Experimental Summary Moriond QCD 2015

1. Experimental SummaryMoriond QCD 2015 Tom LeCompte High Energy Physics DivisionArgonne National Laboratory

2. Necessary preliminaries • Thanks to the organizers for the privilege of giving this talk! • Forty-five minutes is too short to really do justice to the wide variety of interesting experimental outcomes presented. I apologize to those whose material I under-represnted here: which is everybody.Any mistakes you see here are entirely my own • There is some conclusion and opinion in these slides. • I’ll try and label what is opinion

3. Themes of this Summary • At this time in particle physics, we are faced with two problems • The Higgs mass seems to be telling us there is new physics at around the TeV scale • The mass is too light to be heavy and too heavy to be light • Flavor, on the other hand, seems to be telling is there isn’t • We need to reconcile this • Most of the universe is composed of a kind of matter not present in the Standard Model • We need to (at least!) identify this • QCD is… • Necessary to answer the above questions (signals, backgrounds, initial conditions…) • A beautiful theory in its own right: a non-Abelian gauge theory in its purest form

4. Onto QCD…

5. Heavy Ions • Work shown by • Redmer Bertens • Frederike Bock • Bingchu Huang • Matt Lamont • Emilia Leogrande • Valery Pozdnyakov • Christof Roland • Shengquan Tuo • Julia Velovska • Kryztof Wozniak

6. Heavy Ion Cheat Sheet for HEP-ers The basic paradigm: • AA collisions = nucleus-nucleus collisions • Where you expect to see the Quark-Gluon Plasma (or other new physics) • pp collisions = proton-proton collisions • Reference data • pA collisions = proton-nucleus collisions • Reference data but with nuclear size and structure effects included • Centrality = the degree of overlap in collisions • Defined so that “10%” means “only 10% of the events are more central” • Defined so that “90%” means “only 90% of the events are more central” • So these are more peripheral • Unmeasurable – so people use a proxy like energy, multiplicity, etc. LHC just finished a p-Pb run, so lots of new pA results RAA – nuclear modification with respect to pp collisions RCP – nuclear modification comparing central to peripheral Cut me out and take me home!

7. Nuclei and PDFs • A proton in a nucleus is different than a free proton • Nuclei are made largely of neutrons – (15% more d-quarks tha u-quarks) • The same PDF probes used in pp can be used in pA (e.g. pPb) Proton direction These measurements should be very familiar to PDF fitters from the pp community.

8. What is Flow? • Flow is a collective motion of particles produced in collisions. • Implicitly assumes a large number of particles 2p dN/df = 1 + 2v1 cos(f) + 2v2 cos(2f) + 2v3 cos(3f) + … Directed Flow(similar to MET) Elliptical Flow Triangular Flow

9. The Flow Mystery in pA Collisions • pA collisions show evidence of hydrodynamic collective behavior, even though the system size is “small”. • Seen by multiple experiments using multiple techniques.

10. Possibly Related – the Ridge in pA No/small “ridge” in pp Large ridge in AA Why the large “ridge” in pA?

11. A Jet Mystery • It is common in RHI physics to make jets exclusively from charged particles • This is RpA for p-Pb collisions at CMS for charged particle jets and “regular” jets • Why is this different? Remember, RpA is a ratio.

12. Jet quenching A parton moving through a QGP dramatically loses energy, causing its jet to vanish. The world’s hottest substance is the world’s best refrigerator Quarkonium dissociation Proposed by Matsui and Satz (1986) In a QGP, the free color charges interfere with the q-qbar binding. The less bound the system, the easier it is to “melt”. For Lack of Time I encourage everyone to look at the proceedings

13. Heavy Ion Mini-Summary • The idea of “pA is a reference dataset – nothing interesting happens” may not be entirely correct • The flow measurements suggest some sort of hydrodynamic behavior even in “small” systems • Observed in multiple experiments • Improve the measurements and the effect persists • Oddly, Cu-Au data (a “large” system) suggests no QGP. • Is the existence of a “ridge” in pA evidence of the same phenomena? • The RpA results from CMS seems hard to explain • ALICE does not see this • The biggest difference between the experiments is their 7 TeV pp reference datasets • Possibly a clue? • Tremendous amount of work – one could easily spend the entire summary talk just on Heavy Ions.

14. QCD: Light Quarks, PDFs and EWK • Work shown by • Sabine Lammers • Daniel Johnson • Daniel Britzger • Stefano Carmada • Andreas Hafner • Milena Misheva • Peter Svoisky • Georgios Mavromanolakis • Brian Lindquist

15. QCD: Light Quarks, PDFs and EWK Work on using Belle and BaBar data to constrain HVP and LBL in muon magnetic moment experiments doesn’t really fit anywhere in this talk, but it is important. • Work shown by • Sabine Lammers • Daniel Johnson • Daniel Britzger • Stefano Carmada • Andreas Hafner • Milena Misheva • Peter Svoisky • Georgios Mavromanolakis • Brian Lindquist

16. “Extreme QCD” • Experiment is confronting theory at scales that we couldn’t imagine just a few years ago: • W/Z + 7 or more jets • V+Jets out to a TeV • Agreement is overall good, but this does expose some areas for improvement Not just interesting as a QCD measurement – these are key backgrounds to many searches.

17. A Puzzle • It’s not clear why the shape of the ratio is right, but the magnitude is off by 20% • Shouldn’t that only depend on the vector and axial charges of the quarks?

18. More “Extreme QCD” • LHCb provides a unique window into the forward region – it’s well-instrumented at high h. • Looking at W production gives access to very low x sea quarks. • The kinematics are such that you have one high-x and one low-x parton collide; the product of x’s has one in a well-measured region and one relatively unknown.

19. The Higgs and QCD “We are lucky to be at the LHC where gluon fusion dominates” – Bernhard Mitslberger • Among other things, the Higgs discovery gives us a new window to the gluon PDF • Theory is known to ~8% • You have two gluons in the initial state • Higgs + Njet production is a new place to test our calculational understanding This is a good place to mention HERAfitter: in my view, the importance of HERAfitter is that it lets us “crowdsource” PDF fitting – it lowers the barrier to people asking the question “how would/does this measurement affect the PDFs?”

20. Dibosons • Why should this be in Moriond QCD? • Because the experiments are starting to use hadronic W/Z’s decays, especially in cases where the jets are boosted. • Sensitivity to AGCs is largest at high pT – limiting yourself to resolved bosons really cuts into your sensitivity • A key thing to watch • We heard mostly about leptonic W/Z’s • Experiments are starting to use VBF production (ideas from the Higgs search) • Experiments are start to see triboson final states

21. QCD: Onia and Heavy Flavor • Work shown by • Ruslan Chistov • Martino Gagliardi • Tomasz Skwarnicki • Wenbiao Yan • Kai Zhu

22. Charmonium Spectrum Below threshold, things look like the positronium spectrum. With one major exception, things are well understood.

23. Charmonium Spectrum Above threshold, things are confusing – many unpredicted particles! Below threshold, things look like the positronium spectrum. With one major exception, things are well understood.

24. Where are all the c1’s coming from? • Corrected for branching fractions this tells us the c2/c1 ratio is ~1 • Other predictions • Spin-counting: 5/3 • Ratio of hadronic partial widths: ~25 • CSM: ~100 • The NRQCD curves rely on matrix elements fit from the data – they do not predict (although in some cases a measurement of one quantity allows calculation of another) This shows about twice as many c1 as c2. Pretty much everyone sees the same thing here.

25. The X(3872) • The first of the unpredicted “charmonium” states • Unequivocal – everyone who could see it did • There were even pre-observations in the record from FNAL E-705 • Spin-parity 1++ • with few assumptions, as we heard • Produced both promptly and from b-decays

26. The Z(3900) • The Z(3900) cannot be a q-qbar state: it has hidden charm and electric charge • We now know - for sure – that it has isospin: BES sees its neutral partner BESIII Preliminary

27. This Isn’t The First Time This might have been discussed at the 1st Moriond. (Then called the S* and the d) • There are two analogues in the strange sector: a0(980) and f0(980) • They are right at kaon threshold • The upper end of the resonance decays to KK • The lower end, below threshold, decays to pp or hp. • Evidence that they contain a lot of strangeness • The quantum numbers are 0++ • In the quark model, this means a 3P0 state. • How does this end up lighter than the f(1020), which is 3S1? • Why is it not near the 3P1,2 states? • How to explain the other 0++ states? • Unlikely to be a q-qbar state • I leave discussions about tetraquark vs. hadronic molecule to theorists. Opinion History doesn’t repeat itself, but it sometimes rhymes.

28. What Are these States? Opinion • I believe that the X and Z are fundamentally the same kind of particle. • That means not q-qbar • It’s not at all obvious to me that the models to the right truly differ, and are not simply idealizations to expand about. • The X(3872) has been argued to have a significant c-cbar admixture because: • 1. The prompt production rate at hadron colliders is large • 2. The significant radiative branching fractions.

29. What Are these States? (2) Opinion • I believe that the X and Z are fundamentally the same kind of particle. • That means not q-qbar • It’s not at all obvious to me that the models to the right truly differ, and are not simply idealizations to expand about. • The X(3872) has been argued to have a significant c-cbar admixture because: • 1. The prompt production rate at hadron colliders is large, and therefore the particle is “small” • 2. The significant radiative branching fractions. • I think #1 is a bad reason. The f0 has a production rate of 0.5-2.0x of the f(1020), and it is not small. • I think #2 is a good reason.

30. What About Bottom? • The X-analog in bottomonium is not seen by ATLAS • The X(3872)  J/y + 2p decay appears to be dominated by the isospin violating decay J/y + r • It would be good if LHCb, Belle or BESIII could confirm this by measuring the absence of p0p0 decays. • The proximity of the state to the DD* threshold makes this possible. • The X(3872) is in a very special place. The Xb doesn’t have to be. • And apparently isn’t.

31. Onia Mini-Summary Opinion • We see a fundamentally new kind of color singlet in particles like the X, Z and f0. • Near KK or DD* threshold, as appropriate. • This system contains a substantial admixture of 2 quarks and 2 antiquarks, although there is no consensus on the dynamics. Different particles may have different internal dynamics. • When possible, these particles have an admixture of q-qbar as well.

32. Searches for BSM Particles • Work shown by • Zach Marshall • Santiago Folgueras • H. Wells Wulsin • Enrique Kajomovitz • Oleg Ruchayskiy

33. The Bottom Line: No Sign of New Physics Either a generic SUSY limit plot, or the view downhill from a snowboarder in thick fog

34. Next Key Idea: Combinations • Combining multiple channels can slightly (~50 GeV) improve limits over a single channel. • This is much easier to do if planned for from the beginning – one can keep the subsamples orthogonal. • One only gains sensitivity beyond “use the best region” when multiple channels are comparably sensitive. • This is usually the middle of the rage

35. Next Key Idea: Filling The Holes • If the stop is just a bit heavier than the top, its signal can be hidden by the larger top signal. • Mass plots are no good. • One can look for an excess of spin-0 “top” pairs as opposed to the SM (where the top production goes through a gluon) • Similarly, one can design searches around Higgs decays or VBF Production • The VBF tools were developed for the Higgs search

36. It’s not all SUSY • There are well over 100 searches – no evidence for BSM physics. • To pick just one, CMS searches for a b* by b-tagging the q* dijet search: • This would be TeV physics involving flavour

37. Long-Lived or Weakly Interacting Particles • 27% of the p19MSSM models have long-lived particles • Presumably through near-degenerate LSP and NLSP • Experiments have developed a number of searches to go after these signatures • Unfortunately, without success • These are very difficult searches: the detectors were designed to do very different things. • Even things like luminosity become tricky • SAIL: a beam dump proposal to look for ultraweakly interacting particles

38. Dark Matter & Gravity • Work Shown By • Zeynep Demiragli • Greg Landsberg • Jim Hirschauer

39. The Basic Paradigm* * From the Greek “para”, plot and “digm”, overused. • The remarkable thing is that the same objects we are interested in for traditional collider searches (jets, leptons, missing ET) are the same ones we are interested in for DM searches. • In some sense, the collider experimenters get DM searches for “free”. • So far, no significant excesses have been observed.

40. The Problem To this? How do we go from this… • We are sure about the left side. The right is far more model dependent. Going from one to the other is, at best, tricky. (We heard a suggestion on moving forward)

41. The More General Issue • So long as we don’t see an excess, it doesn’t matter which model we use. • Once we see a signal, sorting it out will take some time. • If we saw a signal in the m(ttbar) channel, would we conclude “extra dimensions” or “topcolor Z-prime?”

42. Searches Summary • SUSY colored objects are excluded up to masses around 0.7-1.4 TeV • Electroweak SUSY has limits more like 0.2-0.7 TeV • Nothing new outside of SUSY seen either • Caveat: these limits often make assumptions about branching fractions • Especially “Simplified models” • Your favorite model might not be excluded! LHC Run 2 is about to start:

43. Flavor: Top • Work shown by • Fabrice Balli • Gabriele Benelli • Oleg Brandt • Yuan Chao • Matteo Cremonesi • Carlos Escobar

44. The |Vtb| Story (I) • Shortly after discovery, CDF made the measurement • This really measures |Vtb| relative to |Vts| and |Vtd| • This could be done before single top was expected to be visible. • Now we see new results from CDF:

45. The |Vtb| Story (II) • Now that single top production is visible, one can use it to measure |Vtb| without recourse to |Vts| and |Vtd|: s ~ |Vtb|2.

46. The |Vtb| Story (III) • The R measurement and the single top measurement have comparable uncertainties. • These are systematics limited • |Vtb| is far better known through unitarity than through any measurement, and the Higgs is telling us that there are only 3 sequential familes. • I predict soon that you will see these measurements turned around – using |Vtb| from unitarity and these measurements to control the b-tagging systematics, thereby improving searches. Opinion

47. The Top Asymmetry Story (I) • CDF reported a top forward-backward asymmetry that was 3s above the then-current QCD prediction. • Many exotic explanations (axigluons, etc.) were tendered. • We have new results from D0 and the LHC • The LHC asymmetry changes from front-back to marrow-wide

48. The Top Asymmetry Story (II) • Meanwhile, the theory asymmetry moved up. • The original measurement is now much less improbable, and today is just on the high side of an ensemble of measurements consistent with QCD. • Also, no effect is seen in bottom (granted, the physics is similar, not identical) • I think we can close the book on this. Opinion

49. The Top Mass (1) • Theorists would like experimenters to tell them the pole mass • What we actually measure is the W-b system invariant mass • These differ by ~1 GeV • It weighs about 173 GeV, with statistical uncertainties typically between 0.1 and 1 GeV, and systematics between 0.5 and 1.5 GeV. • This means it’s Yukawa coupling to the Higgs is 0.996 ± 0.004 • This is a clue, I am sure. • The statistical error will fall with the start of LHC Run 2, so the name of the game will switch to beating down systematics. • The dilepton, lepton+jets and all hadronic modes have different systematics, but they are still similar in approach • We saw some very different approaches, with wildly different systematics Opinion

50. The Top Mass (2) • In addition to the in-situ JES calibration, we heard about, One can use the cross-section (including +1 jet) to infer the pole mass. • One can also look at single top production • These are less sensitive than the other channels – but have systematics from very different sources. • Expect more of these alternative methods to appear in the future Opinion