola graph)

7. Vector Boson Fusion to  
H->
Relatively high rate for low-mass Higgs
Distinct signal
VBF
Relatively high rate
Identification of Higgs production via quark products in final state
qqH->: Good potential for discovery!
Plots from hep-ph/ “QCD Effects in Higgs Physics”, M. Spira.
(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!)
Overlay “regions of interest” on graphs to show where we think it is
(“via tagged jets” --> “final state” or “quark”)
Get rid of abbreviations in title (and others)

8. LEP Results SHOULD THIS GO BEFORE PREVIOUS SLIDE?????
Better quality picture?
(What exactly is this plot and what does it mean?)
Where does the plot come from? Lep ew working grp summary paper

9. Large Hadron Collider 27-kilometer ring near Geneva, Switzerland
Proton-proton collisions
Center of mass energy 14 TeV
Design luminosity 1034 cm-2 s-1
Physics in 2008
NEED LUMINOSITY DEF, etc??

10. LHC Magnets Superconducting NbTi magnets require T = 1.9K
1232 dipoles bend proton beam around ring, B = 8T
Quadrupoles focus beam
Field diagram for dipoles in back-up slides (currently)
(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
Know what quadrupoles look like

11. LHC Startup Stage 1 Stage 2 Stage 3 Stage 4 Starts in 2008
Initial commissioning
43x43156x156, 3x1010/bunch
L=3x x1031
Starts in 2008
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

12. Experiments at the LHC ATLAS and CMS : pp, general purpose Circle cms
(Put a white box over “works”)
ATLAS and CMS :
pp, general purpose

13. Compact Muon Solenoid (CMS)
CALORIMETERS
ECAL
HCAL
76k scintillating
PbWO4 crystals
Plastic scintillator/brass
sandwich
IRON YOKE
MUON
ENDCAPS
Cathode Strip Chambers (CSC)
Resistive Plate Chambers (RPC)
TRACKER
Picture at with more info: length, height, etc.
Total weight: 12,500 T <-- IS THIS METRIC TONNES OR WHAT???
Overall diameter: 15.0 m
Overall length: 21.5 m
Magnetic field: 4 Tesla
Have sth on this slide with def of eta/pseudorapidity??
Pixels Silicon Microstrips
210 m2 of silicon sensors
9.6M channels
Weight: 12,500 T
Diameter: 15.0 m
Length: 21.5 m
Superconducting Coil, 4 Tesla
MUON BARREL
Drift Tube
Resistive Plate
Chambers (DT)
Chambers (RPC)

14. 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

15. 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:
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

16. Electromagnetic Calorimeter
ECAL measures e/ energy and position to || < 3
80,000+ lead tungstate (PbWO4) crystals
High density
Small Moliere radius (2.19 cm) compares to 2.2 cm crystal size
Resolution:
 x  = x barrel, increases to 0.05 x 0.05 in endcap
(PbWO4) radiation resistant
Ecal crystal picture in back-up slide
How many radiation lengths? Shower max at 4 rad.leng. Interaction length same thing but with hadrons and nuclear interactions

17. 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
What about note 2006/44 p. 8 and 9 for hf resolution stuff?? Not at all like regular hcal resolution!
HCAL COPPER OR BRASS???

18. Hadronic Calorimeter
HCAL samples showers to measure their energy/position
HB -- central region
Brass/scintillator layers
Eta coverage || < 3
Resolution:
HF -- forward region
Steel plates/quartz fibers
Eta coverage to 5
Resolution:
115%, hcal cartridge brass. Hf 90%/E + same const. Hf: hybrid photodiode
HCAL: 50 mm THICK copper (brass?) plates and 4 mm THICK scintillator tiles -- what’s scintillator material??
HF: Steel and quartz chosen because good at withstanding high radiation
What about note 2006/44 p. 8 and 9 for hf resolution stuff?? Not at all like regular hcal resolution!
HCAL COPPER OR BRASS???
WE HAVEN’T DEFINED JETS YET, HAVE WE???
Just “HCAL measures jet energy/position” maybe? “shower” instead of “jet”? “hadronic shower”?
HF PICTURE TO FILL IN EMPTY SPACE!
Brass/scintillator sampling calorimeter
“HCAL samples particle showers to determine their energy/position” <-- how necessary is “particle”? (won’t fit in one line otherwise)
Total thickness of hb and hob is 11 absorption lengths

19. 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

20. Trigger
GO SEE WESLEY
Wesley’s j-term lecture has better stuff

21. Current CMS Progress
Many components being currently lowered into experimental cavern or already lowered -- including some worked on by Wisconsin.
Picture shows one of the iron yokes -- which one?
Also, what parts exactly by UW are in there already, or will be very soon?
WORDING!!!

22. Seeing Particles in CMS
Lead Tungstate
(Put what cal’s, etc are made of on this slide)
Brass/Scintillator

23. Finding the Higgs
Feynman diagram of higgs production with stuff coming out: H-> tau tau, taus decay hadr or lept -- get 4-pt interaction feynman diagram. Tag quarks: say “become jets -- see next slide”

24. 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

25. Level-1 Trigger Flowchart diagram 441 DAQ tdr II pic
Appendix F or G (depending on version of TDR): “Summary of Level-1 Trigger”

26. Calorimeter Trigger Geometry
Need all the text stuff?

27. 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?
Before this: l1 trigger overview, tower geometry slide
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

28. 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?
This is part of event reconstruction -- need some sort of event reco
Prev slide: trigering on electrons, jets, and taus
This: reconstructing jets
Need: reconstrucitn electrons
After: reconstructing taus

29. Electron Reconstruction
Create “super-clusters” from clusters of energy deposits using Level-1 calorimeter information
Must be in area specified by Level-1 trigger
Must have ET greater than some threshold
Match super-clusters to hits in pixel detector
Electrons create a hit
Photons do not!
Combine with full tracking information
Track seeded with pixel hit
Final cuts made to isolate electrons
DAQ TDR II part 4 (also for tau reconstruction), look in dasu’s 2005 aspen trigger talk, reconstruction stuff also in phys tdr vol. 1(p. 365 for electrons)

30. Tau Reconstruction Reconstruct “tau jet” from calorimeter candidate
Highest-pT track within cone of radius Rm is leading signal track
Tracks within signal cone (radius Rs) having same vertex assumed to come from  decay
No other tracks from that vertex may be in cone of radius Ri
Diagram on p. 78 of dan green’s summer school talk. Originally from DAQ TDR (CERN/LHCC , CMS TDR 6.2, 15 Dec. 2002) p. 330, fig in sec [tau] identification with the pixel detector

31. 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.

32. Monte Carlos (MCs) Parton Level Hadron Level Model Detector Level
Simulated by PYTHIA
Hadron Level Model
Fragmentation Model (PYTHIA)
Detector Level
Detector simulation based on GEANT
Parton Level
Hadron Level
Detector Simulation
STOLEN FROM HOMER
Different picture -- non-ep?
For jets specificially!
“simulating physics”
Get rid of factorization scale -- lalso in picture
Get rid of qcd: under “Parton Level”: QCD Cross section
Cut out text box: Factorization: Long range interactions below certain scale absorbed into proton’s structure
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???

33. 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

34.  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?
All this material already previous

35. Event Selection
Startes with ~50,000 H-> events; no constraints on  decays. Higgs mass set to 130 GeV.
Cuts from PTDR are slides include all of them? (there are four slides’ worth!) Organized how?
PTDR cut summary table below (not all specifics included)
Get table from zeus slides
Need 1 or 2 slides on characteristics of background to make sense of cuts (“call it event selection”)
Put placeholders -- use the ones I know from the TDR, also the plots from there
Just look at the final states in the PTDR, go through cuts, explain what they do to the sample
Before this slide (table) need to say what all the backgrounds are

36. Plots
From Physics TDR:
Diff between qcd and ew tau tau bg

37. What next?

38. Conclusions

39. Extras

40. Tau decay
Tau decay
Require a “narrow” jet in the calorimetry. Require confirmation from the tracking, and isolation around the narrow jet.

41. H-> final states and triggers
Note: Here “jet” means energy deposit consistent with 
->jj (NOT actually a final state in PTDR study)
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

42. 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”

43. 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

44. 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

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

46. H->->+jet

47. H->->e+jet

48. Back-up slides
Put these back-up slides in a different powerpoint file

49. Dipole Magnet Field Diagram

50. ATLAS
ATLAS info

51. ECAL crystal ECAL lead tungstate crystal
Little object in picture: apd (avalanche photodiode) “battery”: vpt vacuum phototriode (better in high-radiation) in ee (like transistor but FAST).