Searching for Physics Beyond the Standard Model @ LHCb Mike - - PowerPoint PPT Presentation

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Searching for Physics Beyond the Standard Model @ LHCb Mike - - PowerPoint PPT Presentation

Feb 15, 2024 101 likes •504 views

Searching for Physics Beyond the Standard Model @ LHCb Mike Williams Department of Physics & Laboratory for Nuclear Science Massachusetts Institute of Technology Los Alamos National Lab September 24, 2013 LHCb Overview LHCb is performing

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Searching for Physics Beyond the Standard Model @ LHCb

Mike Williams Department of Physics & Laboratory for Nuclear Science Massachusetts Institute of Technology Los Alamos National Lab September 24, 2013

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SLIDE 2 Mike Williams LANL | 2

❖ : compare Br vs SM; ❖ Δφ : compare φ vs SM or from trees vs loops; ❖ Lorentz structure: compare angular distributions vs SM.

LHCb Overview

q ¯ b ¯ q b ???????? ??????? b ¯ q ¯ q q′ X ????? ¯ q b X LHCb is performing precise tests of the SM, and searching for physics beyond the SM, by studying rare and CP-violating decays of b and c hadrons. There are no tree-level FCNCs in the SM; FCNCs require loops. TeV-scale particles can make significant contributions here: LHCb is also doing W,Z,t,..., physics, studying exotic spectroscopy, searching for rare τ decays, etc, etc, etc. We now have over 150 papers!

∆|A|

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The Large Hadron Collider

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SLIDE 4 Mike Williams LANL | 4

Flavor Physics @ the LHC

θ¯

b

θb gg → b¯ b

❖ Large cross section; ❖ Access to all b-flavored hadrons; ❖ large b-hadron flight distances O(1 cm).

Advantages of B physics @ the LHC:

❖ High track multiplicity; ❖ BKGD rate ~200x bigger than signal rate!

Challenges of B physics @ the LHC: One trillion bb pairs produced @ LHCb so far!
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SLIDE 5 Mike Williams

LHCb Detector

5

VELO Magnet MUON Tracking CALOs

LHCb is a FWD Spectrometer (2 < η < 5)

RICH stufg

LANL |
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SLIDE 6
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SLIDE 7 20 MHz 1 MHz 5 kHz

LHCb Trigger

Mike Williams 7 We can “only” read out the detector at 1 MHz; thus, a hardware trigger is
  • required. The basic trigger strategy is

❖ hardware requires “large” ET in CALOs or “large” PT in the muon stations,

along with low multiplicity;

❖ software runs ~30k PROCs (giving it 30 ms/event) to reduce the rate by

~200. It uses a combo of simple and inclusive BDT-based selections to produce a nearly 100% pure bb sample. LHCb-DP-2012-004 [arXiv:1211.3055] V.Gligorov & MW, JINST 8, P02013 (2013). [arXiv:1210.6861] LANL |
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SLIDE 8 Mike Williams LANL | 8

LHCb Data Samples

LHCb collected 1.0/fb of data in 2011 and 2.2/fb in 2012. To keep pile-up manageable, we do not take the maximum luminosity the LHC can deliver. We employ “lumi leveling” to keep L constant. Most of the results I will show today use only 2011 data since most analyses have not yet been updated with the full 2011-2012 data set.
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SLIDE 9 Mike Williams LANL | 9 − H b + µ + t t W , + µ B d/s d/s Z , H,h ... W , + µ− W , µ − χ ~ ~ ~ + ν + − t,c,u q ~ l χ d/s B s/d b

SM

The SM predicts the Bs (sb meson) decays into two muons once every 3.4B decays ... but this can be enhanced greatly by BSM. Very interesting channel to explore NP models with extended Higgs sectors. Sensitive to “any” mass scale. Pre-LHC limits not very restrictive.

Bd,s→μ+μ-

It works out to about 1/1.6 trillion pp collisions at LHCb!
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SLIDE 10 Mike Williams LANL | 10 BDT-based selection with data-driven constraints. Published results use the full 2011-2012 data set.

Bd,s→μ+μ-

Only 1/2 of 2012 data shown here!
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SLIDE 11 Mike Williams LANL | 11

Bd,s→μ+μ-

BDT-based selection with data-driven constraints. Published results use the full 2011-2012 data set.
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SLIDE 12 Mike Williams 12

Bd,s → μ+μ-

Pre-LHC limits on SUSY not very restrictive. LANL |

SM

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SLIDE 13 Mike Williams 13

Bd,s → μ+μ-

LHCb+CMS Excluded

Not the best result for SUSY fans. LANL |

SM

Both CMS & LHCb report > 4σ evidence. ] 9 − ) [10 − µ + µ → s B B( 1 2 3 4 5 6 7 preliminary CMS+LHCb 1 − CMS 25fb 1 − LHCb 3fb SM
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SLIDE 14 Mike Williams LANL | 14

Bs → J/ѱφ

Interference between mixing and decay amplitudes gives rise to a CPV phase ɸs = ɸm - 2ɸd. BSM could give a non-SM measurement.

J/ѱφ Bs Bs

φd

  • φd

φm

This phase is accessible experimentally via a time-dependent angular analysis to measure the time-dependent CP asymmetry.

φSM

s

= 2 (arg(VtsV ∗

tb/VcsV ∗ cb)) = 0.036 ± 0.002
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SLIDE 15 Mike Williams LANL | 15

Bs → J/ѱφ

Interference between mixing and decay amplitudes gives rise to a CPV phase ɸs = ɸm - 2ɸd. BSM could give a non-SM measurement. This phase is accessible experimentally via a time-dependent angular analysis to measure the time-dependent CP asymmetry.

φSM

s

= 2 (arg(VtsV ∗

tb/VcsV ∗ cb)) = 0.036 ± 0.002 s B0 s s B s t, c, u W b W b t, c, u s B0 s s B s W − t, c, u b b W + t, c, u s B0 s h+h− s J/ψ c b W + c s s B0 s h+h− s J/ψ c b u, c, t c W + s

BSM?

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SLIDE 16 Mike Williams LANL | 16 Basic strategy to measure Bs oscillations: Reconstruct the Bs in a flavor- specific decay and also tag its flavor at production.

Bs → Dsπ K±

SS Tag OS Tag

µ, e, K, qvtx

LHCb sees ~34k signal events in 1/fb of data (2011) with an effective tagging power of (2.6±0.4)% from OST and (1.2±0.3)% from SST.

Bs Oscillations

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SLIDE 17 Mike Williams LANL | 17 Basic strategy to measure Bs oscillations: Reconstruct the Bs in a flavor- specific decay and also tag its flavor at production.

Bs → Dsπ K±

SS Tag OS Tag

µ, e, K, qvtx

LHCb sees ~34k signal events in 1/fb of data (2011) with an effective tagging power of (2.6±0.4)% from OST and (1.2±0.3)% from SST. LHCb-PAPER-2013-006 [arXiv:1304.4741]

Bs Oscillations

∆ms = 17.768 ± 0.023(stat) ± 0.006(syst)ps−1

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SLIDE 18 ] 2 ) [MeV/c
  • µ
+ µ m( 3 5 3 1 3 1 5 ) 2 Candidates / (2 MeV/c 2 4 6 8 1 1 2 1 4 1 6 LHCb Mike Williams LANL | 18

Bs → J/ѱφ

] 2 ) [ M e V / c
  • K
+ K ψ m ( J / 5 3 2 5 3 4 5 3 6 5 3 8 5 4 5 4 2 ) 2 C a n d i d a t e s / ( 2 . 5 M e V / c 5 1 1 5 2 2 5 3 3 5 4 4 5 L H C b Signal is very clean despite “dirty” LHC environment. ] 2 ) [ M e V / c
  • K
+ m ( K 1 1 2 1 4 ) 2 C a n d i d a t e s / ( 1 M e V / c 5 1 1 5 2 2 5 3 3 5 L H C b

2011 data only

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SLIDE 19

CP+ CP- S-wave

Mike Williams LANL | 19

Bs → J/ѱφ

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SLIDE 20 Mike Williams LANL | 20

Bs → J/ѱφ

There is an ambiguity in the equations for ɸs = ɸs+π. Use interference of ɸ with KK S-wave to break it!

physical ambiguous

ɸs = 0.01±0.07±0.01

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SLIDE 21 Mike Williams LANL | 21

Bd → K*μ+μ-

A fairly rare “penguin” FCNC decay. BSM could enter into these loops and alter the Lorentz structure of the amplitudes. Many angular observables are sensitive to BSM
  • physics. LHCb has more stats in 2011 data than all
previous experiments combined.

BSM?

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SLIDE 22 Mike Williams MIT Grads | 22

Bd → K*μ+μ-

Requires NP > ~50 TeV in (sb)V-A(μμ) for unit couplings! Excellent agreement with the SM.
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SLIDE 23 Mike Williams MIT Grads | 23

Bd → K*μ+μ-

Requires NP > ~50 TeV in (sb)V-A(μμ) for unit couplings! Excellent agreement with the SM.
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SLIDE 24 Mike Williams MIT Grads | 24

Bd → K*μ+μ-

New more theoretically precise observable: New physics? How much do you trust (these) theorists?
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SLIDE 25 Mike Williams LANL | 25

CPV in Bd,s

SM

D0 sees 3σ deviation in like- sign di-muon charge asymmetry

Bs Bs = ? Bs Bs Bd Bd Bd Bd = ?

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SLIDE 26 Mike Williams LANL | 26

CPV in Bd,s

SM

LHCb, Belle & BaBar agree with the SM.

Bs Bs = ? Bs Bs Bd Bd Bd Bd = ?

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SLIDE 27

LHCb LHCb SM LHC Results

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SLIDE 28

LHCb LHCb SM LHC Results LHCb SUSY

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SLIDE 29 Mike Williams The CKM matrix describes the mixing between mass and weak quark
  • eigenstates. In the SM, it is unitary providing 9 constraint equations that relate
its elements to one another. 29

CKM

Six of these constraint equations form “unitary triangles” (each of equal area, but different shapes). By measuring all “sides” and “angles”, the unitary hypothesis and, thus, the SM can be tested (want to over-constrain!). The most “popular” UT Ɣ α β |VudV ∗ ub| |VcdV ∗ cb| |VtdV ∗ tb| |VcdV ∗ cb| LANL |
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SLIDE 30 Mike Williams

CKM

Use interference b/t and to extract .

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(D|D)X B DX DX

A

¯ b→¯ u b→u = Abue±iγ

A

¯ b→¯ c b→c = Abc

= |AD|2 + |A ¯

D|2 + 2|AD||A ¯ D| cos (∆θstrong ± γ)

N± = |AB→DX + AB→ ¯

DX|2

γ

γ

These are tree-level decays; no pollution from penguins, etc. This is SM Ɣ. Can look for BSM by comparing to Ɣ from loops. LANL |
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SLIDE 31 Mike Williams

CKM

LHCb result combining many B→DK modes (only D→KShh uses 3/fb). 31

γ

LANL | Belle and BaBar now have 14o and 16o uncertainties on Ɣ.

Most Precise!

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SLIDE 32 Mike Williams 32

CKMγ

Amazing progress on Ɣ in the past few years, but improving tree-level constraints is still a very high priority.

γ

|Vub| Tree-level constraints

  • n the UT.
Ɣ α β |VudV ∗ ub| |VcdV ∗ cb| |VtdV ∗ tb| |VcdV ∗ cb| LANL |
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SLIDE 33 Mike Williams LANL | 33

PDFs @ LHCb

DGLAP evolution sea valence LHCb collisions are one high-x and one low-x parton. Small overlap with ATLAS/CMS for 2 < y < 2.5.
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SLIDE 34 Mike Williams LANL | 34

Top Asymmetry

[one of the only surviving anomalies]

p p

CDF & D0 see an anomalous asymmetry in top quark production.

t t p p t t

forward backward CMS & ATLAS don’t see any evidence for a forward-central top asymmetry.
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SLIDE 35 Mike Williams LANL | 35

Beauty Asymmetry

y Δ
  • 2
2 Events / 0.3 500 1000 1500 2000 2500 LHCb Preliminary > 100 GeV b b M data mirror data y Δ
  • 2
2 Events / 0.2 5000 10000 15000 20000 25000 LHCb Preliminary data mirror data all Mbb > 100 GeV “Raw” Delta y

(0.5±0.5±0.5)% (4.3±1.7±2.4)%

Improved analysis of 2011 data (including unfolding) out by the end of this year. Analysis using 2012 data expected early 2014. “The beauty AFC could be used to search for similar effects as seen in AFB in truth.” Kahawala, Krohn, Strassler, JHEP, 69 (2012).
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SLIDE 36 Mike Williams LANL | 36

Top Asymmetry

Kagan, Kamenik, Perez, Stone, PRL 107, 082003 (2011). “LHCb may be able to measure a tt production rate asymmetry, and thus indirectly probe an anomalous forward backward tt asymmetry in the forward region”

❖ The large y region is more sensitive to the charge asymmetry. ❖ Measuring the top rate asymmetry @ LHCb can indirectly probe top AFB

physics.

❖ LHCb b jet performance is good (and improving); our beauty AFC analysis

is a prototype for the top measurements (and interesting in its own right).

❖ Work now is focused on top RECO & cross sections. Moving towards a

“real” measurement using post-LS1 data.
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SLIDE 37 Mike Williams LANL | 37

Etc

LHCb has a very broad physics program that also includes the following:

❖ exotic spectroscopy; ❖ p-Pb and Pb-p collisions; ❖ searches for LFV; ❖ searches for sterile neutrinos; ❖ etc.!

We have more physics potential than humanpower. Would you like to join?
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SLIDE 38 Mike Williams LANL | 38

Summary

LHCb has performed excellently and produced very nice results using 1/fb of 2011 data. Unfortunately so far we’re the anomaly terminator. We have 3x the statistics “in hand” with new results expected soon. Hopefully this time we’re the good terminator from the sequel!

LHCb

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SLIDE 39

❝ ❞

The optimist regards the future as uncertain. Eugene Wigner